Figure 4.

Average variance accounted for (VAF) screen plot for rank 1 to 5 nonnegative matrix factorization (NMF) dimensionality reduction across all angles and both positions of the static knee extension task. The 90% VAF threshold indicates that 2 is the appropriate rank to use and therefore the number of synergies to extract. Error bars show SE. In the table, synergy rows (activation patterns) and columns (contribution vectors as defined in Data Preprocessing) were compared across all pairs of participants using cosine similarity analysis giving a value between 0 (uncorrelated) and 1 (highly correlated). For both positions (activating or inactivating the contralateral hip flexors) and for all internal knee angles, there is high correlation between subjects indicating that, during the task, the same synergy patterns are being recruited by the majority of subjects; n = 17 (male: 9; female: 8).