PURPOSE: To determine the effects of squat with different stability and resistance on muscle activities.
METHODS: Fourteen healthy male (age: 21 ± 2 years old, height: 176 ± 5 cm, and mass: 71 ±8 kg) performed squat. A VICON motion-analysis system was used for data collection. The RMS of EMG of rectus abdominis (RA), tensor fasciae latae (TFL), rectus femoris (RF), right tibialis anterior (RTA), left tibialis anterior (LTA),lower lumbar erector spinae (LLES), right gluteus maximus (RGMa),left gluteus maximus (LGMa), gluteus medius (GMe), and biceps femoris (BF) muscles were collected by a Trigno TM wireless EMG system when performing squat on a new six degrees of freedom platform (CAREN, with one stable and two level(A,B) of instability condition) under body weight and 30%RM(repetition maximum), respectively. The sequence of 6 conditions (SO, S30, A0, A30, BO, B30) for each subject was randomized to eliminate the possible fatigue and learning effects. A Polar heart rate monitor was applied to make sure heart rate under 100 b/min after each rest. Differences in EMG activities of the muscles were compared between S0 and the other conditions using the paired t-test.
RESULTS: No significant difference was observed for most muscles EMG between unstable and stable surface (p>.05). Most of muscles EMG significantly increased when 30%RM weight load compared with the body weight load condition (p<.05, Table 1).
CONCLUSIONS: Simply applying moderately unstable surface do not provide more stimulation to the superficial muscles, external weight load can effectively mobilize more muscle activity during squatting in highly resistance-trained people. The effects of external loading might not be replaced by unstable surface if the goal is to increase superficial muscle activation levels.