Neuromuscular recovery from severe- and extreme-intensity exercise in men and women

Abstract

Maximal voluntary contraction force (MVC), potentiated twitch force (Qpot), and voluntary activation (%VA) recover to baseline within 90s following extreme-intensity exercise. However, methodological limitations masked important recovery kinetics. We hypothesized reductions in MVC, Qpot, and %VA at task failure following extreme-intensity exercise would be less than following severe-intensity exercise, and Qpot and MVC following extreme-intensity exercise would show significant recovery within 120s but remain depressed following severe-intensity exercise. Twelve subjects (6 men) completed two severe-intensity (40, 50%MVC) and two extreme-intensity (70, 80%MVC) isometric knee-extension exercise bouts to task failure (Tlim). Neuromuscular function was measured at baseline, Tlim, and through 150s of recovery. Each intensity significantly reduced MVC and Qpot compared to baseline. MVC was greater at T¬lim (p<0.01) and at 150s of recovery (p=0.004) following exercise at 80%MVC compared to severe-intensity exercise. Partial recovery of MVC and Qpot were detected within 150s following Tlim for each exercise intensity; Qpot recovered to baseline values within 150s of recovery following exercise at 80%MVC. No differences in %VA were detected pre- to post-exercise or across recovery for any intensity. Although further analysis showed sex-specific differences in MVC and Qpot, future studies should closely examine sex-dependent responses to extreme-intensity exercise. It is clear, however, that these data reinforce that mechanisms limiting exercise tolerance during extreme-intensity exercise recover quickly. 
 NOVELTY:
 •Severe- and extreme-intensity exercise cause independent responses in fatigue accumulation and the subsequent recovery time courses. 
 •Recovery of MVC and Qpot occurs much faster following extreme-intensity exercise in both men and women. 

Sex differences in the intensity–duration relationships of the severe‐ and extreme‐intensity exercise domains

“…The recovery in MVC and Q pot force was also faster following exercise >70%MVC compared to severe‐intensity exercise (Figure 2). This is consistent with previous findings (Alexander et al, 2021). We have recently shown severe‐intensity dynamic knee‐extension exercise significantly decreased MVC and slowed its recovery, but which were not different from baseline within ∼90s of recovery following extreme‐intensity dynamic (Alexander et al, 2019) and isometric (Alexander et al, 2021) exercise.…”

“…This is consistent with previous findings (Alexander et al, 2021). We have recently shown severe‐intensity dynamic knee‐extension exercise significantly decreased MVC and slowed its recovery, but which were not different from baseline within ∼90s of recovery following extreme‐intensity dynamic (Alexander et al, 2019) and isometric (Alexander et al, 2021) exercise. Together with the finding that T lim at 70%MVC is not different from that predicted by the severe‐intensity power‐duration relationship, the observations of the reduction and recovery in MVC and Q pot force above 70%MVC may provide further support into the range of exercise intensities in which the transition between severe‐ and extreme‐intensity exercise domains occurs.…”

“…Others have observed similar responses regarding the effects of blood flow on exercise tolerance, i.e. exercise tolerance is significantly reduced with blood flow occlusion at intensities up to 40%MVC, but with no further reduction seen for intensities >50%MVC (Alexander et al, 2021;Ansdell et al, 2019;Froberg & Pedersen, 1984;Hunter & Enoka, 2001;Maughan et al, 1986;Oranchuk et al, 2020;Wernbom et al, 2006). Although there is conflicting evidence as to whether contractioninduced ischaemia is the result of an absolute pressure or occurs at the same force relative to MVC (Hunter, Critchlow, Shin, et al, 2004), individuals with lower MVCs typically have greater exercise tolerance.…”

“…Using the effect size between males and females for differences in T lim at 40 and 50%MVC, and the reductions in MVC and Q pot force from Alexander 2021, a power calculation ( α = 0.05, power 0.90) revealed that a minimum of 12 participants were required (Alexander et al, 2021). Seven healthy males (mean ± S.D.…”

“…Within the context of exercise domains, Ansdell et al (2019) found the heavy‐ to severe‐intensity boundary occurs at ∼20% of maximal voluntary contraction (MVC) in males but at ∼24%MVC in females (Ansdell et al, 2019), consistent with greater exercise tolerance in females. The sex difference in exercise tolerance, however, appears to be less dramatic when exercising at target forces >50%MVC, and in some cases non‐existent as intensities approach MVC (Alexander et al, 2021; Froberg & Pedersen, 1984; Maughan et al, 1986; Yoon et al, 2007). Although currently unknown, this suggests W′ ext would not be different between males and females.…”