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Commentary: High-intensity Intermittent Training vs. Moderate-intensity Intermittent Training: Is It a Matter of Intensity or Intermittent Efforts?

Frontiers
Frontiers in Physiology
Authors:
GENERAL COMMENTARY
published: 30 May 2017
doi: 10.3389/fphys.2017.00370
Frontiers in Physiology | www.frontiersin.org 1May 2017 | Volume 8 | Article 370
Edited by:
Billy Sperlich,
University of Würzburg, Germany
Reviewed by:
Thimo Wiewelhove,
Ruhr University Bochum, Germany
*Correspondence:
Paulo Gentil
paulogentil@hotmail.com
Specialty section:
This article was submitted to
Exercise Physiology,
a section of the journal
Frontiers in Physiology
Received: 12 April 2017
Accepted: 18 May 2017
Published: 30 May 2017
Citation:
Gentil P and Del Vecchio FB (2017)
Commentary: High-intensity
Intermittent Training vs.
Moderate-intensity Intermittent
Training: Is It a Matter of Intensity or
Intermittent Efforts?
Front. Physiol. 8:370.
doi: 10.3389/fphys.2017.00370
Commentary: High-intensity
Intermittent Training vs.
Moderate-intensity Intermittent
Training: Is It a Matter of Intensity or
Intermittent Efforts?
Paulo Gentil 1*and Fabrício B. Del Vecchio 2
1Faculdade de Educação Física e Dança, Universidade Federal de Goiás, Goiânia, Brazil, 2Escola Superior de Educação
Física, Universidade Federal de Pelotas, Pelotas, Brazil
Keywords: high intensity interval exercise, high intensity intermittent training, physical fitness, high intensity
exercise, cardiorespiratory fitness
A commentary on
High-intensity intermittent training versus moderate-intensity intermittent training: is it a
matter of intensity or intermittent efforts?
by Jimenéz-Pavón, D., and Lavie, C. J. (2017). Br. J. Sports Med. doi: 10.1136/bjsports-2016-097015.
[Epub ahead of print]
We read with great interest the article by Jimenéz-Pavón and Lavie (2017). While we agree
with the value of prescribing and studying moderate-intensity interval training (MIIT), there are
important aspects that need to be clarified. The authors raise the point that “intensity” is not the
only difference between high-intensity interval training (HIIT) and aerobic continuous training
(ACT). The authors cite three studies to support the notion that the intermittent nature of the
exercise and not the intensity may be responsible for the results. However, the studies cited do
not seem to support the points raised. Rakobowchuk et al. (2012) trained two groups at the same
intensity (120% of the peak work rate obtained in a ramp-incremental test), but with different
working parameters (repeated intervals of 10:20 s vs. intervals of 30:60 s); therefore, this cannot
be considered a comparison between HIIT and MIIT. In the study conducted by Alkahtani et al.
(2013), the protocols differed in intensity but also in interval duration (5 min vs. 30s). Therefore,
one cannot use the study to make inferences about training intensity as the other parameters were
not equal. Moreover, in the study conducted by Alkahtani et al. (2013), the group that exercised at
higher intensity performed 30 s at 90% of the intensity equivalent to VO2peak, interspersed with
30 s of passive rest. Although this intensity was higher than that performed by the other group (20%
above 45% VO2peak), it is still lower than reported in previous studies using the same interval
duration (Billat et al., 1999, 2000a,b; Billat, 2001a,b; Racil et al., 2013, 2016).
The only study that has really compared different intensities is Racil et al. (2013). The authors
equated the number of bouts, rest intervals, etc. In this study, the decreases in waist circumference,
triglyceride and total cholesterol were significant only in the HIIT group. In addition, increases in
maximal aerobic speed and decreases in percentage of body fat, low-density lipoprotein cholesterol
(LDL-C), and insulin were higher in the HIIT group than in the MIIT group. Although the increases
in VO2peak were significant for both groups (7.7% for HIIT and 5.2 for MIIT), only the HIIT group
showed a significant increase compared to the control group. Therefore, the only study that made
comparisons with different intensities while keeping the other parameters constant clearly favored
HIIT exercises. While this may not answer the question of whether intensity or the intermittent
Gentil and Del Vecchio HIIT vs. MIT: Intensity Matters
nature of interval training is the most important parameter, it
suggests that HIIT promotes better results than MIIT.
We must recall, however, that defining HIIT intensity is not
a matter of “the more the better.” The efficiency of HIIT seems
to be a matter of choosing the adequate intensity. In this regard,
Raleigh et al. (2016) investigated the effects of HIIT intensity on
training-induced adaptations in VO2peak and VO2 kinetics. The
authors compared the effects of HIIT (1 min of effort per 1 min
of rest) targeting 80, 115, or 150% of the intensity equivalent
to VO2max while matching total work performed. According
to the results, increases in VO2peak were greater in the group
that trained at 115% than in the group that trained at 80%. No
differences were observed between the groups that trained at 150
and 80% as well as between the groups that trained at 150 and
115% of iVO2max. The greatest proportion of non-responders
was observed in the group that trained at lower intensity and
the greatest proportion of responders was found in the group
that trained at 115%. Therefore, one should not advocate for or
against high intensity, but rather for adequate intensity.
Jimenéz-Pavón and Lavie (2017) suggested that high-intensity
exercise can sometimes deter physically inactive and unfit people;
however, this has not been found in previous studies. Indeed,
Guiraud et al. (2011) reported that patients with chronic heart
disease preferred HIIT to ACT. Jung et al. (2014) reported that
adults with prediabetes can adhere to HIIT at a level that is
greater than ACT. Furthermore, Jung et al. (2015) compared
HIIT (1 min100% W peak and 1 min20% W peak for 20 min),
ACT at moderate intensity (40% W peak for 40 min) and ACT
at high intensity (80% W peak for 20 min). According to the
results, participants reported greater enjoyment related to HIIT
compared to the other protocols and 62% of the participants
reported a preference for engaging in HIIT.
Although we agree that enjoyment ratings might be reduced
when HIIT is strenuous, chronic training may lead to increased
enjoyment due to an increase in achievement. In this regard,
Heisz et al. (2016) randomly assigned sedentary young adults
to HIIT (1 min90–95% peak HR followed by 1 min at
30% PPO for a total of 20 min) or ACT (27.5 min70–75%
peak HR) for 6 weeks. Enjoyment of HIIT increased with
training, whereas enjoyment of ACT remained constant but
lower.
While we agree that MIIT might be an interesting strategy at
some points and that more studies regarding the topic are needed,
the references presented and the limitations raised by the authors
do not seem to support the points raised.
AUTHOR CONTRIBUTIONS
PG and FD conceived, drafted, and revised the manuscript. All
authors read and approved the final manuscript.
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2015-0614
Conflict of Interest Statement: The authors declare that the research was
conducted in the absence of any commercial or financial relationships that could
be construed as a potential conflict of interest.
Copyright © 2017 Gentil and Del Vecchio. This is an open-access article distributed
under the terms of the Creative Commons Attribution License (CC BY). The use,
distribution or reproduction in other forums is permitted, provided the original
author(s) or licensor are credited and that the original publication in this journal
is cited, in accordance with accepted academic practice. No use, distribution or
reproduction is permitted which does not comply with these terms.
Frontiers in Physiology | www.frontiersin.org 2May 2017 | Volume 8 | Article 370
... Jimenéz-Pavón [20] suggested that the benefits obtained from HIIT in obesity, health parameters, and cardiovascular disease factors were not due to its intensity, but its intermittent characteristics. However, Gentil and Del Vecchio questioned this by suggesting that the benefits could actually be from the intensity itself [21]. This controversy underlines the complexity associated with interval training, which prevents the drawing of general conclusions [22]. ...
... Our study included MIIT, in which subjects executed a similar protocol to the HIIT group but at moderate intensity, in order to examine whether the benefits of HIIT were due to its intermittency or its intensity. Our findings suggest the MIIT promoted slightly better results in body composition than MICT, but statistically lower than HIIT, which suggests that intensity is an important factor to consider for this outcome, as previously suggested [21]. Indeed, despite the mean difference of only 0.7 kg could not sound meaningful, it is almost two times higher for the more intense protocol. ...
... Indeed, despite the mean difference of only 0.7 kg could not sound meaningful, it is almost two times higher for the more intense protocol. However, the effects of intermittence cannot be neglected, since MIIT was superior to MICT in some aspects, which reinforces previous propositions of the potential benefits [20], whilst confirms that it might be inferior to HIIT [21]. The HIIT group maintained a reduction in fat mass even after 4 weeks of detraining, but the fat mass returned to baseline levels after 2 weeks of detraining in the MICT and MIIT groups, which seem to confirm the potential cardiometabolic risk of detraining [35]. ...
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Background: The present study compared the effects of training and detraining periods of high-intensity interval training (HIIT), moderate-intensity interval training (MIIT) and moderate-intensity continuous training (MICT) on functional performance, body composition, resting blood pressure and heart rate in elderly women nursing home residents. Methods: Forty-six volunteers (age, 80.8 ± 5.2 y; body mass, 69.8 ± 5.2 kg, height, 164.2 ± 4.12 cm) were divided into groups that performed treadmill exercise twice-weekly HIIT (4 bouts of 4-min intervals at 85-95% of the maximal heart rate [HRmax], interspersed by 4 min at 65% HRmax), MIIT (4 bouts of 4 min intervals at 55-75% HRmax, interspersed by 4 min at 45-50% HRmax) and MICT (30-min at 55-75% HRmax). Tests were performed before and after 8 weeks of training and 2 and 4 weeks of detraining. ANCOVA was used to analyze dependent variable changes. Results: After 8 weeks HIIT promoted greater reductions in body mass (HIIT = - 1.6 ± 0.1 kg; MICT = - 0.9 ± 0.1 kg; MIIT = - 0.9 ± 0.1 kg; p = 0.001), fat mass (HIIT = - 2.2 ± 0.1%; MICT = - 0.7 ± 0.1%; MIIT = - 1.2 ± 0.1%; p < 0.001) and resting heart rate (HIIT = - 7.3 ± 0.3%; MICT = - 3.6 ± 0.3%; MIIT = - 5.1 ± 0.3%; p < 0.001) and greater improvement in the chair stand test (HIIT = 3.4 ± 0.1 reps; MICT = 2.5 ± 0.1 reps; MIIT = 3.1 ± 0.1 reps; p < 0.001) when compared to MIIT and MICT. These improvements were sustained after 2 and 4 weeks of detraining only in the HIIT group. Conclusion: HIIT promoted greater benefits for body composition and functional performance than MICT and MIIT and also showed less pronounced effects of detraining. This suggests that the intensity of physical exercise is an important factor to consider when prescribing exercise to the elderly.
... We have read the Commentary by Gentil and Del Vecchio (2017), and we are grateful for the interest shown. Exactly, the main objective of our article was to highlight the relevance of prescribing and researching on moderate-intensity interval training (MIIT), although not only this, but in parallel with the current research on high-intensity interval training (HIIT). ...
... Commentary: High-intensity Intermittent Training vs. Moderate-intensity Intermittent Training: Is It a Matter of Intensity or Intermittent Efforts? by Paulo Gentil, P., and Del Vecchio, F. B. (2017). Front. ...
... doi: 10.3389/fphys.2017.00370 We have read the Commentary by Gentil and Del Vecchio (2017), and we are grateful for the interest shown. Exactly, the main objective of our article was to highlight the relevance of prescribing and researching on moderate-intensity interval training (MIIT), although not only this, but in parallel with the current research on high-intensity interval training (HIIT). ...
... Considering two recently published meta-analysis 9,15 , we hypothesized that high-intensity exercise promotes higher reductions in BP. Concerning the modality, it seems that interval training may be responsible for better cardiovascular improvements, although it is not a consensus 16,17 . ...
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Background: A family history of arterial hypertension is a significant risk factor for the development of hypertension in youngsters. Thus, primary prevention has been emphasized in those subjects with a genetic predisposition. Methods: This randomized clustered trial aimed to compare the effects of four modalities of aerobic training in postexercise hypotension. The primary outcomes were systolic blood pressure (SBP) and diastolic blood pressure (DBP). Secondly, peak oxygen uptake, heart rate, and subjective perceived exertion were analyzed. Nine normotensive men were randomized in four isocaloric sessions (200 kcal): high-intensity continuous training (HICT), moderate-intensity continuous training (MICT), high-intensity interval training (HIIT), and moderate-intensity interval training (MIIT). Results: The area under the curve (AUC) showed a difference between sessions for SBP (F(3;8)=3.2; P=0.04), with MICT promoting a higher reduction than MIIT (P<0.05). In DBP there was also a difference (F(3;8)=15.3; P<0.001), with HICT reducing more than HIIT (P<0.05) and MIIT (P<0.05). Moderate-intensity protocols provided clinically relevant changes (CRC) in 11.1% of the individuals, and high-intensity protocols presented CRC in 50% of them (χ2=6.41; P=0.011) for SBP. For DBP, there was CRC in 27.8% of continuous conditions and none in the intervals (χ2=5.81; P=0.016). Conclusions: All training sessions promoted postexercise hypotension for DBP, and HICT provided higher reductions in the AUC. CRC for SBP were observed according to the intensity, while CRC for DBP were associated with modality.
... These are critical processes for improving the acquisition of new skills, learning, and memory, and therefore have important implications in clinical populations such as stroke (Bliss and Cooke, 2011;Zeiler and Krakauer, 2013). Presently, there is a focus on determining the specifics of aerobic exercise prescription to optimally prime the brain (Ploughman et al., 2005Singh et al., 2014;Robertson et al., 2015;Saucedo Marquez et al., 2015;Hwang et al., 2016;Charalambous et al., 2017;Gentil and Del Vecchio, 2017;Morais et al., 2017;Nepveu et al., 2017;Neva et al., 2017). The benefits of aerobic exercise appear to be intensity dependent (Ploughman et al., 2007b;Hasan et al., 2016; and several studies have shown that delivering high-intensity aerobic exercise Abbreviations: CSE, corticospinal excitability; FDI, first dorsal interosseous; HIIT, high intensity interval training; MAS, Modified Ashworth Scale; MEP, motor evoked potential; MICE, moderate, constant-load exercise; MSO, maximal stimulator output; NIHSS, National Institute of Health Stroke Scale; TMS, transcranial magnetic stimulation; VCO 2 , volume of dioxide oxygen; VO 2 , volume of oxygen; VO 2max , maximal volume of oxygen uptake. ...
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... These are critical processes for improving the acquisition of new skills, learning, and memory, and therefore have important implications in clinical populations such as stroke (Bliss and Cooke, 2011;Zeiler and Krakauer, 2013). Presently, there is a focus on determining the specifics of aerobic exercise prescription to optimally prime the brain (Ploughman et al., 2005Singh et al., 2014;Robertson et al., 2015;Saucedo Marquez et al., 2015;Hwang et al., 2016;Charalambous et al., 2017;Gentil and Del Vecchio, 2017;Morais et al., 2017;Nepveu et al., 2017;Neva et al., 2017). The benefits of aerobic exercise appear to be intensity dependent (Ploughman et al., 2007b;Hasan et al., 2016; and several studies have shown that delivering high-intensity aerobic exercise Abbreviations: CSE, corticospinal excitability; FDI, first dorsal interosseous; HIIT, high intensity interval training; MAS, Modified Ashworth Scale; MEP, motor evoked potential; MICE, moderate, constant-load exercise; MSO, maximal stimulator output; NIHSS, National Institute of Health Stroke Scale; TMS, transcranial magnetic stimulation; VCO 2 , volume of dioxide oxygen; VO 2 , volume of oxygen; VO 2max , maximal volume of oxygen uptake. ...
Article
Full-text available
Objective: Evaluate intensity-dependent effects of a single bout of high intensity interval training (HIIT) compared to moderate intensity constant-load exercise (MICE) on corticospinal excitability (CSE) and effects on upper limb performance in chronic stroke. Design: Randomized cross-over trial. Setting: Research laboratory in a tertiary rehabilitation hospital. Participants: Convenience sample of 12 chronic stroke survivors. Outcome measures: Bilateral CSE measures of intracortical inhibition and facilitation, motor thresholds, and motor evoked potential (MEP) latency using transcranial magnetic stimulation. Upper limb functional measures of dexterity (Box and Blocks Test) and strength (pinch and grip strength). Results: Twelve (10 males; 62.50 ± 9.0 years old) chronic stroke (26.70 ± 23.0 months) survivors with moderate level of residual impairment participated. MEP latency from the ipsilesional hemisphere was lengthened after HIIT (pre: 24.27 ± 1.8 ms, and post: 25.04 ± 1.8 ms, p = 0.01) but not MICE (pre: 25.49 ± 1.10 ms, and post: 25.28 ± 1.0 ms, p = 0.44). There were no significant changes in motor thresholds, intracortical inhibition or facilitation. Pinch strength of the affected hand decreased after MICE (pre: 8.96 ± 1.9 kg vs. post: 8.40 ± 2.0 kg, p = 0.02) but not after HIIT (pre: 8.83 ± 2.0 kg vs. post: 8.65 ± 2.2 kg, p = 0.29). Regardless of type of aerobic exercise, higher total energy expenditure was associated with greater increases in pinch strength in the affected hand after exercise (R² = 0.31, p = 0.04) and decreases in pinch strength of the less affected hand (R² = 0.26 p = 0.02). Conclusion: A single bout of HIIT resulted in lengthened nerve conduction latency in the affected hand that was not engaged in the exercise. Longer latency could be related to the cross-over effects of fatiguing exercise or to reduced hand spasticity. Somewhat counterintuitively, pinch strength of the affected hand decreased after MICE but not HIIT. Regardless of the structure of exercise, higher energy expended was associated with pinch strength gains in the affected hand and strength losses in the less affected hand. Since aerobic exercise has acute effects on MEP latency and hand strength, it could be paired with upper limb training to potentiate beneficial effects.
... Therefore, the same percentage of HR max and i _ VO 2max can result in different intensities, and studies involving different methods for controlling intensity could lead to different results, even when adopting the same number of bouts and the same effort and pause times. The adequate definition and interpretation of training intensity seems to be vital, since the results of IT are largely dependent on it [46]. For example, Racil et al. [47] compared the effects of IT intensity in groups of obese young females performing the same number of bouts with the same total time and time:effort ratios (6-8 9 30:30 s). ...
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Interval training (IT) has been used for many decades with the purpose to increase performance and promote health benefits while demanding a relatively small amount of time. IT can be defined as intermittent periods of intense exercise separated by periods of recovery and has been divided into high-intensity interval training (HIIT), sprint interval training (SIT) and repeated sprint training (RST). IT use resulted in the publication of many studies and many of them with conflicting results and positions. The aim of this article was to move forward and understand studies’ protocol in order to draw accurate conclusions, as well as to avoid previous mistakes and effectively reproduce previous protocols. When analyzing the literature, we found many inconsistencies, such as, the controversial concept of ‘supramaximal’ effort, a misunderstanding regarding the term ‘high intensity’ and the use of different strategies to control intensity. The adequate definition and interpretation of training intensity seems to be vital, since the results of IT are largely dependent on it. These observations are only a few examples of the complexity involved with IT prescription, discussed to illustrate some problems with the current literature regarding IT. Therefore, it is our opinion that it is not possible to draw general conclusions about IT without considering all variables used in IT prescription, such as, exercise modality, intensity, effort andrest times and participants’ characteristics. In order to help guide researchers and health professionals in their practices it is important that experimental studies report their methods in as much detail as possible and future reviews and meta-analyses should critically discuss the articles included in light of their methods to avoid inadequate generalizations.
... There is little agreement on the extent to which the benefits of HIIT can be attributed to the exercise intensity alone among the other load variables [12,13]. Training at both moderate to high (70-80%) and near-maximal (>90%) intensity can significantly improve health parameters [13]. ...
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We investigated the acute neuromuscular and stress responses to three different high-intensity interval training sessions in young (age 19.5±1.3 years) and older (age 65.7±2.8 years) women. Cycling exercise comprised either 6 × 5 s or 3 × 30 s all-out, or 3 × 60 s submaximal, efforts each performed 5 weeks apart in randomized order. Peak and average power was higher in young than in older women and was largest during the 6 × 5 s strategy in both groups ( p<0.05 ). The decrease in the ratio of torques evoked by 20 and 100 Hz electrical stimulation, representing low-frequency fatigue, was more evident after the 3 × 30 and 3 × 60 s than the 6 × 5 s bout in both groups and was larger in young than in older women ( p<0.05 ). Both groups preferred 6 × 5 s cycling for further training. In conclusion, in young women, very low volume (6 × 5 s) all-out exercise induces significant physiological stress and seems to be an effective means of training. For older women, longer exercise sessions (3 × 60 s) are more stressful than shorter ones but are still tolerable psychologically.
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BACKGROUND Moderate-intensity interval training (MIIT) may be a viable exercise format for improving body composition, aerobic fitness, and health-related variables. OBJECTIVES This randomized trial aimed to analyze the effect of MIIT or high-intensity interval training (HIIT) on aerobic fitness, body composition variables, and resting metabolic rate (RMR) in women with overweight or obesity. METHODS 31 sedentary adult women with overweight or obesity performed 7 weeks [Formula: see text] 3 weekly sessions of either HIIT or MIIT. Physical and physiological tests were applied before and after training. RESULTS In both analyses (intention-to-treat and by adherence to the training), aerobic fitness showed a time effect ([Formula: see text] 0.041 and [Formula: see text] 0.015), but without differences between groups ([Formula: see text] 0.05). No group (HIIT vs. MIIT), time (pre vs. post), or interaction effects (group vs. time) were found for RMR, body composition markers (fat mass, body fat percentage, lean mass), or body mass index – BMI ([Formula: see text] 0.05). In addition, MIIT induced a relatively high drop-out rate. CONCLUSIONS This study suggested that the short-term (7-weeks) interval exercise training was effective for increasing aerobic fitness, and moderate-intensity intervals were as effective as high-intensity intervals. However, neither training format was effective for changing RMR, body composition variables, or BMI of women with overweight or obesity. Clinical trial ID: RBR-9jd7b7.
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This is the first study to show that enjoyment for high-intensity interval exercise increases with chronic training. Prior acute studies typically report high-intensity interval training (HIT) as being more enjoyable than moderate continuous training (MCT) unless the high-intensity intervals are too strenuous or difficult to complete. It follows that exercise competency may be a critical factor contributing to the enjoyment of HIT, and therefore building competency through chronic training may be one way to increase its enjoyment. To test this, we randomly assigned sedentary young adults to six weeks of HIT or MCT, and tracked changes in their enjoyment for the exercise. Enjoyment for HIT increased with training whereas enjoyment for MCT remained constant and lower. Changes in exercise enjoyment were predicted by increases in workload, suggesting that strength adaptions may be important for promoting exercise enjoyment. The results point to HIT as a promising protocol for promoting exercise enjoyment and adherence in sedentary young adults. © 2016 Heisz et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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High-intensity interval training (HIIT) improves peak oxygen uptake (V̇O2peak) and oxygen uptake (V̇O2) kinetics, however, it is unknown whether an optimal intensity of HIIT exists for eliciting improvements in these measures of whole-body oxidative metabolism. The purpose of this study was to (i) investigate the effect of interval intensity on training-induced adaptations in V̇O2peak and V̇O2 kinetics, and (ii) examine the impact of interval intensity on the frequency of nonresponders in V̇O2peak. Thirty-six healthy men and women completed 3 weeks of cycle ergometer HIIT, consisting of intervals targeting 80% (LO), 115% (MID), or 150% (HI) of peak aerobic power. Total work performed per training session was matched across groups. A main effect of training (p < 0.05) and a significant interaction effect was observed for V̇O2peak, with the change in V̇O2peak being greater (p < 0.05) in the MID group than the LO group; however, no differences were observed between the HI group and either the MID or LO groups (ΔV̇O2peak; LO, 2.7 ± 0.7 mL·kg–1·min–1; MID, 5.8 ± 0.7; HI, 4.2 ± 1.0). The greatest proportion of responders was observed in the MID group (LO, 8/12; MID, 12/13; HI, 9/11). A nonsignificant relationship (p = 0.26; r² = 0.04) was found between the changes in V̇O2peak and τV̇O2. These results suggest that training at intensities around V̇O2peak may represent a threshold intensity above which further increases in training intensity provide no additional adaptive benefit. The dissociation between changes in V̇O2peak and V̇O2 kinetics also reflects the different underlying mechanisms regulating these adaptations.
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High-intensity intermittent training (HIIT) has gained popularity in recent years for its similar or higher effects compared with aerobic continuous training (ACT) or controls in different age groups, several health-related parameters and cardiovascular diseases (CVD)1–3 as well as in competitive athletes. To analyse the role of HIIT comparing HIIT group with controls is an adequate approach for describing acute or chronic responses to a particular training model. However, when aiming to compare the efficacy of two training regimens, it has been usual to compare HIIT with ACT.1 In those cases, authors explained the differences largely on the grounds of intensity.4 However, we highlight that these studies compared two training modalities which are different in their training intensity and in the stimulus type—intermittent versus continuous. To the best of our knowledge, only three studies5–7 analysed the influence of intensity itself—by comparing HIIT and moderate-intensity intermittent training (MIIT). Alkahtani et al 5 examined the effect of 4-week MIIT and HIIT on fat oxidation and the responses …