The main focus of this work is to investigate the effect of weight on the stability of human squat exercise. The squat exercise is a common daily activity. Experiments are conducted using one human subject. A VICON motion analysis system integrated with Force Plates is utilized for these experiments. An experimental protocol is developed and followed. This work analyzes the time series of the normal component of the ground reaction forces and each coordinate of the center of pressure. These time series are used to estimate the Lyapunov Exponents using Rosenstein method. MATLAB software package is used for this investigation. The results of this work are compared with results from literature. Present work gives more information relating the safety of the squat exercise when adding additional weight. One can see that the effect of additional weight on stability depends on its value. In the cases of small and moderate additional weight the stability is the same or increases, while for the largest additional weight the investigated stability decreases.