Maintenance of cutaneomuscular neuronal excitability after leg-cycling predicts lower limb muscle strength after incomplete spinal cord injury.

OBJECTIVE

Controlled leg-cycling modulates H-reflex activity after spinal cord injury (SCI). Preserved cutaneomuscular reflex activity is also essential for recovery of residual motor function after SCI. Here the effect of a single leg-cycling session was assessed on cutaneomuscular-conditioned H-reflex excitability in relation to residual lower limb muscle function after incomplete SCI (iSCI).

METHODS

Modulation of Soleus H-reflex activity was evaluated following ipsilateral plantar electrical stimulation applied at 25-100ms inter-stimulus intervals (ISI's), before and after leg-cycling in ten healthy individuals and nine subjects with iSCI.

RESULTS

Leg-cycling in healthy subjects increased cutaneomuscular-conditioned H-reflex excitability between 25 and 75ms ISI (p<0.001), compared to a small loss of excitability at 75ms ISI after iSCI (p<0.05). In addition, change in cutaneomuscular-conditioned H-reflex excitability at 50ms and 75ms ISI in subjects with iSCI after leg-cycling predicted lower ankle joint hypertonia and higher Triceps Surae muscle strength, respectively.

CONCLUSION

Leg-cycling modulates cutaneomuscular-conditioned spinal neuronal excitability in healthy subjects and individuals with iSCI, and is related to residual lower limb muscle function.

SIGNIFICANCE: Cutaneomuscular-conditioned H reflex modulation could be used as a surrogate biomarker of both central neuroplasticity and lower limb muscle function, and could benchmark lower-limb rehabilitation programs in subjects with iSCI.