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Previous research has suggested that concurrent training (CT) may attenuate resistance training (RT)-induced gains in muscle strength and mass, i.e.‚ the interference effect. In 2000, a seminal theoretical model indicated that the interference effect should occur when high-intensity interval training (HIIT) (repeated bouts at 95–100% of the aerobic power) and RT (multiple sets at ~ 10 repetition maximum;10 RM) were performed in the same training routine. However, there was a paucity of data regarding the likelihood of other HIIT-based CT protocols to induce the interference effect at the time. Thus, based on current HIIT-based CT literature and HIIT nomenclature and framework, the present manuscript updates the theoretical model of the interference phenomenon previously proposed. We suggest that very intense HIIT protocols [i.e., resisted sprint training (RST), and sprint interval training (SIT)] can greatly minimize the odds of occurring the interference effect on muscle strength and mass. Thus, very intensive HIIT protocols should be implemented when performing CT to avoid the interference effect. Long and short HIIT-based CT protocols may induce the interference effect on muscle strength when HIIT bout is performed before RT with no rest interval between them. [ABSTRACT FROM AUTHOR]

The aim of this short communication was to compare the individual muscle mass and strength gains with high (HF) vs. low (LF) resistance training (RT) frequencies using data from our previous study. We used a within-subject design in which 20 subjects had one leg randomly assigned to HF (5 x per week) and the other to LF (2 or 3 x per week). Muscle cross-sectional area and 1 repetition maximum were assessed at baseline and after 8 weeks of RT. HF showed a higher 8-week accumulated total training volume (TTV) (p < 0.0001) compared with LF. Muscle cross-sectional area and 1 repetition maximum values increased significantly and similarly for HF and LF protocols (p > 0.05). This short communication highlights that some individuals showed greater muscle mass and strength gains after HF (31.6 and 26.3% of individuals, respectively), other had greater gains with LF (36.8 and 15.8% of individuals, respectively), and even others showed similar responses between HF and LF, regardless of the consequent higher or lower TTV resulted from HF and LF, respectively. Importantly, individual manipulation of RT frequency can improve the intrasubject responsiveness to training, but the effect is limited to each individual's capacity to respond to RT. Finally, individual response to different frequencies and resulted TTV does not necessarily agree between muscle hypertrophy and strength gains. [ABSTRACT FROM AUTHOR]

We aimed to investigate the mechanisms underlying muscle growth after 12 weeks of resistance training performed with blood flow restriction (RT–BFR) and high-intensity resistance training (HRT) in older individuals. Participants were allocated into the following groups: HRT, RT–BFR, or a control group. High-throughput transcriptome sequencing was performed by the Illumina HiSeq 2500 platform. HRT and RT–BFR presented similar increases in the quadriceps femoris cross-sectional area, and few genes were differently expressed between interventions. The small differences in gene expression between interventions suggest that similar mechanisms may underpin training-induced muscle growth. [ABSTRACT FROM AUTHOR]

Background: Gene expression is an important process underpinning the acute and chronic adaptive response to resistance exercise (RE) training.Purpose: To investigate the effect of training status on vastus lateralis muscle global transcriptome at rest and following acute RE.Methods: Muscle biopsies of nine young men (age: 26(2) years; body mass: 69(9) kg; height 172(6) cm) who undertook RE training for 10 weeks were collected pre and 24 h post-RE in the untrained (W1) and trained (W10) states and analysed using microarray. Tests of differential expression were conducted for rested and after RE contrasts in both training states. To control for false discovery rate (FDR), multiple testing correction was performed at a cut-off of FDR < 0.05.Results: Unaccustomed RE (at W1) upregulated muscle gene transcripts related to stress (e.g., heat shock proteins), damage and inflammation, structural remodelling, protein turnover and increased translational capacity. Trained muscles (at W10) showed changes in the transcriptome signature regarding the regulation of energy metabolism, favouring a more oxidative one, upregulated antioxidant- and immune-related genes/terms, and gene transcripts related to the cytoskeleton and extracellular matrix, muscle contraction, development and growth.Conclusions: These results highlight that chronic repetition of RE changes muscle transcriptome response towards a more refined response to RE-induced stress. [ABSTRACT FROM AUTHOR]

Supplemental digital content is available in the text. Introduction: The myonuclear domain theory postulates that myonuclei are added to muscle fibers when increases in fiber cross-sectional area (i.e., hypertrophy) are ≥26%. However, recent studies have reported increased myonuclear content with lower levels (e.g., 12%) of muscle fiber hypertrophy. Purpose: This study aimed to determine whether a muscle fiber hypertrophy “threshold” is required to drive the addition of new myonuclei to existing muscle fibers. Methods: Studies of resistance training endurance training with or without nutrient (i.e., protein) supplementation and steroid administration with measures of muscle fiber hypertrophy and myonuclei number as primary or secondary outcomes were considered. Twenty-seven studies incorporating 62 treatment groups and 903 subjects fulfilled the inclusion criteria and were included in the analyses. Results: Muscle fiber hypertrophy of ≤10% induces increases in myonuclear content, although a significantly higher number of myonuclei are observed when muscle hypertrophy is ~22%. Additional analyses showed that age, sex, and muscle fiber type do not influence muscle fiber hypertrophy or myonuclei addition. Conclusions: Although a more consistent myonuclei addition occurs when muscle fiber hypertrophy is >22%, our results challenge the concept of a muscle hypertrophy threshold as significant myonuclei addition occurs with lower muscle hypertrophy (i.e., <10%). [ABSTRACT FROM AUTHOR]

Purpose: Androgen receptor (AR) expression and signaling have been regarded as a mechanism for regulating muscle hypertrophy. However, little is known about the associations between acute and chronic changes in skeletal muscle total AR, cytoplasmic AR (cAR), nuclear AR (nAR), and AR DNA-binding (AR-DNA) induced by resistance training (RT) and hypertrophy outcomes in women and men. This study aimed to investigate the acute and chronic effects of RT on skeletal muscle total AR, cAR, and nAR contents and AR-DNA in women and men. In addition, we investigated whether these acute and chronic changes in these markers were associated with muscle hypertrophy in both sexes. Methods: Nineteen women and 19 men underwent 10 wk of RT. Muscle biopsies were performed at baseline, 24 h after the first RT session, and 96 h after the last session. AR, cAR, and nAR were analyzed using Western blotting, and AR-DNA using an ELISAoligonucleotide assay. Fiber cross-sectional area (fCSA) was analyzed through immunohistochemistry and muscle cross-sectional area (mCSA) by ultrasound. Results: At baseline, men demonstrated greater nAR than women. Baseline cAR was significantly associated with type II fCSA hypertrophy in men. Acutely, both sexes decreased AR and cAR, whereas men demonstrated greater decreases in nAR. After 10 wk of RT, AR, and nAR remained unchanged, men demonstrated greater cAR compared with women, and both sexes decreased ARDNA activity. Acute and chronic changes in AR markers did not correlate with muscle hypertrophy (type I/II fCSA and mCSA) in women or men. Conclusions: Baseline cAR content may influence hypertrophy in men, whereas neither RT-induced acute nor chronic changes in AR, cAR, nAR, and AR-DNA are associated with muscle hypertrophy in women or men. [ABSTRACT FROM AUTHOR]

While performing aerobic exercise during chemotherapy has been proven feasible and safe, the efficacy of aerobic training on cardiorespiratory fitness (CRF) in women with breast cancer undergoing chemotherapy has not yet been systematically assessed. Therefore, the objective of this work was to determine (a) the efficacy of aerobic training to improve CRF; (b) the role of aerobic training intensity (moderate or vigorous) on CRF response; (c) the effect of the aerobic training mode (continuous or interval) on changes in CRF in women with breast cancer (BC) receiving chemotherapy. A systematic review and meta-analysis were conducted as per PRISMA guidelines, and randomized controlled trials comparing usual care (UC) and aerobic training in women with BC undergoing chemotherapy were eligible. The results suggest that increases in CRF are favored by (a) aerobic training when compared to usual care; (b) vigorous-intensity aerobic exercise (64–90% of maximal oxygen uptake, VO2max) when compared to moderate-intensity aerobic exercise (46–63% of VO2max); and (c) both continuous and interval aerobic training are effective at increasing the VO2max. Aerobic training improves CRF in women with BC undergoing chemotherapy. Notably, training intensity significantly impacts the VO2max response. Where appropriate, vigorous intensity aerobic training should be considered for women with BC receiving chemotherapy. [ABSTRACT FROM AUTHOR]