The effect of variable inertial resistance on force, velocity, power and muscle activation during a chest press exercise.

This study investigated the effect of the inertial component of the resistance (INERTIA) at different intensity levels (LOAD ) on force (FORCE ), velocity (VELOCITY ), power (POWER), and the muscle activity of the pectoralis major (EMGPM), anterior deltoid (EMGDA) and triceps brachii (EMGTB) muscles during a chest press exercise. A motor-driven exercise apparatus was programmed to offer resistance with different inertial profiles over the range of movement (ROM ): gravitational-type constant inertia (IFULL); no-inertia (IZERO); linearly descending inertia along the ROM (IVAR). Nine healthy adults performed five, maximal-effort, explosive movements with each inertial profile at 30, 50 and 70% of their 1 repetition maximum. Meanwhile, the EMGPM, EMGDA and EMGTB signals were obtained jointly with the FORCE, VELOCITY and POWER readings returned by the exercise apparatus. One-dimensional statistical non-parametric maps based on 2-way repeated measures ANOVA (SnPM ) were employed to evaluate the effect of LOAD and INERTIA on the collected timeseries. Paired t-tests were then used as post-hoc tests on the portions of the ROM denoting significant differences in the SnPM. Higher LOAD resulted in elevated outcomes over large portions of the ROM in all the investigated timeseries. Compared to IFULL, IZERO allowed greater VELOCITY at the cost of lower FORCE throughout the ROM, while IVAR, despite the lower VELOCITY than IZERO, resulted in higher FORCE and POWER output. In addition, IZERO and IVAR elevated EMGTB at the end of the ROM with respect to IFULL. IVAR overcame both IFULL and IZERO in terms of FORCE and POWER, which indicates that variable inertial profiles might be effectively integrated into resistance exercise programs. Ultimately, this study suggested that INERTIA acts independently to the imposed LOAD on the FORCE, VELOCITY and POWER production. Coaches and therapists are encouraged to account for the type of INERTIA as one of the parameters considered during the exercise selection for their athletes or patients.