Mikako Sakamaki-Sunaga

The ACTN3 R577X genotype is associated with muscle function in a Japanese population

Homozygosity for the common nonsense polymorphism R577X in the α-actinin-3 gene (ACTN3) causes complete α-actinin-3 deficiency in fast-twitch skeletal muscle fibers. This study investigated whether the ACTN3 R577X polymorphism affects fitness status using a battery of tests in a large Japanese cohort. In the present study, 1227 subjects (age: 25-85 years) were genotyped for the ACTN3 R577X polymorphism (rs1815739) using a TaqMan SNP genotyping assay (Applied Biosystems). All subjects were divided into 2 groups based on their age (<55 years and ≥55 years). All subjects completed a questionnaire about exercise habits and were subjected to a battery of tests to assess their fitness status (including grip strength test, chair stand test, and 8-foot walking test). A significant association between the ACTN3 R577X genotype and chair stand test performance was observed in the group of men ≥55 using ANCOVA adjusted for age and exercise habits (p = 0.036). The ACTN3 R577X genotype accounted for 2.5% of the variability in the results of the chair stand test among men in the ≥55 age group. Moreover, for the ≥55 age group, performance in the chair stand test was lower among those with the XX genotype than among those with the RR genotype (p = 0.024) or RX genotype (p = 0.005), unlike results for the <55 age group. No significant difference was noted for hand grip strength or 8-foot walking time. Thus, our results suggest that the ACTN3 R577X genotype is associated with lower-extremity muscle function in the Japanese population.

Association between ACTN3 R577X Polymorphism and Trunk Flexibility in 2 Different Cohorts

α-Actinin-3 (ACTN3) R577X polymorphism is associated with muscular strength and power. This study was performed to investigate the association between ACTN3 R577X polymorphisms and flexibility as another component of fitness in 2 cohorts. Cohort 1 consisted of 208 men and 568 women (ages 23-88), while Cohort 2 consisted of 529 men and 728 women (ages 23-87). All participants were recruited from the Tokyo metropolitan area and underwent a battery of tests to assess their grip strength and sit-and-reach flexibility. Genotyping results were analyzed for ACTN3 (rs1815739) polymorphism using the TaqMan approach. In Cohort 1, sit-and-reach in the RR genotype (35.3±0.7 cm) was significantly lower than those in the RX and XX genotypes (37.2±0.3 cm) even after adjusting for sex, age, and exercise habit as covariates (P<0.01). In Cohort 2, sit-and-reach tended to be lower in RR (38.1±0.6 cm) than in RX and XX (39.1±0.3 cm), but the differences were not significant (P=0.114). Analysis in pooled subjects indicated that RR was associated with significantly lower flexibility than RX and XX (P=0.009). The RR genotype of ACTN3 R577X in the general Japanese population showed lower flexibility compared to the RX and XX genotypes.

Effects of Menstrual Phase–dependent Resistance Training Frequency on Muscular Hypertrophy and Strength

Abstract Sakamaki-Sunaga, M, Min, S, Kamemoto, K, and Okamoto, T. Effects of menstrual phase–dependent resistance training frequency on muscular hypertrophy and strength. J Strength Cond Res 30(6): 1727–1734, 2016—The present study investigated how different training frequencies during menstrual phases affect muscle hypertrophy and strength. Fourteen eumenorrheic women performed 3 sets of arm curls (8–15 repetitions) until failure for 12 weeks. Depending on the menstrual cycle phase, each subject trained each arm separately after either a 3- or a 1-d·wk−1 training protocol during the follicular phase (FP-T) and a 3- or 1-d·wk−1 training protocol during the luteal phase (LP-T). Cross-sectional area (CSA), 1 repetition maximum, and maximum voluntary contraction significantly increased 6.2 ± 4.4, 36.4 ± 11.9, and 16.7 ± 5.6%, respectively (p ⩽ 0.05 vs. before training), in the FP-T group and 7.8 ± 4.2, 31.8 ± 14.1, and 14.9 ± 12.7%, respectively (p ⩽ 0.05 vs. before training), in the LP-T group. Changes in CSA between the FP-T and the LP-T groups significantly and positively correlated (r = 0.54, p ⩽ 0.05). There were no major differences among the different training protocols with regard to muscle hypertrophy and strength. Therefore, we suggest that variations in female hormones induced by the menstrual cycle phases do not significantly contribute to muscle hypertrophy and strength gains during 12 weeks of resistance training.

Acute effect of brisk walking with graduated compression stockings on vascular endothelial function and oxidative stress

The purpose of this study was to investigate the acute effect of brisk walking with and without graduated compression stockings (GCSs) on vascular endothelial function and oxidative stress. Ten young healthy subjects walked briskly for 30 min with (GCS trial) and without (CON trial) GCSs in a randomized crossover trial. Brachial artery flow‐mediated dilation (FMD) was measured as the per cent rise in the peak diameter from the baseline value at prior occlusion at each FMD measurement using B‐mode ultrasonography before and 30 min after walking in the two trials. Derivatives of reactive oxygen metabolites (d‐ROM), as an index of products of reactive oxygen species, and biological anti‐oxidant potential (BAP), as an index of anti‐oxidant potential, were also measured using a free radical elective evaluator before and 30 min after walking in both trials. FMD significantly decreased after brisk walking in both trials (P<0·05). However, FMD after brisk walking in the GCS trial was significantly higher than that in the CON trial (P<0·05). The d‐ROM did not change before and after both trials, whereas the BAP significantly increased after walking in the GCS trial (P<0·05). These findings demonstrate that brisk walking while wearing GCSs suppresses the decrease in FMD and increases BAP.

Effect of Resistance Exercise on Arterial Stiffness during the Follicular and Luteal Phases of the Menstrual Cycle

Acute high-intensity resistance exercise increases arterial stiffness. Changes in blood concentrations of estrogen and progesterone associated with the menstrual cycle affect the degree of arterial stiffness. Therefore, high-intensity resistance exercise may affect arterial stiffness differently depending on the phase of the menstrual cycle. The purpose of this study was to investigate the effects of different phases of the menstrual cycle on arterial stiffness after one session of resistance exercise. The participants were 9 eumenorrheic females (21.3±0.8 years). All participants performed 5 sets of 5 repetitions using 80% of the one repetition maximum (1RM) bench press and 5 sets of 10 repetitions using 70% of the 1RM biceps curl during both the follicular and luteal phases. Brachial-ankle pulse wave velocity (baPWV), blood pressure, and heart rate were measured before (baseline) and at 30 and 60 min after completing the resistance exercises. During the follicular phase, baPWV was significantly increased at 30 and 60 min after the resistance exercise compared with baseline (P<0.05), whereas during the luteal phase, no significant differences were observed after the resistance exercise. These results suggest that high-intensity resistance exercise affects arterial stiffness differently depending on the phase of the menstrual cycle.

Onset of blood lactate accumulation and peak oxygen uptake during graded walking test combined with and without restricted leg blood flow

The purpose of this study was to compare the peak oxygen uptake (VO2peak) and lactate threshold / onset of blood lactate accumulation (LT/OBLA) during an incremental exercise test with and without blood flow restriction (BFR). Six male subjects performed a graded walking test on a treadmill with and without BFR in random order, and oxygen uptake (VO2), minute ventilation (VE), and blood lactate concentration were measured during each test. During the BFR test, the subjects wore pressure cuff belts on the most proximal portion of each thigh. At a given workload (e.g. during walking at 100 m/min) VO2 was 17% higher in BFR than in free-flow. Exercise time to exhaustion during BFR was shorter compared with free-flow despite the ratings of perceived exertion being similar between both conditions. Peak heart rate did not reach same level in the BFR test as it did in free-flow, with the heart rate 5 beats lower with BFR. VO2peak and VE peak were also 17% and 9%, respectively, lower in BFR than in free-flow. Comp...

Acute Effect of Interval Walking on Arterial Stiffness in Healthy Young Adults

The purpose of this study was to determine the acute effects of interval walking (IW) on arterial stiffness. The participants in this study were 14 healthy men and women (age 27.5±3.8 y). Carotid-femoral pulse wave velocity (cfPWV) was measured using an automatic oscillometric device at 30 min before (baseline) and at 30 and 60 min after walking. Participants repeated five sets of 3-min walks at 30% and 70% of maximum aerobic capacity for a total of 6 min per set in the IW trial. The participants also walked for 30 min at 50% (moderate intensity) of maximum aerobic capacity in a continuous walking (CW) trial. cfPWV was significantly decreased from baseline at 30 min (P=0.02) after the IW trial, and this reduction in cfPWV persisted for 60 min (P=0.01). In contrast, cfPWV was significantly decreased from baseline at 30 min (P=0.03) after the CW trial, but the reduction did not persist for 60 min. Moreover, changes in cfPWV in the IW trial after 30 and 60 min were significantly lower than in the CW trial (P<0.05). These results suggest that IW acutely reduces central arterial stiffness more than CW in healthy young adults.