Publications by authors named "Blair T Crewther"

Testosterone plays important roles in reproductive behaviour in many species. Despite a common belief that testosterone regulates fluctuations in human sexual desire, there is little direct evidence that relates within-person changes in natural testosterone production to within-person changes in sexual desire. Here, we measured daily salivary testosterone concentrations from 41 adult men for one month, along with daily self-reports of sexual desire ( = 759 observations for the main analyses).

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In sport, the awakening responses of cortisol (CAR) and testosterone (TAR) have been used as evaluative tools. Research findings are, however, inconsistent and the mechanisms involved are unclear. This study investigated the CAR and TAR in male athletes across light and heavy training weeks, focusing on skeletal muscle damage as a mediating factor.

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Maturity offset (i.e., age from peak height velocity [PHV]) is widely used to assess maturational status among youth athletes, but details on the skeletal periphery, hormones and training factors are lacking.

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Testosterone (T) has been conceptualized as a biomarker of individual differences, yet T associations with the Big Five personality traits are inconsistent. Athletes provide a suitable model for evaluation here, as T co-expresses traits related to male-to-male competition and fitness with cortisol (C) playing a moderating role. This study investigated associations between the Big Five traits, T, and C in adolescent male athletes.

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Boxing is a combat sport linked to muscle damage (e.g., soreness, rising creatine kinase [CK]) and energetic biomarkers (e.

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The digit ratio (2D:4D) is a negative correlate of boy's physical fitness, and thought to arise from organizational effects of prenatal testosterone on different bodily systems. During human ontogeny, activational effects of testosterone on body size and strength offers another pathway to physical fitness. We tested these hypotheses by examining the organizational and activational effects of testosterone on vertical jump performance in athletic boys.

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The reliability of dual energy X-ray absorptiometry (DXA) to assess body composition is influenced by factors like hydration status. Hence, any factor affecting total body water (TBW) content, such as menstrual shifts in sex hormones, might influence DXA estimates of lean soft tissue (LST) and fat mass (FM). To address this possibility, interrelationships between menstrual fluctuations in sex hormones, LST and FM were examined in a premenopausal female.

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Studies indicate that high-frequency repetitive transcranial magnetic stimulation (HF-rTMS) can lower cortisol concentration or output, with some evidence suggesting a link to testosterone. Together, these stress and social hormones might help regulate the emotional response to HF-rTMS. This pilot study evaluated the effect of HF-rTMS on acute testosterone and cortisol dynamics and emotional state in eleven healthy adults.

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Purpose: To establish if training volume was associated with androgen baselines and androgen responsiveness to acute exercise.

Methods: During a "high-volume" training phase, 28 cyclists (14 men and 14 women) undertook oxygen-uptake and maximal-work-capacity testing. Two days later, they completed a repeat-sprint protocol, which was repeated 3 weeks later during a "low-volume" phase.

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Studies have compared HPA and HPG stress reactivity across the follicular and luteal phases to assess the menstrual impact of estradiol and progesterone fluctuations. Ovulatory shifts in baseline and stressor-induced testosterone among athletic women offer a new framework to explore these responses. Here we investigated menstrual variation in baseline testosterone as a predictor of the acute testosterone and cortisol response to laboratory stressors in female athletes.

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In sport, testosterone has been positioned as a substrate for motivation with both directional and time dependencies. However, evidence is scarce when considering the complexities of competitive sport and no work has explicitly modeled these dependencies. To address these gaps, we investigated the bidirectional and time-dependent interrelationships between testosterone and training motivation in an elite rugby environment.

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Background: The influence of menstrual cycle phase on perceptual responses and exercise performance is still unclear in the literature. Therefore, this study investigated salivary estradiol (sal-E2) and cortisol (sal-C) concentrations, mood, anxiety and exercise (aerobic, anaerobic) performance in physically-active women across two menstrual-cycle phases.

Methods: Twelve women (mean age 24.

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Objectives: Research has linked physiological (e.g., hormonal, affective, fatigue) outcomes to performance indicators in rugby competition, but no work has integrated and contextualised these factors within a test-match environment.

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The cortisol (C) and testosterone (T) responses to experimental stress have been linked to sport and health outcomes several days to years later. Here we examined the utility of these biomarkers, taken across a simulated Olympic weightlifting (OWL) competition, as predictors of future competitive performance in young athletes. Seventy junior athletes (46 males, 24 females) participated in a talent identification and development programme that replicated an OWL competition.

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This study examined a possible link between the elective preferences of medical students (surgical vs. non-surgical) and their emotional and hormonal responses to a psychological stressor. Forty medical students completed a laboratory stressor comprising of 10 puzzles in a time-limited format.

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Literature suggests that women experience ovulatory shifts in risk-taking behaviours across different domains, which might be partly attributed to changes in testosterone (T). Thus, we investigated associations between menstrual variability in T concentrations and economic risk-related decisions among athletic women. Thirty-five women were monitored across three consecutive menstrual cycles.

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Background: The 2nd to 4th digit ratio (2D:4D) is regarded as a sexually dimorphic trait governed by prenatal testosterone (T) and estradiol exposure. However, relationships between the 2D:4D and adult sex hormone concentrations are inconsistent in females. Environmental contingencies (e.

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The concept of competition has implications for educational contexts, as hormonal and emotional changes under competitive stress can modulate learning and memory processes. This study examined the impact of a competitive learning environment and associated hormonal and emotional responses on skill acquisition and expression in a medical domain. Using a cross-over design, sixteen male medical students participated in a competitive (in pairs facing each other) and non-competitive (alone) learning situation.

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Some equivocality exists regarding the effect of testosterone (T) on competitive performance with cortisol (C) implicated as a moderating factor. This study investigated whether C is moderating the T relationship with Olympic weightlifting (OWL) performance during real and simulated competitions. We monitored 105 male athletes (age 19.

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Human gaze is an important indicator of dominant and submissive behaviours related to positioning in a social hierarchy. This study investigated face gazing after a chance-determined contest and its linkage to salivary testosterone (sal-T) reactivity in athletic women. Twenty-six women athletes completed a coin-toss game on days 7 (D7), 14 (D14) and 21 (D21) of a single menstrual cycle.

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Background: There is evidence linking women's testosterone (T) to competitive behaviours in sport and exercise. To advance this work, we examined the longitudinal relationships between salivary T (sal-T) and competitiveness in athletic women who differ in training status.

Methods: Elite (n = 9) and non-elite (n = 21) women athletes were monitored on days 6-8 (follicular phase), 13-15 (ovulatory phase) and 20-22 (Luteal phase) of a menstrual cycle with two repeats.

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Russell, M, Reynolds, NA, Crewther, BT, Cook, CJ, and Kilduff, L. Physiological and performance effects of caffeine gum consumed during a simulated half-time by professional academy rugby union players. J Strength Cond Res 34(1): 145-151, 2020-Despite the prevalence of caffeine (CAF) as an ergogenic aid, few studies have examined the use of caffeinated gums, especially during half-time in team sports.

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Objectives: To investigate the effect of oral contraceptive (OC) use on salivary testosterone (sal-T) concentrations and performance-related statistics in international field hockey matches.

Design: A cohort observational study with repeated measures.

Methods: Twenty-three elite female athletes were monitored across four international field hockey matches over a nine-day period.

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