Proceedings of The Physiological Society

Future Physiology (Leeds, UK) (2017) Proc Physiol Soc 39, PC56

Poster Communications

Muscle synergies are mediated by task and not anatomical placement

P. Sriya1, C. Addington1, G. J. York1, T. C. RICHARDS1, S. Astill1, S. Chakrabarty1

1. School of Biomedical Sciences, University of Leeds, Leeds, Please Select, United Kingdom.

Isometric and dynamic balance tests are used clinically to assess lowerlimb muscle function, these lead to apt rehabilitation strategies. The assessment accepts, anatomical location of the muscle underpins its activity, e.g. knee extension, an agonist-antagonist interaction of flexors(ST, BF) and extensors(RF, VL, VM, VI). Stretched muscle sends proprioceptive signal serving the agonist-antagonist interactions; leading to our hypothesis task and not anatomical position drives recruitment, examined in this study using surface electromyography(sEMG) recordings from lowerlimb muscles controlling the knee, in two clinically relevant tasks. 39 healthy participants joined this study(F=17, M=25.46yrs±4.15). 17 participants(F=8, M=24.29yrs±2.62) performed a static task; 22 participants did a dynamic task(F=9, M=26.23yrs± 4.69), and sEMGs from the right leg were recorded. In the static task, participants executed a maximal voluntary effort of the RF(5s x5, 3min rest between contractions) while knee was held at 0°, 20°, 60°and 90° in position C1(modified Fugl-Meyer) and C2(modified Thomas test). The order of conditions and the angles was randomized and counterbalanced across participants. During the dynamic task (modified Berg's test), the participants kept balance on a stabilometer(2x30s) and right-leg muscle sEMGs were recorded. The muscle sEMGs were then analysed for interactions. Active muscle synergies for each position and angle was explored, normalizing muscle activity to that of RF(static) and SL(dynamic). For the dynamic task, muscle activity was linked to stabilometer position considered stable if close to baseline for at least 1.5s. In C1 knee extensors(RF, VL) were agonistic at 0°, 20° and 60°; knee flexors(BF, ST) and extensors(RF, VL) were alike at 60° in C1 and 90° in C2, but not VM(knee extensor). In dynamic task, SL (ankle flexor) activity was the same in both stable and unstable states, but activity of LG, MG and TA was reduced, while activity of muscles acting at the knee VL, RF and ST increased in stable state. Knee flexors and extensors(RF, BF, ST) played a crucial role in defining the muscle synergies used for both tasks at each angle. The different synergies drafted at the same angle in C1 and C2 is due to modification by proprioceptive feedback, which differs between C1 and C2, however the knee extensor and flexors(RF, BF, ST) in shaped these synergies. During the dynamic task, the knee extensors and flexors (BF, RF) and LG were key to stability; participants activated the knee flexors earlier and delayed SL activation. Overall, data from both tests suggest the activity and interactions of the lowerlimb muscles are dynamically controlled possibly by proprioceptive feedback from muscles and joints, not anatomically. These findings are clinically relevant affecting muscle assessments used routinely to assess recovery of function.

Where applicable, experiments conform with Society ethical requirements