Effect of heavy-resistance exercise training on muscle fiber composition in young rats K. E. YARASHESKI,
P. W. R. LEMON,
AND
J. GILLOTEAUX
Applied Physiology Research Laboratory, Kent State University, Kent 44242; and Department of Anatomy, Northeastern Ohio Universities College of Medicine, Rootstown, Ohio 44272
YARASHESKI, K.E.,P.W.R. LEMON,AND J. GILLOTEAUX. Effect of heavy-resistance exercise training on muscle fiber composition in young rats. J. Appl. Physiol. 69(2): 434-437,1990.The purpose of this investigation was to determine whether heavy-resistance exercise training alters the skeletal muscle fiber composition of young rats. Ten male Long Evans rats (3 wk old) were trained to lift progressively heavier weights, which were secured to the rats’ tails, while they ascended a 40-cm 90” mesh incline 20 times/day 5 days/wk for a food reward. After 8 wk of training, they lifted 406 & 19 (SD) g in addition to their body weight (261 k 9 g). Compared with 10 sedentary pair-fed rats, no hypertrophy of forelimb muscles (biceps brachii and brachialis) was observed, but rectus femoris wet and dry weights were greater (P < 0.01) in the trained group. In the deep region of the rectus femoris, type I fiber area was similar between groups, but the trained rats had both a lower (P < 0.05) percentage of type I fibers and a smaller (P < 0.05) portion of the total area occupied by type I fibers. The percentage of type IIb fibers in the deep region of the rectus femoris was also similar between groups, but the portion of the deep area composed of type IIb fibers was greater (P < 0.05) in the trained rats. In the superficial region of the rectus femoris, the trained rats’ type IIb fibers were larger (P < 0.01) and occupied a greater (P < 0.05) portion of the superficial muscle area. These findings support the contention that, in addition to genetic and hormonal factors, the motor nerve impulse activity associated with the forceful contractions typical of heavy-resistance exercise training can alter the histochemical properties of skeletal muscle in young rats. skeletal muscle fiber types; histochemical properties
hypertrophy;
muscle
plasticity;
DESPITE THEIR marked
specialization, mammalian skeletal muscles adapt to changes in functional overload (26). The biochemical adaptations of skeletal muscle to endurance training have been studied intensively (l4), whereas the adaptations to heavy-resistance training have received much less investigative attention (28). Of particular interest is the observation that highintensity endurance training can induce a fast-twitch-toslow-twitch transition in rat and human skeletal muscle fiber types (1, 11, 12, 27). On the basis of available data (5, 6, 13, 16, 17, 20, 21), it is not clear whether the forceful rapid muscle contractions typical of heavy-resistance training can alter fiber composition. Therefore, the purpose of this study was to determine whether the skeletal muscle fiber composition of young rats can be altered by heavy-resistance exercise training. The mus-
434
0161-7567/90
$1.50 Copyright
cles of young rats were studied because of their faster contractile and sarcoplasmic protein turnover rates (3 1) and the ease with which young animals can be conditioned to exercise. METHODS
Twenty male (3 wk old, 43-54 g) Long Evans rats (Blue Spruce Farms, Altamount, NY) were randomly assigned to either the heavy-resistance training group or the sedentary group. All animals were housed individually and weighed daily. They received 8-12 g rat chow 100 g body weight/day and free access to water. A 12:12h light- (1800-0600 h) dark cycle was used to allow for training during the day. The rats weight trained by lifting progressively heavier loads while climbing (90”) a mesh cylinder to receive a food reward (Fig. 1). The food was powdered rat chow distributed at the top of the apparatus, where the rats were allowed to eat for 5-10 s and then returned to the bottom of the cylinder. The load was a quantity of lead coiled around the base of each rat’s tail and secured with elastic tape. The rats climbed with no added weight for the first five training sessions, while the distance they climbed was gradually increased from 10 to 40 cm. On the 6th training day, 43 g (60% of body weight) were added to each rat. The added weight was removed after each training session. The load was lifted 40 cm, 20 lifts/ day for 5 days/wk and was increased by -30 g every 3 days. Each training session lasted 20-60 min and each lift required 3-4 s. When a rat completed a training session in
P. W. R. LEMON,
AND
J. GILLOTEAUX
Applied Physiology Research Laboratory, Kent State University, Kent 44242; and Department of Anatomy, Northeastern Ohio Universities College of Medicine, Rootstown, Ohio 44272
YARASHESKI, K.E.,P.W.R. LEMON,AND J. GILLOTEAUX. Effect of heavy-resistance exercise training on muscle fiber composition in young rats. J. Appl. Physiol. 69(2): 434-437,1990.The purpose of this investigation was to determine whether heavy-resistance exercise training alters the skeletal muscle fiber composition of young rats. Ten male Long Evans rats (3 wk old) were trained to lift progressively heavier weights, which were secured to the rats’ tails, while they ascended a 40-cm 90” mesh incline 20 times/day 5 days/wk for a food reward. After 8 wk of training, they lifted 406 & 19 (SD) g in addition to their body weight (261 k 9 g). Compared with 10 sedentary pair-fed rats, no hypertrophy of forelimb muscles (biceps brachii and brachialis) was observed, but rectus femoris wet and dry weights were greater (P < 0.01) in the trained group. In the deep region of the rectus femoris, type I fiber area was similar between groups, but the trained rats had both a lower (P < 0.05) percentage of type I fibers and a smaller (P < 0.05) portion of the total area occupied by type I fibers. The percentage of type IIb fibers in the deep region of the rectus femoris was also similar between groups, but the portion of the deep area composed of type IIb fibers was greater (P < 0.05) in the trained rats. In the superficial region of the rectus femoris, the trained rats’ type IIb fibers were larger (P < 0.01) and occupied a greater (P < 0.05) portion of the superficial muscle area. These findings support the contention that, in addition to genetic and hormonal factors, the motor nerve impulse activity associated with the forceful contractions typical of heavy-resistance exercise training can alter the histochemical properties of skeletal muscle in young rats. skeletal muscle fiber types; histochemical properties
hypertrophy;
muscle
plasticity;
DESPITE THEIR marked
specialization, mammalian skeletal muscles adapt to changes in functional overload (26). The biochemical adaptations of skeletal muscle to endurance training have been studied intensively (l4), whereas the adaptations to heavy-resistance training have received much less investigative attention (28). Of particular interest is the observation that highintensity endurance training can induce a fast-twitch-toslow-twitch transition in rat and human skeletal muscle fiber types (1, 11, 12, 27). On the basis of available data (5, 6, 13, 16, 17, 20, 21), it is not clear whether the forceful rapid muscle contractions typical of heavy-resistance training can alter fiber composition. Therefore, the purpose of this study was to determine whether the skeletal muscle fiber composition of young rats can be altered by heavy-resistance exercise training. The mus-
434
0161-7567/90
$1.50 Copyright
cles of young rats were studied because of their faster contractile and sarcoplasmic protein turnover rates (3 1) and the ease with which young animals can be conditioned to exercise. METHODS
Twenty male (3 wk old, 43-54 g) Long Evans rats (Blue Spruce Farms, Altamount, NY) were randomly assigned to either the heavy-resistance training group or the sedentary group. All animals were housed individually and weighed daily. They received 8-12 g rat chow 100 g body weight/day and free access to water. A 12:12h light- (1800-0600 h) dark cycle was used to allow for training during the day. The rats weight trained by lifting progressively heavier loads while climbing (90”) a mesh cylinder to receive a food reward (Fig. 1). The food was powdered rat chow distributed at the top of the apparatus, where the rats were allowed to eat for 5-10 s and then returned to the bottom of the cylinder. The load was a quantity of lead coiled around the base of each rat’s tail and secured with elastic tape. The rats climbed with no added weight for the first five training sessions, while the distance they climbed was gradually increased from 10 to 40 cm. On the 6th training day, 43 g (60% of body weight) were added to each rat. The added weight was removed after each training session. The load was lifted 40 cm, 20 lifts/ day for 5 days/wk and was increased by -30 g every 3 days. Each training session lasted 20-60 min and each lift required 3-4 s. When a rat completed a training session in
