Author(s): PEARMAIN, W., HOLLIDAY, A., JEFFRIES, O., BROWNSTEIN, C., Institution: NEWCASTLE UNIVERSITY, Country: UNITED KINGDOM, Abstract-ID: 235

INTRODUCTION:
The physiological determinants of endurance performance have been well established, and include maximum oxygen uptake (V̇O2max), fractional utilisation of V̇O2max and efficiency [1]. Recent evidence has shown that these determinants transiently deteriorate in response to prolonged exercise [2, 3], with the capacity to resist these declines termed physiological resilience. At present, the mechanisms which contribute to physiological impairments in endurance determinants during prolonged exercise are uncertain. The primary aim of the present study was to assess the association between neuromuscular fatigability, changes in muscle oxidative capacity (OxCap) and changes in key determinants of endurance exercise (V̇O2peak, gas exchange threshold [GET], critical power [CP], the finite work capacity above CP [W’] and gross efficiency [GE]) in response to prolonged exercise.
METHODS:
18 male participants (age = 26±5 years, V̇O2peak = 46.7±8.2 ml·kg·min-1) completed four visits, including a ‘fresh’ ramp-incremental test (Visit 1), fresh OxCap and 3 min-all out (Visit 2) and 90 mins cycling at 110% GET following by a ‘fatigued’ ramp-incremental test or 3 min all-out and OxCap assessment (Visits 3 & 4). Measures of V̇O2peak, GET, CP, W’, and OxCap measured through the NIRS-derived recovery rate constant of muscle oxygen consumption were compared between fresh and fatigued states. Neuromuscular measures of the knee extensors (isometric maximal voluntary contraction, resting twitch responses to femoral nerve stimulation and voluntary activation) and GE were taken at baseline and every 22.5 min thereafter until task completion.
RESULTS:
V̇O2peak was reduced by 7±9% (p=0.005), power output [PO] at GET by 11±16% (p=0.008), CP by 11±15% (p=0.039) and W’ by 27±15% (p<0.001). GE was reduced by 11±5% 90 min relative to 4-6 min (p=0.002). All neuromuscular variables were reduced over time (p≤0.003). The recovery rate constant for mV̇O2, was reduced by 34±12% following prolonged exercise (p<0.001). The reduction in OxCap was associated with reductions in GET and CP (r≥0.636, p≤0.048), while reductions in resting twitch responses were associated with reductions in GE (r≥0.333, p≤0.004).
CONCLUSION:
These results provide novel insight into the correlates and potential mechanisms of physiological resilience during prolonged exercise. The associations between reductions in OxCap with impairments in GET and CP, and the correlation between impaired resting twitch responses and reduced GE, suggests that impairments in oxidative ATP provision and contractile function could represent important determinants of physiological resilience. These results provide a mechanistic basis for future intervention studies aiming to improve physiological resilience.
References
1. Joyner & Coyle, 2008; 2. Clark et al., 2018; 3. Stevenson et al., 2022