Muscle group specific changes in the electromechanical delay following short-term resistance training

Objectives The time delay between the onset of a muscle\u27s electrical activity and force is believed to have important functional implications, and has been shown to decrease following resistance training in males. The purpose of this investigation was to examine changes in the voluntary electromechanical delay (EMD) for the leg extensors and flexors following a short-term resistance training intervention in females. Design Pretest/posttest control group experiment. Methods Twenty-two previously untrained females (mean ± SD age = 21 ± 2 years; mass = 65.4 ± 13.3 kg) were randomly assigned to training (n = 10) and control (n = 12) groups. The training group performed barbell back squats and deadlifts twice per week for four weeks. EMD for the vastus lateralis (extensors) and biceps femoris (flexors) was examined during maximal voluntary contractions at pre- and posttesting. Data were examined using analyses of covariance (ANCOVAs) with the pretest and posttest scores serving as the covariate and dependent variable, respectively, and by evaluating the number of participants that exceeded the minimal difference statistic. Results For the leg extensors, the adjusted EMD posttest mean for the training group was significantly lower than that for the control group (74.3 vs. 91.8 ms; p = 0.015; ή2 = 0.275), and five training participants displayed decreases that exceeded the minimal difference. The ANCOVA for the leg flexors was not significant (adjusted means = 98.0 vs. 90.0 ms; p = 0.487; ή2 = .026). Conclusions Four weeks of multi-joint resistance training resulted in decreased EMD for the leg extensors, but not the flexors