ECSS Paris 2023: OP-PN20
INTRODUCTION: B2-agonists exert small benefits on strength and sprint performance, but high-intensity endurance effects remain equivocal. Literature hints that benefits extend beyond pulmonary effects. Single-muscle isometric exercise studies suggest improved endurance and preservation of peak torque through modulating contractility, recruitment and metabolism, but little is known about how B2-agonists effect fatiguing dynamic exercise. We investigated if acute B2-agonist use alters muscle contractility, recruitment, metabolic demand and fatigue resistance. METHODS: Twenty endurance athletes (3 women) completed a double-blind, randomised crossover study comprising a placebo (PLA) and 54ug inhaled B2-agonist, formoterol (FOR) trial. Participants performed a baseline neuromuscular assessment (NMA) of involuntary unpotentiated (UT), potentiated 10Hz (Db10) and 100Hz (Db100) doublet twitches, maximal voluntary isometric (MVIC) and dynamic (MVDC) contractions. Participants then performed a quadricep intermittent fatigue (QIF) protocol of 100-rep knee extension sets to task failure, each followed by NMA. Set 1 was at 20% of baseline MVDC peak torque, increasing by 10%/set until failure. Endurance performance was measured as torque-time integral normalised to exercised leg lean mass (TTI/LLM), and fatigue resistance by MVIC and MVDC peak torque loss. NMA fatigue was characterised by Db10, Db100, and voluntary activation (%VA). Recruitment and metabolic responses were assessed by EMG and near-infrared spectroscopy. RESULTS: FOR did not alter repetitions or TTI/LLM (p>0.05). Baseline MVDC (p=0.11) and MVIC peak torque (p=0.45) did not differ. MVDC peak torque loss was greater with FOR (p<0.05, ES=-0.4). Baseline Db10 was lower with FOR (p<0.05, ES=-0.3), while Db100 was unchanged leading to a lower Db10:Db100 ratio (p<0.05, ES=-0.6). FOR attenuated exercise-induced reductions in Db10 (p<0.05, ES=0.4) and Db10:Db100 ratio (p<0.05, ES=0.5). Baseline UT kinetics showed faster relaxation in FOR (p<0.05). Whilst overall %VA decline did not differ at task failure (p=0.29), larger reductions were seen after the first two QIF sets in FOR vs PLA (p<0.05). FOR reduced EMG amplitude variability and drift (p<0.05) in the initial sets, and reduced low-frequency spectral drift throughout (p<0.05), ensuing in MPF rise contrary to decline in PLA in late QIF stages (p<0.05, ES=1.2). These were supported by lower muscle oxygenation (p<0.05, ES=-0.5) and faster desaturation rate into later stages of QIF (p<0.05, ES=-0.7). CONCLUSION: Formoterol did not enhance quadricep endurance performance or peak MVIC or MVDC torque, but it reduced fatigue resistance, seen by impaired dynamic peak torque preservation. This could be from transitioning to more fast-twitch contractile characteristics, reducing neural drive, but increasing metabolic cost at submaximal intensities.
Read CV Filip KolodziejECSS Paris 2023: OP-PN20
INTRODUCTION: Mental fatigue (MF) is caused by prolonged cognitive activity and negatively impacts cognitive and physical performance. Despite its prevalence, the underlying neurochemical mechanisms remain poorly understood. Dopamine has been implicated in MF development, with theories suggesting that prolonged cognitive demands may decrease dopamine transmission in brain regions involved in cognitive control. However, direct empirical evidence is lacking. This study examined the effects of dopamine reuptake inhibition on cognitive performance in MF. METHODS: In a placebo-controlled, within-subject design, 16 participants (M: 8; 22±3y) completed a mentally fatiguing protocol with placebo (PLA) and methylphenidate (MPH; 20mg; dopamine reuptake inhibitor). MF was induced using a 60min incongruent Stroop task with task-switching, during which cognitive performance was continuously measured. To evaluate the MF impact on subsequent performance, a Go/No-Go task was performed before and after the Stroop task, assessing sustained attention (Go) and response inhibition (No-Go). Primary outcomes were reaction time (RT) and accuracy. Secondary outcomes were subjective MF, sleepiness and perceived workload. Outcomes were analysed using mixed-effects models (p<0.05). RESULTS: Go- and No-Go-trial accuracy declined following MF (p=0.04; p<0.001), independent of drug condition (all p>0.18). Go-trial RT remained unaffected by MF (p=0.20) and drug intervention (p=0.42). Throughout the Stroop task, performance on switch-task stimuli was maintained, with overall higher accuracy in MPH versus PLA (p=0.004). For standard colour-naming stimuli, accuracy declined over time in both conditions, however, this decline was attenuated in the MPH condition, with significantly better accuracy after the third (p=0.01) and last block (p=0.03) compared to PLA. RT on colour-naming trials decreased over time, with faster responses at 60 mins (p=0.03), showing no significant MPH effect (p=0.39). Subjective MF increased during the Stroop task (all p<0.001) and was significantly lower under MPH compared with PLA (p<0.001). Sleepiness and workload were significantly lower under MPH (all p=0.003). CONCLUSION: MF impaired cognitive control and response inhibition, as evidenced by reduced accuracy on both Go and No-Go trials, without affecting response speed. Dopaminergic modulation did not prevent these transferable MF effects post-task, but selectively preserved accuracy during the sustained Stroop task. The dissociation between improved performance during the MF task and unchanged performance on the subsequent cognitive control task may reflect differences in task nature and difficulty or task-switching effects. Notably, MPH reduced subjective MF, sleepiness, and workload during the prolonged cognitive task. These findings indicate the task-specific nature of dopaminergic influences on cognition and highlight their relevance for maintaining performance during sustained cognitive demands in sport.
Read CV Emilie SchampheleerECSS Paris 2023: OP-PN20
INTRODUCTION: While oxygen delivery during submaximal exercise is considered adequate to support oxidative metabolism (1), evidence from small muscle mass exercise suggests it may be suboptimal for preserving contractile function (2). Augmenting oxygen delivery via non-local ischemic contractions that heighten the muscle metaboreflex has been shown to attenuate contractile impairments of non-ischemic muscles during small muscle mass exercise (2, 3). These findings suggest that normal vasoregulation may meet metabolic demand but may not be optimised for muscle function (2, 4). Whether metaboreflex-mediated augmentation of oxygen delivery influences muscle oxygenation and neuromuscular fatigability during large muscle mass exercise, and whether such effects are intensity dependent, remains unknown. Therefore, this study examined whether this method could enhance muscle oxygenation and attenuate neuromuscular fatigability of the knee extensors during cycling at different intensities. METHODS: Fifteen participants (9 men, 6 women; 25 ± 4 yr) completed six visits. Visit one included a VO2peak test to determine moderate (MOD), heavy (HVY), and severe (SVR) intensities. In a randomised crossover design, participants completed 8-min cycling bouts at each intensity under control conditions and with metaboreflex augmentation induced by ischemic arm contractions from min 3. Arm contractions were performed for 3 min, with cuffs remaining inflated (200 mmHg) until post-exercise measures were taken (MTR protocol). Vastus lateralis oxygenation was recorded using near-infrared spectroscopy. Knee extensor neuromuscular function was assessed pre- and post-exercise using maximal voluntary contractions and electrically evoked twitch and doublet responses via femoral nerve stimulation, as was blood pressure. A specialised cycle ergometer enabled neuromuscular assessments to be performed within 15 s post-exercise. RESULTS: The MTR protocol increased mean arterial pressure at all intensities (p = .001). Oxygenated haemoglobin (O2Hb) was higher during MOD (p = .007) and HVY (p = .039) with MTR compared with control. Reductions in potentiated twitch force (Qtw.pot) and high-frequency doublet force (Db100) were attenuated following MTR compared with control at MOD (Qtw.pot p = .017; Db100 p = .022) and HVY (Qtw.pot p = .006; Db100 p = .047). No differences in neuromuscular fatigability or O2Hb were observed during SVR. CONCLUSION: During cycling below the respiratory compensation point, the MTR protocol increased muscle oxygenation and attenuated contractile impairments. The finding that reductions in contractile function were attenuated even at MOD suggests that contractile impairments are oxygen-delivery dependent across the exercise-intensity spectrum. References (1) Poole et al., Med Sci Sports Exerc, 2008 (2) Drouin et al., J Physiol, 2023 (3) Perrey et al., J Appl Physiol, 2001 (4) Tschakovsky & Hughson, Am J Physiol, 1999
Read CV EMILY DODDECSS Paris 2023: OP-PN20