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Ischemic Preconditioning Improves Time-Trial Performance at Moderate Altitude
Abstract
Purpose:
Endurance athletes often compete and train at altitude where exercise capacity is reduced. Investigating acclimation strategies is therefore critical. Ischemic preconditioning (IPC) can improve endurance performance at sea level through improved O2 delivery and utilization, which could also prove beneficial at altitude. However, data are scarce and there is no study at altitudes commonly visited by endurance athletes.
Methods:
In a randomized, crossover study, we investigated performance and physiological responses in thirteen male endurance cyclists during four 5-km cycling time trials (TT), preceded by either IPC (3x5-minutes ischemia/5-minutes reperfusion cycles at 220 mmHg) or SHAM (20 mmHg) administered to both thighs, at simulated low (FIO2 0.180, ~1200 m) and moderate (FIO2 0.154, ~2400 m) altitudes. Time to completion, power output, cardiac output (Q), arterial O2 saturation (SpO2), quadriceps tissue saturation index (TSI) and ratings of perceived exertion (RPE) were recorded throughout the TT. Differences between IPC and SHAM were analyzed at every altitude using Cohen's effect size (ES) and compared to the smallest worthwhile change.
Results:
At low altitude, IPC possibly improved time to complete the TT (-5.2sec, -1.1%, Cohen's ES ± 90% confidence limits -0.22, -0.44;0.01), power output (2.7%, ES 0.21, -0.08;0.51) and Q (5.0%, ES 0.27, 0.00;0.54), but did not alter SpO2, muscle TSI and RPE. At moderate altitude, IPC likely enhanced completion time (-7.3sec, -1.5%, ES -0.38, -0.55;-0.20) and power output in the second half of the TT (4.6%, ES 0.28, -0.15;0.72), increased SpO2 (1.0%, ES 0.38, -0.05;0.81), and decreased TSI (-6.5%, ES -0.27, -0.73;0.20) and RPE (-5.4%, ES -0.27, -0.48;-0.06).
Conclusion:
IPC may provide an immediate and effective strategy to defend SpO2 and enhance high-intensity endurance performance at moderate altitude.
... Previously, IPC has been demonstrated to have protective properties against the injurious effects of ischemia-reperfusion injury in mammalian animal models (Pérez-Pinzón, 2004;Konstantinov et al., 2005;Kristiansen et al., 2005;Wang et al., 2016) and has been shown in humans to improve various clinical outcomes such as protection against post-ischemia-reperfusion endothelial dysfunction, and post-surgical acute kidney injury, among others (Luca et al., 2013;Khaliulin et al., 2019;Gu et al., 2021;Liu et al., 2021). In sport and exercise research literature, IPC has been repeatedly reported to improve athletic performance using a variety of maximal exercise intensities and modalities such as running, swimming, or cycling lasting from about 30 s to 20 min (Jean-St-Michel et al., 2011;Bailey et al., 2012b;Cruz et al., 2015Cruz et al., , 2016Kraus et al., 2015;Cocking et al., 2018b;Paradis-Deschênes et al., 2018). However, the consistency and magnitude of such ergogenic responses is highly variable throughout the literature and merits further attention (For review of the ergogenic responses to IPC see: Marocolo et al., 2015a;Marocolo et al., 2019;Incognito et al., 2016;Salvador et al., 2016;Caru et al., 2019). ...
... During maximal intensity exercise, IPC resulted in a lower HR despite no performance differences during judo-specific fitness testing (Ceylan and Franchini, 2022) and increased maximal HR along with exercise endurance and work output during incremental cycling exercise (Crisafulli et al., 2011). Another study found IPC resulted in an increased HR at various time points during 5 km cycling time trials at low altitude with no change in performance, whereas at moderate altitude performance was increased with decreases in HR and a concomitant increase in stroke volume from IPC (Paradis-Deschênes et al., 2018). While such responses have been observed after IPC, most investigations reported that IPC had no effect on cardiac output, HR, or stroke volume, regardless of exercise intensity, modality, or performance enhancement (see Supplementary Table S1 for references). ...
... Further supporting the divergence between afferent feedback and perceived effort, the available evidence suggests that IPC has menial effects on RPE. Five of the studies found in Supplementary Table S4 showed attenuated RPE during exercise preceded by IPC (Bailey et al., 2012b;Cruz et al., 2015;Paradis-Deschênes et al., 2018;Beek et al., 2020;Behrens et al., 2020), whereas 25 studies found no influence of IPC on RPE during various exercise interventions. Some of this disagreement may be due to variability in exercise protocols across interventions. ...
Ischemic preconditioning (IPC) has been reported to augment exercise performance, but there is considerable heterogeneity in the magnitude and frequency of performance improvements. Despite a burgeoning interest in IPC as an ergogenic aid, much is still unknown about the physiological mechanisms that mediate the observed performance enhancing effects. This narrative review collates those physiological responses to IPC reported in the IPC literature and discusses how these responses may contribute to the ergogenic effects of IPC. Specifically, this review discusses documented central and peripheral cardiovascular responses, as well as selected metabolic, neurological, and perceptual effects of IPC that have been reported in the literature.
... Time trial performance at moderate altitude ($2,200-2,400 m) is enhanced when preceded by a single IPC bout (13,14). Enhanced physical performance with IPC is linked to improved oxygen extraction (13)(14)(15), enhanced skeletal muscle blood volume (14), and improved arterial oxygen saturation (13). ...
... Time trial performance at moderate altitude ($2,200-2,400 m) is enhanced when preceded by a single IPC bout (13,14). Enhanced physical performance with IPC is linked to improved oxygen extraction (13)(14)(15), enhanced skeletal muscle blood volume (14), and improved arterial oxygen saturation (13). Furthermore, IPC applied for 7 days has elicited reductions in muscle deoxygenated hemoglobin/myoglobin (12-30%) and heightened delta cycling efficiency ($3%) during steady-state submaximal exercise in normoxia (16,17). ...
... Time trial performance at moderate altitude ($2,200-2,400 m) is enhanced when preceded by a single IPC bout (13,14). Enhanced physical performance with IPC is linked to improved oxygen extraction (13)(14)(15), enhanced skeletal muscle blood volume (14), and improved arterial oxygen saturation (13). Furthermore, IPC applied for 7 days has elicited reductions in muscle deoxygenated hemoglobin/myoglobin (12-30%) and heightened delta cycling efficiency ($3%) during steady-state submaximal exercise in normoxia (16,17). ...
This investigation sought to assess whether single or repeated bouts of ischemic preconditioning (IPC) could improve oxyhemoglobin saturation (SpO2) and/or attenuate reductions in muscle tissue saturation index (TSI) during submaximal hypoxic exercise. Fifteen healthy young men completed submaximal graded exercise under four experimental conditions: (1) normoxia (NORM), (2) hypoxia (HYP), FiO2 = 0.14, ~3200 m, (3) hypoxia preceded by a single session of IPC (IPC1-HYP), and (4) hypoxia preceded by seven sessions of IPC, one a day for seven consecutive days (IPC7-HYP). IPC7-HYP heightened VE at 80% HYP Wpeak (+10.47 ± 3.35 L·min-1, p= 0.006), compared to HYP, as a function of increased breathing frequency. Both IPC1-HYP (+0.17 ± 0.04 L·min-1, p< 0.001) and IPC7-HYP (+0.16 ± 0.04 L·min-1, p< 0.001) elicited greater VO2 across exercise intensities compared to NORM, while VO2 was unchanged with HYP alone. SpO2 was unchanged by either IPC condition at any exercise intensity. Yet, the reduction of muscle TSI during resting hypoxic exposure was attenuated by IPC7-HYP (+9.9 ± 3.6%, p= 0.040) compared to HYP, likely as a function of reduced local oxygen extraction. Considering all exercise intensities, IPC7-HYP attenuated reductions of TSI with HYP (+6.4 ± 1.8%, p= 0.001). Seven days of IPC heightens ventilation, posing a threat to ventilatory efficiency, during high intensity submaximal hypoxic exercise and attenuates reductions in hypoxic resting and exercise muscle oxygenation in healthy young men. A single session of IPC may be capable of modulating hypoxic ventilation, however, our current population was unable to demonstrate this with certainty.
... However, despite increasing evidence at sea level suggests that the use of this technique could be relevant when the O 2 availability is compromised, studies on IPC at altitude are still scarce and mostly concern acute exposure and altitudes that are too high for training purposes. Nonetheless, a few studies using endurance Fig. 1 Ischemic preconditioning applied to the upper thighs of a cyclist in a laboratory setting prior to a 5-km cycling time trial exercise have been conducted at relevant altitudes and results certainly do trigger interest to further investigate the ergogenic potential of IPC in this environment and eventually to refine applied protocols for athletic endeavors [25,64]. The following sections will highlight the main effects of IPC and how they relate to physiological changes imposed by acute and chronic exposure to altitude, by focusing on moderate altitude where athletes more typically stay, train and compete, and then on higher altitude that may be detrimental to the human body. ...
... No negative impact or adverse effects were noted. Furthermore, of these seven studies, three only investigated the effects of IPC on time-trial performance (a more reliable type of performance than open-loop tests) in a controlled environment and at moderate altitude that corresponds to elevations commonly visited by athletes for competition and training [25,64,79]. The first study in this area has been published by Paradis-Deschênes and colleagues from Canada [64] and demonstrated that three 5-min cycles of IPC at 220 mmHg improved aerobic power and chronometric performance (by ~ 7 s) during a 5-km time trial at 2400 m simulated altitude (fraction of inspired oxygen (F I O 2 ) 0.15) in endurance athletes (VO 2max 66.0 mL/kg/ min) and attenuated the rate of perceived exhaustion. ...
... Furthermore, of these seven studies, three only investigated the effects of IPC on time-trial performance (a more reliable type of performance than open-loop tests) in a controlled environment and at moderate altitude that corresponds to elevations commonly visited by athletes for competition and training [25,64,79]. The first study in this area has been published by Paradis-Deschênes and colleagues from Canada [64] and demonstrated that three 5-min cycles of IPC at 220 mmHg improved aerobic power and chronometric performance (by ~ 7 s) during a 5-km time trial at 2400 m simulated altitude (fraction of inspired oxygen (F I O 2 ) 0.15) in endurance athletes (VO 2max 66.0 mL/kg/ min) and attenuated the rate of perceived exhaustion. This ergogenic impact was, however, present to a lower extent during a time trial performed at 1200 m (F I O 2 0.18) [64]. ...
Acute exposure to altitude negatively impacts exercise tolerance and reduces athletes’ race performance due to lower atmospheric and body tissues oxygen partial pressures. Chronic exposure to altitude has also been used for several decades by athletes to increase training adaptations. However, the decline in arterial oxygen saturation also impacts 'trainability' and athletes are forced to travel to lower altitude for intensified training. For the athlete preparing for altitude, the advantages of properly timed terrestrial acclimatization and/or sea-level hypoxia-based pre-acclimatization recommendations are clear. However, the associated cost, demands, and time investment make these best-practice strategies difficult or impossible to implement for many athletes. This perspective and opinion article summarizes current knowledge on the potency of ischemic preconditioning (i.e., a sequence of transient ischemic episodes followed by reperfusion) to enhance the pulmonary, vascular, and metabolic determinants of performance at altitude with the aim to derive implications to accelerate or facilitate altitude acclimatization for varied goals. We discuss potential applications for athletes and propose innovative questions for future research in this field.
... In addition, Hittinger et al. did not find a significant influence of RIPC on oxygen saturation or peak exercise capacity during a maximal incremental test to exhaustion at a simulated altitude of approximately 3650 m in trained cyclists (Hittinger et al., 2015). However, Paradis-Deschênes et al. reported that RIPC increased oxygen saturation and enhanced the highintensity endurance performance of cyclists during four 5-km cycling time trials at a simulated altitude of 2400-m simulated altitude, and the authors speculated that the existence of heterogeneous responders to RIPC might account for the discordance between their findings and the findings reported in other studies (Paradis-Deschenes et al., 2018). In Foster's second study, in which the duration of RIPC was extended to 5 days, RIPC not only attenuated hypoxic pulmonary vasoconstriction but also improved oxygen saturation in a 12.8-km run test from an altitude of 3560 m to 4342 m (Foster et al., 2014). ...
... In several previous studies, different RIPC protocols were adopted. RIPC including 4×5 min of ischaemia in both legs interspersed with 5-minute reperfusion periods was the most popular protocol, and modified protocols with 3×5 min or 5×5 min of ischaemia in one leg or both arms were also used in a few studies (Berger et al., 2015;Berger et al., 2017;Foster et al., 2011;Foster et al., 2014;Hittinger et al., 2015;Li et al., 2020;Paradis-Deschenes et al., 2018). We used the modified protocol with 5×5 min of ischaemia in both arms based on our experience of previous studies (Li et al., 2020;Meng et al., 2012;Meng et al., 2015;Zhao et al., 2017). ...
... The effect of RIPC on oxygen saturation at altitude in our findings is consistent with Foster's, Li's and Paradis-Deschênes' reports but contradicts Berger's and Hittinger's findings, and the effect on AMS observed in our study differs from the effects on AMS reported in Foster's and Berger's studies (Berger et al., 2015;Berger et al., 2017;Foster et al., 2011;Foster et al., 2014;Hittinger et al., 2015;Li et al., 2020;Paradis-Deschenes et al., 2018). We speculate that the discrepancies observed in these controversial studies might be partially attributable to the differences among the RIPC regimens used, the short durations of the intervention and the possible existence of heterogeneous responders to RIPC (Incognito, Burr, & Millar, 2016;Paradis-Deschenes et al., 2018), and we speculate that repeated RIPC can prevent AMS and improve oxygen saturation at high altitudes. ...
Background:
This study assessed the effectiveness of 4 different repeated remote ischaemic preconditioning (RIPC) protocols varying in duration and frequency for preventing acute mountain sickness (AMS) after rapid ascent to high altitude.
Methods:
In a randomized but not blinded design, participants were assigned to receive either of the four RIPC treatments at low altitude (Group A, once daily for 1 week; Group B, twice daily for 1 week; Group C, once daily for 4 weeks; and Group D, twice daily for 4 weeks) or control (no specific sham treatment). Participants were then flown to a high altitude (3650 m). The primary outcome was the incidence and severity of AMS evaluated by the Lake Louise score (LLS) after arrival; vital signs were collected simultaneously.
Results:
A total of 250 participants (50 per group; mean age 38.56 ± 0.76 years) were included. The overall AMS incidence was 26.4%. A total of 20 AMS cases (40%) occurred in the control group, 15 cases (30%) both in the RIPC A and RIPC B groups (RR 1.3; 95%CI 0.8-2.3; χ2 = 1.099; p = 0.29), and 8 cases (16%) both in the RIPC C and D groups (RR 2.5; 95%CI 1.2 - 5.2; χ2 = 7.143, p < 0.01), with significantly lower LLSs in the RIPC C and D groups (F = 6.51, p < 0.001). The scores of gastrointestinal symptoms (F = 7.42, p < 0.001) and dizziness (F = 9.82, p < 0.001) but not headache (F = 0.60, p > 0.05) were lower in the RIPC groups compared to control. The blood oxygen saturation level (SpO2) decreased less in the RIPC B, C and D groups compared to control after arrival at a high altitude (F = 11.42, p < 0.001). The number of RIPC treatments received was moderately correlated with SpO2 (R = 0.38, p < 0.001), and SpO2 was moderately inversely correlated with the LLS (R = -0.48, p < 0.001).
Conclusion:
This study demonstrated that a four-week RIPC intervention but not a one-week regimen reduced AMS incidence and severity; however, a placebo effect might have contributed to these results.
... lowed by rapid reperfusion. IPC can acutely improve performance shortly after the manoeuver, particularly during maximal aerobic exercise where the oxidative system is fully taxed (Bailey et al., 2012;Paradis-Deschênes et al., 2018;Salvador et al., 2016). Though the precise mechanisms of action are still under investigation, performance enhancement has been associated with improvements in local vasodilation, blood flow and, ultimately, O 2 uptake (Bailey et al., 2012;Enko et al., 2011;Kilding et al., 2018;Paradis-Deschênes et al., 2016). ...
... This was repeated three times per limb, alternately, with each compression episode separated by 5 min of reperfusion (cuff release). This protocol has previously been shown to completely occlude vascular arterial inflow (Sabino-Carvalho et al., 2016), alter physiological responses and enhance acute endurance performance (Bailey et al., 2012;Paradis-Deschênes et al., 2018). The intervention lasted 30 min. ...
... NIRS data were acquired continuously at 10 Hz and were averaged over 10 sec for every 250 m of the TT, and every 30 sec for a 2-min period immediately after exercise. A 10 th order zero-lag low-pass Butterworth filter was applied to smooth NIRS signal (Paradis-Deschênes et al., 2018). ...
This study investigated the efficacy of ischemic preconditioning (IPC) on the recovery of maximal aerobic performance and physiological responses compared with commonly used techniques. Nine endurance athletes performed two 5-km cycling time trials (TT) interspersed by 45 minutes of recovery that included either IPC, active recovery (AR) or neuromuscular electrical stimulation (NMES) in a randomized crossover design. Performance, blood markers, arterial O2 saturation (SpO2), heart rate (HR), near-infrared spectroscopy-derived muscle oxygenation parameters and perceptual measures were recorded throughout TTs and recovery. Differences were analyzed using repeated-measures ANOVAs and Cohen's effect size (ES). The decrement in chronometric performance from TT1 to TT2 was similar between recovery modalities (IPC: -6.1 sec, AR: -7.9 sec, NMES: -5.4 sec, p = 0.84, ES 0.05). The modalities induced similar increases in blood volume before the start of TT2 (IPC: 13.3%, AR: 14.6%, NMES: 15.0%, p = 0.79, ES 0.06) and similar changes in lactate concentration and pH. There were negligible differences between conditions in bicarbonate concentration, base excess of blood and total concentration of carbon dioxide, and no difference in SpO2, HR and muscle O2 extraction during exercise (all p > 0.05). We interpreted these findings to suggest that IPC is as effective as AR and NMES to enhance muscle blood volume, metabolic by-products clearance and maximal endurance performance. IPC could therefore complement the athlete's toolbox to promote recovery.
... This non-invasive technique, involving repeated episodes of muscle ischemia followed by reperfusion at rest, induces transient peripheral hypoxia and can acutely improve maximal exercise capacity Salvador et al., 2016). For example, IPC improved mean power output during a 60 s cycling sprint, with a greater increase at exercise onset , and time-trial (TT) performance in cyclists (Paradis-Deschênes et al., 2018;Wiggins et al., 2018). However, the precise physiological responses and mechanisms associated with these enhancements are still equivocal. ...
... Non-elastic nylon blood pressure cuffs (WelchAllyn, Skaneateles Falls, NY, USA, width: 21 cm) were positioned around each upper thigh under the gluteal line and rapidly inflated to 220 mmHg (IPC) or 20 mmHg (PLA) for 5 min to prevent arterial inflow, three times per limb, alternatively, with each compression episode separated by 5 min of reperfusion (cuff release). This protocol has previously been shown to alter physiological responses and enhance performance (Bailey et al., 2012a;Paradis-Deschênes et al., 2018), and to completely occlude vascular arterial inflow (Sabino-Carvalho et al., 2016). To minimize any placebo effect, participants were told that the purpose of the study was to compare the impact of two different cuff pressures that could both alter training positively, with venous or arterial effects, according to the pressure used. ...
... NIRS data were acquired continuously at 10 Hz for every testing session. A 10th order zero-lag low-pass Butterworth filter was applied to smooth NIRS signal (Paradis-Deschênes et al., 2018). Data were averaged over 10 s at the end of each step of the maximal cycling test and leading up to every 250 m of the TT. ...
Optimizing traditional training methods to elicit greater adaptations is paramount for athletes. Ischemic preconditioning (IPC) can improve maximal exercise capacity and up-regulate signaling pathways involved in physiological training adaptations. However, data on the chronic use of IPC are scarce and its impact on high-intensity training is still unknown. We investigated the benefits of adding IPC to sprint-interval training (SIT) on performance and physiological adaptations of endurance athletes. In a randomized controlled trial, athletes included eight SIT sessions in their training routine for 4 weeks, preceded by IPC (3 × 5 min ischemia/5 min reperfusion cycles at 220 mmHg, n = 11) or a placebo (20 mmHg, n = 9). Athletes were tested pre-, mid-, and post-training on a 30 s Wingate test, 5-km time trial (TT), and maximal incremental step test. Arterial O2 saturation, heart rate, rate of perceived exertion, and quadriceps muscle oxygenation changes in total hemoglobin (Δ[THb]), deoxyhemoglobin (Δ[HHb]), and tissue saturation index (ΔTSI) were measured during exercise. Blood samples were taken pre- and post-training to determine blood markers of hypoxic response, lipid-lipoprotein profile, and immune function. Differences within and between groups were analyzed using Cohen's effect size (ES). Compared to PLA, IPC improved time to complete the TT (Mid vs. Post: −1.6%, Cohen's ES ± 90% confidence limits −0.24, −0.40;−0.07) and increased power output (Mid vs. Post: 4.0%, ES 0.20, 0.06;0.35), Δ[THb] (Mid vs. Post: 73.6%, ES 0.70, −0.15;1.54, Pre vs. Post: 68.5%, ES 0.69, −0.05;1.43), Δ[HHb] (Pre vs. Post: 12.7%, ES 0.24, −0.11;0.59) and heart rate (Pre vs. Post: 1.4%, ES 0.21, −0.13;0.55, Mid vs. Post: 1.6%, ES 0.25, −0.09;0.60). IPC also attenuated the fatigue index in the Wingate test (Mid vs. Post: −8.4%, ES −0.37, −0.79;0.05). VO2peak and maximal aerobic power remained unchanged in both groups. Changes in blood markers of the hypoxic response, vasodilation, and angiogenesis remained within the normal clinical range in both groups. We concluded that IPC combined with SIT induces greater adaptations in cycling endurance performance that may be related to muscle perfusion and metabolic changes. The absence of elevated markers of immune function suggests that chronic IPC is devoid of deleterious effects in athletes, and is thus a safe and potent ergogenic tool.
... Bailey et al. (3) and Bailey et al. (4) showed that IPC increased performance in a 5 km counter-clock race, but again found no significant difference in HR after the test when comparing the protocols. Paradis-Deschênes et al. (23) helped to ensure improvement in maximal power and improvement in the time of completion in cyclists when applying the IPC. ...
... Incognito et al. (16) reported that the IPC does not change the HR and the activation of the sympathetic nerve during and after vascular occlusion post-exercise. In addition, Mulliri et al. (23) did not identify central and peripheral changes of hemodynamic parameters during exercise. ...
... In this study, after application of IPC, the SBP and the DBP showed no significant differences between the groups. These data support with the findings of Mulliri et al. (23) who reported that the IPC reduced blood pressure during vascular occlusion post-exercise. The justification given for this was that there was a reduction in stroke volume and cardiac output induced by venous return. ...
Ribeiro AAS, Novaes J, Reis N, Telles LG, Sant'Ana L, Raider L, Poggetto LD, Brown A, Panza P, Martinez D, Mansur H, Vianna J. Acute Effect of Ischemic Preconditioning on the Performance and on the Hemodynamic Responses of High-Performance Male Judo Athletes. JEPonline 2019; 22(4):154-164. The purpose of this study was to analyze the acute effect of ischemic preconditioning (IPC) on hemodynamic responses and performance in 12 judo athletes who performed the Special Judo Fitness Test (SJFT). Heart rate, SBP, and DBP at rest and post-test, and the SJFT index were compared via homogeneity of variance, effect size, paired t-test, and two-way ANOVA at an alpha level of P≤0.05. The findings indicate that the SJFT index values were significantly different (P=0.006) between the IPC and SHAM. The SBP response was significantly different (P≤0.05) between IPC and SHAM at the 10th-min vs. the 5th-min of recovery. There were no significant differences in HR immediately after the SJFT, 1 min, and 10 min of recovery between IPC and SHAM. It was concluded that the IPC is an effective strategy to be used in judo athletes' improvement in performance without changes in their hemodynamic responses.
... acclimation has recently emerged (12). It is known that alteration in central convective factors and peripheral oxygen diffusion contributes to the endurance performance decrements at altitude (13). ...
... So the IPC-derived hyperemia and increased oxygen delivery to active muscles could alleviate such detrimental hypoxia-induced effects. Indeed, a recent study suggested a beneficial effect of IPC on endurance time-trial performance in normobaric hypoxia at simulated altitude of 2400 m in trained cyclists (12). The authors attributed the IPC ergogenic impact to a higher blood oxygen saturation, peripheral oxygen utilization, and lower perception of effort. ...
... To avoid a placebo effect (19) , subjects were informed about the testing of two external pressure conditions and that both could improve performance. To prevent a nocebo effect, the subjects were informed that IPC/SHAM would cause no harm, despite discomfort related to the maneuver A C C E P T E D (5,12). The IPC was repeated three times bilaterally, with each ischemic episode separated by 5 min of reperfusion with no pressure (i.e., 3 x 5 min occlusion/5 min reperfusion). ...
Purpose:
The ergogenic effect of ischemic preconditioning (IPC) on endurance exercise performed in hypoxia remains debated and has never been investigated with successive exercise bouts. Therefore, we evaluated if IPC would provide immediate or delayed effects during two 5 km cycling time-trials (TTs) separated by ~1 h in hypoxia.
Methods:
In a counterbalanced randomized cross-over design, thirteen healthy males (27.5 ± 3.6 years) performed two maximal cycling 5 km TTs separated by ~1 h of recovery (TT1 25 min and TT2 2 h post IPC/SHAM), preceded by IPC (3 × 5 min occlusion 220 mmHg/reperfusion 0 mmHg, bilaterally on thighs) or SHAM (20 mmHg) at normobaric hypoxia (inspired fraction of oxygen [FIO2] of 16%). Performance and physiological (i.e., oxyhemoglobin saturation, heart rate, blood lactate, and Vastus Lateralis oxygenation) parameters were recorded.
Results:
Time to complete (P = 0.011) 5 km TT and mean power output (P = 0.005) from TT1 to TT2 were worse in SHAM, but not in IPC (P = 0.381/P = 0.360, respectively). There were no differences in time, power output or in physiological variables during the two TTs between IPC and SHAM. All muscle oxygenation indices differed (P < 0.001) during the IPC/SHAM with a greater deoxygenation in IPC. During the TTs, there was a greater concentration of total hemoglobin ([tHb]) in IPC than SHAM (P = 0.047) and greater [tHb] in TT1 than TT2. Further, the concentration of oxyhemoglobin ([O2Hb]) was lower during TT2 than TT1 (P = 0.005).
Conclusion:
In moderate hypoxia, IPC allowed maintaining a higher blood volume during a subsequent maximal exercise, mitigating the performance decrement between two consecutive cycling time-trials.
... Vale ressaltar que o protocolo do PCIR utilizado por todos os pesquisadores foram semelhantes, variando pouco o número de ciclos de isquemia-reperfusão. 1,[5][6][7][8][17][18][19] A manobra consistia em períodos de isquemia de um membro, através da insuflação de um manguito até 220 mmHg por 5 minutos, seguidos por 5 minutos de reperfusão com a deflação do manguito. Entretanto, os métodos de intervenção foram heterogêneos quanto as variáveis de treinamento, essas diferenças nos protocolos são essenciais na aplicabilidade prática, já que a manipulação de variáveis pode resultar na melhora do desempenho em atletas de endurance. ...
... Os achados desta pesquisa coadunam com outros autores que avaliaram os efeitos do PCIR sobre a Wmáx em atletas. 18,19 Estes resultados podem ser explicados pela baixa variabilidade da Wmáx em atletas de alto rendimento, sendo esta, uma variável mecânica com baixa sensibilidade para detectar alterações fisiológicas agudas, potencializado pelo intervalo de confiança amplo em todas as análises. ...
INTRODUÇÃO: O pré-condicionamento isquêmico remoto (PCIR) é uma intervenção cardioprotetora não invasiva que atenua a lesão celular sofrida por uma isquemia prolongada. Seus efeitos de proteção sobre o coração, quando aplicado ao esporte, pode melhorar o desempenho do exercício. OBJETIVO: Investigar o efeito do pré-condicionamento isquêmico remoto no consumo máximo de oxigênio (VO2máx) e potência máxima (Wmáx) em corredores e ciclistas. METODOLOGIA: Revisão sistemática e metanálise, com ensaios clínicos randomizados. Baseado no PRISMA e avaliado pelo repositório de projetos de revisões sistemática PROSPERO; entretanto, não obteve o registro por se tratar de um desfecho de performance esportiva. As buscas foram realizadas nas bases de dados Medline/PubMed, SciELO, Periódicos CAPES. A seleção dos estudos foi realizada em duas etapas: leitura do título e resumo, e leitura completa dos artigos. A extração dos dados foi realizada pela transcrição das informações. A qualidade metodológica foi avaliada pela escala risco de viés através da ferramenta Cochrane. Excluíram-se estudos que investigaram variáveis diferentes dos desfechos selecionados para esta revisão. RESULTADOS: Foram incluídos oito ensaios clínicos. Verificou-se que nos itens geração de sequência aleatória, ocultação de alocação e cegamento de avaliadores de desfecho em quase todos os estudos tiveram alto risco de viés. Os resultados da metanálise não mostraram diferenças significativas no VO2máx e Wmáx. CONCLUSÃO: O pré-condicionamento isquêmico remoto não se mostrou eficaz para aumentar o VO2máx e a Wmáx em corredores e ciclistas.
... Vale ressaltar que o protocolo do PCIR utilizado por todos os pesquisadores foram semelhantes, variando pouco o número de ciclos de isquemia-reperfusão. 1,[5][6][7][8][17][18][19] A manobra consistia em períodos de isquemia de um membro, através da insuflação de um manguito até 220 mmHg por 5 minutos, seguidos por 5 minutos de reperfusão com a deflação do manguito. Entretanto, os métodos de intervenção foram heterogêneos quanto as variáveis de treinamento, essas diferenças nos protocolos são essenciais na aplicabilidade prática, já que a manipulação de variáveis pode resultar na melhora do desempenho em atletas de endurance. ...
... Os achados desta pesquisa coadunam com outros autores que avaliaram os efeitos do PCIR sobre a Wmáx em atletas. 18,19 Estes resultados podem ser explicados pela baixa variabilidade da Wmáx em atletas de alto rendimento, sendo esta, uma variável mecânica com baixa sensibilidade para detectar alterações fisiológicas agudas, potencializado pelo intervalo de confiança amplo em todas as análises. ...
INTRODUÇÃO: O pré-condicionamento isquêmico remoto (PCIR) é uma intervenção cardioprotetora não invasiva, que atenua a lesão celular sofrida por uma isquemia prolongada. Seus efeitos de proteção sobre o coração, quando aplicado ao esporte, pode melhorar o desempenho do exercício. OBJETIVO: Investigar o efeito do pré-condicionamento isquêmico remoto no consumo máximo de oxigênio (VO2máx) e potência máxima (Wmáx) em corredores e ciclistas. METODOLOGIA: Revisão sistemática e metanálise, com ensaios clínicos randomizados. Baseado no PRISMA e avaliado pelo repositório de projetos de revisões sistemática PROSPERO, entretanto, não obteve o registro por se tratar de um desfecho de performance esportiva. As buscas foram realizadas nas bases de dados Medline/PubMed, SciELO, Periódicos CAPES. A seleção dos estudos foi realizada em duas etapas: leitura do título e resumo e, leitura completa dos artigos. A extração dos dados foi realizada pela transcrição das informações. A qualidade metodológica foi avaliada pela escala risco de viés através da ferramenta Cochrane. Excluíram-se estudos que investigaram variáveis diferentes dos desfechos selecionados para esta revisão. RESULTADOS: Foram incluídos oito ensaios clínicos. Verificou-se que nos itens geração de sequência aleatória, ocultação de alocação e cegamento de avaliadores de desfecho em quase todos os estudos tiveram alto risco de viés. Os resultados da metanálise revelou VO2máx (p < 0,01), o PCIR mostrou ser eficaz; Wmáx não houve diferença significativa. CONCLUSÃO: O pré-condicionamento isquêmico remoto pode ser capaz de aumentar o VO2máx em corredores e ciclistas. A Wmáx demonstra não ser influenciada pelo PCIR.
... On the other hand, reperfusion is defined by the reestablishment of blood flow and the return of oxygenation to the tissues, organs and sectors of the body [9,10]. Studies have shown that IPC improved the performance of athletes in some sports modalities such as running [11][12][13][14][15], swimming [16][17][18][19], rowing [20], diving [20], cycling [21][22][23][24][25], simulated competition indoor cycling [26]. ...
... Kjeld et al. [20] observed improved IPC performance in rowers and divers by reducing tissue oxygenation in the forearm and thigh, decreasing rowing time to 1000 meters, and increasing static and dynamic apnea in divers. Paradis-Deschênes et al. [24], when analysing the performance and physiological responses of IPC in cyclists in low and moderate altitude situations, showed that after IPC, the time for the 5 Km was lower, O 2 saturation increased and there was a reduction in the saturation index of the quadriceps tissues and the subjective perception of exertion. Marocolo et al. [16] analysed amateur swimmers after IPC application and found time reduction in the 100meter swim-crawl test. ...
Background & Study Aim: Ischemic preconditioning may improve the physiological responses and performances of athletes in different sport modalities. Similarly, judokas could also benefit from augmented performance the day of a competition. However, until now, there is no evidence of the effect of ischemic preconditioning procedure (IPC) on the performance of these athletes. Thus, the objective of this study was the effect of IPC on the performance of judo athletes.
Material & Methods: The study involved 17 judo athletes (age 21.35 ±3.46 years, practice judo 8.94 ±3.88 years, height 1.73 ±9 m, body mass 69.34 ± 10,94 kg). In the first session, they answered the questionnaires, performed the anthropometric evaluation, the familiarization of the Special Judo Fitness Test (SJFT). The SJFT was used to evaluate the athletes’ special physical fitness. In the second and third sessions, two experimental protocols were performed in a randomized and counterbalanced manner: a) IPC (3 cycles x 5 min ischemia at 220 mmHg / 5 min reperfusion at 0 mmHg) + SJFT and b) SHAM (placebo session: 3 cycles x 5 min ischemia at 20 mmHg / 5 min reperfusion at 0 mmHg) + SJFT. A 30-minute interval between the experimental protocols and the SJFT and 72 hours between the 2nd and 3rd sessions was observed.
Results: After performing IPC, judokas performed the highest number of throws in the series (A) and the total number of throws (A+B+C). The SJFT index also showed a significant improvement over the SHAM session.
Conclusions: IPC acutely improves specific performance of judo athletes and may therefore be used during competitions.
... On the other hand, reperfusion is defined by the reestablishment of blood flow and the return of oxygenation to the tissues, organs and sectors of the body [9,10]. Studies have shown that IPC improved the performance of athletes in some sports modalities such as running [11][12][13][14][15], swimming [16][17][18][19], rowing [20], diving [20], cycling [21][22][23][24][25], simulated competition indoor cycling [26]. ...
... Kjeld et al. [20] observed improved IPC performance in rowers and divers by reducing tissue oxygenation in the forearm and thigh, decreasing rowing time to 1000 meters, and increasing static and dynamic apnea in divers. Paradis-Deschênes et al. [24], when analysing the performance and physiological responses of IPC in cyclists in low and moderate altitude situations, showed that after IPC, the time for the 5 Km was lower, O 2 saturation increased and there was a reduction in the saturation index of the quadriceps tissues and the subjective perception of exertion. Marocolo et al. [16] analysed amateur swimmers after IPC application and found time reduction in the 100meter swim-crawl test. ...
... Therefore, until more robust and clear evidence demonstrates a beneficial effect in high-level athletes with at least a small ES, it is not advised to extrapolate the results observed in lower-end fitness subjects to high-level competitors. Analyzing the fitness level of subjects among almost 50 experimental studies that measured the effects of IPC on exercise performance in healthy subjects, one of them tested elite speed skaters (Richard and Billaut, 2018) while another evaluated elite cyclists (Paradis-Deschênes et al., 2018). Subjects evaluated in all other studies were amateur or recreational athletes, or even just healthy or sedentary (non-published data), even when the title or some part of the manuscript quoted "highly trained." ...
... Along this line, some evidence exists showing that IPC can, in some cases, enhance performance during the hypoxic insult. A study reported greater power output and faster time to complete a 5-km time trial in cyclists at 2,500-m simulated altitude (Paradis-Deschênes et al., 2018). These enhanced aerobic performances may be related to acute molecular and vascular adaptations that promote local vasodilation, enhance blood flow, and ultimately improve O 2 delivery and utilization (Tapuria et al., 2008;Beaven et al., 2012). ...
... Although, this was not measured during the present case study, it reinforces the potential benefits of pre-screening for hypoxic sensitivity. Our findings suggest that participants who are more sensitive may require additional interventions, such as pre-acclimatisation with hypoxia [16] or heat [82], nutritional strategies [66] or remote ischemic preconditioning [52]. Furthermore, several recent reviews have suggested additional interventions to enhance the success of an altitude training camp [48,74]. ...
PurposeElite endurance runners frequently utilise live high-train high (LHTH) altitude training to improve endurance performance at sea level (SL). Individual variability in response to the hypoxic exposure have resulted in contradictory findings. In the present case study, changes in total haemoglobin mass (tHbmass) and physiological capacity, in response to 4-weeks of LHTH were documented. We tested if a hypoxic sensitivity test (HST) could predict altitude-induced adaptations to LHTH.Methods
Fifteen elite athletes were selected to complete 4-weeks of LHTH (~ 2400 m). Athletes visited the laboratory for preliminary testing (PRE), to determine lactate threshold (LT), lactate turn point (LTP), maximal oxygen uptake VO2max and tHbmass. During LHTH, athletes completed daily physiological measures [arterial oxygen saturation (SpO2) and body mass] and subjective wellbeing questions. Testing was repeated, for those who completed the full camp, post-LHTH (POST). Additionally, athletes completed the HST prior to LHTH.ResultsA difference (P < 0.05) was found from PRE to POST in average tHbmass (1.8% ± 3.4%), VO2max (2.7% ± 3.4%), LT (6.1% ± 4.6%) and LTP (5.4% ± 3.8%), after 4-weeks LHTH. HST revealed a decrease in oxygen saturation at rest (ΔSpr) and higher hypoxic ventilatory response at rest (HVRr) predicted individual changes tHbmass. Lower hypoxic cardiac response at rest (HCRr) and higher HVRr predicted individual changes VO2max.Conclusion
Four weeks of LHTH at ~ 2400 m increased tHbmass and enhanced physiological capacity in elite endurance runners. There was no observed relationship between these changes and baseline characteristics, pre-LHTH serum ferritin levels, or reported incidents of musculoskeletal injury or illness. The HST did however, estimate changes in tHbmass and VO2max. HST prior to LHTH could allow coaches and practitioners to better inform the acclimatisation strategies and training load application of endurance runners at altitude.
... , 2015). Some research has described an improved exercise performance alongside reduced perceptions of fatigue following IPC (Cruz et al., 2015;Paradis-Deschênes et al., 2018). This is in line with a proposed mechanism potentially underlying IPC which involves a nociceptive augmentation where group III/IV muscle afferents become desensitised to the accumulation of fatigue-associated metabolites, reducing muscle afferent feedback. ...
Purpose:
Whilst pre-exercise ischaemic preconditioning (IPC) can improve lower-body exercise performance, its impact on upper-limb performance has received little attention. This study examines the influence of IPC on upper-body exercise performance and oxygen uptake (⩒O2) kinetics.
Methods:
Eleven recreationally-active males (24 ± 2 years) completed an arm-crank graded exercise test to exhaustion to determine the power outputs at the ventilatory thresholds (VT1 and VT2) and ⩒O2peak (40.0 ± 7.4 ml·kg-1·min-1). Four main trials were conducted, two following IPC (4 × 5-min, 220 mmHg contralateral upper-limb occlusion), the other two following SHAM (4 × 5-min, 20 mmHg). The first two trials consisted of a 15-minute constant work rate and the last two time-to-exhaustion (TTE) arm-crank tests at the power equivalents of 95% VT1 (LOW) and VT2 (HIGH), respectively. Pulmonary ⩒O2 kinetics, heart rate, blood-lactate concentration, and rating of perceived exertion were recorded throughout exercise.
Results:
TTE during HIGH was longer following IPC than SHAM (459 ± 115 vs 395 ± 102 s, p = 0.004). Mean response time and change in ⩒O2 between 2-min and end exercise (Δ⩒O2) were not different between IPC and SHAM for arm-cranking at both LOW (80.3 ± 19.0 vs 90.3 ± 23.5 s [p = 0.06], 457 ± 184 vs 443 ± 245 ml [p = 0.83]) and HIGH (96.6 ± 31.2 vs 92.1 ± 24.4 s [p = 0.65], 617 ± 321 vs 649 ± 230 ml [p = 0.74]). Heart rate, blood-lactate concentration, and rating of perceived exertion did not differ between conditions (all p≥0.05).
Conclusion:
TTE was longer following IPC during upper-body exercise despite unchanged ⩒O2 kinetics.
... Previous studies have reported that an acute bout of ischemic preconditioning (IPC) increases whole-body and local exercise performances (de Groot et al., 2010;Crisafulli et al., 2011;Kido et al., 2015;Tanaka et al., 2016;Paradis-Deschênes et al., 2018), mainly assessed with peak O 2 consumption (VO 2 ; VO 2 peak ) and local endurance time. Nevertheless, a meta-analysis by Salvador et al. (2016) showed that this positive effect had a small effect (i.e., effect size = 0.43). ...
An acute bout of ischemic preconditioning (IPC) has been reported to increase exercise performance. Nevertheless, the ineffectiveness of acute IPC on exercise performance has also been reported. Similarly, the effect of a shot-term intervention of IPC on exercise performance remains controversial in previous studies. In this study, we examined the effects of short-term IPC intervention on whole and local exercise performances and its-related parameters. Ten healthy young males undertook a 2-weeks IPC intervention (6 days/weeks). The IPC applied to both legs with three episodes of a 5-min ischemia and 5-min reperfusion cycle. Whole-body exercise performance was assessed by peak O2 consumption (VO2: VO2 peak) during a ramp-incremental cycling test. Local exercise performance was assessed by time to task failure during a knee extensor sustained endurance test. A repeated moderate-intensity cycling test was performed to evaluate dynamics of pulmonary VO2 and muscle deoxygenation. The knee extensor maximal voluntary contraction and quadriceps femoris cross-sectional area measurements were performed to explore the potentiality for strength gain and muscle hypertrophy. The whole-body exercise performance (i.e., VO2 peak) did not change before and after the intervention (P = 0.147, Power = 0.09, Effect size = 0.21, 95% confidence interval: −0.67, 1.09). Moreover, the local exercise performance (i.e., time to task failure) did not change before and after the intervention (P = 0.923, Power = 0.05, Effect size = 0.02, 95% confidence interval: −0.86, 0.89). Furthermore, no such changes were observed for all parameters measured using a repeated moderate-intensity cycling test and knee extensor strength and quadriceps femoris size measurements. These findings suggest that a 2-weeks IPC intervention cannot increase whole-body and local exercise performances, corresponding with ineffectiveness on its-related parameters in healthy young adults. However, the statistical analyses of changes in the measured parameters in this study showed insufficient statistical power and sensitivity, due to the small sample size. Additionally, this study did not include control group(s) with placebo and/or nocebo. Therefore, further studies with a larger sample size and control group are required to clarify the present findings.
... The readily applied, noninvasive technique involves the inflation of blood pressure cuffs on the upper or lower limbs to deliver transient (5 minutes) cycles of ischemia and reperfusion to a target muscle mass. In turn, IPC has been shown to induce vascular (1,18,20,21), humoral (3,15,19,(30)(31)(32)42), and metabolic (8,9,26,34) responses to enhance the body's tolerance to subsequent bouts of ischemic stress (such as exercise), thereby augmenting maximal exercise capacity. However, with the mechanistic understanding still in its infancy, the practical limitations and ecological validity of the technique remain unknown. ...
Halley, SL, Peeling, P, Brown, H, Sim, M, Mallabone, J, Dawson, B, and Binnie, MJ. Repeat application of ischemic preconditioning improves maximal 1,000-m kayak ergometer performance in a simulated competition format. J Strength Cond Res XX(X): 000-000, 2020-This study examined the effects of ischemic preconditioning (IPC) on repeat 1,000-m kayak ergometer time-trial (TT) performance, completed in a simulated competition format. Eight well-trained male kayak athletes performed 3 experimental trials, each consisting of two 1,000-m TTs separated by 80 minutes (TT 1 and TT 2). Trials included; (a) IPC (4 × 5 minutes 220 mm Hg alternating bilateral leg occlusion) 40 minutes before TT 1 only (IPC1); (b) IPC 40 minutes before TT 1 and 20 minutes before TT 2 (IPC2); and (c) no IPC (CON). Time, power, stroke rate, and expired gas variables (V[Combining Dot Above]O2 and accumulated oxygen deficit) were measured throughout each TT; blood gas variables (blood lactate, partial pressure of oxygen and blood pH) and rating of perceived exertion were measured before and after each effort. Physiological, perceptual, and physical measures were analyzed via a repeated measures analysis of variance with the level of significance set at p ≤ 0.05. There were large improvements in completion time for TT 1 in IPC1 (d = 1.24 ± 0.68, p < 0.05) and IPC2 (d = 1.53 ± 0.99, p < 0.05) versus CON. There was also a large improvement in TT 2 completion time in IPC2 versus CON (d = 1.26 ± 1.13, p = 0.03) whereas, IPC1 and CON were indifferent (d = 0.3 ± 0.54, p = 0.23). This study showed that a repeat application of IPC in a simulated competition format may offer further benefit in comparison to a single pre-exercise application of IPC.
... Despite the mixed findings, IPC does appear to have a positive impact on cycling performance. Studies of IPC at altitude, where oxygen availability is also limited, predominantly show increased oxygen saturation and improved exercise performance with IPC (17,47), suggesting that improved VȮ2 kinetics by the working muscle may partly explain the improvement in cycling performance with IPC. ...
Some evidence indicates that ischemic preconditioning (IPC) may positively affect endurance exercise performance, but IPC's effect on running performance is unclear. This study's purpose was to examine the effect of IPC on running performance in recreational runners. Participants (n=12) completed IPC, a sham (SH) condition, and a leg elevation without blood restriction (LE) control condition on separate days (order randomized). For IPC, blood was restricted using blood pressure cuffs inflated to 220 mmHg at the thigh. For SH, the cuffs were inflated to only 20 mmHg. For LE, participants positioned their legs at 90 degrees against a wall while laying supine. The duration of each protocol was 30 minutes (three 5-minute bouts with 5-minute breaks). Following each protocol, participants ran 2.4 kilometers as fast as possible on a motorized treadmill. Run time, heart rate, and perceived exertion were measured and statistically compared, using repeated-measures ANOVA, each 0.8 kilometers. There were no differences in heart rate or time trial performance across protocols (p>0.05; IPC, 612.5±61.2 sec; SH, 608.1±57.9 sec; LE, 612.7±59.1 sec). Rating of perceived exertion at 0.8 kilometers was significantly lower for the IPC protocol than SH in females only (~5.7%, or ~0.8 points on a 6-20 scale; p<0.05). Our IPC protocol did not improve running performance or physiological parameters during a time trial run in recreational runners. The performance benefit seen in this study's most fit individuals suggests that fitness level may influence IPC's efficacy for improving endurance running performance.
... Acute pre-exercise IPC interventions have been reported to enhance lower-limb oxygenation in hypoxia (Wiggins et al., 2019) and increase performance in hypoxic conditions (Paradis-Deschenes et al., 2018). Indeed, five-days of repeated IPC has been shown to enhance endurance performance by ~6.6% at high-altitude (Foster et al., 2014). ...
... The use of the CON strategy could explain the lack of benefit from the application of IPC in the present study compared with previous studies. Several studies reporting benefits from IPC have either performed minimal prior warmup, 23,25,26 no warm-up, 27 or a nonspecified warm-up. 28,29 As suggested in a review by McGowan et al, 1 both passive and active warm-ups may have a beneficial effect on subsequent exercise performance due to improvements in body temperature, muscle glycogen availability, and rate of force development. ...
Purpose:
Ischemic preconditioning (IPC) and postactivation potentiation (PAP) are warm-up strategies proposed to improve high-intensity sporting performance. However, only few studies have investigated the benefits of these strategies compared with an appropriate control (CON) or an athlete-selected (SELF) warm-up protocol. Therefore, this study examined the effects of 4 different warm-up routines on 1-km time-trial (TT) performance with competitive cyclists.
Methods:
In a randomized crossover study, 12 well-trained cyclists (age 32 [10] y, mass 77.7 [4.6] kg, peak power output 1141 [61] W) performed 4 different warm-up strategies-(CON) 17 minutes CON only, (SELF) a self-determined warm-up, (IPC) IPC + CON, or (PAP) CON + PAP-prior to completing a maximal-effort 1-km TT. Performance time and power, quadriceps electromyograms, muscle oxygen saturation (SmO2), and blood lactate were measured to determine differences between trials.
Results:
There were no significant differences (P > .05) in 1-km performance time between CON (76.9 [5.2] s), SELF (77.3 [6.0] s), IPC (77.0 [5.5] s), or PAP (77.3 [5.9] s) protocols. Furthermore, there were no significant differences in mean or peak power output between trials. Finally, electromyogram activity, SmO2, and recovery blood lactate concentration were not different between conditions.
Conclusions:
Adding IPC or PAP protocols to a short CON warm-up appears to provide no additional benefit to 1-km TT performance with well-trained cyclists and is therefore not recommended. Furthermore, additional IPC and PAP protocols had no effect on electromyograms and SmO2 values during the TT or peak lactate concentration during recovery.
... Despite large between-study variability, IPC benefits include a subsequent 1-5% gain in time-trial performance and aerobic capacity (Salvador et al., 2016). IPC is also effective for improving performance at altitude (Paradis-Deschênes et al., 2018). While it represents an attractive ergogenic aid, likely related to local hyperaemia inducing accelerated/greater tissue re-/oxygenation dynamics, mechanisms remain poorly resolved (Incognito et al., 2016). ...
With minimal costs and travel constraints for athletes, the “living low-training high” (LLTH) approach is becoming an important intervention for modern sport. The popularity of the LLTH model of altitude training is also associated with the fact that it only causes a slight disturbance to athletes' usual daily routine, allowing them to maintain their regular lifestyle in their home environment. In this perspective article, we discuss the evolving boundaries of the LLTH paradigm and its practical applications for athletes. Passive modalities include intermittent hypoxic exposure at rest (IHE) and Ischemic preconditioning (IPC). Active modalities use either local [blood flow restricted (BFR) exercise] and/or systemic hypoxia [continuous low-intensity training in hypoxia (CHT), interval hypoxic training (IHT), repeated-sprint training in hypoxia (RSH), sprint interval training in hypoxia (SIH) and resistance training in hypoxia (RTH)]. A combination of hypoxic methods targeting different attributes also represents an attractive solution. In conclusion, a growing number of LLTH altitude training methods exists that include the application of systemic and local hypoxia stimuli, or a combination of both, for performance enhancement in many disciplines.
... An improved exercise performance and a lower effort perception during exercise in response to IPC has also been shown by others (Cruz et al., 2015;Paradis-Deschenes et al., 2018). In line with our data for the 'responders, ' Cruz et al. (2015) have found that the increased constant-load cycling performance after IPC was accompanied by a lower effort perception and higher muscle activity. ...
The present study was designed to provide further insight into the mechanistic basis for the improved exercise tolerance following ischemic preconditioning (IPC) by investigating key-determinants of performance and perceived fatigability.
Using a randomized, counterbalanced, single-blind, sham-controlled, crossover design, 16 males performed an isometric time-to-exhaustion test with the knee extensors at 20% maximal voluntary torque (MVT) after an IPC and a sham treatment (SHAM). Those who improved their time-to-exhaustion following IPC performed a time-matched IPC trial corresponding to the exercise duration of SHAM (IPCtm). Neuromuscular function was assessed before and after exercise termination during each condition (IPC, IPCtm, and SHAM) to analyze the impact of IPC on performance fatigability and its central and peripheral determinants. Muscle oxygenation (SmO2), muscle activity, and perceptual responses (effort and muscle pain) were recorded during exercise. Performance fatigability as well as its central and peripheral determinants were quantified as percentage pre-post changes in MVT (ΔMVT) as well as voluntary activation (ΔVA) and quadriceps twitch torque evoked by paired electrical stimuli at 100 and 10 Hz (ΔPS100 and ΔPS10·PS100–1-ratio), respectively.
Time-to-exhaustion, performance fatigability, its determinants, muscle activity, SmO2, and perceptual responses during exercise were not different between IPC and SHAM. However, six participants improved their performance by >10% following IPC (299 ± 71 s) compared to SHAM (253 ± 66 s, d = 3.23). The time-matched comparisons (IPCtm vs. SHAM) indicated that performance fatigability, its determinants, and SmO2 were not affected, while effort perception seemed to be lower (ηp² = 0.495) in those who improved their time-to-exhaustion. The longer time-to-exhaustion following IPC seemed to be associated with a lower effort perception (ηp² = 0.380) and larger impairments in neuromuscular function, i.e. larger ΔMVT, ΔVA, and ΔPS10·PS100–1 (d = 0.71, 1.0, 0.92, respectively).
IPC did neither affect exercise tolerance, performance fatigability, as well as its central and peripheral determinants, nor muscle activity, SmO2, and perceptual responses during submaximal isometric exercise. However, IPC seemed to have an ergogenic effect in a few subjects, which might have resulted from a lower effort perception during exercise. These findings support the assumption that there are ‘responders’ and ‘non-responders’ to IPC.
... It is largely known that training level of participants is directly related to results analysis. Just two studies selected for this review presented high fitness level participants (based on physiological and performance parameters, e.g., VO 2max , time-trial): Richard and Billaut (2018) tested elite speed skaters, while Paradis-Deschenes analysed cyclists (Paradis-Deschenes et al. 2018). All other studies included amateur or recreational participants, even when the title or some part of the text mentioned "highly trained". ...
Ischemic preconditioning (IPC) has been suggested as a potential ergogenic aid to improve exercise performance, although controversial findings exist. The controversies may be explained by several factors, including the mode of exercise, the ratio between the magnitude of improvement, or the error of measurement and physiological meaning. However, a relevant aspect has been lacking in the literature: the interpretation of the findings considering statistical tests and adequate effect size (ES) according to the fitness level of individuals. Thus, we performed a systematic review with meta-analysis to update the effects of IPC on exercise performance and physiological responses, using traditional statistics (P values), ES, and smallest worth change (SWC) approach contextualizing the IPC application to applied Sports and Exercise performance. Forty-five studies met the inclusion criteria. Overall, the results show that IPC has a minimal or nonsignificant effect on performance considering the fitness level of the individuals, using statistical approaches (i.e., tests with P value, ES, and SWC). Therefore, IPC procedures should be revised and refined in future studies to evaluate if IPC promotes positive effects on performance in a real-world scenario with more consistent interpretation.
... It has been suggested that the large variability in exercise performance response within and between studies may be explained by responders and non-responders to IPC treatment (Incognito, Burr, & Millar, 2016;Koch, Della-Morte, Dave, Sacco, & Perez-Pinzon, 2014). However, few existing studies that suggest individual responses to IPC employ appropriate experimental design (Atkinson & Batterham, 2015), thereby preventing legitimate evaluation of response versus non-response to the IPC stimulus (Paradis-deschÊnes, Joanisse, & Billaut, 2018;Tomschi, Niemann, Bloch, Predel, & Grau, 2018). It is imperative to assess the within-subject variability in the exercise performance for an evaluation of true IPC response versus non-response. ...
Purpose:
To use repeated control trials to measure within-subject variability and assess the existence of responders to ischemic preconditioning (IPC). Secondly, to determine whether repeated IPC can evoke a dosed ergogenic response.
Methods:
Twelve aerobically fit individuals each completed three control and three IPC 5-km cycling time trials. IPC trials included: (i) IPC 15-min preceding the trial (traditional IPC), (ii) IPC 24-h and 15-min preceding (IPC × 2), (iii) IPC 48-h, 24-h, and 15-min preceding (IPC × 3). IPC consisted of 3 × 5-min cycles of occlusion and reperfusion at the upper thighs. To assess the existence of a true response to IPC, individual performance following traditional IPC was compared to each individual's own 5-km TT coefficient of variation. In individuals who responded to IPC, all three IPC conditions were compared to the mean of the three control trials (CONavg) to determine whether repeated IPC can evoke a dosed ergogenic response.
Results:
9 of 12 (75%) participants improved 5-km time (-1.8 ± 1.7%) following traditional IPC, however, only 7 of 12 (58%) improved greater than their own variability between repeated controls (true responders). In true responders only, we observed a significant mean improvement in 5-km TT completion following traditional IPC (478 ± 50 s), IPC × 2 (481 ± 51 s), and IPC × 3 (480.5 ± 49 s) compared to mean CONavg (488 ± 51s; p < 0.006), with no differences between various IPC trials (p > 0.05).
Conclusion:
A majority of participants responded to IPC, providing support for a meaningful IPC-mediated performance benefit. However, repeated bouts of IPC on consecutive days do not enhance the ergogenic effect of a single bout of IPC.
... The exception to this might be when additional stressors are imposed during the fixed-endpoint tasks to induce a comparable oxidative stress, such as exercising in hypoxia ( Kjeld et al. 2014;Par- adis-Deschenes et al. 2018). For example, the ergogenic effect of IPC on 5 km cycling time trial (fixed-end point) performance has been shown to increase under progressively hypoxic conditions (F I O 2 0.18: +1.1%; F I O 2 0.15: +1.7%) (Paradis-Deschenes et al. 2018). ...
Ischemic preconditioning (IPC) has been suggested to preserve neural drive during fatiguing dynamic exercise, however, it remains unclear as to whether this may be the consequence of IPC‐enhanced muscle oxygenation. We hypothesized that the IPC‐enhanced muscle oxygenation during a dynamic exercise task would subsequently attenuate exercise‐induced reductions in voluntary activation. Ten resistance trained males completed three 3 min maximal all‐out tests (AOTs) via 135 isokinetic leg extensions preceded by treatments of IPC (3 × 5 min bilateral leg occlusions at 220 mmHg), SHAM (3 × 5 min at 20 mmHg) or CON (30 min passive rest). Femoral nerve stimulation was utilized to assess voluntary activation and potentiated twitch torque during maximal voluntary contractions (MVCs) performed at baseline (BL), prior to the AOT (Pre), and then 10 sec post (Post). Tissue oxygenation (via near‐infrared spectroscopy) and sEMG activity was measured throughout the AOT. MVC and twitch torque levels declined (MVC: −87 ± 23 Nm, 95% CI = −67 to −107 Nm; P < 0.001, twitch: −30 ± 13 Nm; 95% CI = −25 to −35 Nm; P < 0.001) between Pre and Post without reductions in voluntary activation (P = 0.72); there were no differences between conditions (MVC: P = 0.75, twitch: P = 0.55). There were no differences in tissue saturation index (P = 0.27), deoxyhemoglobin concentrations (P = 0.86) or sEMG activity (P = 0.92) throughout the AOT. These findings demonstrate that IPC does not preserve neural drive during an all‐out 3 min isokinetic leg extension task. This study aimed to investigate how ischemic preconditioning (IPC)‐enhanced muscle oxygenation influences reductions in neural drive induced by a maximal dynamic exercise test. Our results show that pre‐post declines in neural drive were unaffected by IPC and furthermore, neither surface electromyography nor measures of skeletal muscle oxygenation were influenced by IPC throughout the exercise test.
... Two studies found a positive effect of IPC on performance in altitude. One study found a greater impact of IPC on exercise performance at a simulated altitude of 2400 m than at an altitude of 1200 m. 56 The other study found that IPC improved oxygen saturation during a time trial run in altitude. 57 ...
Ischemic preconditioning (IPC) is an attractive method for athletes owing to its potential to enhance exercise performance. However, the effectiveness of the IPC intervention in the field of sports science remains mitigated. The number of cycles of ischemia and reperfusion, as well as the duration of the cycle, varies from one study to another. Thus, the aim of this systematic review was to provide a comprehensive review examining the IPC literature in sports science. A systematic literature search was performed in PubMed (MEDLINE) (from 1946 to May 2018), Web of Science (sport sciences) (from 1945 to May 2018), and EMBASE (from 1974 to May 2018). We included all studies investigating the effects of IPC on exercise performance in human subjects. To assess scientific evidence for each study, this review was conducted following the PRISMA statement. The electronic database search generated 441 potential articles that were screened for eligibility. A total of 52 studies were identified as eligible and valid for this systematic review. The studies included were of high quality, with 48 of the 52 studies having a randomized, controlled trial design. Most studied showed that IPC intervention can be beneficial to exercise performance. However, IPC intervention seems to be more beneficial to healthy subjects who wish to enhance their performance in aerobic exercises than athletes. Thus, this systematic review highlights that a better knowledge of the mechanisms generated by the IPC intervention would make it possible to optimize the protocols according to the characteristics of the subjects with the aim of suggesting to the subjects the best possible experience of IPC intervention.
... The findings of the present study are consistent with previous studies reporting better vigorous to severe aerobic exercise performance (5,12,13,16,25,45) and supramaximal performance with limb-based IPC (14,18,46). However, it is important to note that the exercise performance applications of local and remote IPC remain inconsistent, as some studies have reported neutral outcomes. ...
... Finally, in recent work done by Paradis-Deschenes et al (36) it has been suggested that km p r orm n s "l k ly mprov " ~7.3s t mo r t lt tu m n "poss bly mprov " ~ . s t low lt tu m . ...
Introduction:
Ischemic preconditioning (IPC) before exercise has been shown to be a novel approach to improve performance in different exercise modes in normoxia (NORM). Few studies have been conducted examining potential mechanisms behind these improvements, and less has been done examining its influence during exercise in hypoxia (HYP). Oxygen uptake and extraction kinetics are factors that have been implicated as possible determinants of cycling performance. We hypothesized that IPC would lead to improvements in oxygen extraction and peripheral blood flow kinetics, and this would translate to improvements in cycling time trial (TT) performance in both NORM and HYP.
Methods:
Thirteen men (age, 24 ± 7 yr; V˙O2max, 63.1 ± 5.1 mL·kg·min) participated in the study. Subjects completed trials of each combination of normobaric HYP (FiO2 = 0.16, simulating ~8000 ft/2500 m) or NORM (FiO2 = 0.21) with preexercise IPC protocol (4 × 5 min at 220 mm Hg) or SHAM procedure. Trials included submaximal constant load cycle exercise bouts (power outputs of 15% below gas exchange threshold, and 85% of V˙O2max), and a 5-km cycling performance TT.
Results:
Ischemic preconditioning significantly improved 5-km TT time in NORM by 0.9% ± 1.8% compared with SHAM (IPC, 491.2 ± 35.2 s vs SHAM, 495.9 ± 36.0 s; P < 0.05). Ischemic preconditioning did not alter 5-km TT performance times in HYP (P = 0.231). Ischemic preconditioning did, however, improve tissue oxygen extraction in HYP (deoxygenated hemoglobin/myoglobin: IPC, 21.23 ± 10.95 μM; SHAM, 19.93 ± 9.91 μM; P < 0.05) during moderate-intensity exercise.
Conclusions:
Our data confirm that IPC is an effective ergogenic aid for athletes performing 5-km cycling TT bouts in NORM. Ischemic preconditioning did mitigate the declines in tissue oxygen during moderate-intensity exercise in HYP, but this did not translate to a significant effect on mean group performance. These data suggest that IPC may be of benefit for athletes training and competing in NORM.
... on performance and that IP had a > 99 % and ~58 % chance of benefiting aerobic and anaerobic exercise, respectively [28]. In terms of the magnitude of improvement, during 5-km cycling time-trial performances Paradis-Deschenes et al. (2017) noted a 1.1 % and 1.5 % improvement at low and moderate altitudes, respectively [25]. ...
Ischemic preconditioning (IP) has a small benefit on exercise performance, but differences in the IP method, performance tasks and exercise modality have made providing practical coach guidelines difficult. We investigated the performance-enhancing effects of IP on cyclists by comparing the frequency of IP application over a 7-day period. Using a randomized, sham-controlled, single-blinded experiment, 24 competitive age-group track cyclists (38±12 years) were assigned to one of three twice-daily (sham: 20 and 20 mmHg; once-a-day: 20 and 220 mmHg; twice-a-day: 220 and 220 mmHg) IP leg protocols (4 × 5 min ischemia/5 min reperfusion alternating between legs) over seven consecutive days. A 4000-m cycling-ergometer time trial was completed before, immediately following and one week after the protocols. Neither mean power, nor 4000-m performance time nor VO2 were significantly affected by either of the IP protocols compared to the sham at any time point following treatment. Repeated application of IP over seven days did not enhance the performance of trained cyclists in a 4000-m laboratory time trial. More research is required to understand how changes to methodological variables can improve the chances of IP successfully enhancing athlete performance.
Military and/or emergency services personnel may be required to perform high-intensity physical activity during exposure to elevated inspired carbon dioxide (CO 2 ). Although many of the physiological consequences of hypercapnia are well characterized, the effects of graded increases in inspired CO 2 on self-paced endurance performance have not been determined. The aim of this study was to compare the effects of 0%, 2%, and 4% inspired CO 2 on two-mile run performance as well as physiological and perceptual responses during time trial exercise. Twelve physically active volunteers (peak oxygen uptake = 49±5 mL kg ⁻¹ min ⁻¹ ; 3 women) performed three experimental trials in a randomized, single-blind, crossover manner, breathing 21% oxygen with either 0%, 2%, or 4% CO 2 . During each trial, participants completed 10 minutes of walking at ~40% peak oxygen uptake followed by a self-paced two-mile treadmill time trial. One participant was unable to complete the 4% CO 2 trial due to lightheadedness during the run. Compared to the 0% CO 2 trial, run performance was 5±3% and 7±3% slower in the 2% and 4% CO 2 trials, respectively (both p<0.001). Run performance was significantly slower with 4% vs. 2% CO 2 (p=0.046). The dose-dependent performance impairments were accompanied by stepwise increases in mean ventilation, despite significant reductions in running speed. Dyspnea and headache were significantly elevated during the 4% CO 2 trial compared to both the 0% and 2% trials. Overall, our findings show that graded increases in inspired CO 2 impair endurance performance in a stepwise manner in healthy humans.
Remote ischemic preconditioning (RIPC) may improve exercise performance. However, the influence of RIPC on aerobic performance and underlying physiological mechanisms during hypobaric hypoxia (HH) exposure remains relatively uncertain. Here, we systematically evaluated the potential performance benefits and underlying mechanisms of RIPC during HH exposure. Seventy-nine healthy participants were randomly assigned to receive sham intervention or RIPC (4 × 5 min occlusion 180 mm Hg/reperfusion 0 mm Hg, bilaterally on the upper arms) for 8 consecutive days in phases 1 (24 participants) and phase 2 (55 participants). In the phases 1, we measured the change in maximal oxygen uptake capacity (VO 2 max) and muscle oxygenation (SmO 2 ) on the leg during a graded exercise test. We also measured regional cerebral oxygenation (rSO 2 ) on the forehead. These measures and physiological variables, such as cardiovascular hemodynamic parameters and heart rate variability index, were used to evaluate the intervention effect of RIPC on the changes in bodily functions caused by HH exposure. In the phase 2, plasma protein mass spectrometry was then performed after RIPC intervention, and the results were further evaluated using ELISA tests to assess possible mechanisms. The results suggested that RIPC intervention improved VO 2 max (11.29%) and accelerated both the maximum (18.13%) and minimum (53%) values of SmO 2 and rSO 2 (6.88%) compared to sham intervention in hypobaric hypoxia exposure. Cardiovascular hemodynamic parameters (SV, SVRI, PPV% and SpMet%) and the heart rate variability index (Mean RR, Mean HR, RMSSD, pNN50, Lfnu, Hfnu, SD1, SD2/SD1, ApEn, SampEn, DFA1and DFA2) were evaluated. Protein sequence analysis showed 42 unregulated and six downregulated proteins in the plasma of the RIPC group compared to the sham group after HH exposure. Three proteins, thymosin β4 (Tβ4), heat shock protein-70 (HSP70), and heat shock protein-90 (HSP90), were significantly altered in the plasma of the RIPC group before and after HH exposure. Our data demonstrated that in acute HH exposure, RIPC mitigates the decline in VO 2 max and regional oxygenation, as well as physiological variables, such as cardiovascular hemodynamic parameters and the heart rate variability index, by influencing plasma Tβ4, HSP70, and HSP90. These data suggest that RIPC may be beneficial for acute HH exposure.
INTRODUCTION: Repeated ischemic preconditioning (IPC) can improve muscle and pulmonary oxygen on-kinetics, blood flow, and exercise efficiency, but these effects have not been investigated in severe hypoxia. The aim of the current study was to evaluate the effects of 7 d of IPC on resting and exercising muscle and cardio-pulmonary responses to severe hypoxia.METHODS: A total of 14 subjects received either: 1) 7 d of repeated lower-limb occlusion (4 × 5 min, 217 ± 30 mmHg) at limb occlusive pressure (IPC) or SHAM (4 × 5 min, 20 mmHg). Subjects were tested for resting limb blood flow, relative microvascular deoxyhemoglobin concentration ([HHB]), and pulmonary oxygen (Vo2p) responses to steady state and incremental exercise to exhaustion in hypoxia (fractional inspired O₂ = 0.103), which was followed by 7 d of IPC or SHAM and retesting 72 h post-intervention.RESULTS: There were no effects of IPC on maximal oxygen consumption, time to exhaustion during the incremental test, or minute ventilation and arterial oxygen saturation. However, the IPC group had higher delta efficiency based on pooled results and lower steady state Δ[HHB] (IPC ∼24% vs. SHAM ∼6% pre to post), as well as slowing the [HHB] time constant (IPC ∼26% vs. SHAM ∼3% pre to post) and reducing the overshoot in [HHB]: Vo₂ ratio during exercise onset.CONCLUSIONS: Collectively, these results demonstrate that muscle O₂ efficiency and microvascular O₂ distribution can be improved by repeated IPC, but there are no effects on maximal exercise capacity in severe hypoxia.Chopra K, Jeffries O, Tallent J, Heffernan S, Kilduff L, Gray A, Waldron M. Repeated ischemic preconditioning effects on physiological responses to hypoxic exercise. Aerosp Med Hum Perform. 2022; 93(1):13-21.
RESUMO: O pré-condicionamento isquêmico [do termo em inglês ischemic preconditioning (IPC)] é uma estratégia caracterizada por breves ciclos de restrição do fluxo sanguíneo seguidos de reperfusão, realizados nos membros superiores ou inferiores com o objetivo de melhorar o desempenho físico. Essa intervenção tem chamado atenção devido a sua característica não invasiva, seu baixo custo e a fácil aplicação. Uma vez que não há um consenso sobre a sua efetividade como uma estratégia ergogênica, o objetivo deste estudo foi investigar o seu estado atual de produção científica, o efeito sobre o desempenho físico e o efeito do nível de treinamento dos participantes e diferentes exercícios/testes utilizados para avaliação do desempenho. Sessenta e sete artigos, envolvendo 984 participantes (177 mulheres) de diferentes níveis de treinamento, preencheram os critérios de inclusão. Sete exercícios (ciclismo, exercício resistido, corrida, natação, patinação, futebol, remo) e cinco níveis de treinamento (destreinados, recreacionalmente treinados,
treinados, bem treinados, profissional) foram identificados. A maioria da produção científica sobre IPC e desempenho físico foi publicada
a partir de 2015. Mais da metade dos estudos apresentaram um efeito positivo do IPC sobre o desempenho físico (59,7%, n=40). O teste exato de Fischer mostrou que existe uma relação entre o efeito do IPC sobre o desempenho físico e o nível de treinamento dos participantes [X2(8) = 15,149; p = 0,026], mas não entre o efeito do IPC
e exercício/teste [X2(12) = 19,528; p = 0,129]. Na última década, houve um aumento substancial na produção cientifica sobre IPC e desempenho físico. Nossos achados sustentam um efeito benéfico do IPC na melhora do desempenho físico, sendo este efeito mais pronunciado em indivíduos destreinados e recreacionalmente treinados, independente do exercício/teste realizado.
Despite compelling muscular structure and function changes resulting from blood flow restricted (BFR) resistance training, mechanisms of action remain poorly characterized. Alterations in tissue O 2 saturation (TSI%) and metabolites are potential drivers of observed changes, but their relationships with degree of occlusion pressure are unclear. We examined local TSI% and blood lactate (BL) concentration during BFR training to failure using different occlusion pressures on strength, hypertrophy, and muscular endurance over an 8-week training period. Twenty participants (11 males/9 females) trained 3/wk for 8 wk using high pressure (100% resting limb occlusion pressure, LOP; 20% one-repetition maximum (1RM)), moderate pressure (50% LOP, 20%1RM), or traditional resistance training (TRT; 70%1RM). Strength, size, and muscular endurance were measured pre/post training. TSI% and BL were quantified during a training session. Despite overall increases, no group preferentially increased strength, hypertrophy, or muscular endurance (p > 0.05). Neither TSI% nor BL concentration differed between groups (p > 0.05). Moderate pressure resulted in greater accumulated deoxygenation stress (TSI% × time) (–6352 ± 3081, –3939 ± 1835, –2532 ± 1349 au for moderate pressure, high pressure, and TRT, p = 0.018). We demonstrate that BFR training to task-failure elicits similar strength, hypertrophy, and muscular endurance changes to TRT. Further, varied occlusion pressure does not impact these outcomes or elicit changes in TSI% or BL concentrations.
Novelty: Training to task failure with low-load blood flow restriction elicits similar improvements to traditional resistance training, regardless of occlusion pressure. During blood flow restriction, altering occlusion pressure does not proportionally impact tissue O 2 saturation nor blood lactate concentrations.
Ischemic preconditioning (IPC) has been repeatedly reported to augment maximal exercise performance over a range of exercise durations and modalities. However, an examination of the relevant literature indicates that the reproducibility and robustness of ergogenic responses to this technique are variable, confounding expectations about the magnitude of its effects. Considerable variability among study methodologies may contribute to the equivocal responses to IPC. This review focuses on the wide range of methodologies used in IPC research, and how such variability likely confounds interpretation of the interactions of IPC and exercise. Several avenues are recommended to improve IPC methodological consistency, which should facilitate a future consensus about optimizing the IPC protocol, including due consideration of factors such as: location of the stimulus, the time between treatment and exercise, individualized tourniquet pressures and standardized tourniquet physical characteristics, and the incorporation of proper placebo treatments into future study designs.
O pré-condicionamento isquêmico (PCI) é um procedimento que consiste na aplicação de um aparelho para a oclusão vascular (OV), alternando momentos de OV e reperfusão. O PCI é um método de trabalho empregado para bloquear o fluxo sanguíneo de maneira remota e não invasiva, através de um torniquete pneumático antes de realização de um exercício. Diversos estudos têm investigado os efeitos do PCI no desempenho esportivo e muscular. Entretanto, poucos estudos investigaram os efeitos do PCI sobre as respostas hemodinâmicas após o exercício. Portanto, o objetivo do presente estudo foi investigar o efeito agudo do PCI aplicado antes de testes de força isométrica e de endurance muscular sobre a pressão arterial sistólica (PAS), pressão arterial diastólica (PAD), frequência cardíaca (FC), duplo produto (DP), pressão arterial média (PAM) e saturação de oxigênio (SPO2) em homens treinados. A amostra foi composta por 12 indivíduos saudáveis, treinados recreacionalmente. O estudo foi realizado em um total de 3 visitas em dias não consecutivos (3 a 7 dias de intervalo). Durante a primeira visita ao laboratório foram assinalados os Termos de Consentimentos Livres e Esclarecidos (TCLE), de acordo com a declaração de Helsinki, em seguida, respondidos os Physical Activity Readiness Questionnaire / PAR-Q, imediatamente após foram avaliados a antropometria e em seguida uma familiarização com os testes e o método. Na segunda e terceira visita os voluntários foram divididos aleatoriamente com entrada contrabalanceada e alternada, nos seguintes protocolos experimentais: a) PCI + testes de força isométrica e testes de endurance muscular (PCI); b) protocolo controle (CON) testes de força isométrica e testes de endurance muscular, logo após os foram mensuradas as variáveis hemodinâmicas. Os resultados motraram que as respostas da PAS, PAD, FC, DP, PAM e SPO2 não apresentaram diferenças significativas entre os protocolos PCI e CON (p> 0.05). A PAS foi significativamente maior no PCI comparando o momento pré vs. pós (p=0.01). A FC foi significativamente maior, comparando pré vs. pós, no PCI (p=0.01) e no CON (p=0.01). O DP foi significativamente maior, comparando pré vs. pós, no PCI (p=0.01) e no CON (p=0.01). A PAM não apresentou diferenças significativas, comparando pré vs. pós, nos protocolos PCI e CON (p>0.05). A SPO2 não apresentou diferenças significativas, comparando pré vs. pós, nos protocolos PCI e CON (p>0.05). Em conclusão, nossos achados demonstraram que aplicação do PCI antes de teste de força isométrica e de endurance muscular não alteraram significativamente as respostas hemodinâmicas (PAS, PAD, FC, DP, PAM e SPO2) em homens treinados.
The aim of the present study was to determine whether ischemic preconditioning (IPC)-mediated effects on neuromuscular function are dependent on tissue oxygenation. Eleven resistance-trained males completed four exercise trials (6 sets of 11 repetitions of maximal effort dynamic single-leg extensions) in either normoxic [fraction of inspired oxygen (
F
I
O
2
): 21%) or hypoxic
F
I
O
2
: 14%] conditions, preceded by treatments of either IPC (3 × 5 min bilateral leg occlusions at 220 mmHg) or sham (3 × 5 min at 20 mmHg). Femoral nerve stimulation was utilized to assess voluntary activation and potentiated twitch characteristics during maximal voluntary contractions (MVCs). Tissue oxygenation (via near-infrared spectroscopy) and surface electromyography activity were measured throughout the exercise task. MVC and twitch torque declined 62 and 54%, respectively (MVC: 96 ± 24 N·m, Cohen's d = 2.9, P < 0.001; twitch torque: 37 ± 11 N·m, d = 1.6, P < 0.001), between pretrial measurements and the sixth set without reductions in voluntary activation (P > 0.21); there were no differences between conditions. Tissue oxygenation was reduced in both hypoxic conditions compared with normoxia (P < 0.001), with an even further reduction of 3% evident in the hypoxic IPC compared with the sham trial (mean decrease 1.8 ± 0.7%, d = 1.0, P < 0.05). IPC did not affect any measure of neuromuscular function regardless of tissue oxygenation. A reduction in
F
I
O
2
did invoke a humoral response and improved muscle O2 extraction during exercise, however, it did not manifest into any performance benefit.NEW & NOTEWORTHY Ischemic preconditioning did not affect any facet of neuromuscular function regardless of the degree of tissue oxygenation. Reducing the fraction of inspired oxygen induced localized tissue deoxygenation, subsequently invoking a humoral response, which improved muscle oxygen extraction during exercise. This physiological response, however, did not manifest into any performance benefits.
Purpose:
Recent studies have reported ischemic preconditioning (IPC) can acutely improve endurance exercise performance in athletes. However, placebo and nocebo effects have not been sufficiently controlled, and the effect on aerobic metabolism parameters that determine endurance performance [e.g., oxygen cost of running, lactate threshold, and maximal oxygen uptake (V[Combining Dot Above]O2max)] has been equivocal. Thus, we circumvented limitations from previous studies to test the effect of IPC on aerobic metabolism parameters and endurance performance in well-trained runners.
Methods:
Eighteen runners (14 men/4 women) were submitted to three interventions, in random order: IPC; sham intervention (SHAM); and resting control (CT). Subjects were told both IPC and SHAM would improve performance compared to CT (i.e., similar placebo induction) and IPC would be harmless despite circulatory occlusion sensations (i.e., nocebo avoidance). Next, pulmonary ventilation and gas exchange, blood lactate concentration, and perceived effort were measured during a discontinuous incremental test on a treadmill. Then, a supramaximal test was used to verify the V[Combining Dot Above]O2max and assess endurance performance (i.e., time to exhaustion).
Results:
Ventilation, oxygen uptake, carbon dioxide output, lactate concentration, and perceived effort were similar among IPC, SHAM, and CT throughout the discontinuous incremental test (P > 0.05). Oxygen cost of running, lactate threshold, and V[Combining Dot Above]O2max were also similar among interventions (P > 0.05). Time to exhaustion was longer after IPC (mean ± SEM, 165.34 ± 12.34 s) and SHAM (164.38 ± 11.71 s) than CT (143.98 ± 12.09 s; P = 0.02 and 0.03, respectively), but similar between IPC and SHAM (P = 1.00).
Conclusions:
IPC did not change aerobic metabolism parameters, whereas improved endurance performance. The IPC improvement, however, did not surpass the effect of a placebo intervention.
Muscle ischemia and reperfusion induced by ischemic preconditioning (IPC) can improve performance in various activities. However, the underlying mechanisms are still poorly understood. The purpose of this study was to examine the effects of IPC on muscle hemodynamics and oxygen (O2) uptake during repeated maximal contractions. In a cross-over, randomized, single-blind study, 10 strength-trained men performed 5 sets of 5 maximal voluntary knee extensions of the right leg on an isokinetic dynamometer, preceded by either IPC of the right lower limb (3×5-min compression/5-min reperfusion cycles at 200 mm Hg) or sham (20 mm Hg). Changes in deoxyhemoglobin, expressed as a percentage of arterial occlusion, and total hemoglobin ([THb]) concentrations of the vastus lateralis muscle were monitored continuously by near-infrared spectroscopy. Differences between IPC and sham were analyzed using Cohen's effect size (ES) ± 90% confidence limits, and magnitude-based inferences. Compared with sham, IPC likely increased muscle blood volume at rest (↑[THb], 46.5%; ES, 0.56; 90% confidence limits for ES, -0.21, 1.32). During exercise, peak force was almost certainly higher (11.8%; ES, 0.37; 0.27, 0.47), average force was very likely higher (12.6%; ES, 0.47; 0.29, 0.66), and average muscle O2 uptake was possibly increased (15.8%; ES, 0.36; -0.07, 0.79) after IPC. In the recovery periods between contractions, IPC also increased blood volume after sets 1 (23.6%; ES, 0.30; -0.05, 0.65) and 5 (25.1%; ES, 0.32; 0.09, 0.55). Three cycles of IPC immediately increased muscle perfusion and O2 uptake, conducive to higher repeated force capacity in strength-trained athletes. This maneuver therefore appears relevant to enhancing exercise training stimulus.
In the last decade the study of the human brain and muscle energetics underwent a radical change, thanks to the progressive introduction of noninvasive techniques, including near-infrared (NIR) spectroscopy (NIRS). This review summarizes the most recent literature about the principles, techniques, advantages, limitations, and applications of NIRS in exercise physiology and neuroscience. The main NIRS instrumentations and measurable parameters will be reported. NIR light (700-1000 nm) penetrates superficial layers (skin, subcutaneous fat, skull, etc.) and is either absorbed by chromophores (oxy- and deoxyhemoglobin and myoglobin) or scattered within the tissue. NIRS is a noninvasive and relatively low-cost optical technique that is becoming a widely used instrument for measuring tissue O-2 saturation, changes in hemoglobin volume and, indirectly, brain/muscle blood flow and muscle O-2 consumption. Tissue O-2 saturation represents a dynamic balance between O-2 supply and O-2 consumption in the small vessels such as the capillary arteriolar and venular bed. The possibility of measuring the cortical activation in response to different stimuli, and the changes in the cortical cytochrome oxidase redox state upon O-2 delivery changes, will also be mentioned.
Background
Ischemic preconditioning (IPC) is the exposure to brief periods of circulatory occlusion and reperfusion in order to protect local or systemic organs against subsequent bouts of ischemia. IPC has also been proposed as a novel intervention to improve exercise performance in healthy and diseased populations.
Objective
The purpose of this systematic review is to analyze the evidence for IPC improving exercise performance in healthy humans.
Methods
Data were obtained using a systematic computer-assisted search of four electronic databases (MEDLINE, PubMed, SPORTDiscus, CINAHL), from January 1985 to October 2015, and relevant reference lists.
Results
Twenty-one studies met the inclusion criteria. The collective data suggest that IPC is a safe intervention that may be capable of improving time-trial performance. Available individual data from included studies demonstrate that IPC improved time-trial performance in 67 % of participants, with comparable results in athletes and recreationally active populations. The effects of IPC on power output, oxygen consumption, rating of perceived exertion, blood lactate accumulation, and cardiorespiratory measures are unclear. The within-study heterogeneity may suggest the presence of IPC responders and non-responders, which in combination with small sample sizes, likely confound interpretation of mean group data in the literature.
Conclusion
The ability of IPC to improve time-trial performance is promising, but the potential mechanisms responsible require further investigation. Future work should be directed toward identifying the individual phenotype and protocol that will best exploit IPC-mediated exercise performance improvements, facilitating its application in sport settings.
Ischemic preconditioning (IPC) improves maximal exercise performance. However, the potential mechanism(s) underlying the beneficial effects of IPC remain unknown. The dynamics of pulmonary oxygen uptake (VO2) and muscle deoxygenation during exercise is frequently used for assessing O2 supply and extraction. Thus, this study examined the effects of IPC on systemic and local O2 dynamics during the incremental step transitions from low- to moderate- and from moderate- to severe-intensity exercise. Fifteen healthy, male subjects were instructed to perform the work-to-work cycling exercise test, which was preceded by the control (no occlusion) or IPC (3 × 5 min, bilateral leg occlusion at >300 mmHg) treatments. The work-to-work test was performed by gradually increasing the exercise intensity as follows: low intensity at 30 W for 3 min, moderate intensity at 90% of the gas exchange threshold (GET) for 4 min, and severe intensity at 70% of the difference between the GET and VO2 peak until exhaustion. During the exercise test, the breath-by-breath pulmonary VO2 and near-infrared spectroscopy-derived muscle deoxygenation were continuously recorded. Exercise endurance during severe-intensity exercise was significantly enhanced by IPC. There were no significant differences in pulmonary VO2 dynamics between treatments. In contrast, muscle deoxygenation dynamics in the step transition from low- to moderate-intensity was significantly faster in IPC than in CON (27.2 ± 2.9 vs. 19.8 ± 0.9 sec, P < 0.05). The present findings showed that IPC accelerated muscle deoxygenation dynamics in moderate-intensity exercise and enhanced severe-intensity exercise endurance during work-to-work test. The IPC-induced effects may result from mitochondrial activation in skeletal muscle, as indicated by the accelerated O2 extraction.
© 2015 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society.
Much hypoxia research has been carried out at high altitude in a hypobaric hypoxia (HH) environment. Many research teams seek to replicate high-altitude conditions at lower altitudes in either hypobaric hypoxic conditions or normobaric hypoxic (NH) laboratories. Implicit in this approach is the assumption that the only relevant condition that differs between these settings is the partial pressure of oxygen (PO2), which is commonly presumed to be the principal physiological stimulus to adaptation at high altitude. This systematic review is the first to present an overview of the current available literature regarding crossover studies relating to the different effects of HH and NH on human physiology. After applying our inclusion and exclusion criteria, 13 studies were deemed eligible for inclusion. Several studies reported a number of variables (e.g. minute ventilation and NO levels) that were different between the two conditions, lending support to the notion that true physiological difference is indeed present. However, the presence of confounding factors such as time spent in hypoxia, temperature, and humidity, and the limited statistical power due to small sample sizes, limit the conclusions that can be drawn from these findings. Standardisation of the study methods and reporting may aid interpretation of future studies and thereby improve the quality of data in this area. This is important to improve the quality of data that is used for improving the understanding of hypoxia tolerance, both at altitude and in the clinical setting.
Ischemic preconditioning (IPC) may improve blood flow and oxygen delivery to tissues, including skeletal muscle, and has the potential to improve intense aerobic exercise performance, especially that which results in arterial hypoxemia. The aim of the study was to determine the effects of IPC of the legs on peak exercise capacity (Wpeak), submaximal and peak cardiovascular hemodynamics, and peripheral capillary oxygen saturation (SpO2) in trained males at sea level (SL) and simulated high altitude (HA; 13.3% FIO2, ∼3650 m). Fifteen highly trained male cyclists and triathletes completed 2 Wpeak tests (SL and HA) and 4 experimental exercise trials (10 min at 55% altitude-specific Wpeak then increasing by 30 W every 2 min until exhaustion) with and without IPC. HA resulted in significant arterial hypoxemia during exercise compared with SL (73% ± 6% vs. 93% ± 4% SpO2, p < 0.001) that was associated with 21% lower Wpeak values. IPC did not significantly improve Wpeak at SL or HA. Additionally, IPC failed to improve cardiovascular hemodynamics or SpO2 during submaximal exercise or at Wpeak. In conclusion, IPC performed 45 min prior to exercise does not improve Wpeak or systemic oxygen delivery during submaximal or peak exercise at SL or HA. Future studies must examine the influence of IPC on local factors, such as working limb blood flow, oxygen delivery, and arteriovenous oxygen difference as well as whether the effectiveness of IPC is altered by the volume of muscle made ischemic, the timing prior to exercise, and high altitude acclimatization.
Remote Ischemic Preconditioning (RIPC) is emerging as a new noninvasive intervention that has the potential to protect a number of organs against ischemia–reperfusion (IR) injury. The standard protocols normally used to deliver RIPC involve a number of cycles of inflation of a blood pressure (BP) cuff on the arm and/or leg to an inflation pressure of 200 mmHg followed by cuff deflation for a short period of time. There is little evidence to support what limb (upper or lower) or cuff inflation pressures are most effective to deliver this intervention without causing undue discomfort/pain in nonanesthetized humans. In this preliminary study, a dose–response assessment was performed using a range of cuff inflation pressures (140, 160, and 180 mmHg) to induce limb ischemia in upper and lower limbs. Physiological changes in the occluded limb and any pain/discomfort associated with RIPC with each cuff inflation pressure were determined. Results showed that ischemia can be induced in the upper limb at much lower cuff inflation pressures compared with the standard 200 mmHg pressure generally used for RIPC, provided the cuff inflation pressure is ~30 mmHg higher than the resting systolic BP. In the lower limb, a higher inflation pressure, (~55 mmHg > resting systolic BP), is required to induce ischemia. Cyclical changes in capillary blood O2, CO2, and lactate levels during the RIPC stimulus were observed. RIPC at higher cuff inflation pressures of 160 and 180 mmHg was better tolerated in the upper limb. In summary, limb ischemia for RIPC can be more easily induced at lower pressures and is much better tolerated in the upper limb in young healthy individuals. However, whether benefits of RIPC can also be derived with protocols delivered to the upper limb using lower cuff inflation pressures and with lesser discomfort compared to the lower limb, remains to be investigated.
Field-based team sport matches are composed of short, high-intensity efforts, interspersed with intervals of rest or submaximal exercise, repeated over a period of 60-120 minutes. Matches may also be played at moderate altitude where the lower oxygen partial pressure exerts a detrimental effect on performance. To enhance run-based performance, team-sport athletes use varied training strategies focusing on different aspects of team-sport physiology, including aerobic, sprint, repeated-sprint and resistance training. Interestingly, 'altitude' training (i.e. living and/or training in O(2)-reduced environments) has only been empirically employed by athletes and coaches to improve the basic characteristics of speed and endurance necessary to excel in team sports. Hypoxia, as an additional stimulus to training, is typically used by endurance athletes to enhance performance at sea level and to prepare for competition at altitude. Several approaches have evolved in the last few decades, which are known to enhance aerobic power and, thus, endurance performance. Altitude training can also promote an increased anaerobic fitness, and may enhance sprint capacity. Therefore, altitude training may confer potentially-beneficial adaptations to team-sport athletes, which have been overlooked in contemporary sport physiology research. Here, we review the current knowledge on the established benefits of altitude training on physiological systems relevant to team-sport performance, and conclude that current evidence supports implementation of altitude training modalities to enhance match physical performances at both sea level and altitude. We hope that this will guide the practice of many athletes and stimulate future research to better refine training programmes.
The objectives of this study were to evaluate the reliability and accuracy of a new impedance cardiograph device, the Physio
Flow, at rest and during a steady-state dynamic leg exercise (work intensity ranging from 10 to 50 W) performed in the supine
position. We compared cardiac output determined simultaneously by two methods, the Physio Flow (Q˙
cPF) and the direct Fick (Q˙
cFick) methods. Forty patients referred for right cardiac catheterisation, 14 with sleep apnoea syndrome and 26 with chronic obstructive
pulmonary disease, took part in this study. The subjects' oxygen consumption values ranged from 0.14 to 1.19 l · min−1. The mean difference between the two methods (Q˙
cFick−Q˙
cPF) was 0.04 l · min−1 at rest and 0.29 l · min−1 during exercise. The limits of agreement, defined as mean difference ± 2SD, were −1.34, +1.41 l · min−1 at rest and −2.34, +2.92 l · min−1 during exercise. The difference between the two methods exceeded 20% in only 2.5% of the cases at rest, and 9.3% of the cases
during exercise. Thoracic hyperinflation did not alter Q˙
cPF. We conclude that the Physio Flow provides a clinically acceptable and non-invasive evaluation of cardiac output under these
conditions. This new impedance cardiograph device deserves further study using other populations and situations.
The purpose of this study was to determine the difference in cuff pressure which occludes arterial blood flow for two different types of cuffs which are commonly used in blood flow restriction (BFR) research. Another purpose of the study was to determine what factors (i.e., leg size, blood pressure, and limb composition) should be accounted for when prescribing the restriction cuff pressure for this technique. One hundred and sixteen (53 males, 63 females) subjects visited the laboratory for one session of testing. Mid-thigh muscle (mCSA) and fat (fCSA) cross-sectional area of the right thigh were assessed using peripheral quantitative computed tomography. Following the mid-thigh scan, measurements of leg circumference, ankle brachial index, and brachial blood pressure were obtained. Finally, in a randomized order, arterial occlusion pressure was determined using both narrow and wide restriction cuffs applied to the most proximal portion of each leg. Significant differences were observed between cuff type and arterial occlusion (narrow: 235 (42) mmHg vs. wide: 144 (17) mmHg; p = 0.001, Cohen's D = 2.52). Thigh circumference or mCSA/fCSA with ankle blood pressure, and diastolic blood pressure, explained the most variance in the cuff pressure required to occlude arterial flow. Wide BFR cuffs restrict arterial blood flow at a lower pressure than narrow BFR cuffs, suggesting that future studies account for the width of the cuff used. In addition, we have outlined models which indicate that restrictive cuff pressures should be largely based on thigh circumference and not on pressures previously used in the literature.
Intermittent arm ischemia before percutaneous coronary intervention induces remote ischemic preconditioning (RIPC) and attenuates myocardial injury in patients with myocardial infarction. Several studies have shown that intermittent arm ischemia increases coronary flow and is related to autonomic nerve system. The aim of this study was to determine whether intermittent arm ischemia induces vasodilatation of other arteries and to assess changes in the autonomic nerve system during intermittent arm ischemia in humans. We measured change in the right brachial artery diameter during intermittent left arm ischemia through three cycles of 5-min inflation (200 mmHg) and 5-min deflation of a blood-pressure cuff using a 10-MHz linear array transducer probe in 20 healthy volunteers. We simultaneously performed power spectral analysis of heart rate. Ischemia-reperfusion of the left arm significantly dilated the right brachial artery time-dependently, resulting in a 3.2 ± 0.4% increase after the 3rd cycle. In the power spectral analysis of heart rate, the high-frequency domain (HF), which is a marker of parasympathetic activity, was significantly higher after the 3rd cycle of ischemia-reperfusion than baseline HF (P = 0.02). Intermittent arm ischemia was accompanied by vasodilatation of another artery and enhancement of parasympathetic activity. Those effects may play an important role in the mechanism of RIPC.
New methods and devices for pursuing performance enhancement through altitude training were developed in Scandinavia and the USA in the early 1990s. At present, several forms of hypoxic training and/or altitude exposure exist: traditional ‘live high-train high’ (LHTH), contemporary ‘live high-train low’ (LHTL), intermittent hypoxic exposure during rest (IHE) and intermittent hypoxic exposure during continuous session (IHT). Although substantial differences exist between these methods of hypoxic training and/ or exposure, all have the same goal: to induce an improvement in athletic performance at sea level. They are also used for preparation for competition at altitude and/or for the acclimatization of mountaineers.
The underlying mechanisms behind the effects of hypoxic training are widely debated. Although the popular view is that altitude training may lead to an increase in haematological capacity, this may not be the main, or the only, factor involved in the improvement of performance. Other central (such as ventilatory, haemodynamic or neural adaptation) or peripheral (such as muscle buffering capacity or economy) factors play an important role.
LHTL was shown to be an efficient method. The optimal altitude for living high has been defined as being 2200–2500 m to provide an optimal erythropoietic effect and up to 3100m for non-haematological parameters. The optimal duration at altitude appears to be 4 weeks for inducing accelerated erythropoiesis whereas <3 weeks (i.e. 18 days) are long enough for beneficial changes in economy, muscle buffering capacity, the hypoxic ventilatory response or Na+/K+-ATPase activity. One critical point is the daily dose of altitude. A natural altitude of 2500 m for 20–22 h/day (in fact, travelling down to the valley only for training) appears sufficient to increase erythropoiesis and improve sea-level performance. ‘Longer is better’ as regards haematological changes since additional benefits have been shown as hypoxic exposure increases beyond 16 h/day. The minimum daily dose for stimulating erythropoiesis seems to be 12 h/day. For non-haematological changes, the implementation of a much shorter duration of exposure seems possible.
Athletes could take advantage of IHT, which seems more beneficial than IHE in performance enhancement. The intensity of hypoxic exercise might play a role on adaptations at the molecular level in skeletal muscle tissue. There is clear evidence that intense exercise at high altitude stimulates to a greater extent muscle adaptations for both aerobic and anaerobic exercises and limits the decrease in power. So although IHT induces no increase in V̇O2max due to the low‘altitude dose’, improvement in athletic performance is likely to happenwith high-intensity exercise (i.e. above the ventilatory threshold) due to an increase in mitochondrial efficiency and pH/lactate regulation. We propose a new combination of hypoxic method (which we suggest naming Living High-Training Low and High, interspersed; LHTLHi) combining LHTL (five nights at 3000 m and two nights at sea level) with training at sea level except for a few (2.3 per week) IHT sessions of supra-threshold training. This review also provides a rationale on how to combine the different hypoxic methods and suggests advances in both their implementation and their periodization during the yearly training programme of athletes competing in endurance, glycolytic or intermittent sports.
Maximal cardiac output is reduced in severe acute hypoxia but also in chronic hypoxia by mechanisms that remain poorly understood. In theory, the reduction of maximal cardiac output could result from: (1) a regulatory response from the central nervous system, (2) reduction of maximal pumping capacity of the heart due to insufficient coronary oxygen delivery prior to the achievement of the normoxic maximal cardiac output, or (3) reduced central command. In this review, we focus on the effects that acute and chronic hypoxia have on the pumping capacity of the heart, particularly on myocardial contractility and the molecular responses elicited by acute and chronic hypoxia in the cardiac myocytes. Special emphasis is put on the cardioprotective effects of chronic hypoxia.
A study of a sample provides only an estimate of the true (population) value of an outcome statistic. A report of the study therefore usually includes an inference about the true value. Traditionally, a researcher makes an inference by declaring the value of the statistic statistically significant or nonsignificant on the basis of a P value derived from a null-hypothesis test. This approach is confusing and can be misleading, depending on the magnitude of the statistic, error of measurement, and sample size. The authors use a more intuitive and practical approach based directly on uncertainty in the true value of the statistic. First they express the uncertainty as confidence limits, which define the likely range of the true value. They then deal with the real-world relevance of this uncertainty by taking into account values of the statistic that are substantial in some positive and negative sense, such as beneficial or harmful. If the likely range overlaps substantially positive and negative values, they infer that the outcome is unclear; otherwise, they infer that the true value has the magnitude of the observed value: substantially positive, trivial, or substantially negative. They refine this crude inference by stating qualitatively the likelihood that the true value will have the observed magnitude (eg, very likely beneficial). Quantitative or qualitative probabilities that the true value has the other 2 magnitudes or more finely graded magnitudes (such as trivial, small, moderate, and large) can also be estimated to guide a decision about the utility of the outcome.
The aim of this study was to investigate local muscle O(2) consumption (muscV(O(2))) and forearm blood flow (FBF) in resting and exercising muscle by use of near-infrared spectroscopy (NIRS) and to compare the results with the global muscV(O(2)) and FBF derived from the well-established Fick method and plethysmography. muscV(O(2)) was derived from 1) NIRS using venous occlusion, 2) NIRS using arterial occlusion, and 3) the Fick method [muscV(O(2(Fick)))]. FBF was derived from 1) NIRS and 2) strain-gauge plethysmography. Twenty-six healthy subjects were tested at rest and during sustained isometric handgrip exercise. Local variations were investigated with two independent and simultaneously operating NIRS systems at two different muscles and two measurement depths. muscV(O(2)) increased more than fivefold in the active flexor digitorum superficialis muscle, and it increased 1.6 times in the brachioradialis muscle. The average increase in muscV(O(2(Fick))) was twofold. FBF increased 1.4 times independent of the muscle or the method. It is concluded that NIRS is an appropriate tool to provide information about local muscV(O(2)) and local FBF because both place and depth of the NIRS measurements reveal local differences that are not detectable by the more established, but also more global, Fick method.
We previously demonstrated in the pig that instigation of three cycles of 10 min of occlusion and reperfusion in a hindlimb by tourniquet application (approximately 300 mmHg) elicited protection against ischemia-reperfusion injury (infarction) in multiple distant skeletal muscles subsequently subjected to 4 h of ischemia and 48 h of reperfusion, but the mechanism was not studied. The aim of this project was to test our hypothesis that mitochondrial ATP-sensitive potassium (KATP) (mKATP) channels play a central role in the trigger and mediator mechanisms of hindlimb remote ischemic preconditioning (IPC) of skeletal muscle against infarction in the pig. We observed in the pig that hindlimb remote IPC reduced the infarct size of latissimus dorsi (LD) muscle flaps (8 x 13 cm) from 45 +/- 2% to 22 +/- 3% (n = 10; P < 0.05). The nonselective KATP channel inhibitor glibenclamide (0.3 mg/kg) or the selective mKATP channel inhibitor 5-hydroxydecanoate (5-HD, 5 mg/kg), but not the selective sarcolemmal KATP (sKATP) channel inhibitor HMR-1098 (3 mg/kg), abolished the infarct-protective effect of hindlimb remote IPC in LD muscle flaps (n = 10, P < 0.05) when these drugs were injected intravenously at 10 min before remote IPC. In addition, intravenous bolus injection of glibenclamide (1 mg/kg) or 5-HD (10 mg/kg) at the end of hindlimb remote IPC also abolished the infarct protection in LD muscle flaps (n = 10; P < 0.05). Furthermore, intravenous injection of the specific mKATPchannel opener BMS-191095 (2 mg/kg) at 10 min before 4 h of ischemia protected the LD muscle flap against infarction to a similar extent as hindlimb remote IPC, and this infarct-protective effect of BMS-191095 was abolished by intravenous bolus injection of 5-HD (5 mg/kg) at 10 min before or after intravenous injection of BMS-191095 (n = 10; P < 0.05). The infarct protective effect of BMS-191095 was associated with a higher muscle content of ATP at the end of 4 h of ischemia and a decrease in muscle neutrophilic myeloperoxidase activity at the end of 1.5 h of reperfusion compared with the time-matched control (n = 10, P < 0.05). These observations led us to conclude that mKATP channels play a central role in the trigger and mediator mechanisms of hindlimb remote IPC of skeletal muscle against infarction in the pig, and the opening of mKATP channels in ischemic skeletal muscle is associated with an ATP-sparing effect during sustained ischemia and attenuation of neutrophil accumulation during reperfusion.
It has been hypothesized that one reason for decreased
\(\dot V\hbox{O}_{2\max}\) in hypoxia could be the lower maximal exercise intensity achieved in incremental, time or distance trial tests. We hypothesized that (1)
\(\dot V\hbox{O}_{2\max}\) would be decreased at altitude even when exercising at the same absolute maximal exercise intensity as at sea level and; (2) the decline in
\(\dot V\hbox{O}_{2\max}\) in endurance-trained athletes (ETA) would be linear across the range from sea level through moderate altitudes. Eight ETA performed combined
\(\dot V\hbox{O}_{2\max}\) and performance tests running to exhaustion at the same speed in a randomized double blind fashion at simulated altitudes of 300, 800, 1,300, 1,800, 2,300 and 2,800 m above sea level using a hypobaric chamber. Douglas bag system was used for respiratory measurements and pulse oximetry was used to estimate arterial O2 saturation.
\(\dot V\hbox{O}_{2\max}\) declined linearly from 66±1.6 ml kg−1 min−1 at 300 m to 55±1.6 ml kg−1 min−1 at 2,800 m corresponding to a 6.3% decrease per 1,000 m increasing altitude (range 4.6–7.5%). Time to exhaustion (performance) at a constant velocity associated with 107% of sea level
\(\dot V\hbox{O}_{2\max}\) decreased with 14.5% (P<0.001) per 1,000 m altitude between 300 and 2,800 m. Both
\(\dot V\hbox{O}_{2\max}\) and performance decreased from 300 to 800 m (P<0.01; P<0.05). Arterial haemoglobin oxygen saturation at test cessation (SpO2min) declined from 89.0±2.9% at 300 m to 76.5±4.0% at 2,800 m (P=0.001). This study report that in ETA during acute exposure to altitude both performance and
\(\dot V\hbox{O}_{2\max}\) decline from 300 to 800 m above sea level and continued to decrease linearly to 2,800 m.
We hypothesized that severe hypoxia limits exercise performance via decreased contractility of limb locomotor muscles. Nine male subjects [mean +/- SE maximum O(2) uptake (Vo(2 max)) = 56.5 +/- 2.7 ml x kg(-1) x min(-1)] cycled at > or =90% Vo(2 max) to exhaustion in normoxia [NORM-EXH; inspired O(2) fraction (Fi(O(2))) = 0.21, arterial O(2) saturation (Sp(O(2))) = 93 +/- 1%] and hypoxia (HYPOX-EXH; Fi(O(2)) = 0.13, Sp(O(2)) = 76 +/- 1%). The subjects also exercised in normoxia for a time equal to that achieved in hypoxia (NORM-CTRL; Sp(O(2)) = 96 +/- 1%). Quadriceps twitch force, in response to supramaximal single (nonpotentiated and potentiated 1 Hz) and paired magnetic stimuli of the femoral nerve (10-100 Hz), was assessed pre- and at 2.5, 35, and 70 min postexercise. Hypoxia exacerbated exercise-induced peripheral fatigue, as evidenced by a greater decrease in potentiated twitch force in HYPOX-EXH vs. NORM-CTRL (-39 +/- 4 vs. -24 +/- 3%, P < 0.01). Time to exhaustion was reduced by more than two-thirds in HYPOX-EXH vs. NORM-EXH (4.2 +/- 0.5 vs. 13.4 +/- 0.8 min, P < 0.01); however, peripheral fatigue was not different in HYPOX-EXH vs. NORM-EXH (-34 +/- 4 vs. -39 +/- 4%, P > 0.05). Blood lactate concentration and perceptions of limb discomfort were higher throughout HYPOX-EXH vs. NORM-CTRL but were not different at end-exercise in HYPOX-EXH vs. NORM-EXH. We conclude that severe hypoxia exacerbates peripheral fatigue of limb locomotor muscles and that this effect may contribute, in part, to the early termination of exercise.
We aimed to evaluate 1) the altitude where maximal heart rate (HR (max)) decreases significantly in both trained and untrained subjects in moderate acute hypoxia, and 2) if the HR (max) decrease could partly explain the drop of V.O (2max). Seventeen healthy males, nine trained endurance athletes (TS) and eight untrained individuals (US) were studied. Subjects performed incremental exercise tests at sea level and at 5 simulated altitudes (1000, 1500, 2500, 3500, 4500 meters). Power output (PO), heart rate (HR), arterial oxygen saturation (SaO (2)), oxygen uptake (V.O (2)), arterialized blood pH and lactate were measured. Both groups showed a progressive reduction in V.O (2max). The decrement in HR (max) (DeltaHR (max)) was significant from 1000 m for TS and 2500 m for US and more important in TS than US (at 1500 m and 3500 m). At maximal exercise, TS had a greater reduction in SaO (2) (DeltaSaO (2)) at each altitude. DeltaHR (max) observed in TS was correlated with DeltaSaO (2). When the two groups were pooled, simple regressions showed that DeltaV.O (2max) was correlated with both DeltaSaO (2) and DeltaHR (max). However, a multiple regression analysis demonstrated that DeltaSaO (2) alone may account for DeltaV.O (2max). Furthermore, in spite of a greater reduction in SaO (2) and HR (max) in TS, no difference was evidenced in relative DeltaV.O (2max) between groups. Thus, in moderate acute hypoxia, the reduction in SaO (2) is the primary factor to explain the drop of V.O (2max) in trained and untrained subjects.
Application of repeated short duration bouts of ischemia to the limbs, termed remote ischemic preconditioning (RIPC), is a novel technique that may have protective effects on vascular function during hypoxic exposures. In separate parallel-design studies, at sea-level (SL; n = 16), and after 8-12 days at high-altitude (HA; n = 12; White Mountain, 3800 m), participants underwent either a sham protocol or one session of 4 × 5 minutes of dual-thigh cuff occlusion with 5 minutes recovery. Brachial artery flow-mediated dilation (FMD; ultrasound), pulmonary artery systolic pressure (PASP; echocardiography), and internal carotid artery flow (ICA; ultrasound) were measured at SL in normoxia and isocapnic hypoxia [end-tidal PO₂ (PETO₂) maintained to 50 mmHg], and during normal breathing at HA. The hypoxic ventilatory response (HVR) was measured at each location. All measures at SL and HA were obtained at baseline (BL), 1 hour, 24 hours, and 48 hours post-RIPC or sham. At SL, RIPC produced no changes in FMD, PASP, ICA flow, end-tidal gases or HVR in normoxia or hypoxia. At HA, although HVR increased 24 hours post RIPC compared to BL (2.05 ± 1.4 vs. 3.21 ± 1.2 l min(-1) ·%SaO2 -1, P < 0.01), there were no significant differences in FMD, PASP, ICA flow, resting end-tidal gases. Accordingly, a single session of RIPC is insufficient to evoke changes in peripheral, pulmonary, and cerebral vascular function in healthy adults. Although chemosensitivity may increase following RIPC at HA, this did not confer any vascular changes. The utility of a single RIPC session seems unremarkable during acute and chronic hypoxia. This article is protected by copyright. All rights reserved.
In the oxygen (O2) cascade downstream steps can never achieve higher flows of O2 than the preceding ones. At the lung the transfer of O2 is determined by the O2 gradient between the alveolar space and the lung capillaries and the O2 diffusing capacity (DLO2). While DLO2 may be increased several times during exercise by recruiting more lung capillaries and by increasing the oxygen carrying capacity of blood due to higher peripheral extraction of O2, the capacity to enhance the alveolocapillary PO2 gradient is more limited. The transfer of oxygen from the alveolar space to the hemoglobin (Hb) must overcome first the resistance offered by the alveolocapillary membrane (1/DM) and the capillary blood (1/θVc). The fractional contribution of each of these two components to DLO2 remains unknown. During exercise these resistances are reduced by the recruitment of lung capillaries. The factors that reduce the slope of the oxygen dissociation curve of the Hb (ODC) (i.e., lactic acidosis and hyperthermia) increase 1/θVc contributing to limit DLO2. These effects are accentuated in hypoxia. Reducing the size of the active muscle mass improves pulmonary gas exchange during exercise and reduces the rightward shift of the ODC. The flow of oxygen from the muscle capillaries to the mitochondria is pressumably limited by muscle O2 conductance (DmcO2) (an estimation of muscle oxygen diffusing capacity). However, during maximal whole body exercise in normoxia, a higher flow of O2 is achieved at the same pressure gradients after increasing blood [Hb], implying that in healthy humans exercising in normoxia there is a functional reserve in DmcO2. This conclusion is supported by the fact that during small muscle exercise in chronic hypoxia, peak exercise DmcO2 is similar to that observed during exercise in normoxia despite a markedly lower O2 pressure gradient driving diffusion.
Purpose:
This study investigated the effects of ischemic preconditioning (IPC) on the ratings of perceived exertion (RPE), surface electromyography (EMG), and pulmonary oxygen uptake (V̇O2) onset kinetics during cycling until exhaustion at the peak power output attained during an incremental test (PPO).
Methods:
A group of 12 recreationally trained cyclists volunteered for this study. After determination of PPO, they were randomly subjected on different days to a performance protocol preceded by intermittent bilateral cuff pressure inflation to 220 mm Hg (IPC) or 20 mm Hg (control). To increase data reliability, the performance visits were replicated, also in a random manner.
Results:
There was an 8.0% improvement in performance after IPC (Control: 303 s, IPC 327 s, factor SDs of ×/÷1.13, P = 0.01). This change was followed by a 2.9% increase in peak V̇O2 (Control: 3.95 L·min(-1), IPC: 4.06 L·min(-1), factor SDs of ×/÷ 1.15, P = 0.04) owing to a higher amplitude of the slow component of the V̇O2 kinetics (Control: 0.45 L·min(-1), IPC: 0.63 L·min(-1), factor SDs of ×/÷ 2.21, P = 0.05). There was also an attenuation in the rate of increase in RPE (P = 0.01) and a progressive increase in the myoelectrical activity of the vastus lateralis muscle (P = 0.04). Furthermore, the changes in peak V̇O2 (r = 0.73, P = 0.007) and the amplitude of the slow component (r = 0.79, P = 0.002) largely correlated with performance improvement.
Conclusion:
These findings provide a link between improved aerobic metabolism and enhanced severe-intensity cycling performance after IPC. Furthermore, the delayed exhaustion after IPC under lower RPE and higher skeletal muscle activation suggest they have a role on the ergogenic effects of IPC on endurance performance.
Background:
Ischemic preconditioning (IPC) is described as brief ischemia-reperfusion (I/R) cycles to induce tolerance to subsequent in response to longer I/R insults. Various IPC protocols can be performed in four combinations as follows: at early or late phases and on local or distant organs. Although many experimental studies have been performed on IPC, no consensus has been established on which IPC protocol is most effective. The aims of the present study were as follows: (1) to compare the variables of preconditioning in different combinations (in early versus late phases; local versus remote organ implementations) and (2) to determine the most therapeutic IPC protocol(s).
Materials and methods:
A subtotal hind limb amputation model with clamping an intact femoral pedicle was used for I/R injury. IPC was induced using hind limb tourniquet with 3 × 10 min I/R cycles before longer I/R insult. Forty-nine rats were divided into seven groups (n = 7), sham, IsO (ischemia only), I/R, early ischemic preconditioning (e-IPC), late ischemic preconditioning (l-IPC), early remote ischemic preconditioning (e-RIPC), and l-RIPC (late-remote) groups, respectively. In the sham group, pedicle occlusion was not performed. Six hours ischemia was challenged in the IsO group. Three hours ischemia followed by 3 h reperfusion was performed in the I/R group. The e-IPC group was immediately preconditioned, whereas the l-IPC group was preconditioned 24 h before I/R injury on the same hind limb. In the e-RIPC and l-RIPC groups, the same protocols were performed on the contralateral hind limb. At the end of the experiments, skeletal muscle tissue samples were obtained for biochemical analysis (Malondialdehyde [MDA], catalase, myeloperoxidase [MPO], and nitric oxide end products [NOx]), light microscopy, and caspase-3 immunohistochemistry for determination of apoptosis.
Results:
Tissue biochemical markers were improved in nearly all the IPC groups compared with IsO and I/R groups (P < 0.05). Similarly, the histologic damage scores were decreased in all the IPC groups (P < 0.05). The lowest damage score was in the e-RIPC group followed by the l-RIPC, e-IPC, and l-IPC groups, respectively. The apoptosis scores were significantly high in the I/R group compared with the e-RIPC and l-RIPC groups (P < 0.05). Although apoptosis scores of the e-IPC and l-IPC groups were lower than the I/R group, this finding was not statistically significant (P > 0.05).
Conclusions:
All IPC protocols were effective in reducing I/R injury. Among these protocols, e-RIPC achieved most protection.
Abstract Foster, Gary P., Paresh C. Giri, Douglas M. Rogers, Sophia R. Larson, and James D. Anholm. Ischemic preconditioning improves oxygen saturation and attenuates hypoxic pulmonary vasoconstriction at high altitude. High Alt Med Biol 15, 000-000. 2014.-Exposure to hypoxic environments is associated with decreased arterial oxygen saturation and increased pulmonary artery pressures. Ischemic preconditioning of an extremity (IPC) is a procedure that stimulates vasoactive and inflammatory pathways that protect remote organ systems from ongoing or future ischemic injury. To test the effects of IPC on oxygen saturation and pulmonary artery pressures at high altitude, 12 healthy adult volunteers were evaluated in a randomized cross-over trial. IPC was administered utilizing a standardized protocol. IPC or placebo was administered daily for 5 days prior to ascent to altitude. All participants were evaluated twice at 4342 m altitude (placebo and IPC conditions separated by 4 weeks, randomized). The pulmonary artery systolic pressure (PASP) at 4342 m was significantly lower in the IPC condition than the placebo condition (36±6.0 mmHg vs. 38.1±7.6 mmHg, respectively, p=0.035). Oxygen saturation at 4342 m was significantly higher with IPC compared to placebo (80.3±8.7% vs. 75.3±9.6%, respectively, p=0.003). Prophylactic IPC treatment is associated with improved oxygen saturation and attenuation of the normal hypoxic increase in pulmonary artery pressures following ascent to high altitude.
Abstract Chapman, Robert F., Abigail S. Laymon, and Benjamin D. Levine. Timing of arrival and pre-acclimatization strategies for the endurance athlete competing at moderate to high altitudes. High Alt Med Biol 14:319-324, 2013.-With the wide array of endurance sport competition offerings at moderate and high altitudes, clinicians are frequently asked about best practice recommendations regarding arrival times prior to the event and acclimatization guidelines. This brief review will offer data and current advice on when to arrive at altitude and various potential sea level-based pre-acclimatization strategies in an effort to maximize performance and minimize the risk of altitude sickness.
Ischemic preconditioning enhances ergometer cycling and swimming performance. We evaluated whether ischemic preconditioning of one forearm (4 times 5 min) also affects static breath-hold and underwater swimming, while the effect of similar preconditioning on ergometer rowing served as control since the warm-up for rowing regularly encompasses intense exercise and therefore reduced muscle oxygenation.
Six divers performed a dry static breath-hold, 11 divers swam underwater in an indoor pool, and 14 oarsmen rowed "1000 m" on an ergometer.
Ischemic preconditioning reduced the spatial resulted near-infrared determined forearm oxygen saturation from 65 ± 7% to 19 ± 7% (mean±SD; P<0.001). During the breath-hold (315 s, range 280 to 375 s) forearm oxygenation decreased to 29 ± 10% and in preparation for rowing, right thigh oxygenation decreased from 66 ± 7% to 33 ± 14% (P<0.05). Ischemic preconditioning prolonged the breath-hold from 279 ± 72 to 327 ± 39 s and the underwater swimming distance from 110 ± 16 to 119 ± 14 m (P<0.05) and also the rowing time was reduced (from 186.5 ± 3.6 to 185.7 ± 3.6 s; P<0.05).
We conclude that while the effect of ischemic preconditioning (of one forearm) on ergometer rowing was minimal, probably because of reduced muscle oxygenation during the warm-up, ischemic preconditioning does enhance both static and dynamic apnea, supporting that muscle ischemia is an important preparation for physical activity.
Strenuous exercise is associated with an immediate decrease in endothelial function. Repeated bouts of ischemia followed by reperfusion, known as remote ischemic preconditioning (RIPC), is able to protect the endothelium against ischemia-induced injury beyond the ischemic area. We examined the hypothesis that RIPC prevents the decrease in endothelial function observed after strenuous exercise in healthy men. In a randomized, crossover study, 13 healthy men performed running exercise preceded by RIPC of the lower limbs (4 × 5-min 220-mmHg bilateral occlusion) or a sham intervention (sham; 4 × 5-min 20-mmHg bilateral occlusion). Participants performed a graded maximal treadmill running test, followed by a 5-km time trial (TT). Brachial artery endothelial function was examined before and after RIPC or sham, as well as after the 5-km TT. We measured flow-mediated dilation (FMD), an index of endothelium-dependent function, using high-resolution echo-Doppler. We also calculated the shear rate area-under-the-curve (from cuff deflation to peak dilatation; SR(AUC)). Data are described as mean and 95% confidence intervals. FMD changed by <0.6% immediately after both ischemic preconditioning (IPC) and sham interventions (P > 0.30). In the sham trial, FMD changed from 5.1 (4.4-5.9) to 3.7% (2.6-4.8) following the 5-km TT (P = 0.02). In the RIPC trial, FMD changed negligibly from 5.4 (4.4-6.4) post-IPC and 5.7% (4.6-6.8) post 5-km TT (P = 0.60). Baseline diameter, SR(AUC), and time-to-peak diameter were all increased following the 5-km TT (P < 0.05), but these changes did not influence the IPC-mediated maintenance of FMD. In conclusion, these data indicate that strenuous lower-limb exercise results in an acute decrease in brachial artery FMD of ∼1.4% in healthy men. However, we have shown for the first time that prior RIPC of the lower limbs maintains postexercise brachial artery endothelium-dependent function at preexercise levels.
Ischemic pre-condition of an extremity (IPC) induces effects on local and remote tissues that are protective against ischemic injury. To test the effects of IPC on the normal hypoxic increase in pulmonary pressures and exercise performance, 8 amateur cyclists were evaluated under normoxia and hypoxia (13% F(I)O(2)) in a randomized cross-over trial. IPC was induced using an arterial occlusive cuff to one thigh for 5 min followed by deflation for 5 min for 4 cycles. In the control condition, the resting pulmonary artery systolic pressure (PASP) increased from a normoxic value of 25.6±2.3 mmHg to 41.8±7.2 mmHg following 90 min of hypoxia. In the IPC condition, the PASP increased to only 32.4±3.1 mmHg following hypoxia, representing a 72.8% attenuation (p=0.003). No significant difference was detected in cycle ergometer time trial duration between control and IPC conditions with either normoxia or hypoxia. IPC administered prior to hypoxic exposure was associated with profound attenuation of the normal hypoxic increase of pulmonary artery systolic pressure.
Brief episodes of nonlethal ischemia, commonly known as "ischemic preconditioning" (IP), are protective against cell injury induced by infarction. Moreover, muscle IP has been found capable of improving exercise performance. The aim of the study was the comparison of standard exercise performances carried out in normal conditions with those carried out following IP, achieved by brief muscle ischemia at rest (RIP) and after exercise (EIP). Seventeen physically active, healthy male subjects performed three incremental, randomly assigned maximal exercise tests on a cycle ergometer up to exhaustion. One was the reference (REF) test, whereas the others were performed after the RIP and EIP sessions. Total exercise time (TET), total work (TW), and maximal power output (W(max)), oxygen uptake (VO(2max)), and pulmonary ventilation (VE(max)) were assessed. Furthermore, impedance cardiography was used to measure maximal heart rate (HR(max)), stroke volume (SV(max)), and cardiac output (CO(max)). A subgroup of volunteers (n = 10) performed all-out tests to assess their anaerobic capacity. We found that both RIP and EIP protocols increased in a similar fashion TET, TW, W(max), VE(max), and HR(max) with respect to the REF test. In particular, W(max) increased by ∼ 4% in both preconditioning procedures. However, preconditioning sessions failed to increase traditionally measured variables such as VO(2max), SV(max,) CO(max), and anaerobic capacity(.) It was concluded that muscle IP improves performance without any difference between RIP and EIP procedures. The mechanism of this effect could be related to changes in fatigue perception.
Remote ischemic preconditioning (RIPC) induced by transient limb ischemia releases a dialysable circulating protective factor that reduces ischemia-reperfusion injury. Exercise performance in highly trained athletes is limited by tissue hypoxemia and acidosis, which may therefore represent a type of ischemia-reperfusion stress modifiable by RIPC.
National-level swimmers, 13-27 yr, were randomized to RIPC (four cycles of 5-min arm ischemia/5-min reperfusion) or a low-pressure control procedure, with crossover. In study 1, subjects (n=16) performed two incremental submaximal swimming tests with measurement of swimming velocity, blood lactate, and HR. For study 2, subjects (n=18) performed two maximal competitive swims (time trials). To examine possible mechanisms, blood samples taken before and after RIPC were dialysed and used to perfuse mouse hearts (n=10) in a Langendorff preparation. Infarct sizes were compared with dialysate obtained from nonathletic controls. RIPC released a protective factor into the bloodstream, which reduced infarct size in mice (P<0.05 for controls and swimmers). There was no statistically significant difference between the effect of RIPC and the low-pressure control protocol on submaximal exercise performance. However, RIPC was associated with a mean improvement of maximal swim time for 100 m of 0.7 s (P=0.04), an improvement in swim time relative to personal best time (-1.1%, P=0.02), and a significant improvement in average International Swimming Federation points (+22 points, P=0.01).
RIPC improves maximal performance in highly trained swimmers. This simple technique may be applicable to other sports and, more importantly, to other clinical syndromes in which exercise tolerance is limited by tissue hypoxemia or ischemia.
Statistical guidelines and expert statements are now available to assist in the analysis and reporting of studies in some biomedical disciplines. We present here a more progressive resource for sample-based studies, meta-analyses, and case studies in sports medicine and exercise science. We offer forthright advice on the following controversial or novel issues: using precision of estimation for inferences about population effects in preference to null-hypothesis testing, which is inadequate for assessing clinical or practical importance; justifying sample size via acceptable precision or confidence for clinical decisions rather than via adequate power for statistical significance; showing SD rather than SEM, to better communicate the magnitude of differences in means and nonuniformity of error; avoiding purely nonparametric analyses, which cannot provide inferences about magnitude and are unnecessary; using regression statistics in validity studies, in preference to the impractical and biased limits of agreement; making greater use of qualitative methods to enrich sample-based quantitative projects; and seeking ethics approval for public access to the depersonalized raw data of a study, to address the need for more scrutiny of research and better meta-analyses. Advice on less contentious issues includes the following: using covariates in linear models to adjust for confounders, to account for individual differences, and to identify potential mechanisms of an effect; using log transformation to deal with nonuniformity of effects and error; identifying and deleting outliers; presenting descriptive, effect, and inferential statistics in appropriate formats; and contending with bias arising from problems with sampling, assignment, blinding, measurement error, and researchers' prejudices. This article should advance the field by stimulating debate, promoting innovative approaches, and serving as a useful checklist for authors, reviewers, and editors.
Near-infrared spectroscopy (NIRS) measures hemoglobin saturation in small vessels. A number of interesting studies have used this method. However, difficulties with signal quantification and studies in which NIRS oxygen saturation did not behave as expected raise concerns. NIRS remains promising for studies of skeletal muscle, but a better understanding of the method is needed.
Unlike the early phase of preconditioning (PC), which lasts 2 to 3 hours and protects against infarction but not against stunning, the late phase of PC lasts 3 to 4 days and protects against both infarction and stunning, suggesting that it may have greater clinical relevance. It is now clear that late PC is a polygenic phenomenon that requires the simultaneous activation of multiple stress-responsive genes. Chemical signals released by a sublethal ischemic stress (such as NO, reactive oxygen species, and adenosine) trigger a complex cascade of signaling events that includes the activation of protein kinase C, Src protein tyrosine kinases, and nuclear factor kappaB and culminates in increased synthesis of inducible NO synthase, cyclooxygenase-2, aldose reductase, Mn superoxide dismutase, and probably other cardioprotective proteins. An analogous sequence of events can be triggered by a variety of stimuli, such as heat stress, exercise, and cytokines. Thus, late PC appears to be a universal response of the heart to stress in general. Importantly, the cardioprotective effects of late PC can be reproduced pharmacologically with clinically relevant agents (eg, NO donors, adenosine receptor agonists, endotoxin derivatives, or opioid receptor agonists), suggesting that this phenomenon might be exploited for therapeutic purposes. The purpose of this review is to summarize current information regarding the pathophysiology and mechanism of late PC.
One of the greatest challenges in exercise physiology is to develop a valid, reliable, non-invasive and affordable measurement of cardiac output (CO). The purpose of this study was to evaluate the reproducibility and accuracy of a new impedance cardiograph device, the Physio Flow, during a 1-min step incremental exercise test from rest to maximal peak effort. A group of 12 subjects was evaluated to determine the reproducibility of the method as follows: (1) each subject performed two comparable tests while their CO was measured by impedance cardiography using the new device (COImp1, COImp2), and (2) in a subgroup of 7 subjects CO was also determined by the direct Fick method (COFick) during the second test. The mean difference between the values obtained by impedance (i.e. COImp1-COImp2) was -0.009 l.min-1 (95% confidence interval: -4.2 l.min-1, 4.2 l.min-1), and CO ranged from 3.55 l.min-1 to 26.75 l.min-1 (n = 146). When expressed as a percentage, the difference (COImp1-COImp2) did not vary with increasing CO. The correlation coefficient between the values of COImp and COFick obtained during the second exercise test was r = 0.94 (P < 0.01, n = 50). The mean difference expressed as percentage was -2.78% (95% confidence interval: -27.44%, 21.78%). We conclude that COImp provides a clinically acceptable evaluation of CO in healthy subjects during an incremental exercise.
During exercise, pulse oximetry is problematic due to motion artifact and altered digital perfusion. New pulse oximeter technology addresses these issues and may offer improved performance. We simultaneously compared Nellcor N-395 (Oxismart XLTM) pulse oximeters with an RS-10 forehead sensor (RS-10), a D-25 digit sensor (D-25), and the Ivy 2000 (Masimo SETTM)/LNOP-Adt digit sensor (Ivy) to arterial blood oxygen saturation (Sa(O(2))) by cooximetry. Nine normal subjects, six athletes, and four patients with chronic disease exercised to maximum oxygen consumption (VO(2 max)) under various conditions [normoxia, hypoxia inspired oxygen fraction (FI(O(2))) = 0.125; hyperoxia, FI(O(2)) = 1.0]. Regression analysis for normoxia and hypoxic data was performed (n = 161 observations, Sa(O(2)) = 73-99.9%), and bias (B) and precision (P) were calculated. RS10 offered greater validity than the other two devices tested (y = 1.009x - 0.52, R(2) = 0.90, B+/-P = 0.3 +/- 2.5). Finger sensors had low precision and a significant negative bias (D-25: y = 1.004x - 2.327, R(2) = 0.52, B+/-P = -2.0 +/- 7.3; Ivy: y = 1.237x - 24.2, R(2) = 0.78, B+/-P = -2.0 +/- 5.2). Eliminating measurements in which heart rate differed by >10 beats/min from the electrocardiogram value improved precision minimally and did not affect bias substantially (B+/-P = 0.5 +/- 2.0, -1.8 +/- 8.4, and -1.25+/-4.33 for RS-10, D-25, and Ivy, respectively). Signal detection algorithms and pulse oximeter were identical between RS-10 and D-25; thus the improved performance of the forehead sensor is likely because of sensor location. RS-10 should be considered for exercise testing in which pulse oximetry is desirable.