Proceedings of The Physiological Society

Future Physiology (Leeds, UK) (2017) Proc Physiol Soc 39, PC69

Poster Communications

Identifying changes in the pattern of muscle synergy due to task dependent changes:

G. J. York1

1. Faculty of Biological Science, Leeds University, Leeds, United Kingdom.

Muscle synergies are repeatable patterns of temporally linked muscle activity which are observed during movement (Bizzi and Cheung, 2013). It is commonly assumed that a muscle synergy performs a natural dimensionality reduction, providing a self-limiting system for maximal efficiency by reducing the ways a task can be achieved (Antuvan et al, 2016). Targeting the muscles which contributes most to a muscle synergy could revolutionize therapy planning for aging patients, or those with nerve damage, providing more direct and effective care. Developing an algorithm to detect which muscles dominate a muscle synergy in static and dynamic tasks is the aim of this study. This algorithm will also assist decoding motor output from neural activity for a brain machine interface (BMI). This study describes a method for identifying muscle synergies using a dimensionality reduction algorithm known as principal component analysis (PCA). The contribution of different muscles to muscle synergies was compared across different angles of an isometric knee extension task. 17 subjects were asked to perform maximal voluntary contraction of the right leg (5s x 6 trials with a 3 min rest between contractions). The knee was fixed at four angles 0°, 20°, 60° and 90°, across two different positions. In the first position the participant was laid flat on a bed with legs supported, and in the second the left hip and knee were flexed so that the sole of the foot rested on the bed and the right hip and knee flexed and rested on a chair below the bed. Data was sampled at 2000 kHz using a Delsys Trigno EMG system and 7 muscles were recorded; RF, vastus lateralis (VL), vastus medialis (VM), semitendinosus (ST), biceps femoris (BF), medial gastrocnemius (MG) and tibialis anterior (TA). All recordings were made in accordance with Leeds University ethical guidelines for working with human participants, which follows all requirements laid out by the UK government. The results from this study demonstrate that joint angle significantly alters the degree to which muscles contribute to muscle synergies. Different principal components correspond to biologically meaningful distinctions in activity e.g. hamstrings vs quadriceps. Within these synergies certain muscles, such as the biarticular muscles ST, BF and RF, may be determining the contribution of other muscles towards the overall synergy. The degree to which an individual's synergy patterns differed from the cohort mean suggests that there may be unidentified groupings within the cohort, and that certain subjects may achieve a task in a completely unique manner. Identifying key muscles within a synergy will further the understanding of physiological systems determining how a task is actioned and achieved. This algorithm's results will provide relevant information regarding muscle synergies to clinicians for treatment plans.

Where applicable, experiments conform with Society ethical requirements