Resistance training-induced increases in muscle mass and performance in ponies

The purpose of this study was to determine whether 8 wk of progressive resistance exercise training would produce increases in strength and changes in foreleg muscle characteristics indicative of hypertrophy in ponies. Two mature 3- to 6-yr-old, male ponies (188 +/- 16 kg) were taught to carry sheets of lead over their saddle region (wither) while walking on a level treadmill at 1.9 m.s-1. This initial familiarization period was followed by 8 wk of training (3 d per wk), in which the ponies performed a series of progressive sets of weight carrying to fatigue. Each workout started with a 2-min walk at 1.9 m.s-1 followed by sets of weight carrying. The ponies carried 44.5 kg for the first set with increases of 22.3 kg per set until fatigue. Weights were applied and then removed for 60-90 s between sets using a chain hoist and sling apparatus. Measurements of forelimb girth, body weight, and total weight carried were recorded at each workout session. Ultrasound measurement of the diameters of the superdigital flexor muscles and muscle biopsies were performed before and after the 8-wk training period. Eight weeks of resistance training resulted in significant increases in peak weight carried (260%, P < 0.05) and total weight carried (1525%, P < 0.05) during each workout. Forelimb girth increased 12 +/- 1% (P < 0.05) with a corresponding 19 +/- 3% (P < 0.05) increase in muscle cross-sectional diameter. There were no changes (P > 0.05) in Type I muscle fiber area; however, there was a nonsignificant 26% increase in Type IIA+IIB fiber area. These data suggest that 8 wk of progressive resistance exercise training increase strength and cause changes in muscle size and characteristics consistent with hypertrophy.