J Manipulative Physiol Ther. 1998 Feb; 21(2): 94-6.

Effects of Sl nerve-root lengthening on tibial nerve F-wave latency in healthy subjects.

Humphreys CR, Cooley JL, Hoxie S, Davis SR.

Department of Diagnosis, National College of Chiropractic, Lombard, IL 60148, USA.

OBJECTIVE: To determine if lengthening the tibial portion of the sciatic nerve in healthy patients significantly alters F-wave latency. SUBJECTS: Ten volunteer students (6 men and 4 women). SETTING: Chiropractic college clinic. METHODS: F-wave latency was measured bilaterally in the supine position and supine in 40-50 degrees of passive hip flexion. Block randomization determined the test sequence. Supramaximal surface stimulation was delivered over the tibial nerve using transcutaneous electrical stimulation. The nerve was stimulated no more than 30 times at a rate of 1 Hz for 0.5 ms to get 16 F-wave latencies. The paired t test was used to determine mean difference between neutral and flexion. RESULTS: The F-wave latency was found to be longer in hip flexion (average 46.12 +/- 3.80 ms) than neutral (average 45.12 +/- 3.33 ms). CONCLUSION: Positioning a patient to optimize nerve lengthening and elicit symptoms may reveal occult dysfunction in electrodiagnostic examination.