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Static stretching increases muscle fatigue during submaximal sustained isometric contractions
Abstract
AIM: The purpose of this study was to examine the acute effects of a static stretching protocol on neuromuscular fatigue of the flexor carpi radialis (FC) and flexor digitorum (FD).
METHODS: Twenty-six healthy and right-handed men with a mean (SD) age of 27.1 (2.9) years volunteered for this study. The fatigue test was performed before (Pre) and after three sets of 50 s stretching (Post) applied to the right hand, and twice (T1 and T2) without stretching to the left hand as a control condition. Isometric handgrip fatigue exercise was maintained for 30s within the range 50-60% of the maximal voluntary contraction. From the electromyography (EMG), root mean squares (RMS) values and mean frequency (MF) were obtained for each 2s consecutive windows of test and normalized by the MVC obtained in 6s tests. From time series, coefficients of linear regression were determined used to compare Pre with Post and T1 with T2 by paired samples t-tests.
RESULTS: Higher rate of increase in EMG on Post compared to Pre was found in both FC (P=0.015) and FD (P=0.006). A higher rate of decrease of MF for FC (P=0.004) and FD (P=0.005) was observed with Post compared to Pre. Conversely, the differences between T1 and T2 were not significant (P>0.05).
CONCLUSION: These findings indicate that static stretching performed immediately before submaximal isometric muscle actions may increase neuromuscular fatigue assessed by EMG, suggesting that could reduce muscle’s endurance capacity.
... 9,15 According to previous reports, to perform stretching before maximal contraction reduces amplitude of electromyography (EMG), frequency and force production. [16][17][18] Fowles et al. 16 reported a decrease of 28% in the maximal voluntary contraction (MVC) of the plantar flexors and 15% of the EMG amplitude during MVC after a stretching protocol. Furthermore, Kay et al. 18 showed a reduction in peak flexor moment after stretch, as well as a good correlation between the decrease in EMG amplitude and peak flexor moment. ...
... Furthermore, Kay et al. 18 showed a reduction in peak flexor moment after stretch, as well as a good correlation between the decrease in EMG amplitude and peak flexor moment. In contrast, Trajano et al. 17 reported an increase in EMG amplitude during submaximal sustained isometric contractions after stretch, but the increase in EMG amplitude was accompanied by the decrease in EMG median frequency. Thus, it appears that stretch negatively influence mechanical stimuli during ST. ...
... However, studies reported that implementing ISS may increase the neuromechanical and metabolic stimuli by adding to total session time under tension to the session. 4,5 It is important to note, that the aforementioned influence of stretching on acute neuromuscular adaptations were based on experimental studies with stretch performed before only one maximal muscle action with short duration, 16,18 or sustained submaximal isometric contractions, 17 that are different of repeated dynamic muscle contractions generally applied during ST. Therefore, considering that the results of chronic studies on ISS are controversial, and the acute studies on the effects of stretching on neuromuscular performance do not resemble application in ST routines, 19,20 it remains unclear whether the ISS applied to ST routines will be able to influence the physiologic changes associated with neuromuscular adaptations. ...
This study investigated the acute effects of inter-set static stretching (ISS) during resistance exercise (RE) on the subsequent neuromuscular and metabolic responses. Twelve resistance-trained men performed three different knee extension RE protocols comprised of seven sets of 10 repetitions in a counterbalanced fashion. The three protocols were: 1) ISS (subjects performed 25 sec of quadriceps stretching between sets during 40 sec rest interval); 2) control (CON, subject passively rested between sets for 40 sec); 3) traditional (TRA, subject passively rested between sets for 120 sec). Total work was lower (p < 0.05) in ISS than CON and TRA (p <0.05). The fatigue index was greater (p < 0.05) in ISS compared with CON and TRA. ISS also resulted in lower (p < 0.05) electromyography (EMG) amplitude during the 6th and 7th sets compared with TRA. Additionally, EMG frequency was lower (p < 0.05) from the 3rd to 5th sets during ISS compared to CON, and from the 3rd to 7th sets compared to TRA. Muscle swelling and blood lactate similarly increased (p > 0.05) in response to all protocols. These results indicate that ISS negatively impacts neuromuscular performance, and does not increase the metabolic stress compared to passive rest intervals.
... 9,15 According to previous reports, to perform stretching before maximal contraction reduces amplitude of electromyography (EMG), frequency and force production. [16][17][18] Fowles et al. 16 reported a decrease of 28% in the maximal voluntary contraction (MVC) of the plantar flexors and 15% of the EMG amplitude during MVC after a stretching protocol. Furthermore, Kay et al. 18 showed a reduction in peak flexor moment after stretch, as well as a good correlation between the decrease in EMG amplitude and peak flexor moment. ...
... Furthermore, Kay et al. 18 showed a reduction in peak flexor moment after stretch, as well as a good correlation between the decrease in EMG amplitude and peak flexor moment. In contrast, Trajano et al. 17 reported an increase in EMG amplitude during submaximal sustained isometric contractions after stretch, but the increase in EMG amplitude was accompanied by the decrease in EMG median frequency. Thus, it appears that stretch negatively influence mechanical stimuli during ST. ...
... However, studies reported that implementing ISS may increase the neuromechanical and metabolic stimuli by adding to total session time under tension to the session. 4,5 It is important to note, that the aforementioned influence of stretching on acute neuromuscular adaptations were based on experimental studies with stretch performed before only one maximal muscle action with short duration, 16,18 or sustained submaximal isometric contractions, 17 that are different of repeated dynamic muscle contractions generally applied during ST. Therefore, considering that the results of chronic studies on ISS are controversial, and the acute studies on the effects of stretching on neuromuscular performance do not resemble application in ST routines, 19,20 it remains unclear whether the ISS applied to ST routines will be able to influence the physiologic changes associated with neuromuscular adaptations. ...
... Specifically, low-level static muscle activation, such as the contraction encountered during prolonged sitting, could cause fluctuations in blood oxygen (Callaghan et al. 2010). Additionally, passive static muscle stretching could cause muscle fatigue indicated by decreases in the mean power frequency (MPF), muscle discharge rates, and muscle force production (Cornwell et al. 2002;Pulverenti et al. 2020;Trajano et al. 2015Trajano et al. , 2020. The second manifestation is that the compression of tissue would cause increased internal pressure of the tissue, occlusion of the blood flow, and a decrease in metabolism over time (Reenalda et al. 2010), which could cause harm to the tissue or physical discomfort. ...
... There was a significant difference between MPF changes in the rectus femoris in P1 and P3 (greater decrease in P3), which indicates that the passive stretching of muscle brings about neurological fatigue in muscle. This is consistent with the viewpoint of Trajano et al. (2015). Most muscles' sEMG and oxygenation performances did not show consistent synchronization or contradiction, so it can be concluded that passive stretch of muscle is not the main factor influencing body oxygenation level here. ...
The purpose of this study was to determine the biomechanical mechanisms driving passengers’ lower-limb postural shifts during seated sleep on a flight to prevent negative effects on passengers’ physical health. Twenty subjects participated in an observational study and a subsequent experiment on fatigue development and tissue oxygenation changes during seated sleep in an economy-class aircraft seat. Three of the most frequently used postures, which involved four targeted muscles of the legs and the thigh-buttock region, were selected and examined in the experiment with the following measures: muscle electromyogram, tissue oxygenation, and body contact pressure distribution. The results showed that the fatigue of the tibialis anterior and gastrocnemius and the compression of the region under the medial tuberosities were relieved by alternations among the three positions—position 1 (placing the shanks forwards), position 2 (placing the shanks neutrally), and position 3 (placing the shanks backwards). This research reveals the mechanical properties of the biomechanical factors functioning in lower-limb postural shifts during seated sleep and provides design optimization strategies for economy-class aircraft seats to reduce the negative effects on passenger health.
... The roughly 20% decrease in submaximal torque was moderate, but relevant, and was not overcome after 20 min of poststretch recovery. These findings are similar to previous findings where greater EMG activity was needed to reach the same force output (Kato et al. 2011;Trajano et al. 2015) and where a small (~5%) ongoing decrement in maximal torque was observed despite several measures of central drive returning to prestretch values (Trajano et al. 2014a). The cause of this small loss of peripheral function is unclear, although it might speculatively result from changes in the mechanical properties of intramuscular connective tissues (and extracellular matrix), alteration in the force-length prop-erties of muscle (Kato et al. 2011), or changes in Ca 2ϩ sensitivity of actin and myosin binding sites (Trajano et al. 2013(Trajano et al. , 2017. ...
... The cause of this small loss of peripheral function is unclear, although it might speculatively result from changes in the mechanical properties of intramuscular connective tissues (and extracellular matrix), alteration in the force-length prop-erties of muscle (Kato et al. 2011), or changes in Ca 2ϩ sensitivity of actin and myosin binding sites (Trajano et al. 2013(Trajano et al. , 2017. Importantly, this sustained decrease in submaximal torque may be of practical interest, because this ongoing loss of muscle function may particularly impair performance of submaximal tasks or ensure that a greater voluntary effort is required to complete a movement task (Trajano et al. 2015). This may be particularly relevant to locomotion or balance tasks, and it is noteworthy that static stretch-induced impairments have previously been shown in such tasks (Chatzopoulos et al. 2014;Han et al. 2014). ...
This study investigated whether modulation of corticospinal-motoneuronal excitability and/or synaptic transmission of the Ia afferent spinal reflex contributes to decreases in voluntary activation and muscular force after an acute bout of prolonged static muscle stretching. Fifteen males performed 5×60-s constant-torque stretches (15-s rest intervals; total duration 5-min) of the plantar flexors on an isokinetic dynamometer and a non-stretching control condition in random order on two separate days. Maximum isometric plantar flexor torque and triceps surae muscle electromyographic activity (normalized to M-wave; EMG/M) were simultaneously recorded immediately before and after each condition. Motor-evoked potentials (using transcranial magnetic stimulation) and H-reflexes were recorded from soleus during EMG-controlled submaximal contractions (23.46.9% EMG maximum). No changes were detected in the control condition. After stretching, however, peak torque (mean±SD; -14.3±7.0%) and soleus EMG/M (-17.8±6.2%) decreased and these changes were highly correlated (r=0.83). No changes were observed after stretching in soleus MEP or H-reflex amplitudes measured during submaximal contractions, and inter-individual variability of changes were not correlated with changes in EMG activity or maximum torque. During EMG-controlled submaximal contractions, torque production was significantly decreased after stretching (-22.7±15.0%), indicating a compromised muscular output. These data provide support that changes in the excitability of the corticospinal-motoneuronal and Ia afferent spinal reflex pathways do not contribute to post-stretch neural impairment.
... Studies examining the effect of stretching on proprioception have focussed on SS (Larsen et al., 2005;Björklund et al., 2006;Ghaffarinejad et al., 2007). In recent times the utility of SS as exercise preparation has been questioned (Simic, Sarabon, & Markovic, 2013), because acute effects of SS include decreased muscle strength (Cramer et al., 2004), sprint performance ( Fletcher & Anness, 2007;Haddad et al., 2014), and increased fatigability (Trajano, Pinho, Costa, & Oliveira, 2015). An alternative of increasing popularity is dynamic stretching (DS), which involves a repeated controlled movement through the joint range of motion (Fletcher & Anness, 2007). ...
... Negative effects of SS on muscle strength (Cramer et al., 2004;Power, Behm, Cahill, Carroll, & Young, 2004) and athletic performance ( Fletcher & Anness, 2007;Haddad et al., 2014;Trajano et al., 2015) have been established previously, and the findings of the present study are in agreement. Concentric strength of the knee extensors and flexors were greater in both DS and CON compared to SS conditions. ...
Background:
The importance of warm up procedures prior to athletic performance is well established. A common component of such procedures is muscle stretching. There is conflicting evidence regarding the effect of static stretching (SS) as part of warm up procedures on knee joint position sense (KJPS) and the effect of dynamic stretching (DS) on KJPS is currently unknown. The aim of this study was to determine the effect of dynamic and static stretching as part warm up procedures on KJPS and knee extension and flexion strength.
Methods:
This study had a randomised cross-over design and ten healthy adults (20±1years) attended 3 visits during which baseline KJPS, at target angles of 20° and 45°, and knee extension and flexion strength tests were followed by 15min of cycling and either a rest period (CON), SS, or DS and repeat KJPS and strength tests. All participants performed all conditions, one condition per visit.
Results:
There were warm up×stretching type interactions for KJPS at 20° (p=0.024) and 45° (p=0.018), and knee flexion (p=0.002) and extension (p<0.001) strength. The SS and DS improved KJPS but CON condition did not and SS decreased strength. No change in strength was present for DS or CON.
Conclusions:
Both SS and DS improve KJPS as part of pre-exercise warm up procedures. However, the negative impact of SS on muscle strength limits the utility of SS before athletic performance. If stretching is to be performed as part of a warm up, DS should be favoured over SS.
... During contraction efforts, participants were instructed to brace through their core while keeping their back and shoulder blades against the seat. After a 1-2-min rest, where the participant was encouraged to bend their knee to avoid the potential fatigue that could result from maintaining a static stretch (Trajano et al., 2015) the participant proceeded with a set of 4, 3-s MVICs with a 30-s rest between each set. Investigators provided scripted verbal encouragement for motivational purposes. ...
... static stretching, dynamic stretching, ballistic stretching, and proprioceptive neuromuscular facilitation. Some authors have a predominant view that performance of a sportsman is decreasing after static stretching [17,18] and even exhaustion is increasing [19]. Other studies [20,21,22] show that if static stretching is exercised 30 seconds, it has negligible or none negative influence on power formation. ...
Introduction: The aim of the pilot study was an effect comparison of stretching between foam rolling and dynamic stretching on performance in motion tests by young volleyball players. Methods: 1. Experimental sample-ESFR (n=8, age = 13.4±0.5 years, height = 173.8±7.7 cm, weight = 59.8±7.1 kg) absolved 6 measurements of indicators of stretching with foam rolling during 6 weeks. 2. Experimental sample-ESDS (n=8, age = 13.4±0.5 years, height = 174.5±9.5 cm, weight = 59.4±11.0 kg) absolved dynamic stretching. We had determined the stretching effect between ESFR and ESDS by comparison of performance in tests: spike jump (SS), block jump (BS) E-test (ET), run to cones (RC), throw with 1 kg ball (H2), sit and reach test (SR) and sit-ups (SU). Results: The most important determination was that better level of stretching presented in performance and it was determined in RC in two examples with medium effect and in three examples with large effect in behalf of ESFR. By contrast, one example from ESDS in parameter PS had better level of stretching with medium effect and one example with medium effect in H2. In other parameters (BS, SS, SU and ET) were the differences only small or none between ESFR and ESDS. Conclusion: The results of the pilot study indicate that using of foam rolling and dynamic stretching can have different influence on the level of stretching and preparation of young volleyball players. These results must be verified on larger experimental sample.
... The submaximal fatigue test consists of either sustained (static) or repetitive (dynamic) contractions at a target value of 30-75% of MVIC. While this test is not typically used to calculate motor fatigability, we included this method in the current protocol because it is often used to induce fatigue during concurrent assessments such as drug treatment effects, blood biomarker analysis, electromyography, and functional magnetic resonance imaging (fMRI) 27,28,29 . Submaximal fatigue tests cause less discomfort in research subjects 30 . ...
Cancer-related fatigue (CRF) is commonly reported by patients both during and after receiving treatment for cancer. Current CRF diagnoses rely on self-report questionnaires which are subject to report and recall biases. Objective measurements using a handheld dynamometer, or handgrip device, have been shown in recent studies to correlate significantly with subjective self-reported fatigue scores. However, variations of both the handgrip fatigue test and fatigue index calculations exist in the literature. The lack of standardized methods limits the utilization of the handgrip fatigue test in the clinical and research settings. In this study, we provide detailed methods for administering the physical fatigue test and calculating the fatigue index. These methods should supplement existing self-reported fatigue questionnaires and help clinicians assess fatigue symptom severity in an objective and quantitative manner.
... It has been found that the instantaneous MF of sEMG spectrum is more reliable for assessing muscle activation patterns during dynamic contractions by the time-frequency method (Bonato et al. 2001). Additionally, some studies have demonstrated that the sEMG spectrum component decreases during a fatiguing task (Córdova et al. 2017;Trajano et al. 2015;Izquierdo et al. 2009). As for the sEMG power spectrum in our study, the instantaneous MF of the FDS and BB declined during the speed climb and these muscles all represent a negative slope with the climbing time, which is similar to the Quaine's study (Quaine et al. 2003). ...
Purpose
The purpose of this study was to investigate the changes in blood lactate concentration (BL) and muscle activity patterns during a 15-m speed climbing competition that consisted of ten consecutive climbing actions on a standardized artificial wall in trained rock climbers.
Methods
Twelve trained rock climbers participated in this study. Surface electromyography (sEMG) and video signals were synchronized and recorded during climbing. The blood lactate was also tested 3 min after completing the climb.
Results
The average climbing time was 8.1 ± 2.1 s for the 15-m speed climb across all subjects, accompanied by a BL of 7.6 ± 1.9 mmol/L. The climbing speed and power firstly increased and then slightly decreased relative to peak value during the 15-m speed climbing. The results showed there was a positive correlation between the BL and the climbing time, r = 0.59, P = 0.043. The sEMG showed the flexor digitorum superficialis (FDS) electric activity was the highest, followed by the biceps brachii (BB) and latissimus dorsi. The instantaneous median frequency of sEMG of FDS and BB significantly decreased during the 15-m speed climbing. All the participants showed the higher sEMG RMS (%) in the terminal phase than that in the initial phase, especially with a greater increase in the left upper limbs. However, the lower limbs muscles presented no significant changes in the sEMG amplitude during climbing.
Conclusions
The FDS and BB play an important role in completing the 15-m speed climbing. The median frequency of arm EMG decreased more than that of legs, suggesting more fatigue. The blood lactate concentration increases in the current study suggest that a certain amount of glycolysis supplies energy in completing 15-m speed rock climbing. Based on the current data, it is suggested that muscular endurance of FDS and BB muscles in upper limbs should be improved for our climbers in this study.
Objetivo: Verificar o efeito do exercício de alongamento estático passivo realizado sob dois protocolos (fracionado versus contínuo) com a mesma duração, sobre o número de repetições máximas com carga habitualmente utilizada nas sessões de treino para dez repetições no supino reto com barra livre. Método: Um grupo de 16 homens (idade: 23.4 ± 2.8 anos; massa corporal: 81.8 ± 10.4 kg; estatura: 178.7 ± 2.6 cm) treinados e assintomáticos, que foram submetidos aos protocolos fracionado e contínuo. Para a análise dos efeitos dos exercícios de alongamento sobre a capacidade de gerar força foi utilizada a ANOVA para medidas repetidas com post hoc de Bonferroni. Resultados: Não houve diminuição no desempenho no teste de repetições máximas, independentemente da situação testada (p = 0.842). Em todos protocolos, os indivíduos executaram em média 17 repetições máximas (desvio‐padrão variando entre 2.9‐3.6 repetições máximas), sem diferença entre si. Conclusão: Executar um exercício de alongamento estático passivo durante 60 s, seja ele fracionado ou contínuo, não diminui o desempenho no teste de repetições máximas em relação à condição sem alongamento prévio.
Different stretching techni- ques have been used during warm-up routines. However, these routines may decrease force production. The purpose of this study was to compare the acute effect of a ballistic and a static stretching protocol on lower-limb maximal strength. Fourteen physically active women (169.3 6 8.2 cm; 64.9 6 5.9 kg; 23.1 6 3.6 years) performed three experimental sessions: a control session (estimation of 45° leg press one-repetition maximum [1RM]), a ballistic session (20 minutes of ballistic stretch and 45° leg press 1RM), and a static session (20 minutes of static stretch and 45° leg press 1RM). Maximal strength decreased after static stretching (213.2 6 36.1 to 184.6 6 28.9 kg), but it was unaffected by ballistic stretching (208.4 6 34.8 kg). In addition, static stretching exercises produce a greater acute improvement in flexibility compared with ballistic stretching exercises. Consequently, static stretching may not be recom- mended before athletic events or physical activities that require high levels of force. On the other hand, ballistic stretching could be more appropriate because it seems less likely to decrease maximal strength.
The purpose of endurance time (T
lim) prediction is to determine the exertion time of a muscle contraction before it occurs. T
lim prediction would then allow the evaluation of muscle capacities limiting fatigue and deleterious effects associated with exhaustive exercises. The present study aimed to analyze the influence of exercise intensity and joint angle on T
lim prediction using changes in surface electromyographic (sEMG) signals recorded during the first moments of the exercise. Fifteen male performed four knee extensions sustained until exhaustion that were different in exercise intensity (20% or 50% of maximal voluntary torque-MVT) and in joint angle (40 or 70º, 0° = full extension). T
lim prediction was explored using some parameters of the sEMG signals from rectus femoris, vastus medialis and vastus lateralis muscles. Changes in sEMG parameters (root mean square, mean power frequency and frequency banding 6–30 Hz) were expressed using the slope of the linear regression and the area ratio index. Results indicated that relationships between changes in sEMG signal and T
lim (0.51 < r < 0.83) were greater for experimental conditions associated with higher exercise intensity (50% MVT) and so to lower time duration. Knee joint angle had little influence on T
lim prediction results. Results also showed higher T
lim prediction considering spectral parameters and area ratio. This could be in relation to differences in relative contribution of central and peripheral fatigue that seems to change according to the exercise intensity, but also to the influence of psychological factors that increases with the duration of the task.
Since strength and muscular strength endurance are linked, it is possible that the inhibitory influence that prior stretching has on strength can also extend to the reduction of muscle strength endurance. To date, however, studies measuring muscle strength endurance poststretching have been criticized because of problems with their reliability. The purpose of this study was twofold: both the muscle strength endurance performance after acute static stretching exercises and the repeatability of those differences were measured. Two separate experiments were conducted. In experiment 1, the knee-flexion muscle strength endurance exercise was measured by exercise performed at 60 and 40% of body weight following either a no-stretching or stretching regimen. In experiment 2, using a test-retest protocol, a knee-flexion muscle strength endurance exercise was performed at 50% body weight on 4 different days, with 2 tests following a no-stretching regimen (RNS) and 2 tests following a stretching regimen (RST). For experiment 1, when exercise was performed at 60% of body weight, stretching significantly (p < 0.05) reduced muscle strength endurance by 24%, and at 40% of body weight, it was reduced by 9%. For experiment 2, reliability was high (RNS, intraclass correlation = 0.94; RST, intraclass correlation = 0.97). Stretching also significantly (p < 0.05) reduced muscle strength endurance by 28%. Therefore, it is recommended that heavy static stretching exercises of a muscle group be avoided prior to any performances requiring maximal muscle strength endurance.
The benefits of preexercise muscle stretching have been recently questioned after reports of significant poststretch reductions in force and power production. However, methodological issues and equivocal findings have prevented a clear consensus being reached. As no detailed systematic review exists, the literature describing responses to acute static muscle stretch was comprehensively examined.
MEDLINE, ScienceDirect, SPORTDiscus, and Zetoc were searched with recursive reference checking. Selection criteria included randomized or quasi-randomized controlled trials and intervention-based trials published in peer-reviewed scientific journals examining the effect of an acute static stretch intervention on maximal muscular performance.
Searches revealed 4559 possible articles; 106 met the inclusion criteria. Study design was often poor because 30% of studies failed to provide appropriate reliability statistics. Clear evidence exists indicating that short-duration acute static stretch (<30 s) has no detrimental effect (pooled estimate = -1.1%), with overwhelming evidence that stretch durations of 30-45 s also imparted no significant effect (pooled estimate = -1.9%). A sigmoidal dose-response effect was evident between stretch duration and both the likelihood and magnitude of significant decrements, with a significant reduction likely to occur with stretches ≥ 60 s. This strong evidence for a dose-response effect was independent of performance task, contraction mode, or muscle group. Studies have only examined changes in eccentric strength when the stretch durations were >60 s, with limited evidence for an effect on eccentric strength.
The detrimental effects of static stretch are mainly limited to longer durations (≥ 60 s), which may not be typically used during preexercise routines in clinical, healthy, or athletic populations. Shorter durations of stretch (<60 s) can be performed in a preexercise routine without compromising maximal muscle performance.
Muscle stretching transiently decreases muscle-blood flow corresponding to a muscle extension. It may disturb a balance between muscular oxygen demand and oxygen supply to muscles and reduce muscle oxygenation. However, muscle-stretching training may improve blood circulatory condition, resulting in the maintained muscle oxygenation during muscle stretching. The aim of this study was to investigate changes in muscle-blood volume (tHb) and tissue oxygenation index (TOI) during muscle stretching determined by using near-infrared spectroscopy (NIRS) in ballet-trained (BT) and untrained (C) subjects. 11 BT women who regularly perform muscle stretching and 11 C women participated in this study. Fascicle lengths, tHb and TOI in the tibialis anterior muscle were measured during passive plantar flexion from ankle joint angles of 120° (baseline) to 140°, 160°, the maximal comfortable position without pain (CP), and the maximal position (MP). At 160°, the % fascicle-length change from baseline was significantly lower in the BT than the C group, however, for the changes in tHb and TOI the significant interaction effect between the 2 groups was not detected. On the other hand, although the increases in the fascicle length from baseline to CP and MP were greater in BT than C, the tHb and TOI reductions were comparable between groups. We concluded that it appears that BT can extend their muscles without excessive reduction in muscle-blood volume and muscle oxygenation at relatively same but absolutely greater muscle-stretching levels than C. The attenuation in these indices during high-level muscle stretching may be associated with the repetitive muscle stretching of long-term ballet training.
Previous studies have suggested that chronic stretch might be able to produce skeletal muscle hypertrophy. However, stretching might also restrict blood flow, which could in turn influence any stretch-training program. This study evaluated the influence of muscle stretch on muscle oxygen saturation using near infrared spectroscopy (NIRS). A 16 channel NIRS probes were placed on the medial gastrocnemius, quadriceps, and hamstring muscles of young healthy adults. Oxygen saturation during maximal tolerated stretch was measured and normalized with cuff-induced ischemia and reperfusion. Oxygen saturation decreased in the gastrocnemius and quadriceps in a position dependent fashion, but did not change in the hamstring muscles. Passive stretching may also have a significant hypoxic component in some muscles but not others.
The purpose of this study was to investigate neuromuscular activation of the vastus intermedius (VI) muscle during fatiguing contraction. Seven healthy men performed sustained isometric knee extension exercise at 50% of maximal voluntary contraction until exhaustion. During the fatiguing task, surface electromyograms (EMGs) were recorded from four muscle components of the quadriceps femoris muscle group: VI; vastus lateralis (VL); vastus medialis (VM); and rectus femoris (RF) muscles. For the VI muscle, our recently developed technique was used. Root mean square (RMS) and median frequency (MF) of the surface EMG signal were calculated and these variables were then normalized by the value at the beginning of the task. Normalized RMS of the VI muscle resembled those of the other three muscles at all given times. At 95% of exhaustion time, normalized MF of the VI muscle was significantly higher than that of the VL muscle (p<0.05). These results suggested that neuromuscular activation is not consistent between the VI and VL muscles at the exhaustion for isometric submaximal contraction and this could reflect the dissimilar intramuscular metabolism between these muscles.
The effects of concentric contractions and passive stretching on musculotendinous stiffness and muscle activity were studied in 18 healthy human volunteers. Passive and concentric plantar flexor joint moment data were recorded on an isokinetic dynamometer with simultaneous electromyogram (EMG) monitoring of the triceps surae, real-time motion analysis of the lower leg, and ultrasound imaging of the Achilles-medial gastrocnemius muscle-tendon junction. The subjects then performed six 8-s ramped maximal voluntary concentric contractions before repeating both the passive and concentric trials. Concentric moment was significantly reduced (6.6%; P < 0.01), which was accompanied by, and correlated with (r = 0.60-0.94; P < 0.05), significant reductions in peak triceps surae EMG amplitude (10.2%; P < 0.01). Achilles tendon stiffness was significantly reduced (11.7%; P < 0.01), but no change in gastrocnemius medialis muscle operating length was detected. The subjects then performed three 60-s static plantar flexor stretches before being retested 2 and 30 min poststretch. A further reduction in concentric joint moment (5.8%; P < 0.01) was detected poststretch at 90% of range of motion, with no decrease in muscle activity or Achilles tendon stiffness, but a significant increase in muscle operating length and decrease in tendon length was apparent at this range of motion (P < 0.05). Thirty minutes after stretching, muscle activity significantly recovered to pre-maximal voluntary concentric contractions levels, whereas concentric moment and Achilles tendon stiffness remained depressed. These data show that the performance of maximal concentric contractions can substantially reduce neuromuscular activity and muscle force, but this does not prevent a further stretch-induced loss in active plantar flexor joint moment. Importantly, the different temporal changes in EMG and concentric joint moment indicate that a muscle-based mechanism was likely responsible for the force losses poststretch.
The aim of this study was to explore the effects of static and dynamic stretching of the leg flexors and extensors on concentric and eccentric peak torque (PT) and electromyography (EMG) amplitude of the leg extensors and flexors in women athletes. Ten elite women athletes completed the following intervention protocol in a randomized order on separate days: (a) non-stretching (control), (b) static stretching, and (c) dynamic stretching. Stretched muscles were the quadriceps and hamstring muscles. Before and after the stretching or control intervention, concentric and eccentric isokinetic PT and EMG activity of the leg extensors and flexors were measured at 60 and 180 degrees/s. Concentric and eccentric quadriceps and hamstring muscle strength at both test speeds displayed a significant decrease following static stretching (P<0.01-0.001). In contrast, a significant increase was observed after dynamic stretching for these strength parameters (P<0.05-0.001). Parallel to this, normalized EMG amplitude parameters exhibited significant decreases following static (P<0.05-0.001) and significant increases following dynamic stretching (P<0.05-0.001) during quadriceps and hamstring muscle actions at both concentric and eccentric testing modes. Our findings suggest that dynamic stretching, as opposed to static or no stretching, may be an effective technique for enhancing muscle performance during the pre-competition warm-up routine in elite women athletes.