Subject specific muscle synergies and mechanical output during cycling with arms or legs

Abstract

Background Upper (UL) and lower limb (LL) cycling is extensively used for several applications, especially for rehabilitation for which neuromuscular interactions between UL and LL have been shown. Nevertheless, the knowledge on the muscular coordination modality for UL is poorly investigated and it is still not known whether those mechanisms are similar or different to those of LL. The aim of this study was thus to put in evidence common coordination mechanism between UL and LL during cycling by investigating the mechanical output and the underlying muscle coordination using synergy analysis. Methods Twenty-five revolutions were analyzed for six non-experts’ participants during sub-maximal cycling with UL or LL. Crank torque and muscle activity of eleven muscles UL or LL were recorded. Muscle synergies were extracted using nonnegative matrix factorization (NNMF) and group- and subject-specific analysis were conducted. Results Four synergies were extracted for both UL and LL. UL muscle coordination was organized around several mechanical functions (pushing, downing, and pulling) with a proportion of propulsive torque almost 80% of the total revolution while LL muscle coordination was organized around a main function (pushing) during the first half of the cycling revolution. LL muscle coordination was robust between participants while UL presented higher interindividual variability. Discussion We showed that a same principle of muscle coordination exists for UL during cycling but with more complex mechanical implications. This study also brings further results suggesting each individual has unique muscle signature.

Evidence of synergy coordination patterns of upper-limb motor control in stroke patients with mild and moderate impairment

“…Despite the promising results when using muscle synergies as physiological markers to assess motor function ( Wang et al, 2020 ; Sheng et al, 2022 ), muscle synergies have not been fully investigated and widely used in clinical scenarios ( Zhao et al, 2023 ), and there is room for more evidence as how to use synergies as biomarkers is still an open question, as a few evidence are available and not always in agreement. Besides some subjective factors, such as experimental protocols and synergy analysis methods ( Steele et al, 2013 ; Banks et al, 2017 ; Zhao et al, 2022b ; Zhao et al, 2022c ), individual variability and subject- and task-specific muscle synergies make the outputs difficult to generalize and compare across studies ( Zhao et al, 2021 ; Cartier et al, 2022 ). To promote the use of muscle synergy analysis in clinical assessment and personalized therapy and deepen the understanding of the pathological mechanisms in post-stroke patients, this study focused on the alterations of synergy structure in post-stroke patients by synergy reconstruction analysis and hypothesized that stroke patients adopted specific synergy coordination patterns for upper-limb motor control as described in previous work ( Cheung et al, 2012 ) and coordination patterns were associated with the motor function.…”