Optimal trajectory of squat to stand movement by using different cost function

The aim of this study was to determine optimal trajectory of squat to stand movement, using several different cost function.
For this Purpose, the trajectories of squat to stand Movement generate by three cost functions (minimum torque, mechanical energy cost and multi-cost model). Multi-cost model was designed to reduce total torque and mechanical energy, maximum torque of the knee joint and risk of instability, simultaneously. To build model and compare with optimal trajectory, squat to stand movement of six healthy young subjects (age, 24/6 ± 1/2 years, body mass, 72/5 ± 5/2 kg, height, 177 ± 4/2 cm) were filmed. A 2-dimensional model, with four segments was built based on the governing equations of motion. After applying constraints and cost functions, genetic algorithm was used to find the optimal model.
The results revealed that the mechanical energy consumption, total torque of joints, peak torque of the knee, were decrease to 2/5%, 3/5% and 43/3% respectively in multi cost pattern compared with subject's pattern. Also compared with other methods, the trajectory which generated by multi-cost model, was safer and more similar to subjects.
During the optimization of different movement, the best trajectory of any task will be detected by selecting the main factors which affecting the movement and using a suitable cost function. The application areas of the proposed models could be generating optimized trajectories of squat to stand movement for clinical applications or providing clinical and engineering insights to develop more efficient rehabilitation devices and protocols.