Variability of trunk muscle synergies underlying the multidirectional movements and stability trunk motor tasks in healthy individuals

Muscle synergy analysis is a useful approach for investigating the nature of trunk coordination patterns based on the assumption that the central nervous system reduces the dimensionality of muscle activation to simplify movement. This study aimed to quantify the variability in trunk muscle synergy during 11 trunk motor tasks in healthy participants to provide reference data for evaluating trunk control strategies in patients and athletes. Even in a highly variable task context, the five trunk muscle synergies with their temporal patterns presented well-reconstructed original electromyography data. While the variability in trunk synergies between participants and sessions were comparable to those for other body parts in previous studies, these metrics had a broad range, reflecting some level of redundancy of the musculoskeletal system in healthy individuals. Furthermore, the significant differences in the degree of variability between the trunk synergies may reflect the different neural features of trunk synergy organization and strategies to overcome the various mechanical demands of a motor task. The quantification of the variability of trunk muscle synergy may guide the assessment of stereotypes or diverse features of trunk control strategies and the interpretation of adaptability in the presence of diseases or the process of motor training in future research.