Hayao Ozaki

Increases in Thigh Muscle Volume and Strength by Walk Training with Leg Blood Flow Reduction in Older Participants

We examined the effects of walk training combined with leg blood flow reduction (BFR) on muscle hypertrophy as well as on peak oxygen uptake (VO₂ peak) in older individuals. Both the BFR walk training (BFR-Walk, n = 10, age; 64 ± 1 years, body mass index [BMI]; 22.5 ± 0.9 kg/m²) and control walk training (CON-Walk, n = 8, age; 68 ± 1 years, BMI; 23.2 ± 1.0 kg/m²) groups performed 20 minutes of treadmill walking at an exercise intensity of 45% of heart rate reserve, 4 days per week, for 10 weeks. The BFR-Walk group wore pressure belts (160-200 mm Hg) on both legs during training. After the training, magnetic resonance imaging-measured thigh muscle cross-sectional area (3.1%, p < .01) and muscle volume (3.7%, p < .01) as well as maximal isometric (5.9%, p < .05) and isokinetic (up to 22%, p < .01) strength increased in the BFR-Walk group, but not in the CON-Walk group. Estimated VO₂ peak during a bicycle graded exercise test increased (p < .05) and correlated with oxygen pulse in both groups. In conclusion, BFR walk training improves both muscle volume and strength in older women.

Effects of 10 weeks walk training with leg blood flow reduction on carotid arterial compliance and muscle size in the elderly adults.

High-intensity resistance training increases muscle size, but reduces arterial compliance. Muscular blood flow reduction (BFR) during low-intensity training has been shown to elicit muscle hypertrophy. However, the effect on arterial compliance is unknown. We examined the effects of walk training with BFR on carotid arterial compliance and muscle size in the elderly adults. Both BFR-walk training (BFR-W, n = 13, 66 ± 1 year) and control-walk training (CON-W, n = 10, 68 ± 1 year) groups performed 20 minutes treadmill walking at an exercise intensity of 45% of heart rate reserve, 4 days/week for 10 weeks. The BFR-W group wore pressure cuffs on both legs during training. Maximum knee joint strength (∼15%) and MRI-measured thigh muscle cross-sectional area (3%) increased in the BFR-W, but not in the CON-W. Carotid arterial compliance improved in both BFR-W (50%) and CON-W (59%) groups. Walk training with blood flow reduction can improve thigh muscle size/strength as well as carotid arterial compliance, unlike high-intensity training, in the elderly.

Muscle growth across a variety of exercise modalities and intensities: Contributions of mechanical and metabolic stimuli

This paper reviews the existing evidence for the potential contribution of metabolic and mechanical stimuli to muscle growth in response to a variety of exercise modalities and intensities. Recent research has demonstrated that low-load resistance training can elicit comparable hypertrophy to that of high-load resistance training when each set is performed until failure. The degree of metabolic fatigue would be greater for resistance training with lower loads compared to higher loads at the point of muscle failure, which may compensate for the lower mechanical stress. This may also explain why muscle hypertrophy occurs to varying magnitudes when activities such as cycling and walking are performed. Furthermore, the application of blood flow restriction to the working muscles during these activities induces greater hypertrophy albeit at the same level of mechanical stress, which would suggest a possible contribution from metabolic stress. Thus, it is plausible that both mechanical and metabolic stimuli are primary mechanisms for muscle hypertrophy and the degree of contributions of both stimuli determines the exercise-induced muscle hypertrophy.

Possibility of leg muscle hypertrophy by ambulation in older adults: a brief review.

It is known that ambulatory exercises such as brisk walking and jogging are potent stimuli for improving aerobic capacity, but it is less understood whether ambulatory exercise can increase leg muscle size and function. The purpose of this brief review is to discuss whether or not ambulatory exercise elicits leg muscle hypertrophy in older adults. Daily ambulatory activity with moderate (>3 metabolic equivalents [METs], which is defined as the ratio of the work metabolic rate to the resting metabolic rate) intensity estimated by accelerometer is positively correlated with lower body muscle size and function in older adults. Although there is conflicting data on the effects of short-term training, it is possible that relatively long periods of walking, jogging, or intermittent running for over half a year can increase leg muscle size among older adults. In addition, slow-walk training with a combination of leg muscle blood flow restriction elicits muscle hypertrophy only in the blood flow restricted leg muscles. Competitive marathon running and regular high intensity distance running in young and middle-aged adults may not produce leg muscle hypertrophy due to insufficient recovery from the damaging running bout, although there have been no studies that have investigated the effects of running on leg muscle morphology in older subjects. It is clear that skeletal muscle hypertrophy can occur independently of exercise mode and load.

Effects of periodic and continued resistance training on muscle CSA and strength in previously untrained men.

To determine muscle adaptations to retraining after short‐term detraining, we examined the effects of continuous and interrupted resistance training on muscle size and strength in previously untrained men. Fifteen young men were divided into continuous training (CTr) or retraining (RTr) groups and performed high‐intensity bench press training. The CTr group trained continuously for 15 weeks, while the RTr group trained for 6 weeks, stopped for a 3‐week detraining period and resumed training at week 10. After the initial training phase, increases (P<0·01) in one repetition maximum (1‐RM) and magnetic resonance imaging‐measured triceps brachii and pectorals major muscle cross‐sectional areas (CSAs) were similar in both groups. Muscle CSA and 1‐RM increased (P<0·05) continuously for the CTr group, but the muscle adaptations were lower (P<0·05) after the last 6‐week training period than after the initial phase. In the RTr group, there were no significant decreases in muscle CSA and 1‐RM after the 3‐week detraining period, and increases in muscle CSA after retraining were similar to those observed after initial training. Ultimately, improvements in 1‐RM and muscle CSA in both groups were similar after the 15‐week training period. Our results suggest that compared with continuous 15‐week training, 3‐week detraining does not inhibit muscle adaptations.

Cycle training induces muscle hypertrophy and strength gain: strategies and mechanisms

Cycle training is widely performed as a major part of any exercise program seeking to improve aerobic capacity and cardiovascular health. However, the effect of cycle training on muscle size and strength gain still requires further insight, even though it is known that professional cyclists display larger muscle size compared to controls. Therefore, the purpose of this review is to discuss the effects of cycle training on muscle size and strength of the lower extremity and the possible mechanisms for increasing muscle size with cycle training. It is plausible that cycle training requires a longer period to significantly increase muscle size compared to typical resistance training due to a much slower hypertrophy rate. Cycle training induces muscle hypertrophy similarly between young and older age groups, while strength gain seems to favor older adults, which suggests that the probability for improving in muscle quality appears to be higher in older adults compared to young adults. For young adults, higher-intensity intermittent cycling may be required to achieve strength gains. It also appears that muscle hypertrophy induced by cycle training results from the positive changes in muscle protein net balance.

Effects of walking combined with restricted leg blood flow on mTOR and MAPK signalling in young men

Walking combined with blood flow reduction (BFR‐walk) elicits muscle hypertrophy. However, the skeletal muscle intracellular signalling behind this response is currently unknown.

Hypertension risk: exercise is medicine* for most but not all

Hypertension is a risk factor for heart disease, and chronic exercise is recognized as a method for reducing resting blood pressure. Recent studies report that while exercise may benefit the majority of the population, the blood pressure adaptation is not always uniform; some individuals have an adverse blood pressure response to chronic aerobic exercise programmes. The purpose of this study was to examine the individual changes in resting blood pressure in response to exercise training regimens aimed at increasing muscle mass and strength. We have also included exercise (resistance and aerobic) in combination with blood flow restriction (BFR). Of 74 individuals, 11% had an increased risk, 16% had a decreased risk and 73% had no change in risk classification following exercise. The statistical analysis found that the group that decreased risk with exercise tended to have higher baseline levels of blood pressure. However, there were little baseline differences between the group that increased risk or the group that had no change in risk, suggesting that starting values may not necessarily determine who will see a beneficial response. In conclusion, the blood pressure adaptation to resistance training and exercise with BFR is not homogeneous with some participants increasing, decreasing or staying in the same risk category following an exercise intervention. These are important findings as they would not have been noted or discussed when looking only at the group means. Future research may identify molecular predictors so that individuals at risk for adverse events can be identified prior to exercise.

Effects of Electrostimulation with Blood Flow Restriction on Muscle Size and Strength

PURPOSE Low-load voluntary exercise can induce muscle hypertrophy and strength gain in working muscles when combined with blood flow restriction (BFR). However, it is unknown whether such hypertrophy and strength gain can be induced by involuntary muscle contractions triggered via low-intensity neuromuscular electrical stimulation (NMES) combined with BFR. The purpose of this article was to investigate whether low-intensity NMES combined with BFR (NMES-BFR) could elicit muscle hypertrophy and strength gain in the quadriceps. METHODS Eight untrained young male participants (mean ± SE; age, 26.2 ± 0.7 yr; height, 1.74 ± 0.02 m; body weight, 71.4 ± 4.8 kg) were subjected to 23 min of unilateral low-intensity (5%-10% of maximal voluntary contraction) NMES twice per day (5 d·wk⁻¹) for 2 wk: one leg received NMES-BFR and the other leg received NMES alone. Quadriceps muscle thickness and isometric and isokinetic strength were measured before and every week throughout the training and detraining periods. RESULTS In NMES-BFR legs, muscle thickness increased after 2 wk of training (+3.9%) and decreased after 2 wk of detraining (-3.0%). NMES-BFR training also increased maximal knee extension strength in isometric (+14.2%) and isokinetic (+7.0% at 90°·s⁻¹ and +8.3% at 180°·s⁻¹) voluntary contractions. In addition, maximal isometric strength decreased (-6.8%), whereas no large fall (-1.9% at 90°·s⁻¹ and -0.6% at 180°·s⁻¹) in isokinetic maximal strength was evident after 2 wk of detraining. In legs that received NMES alone, no prominent change was observed; there was a negligible effect on isometric strength. CONCLUSION Low-intensity NMES-BFR induces muscle hypertrophy and strength gain in untrained young male participants.

Muscle volume and strength and arterial compliance after walk training with blood flow reduction in elderly women.

To the Editor: Traditional high-intensity resistance training (HI-RT) is an effective tool to improve sarcopenia or osteoporosis, but previous research has indicated that HIRT reduces central arterial compliance, and the reduction may be associated with high rates of mortality in patients with end-stage renal failure and essential hypertension. Muscular blood flow restriction (BFR) during resistance training has been shown to elicit muscle hypertrophy similar to that during traditional HI-RT but with much lower training intensity. An intensity as low as that associated with walking, when combined with BFR, can lead to significant improvements in muscle size and strength, although the effect of low-intensity walk training with BFR on carotid arterial compliance has not been explored. Thus, the purpose of this study was to investigate the effects of BFR-walk training on carotid arterial compliance and muscle size and function in older people. Eighteen sedentary women aged 57 to 73 were divided into two walk training groupsFone with BFR (BFR-W, n 5 10) and one without (CON-W, n 5 8). The subjects in both groups performed 20 minutes treadmill walking at an exercise intensity of predetermined 45% of heart rate reserve (HRR) 4 days per week for 10 weeks. Age-predicted maximal heart rate (220–age) was used to determine HRR for each subject. Subjects in the BFR-W group wore elastic cuffs on the most proximal portion of both legs during training session (external compression: 200 mmHg). Magnetic resonance imaging–measured midthigh-muscle cross-sectional area (CSA) and maximum isokinetic knee extension and flexion strength (301/s) were measured before (pre) and after (post) training. Brachial blood pressure was measured using a semiautomated oscillometric device after subjects had rested in the supine position at least 15 minutes in quiet. Carotid arterial compliance was calculated according to the combination of ultrasound imaging and applanation of tonometrically obtained arterial pressure from the carotid artery. At the start of the experiment, there were no significant differences between BFR-Wand CON-W groups in terms of mean age (SE) (64 (1) and 68 (1), respectively), body mass index (22.8 (0.8) and 23.2 (1.0) kg/m), midthigh-muscle CSA, and knee extension and flexion strength. Resting blood pressure, heart rate, and carotid arterial compliance were also similar between the two groups. After 10 weeks of walk training, maximum isokinetic knee extension and flexion torques increased (P 5.004) in the BFR-W group but not in the CON-W group. Thigh muscle CSA also increased (P 5.001) in the BFR-W group but not in the CON-W group. Relative isokinetic strength per unit of muscle CSA increased in the BFR-W group, but there was no change in the CON-W group. Carotid arterial compliance improved (Po.05) in both groups, but the percentage change between the two groups was similar (Figure 1). There was no change in carotid and brachial blood pressure at rest for either group before and after the training. HI-RT is an effective tool for reversing sarcopenia and osteoporosis but has deleterious effects on central arterial compliance, but these results demonstrate that BFR walk training improves not only carotid arterial compliance, but also thigh muscle hypertrophy, which might be a useful method to improve muscle size and function and arterial compliance with a single type of training. A previous study found that the major contributor of resistance training– induced arterial stiffening is the elevation of blood pressure (250–320 mmHg) during each bout of HI-RT, although elevations of arterial blood pressure during moderate intensity aerobic exercise bout, as well as walking with BFR, are lower than during HI-RT. A study reported that total aortic elastin content was greater and calcium content of elastin was lower after aerobic exercise training in rats, which may contribute to the beneficial effects of BFR-walk training on arterial compliance. The findings of the current study also showed that significant hypertrophic response occurred in the thigh muscle only for the BFR-W group. This finding is consistent with previous investigations in young and older subjects. Another study demonstrated that a single bout of 20% of one-repetition maximum intensity knee extension exercise with BFR increased vastus lateralis muscle protein synthesis and the Akt/mammalian target of the rapamycin signaling pathway in young men. A low-intensity BFR exercise–induced increase in muscle protein synthesis was also confirmed in older men. These anabolic responses may contribute significantly to BFR walk training–induced muscle hypertrophy. In conclusion, walk training with BFR can produce thigh muscle hyper-