
Blair T CrewtherInstitute of Sport - National Research Institute · Department of Endocrinology
Blair T Crewther
PhD
About
124
Publications
93,762
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
5,595
Citations
Introduction
Publications
Publications (124)
Rugby training and competition both impose a stress or training load (TL) affecting athlete well-being. Current understanding of the TL dose-response and time-lagged changes (i.e., delayed effects) in well-being is limited. We addressed these gaps using data from a 3-week international series. Twenty-two elite male rugby players were assessed 4–5 d...
Understanding and predicting individual responses to common stressors is essential for optimising performance in high-stress environments. This article outlines a protocol for a study to identify biomarkers that predict performance under heat, musculoskeletal, psychosocial and sleep stress, for future integration into a wearable sensor system. In P...
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 testo...
Purpose
Opinions are often linked to emotions and stress. It is well established that testosterone and cortisol are useful biomarkers of stress and can predict human emotion and behavior. Therefore, the purpose of this work was to explore whether changes in testosterone and cortisol concentration map to shifts in opinions.
Methods
We present three...
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....
The human stress response triggers a complex array of physiological, psychological, and biochemical reactions, involving neuroendocrine pathways such as the sympathetic adrenomedullary axis and hypothalamic–pituitary–adrenal axis. Prolonged experience of stress can have adverse effects on overall cognitive and physical well-being, making the routin...
Boxing is a combat sport linked to muscle damage (e.g., soreness, rising creatine kinase [CK]) and energetic biomarkers (e.g., urea, glucose). These factors have not, however, been examined dynamically in terms of day-to-day, lagged and reciprocal effects during normal training. This study investigated the dynamic interplay between muscle damage an...
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 investiga...
Day-to-day coordination of the stress (i.e., hypothalamic-pituitary-adrenal [HPA]) and reproductive (i.e., hypothalamic-pituitary-gonadal [HPG]) axes is central to allostatic regulation, reproductive success, and survival. Reports of positive, within-person testosterone and cortisol relationships (or coupling) suggest cross-talk of a facilitative n...
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 th...
Research has demonstrated that increases in testosterone (T) concentration can affect the expression of behaviours and preferences that are typical of high mating effort. However, little research has considered whether such T increases affect mating strategy more generally and whether this is achievable using a physical intervention. In this pilot...
Background:
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...
Objective
The hypothalamic-pituitary-gonadal (HPG) and -adrenal (HPA) axes are traditional viewed as mutually inhibitory systems. However, several diurnal studies have reported positive within-person testosterone and cortisol relationships, as evidence of facilitative processes, but with some constraints (e.g., low-frequency sampling, use of static...
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 test...
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 w...
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 basel...
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...
Purpose:
Reported associations between vitamin 25(OH)D and exercise performance are equivocal, perhaps due to complex interplay with cortisol and testosterone. In this study, the authors investigated serum 25(OH)D and cortisol as moderators of the testosterone relationship with exercise performance in adolescent male athletes.
Methods:
A total o...
Background:
The influence of menstrual cycle phase in perceptual responses and exercise performance still unclear in the literature. Therefore, the main aim of 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 me...
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 atest-match environment. We addressed this gap by monitoring 29 athletes from a training squad across eight international rugby matches.
Design...
Background:
Testosterone (T) is taken or prescribed to enhance appearance, increase athletic performance and libido and to treat hypogonadism. Digit ratio (2D:4D) is thought to be a negative correlate of prenatal T. Here we consider the relationship between 2D:4D and T supplementation.
Aims:
Our sample was taken from the BBC internet study. Resp...
Muscle strength is a highly heritable trait. So far, 196 single nucleotide polymorphisms (SNPs) associated with handgrip strength have been identified in 3 genome-wide association studies. The aim of our study was to validate the association of 35 SNPs with strength of elite Russian weightlifters and replicate the study in Polish weightlifters. Gen...
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 monitore...
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.g., physical training) may provide a stronger basis for estab...
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. Emotional state was assessed before (competitiveness, a...
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 athlet...
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. Usi...
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) an...
D-aspartic acid (DAA) is promoted as a testosterone (T) enhancing supplement via mechanisms involving the hypothalamic-pituitary-gonadal (HPG) axis. Here we investigated the short-term effects of DAA on serum biomarkers of the HPG-axis in male climbers. Using a single-blinded, placebo-controlled design, 16 climbers were randomly assigned to either...
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 19.3±3.7 years);...
Background:
There is evidence linking women's T to competitive behaviours in sport and exercise. To advance this work, we examined the longitudinal relationships between salivary testosterone (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...
This study investigated salivary testosterone (sal-T) variation across the menstrual cycle in female athletes, at different competitive levels, and its association with motivation and neuromuscular power. Six elite and 16 non-elite female athletes were monitored on days 7 (D7), 14 (D14) and 21 (D21) across three menstrual cycles for basal sal-T con...
Despite the prevalence of caffeine as an ergogenic aid, few studies have examined the use of caffeinated gums, especially during half-time in team sports. The physiological (blood lactate, salivary hormone concentrations) and performance (repeated sprints, cognitive function) effects of consuming caffeine gum during a simulated half-time were exami...
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 ho...
Objectives
Evidence suggests that stress-induced changes in testosterone and cortisol are related to future competitive behaviours and team-sport outcomes. Therefore, we examined whether salivary testosterone and cortisol reactivity to a mid-week stress test can discriminate a match outcome in international rugby union competition.
Design
Single g...
This study examined the moderating effect of cortisol (C) on the relationship between testosterone (T) and hand-grip strength (HGS) in healthy young men. Sixty-five males were monitored for salivary T, C and HGS before and 15 min after a short bout (5 × 6-s trials) of sprint cycling exercise. Sprint exercise promoted (p < .05) positive changes in T...
Background:
This study examined the utility of salivary testosterone (T) and cortisol (C) concentration measures for assessing the acute stress responses of junior athletes during a sporting competition.
Methods:
Paired capillary blood and saliva samples were taken from 71 junior athletes (45 males, 26 females) before and after a simulated Olymp...
Purpose:
To examine the steroid hormone effect on the physical performance of young athletes during an Olympic weightlifting competition.
Methods:
26 boys and 26 girls were monitored across 2 weightlifting competitions. Pre- and post-competition testosterone (T), cortisol (C) and dehydroepiandrosterone-sulphate (DHEA-s) were measured in blood, w...
In sport, exercise and healthcare settings, there is a need for continuous, non-invasive monitoring of biomarkers to assess human performance, health and wellbeing. Here we report the development of a flexible microfluidic platform with fully integrated sensing for on-body testing of human sweat. The system can simultaneously and selectively measur...
Background:
Surgical training and practice is stressful, but adaptive changes in the stress circuitry (e.g. perceptual, physiological, hormonal, neural) could support skill development. This work examined skill acquisition and stress adaptations in novice surgeons during laparoscopic surgery (LS) training and detraining.
Methods:
Twelve medical...
Objective:
To address the rapid influence of testosterone (T) on neuromuscular performance, we compared the T and physical performance responses of adults exposed to a physical and psychological stimulus.
Design:
A group of healthy men (n=12) and women (n=14) each completed three treatments using a randomised, crossover design: exercise involvin...
To advance our understanding of the hormonal contribution to athletic performance, we examined the temporal associations between individual changes in testosterone (T) and/or cortisol (C) concentrations, training motivation and physical performance in elite and non-elite trained men. Two male cohorts classified as elites (n = 12) and non-elites (n...
This study examined the effects of two equal-volume resistance-training protocols upon strength, body composition and salivary hormones in male rugby union players. Using a crossover design, 24 male rugby players completed a 4-week full-body (FB) and split-body (SB) training protocol of equal volume during the competitive season. One repetition max...
There is demand in applied sport settings to measure recovery briefly and accurately. Research indicates mood disturbance as the strongest psychological predictor of mental and physical recovery. The Brief Assessment of Mood (BAM) is a shortened version of the Profile of Mood States that can be completed in less than 30 s. The purpose of this study...
Digit ratio (2D:4D) is a marker for prenatal sex steroids and a correlate of sporting performance. This association may exist because low 2D:4D is linked to high prenatal levels of testosterone (T) and low oestrogens (E). It was recently suggested that low 2D:4D, and particularly low right-left 2D:4D (or Dr-l), is a marker for T changes in response...
This study examined the salivary testosterone (T) and cortisol (C) responses of elite women hockey players across 4 activities (light and heavy training, club and International competitions). The players formed an oral contraceptive (OC) group (n=10) and a Non-OC (n=19) group for analysis. The Non-OC group had higher T levels (by 31-52%) across all...
This study assessed the positional and temporal movement patterns of professional rugby union players during competition using global positioning system (GPS) units. GPS data were collected from 33 professional rugby players from 13 matches throughout the 2012-2013 season sampling at 10 Hz. Players wore GPS units from which information on distances...
The aim of this study was to determine the acute neuromuscular, biochemical and endocrine responses to a maximal speed training (MST) session. Eighteen male rugby players completed the protocol, which involved performing six maximal effort repetitions of 50 m running sprints with 5 minutes recovery between each sprint. Testosterone (T), cortisol (C...
Background:
The testosterone (T) responses to a physical stimulus are thought to be more stable and reproducible compared to a psychological stimulus.
Purpose:
This study compared the salivary T (Sal-T) responses to both stimuli in four groups of men: professional rugby players (n = 17), recreational rugby players (n = 10), a mixed athlete group...
Videos of the conference are now available online!
http://www.canal-insep.fr/enhancing-muscle-capacities-strength-power-velocity
INSEP, the French National Institute of Sport, is proud to announce the organization of an international conference entitled "Enhancing muscle capacities: strength, power, velocity", to take place in Paris on 19-20 May 2...
This study investigated the effect of a periodized training program on internal training load (ITL), recovery-stress state, immune-endocrine responses and physical performance in 19 elite female basketball players. The participants were monitored across a 12-week period before an international championship, which included 2 overloading and tapering...
This study examined the social environment effects during a post-match video presentation on the hormonal responses and match performance in professional male rugby union players. The study participants (n=12) watched a 1-hour video of mixed content (player mistakes and successes) from a match played 1day earlier in the presence of; (1) strangers w...
Digit ratio (2D:4D) denotes the relative length of the second and fourth digits. This ratio is considered to be a biomarker of the balance between fetal testosterone (T) and estrogen (E) in a narrow window of early ontogeny. Evidence for this assertion is derived from direct and indirect measures of prenatal hormonal exposure (in experimental anima...
The relative lengths of the 2nd and 4th digits (2D:4D) is a negative biomarker for prenatal testosterone, and low 2D:4D may be associated with aggression. However, the evidence for a 2D:4D-aggression association is mixed. Here we test the hypothesis that 2D:4D is robustly linked to aggression in "challenge" situations in which testosterone is incre...
The first aim of this investigation was to determine if performance indicator (PI) scores generated from rugby union game statistics discriminated between outcomes. Thirty one elite professional rugby games were analysed. For each game three cumulative PI scores were generated based upon skill actions (SkillPI), aggressive actions (AggPI) and an ad...
Purpose:
To assess the measures of salivary free testosterone and cortisol concentrations across selected rugby union matches according to game outcome.
Methods:
Twenty-two professional male rugby union players were studied across 6 games (3 wins and 3 losses). Hormone samples were taken 40 min before the game and 15 min after. The hormonal data...
Objectives
To determine if a morning training session could alter afternoon physical performance. Moreover, as testosterone (T) and cortisol (C) concentrations are significant predictors of physical performance, and both show circadian declines across the day, we examined the effects of morning training on diurnal T and C responses. DesignEighteen...
Assessing psychological stress is essential for monitoring general health and wellbeing. One key element is the detection of the stimulus, i.e., stressor that evokes a stress response. Visual and verbal stimuli are elementary arousal elements of daily stress responses. The study aim was to discriminate the stress responses from watching videos and...
We examined the metabolic, hormonal, biochemical and neuromuscular (NMF) responses to a backward sled-drag training session (STS) in strength-trained males (n = 11). After baseline collection of saliva (testosterone and cortisol), whole blood (lactate and creatine kinase [CK]) and countermovement jumps (peak power output [PPO]), participants comple...
Aim:
The ability to accelerate and attain high levels of speed is an essential component of success in team sports; however, the physical qualities that underpin these activities remain unclear. This study aimed to determine some of the key strength and power predictors of speed within professional rugby union players.
Methods:
Twenty profession...
Aim:
After postactivation potentiation (PAP) has been induced, current research recommends that, on average, an 8 minute passive recovery period is applied before engaging in subsequent dynamic exercise. However, given the importance of maximizing time usage during the warm-up of elite athletes, it is likely that further exercise would be incorpor...
We examined the recovery time-course of neuromuscular function (NMF), the testosterone and cortisol hormonal milieu and mood for 60 hours following a competitive match, in professional rugby union players (n=14). Thirty-six hours pre-match (19:30 hours kick-off), baseline saliva (testosterone, cortisol and testosterone-cortisol [T/C] ratio), counte...
Aim:
To examine the effects of a resistance-training program on strength, body composition and baseline hormones in male athletes training concurrently for rugby union 7's.
Methods:
Participants (N.=12) completed a six-week resistance-training program focusing on general strength development while still performing additional rugby union 7's trai...
Abstract There is evidence that the digit ratio (2D:4D) is a negative correlate of prenatal levels of testosterone, but there is no association between 2D:4D and the circulating levels of both total and free testosterone. Sports provide a physical challenge and participants often show increased levels of free testosterone immediately preceding and...
The use of heavy resistance exercise provides an effective preload stimulus for inducing postactivation potentiation (PAP) and increasing peak power output (PPO). However, this approach has limited application in many sporting situations (e.g. incorporation in a pre-competition warm-up) and therefore more practical strategies for inducing PAP need...
The present study compared the ratings of perceived exertion (RPE) and immune-endocrine (IgA and cortisol) responses to simulated training matches (TM) and official matches (OM) in elite young male basketball players (N.=10). Saliva samples were collected from each player before and after three TM and two OM and subsequently tested for cortisol and...
Objectives:
Salivary testosterone (T) and cortisol (C) concentrations were monitored across a sports competition. Data were compared using two enzyme-immunoassay (EIA) methods and two sample preparations to determine their influence on hormone concentrations.
Design and methods:
A group of male athletes (n=19) provided a saliva sample the mornin...
To compare the baseline free testosterone (T) and cortisol (C) concentrations of elite and non-elite female athletes.
Eighteen females from different sports (track and field, netball, cycling, swimming, bob skeleton) were monitored over a 12-week period. Baseline measures of salivary free T and C concentrations were taken weekly prior to any traini...
Objectives:
Swimmers must enter a marshalling call-room 20min prior to racing, which results in some swimmers completing their warm-up 45min pre-race. Since a recovery period longer than 15-20min may prove problematic, this study examined 200m freestyle performance after a 20 and 45min post-warm-up recovery period.
Design:
Eight international sw...
The use of weighted sled towing as a training tool to improve athlete acceleration has received considerable attention; however, its effectiveness for developing acceleration is equivocal. This study compared the effects of combined weighted sled towing and sprint training against traditional sprint training on 10 and 30 m speed in professional rug...
We examined the effect of different pre-match motivational interventions on athlete free testosterone (T) and cortisol (C) concentrations and subsequent match performance in professional rugby union. Male participants (n=12) playing at a senior or academy level in rugby union were recruited and each completed three interventions (15 min each) befor...
The present study examined the effect of a 20-day period of competition on salivary cortisol, mucosal immunity, and upper respiratory tract infections (URTI) in young male soccer players (n = 14). The players were monitored during the main under-19 Brazilian soccer championship, in which 7 matches were played in 20 days. Saliva samples were collect...