Supplementary Material for "A Stochastic Framework for Movement Strategy Identification and Analysis" 

The human body has many biomechanical degrees of freedom and thus multiple movement strategies can be employed to execute a given task. Joint loading patterns and risk of injury are highly sensitive to the choice of movement strategy. This paper develops a computational framework for automatically identifying and recognizing different movement strategies for performing a task from human motion data. A divisive clustering approach is developed for identifying movement strategies. Hidden Markov Models (HMMs) are trained with the clustered observation sequences to generate strategy-specific models which are improved iteratively by using the maximum likelihood to relocate sequences to the most suitable cluster. Differences in individual joint trajectories are compared across strategies using a stochastic distance measure. The proposed algorithm is compared against two existing algorithms for motion clustering the Joint Component Vector (JCV) clustering and HMM based agglomerative clustering. Experimental results indicate that the proposed approach performs better than existing algorithms for detecting motion strategies and automatically determining the differences between the strategies.

Additional information on the generation of the artificial dataset:

Two Link Configuration

Visualization of the resulting trajectories in the artificial dataset:

Generated Trajectories

Videos of exemplar motions for the sagittal lifting task:

Squat - Substrategy 1 - S25 - Heavy Trial 2

Squat - Substrategy 1 - S58 - Light

Squat - Substrategy 1 - S73 - Light

Squat - Substrategy 2 - S06 - Heavy

Squat - Substrategy 2 - S58 - Heavy

Squat - Substrategy 2 - S81 - Heavy

Squat - Substrategy 2 - S83 - Heavy

Stoop - S03 - Heavy

Stoop - S22 - Heavy

Stoop - S05 - Light

Stoop - S06 - Light

Videos of exemplar motions for the out-of-plane lifting task:

3to4 - Strategy 1 - S02 - Heavy Brace

3to4 - Strategy 1 - S03 - Heavy No Brace

3to4 - Strategy 1 - S04 - Heavy No Brace

3to4 - Strategy 1 - S08 - Heavy Brace

3to4 - Strategy 2 - S01 - Heavy Brace

3to4 - Strategy 2 - S03 - Heavy Brace

3to4 - Strategy 2 - S04 - Heavy Brace

3to4 - Strategy 2 - S05 - Heavy Brace

3to4 - Strategy 2 - S06 - Heavy Brace

3to4 - Strategy 2 - S07 - Heavy Brace

3to4 - Strategy 2 - S09 - Heavy Brace

3to4 - Strategy 2 - S10 - Heavy Brace