Analysis of myoelectric activity, blood lactate concentration and time under tension in repetitions maximum in the squat exercise

The purpose of the present study was to compare the load influence on the time under tension (TUT), electromyographic activity (EMG) and blood lactate concentration (LAC) in 8, 10, and 12RM and the relationship between the TUT and the number of repetitions in the squat exercise. The sample consisted of ten military men (age: 18.90 ± 0.32 years, height: 1.73 ± 0.05 m, body mass: 67.55 ± 4.96 kg, body fat: 6.54 ± 1.87%). The TUT for 8, 10, and 12RM was verified by kinematic using the timing technique of the Kinovea software. After 48 hours, the subjects performed the squat exercise with the TUT and the load obtained in the tests, where the EMG and LAC were evaluated. The electrodes to capture the EMG signal were positioned in the following muscles: vastus medialis (VM), vastus lateralis (VL), rectus femoris (RF), and femoral biceps (FB). The ANOVA showed significant differences in all protocols in the TUT and LAC variables (p < 0.05) in increasing order to the number of repetitions (8 RM < 10RM < 12RM). The EMG showed a significant reduction in the RF activation in the 10RM for the 12RM in comparison with 8RM, as well as at VL activation for the 8 and 12RM protocols in comparison with 10RM. The study concluded that smaller loads and higher numbers of repetitions generate higher TUT and LAC. However, they result in smaller muscle activation for RF and VL. According to the results of the present study, there is no difference between 8, 10 and 12RM for the VM and FB muscles in the squat exercise.