INTRODUCTION: Muscle fatigability corresponds to the decrease in the ability of muscles to generate force. The Critical Power (Pc) concept [1] predicts the point at which fatigue develops, in such a way that the required constant intensity will no longer be sustainable (W’ reserve is emptied). During all-out tests the power plateau reached at the end of the test and the work done above this value have been numerically and conceptually related to Pc and W’, respectively. These two mathematical models, characterizing similar phenomena but based on very different exercises (steady state versus all-out) have not been directly linked. Thus, the aims of this study were to i) develop an integrative model of exercise fatigability and ii) propose a submaximal test based on this model to determine critical intensity. METHODS: From Mortons 3-parameters model [2] one can make the assumption that fatigability is proportional to the impulse accumulation above the critical force (Fc) so Fmax(t)=(-1/Tau)integral(F(t)-Fc)dt+Fi. Since the model can be applied to any exercises, a specific Ramp Above CriticaL Exhaustion Test (RACLET) was proposed. The test was designed so that the target intensity starts above the critical intensity and decrease below it, before exhaustion of W’, so before exhaustion of the participant. It was tested for a cycling task with a 300s ramp test decreasing from 40% to 5% of initial force (Fi), where maximal capacities (Fmax) were assessed every 30s from 6-pedal-strokes sprints. Twenty participants realized 5 experimental sessions: 2 RACLET and 3 time to exhaustion (TTE). A custom friction regulated instrumented cyclo-ergometer was developed to measure crank torque and velocity. Each Fmax was used to adjust the model’s parameters. The model’s reliability and validity were tested by determination of individual parameters Fc & Tau by adjusting the model to Fmax and time data from RACLET and TTE tests. RESULTS: The model’s goodness of the fit on RACLET test experimental data was excellent (median adjusted R²=0.95; RMSE=3.4%Fi). Mean±SD Fc &Tau were 29.6±7.2%Fi and 22.7±13.9s, respectively. Fc parameter in RACLET demonstrated good relative (ICC=0.9) and absolute reliability (SEM=4.5%). The comparison of Fc between RACLET and reference TTE method was acceptable (R²=0.8, SEM=5.8%). CONCLUSION: The proposed model fit very well with the experimental data obtained during the RACLET. The latter showed very good test-retest reliability. Moreover, the fitted parameters were very similar to those obtained with the gold standard method TTE. The present results show that it is possible to determine individual model parameters (Fi, Fc, and Tau) from experimental data obtained from the proposed RACLET. As this test does not lead to the participants exhaustion, it could be interesting for athletes monitoring tranings, or patients with pathologies that make it difficult to use traditional methods (TTE and all-out tests). REFERENCES: [1] - Monod & Scherrer, Ergonomics 1965 [2] - Morton et al, EJAP 1996