Naokata Ishii

Applications of vascular occlusion diminish disuse atrophy of knee extensor muscles.

PURPOSE We have previously shown that the combination of low-intensity resistive exercise and moderate vascular occlusion induces in humans a marked increase in growth hormone secretion and muscular hypertrophy. The present study investigated the effects of vascular occlusion on the size of thigh muscles in patients who underwent an operation for the reconstruction of the anterior cruciate ligament to see whether it attenuates the disuse muscular atrophy without any exercise combined. METHODS Two sessions of occlusive stimulus, each consisting of five repetitions of vascular occlusion (mean maximal pressure, 238 mm Hg) for 5 min and the release of occlusion for 3 min, were applied daily to the proximal end of the thigh from 3rd to 14th days after the operation. Changes in the cross-sectional area (CSA) of thigh muscles were analyzed with magnetic resonance images taken on the 3rd and 14th day after the operation. RESULTS Without occlusive stimulus (control), the CSAs of knee extensors and flexors decreased by 20.7 +/- 2.2% and 11.3 +/- 2.6% (mean +/- SEM, N = 8), whereas with the occlusive stimulus, they decreased by 9.4 +/- 1.6% and 9.2 +/- 2.6% (N = 8), respectively. The relative decrease in CSA of knee extensors was significantly (P < 0.05) larger in the control group than in the experimental group. CONCLUSION The results indicate that the occlusive stimulus effectively diminishes the postoperation disuse atrophy of knee extensors.

Cross-transfer effects of resistance training with blood flow restriction.

PURPOSE This study investigated whether muscle hypertrophy-promoting effects are cross-transferred in resistance training with blood flow restriction, which has been shown to evoke strong endocrine activation. METHODS Fifteen untrained men were randomly assigned into the occlusive training group (OCC, N = 8) and the normal training group (NOR, N = 7). Both groups performed the same unilateral arm exercise (arm curl) at 50% of one-repetition maximum (1RM) without occlusion (three sets, 10 repetitions). Either the dominant or nondominant arm was randomly chosen to be trained (OCC-T, NOR-T) or to serve as a control (OCC-C, NOR-C). After the arm exercise, OCC performed leg exercise with blood flow restriction (30% of 1RM, three sets, 15-30 repetitions), whereas NOR performed the same leg exercise without occlusion. The training session was performed twice a week for 10 wk. In a separate set of experiments, acute changes in blood hormone concentrations were measured after the same leg exercises with (N = 5) and without (N = 5) occlusion. RESULTS Cross-sectional area (CSA) and isometric torque of elbow flexor muscles increased significantly in OCC-T, whereas no significant changes were observed in OCC-C, NOR-T, and NOR-C. CSA and isometric torque of thigh muscles increased significantly in OCC, whereas no significant changes were observed in NOR. Noradrenaline concentration showed a significantly larger increase after leg exercise with occlusion than after exercises without occlusion, though growth hormone and testosterone concentrations did not show significant differences between these two types of exercises. CONCLUSION The results indicate that low-intensity resistance training increases muscular size and strength when combined with resistance exercise with blood flow restriction for other muscle groups. It was suggested that any circulating factor(s) was involved in this remote effect of exercise on muscular size.

Muscular adaptations to combinations of high- and low-intensity resistance exercises.

Acute and long-term effects of resistance-training regimens with varied combinations of high- and low-intensity exercises were studied. Acute changes in the serum growth hormone (GH) concentration were initially measured after 3 types of regimens for knee extension exercise: a medium intensity (approximately 10 repetition maximum [RM]) short interset rest period (30 s) with progressively decreasing load (“hypertrophy type‘’); 5 sets of a high-intensity (90% of 1RM) and low-repetition exercise (“strength type‘’); and a single set of low-intensity and high-repetition exercise added immediately after the strength-type regimen (“combi-type‘’). Postexercise increases in serum GH concentration showed a significant regimen dependence: hypertrophy-type > combi-type > strength-type (p < 0.05, n = 8). Next, the long-term effects of periodized training protocols with the above regimens on muscular function were investigated. Male subjects (n = 16) were assigned to either hypertrophy/combi (HC) or hypertrophy/strength (HS) groups and performed leg press and extension exercises twice a week for 10 weeks. During the first 6 weeks, both groups used the hypertrophy-type regimen to gain muscular size. During the subsequent 4 weeks, HC and HS groups performed combi-type and strength-type regimens, respectively. Muscular strength, endurance, and cross sectional area (CSA) were examined after 2, 6, and 10 weeks. After the initial 6 weeks, no significant difference was seen in the percentage changes of all variables between the groups. After the subsequent 4 weeks, however, 1RM of leg press, maximal isokinetic strength, and muscular endurance of leg extension showed significantly (p < 0.05) larger increases in the HC group than in the HS group. In addition, increases in CSA after this period also tended to be larger in the HC group than in the HS group (p = 0.08). The results suggest that a combination of high- and low-intensity regimens is effective for optimizing the strength adaptation of muscle in a periodized training program.

Content and localization of myostatin in mouse skeletal muscles during aging, mechanical unloading and reloading

Changes in myostatin content and localization in mouse skeletal muscles were investigated during aging, hindlimb suspension (HS) and reloading after HS. During aging, the content of myostatin among solubilized proteins in gastrocnemius and plantaris muscles (Gast/Plant) was initially low and increased until their wet weight/body weight ratio reached a peak. It remained unchanged with further aging, although gradual atrophy of the muscles was seen to occur. Also, the myostatin content did not change significantly during HS (up to 14 days) in both Gast/Plant and soleus muscles, though the muscles showed morphological signs of atrophy. However, reloading for 2 days after a 14-day HS caused significant decreases in the myostatin content in both of these muscles. Immunohistochemical observations showed the sarcoplasmic existence of myostatin, the amount of which appeared to decrease after reloading. The results suggest that myostatin plays a part in the processes of muscular growth and loading-induced hypertrophy, but is not involved in either aging-related or unloading-induced muscular atrophy.

RELATIONS BETWEEN FORCE-VELOCITY CHARACTERISTICS OF THE KNEE-HIP EXTENSION MOVEMENT AND VERTICAL JUMP PERFORMANCE

Relations between force-velocity characteristics of the multijoint movement of the lower limbs and vertical jump performance were investigated. A total of 67 untrained subjects (age: 19.54 ± 2.38 years; height: 166.88 ± 8.53 cm; body mass: 59.14 ± 10.82 kg, mean ± SD) performed isometric and isotonic knee-hip extension movements on a servo-controlled dynamometer, and the force-velocity relations were determined. Also, vertical jump (VJ) performance was measured with a jump gauge. The force-velocity relation was described with a linear function so that the maximum isometric force (Fmax) and the maximum unloaded velocity (Vmax) for the knee-hip extension movement were estimated by extrapolation. Maximum isometric force coincided with maximum isometric force, F0 (F0/Fmax = 1.03 ± 0.24). Maximum isometric force, Vmax, and maximum power output (Pmax) were positively correlated with VJ (r = 0.48, 0.68, and 0.76, respectively; p > 0.001). However, when Fmax, Vmax, and Pmax were normalized with body mass (BM), leg length (LL), and BM, respectively, no correlation was seen between Fmax/BM and VJ (r = 0.24, p > 0.05), and significant correlations were seen between Vmax/LL and VJ (r = 0.56, p > 0.001) and between Pmax/BM and VJ (r = 0.65, p > 0.001). On the other hand, Fmax and Vmax (r = 0.12, p > 0.05) and Fmax/BM and Vmax/LL (r = 0.05, p > 0.05) were not significantly correlated, indicating that Fmax and Vmax were independent variables. The present estimates of Fmax, Vmax, and Pmax can be useful for evaluating the actual performance of multijoint movement of the lower limbs. It is suggested that, although in untrained individuals the speed of movement might be a more important determinant of jump performance, jump performance ability has a potential to improve with increases in strength of the lower limb.

mTOR signaling response to resistance exercise is altered by chronic resistance training and detraining in skeletal muscle.

Resistance training-induced muscle anabolism and subsequent hypertrophy occur most rapidly during the early phase of training and become progressively slower over time. Currently, little is known about the intracellular signaling mechanisms underlying changes in the sensitivity of muscles to training stimuli. We investigated the changes in the exercise-induced phosphorylation of hypertrophic signaling proteins during chronic resistance training and subsequent detraining. Male rats were divided into four groups: 1 bout (1B), 12 bouts (12B), 18 bouts (18B), and detraining (DT). In the DT group, rats were subjected to 12 exercise sessions, detrained for 12 days, and then were subjected to 1 exercise session before being killed. Isometric training consisted of maximum isometric contraction, which was produced by percutaneous electrical stimulation of the gastrocnemius muscle every other day. Muscles were removed 24 h after the final exercise session. Levels of total and phosphorylated p70S6K, 4E-BP1, rpS6, and p90RSK levels were measured, and phosphorylation of p70S6K, rpS6, and p90RSK was elevated in the 1B group compared with control muscle (CON) after acute resistance exercise, whereas repeated bouts of exercise suppressed those phosphorylation in both 12B and 18B groups. Interestingly, these phosphorylation levels were restored after 12 days of detraining in the DT group. On the contrary, phosphorylation of 4E-BP1 was not altered with chronic training and detraining, indicating that, with chronic resistance training, anabolic signaling becomes less sensitive to resistance exercise stimuli but is restored after a short detraining period.

Effects of low-intensity resistance exercise with short interset rest period on muscular function in middle-aged women.

We investigated the effect of low-intensity resistance exercise training on muscular size and strength where the interset rest period was shortened so as to reduce the metabolite clearance. Female subjects (aged 45.4 ± 9.5 years, n = 10) performed bilateral knee extension exercises in a seated position on an isotonic leg extension machine. The exercise sessions consisted of 3 sets of exercise at a mean intensity of ∼50% 1RM with an interset rest period of 30 seconds and was performed twice a week for a period of 12 weeks. The strength and the cross-sectional area (CSA) of the knee extensors and flexors were examined with an isokinetic dynamometer and magnetic resonance imaging (MRI), respectively. The CSAs of the knee extensors and flexors increased by 7.1 ± 1.6% (p < 0.01, Wilcoxon signed rank test) and 2.5 ± 1.4% (not significant), respectively. Isometric and isokinetic strengths increased significantly (p < 0.01) at all velocities examined, whereas no significant change was observed in those of knee flexors. These results indicate that a low-intensity resistance exercise with a short interset rest period is substantially effective in inducing muscular hypertrophy and concomitant increase in strength.

Effects of whole-body low-intensity resistance training with slow movement and tonic force generation on muscular size and strength in young men.

Tanimoto, M, Sanada, K, Yamamoto, K, Kawano, H, Gando, Y, Tabata, I, Ishii, N, and Miyachi, M. Effects of whole-body low-intensity resistance training with slow movement and tonic force generation on muscular size and strength in young men. J Strength Cond Res 22(6): 1926-1938, 2008-Our previous study showed that relatively low-intensity (~50% one-repetition maximum [1RM]) resistance training (knee extension) with slow movement and tonic force generation (LST) caused as significant an increase in muscular size and strength as high-intensity (~80% 1RM) resistance training with normal speed (HN). However, that study examined only local effects of one type of exercise (knee extension) on knee extensor muscles. The present study was performed to examine whether a whole-body LST resistance training regimen is as effective on muscular hypertrophy and strength gain as HN resistance training. Thirty-six healthy young men without experience of regular resistance training were assigned into three groups (each n = 12) and performed whole-body resistance training regimens comprising five types of exercise (vertical squat, chest press, latissimus dorsi pull-down, abdominal bend, and back extension: three sets each) with LST (~55-60% 1RM, 3 seconds for eccentric and concentric actions, and no relaxing phase); HN (~80-90% 1RM, 1 second for concentric and eccentric actions, 1 second for relaxing); and a sedentary control group (CON). The mean repetition maximum was eight-repetition maximum in LST and HN. The training session was performed twice a week for 13 weeks. The LST training caused significant (p < 0.05) increases in whole-body muscle thickness (6.8 ± 3.4% in a sum of six sites) and 1RM strength (33.0 ± 8.8% in a sum of five exercises) comparable with those induced by HN training (9.1 ± 4.2%, 41.2 ± 7.6% in each measurement item). There were no such changes in the CON group. The results suggest that a whole-body LST resistance training regimen is as effective for muscular hypertrophy and strength gain as HN resistance training.

Influence of icing on muscle regeneration after crush injury to skeletal muscles in rats

The influence of icing on muscle regeneration after crush injury was examined in the rat extensor digitorum longus. After the injury, animals were randomly divided into nonicing and icing groups. In the latter, ice packs were applied for 20 min. Due to the icing, degeneration of the necrotic muscle fibers and differentiation of satellite cells at early stages of regeneration were retarded by ∼1 day. In the icing group, the ratio of regenerating fibers showing central nucleus at 14 days after the injury was higher, and cross-sectional area of the muscle fibers at 28 days was evidently smaller than in the nonicing group. Besides, the ratio of collagen fibers area at 14 and 28 days after the injury in the icing group was higher than in the nonicing group. These findings suggest that icing applied soon after the injury not only considerably retarded muscle regeneration but also induced impairment of muscle regeneration along with excessive collagen deposition. Macrophages were immunohistochemically demonstrated at the injury site during degeneration and early stages of regeneration. Due to icing, chronological changes in the number of macrophages and immunohistochemical expression of transforming growth factor (TGF)-β1 and IGF-I were also retarded by 1 to 2 days. Since it has been said that macrophages play important roles not only for degeneration, but also for muscle regeneration, the influence of icing on macrophage activities might be closely related to a delay in muscle regeneration, impairment of muscle regeneration, and redundant collagen synthesis.

Force–velocity, force–power relationships of bilateral and unilateral leg multi-joint movements in young and elderly women

The present study investigated force-velocity and force-power relationships of bilateral and unilateral knee-hip extension movement in young and elderly women. Twelve healthy young (age, 19-31 yr) and 12 healthy elderly (age, 60-82 yr) women performed bilateral and unilateral knee-hip extension movements on the dynamometer against loads controlled by the servo system. Under the isotonic force condition, force-velocity relationships were measured. The maximum isometric force (F(max)), unloaded velocity (V(max)) and power output (P(max)) of the movements were calculated from extrapolating force-velocity and force-power relationships. F(max) and P(max) of bilateral and unilateral knee-hip extension movements were 20-30% lower in elderly than in young women. On the other hand, there were no significant differences in V(max) between young and elderly women and between bilateral and unilateral movements. Bilateral deficit was larger as the generation of force was larger in both young and elderly women. Also, bilateral deficit of F(max) and P(max) were not different between young and elderly women. The results were that lower maximum power output of bilateral and unilateral leg multi-joint movements in elderly women did not depend on the intrinsic shortening velocity of muscle action, but largely on reduction in force generating capacity. This suggests the importance of preventing a loss of force generating capacity of muscles during leg multi-joint movements in elderly women.