In the wake of the COVID-19 pandemic, social restrictions to contain the spread of the virus have disrupted behaviors across the 24-h day including physical activity, sedentary behavior, and sleep among children (5–12 years old) and adolescents (13–17 years old). Preliminary evidence reports significant decreases in physical activity, increases in sedentary behavior, and disrupted sleep schedules/sleep quality in children and adolescents. This commentary discusses the impact of COVID-19-related restrictions on behaviors across the 24-h day in children and adolescents. Furthermore, we suggest recommendations through the lens of a socio-ecological model to provide strategies for lasting behavior change to insure the health and well-being of children and adolescents during the COVID-19 pandemic.

The purpose of this study was to examine the relative importance of physiological characteristics during firefighting performance, as assessed by the Candidate Physical Ability Test (CPAT). Participants included professional and volunteer firefighters, ages 18-39 (n=33). Muscle strength, muscle endurance, muscle power, body composition, aerobic capacity, anaerobic fitness, and the cardiovascular response to stairclimbing were assessed to determine the physiological characteristics of the participants. To quantify firefighting performance, the CPAT was administered by members of the fire service.Absolute and relative mean power during Wingate anaerobic cycling test (WAnT), relative peak power during WAnT, and absolute maximal oxygen uptake (VO 2 max) were significantly higher in those who passed the CPAT (n=18), compared to those who failed (n=15) (P < 0.01). Absolute and relative mean power during WAnT, fatigue index during WAnT, absolute VO 2 max, upper body strength, and the heart rate response to stairclimbing were all significantly related to CPAT performance time (all P < 0.01).However, absolute VO 2 max and anaerobic fatigue resistance during WAnT combined were the best predictors of total CPAT performance (Adj. R 2 = 0.817; P < 0.001).

The ability of skeletal muscles to produce force at a high velocity, which is crucial for success in power and sprint performance, is strongly influenced by genetics and without the appropriate genetic make-up, an individual reduces his/her chances of becoming an exceptional power or sprinter athlete. Several genetic variants (i.e. polymorphisms) have been associated with elite power and sprint performance in the last few years and the current paradigm is that elite performance is a polygenic trait, with minor contributions of each variant to the unique athletic phenotype. The purpose of this review is to summarize the specific knowledge in the field of genetics and elite power performance, and to provide some future directions for research in this field. Of the polymorphisms associated with elite power and sprint performance, the α-actinin-3 R577X polymorphism provides the most consistent results. ACTN3 is the only gene that shows a genotype and performance association across multiple cohorts of elite power athletes, and this association is strongly supported by mechanistic data from an Actn3 knockout mouse model. The angiotensin-1 converting enzyme insertion/deletion polymorphism (ACE I/D, registered single nucleotide polymorphism [rs]4646994), angiotensinogen (AGT Met235Thr rs699), skeletal adenosine monophosphate deaminase (AMPD1) Gln(Q)12Ter(X) [also termed C34T, rs17602729], interleukin-6 (IL-6 -174 G/C, rs1800795), endothelial nitric oxide synthase 3 (NOS3 -786 T/C, rs2070744; and Glu298Asp, rs1799983), peroxisome proliferator-activated receptor-α (PPARA Intron 7 G/C, rs4253778), and mitochondrial uncoupling protein 2 (UCP2 Ala55Val, rs660339) polymorphisms have also been associated with elite power performance, but the findings are less consistent. In general, research into the genetics of athletic performance is limited by a small sample size in individual studies and the heterogeneity of study samples, often including athletes from multiple-difference sporting disciplines. In the future, large, homogeneous, strictly defined elite power athlete cohorts need to be established though multinational collaboration, so that meaningful genome-wide association studies can be performed. Such an approach would provide unbiased identification of potential genes that influence elite athletic performance.

We determined the effects of cold water immersion (CWI) on long-term adaptations and post-exercise molecular responses in skeletal muscle before and after resistance training. Sixteen men (22.9 ± 4.6 y; 85.1 ± 17.9 kg; mean ± SD) performed resistance training (3 day/wk) for 7 wk, with each session followed by either CWI [15 min at 10°C, CWI (COLD) group, n = 8] or passive recovery (15 min at 23°C, control group, n = 8). Exercise performance [one-repetition maximum (1-RM) leg press and bench press, countermovement jump, squat jump, and ballistic push-up], body composition (dual X-ray absorptiometry), and post-exercise (i.e., +1 and +48 h) molecular responses were assessed before and after training. Improvements in 1-RM leg press were similar between groups [130 ± 69 kg, pooled effect size (ES): 1.53 ± 90% confidence interval (CI) 0.49], whereas increases in type II muscle fiber cross-sectional area were attenuated with CWI (−1,959 ± 1,675 µM2 ; ES: −1.37 ± 0.99). Post-exercise mechanistic target of rapamycin complex 1 signaling (rps6 phosphorylation) was blunted for COLD at post-training (POST) +1 h (−0.4-fold, ES: −0.69 ± 0.86) and POST +48 h (−0.2-fold, ES: −1.33 ± 0.82), whereas basal protein degradation markers (FOX-O1 protein content) were increased (1.3-fold, ES: 2.17 ± 2.22). Training-induced increases in heat shock protein (HSP) 27 protein content were attenuated for COLD (−0.8-fold, ES: −0.94 ± 0.82), which also reduced total HSP72 protein content (−0.7-fold, ES: −0.79 ± 0.57). CWI blunted resistance training-induced muscle fiber hypertrophy, but not maximal strength, potentially via reduced skeletal muscle protein anabolism and increased catabolism. Post-exercise CWI should therefore be avoided if muscle hypertrophy is desired. NEW & NOTEWORTHY This study adds to existing evidence that post-exercise cold water immersion attenuates muscle fiber growth with resistance training, which is potentially mediated by attenuated post-exercise increases in markers of skeletal muscle anabolism coupled with increased catabolism and suggests that blunted muscle fiber growth with cold water immersion does not necessarily translate to impaired strength development.

We determined the effect of concurrent training incorporating either high-intensity interval training (HIT) or moderate-intensity continuous training (MICT) on maximal strength, counter-movement jump (CMJ) performance, and body composition adaptations, compared with single-mode resistance training (RT). Twenty-three recreationally-active males (mean ± SD: age, 29.6 ± 5.5 y; trueV˙O2peak, 44 ± 11 mL kg−1·min−1) underwent 8 weeks (3 sessions·wk−1) of either: (1) HIT combined with RT (HIT+RT group, n = 8), (2) work-matched MICT combined with RT (MICT+RT group, n = 7), or (3) RT performed alone (RT group, n = 8). Measures of aerobic capacity, maximal (1-RM) strength, CMJ performance and body composition (DXA) were obtained before (PRE), mid-way (MID), and after (POST) training. Maximal (one-repetition maximum [1-RM]) leg press strength was improved from PRE to POST for RT (mean change ± 90% confidence interval; 38.5 ± 8.5%; effect size [ES] ± 90% confidence interval; 1.26 ± 0.24; P < 0.001), HIT+RT (28.7 ± 5.3%; ES, 1.17 ± 0.19; P < 0.001), and MICT+RT (27.5 ± 4.6%, ES, 0.81 ± 0.12; P < 0.001); however, the magnitude of this change was greater for RT vs. both HIT+RT (7.4 ± 8.7%; ES, 0.40 ± 0.40) and MICT+RT (8.2 ± 9.9%; ES, 0.60 ± 0.45). There were no substantial between-group differences in 1-RM bench press strength gain. RT induced greater changes in peak CMJ force vs. HIT+RT (6.8 ± 4.5%; ES, 0.41 ± 0.28) and MICT+RT (9.9 ± 11.2%; ES, 0.54 ± 0.65), and greater improvements in maximal CMJ rate of force development (RFD) vs. HIT+RT (24.1 ± 26.1%; ES, 0.72 ± 0.88). Lower-body lean mass was similarly increased for RT (4.1 ± 2.0%; ES; 0.33 ± 0.16; P = 0.023) and MICT+RT (3.6 ± 2.4%; ES; 0.45 ± 0.30; P = 0.052); however, this change was attenuated for HIT+RT (1.8 ± 1.6%; ES; 0.13 ± 0.12; P = 0.069). We conclude that concurrent training incorporating either HIT or work-matched MICT similarly attenuates improvements in maximal lower-body strength and indices of CMJ performance compared with RT performed alone. This suggests endurance training intensity is not a critical mediator of interference to maximal strength gain during short-term concurrent training.

Strength training (ST) has long been considered a promising intervention for reversing the loss of muscle function and the deterioration of muscle structure associated with advanced age but, until recently, the evidence was insufficient to support its role in the prevention or treatment of disease. In recent decades, there has been a long list of quality reviews examining the effects of ST on functional abilities and a few on risk factors for specific diseases, but none have provided a comprehensive assessment of ST as an intervention for a broad range of diseases. This review provides an overview of research addressing the effectiveness of ST as an intervention for the prevention or treatment of the adverse consequences of (i) aging muscle; (ii) the metabolic syndrome (MetS) and its components, i.e. insulin resistance, abdominal obesity, hyperlipidaemia and hypertension; (iii) fibromyalgia; (iv) rheumatoid arthritis; and (v) Alzheimer's disease. Collectively, these studies indicate that ST may serve as an effective countermeasure to some of the adverse consequences of the MetS, fibromyalgia and rheumatoid arthritis. Evidence in support of the hypothesis that ST reduces insulin resistance or improves insulin action comes both from indirect biomarkers, such as glycosylated haemoglobin (HbA(1c)), and insulin responses to oral glucose tolerance tests, as well as from more direct procedures such as hyperglycaemic and hyperinsulinaemic-euglycaemic clamp techniques. The evidence for the use of ST as a countermeasure of abdominal obesity is less convincing. Although some reports show statistically significant reductions in visceral fat, it is unclear if the magnitude of these changes are physiologically meaningful and if they are independent of dietary influences. The efficacy of ST as an intervention for reducing dyslipidaemia is at best inconsistent, particularly when compared with other pharmacological and non-pharmacological interventions, such as aerobic exercise training. However, there is more consistent evidence for the effectiveness of ST in reducing triglyceride levels. This finding could have clinical significance, given that elevated triglyceride is one of the five criterion measures for the diagnosis of the MetS. Small to moderate reductions in resting and exercise blood pressure have been reported with some indication that this effect may be genotype dependent. ST improves or reverses some of the adverse effects of fibromyalgia and rheumatoid arthritis, particularly pain, inflammation, muscle weakness and fatigue. Investigations are needed to determine how these effects compare with those elicited from aerobic exercise training and/or standard treatments. There is no evidence that ST can reverse any of the major biological or behavioural outcomes of Alzheimer's disease, but there is evidence that the prevalence of this disease is inversely associated with muscle mass and strength. Some indicators of cognitive function may also improve with ST. Thus, ST is an effective countermeasure for some of the adverse...

Purpose-Previous studies have linked an insertion/deletion polymorphism in the angiotensinconverting enzyme (ACE) gene with variability in muscle strength responses to strength training (ST), though conclusions have been inconsistent across investigations. Moreover, most previous studies have not investigated the influence of sex on the association of ACE I/D genotype with muscle phenotypes. The purpose of this study was to investigate the association of ACE genotype with muscle phenotypes before and after ST in older men and women.Methods-Eighty-six inactive men and 139 inactive women, ages 50-85 yr (mean: 62 yr), were studied before and after 10 wk of unilateral knee extensor ST. The one-repetition maximum (1RM) test was used to assess knee extensor muscle strength, and computed tomography was used to measure quadriceps muscle volume (MV). Differences were compared among ACE genotype groups (II vs ID vs DD).Results-Across the entire cohort at baseline, ACE genotype was significantly associated with total lean mass and body weight, with higher values in DD genotype carriers (both P < 0.05). At baseline, DD genotype carriers exhibited significantly greater MV compared with II genotype carriers for both the trained leg (men: 1828 ± 44 vs 1629 ± 70; women: 1299 ± 34 vs 1233 ± 49; P = 0.02) and untrained leg (men: 1801 ± 46 vs 1559 ± 72; women: 1268 ± 36 vs 1189 ± 51; P = 0.01), with no significant genotype × sex interaction. No ACE genotype associations were observed for the 1RM or MV adaptations to ST in either men or women.Conclusions-In the present study, ACE genotype was associated with baseline differences in muscle volume, but it was not associated with the muscle hypertrophic response to ST. Keywords ANGIOTENSIN-CONVERTING ENZYME; GENETICS; MUSCLE MASS; MUSCLE SIZE; SKELETAL MUSCLEMuscle strength and mass are heritable phenotypes, with a heritability range of 14-80% for strength (1,21,28,30) and 20-85% for muscle mass (1,14,24,28). Although the heritability of the adaptation of these muscle phenotypes to strength training (ST) has not been well studied, the adaptive response also appears to have a genetic component (26,27 The purpose of the present study was to investigate the association of ACE genotype with muscle phenotypes before and after ST in older men and women. Though the literature is inconclusive, the biological rationale suggests an advantage for the D allele with regard to muscle phenotypes; thus, we hypothesized that the D allele would be associated with higher values for muscle phenotypes before ST, and greater increases in muscle phenotypes in response to ST. As most studies have investigated only men, we investigated men and women to determine possible sex differences. METHODS SubjectsParticipants in the study consisted of 243 inactive, healthy volunteers between the ages of 50 and 85 yr. For this investigation, "inactive" was operationally defined as a person who performs less than 20 min of vigorous activity per week. Subjects were required to be nonsmokers with no significant car...

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