Physiological adaptations and myocellular stress in short-term, high-frequency blood flow restriction training: A scoping review.

BACKGROUND: High frequency (1-2 times per day) low-intensity blood flow restriction (BFR) training has been recommended as a prescription approach for short durations of time to maximize relevant physiological adaptations. However, some studies demonstrate negative physiological changes after short periods of high-frequency BFR training, including prolonged strength decline and muscle fiber atrophy. OBJECTIVES: To provide a comprehensive overview of short-term, high-frequency blood flow restriction training, including main adaptations, myocellular stress, limitations in the literature, and future perspectives. METHODS: A systematic search of electronic databases (Scopus, PubMed®, and Web of Science) was performed from the earliest record to April 23, 2022. Two independent reviewers selected experimental studies that analyzed physical training protocols (aerobic or resistance) of high weekly frequency (>4 days/week) and short durations (≤3 weeks). RESULTS: In total, 22 studies were included in this review. The samples were composed exclusively of young predominantly male individuals. Muscle strength and hypertrophy were the main outcomes analyzed in the studies. In general, studies have demonstrated increases in strength and muscle size after short term (1-3 weeks), high-frequency low-intensity BFR training, non-failure, but not after control conditions (non-BFR; equalized training volume). Under failure conditions, some studies have demonstrated strength decline and muscle fiber atrophy after BFR conditions, accompanying increases in muscle damage markers. Significant limitations exist in the current HF-BFR literature due to large heterogeneities in methodologies. CONCLUSION: The synthesis presented indicates that short-term, high-frequency BFR training programs can generate significant neuromuscular adaptations. However, in resistance training to failure, strength declines and muscle fiber atrophy were reported. Currently, there are no studies analyzing low-frequency vs. high-frequency in short-term BFR training. Comparisons between resistance exercises of similar intensities (e.g., combined effort) are lacking, limiting conclusions on whether the effect is a product of proximity to failure or a specific effect of BFR.

Relationship of Biological Maturation with Muscle Power in Young Female Athletes.

There is still no consensus on how biological maturation (BM) affects the muscle power of upper and lower limbs in young people. The objective was to verify associations between BM and muscle power, as well as to compare the muscle power of upper (ULP) and lower limbs (LLP) among young athletes in different stages of BM. The sample consisted of 79 female athletes (10.9 ± 1.11 years old). Regarding BM, the sample was divided into three groups: delayed BM, synchronized BM, and accelerated BM. BM was identified by subtracting chronological age from bone age (BA). BA was measured by a mathematical model based on anthropometry. The muscular power of the upper limbs was analyzed by the medicine ball launch test, and that of the lower limbs was analyzed by the countermovement jump on a force platform. BM and BA correlated with ULP (BA: r =0.74; BM: r =0.65) and LLP (BA: r = 0.50; BM: r =0.41). In the comparisons of the tests of ULP and LLP, the groups with synchronized and accelerated BM were superior to the group with delayed BM. The advance of BM is associated with the ULP and LLP, as well as the advance of the BM affects muscle power in young female athletes. This occurs due to the increase in body mass resulting from the advancement of BM, which may favor the predominance of lean body mass, assisting in the production of muscle strength.

Comparison of Muscle Strength, Aerobic Capacity and Body Composition between Healthy Adolescents and Those Living with HIV: A Systematic Review and Meta-Analysis.

Background: The adverse effects of antiretroviral therapy associated with complications generated by human immunodeficiency virus (HIV) promote impairments in physical fitness in adolescents. Objective: To analyze the aerobic capacity, muscle strength, and body composition of adolescents living with HIV compared with a healthy population of the same age. Methods: Searches were performed in the MEDLINE, Embase, Web of Science, Scopus and SportDiscus databases until September 2019 and updated in April 2020. Eligibility Criteria: adolescents of both sexes in the age group from 10 to 19 years; living with HIV; cross-sectional, case-control, cohort studies; comparing with a healthy population. Mean differences and 95% Confidence intervals (CIs) were calculated using RevMan (software for systematic reviews). Results: Five articles were included, involving 197 adolescents living with HIV (16 to 18 years) and 185 without infection (13 to 18 years), with the sample in each study ranging from 15 to 65 adolescents. Aerobic capacity and muscle strength were reduced in adolescents with HIV, and body mass index was also significantly lower in this group. Conclusion: Adolescents living with HIV have impaired cardiorespiratory fitness, muscle strength, and body composition when compared to their uninfected peers. However, this systematic review provides limited evidence on the differences between the physical fitness outcomes of adolescents living with HIV compared to healthy adolescents.