Objectives: To determine the effect of facilitation on H reflex side-to-side amplitude ratio and to determine the effect of averaging under the assumption that an averaging could further stabilize the amplitude ratio in a facilitated condition.

Method
FCR H reflex amplitude ratios of direct and averaged potentials were measured in fifty asymptomatic subjects under three conditions, during rest, during a constant 5 pound isometric contraction under the hand-dynamometer monitoring, and during a moderate constant isometric contraction under the electromyographer's verbal guidance.

Results
The lower limits of the amplitude ratios that encompass 97.5% of subjects by the percentile method under three conditions were as follows; (1) during the rest (n=37); 0.47 (direct) and 0.50 (average), (2) during the constant 5 pound isometric contraction under the hand- dynamometer monitoring; 0.47 (direct) and 0.48 (average), and (3) during the moderate constant isometric contraction under the electromyographer's verbal guidance; 0.48 (direct) and 0.46 (average), respectively.

Conclusion
There seems to be no definite effect of facilitation and averaging on H reflex amplitude ratio. H reflex amplitude ratio measured in facilitated condition without averaging is still useful for the diagnosis of unilateral radiculopathy.