Strength training effects on rearfoot motion in running.

The investigation examined isokinetic (IK) and nonisokinetic (NIK) strength training programs for the inversion (INV) and eversion (EV) muscles on pronation during running. Seventy-seven volunteers were videotaped running on a treadmill at 3.8 m.s-1 and total pronation (delta beta PRO) was computed. Eighteen heel-strike runners with the largest values of delta beta PRO (X = 16.7 degrees) were selected as subjects. During the pre- and posttests, isokinetic muscle strength at 20 and 180 degrees.s-1 was determined for the concentric (CON) and eccentric (ECC) actions of the INV and EV muscle groups. The subjects also were videotaped running on a treadmill (3.8 m.s-1). The IK training group performed three sets of eight CON and ECC repetitions at 20, 90, and 180 degrees.s-1 for both muscle groups; and the NIK subjects did exercises commonly used in ankle rehabilitation. Each group trained three times weekly for 8 wk. The IK group showed significantly (P < or = 0.05) CON and ECC strength increases for all INV test conditions and three of the four EV conditions (20 degrees.s-1 CON and ECC, and 180 degrees.s-1 CON). They also demonstrated significant decreases in the rearfoot (2.2 degrees) and pronation/supination (2.9 degrees) angles at heel strike and in delta beta PRO (-2.2 degrees).l The NIK group exhibited no change in rearfoot motion and only increased INV strength at the 180 degrees.s-1 ECC test condition. The findings suggest that pronation can be decreased by an isokinetic strength training program for the INV and EV muscles.