Linear and Nonlinear Modeling of Critical Load

Dinyer TK, Byrd MT, Vesotsky AN, Succi PJ, Bergstrom HC. Linear and Nonlinear Modeling of Critical Load. JEPonline 2020; 23(5):1-13. The purpose of this study was to examine the estimates of critical load (CL) and strength’ (S') for the deadlift from four different mathematical models (Linear-TW, Linear-Load, Nonlinear-2, and Nonlinear-3). Eleven subjects completed one-repetition maximum (1RM) testing for the deadlift that was followed by the completion of repetitions to failure at four intensities (50%, 60%, 70%, and 80% 1RM) on separate days. The load used, repetitions completed, and total work (load [kg] x repetitions) were recorded to determine the CL and S' parameters from the four mathematical models. All four models provided goodness of fit values ranging from 0.457 to 0.995. The Linear-Load model provided the highest estimate of CL, while the Nonlinear-2 and Nonlinear-3 models provided the lowest estimates. For S', the Nonlinear-2 and Nonlinear-3 models provided the highest estimates, while the Linear-Load model provided the lowest. The four mathematical models indicated a moderate to strong relationship between total work and repetitions completed for the deadlift. The CL may reflect the highest sustainable load that can be completed for an extended number of repetitions and may represent the point of compromised blood flow, while the S' parameter may reflect factors that modulate fatigue such as muscle fiber type distribution patterns, motor unit activation strategies, muscle ischemia, and the formation of cross-bridges.