Effects of electrically induced muscle contraction on flexion reflex in human spinal cord injury.

STUDY DESIGN

Flexion reflex study in motor complete human spinal cord injury (SCI).

OBJECTIVES

To examine changes in the magnitude of the flexion reflex following functional electrical stimulation (FES) of the rectus femoris (RF) muscle.

SETTING

Bioengineering Unit, University of Strathclyde, Glasgow, Scotland, UK.

METHODS

The flexion reflex was evoked by electrical stimulation of the sural nerve, and was recorded in the tibialis anterior (TA) muscle. RF muscle conditioning stimulation was performed at 0.7, 1, and 2 times motor threshold ( x MT) over a range of conditioning test intervals.

RESULTS

The incidence of the early component of the flexion reflex (<100 ms) was low, suggesting that this reflex component might be suppressed in SCI. The long latency flexion reflex component (>120 ms) was observed in all subjects during control conditions and following sensorimotor conditioning. FES applied to the RF muscle (above and below MT) in the main induced a significant early and long lasting depression of the long latency flexion reflex.

CONCLUSION

The depression of the flexion reflex was a result of multisensory actions on flexion reflex pathways resulting from the direct and indirect (mechanical) consequences of electrically induced muscle contraction on cutaneous and muscle afferents. Our findings emphasize the importance of sensory feedback mechanisms in modulating flexion reflex excitability, and highlight the need for rehabilitation professionals to consider the central actions of FES-induced afferent feedback when incorporating FES into a rehabilitation program.

SPONSORSHIP

State Scholarships Foundation (IKY) of Hellas.