bims-exemet 2021-04-11 papers

Issue of 2021–04–11
four papers selected by
Javier Botella Ruiz, Victoria University

Eur J Appl Physiol. 2021 Apr 08.

Molecular regulation of skeletal muscle mitochondrial biogenesis following blood flow-restricted aerobic exercise: a call to action.

Nicholas Preobrazenski, Hashim Islam, Brendon J Gurd.

Blood flow-restricted (BFR) exercise can induce training adaptations comparable to those observed following training in free flow conditions. However, little is known about the acute responses within skeletal muscle following BFR aerobic exercise (AE). Moreover, although preliminary evidence suggests chronic BFR AE may augment certain training adaptations in skeletal muscle mitochondria more than non-BFR AE, the underlying mechanisms are poorly understood. In this review, we summarise the acute BFR AE literature examining mitochondrial biogenic signalling pathways and provide insight into mechanisms linked to skeletal muscle remodelling following BFR AE. Specifically, we focus on signalling pathways potentially contributing to augmented peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) mRNA following work-rate-matched BFR AE compared with non-BFR AE. We present evidence suggesting reductions in muscle oxygenation during acute BFR AE lead to increased intracellular energetic stress, AMP-activated protein kinase (AMPK) activation and PGC-1α mRNA. In addition, we briefly discuss mitochondrial adaptations to BFR aerobic training, and we assess the risk of bias using the Cochrane Collaboration risk of bias assessment tool. We ultimately call for several straightforward modifications to help minimise bias in future BFR AE studies.

Keywords: AMPK; Aerobic exercise; BFR; Ischemic training; Mitochondria; Occlusion training; PGC-1α; Risk of bias

DOI: https://doi.org/10.1007/s00421-021-04669-6

J Sports Sci. 2021 Apr 07. 1-10

Interval training versus moderate-intensity continuous training for cardiorespiratory fitness improvements in middle-aged and older adults: a systematic review and meta-analysis.

Eric Tsz-Chun Poon, Waris Wongpipit, Robin Sze-Tak Ho, Stephen Heung-Sang Wong.

Interval training has been promoted as a superior, time-efficient exercise strategy for enhancing cardiorespiratory fitness in the ageing population. This study assessed the effectiveness of interval training compared with that of moderate-intensity continuous training (MICT) for improving cardiorespiratory fitness in middle-aged and older adults. Six databases were systematically searched for studies with exercise interventions (minimum 2-week duration). Meta-analyses were conducted for within-group and between-group comparisons of maximal oxygen uptake (VO2max). Sub-group analysis was performed using the nature of interval training (high-intensity interval training [HIIT] and sprint interval training [SIT]). Of 3,257 studies, 14 were included (429 participants). Within-group analyses demonstrated significant VO2max improvements (mL/kg/min) following interval training (mean difference: MD = 2.26; 95% confidence interval [CI] = 1.50-3.02) and MICT (MD = 1.34; 95% CI = 0.45-2.23]. When comparing the modes of training, the gain in VO2max was significantly greater following interval training (MD = 1.10; CI = 0.55-1.64). Sub-group analysis showed that HIIT (MD = 1.04; CI = 0.21-1.88) and SIT (MD = 1.18; CI = 0.60-1.76) resulted in superior VO2max gain than MICT. This study provides evidence synthesis for interval training as a viable exercise strategy to improve cardiorespiratory function in healthy ageing.

Keywords: HIIT; aerobic fitness; continuous exercise; interval exercise; public health

DOI: https://doi.org/10.1080/02640414.2021.1912453

Physiol Behav. 2021 Apr 03. pii: S0031-9384(21)00108-6. [Epub ahead of print] 113416

The impact of high intensity interval training on liver fat content in overweight or obese adults: a meta-analysis.

Mousa Khalafi, Michael E Symonds.

Liver fat is a marker of the metabolic derangements associated with obesity for which exercise training is a potential therapy. We therefore performed a systematic meta-analysis to investigate the effect of high intensity interval training (HIIT) on liver fat content in overweight or obese adults with metabolic disorders. PubMed, Scopus, Web of Science and the Cochrane were searched up to October 2020 for HIIT vs. Control (CON) or HIIT vs. moderate intensity interval training (MICT) studies on liver fat content in overweight and obese individuals with metabolic disorders. Standardized mean differences (SMD) and 95% confidence intervals (95% CIs) were calculated. Ten studies involving 333 participants were included in the meta-analysis. Based on studies that directly compared HIIT and CON (6 studies), HIIT was beneficial for promoting a reduction in liver fat [-0.51 (95 % CI: -0.85 to -0.17), p=0.003]. However, there were no significant evidence for an effect of HIIT on liver fat [-0.07 (95 % CI: -0.33 to 0.19), p=0.59], when compared with MICT (7 studies). These results suggest that a HIIT could induce improvements in liver fat of overweight and obese adults with metabolic disorders despite no weight loss.

Keywords: Exercise training; High intensity interval training; Liver fat; Metabolic disorder; Obesity

DOI: https://doi.org/10.1016/j.physbeh.2021.113416

Sci Rep. 2021 Apr 08. 11(1): 7733

Neuromuscular fatigue and recovery after strenuous exercise depends on skeletal muscle size and stem cell characteristics.

Philipp Baumert, S Temple, J M Stanley, M Cocks, J A Strauss, S O Shepherd, B Drust, M J Lake, C E Stewart, R M Erskine.

Hamstring muscle injury is highly prevalent in sports involving repeated maximal sprinting. Although neuromuscular fatigue is thought to be a risk factor, the mechanisms underlying the fatigue response to repeated maximal sprints are unclear. Here, we show that repeated maximal sprints induce neuromuscular fatigue accompanied with a prolonged strength loss in hamstring muscles. The immediate hamstring strength loss was linked to both central and peripheral fatigue, while prolonged strength loss was associated with indicators of muscle damage. The kinematic changes immediately after sprinting likely protected fatigued hamstrings from excess elongation stress, while larger hamstring muscle physiological cross-sectional area and lower myoblast:fibroblast ratio appeared to protect against fatigue/damage and improve muscle recovery within the first 48 h after sprinting. We have therefore identified novel mechanisms that likely regulate the fatigue/damage response and initial recovery following repeated maximal sprinting in humans.

DOI: https://doi.org/10.1038/s41598-021-87195-x