ECSS Paris 2023: OP-PN18
INTRODUCTION: During constant power cycling in the heavy and severe domains, the steady-state VO2 is delayed or prevented due to the VO2 slow component (SC). The rising oxygen uptake has been assumed to represent a progressive loss of muscle efficiency, resulting primarily from skeletal muscle fatigue, however evidence for a causal relationship is equivocal. Notably, it has also been demonstrated that alterations in pedaling technique may occur during fatiguing cycling exercise. If these alterations impair cycling efficiency, this could represent a moderating factor between the development of fatigue and the increase in oxygen cost observed with the SC. However, little is known about the existence of pedaling technique adjustments during fatiguing cycling exercise in association with the SC. Therefore, the purpose of this study was to explore the association between the VO2 SC and skeletal muscle fatigue, and the impact that changes in pedaling technique may have on the development of the VO2 SC. METHODS: Eleven participants completed an incremental exercise test to determine lactate threshold, followed by constant power trials to exhaustion at 10% above lactate threshold (power output 194 ± 55W). Utilizing femoral nerve stimulation and instrumented pedals, muscle fatigue was assessed, along with oxygen uptake, quadriceps oxygenation, electromyography (EMG), and pedal force components. To explore the temporal relationship between muscle fatigue and the appearance of the SC, Pearson’s correlation coefficient was calculated between the relative reductions in twitch force across the first 2.5 min of exercise and the time of onset of the SC. To explore the association between the SC and alterations in pedaling technique, repeated measures correlations between physiological and mechanical variables were estimated at both a group and individual level. RESULTS: There was no significant correlation between the time of onset of the VO2 SC and initial reductions in twitch force (r = -0.076, p = 0.852). At a group level, the SC (387 ± 172 ml/min at peak) was significantly correlated with quadriceps twitch force (r = -0.48, p < 0.001), root mean square EMG (r = 0.18, p = 0.016), and muscle oxygenation (r = -0.50, p < 0.001), as well as with pedaling mechanical variables such as peak total downstroke force (r = -0.16, p = 0.022), minimum total upstroke force (r = -0.15, p = 0.029), and upstroke index of effectiveness (r = 0.18, p = 0.012). However, there was large interindividual variability for all these correlations. At an individual level, repeated measures correlations between twitch force and the SC ranged from -0.03 to -0.87, while correlations between the SC and some pedaling mechanical variables were seen to be as high as 0.80 for some individuals. CONCLUSION: From the heterogeneity of the data, we question a direct causal link between fatigue and the SC, and suggest that alterations in pedaling technique may also be a factor in its development.
Read CV Keenan MacDougallECSS Paris 2023: OP-PN18
INTRODUCTION: The extent of performance and perceived fatigability varies based on the volume of exercised muscle mass (1,2). However, no study to date has explored this effect across the entire intensity spectrum. Accordingly, this study aims to investigate alterations in muscle contractile function, central voluntary activation and perceived responses to single-leg (SL) and double-leg (DL) cycling tasks performed within four intensity domains. METHODS: Eleven males (29±4 years) performed SL and DL cycling to task failure in the moderate (MOD), heavy (HVY), severe (SVR), and extreme (EXT) intensity domains, as characterized by gas exchange threshold, respiratory compensation point, and maximal aerobic capacity from a DL ramp incremental test. SL cycling was performed at 60% of the power output corresponding to DL trials. Voluntary and evoked contractions, including 5s MVC of the dominant knee extensors combined with superimposed 100 Hz doublets (Db100) and resting Db100, 10 Hz doublets (Db10), and single twitch electrical stimuli of the femoral nerve were performed at baseline, immediately upon task failure, and following 1, 4, and 8 min of recovery. Perceived fatigue, leg pain, dyspnea, and effort were collected during trials. Two-way repeated measures ANOVAs with Bonferroni post hoc examined 2 modes × 4 timepoints within each domain. RESULTS: Time to task failure was similar between SL and DL cycling in all domains. MVC declined more following SL in SVR (SL vs. DL: -41±12% vs. -31±15%; P=0.036) and HVY domains (-42±16% vs. -30±18%; P=0.011). Also, peak twitch force declined more following SL at SVR (-49±13% vs. -40±7%; P=0.048) and HVY domains (-31±12% vs. -22±10%; P=0.007). Voluntary activation declined more following SL than DL at HVY (-20±15% vs. -9±10%; P=0.008). Dyspnea was greater following DL at HVY (7±3 vs. 6±3; P=0.031), SVR (8±2 vs. 6±2; P=0.001), and EXT domains (7±2 vs. 5±2; P=0.025), whereas ratings of fatigue, pain, and effort were similar between exercise modes. CONCLUSION: These findings suggest that metabolic perturbations within smaller muscle mass exercise (e.g., SL vs. DL cycling) can result in greater impairments in muscle contractile function within the SVR and HVY domains. However, the impairment in muscle function may be exacerbated for DL cycling within the MOD domain. Also, except for greater dyspnea, perceived responses between exercised muscle masses did not show any difference between domains. Collectively, these findings indicate that the modulatory effect of muscle mass on the extent of performance and perceived fatigability is exercise intensity-dependent. 1. Rossman et al., 2012, Acta Physiol 2. Zhang et al., 2021, AJP-Regul Integr Comp Physiol
Read CV Jalal AboodardaECSS Paris 2023: OP-PN18
INTRODUCTION: Molecular hydrogen has been suggested to have antioxidation and anti-inflammatory properties which may serve as ergogenic aids for sport and exercise performance. Studies have investigated the potential effects of molecular hydrogen, mainly given as hydrogen-rich water, on endurance performance and muscle damage. However, little has been known in terms of the effects of inhaling hydrogen gas on high intensity intermittent exercise (HIIE). Thus, the purpose of current study was to explore the potential effects of acute inhalation of hydrogen gas on high intensity repeated sprint performance. METHODS: Fourteen healthy active males (age:22.9±5.4yrs, height:177.8±6.3cm, weight:70.5±8kg) were recruited to participate in this randomized, double-blinded, placebo-controlled, crossover study. Subjects were randomized to inhale either hydrogen gas (H2) (gas generation rate was 1.5L/min, containing 70% hydrogen and 30% oxygen) or normal gas (placebo, ambient air) for 30 mins (including a 10-min warm up), before performing the HIIE test. They were asked to return to the laboratory, after a 7-day washout period, to inhale the other gas in a crossover fashion. The HIIE test, conducting after gas inhalation, comprised 15x6s all-out repeated sprints (20s active recovery between sprints) on a cycle ergometer, and the work load was fixed at 9% of body weight. Blood samples were collected at baseline, pre-test and post-test to analyze blood lactate and arterialized venous blood gas. Rate of perceive exertion (RPE) were recorded at the end of the test. Peak power (PP), mean power (MP), minimum power (MinP), work done (WD), cadence (rpm), fatigue index (FI) and decrement score (Sdec) were recorded during the test. Data were analyzed by using repeated measures ANOVA, and were presented as mean±SD. RESULTS: Significant group by time interactions were found in venous blood partial pressure of oxygen (PO2) (p=.012), partial pressure of carbon dioxide (PCO2) (p=.012), total carbon dioxide content (tCO2) (p=.013), base excess (BE) (p=.016), bicarbonate (HCO3) (p=.013) and standard bicarbonate (stHCO3) (p=.022), but not in pH and blood lactate. Furthermore, blood BE (-9±2.8 vs. -10.6±2.9 mmol/L, p<.05) and stHCO3 (17.2±2 vs. 16.1±2 mmol/L, p<.05) concentrations were both found higher at post-test in the H2 trial, which corresponded to the trend of lower variations in BE (p<.05), HCO3 (p<.01) and stHCO3 (p<.05) while performing the HIIE in the H2 trial. As for the sprint performance, no significant differences were observed in PP, MP, MinP, WD, rpm, FI, Sdec and RPE between trials. CONCLUSION: The results suggested that pre-exercise acute inhalation of H2 might facilitate a more effective buffering system in blood, which might be explained by the relatively moderate variations in BE and HCO3 during exercise. However, the enhanced magnitude of buffering capacity was not able to alter blood pH and lactate production, which, taken together, resulted in trivial effects on the repeated sprint performance.
Read CV Calvin Wei-Ting ChenECSS Paris 2023: OP-PN18