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The Relationship Between Objectively Measured Physical Activity, Salivary Cortisol, and the Metabolic Syndrome Score in Girls

Katrina D. DuBose and Andrew J. McKune

The relationship between physical activity levels, salivary cortisol, and the metabolic syndrome (MetSyn) score was examined. Twenty-three girls (8.4 ± 0.9 years) had a fasting blood draw, waist circumference and blood pressure measured, and wore an ActiGraph accelerometer for 5 days. Saliva samples were collected to measure cortisol levels. Previously established cut points estimated the minutes spent in moderate, vigorous, and moderate-to-vigorous physical activity. A continuous MetSyn score was created from blood pressure, waist circumference, high-density-lipoprotein (HDL), triglyceride, and glucose values. Correlation analyses examined associations between physical activity, cortisol, the MetSyn score, and its related components. Regression analysis examined the relationship between cortisol, the MetSyn score, and its related components adjusting for physical activity, percent body fat, and sexual maturity. Vigorous physical activity was positively related with 30 min post waking cortisol values. The MetSyn score was not related with cortisol values after controlling for confounders. In contrast, HDL was negatively related with 30 min post waking cortisol. Triglyceride was positively related with 30 min post waking cortisol and area under the curve. The MetSyn score and many of its components were not related to cortisol salivary levels even after adjusting for physical activity, body fat percentage, and sexual maturity.

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Training and Competition Loads in Women’s Rugby Sevens Athletes: Are There Implications for Cardiovascular Health?

Luca Napoli, Stuart Semple, and Andrew J. McKune

National- and international-level rugby sevens athletes are exposed to high training and competition loads over the course of a competitive season. Research on load monitoring and body-system responses is widespread; however, the primary focus has been on optimizing performance rather than investigating or improving cardiovascular health. There is a degree of cardiovascular remodeling, as well as local and systemic inflammation, in response to excessive exercise. These responses are moderated by many factors including previous exercise exposure, current exercise intensity and duration, age, race, and gender, as well as sport-specific physiology. For these reasons, high-performing female rugby sevens athletes may have a unique cardiovascular risk profile different from males and other rugby codes. This review aimed to characterize the training and competition loads, as well as the anthropometric and physiological profiles, of female rugby sevens athletes; discuss the potential impacts these may have on the cardiovascular system; and provide recommendations on future research regarding the relationship between rugby sevens training and competition loads and cardiovascular health. Movement demands, competition formatting, and training routines could all contribute to adverse cardiovascular adaptations. Anthropometric data and physiological characteristics may also increase the risk of cardiovascular disease. Future research needs to adopt measures of cardiovascular health to obtain a greater understanding of cardiovascular profiles and risk factors in female rugby sevens athletes.

Open access

Hydrogen-Rich Water Supplementation and Up-Hill Running Performance: Effect of Athlete Performance Level

Michal Botek, Jakub Krejčí, Andrew J. McKune, and Barbora Sládečková

Purpose: Hydrogen-rich water (HRW) has been shown to have an antifatigue effect. This study assessed up-hill running performance, as well as physiological and perceptual responses after supplementation with 1680 mL HRW between 24 h and 40 min before running, in athletes of heterogeneous running ability. Methods: Sixteen males (mean [SD] age 31.6 [8.6] y, VO2max 57.2 [8.9] mL·kg−1·min−1, body fat 13.4% [4.4%]) participated in this study. Using a randomized, double-blind, placebo-controlled crossover design, participants consumed either HRW or placebo prior to performing two 4.2-km up-hill races separated by a week. Race time (RT), average race heart rate, and immediately postrace rating of perceived exertion were assessed. Results: After analysis of data for all runners, HRW effect was unclear (−10 to 7 s, 90% confidence interval) for RT, likely trivial for heart rate (−2 to 3 beats·min−1), and likely trivial for postrace rating of perceived exertion (−0.1 to 1.0). A possible negative correlation was found between RT differences and average RT (r = −.79 to −.15). HRW for the 4 slowest runners (RT = 1490 [91] s) likely improved the RT (−36 to −3 s), whereas for the 4 fastest runners (RT = 1069 [53] s) the performance effect of HRW was unclear (−10 to 26 s). Conclusions: HRW intake had an unclear antifatigue effect on performance in terms of mean group values. However, it appears that the magnitude of the antifatigue effect of HRW on performance depends on individual running ability.

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Partial-Body Cryotherapy Exposure 2 Hours Prior to a Shuttle Run Does Not Enhance Running Performance

Emily M. Partridge, Julie Cooke, Andrew J. McKune, and David B. Pyne

Purpose: To determine whether a single acute preexercise bout of partial-body cryotherapy (PBC) enhanced maximal-effort shuttle run performance, salivary enzyme concentration, and self-reported performance readiness. Methods: A total of 18 male rugby league players (age = 20.1 [0.5] y; mass = 91.4 [12.4] kg) were exposed to either PBC for 3 minutes at −136°C (1°C) or a control condition prior to a continuous, high-intensity 6 × 40-m shuttle run test. Passive saliva samples were collected to determine salivary alpha amylase (sAA) concentration. Perceived performance readiness and well-being questionnaires were completed using a 1-to-7 Likert scale. Results: The PBC exposure did not elicit a greater improvement in 6 × 40-m shuttle run performance in comparison with the control condition (standardized difference; +0.4 [5.9%]; P = .881; mean ± 90% confidence limits). The increase in sAA concentration was moderately greater 15 minutes after PBC compared with the control group (+67 [32%], P = .012) and remained moderately higher up to 2 hours post-PBC exposure compared with the control condition (+41 [40%], P = .045). There were greater improvements in self-reported perceptions of muscle soreness (+0.6 [0.4%], P = .043; units ±90% confidence limits) and mood (+0.6 [0.7%], P = .038) after PBC compared with control. Conclusions: It appears that a single 3-minute bout of PBC does not augment maximal effort shuttle run performance in elite rugby league players. Beneficial increases in sAA concentration, coupled with improved perceptions of muscle soreness and mood, should be explored further for alternative training or precompetition practices.

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The Relationship Between Physical Activity and the Metabolic Syndrome Score in Children

Katrina D. DuBose, Andrew J. McKune, Patricia Brophy, Gabriel Geyer, and Robert C. Hickner

The relationship between physical activity levels and the metabolic syndrome (MetSyn) score was examined in 72 boys and girls (9.5 ± 1.2 years). A fasting blood draw was obtained; waist circumference and blood pressure measured, and an accelerometer was worn for 5 days. Established cut points were used to estimate time spent in moderate, vigorous, moderate-to-vigorous (MVPA), and total physical activity. A continuous MetSyn score was created from blood pressure, waist circumference, high-density-lipoprotein, triglyceride, and glucose values. Regression analysis was used to examine the relationship between physical activity levels, the MetSyn score, and its related components. Logistic regression was used to examine the association between meeting physical activity recommendations, the MetSyn score, and its related components. All analyses were controlled for body mass index group, age, sex, and race. Time spent in different physical activity levels or meeting physical activity recommendations (OR: 0.87, 95%CI: 0.69–1.09) was not related with the MetSyn score after controlling for potential confounders (p > .05). Moderate physical activity, MVPA, and meeting physical activity recommendations were related to a lower diastolic blood pressure (p < .05). No other relationships were observed (p > .05). While physical activity participation was not related with the MetSyn, lower diastolic blood pressure values were related to higher physical activity levels.

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Timing of Preexercise Partial-Body Cryotherapy Exposure to Promote Jump Performance

Emily M. Partridge, Julie Cooke, Andrew J. McKune, and David B. Pyne

Purpose: This study evaluated the effect of partial-body cryotherapy (PBC) exposure 1, 2, or 3 hours before maximal-effort jump performance, salivary enzyme concentration, perceived readiness, and well-being. Methods: Male team-sport players (N = 27; 24.2 [3.6] y; 91.5 [13.2] kg) were exposed to a blinded bout of PBC (−135°C [6°C]) and control (−59°C [17°C]) either 1, 2, or 3 hours prior to countermovement jumps. Passive saliva samples were collected to determine α-amylase concentration. Self-reported performance readiness and well-being questionnaires were completed using a 1–5 Likert scale. Results: Differences in the change in mean countermovement jump velocity and absolute power between PBC and control were unclear at 1 hour (+1.9% [5.3%], P = .149; +0.7% [10.6%], P = .919; mean difference [90% confidence limits]), 2 hours (+3.3% [2.7%], P = .196; +7.8% [7.4%], P = .169), and 3 hours postexposure (+3.1% [3.3%], P = .467; +0.7% [4.8%], P = .327). Salivary α-amylase concentration was elevated 15 minutes postexposure in the 1-hour (+61% [14%], P = .008) and 2-hour groups (+55% [12%], P = .013). The increase in self-reported performance readiness was higher after PBC (+2.4 [1.2] units, P = .046) in the 2-hour group and by 1.4 (1.1) units (P = .023) after 3 hours. Mental fatigue was favorably decreased 2 hours after PBC exposure (+0.5 [0.1], P = .041). Conclusions: An acute exposure of PBC elicits potentially favorable but unclear changes in countermovement jump performance. The PBC enhances salivary α-amylase concentration and perceived performance readiness, reduces mental fatigue, and could be useful in sport-specific training or competitions.

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The Effects of a Field-Based Priming Session on Perceptual, Physiological, and Performance Markers in Female Rugby Sevens Players

Billy R.J. Mason, Andrew J. McKune, Kate L. Pumpa, Jocelyn K. Mara, Alexander C. Engel, Liam P. Kilduff, and Nick B. Ball

Purpose: This study aimed to determine the effects of a field-based priming session on perceptual, physiological, and performance responses in female rugby sevens athletes. Methods: Thirteen highly trained female rugby sevens players (age: 20.7 [2.0] y; height: 169.3 [4.8] cm; weight: 68.8 [7.9] kg) completed either a 20-minute field-based priming session or a control condition. Perceptual, physiological, and performance variables were collected at baseline (PRE) and 5 (POST5), 30 (POST30), and 120 minutes (POST120) postintervention. Data were analyzed using Bayesian mixed effects models. Results: The priming protocol had a larger increase in mental readiness (maximum a posteriori [MAP] = 20, 95% high-density intervals [HDI] = −4 to 42, probability of direction [PD]% = 95, % in region of practical equivalence [ROPE] = 9.7), physical readiness (MAP = 20.1, 95% HDI = −4.6 to 42.1, PD% = 93, % in ROPE = 10.6), and testosterone (MAP = 14.9, 95% HDI = 0.5 to 27.7, PD% = 98, % in ROPE = 5.6) than the control POST30. Cognitive performance decreased POST120 in the priming condition for congruent (MAP = 0.02, 95% HDI = −0.06 to 0.00, PD% = 95, % in ROPE = 6.4) and incongruent tasks (MAP = 0.00, 95% HDI = −0.07 to 0.00, PD% = 98, % in ROPE = 3.2) when compared with the control. Conclusions: Perceptual and physiological markers improved POST30 in the priming condition. Findings indicate that perceptual and physiological responses to priming were not coupled with performance improvements. Priming was not accompanied by perceptual, physiological, or performance improvements at POST120.

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Running at Increasing Intensities in the Heat Induces Transient Gut Perturbations

Alice M. Wallett, Naroa Etxebarria, Nicole A. Beard, Philo U. Saunders, Marijke Welvaert, Julien D. Périard, Andrew J. McKune, and David B. Pyne

Purpose: The risk of exercise-induced endotoxemia is increased in the heat and is primarily attributable to changes in gut permeability resulting in the translocation of lipopolysaccharides (LPS) into the circulation. The purpose of this study was to quantify the acute changes in gut permeability and LPS translocation during submaximal continuous and high-intensity interval exercise under heat stress. Methods: A total of 12 well-trained male runners (age 37 [7] y, maximal oxygen uptake [VO2max] 61.0 [6.8] mL·min−1·kg−1) undertook 2 treadmill runs of 2 × 15-minutes at 60% and 75% VO2max and up to 8 × 1-minutes at 95% VO2max in HOT (34°C, 68% relative humidity) and COOL (18°C, 57% relative humidity) conditions. Venous blood samples were collected at the baseline, following each running intensity, and 1 hour postexercise. Blood samples were analyzed for markers of intestinal permeability (LPS, LPS binding protein, and intestinal fatty acid–binding protein). Results: The increase in LPS binding protein following each exercise intensity in the HOT condition was 4% (5.3 μg·mL−1, 2.4–8.4; mean, 95% confidence interval, P < .001), 32% (4.6 μg·mL−1, 1.8–7.4; P = .002), and 30% (3.0 μg·mL−1, 0.03–5.9; P = .047) greater than in the COOL condition. LPS was 69% higher than baseline following running at 75% VO2max in the HOT condition (0.2 endotoxin units·mL−1, 0.1–0.4; P = .011). Intestinal fatty acid–binding protein increased 43% (2.1 ng·mL−1, 0.1–4.2; P = .04) 1 hour postexercise in HOT compared with the COOL condition. Conclusions: Small increases in LPS concentration during exercise in the heat and subsequent increases in intestinal fatty acid–binding protein and LPS binding protein indicate a capacity to tolerate acute, transient intestinal disturbance in well-trained endurance runners.

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The Impact of a Short-Term Ketogenic Low-Carbohydrate High-Fat Diet on Biomarkers of Intestinal Epithelial Integrity and Gastrointestinal Symptoms

Alannah K.A. McKay, Alice M. Wallett, Andrew J. McKune, Julien D. Périard, Philo Saunders, Jamie Whitfield, Nicolin Tee, Ida A. Heikura, Megan L.R. Ross, Avish P. Sharma, Ricardo J.S. Costa, and Louise M. Burke

Endurance exercise can disturb intestinal epithelial integrity, leading to increased systemic indicators of cell injury, hyperpermeability, and pathogenic translocation. However, the interaction between exercise, diet, and gastrointestinal disturbance still warrants exploration. This study examined whether a 6-day dietary intervention influenced perturbations to intestinal epithelial disruption in response to a 25-km race walk. Twenty-eight male race walkers adhered to a high carbohydrate (CHO)/energy diet (65% CHO, energy availability = 40 kcal·kg FFM−1·day−1) for 6 days prior to a Baseline 25-km race walk. Athletes were then split into three subgroups: high CHO/energy diet (n = 10); low-CHO, high-fat diet (LCHF: n = 8; <50 g/day CHO, energy availability = 40 kcal·kg FFM−1·day−1); and low energy availability (n = 10; 65% CHO, energy availability = 15 kcal·kg FFM−1·day−1) for a further 6-day dietary intervention period prior to a second 25-km race walk (Adaptation). During both trials, venous blood was collected pre-, post-, and 1 hr postexercise and analyzed for markers of intestinal epithelial disruption. Intestinal fatty acid-binding protein concentration was significantly higher (twofold increase) in response to exercise during Adaptation compared to Baseline in the LCHF group (p = .001). Similar findings were observed for soluble CD14 (p < .001) and lipopolysaccharide-binding protein (p = .003), where postexercise concentrations were higher (53% and 36%, respectively) during Adaptation than Baseline in LCHF. No differences in high CHO/energy diet or low energy availability were apparent for any blood markers assessed (p > .05). A short-term LCHF diet increased intestinal epithelial cell injury in response to a 25-km race walk. No effect of low energy availability on gastrointestinal injury or symptoms was observed.