Are Leg Electromyogram Profiles Symmetrical During Full Squat?

In order to see how electromyogram (EMG) profiles change during the squat movement with increasing loads, we determined the degree of symmetry of selected homologous muscles. Seven healthy men (age range 20–42 years), recreationally performing strength exercises voluntarily participated in the research. The participants varied in height from 172 to 183 cm and in mass from 74 to 94 kg. The participants performed consecutive sets of a single repetition of full back squatting, each time with an increased load (70–100% 1RM). To record the parameters of participant and barbell movement, the Smart-E measuring system (six infrared cameras and a wireless module for measuring the bioelectric activity of muscles) were used. Electrical activity was recorded using surface electrodes for muscles on both sides of the body (homologous): tibialis anterior (TA), gastrocnemius medialis (G_med), biceps femoris (BF), rectus femoris (RF), gluteus maximus (G_max) and erector spinae (ES). The mean of averages of modules of amplitude differences (MAMAD) between individual pairs of normalized homologous muscles for squat movement was accepted as a measure of symmetry of homologous muscles. A statistically significant increase of symmetry of EMG profiles (MAMAD) with increasing loads was seen only for TA and ES muscles and only in two of the six of analyzed cases. Of particular interest was the statistically significant large MAMAD increase for BF and ES muscles and for the so called prime mover (G_max) in the ascent phase of the squat compared to the descent phase.