Voluntary Resistance Exercise Research Articles

Growth hormone and lactate responses induced by maximal isometric voluntary contractions and whole-body vibrations in healthy subjects

In contrast with maximal voluntary resistance exercise, which is allegedly considered a potent GH stimulus in young subjects, evaluation of GH response to whole-body vibrations (WBV) has yielded conflicting results. The acute effects of WBV alone (test A), maximal voluntary isometric contractions (MVC) (test B), and combination of WBV and MVC (test C) on serum GH and blood lactate (LA) levels were studied in 9 healthy adult males. Muscle soreness was assessed 24 and 48 h after exercise by a visual analogue scale. GH responses were significantly higher after tests B and C than after test A (GH peaks: 18.8 ± 9.5 ng/ml or 20.8 ± 13.7 ng/ml, respectively, vs 4.3 ± 3.5 ng/ml; p<0.05), with no difference between tests B and C. LA concentrations significantly increased after tests A, B, and C, being significantly higher after tests B and C than after test A (LA peaks: 2.0 ± 0.5 mmol/l or 6.7 ± 2.3 mmol/l, respectively, vs 7.6 ± 0.9 mmol/l; p<0.05). Peak LA values were significantly correlated to GH peaks in the 3 tests (r=0.48; p<0.05). Muscle soreness was significantly higher 24-48 h after tests B and C than after test A, no significant differences being present between tests B and C. WBV stimulates GH secretion and LA production, with no additive effect when combined with repeated isometric voluntary contractions. Optimization of protocols based on WBV seems important to maximize the positive effects of this intervention on the somatotropic function.

Voluntary Resistance Exercise Training With Obese and Lean Zucker Rats

Voluntary Resistance Exercise Training With Obese and Lean Zucker Rats

Voluntary Resistance Exercise Training With Obese and Lean Zucker Rats

PURPOSE Fatty Zucker rats have been used to examine the effects of obesity, and diabetes on the physiological mechanisms associated with exercise-induced musculosketetal adaptation. Because many volitional exercise models use operant conditioning techniques that rely on dietary restrictions to sufficiently motivate voluntary behavior, a study was conducted to determine if obese Zucker rats could be trained to perform a voluntary weight-lifting movement without altering their diet. METHODS Using a custom-designed hind limb loading apparatus, eight 6-weekold male genetically obese Zucker rats (fa/fa) and eight Zucker lean rats (+/fa) were trained with positive reinforcement to enter a vertical tube, insert their head into a neck ring, and repeatedly lift and lower their body weight in a movement that targeted the plantar flexor muscle group. Training sessions were conducted 5 days per week and each lasted until at least 50 lifting and lowering movements were performed or 1.5 hrs. One 45-mg sucrose pellet was given as a reinforcer, after every second lift. Food and water were available in the home cage at all times. RESULTS As expected, mean body weights increased rapidly in the obese rats from 201 g at 6 weeks old to 789 g at 23 weeks old. During the same period mean body weights of the Zucker leans increased from 183 g to 457 g. All rats successfully acquired the weight-lifting movement. However, of the obese Zucker rats only 2 were able to approach the goal of 50 lifts per session with a mean of 47 lifts per session. The mean lifts per session for the remaining 6 obese rats ranged from 5 to 25. 5 of 8 lean Zucker rats were able to approach the 50-lifts/session goal with a mean range of 47–51. The 3 other lean rats recorded means of 28, 30, 35, lifts per session, respectively. CONCLUSIONS Results demonstrate that genetically obese Zucker rats can be trained to perform a voluntary movement for reward. However, food reward was unable to continually motivate the Zucker obese rats towards a goal of 50-body weight lifts per day. Conversely, it was sufficient to elicit continual lifting of Zucker leans. In summary the procedures used in this study were not sufficient to maintain a consistent lifting pattern in obese Zucker rats.

Effects of voluntary resistance exercise and high-protein snack on bone mass, composition, and strength in rats given glucocorticoid injections.

We examined the effects of a voluntary resistance exercise (climbing) together with high-protein snacks (60% protein) on bone mass and strength in rats given glucocorticoid-injections (2 mg/kg/day) as a model of age-related osteopenia. Fifty-two male Sprague-Dawley rats, 8 weeks age, were assigned to exercise or sedentary groups. These groups were further divided into groups that received no snack, snack during activity or a snack during rest. All groups were meal-fed 7:30-8:30 h and 19:30-20:30 h and the snack was fed 23:30-0:30 h (active) or 11:30-12:30 h (resting). Energy and protein intake were approximately equal in all groups. The exercise groups were allowed to climb a wire-mesh tower cage (phi 20 cm x 200 cm) to drink water from a bottle set at the top. Weight gain during the 8-week experimental period was inhibited by a glucocorticoid-injection. Bone mass and strength were increased by climbing exercise with a high-protein snack, while no effect of snack nor any effect of snack timing was observed. Bone weight, calcium content and protein content were positively correlated to maximum load or structural stiffness. These results suggest that resistance exercise and high-protein supplementation may be a preventive therapy for osteoporosis associated with aging.

Voluntary resistance exercise improves blood hemoglobin concentration in severely iron-deficient rats.

To evaluate the effects of long-term voluntary resistance exercise (climbing) compared with aerobic exercise (swimming) on iron status in severely (4 mg Fe/kg diet) and mildly (18-29 mg Fe/kg diet) iron-deficient rats, we trained male Wistar rats for 8 wk to climb a wire-mesh tower (phi20 cm x 200 cm, CLIMB) and to swim in a plastic pool (phi50 cm x 50 cm, SWIM). These rats were compared with sedentary (SED) rats. After the experimental period, blood hemoglobin level, plasma iron concentration, and transferrin saturation were significantly lower in the 4 mg Fe/kg diet rats than in the 18, 29, and 40 mg Fe/kg diet rats. In 4 mg Fe/kg diet rats, the hemoglobin level was significantly higher in the CLIMB group than in the SED and SWIM groups. On the other hand, neither exercise affected iron status in mildly iron-deficient rats. Bone marrow delta-aminolevulinic acid dehydratase activity was significantly higher in the CLIMB group than in the SWIM and SED groups. These results suggest that long-term resistance exercise is more effective than aerobic exercise in improving blood hemoglobin concentration in severely iron-deficient rats, probably because of an increase in heme biosynthesis. Resistance exercise may be a useful therapy for iron-deficient anemia.

Effects of voluntary resistance exercise on heme biosynthesis in rats given glucocorticoid-injections.

To identify the effects of a tower-climbing exercise on bone marrow heme biosynthesis and hematological status in rats given glucocorticoid-injections as a model of aging, 29 male Sprague-Dawley rats, 10 weeks of age, were assigned to three groups: a saline control (C, n = 9), a glucocorticoid-sedentary (GS, n = 10) group, and a glucocorticoid-exercise (GE, n = 10) group. The GS and GE groups were given 2 mg/kg prednisolone daily, and the C group was given 2 ml of saline daily, subcutaneously. Each group was meal-fed commercial rat chow isoenergetically and given free access to water for 8 weeks. The GE group were allowed to climb a 200-cm tower to drink water from a bottle set at the top of it. Weight gain during the 8-week experimental period was greater in the C group than in the GS and GE groups. The gastrocnemius and tibialis anterior muscles were heavier in the C group than in other groups. The hematological parameters were not influenced by glucocorticoid administration with or without climbing exercise. Bone marrow delta-aminolevulinic acid dehydratase activity was significantly higher in the GE group than in the C group. These results suggest that 8 weeks of climbing exercise increases heme biosynthesis without alteration of hematological status in rats given glucocorticoid-injections. Resistance exercise may be a preventive therapy for iron-deficiency anemia associated with aging.

Resistance Exercise Increases the Capacity of Heme Biosynthesis More Than Aerobic Exercise in Rats.

To evaluate the effects of voluntary resistance exercise and aerobic exercise on iron status in rats fed an iron-deficient diet (5mg Fe/kg, ID) or rats fed a control diet (35mg Fe/kg, CN), we trained female Wistar rats for 3 weeks to climb a wire-mesh tower (∅20cm×200cm, CLIMB) and to swim in a plastic pool (∅50cm×50cm, SWIM). These animals were compared with sedentary (SED) rats. After the experimental period, the blood hemoglobin concentration, hematocrit, plasma iron, and transferrin saturation were significantly lower (p<0.05) in the ID rats than in the CN rats; as was the content in the liver, spleen, heart, kidney, skeletal muscles, and carcass (p<0.05). The activity of δ-aminolevulinic acid dehydratase, the marker enzyme for heme biosynthesis, in bone marrow was significantly higher (p<0.05) in the CLIMB group than in the SWIM group. These results suggest that resistance exercise increases heme biosynthesis more than aerobic exercise but that neither exercise improved severe iron deficiencies.

Effect of Voluntary Resistance Exercise on Mitochondrial Heme Biosynthesis in Rat Liver.

To evaluate the effects of voluntary resistance exercise training on mitochondrial heme biosynthesis in the liver, we trained adult male Sprague-Dawley rats for 4 or 8 weeks to climb a wire-mesh tower (∅20cm×200cm), and then measured δ-aminolevulinic acid synthetase (ALAS) activity, the rate-limiting enzyme of heme synthesis, and cytochrome c content in their liver. The activity of citrate synthase in the skeletal muscle was also determined to establish whether the training protocol had any aerobic effect. Resistance training resulted in significant increases (p<0.05) in citrate synthase activities in gastrocnemius and forearm muscles, whereas ALAS activity and cytochrome c content in the liver of rats trained for 4 and 8 weeks were the same as those of corresponding sedentary rats. The relative weight of forearm muscle to body mass was significantly greater (p<0.05) in the training group than in the sedentary group. These results suggest that voluntary resistance exercise does not accelerate hepatic heme biosynthesis in spite of increasing aerobic capacity in the skeletal muscles.