1 St Mary’s University, Waldegrave Road, Twickenham, TW1 4SX, United Kingdom 2 Institute for Globally Distributed Open Research and Education (IGDORE)
Background: The musculoskeletal system has a relatively large number of mechanical degrees of freedom. In order to permit coordinated movement, it is thought that these degrees of freedom are constrained, reducing the complexity of the motor control problem. For this reason, principal component analysis can be a powerful technique for understanding the organisation of movement by calculating the number of functional degrees of freedom present in a particular movement task.
Material and methods: In this study, we used principal component analysis to find the number of functional degrees of freedom exhibited during vertical jumping. We applied the technique to both the inter-segmental moments and the muscle forces (that were estimated based upon a publicly available musculoskeletal model of the lower limb).
Results: We found that over 90% of the variance in the 3 dimensional inter-segmental moments could be described by 3 principal components (PC1 = 61.0%, PC2 = 15.8%, PC3 = 13.4%), suggesting the presence of 3 functional degrees of freedom. Similarly, only 4 principal components (PC1 = 50.1%, PC2 = 22.5%, PC3 = 13.5%, PC4 = 4.8%) were required to capture 90% of the variance in muscle forces.
Conclusions: These results suggest that there is a marked inter-individual similarity in both moments and muscle forces during vertical jumping.
Key words: principal component analysis, degrees of freedom, muscle force, proximal to distal, FreeBody, musculoskeletal modelling.