Author(s): DI DOMENICO, H., BLERVAQUE, L., BOWEN, M., PERNOT, J., SAMOZINO, P., MOREL, B., Institution: SAVOIE MONT-BLANC UNIVERSITY, Country: FRANCE, Abstract-ID: 2450

INTRODUCTION:
Critical power is an important fatigue threshold in exercise physiology, separating moderate to severe intensity domains. When muscle effort is performed above the critical force (Fc), acute muscle fatigue drastically occurs. This critical threshold has great potential application in optimizing athletic training programs and performance as well as improving the life quality for chronic disease (e.g. chronic obstructive pulmonary disease (COPD)) patients (1). Historically, Fc has been provided by the asymptotic force-time relationship, obtained during multiple time-to-exhaustion or all-out test. The difficulty of these tests prevents them from being used routinely in clinical context. Based on Bowen et al. (2) model, we proposed an innovative non-exhaustive test to determine the Fc: the Ramp Above Critical Level Endurance Test (RACLET). The aims of this study were to i) test the validity of the RACLET and ii) its feasibility with COPD patients.
METHODS:
Sixteen healthy participants and ten COPD patients completed a RACLET on an isometric knee extension ergometer. The test consists in a 5-min decreasing ramp, from severe to moderate intensity domains, composed of intermittent contraction (3s on, 2s off) and brief maximal voluntary contraction (MVC) every 30s. RACLET started at 60% of the initial maximal force (Fi) and gradually decreased to reach 0 N after 5 min. Visual feedback enabled the participant to follow the target force. Healthy participants also performed, on a separated day, a 5-min all-out isometric test. Forces reached during all-out or MVCs performed during RACLET were modelled using derived equations based on: Fmax(t) = –(1/Tau)*int(F(t)-Fc)dt+Fi, where F is the target force and Tau is a time constant (2). The validity of the RACLET was assessed by examining the correlation and the root-mean-square error (RMSE) compared to the gold standard method being the 5-min all-out.
RESULTS:
The model’s goodness of the fit on RACLET and all-out test experimental data was excellent (median r2 = 0.96 and 0.97, respectively). Fi, Fc and Tau obtained from RACLET (656 ± 152 N, 283 ± 80 N and 64 ± 33 s, respectively) and from all-out test were highly correlated (r2 = 0.94, 0.92, 0.83, respectively, all p<0.001, RMSE = 6.4, 5.9, 20.8%). All COPD patients were able to complete the RACLET, the goodness of fit being excellent (median r2 = 0.95). The Fc expressed relatively to initial capacity was significantly lower than healthy participants (33 ± 11 vs 41 ± 7 %Fi respectively, p<0.05).
CONCLUSION:
Compared to the gold standard all-out method, the RACLET is valid to assess Fc in isometric knee extension. This innovative test does not lead to exhaustion. Thus, it has demonstrated to be feasible to determine Fc in COPD patients (stage 1 to 3). The RACLET could thus be a useful tool for determining a muscle intensity threshold (i.e. Fc) to tailor intervention or evaluate the effect of patient rehabilitation.
REFERENCES:
1. Poole et al., MMSE, 2016
2. Bowen et al., JTB, 2023