The bodyweight squat: Kinematic changes during exercise and effects on ground reaction forces

The aim of this study was to analyze in detail the effects of ROMs of trunk, knee, hip, ankle and ground reaction forces during bodyweight squat exercise. 20 volunteer male who have dominant right leg, strenght exercise background and continue to strenght exercises for at least 3 days a week (age: 23,7±3,2, height: 178,8±7,12cm., weight: 78,74±11,48 kg., BMI: 25±3,83 kg/m2, fat rate: %12,83±,4,74) were participated in this study. Squat exercise was performed on 4 load cells (the fore and hind parts of each foot on two different load cells for one foot) until the participants were failure to continue without any additional weight. They performed self-selected depth squat. Simultaneously, video recording was started for range of motion analysis during performance. Squat tempo was fixed with metronome (45 bpm./min., 1:0:1:0). The obtained data were divided into three 33% sections and also skewness, kurtosis and normal distribution statistics (Shapiro-Wilks) tests were performed in 95% confidence interval. Paired Sample T-test difference statistics were used to compare the data and statistical significance level was set at "p≤0.05". 1st. 33%, 2nd. 33% and 3rd. 33% of squat's performance; no significant difference was found on the ground reaction forces between the right and left feet. (respectively ;p = 0.974; p = 0.484; p = 0.715,). A significant difference was found between all the ground reaction forces applied to ground by the back parts of the right feet and left feet (1st.33% p = 0.001; 2nd.33% p = 0.001; 3rd.33% p = 0.002). A significant difference was found between 1st., 2nd. and 3rd. 33% sections on the ground reaction forces by the fore and hind parts of the right foot. (respectively; p = 0.001; p = 0.001; p = 0.002). On the ground reaction forces applied to the fore and hind parts of the left foot only a significant difference was found in 1st.33% section (p = 0,024), while there was no significant difference in the second and third 33% section (respectively; p = 0,114; p = 0,343 ). In terms of range of motions in the squat performance , significant differences were found between the range of motion of the trunk, between 1st.33% and 3rd.33% (p = 0.044), 2nd.33% and 3rd.33%, (p = 0.034). Significant differences were found between range of motions knee joint 1st. 33% and 3rd. 33% (p = 0.014); 2nd. 33% and 3rd.33% (0.005). Significant differences were only found between 1st. 33% and 2nd. 33% of the range of motion of ankle (p = 0.045). There was no significant difference in the range of motion of ankle joint in other sections. According to these results, there is a balance in terms of the force applied to the ground between the dominant leg and the support leg during the performance of squat. Although the body weight distribution is at the back of the feet, there is a load transfer towards the forefoots at the end of the performance. The differences applied to ground reaction forces by the fore and hind parts of the left (support foot) foot was balanced by the load distribution towards the end of the performance. This suggests that the support foot makes more effort for balance as fatigue occurs. End-of-performance fatigue can cause trunk, knee and ankle of range of motions increase. It can be said that increase of ground reaction forces towards to front, these forces is effected by increases of range of motions.