ECSS Paris 2023: OP-PN21
INTRODUCTION: W' balance (W'BAL) models estimate dynamic changes in work capacity (W') above critical power (CP), accounting for linear depletion and curvilinear recovery during high-intensity intermittent exercise. However, current models using generalized time constants (tau) inadequately account for prior W' utilization and differences in W' reconstitution between passive and active recovery across depletion states. This study aimed to compare the performance of integral convolution equation (W'BAL-INT) and ordinary differential equation (W'BAL-ODE) models using tau derived from all-out effort tests involving different depletion states and recovery modes (i.e., passive versus active recovery) when applied to exhaustive intermittent exercise with active recovery. We hypothesized that active recovery-based tau would improve model performance. METHODS: 15 recreationally active adults (male/females: 10/5; age: 29 +/- 7 years; body mass, 72.9 +/- 8.5 kg; height 1.74 +/- 0.08 m) completed an initial ramp test and four further tests, involving a 3-min all-out test (3MT) paired with a 1-min sprint performed either before or after the 3MT. CP and W' were derived from fresh condition 3MT. The two sprint segments were separated by either 60 s of active recovery at 80% gas exchange threshold (GET) or complete rest. Subsequently, the participants completed an intermittent exercise session consisting of ten 1-min self-paced work bouts interspersed with 1-min recovery at 80% GET, with the instruction to reach volitional exhaustion by the 10th bout. Recovery tau was derived from the test through an iterative process and used to estimate W'BAL during intermittent sessions, assuming W' = 0 at volitional exhaustion. RESULTS: There was a significant difference between adjusted model variations (F = 27.09, p < 0.001, eta_p^2 = 0.66). The individualized, test-derived tau did not improve exhaustion prediction accuracy for the novel W'BAL-INT and W'BAL-ODE model permutations compared with the standard W'BAL-INT (F = 39.31, p < 0.001, eta_p^2 = 0.74) and W'BAL-ODE permutations (F = 5.76, p < 0.001, eta_p^2 = 0.29). During intermittent exercise, test-based W'BAL-INT permutations overestimated the W' reconstitution (p < 0.001), whereas test-based W'BAL-ODE permutations underestimated the W' reconstitution (p < 0.05). A significant negative correlation was found between the W'BAL-ODE test-derived tau and the magnitude of observed W' reconstitution (r = -0.66, p < 0.001), with larger tau values associated with lower W' recovery between all-out effort bouts. There was no correlation between CP and observed W' reconstitution (p = 0.47). CONCLUSION: Recovery tau derived from all-out effort tests do not improve W'BAL prediction accuracy for intermittent exercise. These findings indicate that W' reconstitution behaviour differs between short-duration, fast-depletion efforts and intermittent exercise, suggesting limited transferability of recovery parameters between fast-depletion and intermittent exercise contexts.
Read CV Yujie LiuECSS Paris 2023: OP-PN21
INTRODUCTION: Muscle cramps are painful, involuntary contractions affecting 30–50% of healthy individuals with unclear pathophysiology (Schwellnus, 2007). While dehydration theories have historically dominated, emerging evidence implicates a dysregulation of spinal motoneuron excitability (Minetto et al., 2011), potentially involving persistent inward currents (PICs). This study examines whether cramp susceptibility is associated with enhanced PIC-related motoneuron activity and whether an electrically-induced cramp acutely modifies these estimates. METHODS: Twenty-eight healthy adults performed voluntary triangular contractions of the plantar flexors before and after a cramp threshold frequency test designed to evoke a cramp in the gastrocnemius medialis (GM). Participants were classified as crampers (cramp elicited) or controls (no cramp elicited). Contributions of PICs to motoneuron discharge were estimated in soleus (SOL) and GM muscles from high-density surface electromyographic (EMG) signals that were decomposed into motor unit spike trains. Maximal discharge rate was used as an index of overall motor unit firing capacity and net excitatory drive. The paired motor unit analysis technique assessed discharge rate hysteresis (ΔF); brace height and related slopes assessed nonlinearity of the ascending discharge rate profile; and self-sustained duration (SSD) assessed motor unit discharge prolongation. Spinal reflex excitability (H reflex) as well as the torque and EMG responses to wide-pulse high-frequency neuromuscular electrical stimulation (WPHF NMES) were compared between both groups. RESULTS: At baseline, ΔF in GM was lower in crampers than in controls, whereas the other PIC-related estimates were not different between groups. No differences were found in WPHF-evoked torque, sustained EMG activity, or H-reflex amplitudes between crampers and controls. In both groups, following the cramp-inducing protocol, ΔF increased in GM and SSD increased in both muscles, whereas brace height remained unchanged in GM but decreased in SOL. In addition, maximal discharge rate in GM increased in controls but not in crampers. CONCLUSION: These findings suggest that cramp susceptibility is not associated with generalized motoneuronal hyperexcitability but with an altered, subtle muscle-dependent modulation of motoneuron discharge dynamics. Cramp induction appears to further modulate PIC contributions to discharge patterns in the targeted muscle, with distinct responses observed in synergistic motoneuron pools. Minetto, M. A., Holobar, A., Botter, A., Ravenni, R., & Farina, D. (2011). Mechanisms of cramp contractions: Peripheral or central generation? The Journal of Physiology, 589(Pt 23), 5759–5773. Schwellnus, M. P. (2007). Muscle cramping in the marathon: Aetiology and risk factors. Sports Medicine (Auckland, N.Z.), 37(4–5).
Read CV Timothée PopescoECSS Paris 2023: OP-PN21
INTRODUCTION: Cognitive-motor dual-task performance is prevalent in many sports and appears to be impaired during high-intensity exertion, in association with exacerbated neuromuscular central fatigue and cerebral deoxygenation. It has been reported that women may exhibit lower neuromuscular fatigability during exercise, and studies assessing cognitive performance in isolation have yielded mixed findings, with some favoring males, others favoring females, and still others reporting no sex differences. However, the extent to which these responses differ between males and females during low to high-intensity cognitive-motor dual-tasking remains unknown. METHODS: Forty-eight trained young adults (16 females), matched for fitness level completed an incremental cycling test with concurrent sustained attention Mackworth task. The protocol consisted of 3-min ramp stages (starting at 1 W/kg, +0.4 W/kg per stage) until “extremely strong” perceived effort (Borg CR100 scale), considered as task-failure. At each stage, cognitive performance (Mackworth score), quadriceps isometric maximal voluntary contraction (IMVC), neuromuscular fatigue assessed via femoral nerve stimulation (peripheral: twitch force, Pt; central: voluntary activation), and prefrontal oxygenation measured by near-infrared spectroscopy (tissue saturation index, TSI) were evaluated. RESULTS: Both sexes reached similar normalized power output (⁓3.3±0.5 W/kg) and heart rate (⁓175±7 bpm) at task-failure (all P>=0.25). Mackworth performance declined at task-failure (P=0.014), with no sex differences (males: -9±28%; females: -4±28%; P=0.56). However, prefrontal oxygenation was lower in women than men at baseline and task-failure (main effect of sex; TSI -3.0±2.6% in females; P=0.031, ηp2=0.13), and female participants exhibited a smaller increase in prefrontal total-haemoglobin throughout the test (time X sex interaction; P<0.001, ηp2=0.27). IMVC declined less in women throughout the cognitive-motor test (time X sex interaction, P=0.021, ηp2=0.25), which was accompanied by smaller impairments in potentiated twitch force (main effect of sex; P=0.008, ηp2=0.16), similar reductions in voluntary activation in both sexes (P=0.62), and comparable increases in perceived effort (P=0.73). CONCLUSION: Although high-intensity exercise similarly impaired concurrent sustained attention performance and voluntary activation in both sexes, women exhibited lower neuromuscular and peripheral fatigability, along with a blunted prefrontal oxygenation response. These results extend the understanding of women’s reduced (primarily peripheral) fatigability to whole-body exercise under a challenging dual-task paradigm. Further research is needed to determine whether cognitive-motor dual-task training should be sex-specific and whether men and women differ in their responses.
Read CV Thomas RUPPECSS Paris 2023: OP-PN21