Neural and muscular changes to detraining after electrostimulation training

We investigated the effects of 4 weeks of detraining subsequent to an 8-week electrostimulation (ES) training program on changes in muscle strength, neural and muscular properties of the knee extensor muscles. Nine male subjects followed the training program consisting of 32 sessions of isometric ES training over an 8-week period. All subjects were tested before and after 8 weeks of ES training, and were then retested after 4 weeks of detraining. Quadriceps muscle anatomical cross-sectional area (ACSA) was assessed by ultrasonography imaging. The electromyographic (EMG) activity and muscle activation (i.e., by means of the twitch interpolation technique) obtained during maximal voluntary contractions (MVC) were used to examine neural adaptations. After training, the knee extensor voluntary torque increased significantly by 26%. Torque gains were accompanied by an increase in vastii EMG activity normalized to respective M-wave (+43%), muscle activation (+6%) and quadriceps ACSA (+6%). After detraining, knee extensor MVC, vastii EMG activity, muscle activation and quadriceps ACSA decreased significantly by 9%, 20%, 5% and 3%, respectively. Also, the knee extensor MVC values remained significantly elevated (14%) above baseline levels at the end of the detraining period and this was associated with a larger quadriceps ACSA (+3%) but not with a higher neural activation. We concluded that the voluntary torque losses observed after detraining could be attributed to both neural and muscular alterations. Muscle size preservation could explain the higher knee extensor MVC values observed after the cessation of training compared to those obtained before training, therefore indicating that muscle size changes are slower than neural drive reduction.