Effect of High-intensity Exercise Training on Functional Capacity of Limb Skeletal Muscle

The purpose of this study was to determine whether a program of regular sprint exercise training alters the functional properties or protects against the development of fatigue in fast- and slow-twitch rat skeletal muscle. The training program consisted of 6 sprints of 4.5-min duration at 40 m/min and 15% slope with 2.5-min rest intervals, performed 5 days/wk for 6 wk. The exercise program significantly increased (P-1·min-1) in the predominantly type I soleus (SOL) from 28 ± 2 to 44 ± 2; the type IIb superficial region of the vastus lateralis (SVL) from 10 ± 1 to 16 ± 1; and the type IIa deep region of the vastus lateralis (DVL) from 34 ± 2 to 53 ± 2. Phosphofructokinase activity (µmol·g-1·min-1) also increased with training in the SOL (17 ± 1 vs. 23 ± 1) and the DVL (64 +/- 5 vs. 79 +/- 5). Sprint training reduced (P less than 0.05) the contraction time (CT) (111 +/- 7 vs. 92 +/- 3 ms) and the one-half relaxation time (118 ± 3 vs. 104 ± 2 ms) in the slow-twitch soleus. The exercise program also induced a decreased CT in the fast-twitch extensor digitorum longus (EDL), but significance was limited to the P \u3c 0.1 level. Muscle fatigue was produced by electrical stimulation at 45 trains/min and either 15 trains/min in SOL or 10 trains/min in the EDL and SVL for 1, 5, or 10 min.(ABSTRACT TRUNCATED AT 250 WORDS