The Effect of a Stretch-Shortening Cycle on Muscle Activation and Muscle Oxygen Consumption: A Study of History-Dependence

Caron, KE, Burr, JF, and Power, GA.. The effect of a stretch-shortening cycle on muscle activation and muscle oxygen consumption: a study of history-dependence. J Strength Cond Res 34(11): 3139-3148, 2020-Stretch-shortening cycles (SSCs) are observed in a variety of human movements and are associated with increases in performance. Few studies have considered the effects of stretch-induced residual force enhancement (rFE) and shortening-induced residual force depression (rFD) during an SSC, and none have considered these properties during voluntary contractions. With force matched via a robotically resisted Smith machine, we hypothesized that in the isometric steady-state following an SSC (a) muscle activation (electromyography) of the knee and hip extensors would be greater and (b) muscle oxygen consumption be higher than the reference isometric condition (ISO), but less than the rFD condition. Subjects (n = 20, male, 24.9 +/- 3.9 year) performed a squat exercise over 100-140 degrees knee angle and a matched ISO at the top and bottom of the squat. After active shortening, the vastus medialis (VM), vastus lateralis (VL), and gluteus maximus (GM) showed activation increase in the rFD-state compared with ISO (similar to 15%, similar to 11%, and similar to 25% respectively). During the isometric steady-state following the SSC, there was no difference in activation as compared with ISO for VM, VL, but GM showed an activation increase of similar to 15%. VM and VL showed an activation increase in the rFD-state compared with the isometric steady-state following SSC (similar to 16 and similar to 10% respectively). Muscle oxygen consumption (tissue saturation index) was not different during the isometric steady-states following rFD and SSC compared with ISO. During a voluntary SSC exercise, the activation increase expected in the FD-state was attenuated, with no change in muscle oxygen consumption. The concomitant role of rFE and rFD during a voluntary position-matched SSC seems to counteract shortening-induced activation increase and may optimize movement economy.