Influence of duty cycle on the power-duration relationship: Observations and potential mechanisms

Broxterman, Ryan M.; Ade, Carl J.; Wilcox, Samuel L.; Schlup, Susanna J.; Craig, Jesse C.; Barstow, Thomas J.

doi:10.1016/j.resp.2013.11.010

Cited by 60 publications

(88 citation statements)

References 77 publications

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“…1. The determination of the control power-duration relationship in one subject was found to be greatly weighted toward a specific constant-power test, as previously described (4,12,38,39,42,51). Therefore, this subject's control power-duration relationship was determined using three constant-power tests (4,12,38,39,42,51).…”

Section: Resultsmentioning

confidence: 89%

“…The asymptote in this model represents CP, which distinguishes an exercise intensity above which a physiological steady state is not attained and exercise T lim is limited by W=. As such, CP represents the highest sustainable rate of aerobic ATP production for which W= will not be continuously utilized (4,12,38,39,42,51). The curvature constant in this model represents W=, modeled as a finite amount of work that can be performed above CP that, when fully expended, results in T lim (21,38,43,55).…”

Section: Discussionmentioning

confidence: 99%

“…To date, evidence suggests that CP represents the highest attainable steady state for aerobic energy production without continuously drawing upon W= (4,12,38,39,42,51). It was with this interpretation of CP in mind that Monod and Scherrer (38) postulated that the maximum amount of work performed under blood flow occlusion would be equal to W=, which would necessitate a CP equal to 0 W. In contrast to this prediction, the present study demonstrated that the calculated occlusion CP was actually reduced to a power output slightly, but significantly, Ͻ0 W. While a negative CP is only theoretical and not physiologically attainable, nonetheless, this estimate provides mechanistic insight into CP.…”

Section: Discussionmentioning

confidence: 99%

“…Building evidence supports that complete utilization of W= is associated with consistent muscle phosphocreatine ([PCr]), inorganic phosphate ([P i ]), and hydrogen ion concentration ([H ϩ ]) perturbations, which may limit the amount of work performed above CP (28,43,51). Additionally, the rate of W= utilization (but not the magnitude of W=) is influenced by manipulations in O 2 delivery and O 2 extraction via alterations in muscle contraction duty cycle (4). While much has been revealed regarding the mechanisms of CP and W=, it is not clear how blood flow occlusion influences each parameter.…”

mentioning

confidence: 97%

“…Nevertheless, the precise physiological mechanisms of the curvature constant (W=), and to a lesser degree critical power (CP), have remained elusive. The growing body of evidence supports that CP represents the highest attainable steady state for aerobic energy production without continually drawing on W= and, as such, demarcates the boundary between the heavy-and severe-intensity exercise domains (4,12,38,39,42,51). It is also evident that W= is a constant term that determines the limit of exercise tolerance (T lim ) for severe-intensity exercise (21,55).…”

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confidence: 99%

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Influence of blood flow occlusion on muscle oxygenation characteristics and the parameters of the power-duration relationship

Broxterman

Ade

Craig

et al. 2015

Journal of Applied Physiology

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Broxterman RM, Ade CJ, Craig JC, Wilcox SL, Schlup SJ, Barstow TJ. Influence of blood flow occlusion on muscle oxygenation characteristics and the parameters of the power-duration relationship. J Appl Physiol 118: 880 -889, 2015. First published February 6, 2015 doi:10.1152/japplphysiol.00875.2014.-It was previously (Monod H, Scherrer J. Ergonomics 8: 329 -338, 1965 postulated that blood flow occlusion during exercise would reduce critical power (CP) to 0 Watts (W), while not altering the curvature constant (W=). We empirically assessed the influence of blood flow occlusion on CP, W=, and muscle oxygenation characteristics. Ten healthy men (age: 24.8 Ϯ 2.6 yr; height: 180 Ϯ 5 cm; weight: 84.6 Ϯ 10.1 kg) completed four constant-power handgrip exercise tests during both control blood flow (control) and blood flow occlusion (occlusion) for the determination of the power-duration relationship. Occlusion CP (Ϫ0.7 Ϯ 0.4 W) was significantly (P Ͻ 0.001) lower than control CP (4.1 Ϯ 0.7 W) and significantly (P Ͻ 0.001) lower than 0 W. Occlusion W= (808 Ϯ 155 J) was significantly (P Ͻ 0.001) different from control W= (558 Ϯ 129 J), and all 10 subjects demonstrated an increased occlusion W= with a mean increase of ϳ49%. The present findings support the aerobic nature of CP. The findings also demonstrate that the amount of work that can be performed above CP is constant for a given condition, but can vary across conditions. Moreover, this amount of work that can be performed above CP does not appear to be the determinant of W=, but rather a consequence of the depletion of intramuscular energy stores and/or the accumulation of fatigue-inducing metabolites, which limit exercise tolerance and determine W=. critical power; curvature constant; oxygen delivery; muscle ischemia THE ROBUST NATURE OF THE power-duration relationship (and its equivalents for other modes of exercise) has been well established (26, 27, 52). Nevertheless, the precise physiological mechanisms of the curvature constant (W=), and to a lesser degree critical power (CP), have remained elusive. The growing body of evidence supports that CP represents the highest attainable steady state for aerobic energy production without continually drawing on W= and, as such, demarcates the boundary between the heavy-and severe-intensity exercise domains (4,12,38,39,42,51). It is also evident that W= is a constant term that determines the limit of exercise tolerance (T lim ) for severe-intensity exercise (21, 55). Intramuscular energy stores (35,36,38), the accumulation of fatigue-inducing metabolites (7,18,21,28), and/or the magnitude of the severe-intensity domain (5, 51) have all been postulated to determine W=. Building evidence supports that complete utilization of W= is associated with consistent muscle phosphocreatine ([PCr]), inorganic phosphate ([P i ]), and hydrogen ion concentration ([H ϩ ]) perturbations, which may limit the amount of work performed above CP (28,43,51). Additionally, the rate of W= utilization (but not the magnitude of W=) is influenced by mani...

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Section: Resultsmentioning

confidence: 89%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 97%

mentioning

confidence: 99%

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Influence of blood flow occlusion on muscle oxygenation characteristics and the parameters of the power-duration relationship

Broxterman

Ade

Craig

et al. 2015

Journal of Applied Physiology

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Estimation of critical end-test torque using neuromuscular electrical stimulation of the quadriceps in humans

et al. 2018

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Characterization of critical power/torque (CP/CT) during voluntary exercise requires maximal effort, making difficult for those with neuromuscular impairments. To address this issue we sought to determine if electrically stimulated intermittent isometric exercise resulted in a critical end-test torque (ETT) that behaved similar to voluntary CT. In the first experiment participants (n = 9) completed four bouts of stimulated exercise at a 3:2 duty cycle, at frequencies of 100, 50, 25 Hz, and a low frequency below ETT (Sub-ETT; ≤ 15 Hz). The second experiment (n = 20) consisted of four bouts at a 2:2 duty cycle-two bouts at 100 Hz, one at an intermediate frequency (15-30 Hz), and one at Sub-ETT. The third experiment (n = 12) consisted of two bouts at 50 Hz at a 3:2 duty* cycle with proximal blood flow occlusion during one of the bouts. ETT torque was similar (p ≥ 0.43) within and among stimulation frequencies in experiment 1. No fatigue was observed during the Sub-ETT bouts (p > 0.05). For experiment 2, ETT was similar at 100 Hz and at the intermediate frequency (p ≥ 0.29). Again, Sub-ETT stimulation did not result in fatigue (p > 0.05). Altering oxygen delivery by altering the duty cycle (3:2 vs. 2:2; p = 0.02) and by occlusion (p < 0.001) resulted in lower ETT values. Stimulated exercise resulted in an ETT that was consistent from day-to-day and similar regardless of initial torque, as long as that torque exceeded ETT, and was sensitive to oxygen delivery. As such we propose it represents a parameter similar to voluntary CT.

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A model-based estimation of critical torques reduces the experimental effort compared to conventional testing

Herold

Sommer

2020

Eur J Appl Physiol

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Purpose Critical torque (CT) is an important fatigue threshold in exercise physiology and can be used to analyze, predict, or optimize performance. The objective of this work is to reduce the experimental effort when estimating CTs for sustained and intermittent isometric contractions using a model-based approach. Materials and methods We employ a phenomenological model of the time course of maximum voluntary isometric contraction (MVIC) torque and compute the highest sustainable torque output by solving an optimization problem. We then show that our results are consistent with the steady states obtained when simulating periodic maximum loading schemes. These simulations correspond to all-out tests, which are used to estimate CTs in practice. Based on these observations, the estimation of CTs can be formulated mathematically as a parameter estimation problem. To minimize the statistical uncertainty of the parameter estimates and consequently of the estimated CTs, we compute optimized testing sessions. This reduces the experimental effort even further. Results We estimate CTs of the elbow flexors for sustained isometric contractions to be 28% of baseline MVIC torque and for intermittent isometric contractions consisting of a 3 s contraction followed by 2 s rest to be 41% of baseline MVIC torque. We show that a single optimized testing session is sufficient when using our approach. Conclusions Our approach reduces the experimental effort considerably when estimating CTs for sustained and intermittent isometric contractions.

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Influence of duty cycle on the power-duration relationship: Observations and potential mechanisms

Cited by 60 publications

References 77 publications

Influence of blood flow occlusion on muscle oxygenation characteristics and the parameters of the power-duration relationship

Influence of blood flow occlusion on muscle oxygenation characteristics and the parameters of the power-duration relationship

Estimation of critical end-test torque using neuromuscular electrical stimulation of the quadriceps in humans

A model-based estimation of critical torques reduces the experimental effort compared to conventional testing

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