RACLET: the Ramp Above Critical Level Endurance Test to evaluate critical force in isometric task

Abstract The Ramp Above Critical Level Endurance Test (RACLET) is a novel submaximal test designed to evaluate the parameters of the critical force model without strenuous exercise. This study aimed to validate the RACLET in healthy and pathological populations and to assess its reliability, concurrent validity, and predictive capacity. Sixteen healthy volunteers and ten patients with respiratory pathologies participated in this study. The RACLET consisted of a decreasing ramp force starting at 60% and ending at 15% of the maximum force for a total duration of 425 s with brief regular maximal voluntary contractions. The goodness of fit for the RACLET model on the maximal contraction force was excellent in both populations (median r2 ≈ 0.95). In patients, RACLET parameters demonstrated excellent reliability (ICC > 0.90). The concurrent validity of the critical force estimate compared with the all-out method was high (error: −0.3±7.4%). The model’s predictive capacity for time-to-exhaustion and fatigue during constant-intensity exercise was excellent (r2 = 0.910 and 0.907, respectively). The RACLET provides a reliable and valid estimate of critical force model parameters opening up numerous practical applications in vulnerable populations, individualised physical activity programs, and longitudinal monitoring. The feasibility and performance of the test make it a promising tool for assessing muscle function in various contexts. Competing Interest Statement The authors have declared no competing interest. Footnotes This research has been funded by the Agence Nationale de la Recherche [ANR-22-CE14-0073]. https://gricad-gitlab.univ-grenoble-alpes.fr/fove/methods/raclet Abbreviations - COPD - Chronic obstructive pulmonary disease - CM - Change in the Mean - Fc - Critical theoretical force - Fi - Initial maximal theoretical force - Fmax - Maximal theoretical force - F⋆ - Force at the start of RACLET ICC Intraclass Correlation Coeficient - JAC - Impulse done Above Critical Force - Maximal JAC - that can be done JEF Impulse done Above End force - RACLET - Ramp Above Critical Level Endurance Test - RE - Random Error - RMSE - Root mean square error - S - Force ramp slope of RACLET - SE - Standard Error - τ - Typical time of fatigability - tc - time at which critical power is reached - TEM - Typical Error of Measurement - tlim - Duration of Time to exhaustion