Facilitation of the isometric maximum voluntary contraction with traction. A test of PNF predictions

Mean rectified electromyographic activity in vastus lateralis (VL) was recorded with surface electrodes during several Ss isometric maximum voluntary contractions performed in the PNF pattern of flexion-abduction-internal rotation, with the subject supine. The effects of longitudinally applied traction forces were compared in a within subject design employing latin square and counterbalanced presentation. Consistent with predictions, as traction force increased the group mean EMG showed a statistically significant increase. A brief survey using force platform measurements indicated that trained physical therapists tended to apply equal or greater forces than the 20 lb maximum used in the experiment.