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

Abstract

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...

The effect of resting blood flow occlusion on exercise tolerance and W′

“…There was no further change in muscle deoxygenation with the onset of muscle contraction and the %Sat remained elevated above zero throughout each protocol. These results further support that muscle oxygenation decreases until the capillary-mitochondria PO 2 gradient attains equilibrium with the inherent resistance to diffusion (Ḋ O2 Ϫ1 ) (1), so that complete deoxygenation is not attained in the microvasculature (1,8,18,28,29) during blood flow occlusion.…”

“…The depletion of intramuscular energy stores and accumulation of fatigueinducing metabolites consequent to the increased reliance on anaerobic energy production would be expected to diminish W= despite no mechanical work being performed (i.e., rest). Consistent with this, we have previously suggested that W= may be utilized in its entirety if the duration of resting blood flow occlusion is sufficient, despite no mechanical work being performed (1).…”

Critical Power

“…When the power-duration curve is measured, W′ has units of work, and thus only a small jump of logic is required to extrapolate this “amount of work” to a biological equivalent of stored energy. The early work of Monod and Scherrer (61) implied that this stored energy was of non-oxidative origin: a proposal recently supported by Broxterman et al (12,14) using occluded handgrip exercise. Intramuscular energy stores such as muscle glycogen and PCr are obvious targets, and indeed the cycle-ergometry W′ is increased following creatine supplementation (58,c.f., 101) and decreased following glycogen depletion (59).…”

“…Using brachial occlusion in a hand-grip exercise model, Broxterman et al (12) reduced CP to less than zero, while W′ significantly increased. Putative explanations for this elevated W′ include: a) some of the oxidative ATP turnover normally quantified within CP appeared as W′, b) the muscle somehow accessed more substrate level phosphorylation, c) the efficiency of muscle contraction and/or ATP resynthesis increased.…”

“…Moreover, it can help assess what feats are within the realms of human capabilities including human-powered flight (12,47), the sub-2 hour marathon (89) and the rehabilitation of patient populations. The purpose of this article is to synthesize our current understanding of the ‘CP concept’ from neuromuscular, metabolic and cardiovascular perspectives, and to consider the bioenergetic and performance-related consequences of traversing CP in healthy individuals and in patients suffering from chronic diseases such as heart failure (CHF) and chronic obstructive pulmonary disease (COPD).…”