Kazumichi Kurobe

Effects of resistance training under hypoxic conditions on muscle hypertrophy and strength

It has been reported that exercise under hypoxic conditions elevates acute growth hormone secretion after exercise compared with that under normoxic conditions. This study examined the influence of resistance training under moderate hypoxic conditions on muscle thickness, strength and hormonal responses. Thirteen healthy men were assigned into two groups matched for physical fitness level and then randomized into two groups that performed exercise under normoxic (FiO2 = 20·9%) or hypoxic (FiO2 = 12·7%) conditions. Three sets of elbow extensions with unilateral arm were performed to exhaustion at a workload of a 10 repetition maximum with 1‐minute intervals for 3 days per week for 8 weeks. The thickness of the biceps and triceps brachii was determined using B‐mode ultrasound before and after training. Blood sampling was carried out before and after exercise, as well as during the first and last training sessions. Increase in the thickness of the triceps brachii in trained arm was significantly greater in the hypoxic group than in the normoxic group. The 10 repetition maximum was significantly increased not only in the trained arm but also in the untrained arm in both groups. Serum growth hormone concentrations after exercise were significantly higher in the hypoxic group than in the normoxic group on both the first and last training sessions. These findings suggest that hypoxic resistance training elicits more muscle hypertrophy associated with a higher growth hormone secretion, but that the greater muscle hypertrophy did not necessarily contribute a greater gain of muscle strength.

Sex Differences in Flexibility-Arterial Stiffness Relationship and Its Application for Diagnosis of Arterial Stiffening: A Cross-Sectional Observational Study

Purpose Arterial stiffness might be related to trunk flexibility in middle-aged and older participants, but it is also affected by age, sex, and blood pressure. This cross-sectional observational study investigated whether trunk flexibility is related to arterial stiffness after considering the major confounding factors of age, sex, and blood pressure. We further investigated whether a simple diagnostic test of flexibility could be helpful to screen for increased arterial stiffening. Methods According to age and sex, we assigned 1150 adults (male, n = 536; female, n = 614; age, 18–89 y) to groups with either high- or poor-flexibility based on the sit-and-reach test. Arterial stiffness was assessed by cardio-ankle vascular index. Results In all categories of men and in older women, arterial stiffness was higher in poor-flexibility than in high-flexibility (P<0.05). This difference remained significant after normalizing arterial stiffness for confounding factors such as blood pressure, but it was not found among young and middle-aged women. Stepwise multiple-regression analysis also supported the notion of the sex differences in flexibility-arterial stiffness relationship. Receiver operating characteristic curve analysis revealed that cut-off values for sit-and-reach among men and women were 33.2 (area under the curve [AUC], 0.711; 95% confidence interval [CI], 0.666–0.756; sensitivity, 61.7%; specificity, 69.7%) and 39.2 (AUC, 0.639; 95% CI, 0.592–0.686; sensitivity, 61.1%; specificity, 62.0%) cm, respectively. Conclusion Our results indicate that flexibility-arterial stiffness relationship is not affected by BP, which is a major confounding factor. In addition, sex differences are observed in this relationship; poor trunk flexibility increases arterial stiffness in young, middle-aged, and older men, whereas the relationship in women is found only in the elderly. Also, the sit-and-reach test can offer a simple method of predicting arterial stiffness at home or elsewhere.

Cardiovascular drift during low intensity exercise with leg blood flow restriction.

Previous studies reported that aerobic-type exercise such as walking or cycling with blood flow restriction (BFR) has been shown to elicit increases in leg muscle hypertrophy and strength, as well as improved aerobic capacity. Although previous studies investigated cardiovascular responses during a relatively short duration of exercise (∼5 min), the effects of prolonged leg muscular BFR have remained unknown. The purpose of this study was to examine the cardiovascular effects of longer duration low intensity exercise combined with BFR. Eight men performed 30 min of exercise at 40% of a predetermined maximal oxygen uptake under both BFR and normal flow (CON) conditions. Cardiovascular parameters were measured at rest and every 10 min during exercise. The main findings were that 1) the SV and HR did not change significantly between 10 to 30 min of exercise in BFR and CON conditions, although BFR-induced reduction of SV and increased HR were found at 10 min exercise compared with normal flow, 2) blood pressure was increased at 10 min of exercise in BFR compared to the CON, however the blood pressure decreased gradually with BFR from 10 to 30 min of exercise, and 3) blood lactate and RPE increased gradually during exercise with BFR. In conclusion, our results suggest that the BFR-induced reduction of SV and increased HR within the first 10 min of exercise are representative of changes in these parameters.

Augmented Carbohydrate Oxidation under Moderate Hypobaric Hypoxia Equivalent to Simulated Altitude of 2500 m

Hypoxia itself stimulates glucose uptake mediated by a mechanism independent of insulin. However, whether moderate hypoxia causes similar metabolic effect in humans remains unclear. The present study aimed to determine glycemic regulation following glucose load at a simulated moderate altitude of 2,500 m. Eight healthy young males (mean ± standard error: 24 ± 1 years; 171.3 ± 1.6 cm; 66.9 ± 3.7 kg; 22.8 ± 1.0 kg/m(2)) consumed 75 g of glucose solution under either hypobaric condition (560 mmHg) or normobaric condition (745 mmHg). In the hypobaric chamber, the oxygen partial pressure is proportionally reduced with a reduction of atmospheric pressure, consequently leading to the hypoxic condition. Plasma glucose and serum insulin concentrations increased significantly following glucose load in both conditions (P < 0.05). However, no significant interaction (condition × time) or main effect for condition was observed. There were no significant differences in serum glycerol, plasma epinephrine, or plasma norepinephrine concentrations between the two conditions. No significant differences between the conditions were observed in changes in VO2 or VCO2. However, the hypobaric condition showed significantly higher respiratory exchange ratio (VCO2/VO2) at 90 and 120 min following glucose load (P < 0.05 vs. normobaric condition), suggesting that carbohydrate oxidation following glucose load was enhanced in moderate hypobaric hypoxia. In conclusion, acute exposure to moderate hypobaric hypoxia significantly augmented carbohydrate oxidation following the glucose load, without affecting glucose or insulin responses. Thus, a short-time exposure to moderate hypobaric hypoxia may be beneficial for people with impaired glucose tolerance.

A pilot lifestyle intervention study: Effects of an intervention using an activity monitor and Twitter on physical activity and body composition

BACKGROUND This pilot study aimed to examine the effects of a lifestyle intervention comprising an activity monitor and the concurrent use of Twitter, on physical activity (PA) and body composition. METHODS Seventeen healthy volunteers (36±3 years) were randomly assigned to normal (N, N.=8) or Twitter (T, N.=9) intervention groups for six weeks. Participants in both groups wore an activity monitor but those in the T group also tweeted daily about their PA. An observer read the tweets from each participant and provided feedback. Body composition was determined using bioelectrical impedance analysis before and after the intervention. RESULTS Significantly more daily steps and PA at an intensity of ≥3 metabolic equivalents (METs) were recorded by the T than the N during six weeks. The number of steps and PA did not significantly change over time in the N, but significantly increased in the T from weeks one to six (8170±1130 to 12,934±1400 steps/day and 2.6±0.5 to 5.0±0.8 METs·h/day). In addition, significantly more body fat was lost in the T, than in the N (-1.1±0.2 vs. -0.1±0.3 kg), and the changes in PA significantly correlated with the changes in body fat (r=-0.713). CONCLUSIONS Lifestyle intervention can increase daily PA and reduce body fat more effectively when using an activity monitor and Twitter than an activity monitor alone.

Effects of intermittent hypobaric hypoxic exercise for four weeks on cardiovascular responses

The present study examined the effects of intermittent hypobaric hypoxic exercise over a period of four weeks on cardiovascular adaptations. Twenty-four healthy male adults (age, 24 ± 3 yrs) who were matched for physical fitness levels were randomized into two groups, and was adjusted to be either normobaric normoxic (N; n = 12) or hypobaric hypoxic (H; n = 12). Both groups performed aquatic activities at an intensity of about 50% VO_2max for 30min/session, four days per week for four weeks in a pool within a chamber where the atmospheric pressure can be regulated. The H group exercised under hypobaric conditions corresponding to 2,000m above sea level, and were exposed for a total of 2.5h/session. Before and after experimental period, VO_2max and cardiovascular responses such as heart rate (HR), stroke volume (SV), cardiac output (CO), as well as systolic (SBP), diastolic (DBP), and mean blood pressure (MBP) were measured during cycling on an ergometer at an intensity of 50% VO_2max. Flowmediated vasodilation (FMD) was also evaluated by measuring changes in the diameter of the popliteal artery between rest and during reactive hyperemia. The VO_2max was not significantly changed after the four-week exercise period in both groups and changes in cardiovascular responses during moderate exercise were not evident in the N group. On the other hand, SV and CO were significantly increased (P＜0.05) in the H group, whereas DBP and MBP as well as the calculated TPR (MBP/CO) were significantly decreased (P＜0.05 for all). The FMD was significantly increased only in the H group (P＜0.05). These findings indicated that exercise under hypobaric hypoxic conditions could induce more beneficial cardiovascular adaptations in healthy male adults such as reductions in TPR and BP with an increase in FMD compared with exercise under normal conditions.

Metabolic responses to exercise on land and in water following glucose ingestion

Although aerobic exercise after a meal decreases postprandial blood glucose, the differences in glucose response between land and aquatic exercise are unclear. Thus, we examined the effect of different modes of exercise with same energy expenditure following glucose ingestion on carbohydrate metabolism. Ten healthy sedentary men (age, 22 ± 1 years) participated in this study. All subjects performed each of three exercise modes (cycling, walking and aquatic exercise) for 30 min after ingestion of a 75‐g glucose solution with 1–2 weeks between trials. The exercise intensity was set at 40% of the maximum oxygen uptake that occurred during cycling. The velocity during walking and the target heart rate during aquatic exercise were predetermined in a pretest. The plasma glucose concentration at 30 min after exercise was significantly lower with aquatic exercise compared to that with cycling and walking (P<0·05). However, there were no significant differences among the three exercise modes in respiratory exchange ratio. On the other hand, serum free fatty acid concentration with aquatic exercise was significantly higher at 120 min after exercise compared with that after walking (P<0·05). These results suggest that aquatic exercise reduces postprandial blood glucose compared with both cycling and walking with the same energy expenditure. Aquatic exercise shows potential as an exercise prescription to prevent postprandial hyperglycaemia.

Combined effect of coffee ingestion and repeated bouts of low-intensity exercise on fat oxidation.

We investigated the effect of the combination of coffee ingestion and repeated bouts of low‐intensity exercise on fat oxidation. Subjects were seven young, healthy male adults. They performed four trials: a single 30‐min bout of exercise following ingestion of plain hot water (WS) or coffee (CS); a trial with three 10‐min bouts of exercise separated by 10‐min periods of rest following ingestion of plain hot water (WR) or coffee (CR). The coffee contained 5 mg kg−1 of caffeine. All trials were performed on a cycle ergometer at 40% maximal oxygen uptake for each subject an hour after beverage ingestion. Oxygen uptake in the CS and CR trials was higher compared with the WS and WR trials at 90 min after exercise (P<0·05). Respiratory exchange ratio (RER) in the CS and CR trials was decreased during the whole recovery period compared with baseline (P<0·05), whereas no significant decreases were observed in either the WS or WR trials. Moreover, RER was significantly lower at 30 min after exercise in the CR trial than in either the WS or WR trials (P<0·05 each). Similarly, it is notable that fat oxidation rate in the CR trial was significantly higher at 30 min after exercise compared to that in the WS and WR trials (P<0·05). These results suggest that the combination of coffee intake and repeated bouts of low‐intensity exercise enhances fat oxidation in the period after exercise.

Intra-abdominal pressure during swimming

The present study aimed to determine the intra-abdominal pressure during front crawl swimming at different velocities in competitive swimmers and to clarify the relationships between stroke indices and changes in intra-abdominal pressure. The subjects were 7 highly trained competitive collegiate male swimmers. Intra-abdominal pressure was measured during front crawl swimming at 1.0, 1.2 and 1.4 m · s(-1) and during the Valsalva maneuver. Intra-abdominal pressure was taken as the difference between minimum and maximum values, and the mean of 6 stable front crawl stroke cycles was used. Stroke rate and stroke length were also measured as stroke indices. There were significant differences in stroke rate among all velocities (P < 0.05). However, there was no significant difference in stroke length by velocity. Significant within-subject correlations between intra-abdominal pressure and stroke rate or stroke length (P < 0.01) were observed, although there were no significant correlations between intra-abdominal pressure and stroke indices when controlling for swimming velocity. These findings do not appear to support the effectiveness of trunk training performed by competitive swimmers aimed at increasing intra-abdominal pressure.