Assessment of the influence of lower limb cycling on arm muscle coordination during upper limb cycling: a pilot study

INTRODUCTION: Arm cycling and leg cycling are motor tasks commonly used in medical rehabilitation. Although there is agreement on the existence of common neural generators between arm and leg cyclic movements, most studies have assessed the effects of upper limb cycling on lower limb activation. This study aimed to investigate whether leg cycling, added simultaneously to arm cycling induces changes in upper limb muscle coordination. The muscle synergy framework was used for the examination. METHODS: Ten able-bodied women performed cycling trials on an arm and leg cycle ergometer, with two different cycling modes: a) only arm cycling, b) cycling with arms and legs simultaneously. In each cycling mode, the arms cycled against two crank resistances (low and moderate), whereas the resistance of the cranks for the legs was always low. For each combination of cycling mode and resistance (cycling setup), participants cycled for three minutes, and electromyography signals from six arm muscles from each side were recorded. For each cycling setup, muscle synergy analysis was carried out, using a non-negative matrix factorization algorithm. RESULTS: Four synergies accounted for more than 90% of muscle activation variance in all the setups. Overall, arm muscle synergies were not affected by leg cycling and by the addition of arm crank resistance. DISCUSSION: These results suggest that the central nervous system applies similar control strategies for arm cycling regardless of the inclusion of leg cycling. These findings enhance our understanding of the motor control mechanisms of arm cycling. This is probably the first study investigating motor control of arm cycling during simultaneous arm and leg cycling.