Slight power output manipulations around the maximal lactate steady state have a similar impact on fatigue in females and males

Abstract

Neuromuscular fatigue (NMF) and exercise performance are affected by exercise intensity and sex differences. However, whether slight changes in power output (PO) below and above the maximal lactate steady-state (MLSS) impact NMF and subsequent performance (time to exhaustion, TTE) is unknown. Purpose: This study compared NMF and TTE in females and males in response to exercise performed at MLSS, 10 W below (MLSS-10) and above (MLSS+10). Methods: Twenty participants (9 females) performed three 30-min constant-PO exercise bouts followed (1 min delay) by a TTE at 80% of the peak-PO. NMF was characterized by isometric maximal voluntary contractions (IMVC) and femoral nerve electrical stimulation of knee extensors [e.g. peak torque of potentiated high-frequency (Db100) and single twitch (TwPt)] before and immediately after the constant-PO and TTE bouts. Results: IMVC declined less after MLSS-10 (-18±10%) compared to MLSS (-26±14%) and MLSS+10 (-31±11%) (all p<0.05), and the Db100 decline was greater after MLSS+10 (-24±14%) compared to the other intensities (MLSS-10: -15±9%; MLSS: -18±11%) (all p<0.05). Females showed smaller reductions in IMVC and TwPt compared to males after constant-PO bouts (all p<0.05), this difference being not dependant on intensity. TTE was negatively impacted by increasing the PO in the constant-PO (p<0.001), with no differences in end-exercise NMF (p>0.05). Conclusion: Slight changes in PO around MLSS elicited great changes in the reduction of maximal voluntary force and impairments in contractile function. Although NMF was lower in females compared to males, the changes in PO around the MLSS impacted both sexes similarly.

Cardiac Autonomic Modulation in Response to Muscle Fatigue and Sex Differences During Consecutive Competition Periods in Young Swimmers: A Longitudinal Study

“…Sex determines differences in the biological organization at all levels ( Holdcroft, 2007 ), including cardiac modulatory balance, which has been related to a greater tone in the autonomic vagal branch in females and a greater tone in the sympathetic branch in males ( Spina et al, 2019 ). As effort intensity also influences HRV recovery, it is noteworthy that females have an advantage in resistance to fatigue during submaximal contractions, with less impairment in neuromuscular activation after strenuous exercise; however, this advantage diminishes as the intensity of contractions increases ( Azevedo et al, 2021 ). Therefore, considering the differences in cardiac autonomic modulation and resistance to fatigue between males and females, muscle fatigue during a competitive period may influence cardiac autonomic control in a sex-specific manner during a competitive period in swimming athletes.…”

Power Output Manipulation from Below to Above the Gas Exchange Threshold Results in Exacerbated Performance Fatigability

“…Indeed, Burnley et al (9) showed that the rate of impairments in isometric maximal voluntary torque and contractile function, measured through electrically evoked responses to relaxed muscle, was four to five times faster when performing isometric exercise moderately above versus below critical torque. Consequently, even power outputs marginally above critical power or the maximum lactate steady state (10) are associated with inexorable perturbations in metabolic homeostasis and, concurrently, impairments in neuromuscular function owing primarily to disturbances at the contractile level.…”

Time Course of Performance Fatigability during Exercise below, at, and above the Critical Intensity in Females and Males

“…Even though exercise intensity and duration are accepted as major contributors that determine the amplitude of decline in performance fatigability after exercise cessation (9,10), recent studies have highlighted the key role that a critical metabolic boundary such as the maximal lactate steady state (MLSS) plays on the amplitude of decline in contractile function (11,12). For example, we have recently shown that even 10-W increments or decrements in power output (PO) from the MLSS elicit greater and lower contractile function impairments after a 30-min cycling, respectively (12).…”

“…Even though exercise intensity and duration are accepted as major contributors that determine the amplitude of decline in performance fatigability after exercise cessation (9,10), recent studies have highlighted the key role that a critical metabolic boundary such as the maximal lactate steady state (MLSS) plays on the amplitude of decline in contractile function (11,12). For example, we have recently shown that even 10-W increments or decrements in power output (PO) from the MLSS elicit greater and lower contractile function impairments after a 30-min cycling, respectively (12). However, likely because of the technical challenges associated with the evaluation of performance fatigability during exercise, a majority of studies to date have limited their measurements to task failure (10,13,14), ultimately neglecting the assessment of VA and contractile function throughout the exercise bout (i.e., time course) and at different intensities.…”

“…Another relevant aspect to consider in the evaluation of performance fatigability is the sex of the participants. Emerging evidence suggests that the amplitude of the decline in contractile function is lower in females compared with males, even when exercise intensity is normalized by each participants metabolic and/or force responses (7,8,12,15). These sex-related differences seem to be mostly explained by distinct morphological characteristics (e.g., females show greater percentage of type I fibers and mitochondrial volume density than males) (16,17) and physiological responses to exercise (e.g., greater exerciseinduced vasodilation are seen in females than in their males counterparts) (18), which are proposed to result in lower metabolic disturbance and decline in contractile function in females (15).…”