Impact of high versus low fixed loads and non-linear training loads on muscle hypertrophy, strength and force development.

BACKGROUND: In this study, we investigated the effects of resistance training protocols with different loads on muscle hypertrophy and strength. METHODS: Twenty-one participants were randomly assigned to 1 of 3 (n = 7 for each) resistance training (RT) protocols to failure: High load 80 % 1RM (8-12 repetitions) (H group), low load 30 % 1RM (30-40 repetitions) (L group) and a mixed RT protocol (M group) in which the participants switch from H to L every 2 weeks. RT consisted of three sets of unilateral preacher curls performed with the left arm 3 times/week with 90 s rest intervals between sets. The right arm served as control. Maximum voluntary contraction (MVC) of the elbow flexors (elbow angle: 90°) and rate of force development (RFD, 0-50, 50-100, 100-200 and 200-300 ms) were measured. Cross-sectional area (CSA) of the elbow flexors was measured via magnetic resonance imaging (MRI). All measurements were conducted before and after the 8 weeks of RT (72-96 h after the last RT). Statistical evaluations were performed with two-way repeated measures (time × group). RESULTS: After 8 weeks of 3 weekly RT sessions, significant increases in the left elbow flexor CSA [H: 9.1 ± 6.4 % (p = 0.001), L: 9.4 ± 5.3 % (p = 0.001), M: 8.8 ± 7.9 % (p = 0.001)] have been observed in each group, without significant differences between groups. Significant changes in elbow flexor isometric MVC have been observed in the H group (26.5 ± 27.0 %, p = 0.028), while no significant changes have been observed in the M (11.8 ± 36.4 %, p = 0.26) and L (4.6 ± 23.9 %, p = 0.65) groups. RFD significantly increased during the 50-100 ms phase in the H group only (p = 0.049). CONCLUSIONS: We conclude that, as long as RT is conducted to failure, training load might not affect muscle hypertrophy in young men. Nevertheless, strength and RFD changes seem to be load-dependent. Furthermore, a non-linear RT protocol switching loads every 2 weeks might not lead to superior muscle hypertrophy nor strength gains in comparison with straight RT protocols.

The Effect of High-Intensity Interval Cycling Sprints Subsequent to Arm-Curl Exercise on Upper-Body Muscle Strength and Hypertrophy.

Kikuchi, N, Yoshida, S, Okuyama, M, and Nakazato, K. The effect of high-intensity interval cycling sprints subsequent to arm-curl exercise on upper-body muscle strength and hypertrophy. J Strength Cond Res 30(8): 2318-2323, 2016-The purpose of this study was to examine whether lower limb sprint interval training (SIT) after arm resistance training (RT) influences training response of arm muscle strength and hypertrophy. Twenty men participated in this study. We divided subjects into RT group (n = 6) and concurrent training group (CT, n = 6). The RT program was designed to induce muscular hypertrophy (3 sets × 10 repetitions [reps] at 80% 1 repetition maximum [1RM] of arm-curl exercise) and was performed in an 8-week training schedule performed 3 times per week on nonconsecutive days. Subjects assigned to the CT group performed identical protocols as strength training and modified SIT (4 sets of 30-s maximal effort, separated in 4 m 30-s rest intervals) on the same day. Pretest and posttest maximal oxygen consumption (V[Combining Dot Above]O2max), muscle cross-sectional area (CSA), and 1RM were measured. Significant increase in V[Combining Dot Above]O2max from pretest to posttest was observed in the CT group (p = 0.010, effect size [ES] = 1.84) but not in the RT group (p = 0.559, ES = 0.35). Significant increase in CSA from pretest to posttest was observed in the RT group (p = 0.030, ES = 1.49) but not in the CT group (p = 0.110, ES = 1.01). Significant increase in 1RM from pretest to posttest was observed in the RT group (p = 0.021, ES = 1.57) but not in the CT group (p = 0.065, ES = 1.19). In conclusion, our data indicate that concurrent lower limb SIT interferes with arm muscle hypertrophy and strength.

Arterial stiffness after glucose ingestion in exercise-trained versus untrained men.

Postprandial hyperglycemia increases arterial stiffness. Arterial stiffness and insulin resistance are lower in exercise-trained humans than in untrained humans. However, the effect of exercise on arterial stiffness after glucose ingestion in young adults remains unknown. The present study investigates the effect of regular aerobic exercise on arterial stiffness after glucose ingestion in young males. Ten exercise-trained males (age, 20.8 ± 0.2 years; ETR) and 9 healthy untrained males (age, 22.2 ± 0.7 years; UTR) participated in this study. Carotid-femoral (aortic) pulse wave velocity (PWV), femoral-ankle (leg) PWV, carotid augmentation index (AIx) (applanation tonometry), brachial and ankle blood pressure (BP), heart rate (oscillometric device and electrocardiography), and blood glucose (glucose oxidase method) were measured at 30 min before (baseline) and 30, 60, and 120 min after a 75-g oral glucose tolerance test. Leg PWV at 30 min after glucose ingestion was significantly higher (P < 0.01) in the UTR group than in the ETR group. Ankle systolic BP at 30 min after glucose ingestion was also significantly higher in the UTR group than in the ETR group (P < 0.05). Blood glucose increased from baseline at 30 min (P < 0.01) and 60 min (P < 0.05) after glucose ingestion in both groups. Aortic PWV, carotid AIx, and brachial systolic BP did not change from baseline after glucose ingestion in both groups. The present findings indicate that leg PWV and ankle systolic BP after glucose ingestion were significantly lower in the ETR group than in the UTR group.

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.