Muscle Blood Flow Restriction Research Articles

Boys vs men differences in muscular fatigue, muscle and cerebral oxygenation during maximal effort isometric contractions: the effect of muscle blood flow restriction.

To examine whether the children's superiority, over adults, to resist fatigue during repeated maximal-efforts depends on their often-cited oxidative advantage, attributed to greater muscle blood flow and O2-delivery. We also investigated the mechanisms underlying child-adult differences in muscle-oxygenation (due to O2-supply or O2-utilization) and examined if there are age-differences in cerebral-oxygenation response (a brain-activation index). Eleven men (23.3 ± 1.8yrs) and eleven boys (11.6 ± 1.1yrs) performed 15 maximal-effort handgrips (3-s contraction/3-s rest) under two conditions: free-flow circulation (FF) and arterial-occlusion (OCC). Force, muscle-oxygenation (TSImuscle) and cerebral-oxygenation (oxyhemoglobin-O2Hbcerebral; total hemoglobin-tHbcerebral; deoxyhemoglobin-HHbcerebral) were assessed. In boys, force declined less (-26.3 ± 2.6 vs. -34.4 ± 2.4%) and at slower rate (-1.56 ± 0.16 vs. -2.24 ± 0.17%·rep-1) vs. men in FF (p < 0.01-0.05; d = 0.60-1.24). However, in OCC there were no age-differences in the magnitude (-38.3 ± 3.0 vs. -37.8 ± 3.0%) and rate (-2.44 ± 0.26 vs. -2.54 ± 0.26%·rep-1) of force decline. Boys compared to men, exhibited less TSImuscle decline in both protocols, and lower muscle VO2 (p < 0.05). Boys, also, presented a smaller O2Hbcerebral and tHbcerebral rise than men in FF; exercising with OCC increased the O2Hbcerebral and tHbcerebral response in boys. Using MVIC as a covariate in FF condition, abolished boys-men differences in force and TSImuscle decline and O2Hbcerebral rise. During repeated maximal-efforts: (i) blood flow is a significant contributor to children's superiority over adults to resist fatigue; (ii) age-difference in muscle hypoxia/deoxygenation is rather attributed to men's greater metabolic demand than to lower muscle-perfusion; and (iii) cerebral oxygenation/blood volume increase more in men than boys under free circulation, implying greater brain activation.

Effect of One Session of Muscle Blood Flow Restriction Training Versus Normal Training on Blood Lactate Level.

Blood flow restriction training (BFRT) is useful for improving muscle strength. However, it involves a long training time and is unsuitable for vigorous exercise. Muscle blood flow restriction training (MBFRT), which uses multiple parallel pneumatic cuffs (MPCs) to compress large areas of the extremities and restrict blood flow, was subsequently developed to address these issues. This study compared the effects of MBFRT with normal training (NT). Ten healthy adults underwent low-intensity MBFRT. MPC pressure was increased to 200 mmHg just before training. The exercise was a bodyweight half-squat. Three sets of 30 squats were performed. Two weeks later, the participants underwent NT with the same exercise. Blood lactate levels were measured before the start of training and at 1 and 5 min after training. The Borg index was also measured at the end of the training. The blood lactate level was elevated at 1 min after MBFRT and NT. The elevated blood lactate level was maintained at 5 min after MBFRT, whereas the lactate level was significantly decreased at 5 min after NT. The Borg index at the end of the training was significantly higher in MBFRT than in NT. Lactic acid accumulates in the muscles during low-intensity MBFRT, thereby initiating type II fiber activity.

The Effect of Skeletal Muscle Oxygenation on Hemodynamics, Cerebral Oxygenation and Activation, and Exercise Performance during Incremental Exercise to Exhaustion in Male Cyclists.

This study aimed to elucidate whether muscle blood flow restriction during maximal exercise is associated with alterations in hemodynamics, cerebral oxygenation, cerebral activation, and deterioration of exercise performance in male participants. Thirteen healthy males, cyclists (age 33 ± 2 yrs., body mass: 78.6 ± 2.5 kg, and body mass index: 25.57 ± 0.91 kg·m-1), performed a maximal incremental exercise test on a bicycle ergometer in two experimental conditions: (a) with muscle blood flow restriction through the application of thigh cuffs inflated at 120 mmHg (with cuffs, WC) and (b) without restriction (no cuffs, NC). Exercise performance significantly deteriorated with muscle blood flow restriction, as evidenced by the reductions in V˙O2max (-17 ± 2%, p < 0.001), peak power output (-28 ± 2%, p < 0.001), and time to exhaustion (-28 ± 2%, p < 0.001). Muscle oxygenated hemoglobin (Δ[O2Hb]) during exercise declined more in the NC condition (p < 0.01); however, at exhaustion, the magnitude of muscle oxygenation and muscle deoxygenation were similar between conditions (p > 0.05). At maximal effort, lower cerebral deoxygenated hemoglobin (Δ[HHb]) and cerebral total hemoglobin (Δ[THb]) were observed in WC (p < 0.001), accompanied by a lower cardiac output, heart rate, and stroke volume vs. the NC condition (p < 0.01), whereas systolic blood pressure, rating of perceived exertion, and cerebral activation (as assessed by electroencephalography (EEG) activity) were similar (p > 0.05) between conditions at task failure, despite marked differences in exercise duration, maximal aerobic power output, and V˙O2max. In conclusion, in trained cyclists, muscle blood flow restriction during an incremental cycling exercise test significantly limited exercise performance. Exercise intolerance with muscle blood flow restriction was mainly associated with attenuated cardiac responses, despite cerebral activation reaching similar maximal levels as without muscle blood flow restriction.

Potential Role of Blood Flow Restricted Exercise for Older Adults

Sarcopenia is the age-related loss of muscle mass and strength which is associated with the loss of physical performance, lower quality of life, and other negative health outcomes. Resistance training (RT) is a recognized method to increase muscle strength and mass, however some older adults may be limited in their ability to perform RT with traditionally recommended higher-loads. Occluding blood flow to a limb, commonly referred to as muscle blood flow restriction (MBFR), has been investigated as an adjunct to RT to elicit muscle strength and hypertrophy adaptations while utilizing lower-loads of resistance as compared to traditional training recommendations. This technique could be of particular interest for older adults who may be limited in their ability to otherwise complete RT due to health reasons or may be debilitated due to a lack of muscle mass and strength. The aim of this narrative review is to discuss the current literature investigating the use of MBFR with and without a combination of exercise, in older adults and its effects on skeletal muscle strength, hypertrophy, and physical function.

The effect of muscle blood flow restriction on hemodynamics, cerebral oxygenation and activation at rest.

This study tested the hypothesis that muscle blood flow restriction reduces muscle and cerebral oxygenation at rest. In 26 healthy males, aged 33± 2 yrs, physiological variables were continuously recorded during a 10-min period in 2 experimental conditions: a) with muscle blood flow restriction through thigh cuffs application inflated at 120mm Hg (With Cuffs, WC) and b) without restriction (No Cuffs, NC). Muscle and cerebral oxygenation were reduced by muscle blood flow restriction as suggested by the increase in both muscle and cerebral deoxygenated hemoglobin (Δ[HHb]; p< 0.01) and the decrease of muscle and cerebral oxygenation index (Δ[HbDiff]; p< 0.01). Hemodynamic responses were not affected by such muscle blood flow restriction, whereas baroreflex sensitivity was reduced (p= 0.009). The perception of leg discomfort was higher (p< 0.001) in the WC than in the NC condition. This study suggests that thigh cuffs application inflated at 120mm Hg is an effective method to reduce muscle oxygenation at rest. These changes at the muscular level seem to be sensed by the central nervous system, evoking alterations in cerebral oxygenation and baroreflex sensitivity. Novelty: Thigh cuffs application inflated at 120mm Hg effectively reduces muscle oxygenation at rest. Limiting muscle oxygenation appears to reduce cerebral oxygenation, and baroreflex sensitivity, at rest. Even in healthy subjects, limiting muscle oxygenation, at rest, affects neural integration.

Local and Systemic Effects of Blood Flow Restriction Therapy in an Animal Model

Background: Blood flow restriction therapy (BFRT) has been increasingly applied to improve athletic performance and injury recovery. Validation of BFRT has lagged behind commercialization, and currently the mechanism by which this therapy acts is unknown. BFRT is one type of ischemic therapy, which involves exercising with blood flow restriction. Repetitive restriction of muscle blood flow (RRMBF) is another ischemic therapy type, which does not include exercise. Hypothesis/Purpose: The purpose was to develop a rat model of ischemic therapy, characterize changes to muscle contractility, and evaluate local and systemic biochemical and histologic responses of 2 ischemic therapy types. We hypothesized that ischemic therapy would improve muscle mass and strength as compared with the control group. Study Design: Controlled laboratory study. Methods: Four groups of 10 Sprague-Dawley rats were established: control, stimulation, RRMBF, and BFRT. One hindlimb of each subject underwent 8 treatment sessions over 4 weeks. To simulate exercise, the stimulation group underwent peroneal nerve stimulation for 2 minutes. The RRMBF group used a pneumatic cuff inflated to 100 mm Hg with a 48-minute protocol. The BFRT group involved 100–mm Hg pneumatic cuff inflation and peroneal nerve stimulation for a 5-minute protocol. Four methods of evaluation were performed: in vivo contractility testing, histology, immunohistochemistry, and ELISA. Analysis of variance with post hoc Tukey test and linear mixed effects modeling were used to compare the treatment groups. Results: There was no difference in muscle mass among groups (P = .40) or between hindlimbs (P = .73). In vivo contractility testing showed no difference in maximum contractile force among groups (P = .64) or between hindlimbs (P = .30). On histology, myocyte cross-sectional area was not different among groups (P = .55) or between hindlimbs (P = .44). Pax7 immunohistochemistry demonstrated no difference in muscle satellite cell density among groups (P = .06) or between hindlimbs (P = .046). ELISA demonstrated the RRMBF group as eliciting elevated GH levels as compared with the other groups (P < .001). Conclusion: Ischemic therapy did not induce gains in muscle mass, contractility strength, fiber cross-sectional area, or satellite cell density locally or systemically in this model, although the RRMBF group did have elevated GH levels on ELISA. Clinical Relevance: This animal model does not support ischemic therapy as a method to improve muscle mass, function, or satellite cell density.

Cardiorespiratory and Cerebrovascular Responses to Leg Cycling Exercise during Muscle Metaboreflex Activation with Blood Flow Restriction in Moderate Normobaric Hypoxia

Skeletal muscle blood flow restriction and normobaric hypoxia are strategies adopted during exercise training because the associated reductions in local or systemic oxygenation may enhance athletic performance. Both manoeuvres evoke cardiorespiratory and cerebrovascular responses but have not been studied in combination. Blood flow restriction during exercise activates metabolically sensitive group III and IV skeletal muscle afferents (i.e., muscle metaboreflex activation), while systemic hypoxia activates the peripheral chemoreflex. We sought to determine whether the cardiorespiratory and cerebrovascular response to muscle metaboreflex activation with blood flow restriction during leg cycling exercise is augmented in moderate normobaric hypoxia.Nine healthy men (age 23±2 years; mean±SE) participated in two experimental trials performed under normoxic (fraction of inspired O2 [FiO2] = 21 %) and hypoxic (FiO2 = 13.5 %; equivalent of altitude of 3500 m) conditions whilst seated in a semi‐recumbent position in an environmental chamber. Trials consisted of a resting baseline period (3 min), followed by low intensity leg cycling exercise (64±7 Watts) under free‐flow conditions (~3½ min), and then bilateral thigh cuff inflation to 100 mmHg to induce blood flow restriction and muscle metaboreflex activation (~3 ½ min). Peripheral capillary oxygen saturation (SpO2; finger pulse oximetry), mean arterial pressure (MAP; Finometer and SunTech), heart rate (HR; electrocardiogram), the partial pressure of end‐tidal carbon dioxide (PETCO2; capnography), minute ventilation (VE; pneumotachometer) and middle cerebral artery mean blood flow velocity (MCAV; transcranial Doppler) were recorded.At baseline, SpO2 was lower during hypoxia (87±1 %) than normoxia (97±1 %; P&lt;0.05), but MAP, HR, PETCO2, VE and MCAv were not different between trials (P&gt;0.05). Leg cycling under free‐flow conditions significantly increased MAP, HR, PETCO2, VE and MCAv (P&lt;0.05 vs. baseline), with no differences observed between hypoxic and normoxic trials (P&gt;0.05). MAP (Δ14±2 vs. Δ16±2 mmHg; P=0.215), HR (Δ10±2 vs. Δ8±3 b·min−1; P=0.251), PETCO2 (Δ−1.1±0.3 vs. Δ−3.4±1.8 mmHg; P=0.596), VE (Δ4±1 vs. Δ4±1 L·min−1; P=0.446) and MCAv (Δ4±2 vs. Δ4±1 cm·s−1; P=0.408) responses to blood flow restriction during leg cycling (i.e., muscle metaboreflex activation) were not different in the hypoxic and normoxic trials.These preliminary findings suggest that moderate normobaric hypoxia (FiO2 = 13.5 %) does not augment the cardiorespiratory and cerebrovascular responses to muscle metaboreflex activation with blood flow restriction during low intensity leg cycling.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Prefrontal and muscle oxygenation responses to supraventricular tachycardia

Supraventricular tachycardia (SVT) causes hypotension and cerebral hypoperfusion leading to syncope at times. The cerebral and peripheral vascular systems probably operate to maintain cerebral oxygenation against SVT‐induced hypoperfusion. However, time courses of cerebral and peripheral oxygenation responses to SVT has not been fully understood. The aim of this study was to examine the time course and relationship between cerebral and peripheral oxygenation responses and SVT‐induced hypotension. Prefrontal and forearm tissue oxygen index (TOI) and normalized tissue hemoglobin index (nTHI) were collected by near‐infrared spectroscopy (NIRS) during electrophysiological study (EPS) in 14 patients (55 ± 4 years old, 9 men) with SVT. AP decreased during 2–20 s of SVT. The prefrontal TOI and nTHI began to decrease (P &lt; 0.05) transiently at 6 s of SVT and then returned to the baseline level from 14 s. The initial decrease of prefrontal TOI appears to occur when hypotension was over approximately 20 mmHg. In contrast, the forearm TOI and nTHI decreased continuously from 11 s (P &lt; 0.05). The AP and prefrontal NIRS responses suggest that SVT‐induced great hypotension (&gt;20 mmHg) caused the transient reduction of cerebral oxygenation and blood volume, which may be followed by a recovering process owing to cerebral vasodilatation. The continuous reductions of forearm TOI and nTHI during SVT suggest restriction of muscle blood flow by vasoconstriction, which may contribute to redistribution of the blood to the brain.Support or Funding InformationThis research is supported by Automotive and Medical Concert Consortium (AMECC).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

The effects of muscle blood flow restriction during running training on measures of aerobic capacity and run time to exhaustion.

Training with blood flow restriction (BFR) is known to enhance muscle mass and strength during resistance training activities. However, little is known about the BFR effects during aerobic training. This investigation examines the effects of running training performed with or without BFR on physiology and performance. Sixteen subjects (age 24.9 ± 6.9years, height 172.9 ± 7.8cm, weight 75.1 ± 13.8kg) were assigned to a BFR or control (CON) group for eight sessions of training. Before and after training, subjects completed an incremental test to determine peak running velocity (PRV) maximal oxygen uptake ([Formula: see text]) and running economy (RE), followed by a time to exhaustion run (TTE) performed at PRV. Training for both groups consisted of progressively increasing volumes of 30-s repetitions completed at 80% of PRV. The BFR and CON groups reported gains (6.3 ± 3.5 vs 4.0 ± 3.3%) in [Formula: see text] following training with only trivial (ES = 0.18) differences between groups. Similarly, PRV and incremental test time increased in both training groups with a small (ES ~ 0.3) additional enhancement in favour of the BFR group. Running economy improved in the BFR group but not in CON (ES = 0.4). TTE also increased in both BFR (27 ± 9%) and CON groups (17 ± 6%) with a small (ES = 0.31) additional benefit in favour of the BFR group. Using BFR during training appears to confer small but potentially worthwhile improvements in RE, PRV and TTE measures. The improvements following BFR training are likely due to muscular rather than cardiovascular function.

Repetitive restriction of muscle blood flow enhances mTOR signaling pathways in a rat model.

Skeletal muscle is a plastic organ that adapts its mass to various stresses by affecting pathways that regulate protein synthesis and degradation. This study investigated the effects of repetitive restriction of muscle blood flow (RRMBF) on microvascular oxygen pressure (PmvO2), mammalian target of rapamycin (mTOR) signaling pathways, and transcripts associated with proteolysis in rat skeletal muscle. Eleven-week-old male Wistar rats under anesthesia underwent six RRMBF consisting of an external compressive force of 100mmHg for 5min applied to the proximal portion of the right thigh, each followed by 3min rest. During RRMBF, PmvO2 was measured by phosphorescence quenching techniques. The total RNA and protein of the tibialis anterior muscle were obtained from control rats, and rats treated with RRMBF 0-6h after the stimuli. The protein expression and phosphorylation of various signaling proteins were determined by western blotting. The mRNA expression level was measured by real-time RT-PCR analysis. The total muscle weight increased in rats 0h after RRMBF, but not in rats 1-6h. During RRMBF, PmvO2 significantly decreased (36.1±5.7 to 5.9±1.7torr), and recovered at rest period. RRMBF significantly increased phosphorylation of p70 S6-kinase (p70S6k), a downstream target of mTOR, and ribosomal protein S6 1h after the stimuli. The protein level of REDD1 and phosphorylation of AMPK and MAPKs did not change. The mRNA expression levels of FOXO3a, MuRF-1, and myostatin were not significantly altered. These results suggested that RRMBF significantly decreased PmvO2, and enhanced mTOR signaling pathways in skeletal muscle using a rat model, which may play a role in diminishing muscle atrophy under various conditions in human studies.

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.

Blood flow restriction by low compressive force prevents disuse muscular weakness

Repetitive blood flow restriction prevents muscular atrophy and weakness induced by chronic unloading. However, it was unclear which external compressive force for blood flow restriction was optimal to prevent muscular dysfunction. The present study was intended to investigate the effects of repeated muscle blood flow restriction at low pressure on muscular weakness induced by immobilization without weight bearing. Using casts, the left ankles of 11 healthy males were immobilized for 2 weeks. Subjects were instructed to walk using crutches with no weight bearing during the period. Subjects were divided randomly into two groups: a restriction of blood flow (RBF) group (application of external compressive force of 50 mm Hg) and a control (CON) group (no intervention). We measured changes in the muscle strength of the knee extensor–flexor and ankle plantar flexor. The percent changes in knee extensor torque at 60°/s under eccentric contraction in the RBF group were significantly smaller than in the CON group (−12.5 ± 10.7% and −30.1 ± 10.9%, p < 0.05). The percent changes in knee flexor torque when performing an eccentric contraction at 60°/s, an isometric contraction, or a concentric contraction at both 60 and 300°/s in the RBF group were significantly smaller than those in the CON group ( p < 0.05). In conclusion, our results show that repetitive restriction of blood flow with 50 mm Hg cuff pressure to the lower extremity reduces muscular weakness induced by chronic unloading.

Skeletal muscle size and strength are increased following walk training with restricted leg muscle blood flow: implications for training duration and frequency

The purpose of this study was to investigate once-daily walk training with restricted leg blood flow (KAATSU) on thigh muscle size and strength. Twelve young men performed walk training: KAATSU-walk training (n=6) and control (no KAATSU-walk; n=6). Training was conducted once daily, 6 days per week, for 3 weeks. Treadmill walking (50 m/min) was performed for 5 sets of 2-min bouts interspersed with 1-min rest periods. The KAATSU-walk group wore pressure cuff belts (5 cm wide) on both legs during training, with incremental increases in external compression starting at 160 mmHg and ending at 230 mmHg. Thigh muscle volume and isometric and 1-repetition maximal (1-RM) strength were measured before and after training. In the KAATSU-walk group, quadriceps and hamstrings muscle volume increased 1.7 and 2.4% (both P<0.05), respectively, following training. One-RM leg press and leg curl increased 7.3 and 8.6% (both P<0.05), respectively, following KAATSU-walk training. Also, isometric knee extension strength (4.4%; P<0.01), but not knee flexion strength (1.7%), increased following KAATSU-walk training. There were no changes in muscle volume or strength in the control-walk group. These results confirm previous work showing that the combination of slow walk training and leg muscle blood flow restriction induces muscle hypertrophy and strength gains. However, the magnitude of change in muscle mass and strength following once-daily KAATSU-walk training was approximately one-half that reported for twice-daily KAATSU-walk training over a 3-week period. These results in combination with previous observations lead to the conclusion that the impact of KAATSU-walk training on muscle size and strength is related to an ability to accomplish a high number of training bouts within a compressed training duration. Second, frequency-dependent muscle enlargement appears to be associated with KAATSU-walk training.

Muscle, tendon, and somatotropin responses to the restriction of muscle blood flow induced by KAATSU‐walk training

The efficacy of KAATSU training has been demonstrated in human athletes, both as a therapeutic method as well as a training aid. The purpose of this study was to investigate the effects of slow walk training combined with restriction of muscle blood flow (KAATSU) on muscle and tendon size. Six healthy, unfit Standardbred mares performed walking (240 m/min for 10 min and then 5 min recovery) with KAATSU, and 6 mares performed walking without KAATSU. A specially designed elastic cuff1 was placed at the most proximal position of the forelegs and inflated to a pressure of 200-230 mmHg throughout the walking and recovery sessions. The training was conducted once a day, 6 days/week for 2 weeks. Skeletal muscle thickness and tendon thickness were measured using B-mode ultrasound at baseline and after 2 weeks of training. Venous blood samples were obtained before the first acute exercise and 5, 15 and 60 min afterwards. Serum somatotropin concentration was determined using a commercially available equine-specific ELISA kit. The acute increase in plasma somatotropin was 40% greater (P<0.05) in the KAATSU-walk group than in the Control-walk group 5 min after exercise and remained elevated (P<0.05) at 15 and 60 min post exercise compared with the Control-walk group. After 2 weeks of training, muscle thickness increased (P<0.05) 3.5% in the KAATSU-walk group but did not change in the Control-walk group (0.7%). Tendon thickness did not change (P>0.05) in either group. These data demonstrate that KAATSU training can induce muscle hypertrophy in horses and suggest that KAATSU training may provide significant therapeutic/ rehabilitative value in horses, as has been shown in man.

Does blood flow restriction enhance hypertrophic signaling in skeletal muscle?

in the last decade, there was a dramatic increase in our knowledge of the molecular events that accompany changes in skeletal muscle mass in response to resistance exercise training or to chronic unloading. For example, the role of myostatin in limiting skeletal muscle growth during development was

Muscle size and strength are increased following walk training with restricted venous blood flow from the leg muscle, Kaatsu-walk training

Previous studies have shown that low-intensity resistance training with restricted muscular venous blood flow (Kaatsu) causes muscle hypertrophy and strength gain. To investigate the effects of daily physical activity combined with Kaatsu, we examined the acute and chronic effects of walk training with and without Kaatsu on MRI-measured muscle size and maximum dynamic (one repetition maximum) and isometric strength, along with blood hormonal parameters. Nine men performed Kaatsu-walk training, and nine men performed walk training alone (control-walk). Training was conducted two times a day, 6 days/wk, for 3 wk using five sets of 2-min bouts (treadmill speed at 50 m/min), with a 1-min rest between bouts. Mean oxygen uptake during Kaatsu-walk and control-walk exercise was 19.5 (SD 3.6) and 17.2 % (SD 3.1) of treadmill-determined maximum oxygen uptake, respectively. Serum growth hormone was elevated (P < 0.01) after acute Kaatsu-walk exercise but not in control-walk exercise. MRI-measured thigh muscle cross-sectional area and muscle volume increased by 4-7%, and one repetition maximum and maximum isometric strength increased by 8-10% in the Kaatsu-walk group. There was no change in muscle size and dynamic and isometric strength in the control-walk group. Indicators of muscle damage (creatine kinase and myoglobin) and resting anabolic hormones did not change in both groups. The results suggest that the combination of leg muscle blood flow restriction with slow-walk training induces muscle hypertrophy and strength gain, despite the minimal level of exercise intensity. Kaatsu-walk training may be a potentially useful method for promoting muscle hypertrophy, covering a wide range of the population, including the frail and elderly.

Acute Hormonal Responses To Restriction Of Leg Muscle Blood Flow During Walking

Low-intensity resistance exercise (20% of one-repetition maximal) combined with restriction of muscle blood flow (namely KAATSU) increases plasma growth hormone (GH) concentration. In general, walking slowly has no effect on acute GH response. PURPOSE To examine the acute responses of serum GH, free testosterone, and cortisol to slow walking combined with KAATSU. METHODS 11 male college students performed walking (50 m/min for five 2 min bouts; 1 min rest between bouts) with and without KAATSU (the proximal end of their thigh compressed at 130% of resting systolic blood pressure throughout the walking session) on separate days. Venous blood samples were obtained prior to the start of exercise (Pre), and immediately (IP), 15- (15P) and 60-min (60P) after exercise. RESULTS Serum GH concentration was elevated (P<0.01) from Pre [1.72 (0.83) ng/ml] to IP [12.4 (3.2) ng/ml] and 15P [13.1 (2.4) ng/ml] in the walking with KAATSU. Free testosterone was also elevated (P<0.05) from Pre [12.7 (1.2) pg/ml] to IP [16.0 (1.3) pg/ml] in the walking with KAATSU. Neither GH [Pre, 1.67 (0.97) ng/ml; IP, 1.39 (0.91), 15P, 1.26 (0.92)] nor free testosterone [Pre, 14.3 (1.3) pg/ml; IP, 14.1 (1.2)] increased during the walking without KAATSU. Cortisol concentration showed a gradual decrease (P<0.05) during the experiments in both walking with and without KAATSU. CONCLUSIONS The results of the present investigation with young male students indicated that slow walking with KAATSU caused greater responses in serum GH and free testosterone compared to normal slow walking.

Acute Hormonal Responses To Restriction Of Leg Muscle Blood Flow During Walking

Low-intensity resistance exercise (20% of one-repetition maximal) combined with restriction of muscle blood flow (namely KAATSU) increases plasma growth hormone (GH) concentration. In general, walking slowly has no effect on acute GH response. PURPOSE To examine the acute responses of serum GH, free testosterone, and cortisol to slow walking combined with KAATSU. METHODS 11 male college students performed walking (50 m/min for five 2 min bouts; 1 min rest between bouts) with and without KAATSU (the proximal end of their thigh compressed at 130% of resting systolic blood pressure throughout the walking session) on separate days. Venous blood samples were obtained prior to the start of exercise (Pre), and immediately (IP), 15- (15P) and 60-min (60P) after exercise. RESULTS Serum GH concentration was elevated (P<0.01) from Pre [1.72 (0.83) ng/ml] to IP [12.4 (3.2) ng/ml] and 15P [13.1 (2.4) ng/ml] in the walking with KAATSU. Free testosterone was also elevated (P<0.05) from Pre [12.7 (1.2) pg/ml] to IP [16.0 (1.3) pg/ml] in the walking with KAATSU. Neither GH [Pre, 1.67 (0.97) ng/ml; IP, 1.39 (0.91), 15P, 1.26 (0.92)] nor free testosterone [Pre, 14.3 (1.3) pg/ml; IP, 14.1 (1.2)] increased during the walking without KAATSU. Cortisol concentration showed a gradual decrease (P<0.05) during the experiments in both walking with and without KAATSU. CONCLUSIONS The results of the present investigation with young male students indicated that slow walking with KAATSU caused greater responses in serum GH and free testosterone compared to normal slow walking.

Changes in blood volume and oxygenation level in a working muscle during a crank cycle.

This study examined circulatory and metabolic changes in a working muscle during a crank cycle in a pedaling exercise with near-infrared spectroscopy (NIRS). NIRS measurements sampled under stable metabolic and cadence conditions during incremental pedaling exercise were reordered according to the crank angles whose signals were obtained in eight male subjects. The reordered changes in muscle blood volume during a crank cycle demonstrated a pattern change that corresponded to changes in pedal force and electrical muscle activity for pedal thrust. The top and bottom peaks for muscle blood volume change at work intensities of 180 W and 220 W always preceded (88 +/- 32 and 92 +/- 23 ms, respectively) those for muscle oxygenation changes. Significant differences in the level of NIRS parameters (muscle blood volume and oxygenation level) among work intensities were noted with a common shape in curve changes related to pedal force. In addition, a temporary increase in muscle blood volume following a pedal thrust was detected at work intensities higher than moderate. This temporary increase in muscle blood volume might reflect muscle blood flow restriction caused by pedal thrusts. The results suggest that circulatory and metabolic conditions of a working muscle can be easily affected during pedaling exercise by work intensity. The present method, reordering of NIRS parameters against crank angle, serves as a useful measure in providing additional findings of circulatory dynamics and metabolic changes in a working muscle during pedaling exercise.

Blood pressure responses to dynamic exercise with lower-body positive pressure.

Cardiovascular responses were obtained during cycling with graded levels of lower-body positive pressure (LBPP) applied to the exercising limbs. Seven men performed four incremental work rate (25 W.min-1) exercise (IWREx) tests to their limit of tolerance while exposed to 0, 15, 30, or 45 Torr LBPP. They also performed four, 6-min constant work rate exercise (CWREx) bouts at two work rates with LBPP's of 0 and 45 Torr. Cardiovascular data were obtained at rest and at 40%, 55%, 75%, and 90% of VO2peak, as well as at minute 5 of CWREx. LBPP did not alter VO2, HR, SV, or cardiac output (Qc) responses at rest or during exercise. However, both 30 and 45 Torr LBPP produced increases in MAP at rest and during exercise (P < 0.05). During CWREx, elevations in blood pressure were mediated via increases in TPR (P < 0.05). Only 45 Torr LBPP elicited a significantly greater blood pressure increase during exercise than rest, suggesting muscle blood flow restriction at this level of LBPP was sufficient to activate a muscle metabo-reflex. These findings suggest that the muscle metabo-reflex is not tonically active during dynamic exercise under normal conditions, but may instead require a critical reduction in muscle blood flow before it is activated.