Geoffrey M. Minett

Volume-dependent response of precooling for intermittent-sprint exercise in the heat.

PURPOSE This study aimed to assess the effects of precooling volume on neuromuscular function and performance in free-paced intermittent-sprint exercise in the heat. METHODS Ten male, team-sport athletes completed four randomized trials involving an 85-min free-paced intermittent-sprint exercise protocol in 33°C ± 33% relative humidity. Precooling sessions included whole body (WB), head + hand (HH), head (H), and no cooling (CONT) applied for 20 min before exercise and 5 min during exercise. Maximal voluntary contractions were assessed before and after intervention and during and after exercise. Exercise performance was assessed with sprint times, percent decline and distances covered during free-paced bouts. Measures of core (Tc) and skin (Tsk) temperatures, HR, perceptual exertion, and thermal stress were monitored throughout. Venous and capillary blood samples were analyzed for metabolite, muscle damage, and inflammatory markers. RESULTS WB precooling facilitated the maintenance of sprint times during the exercise protocol with reduced percent decline (P = 0.04). Mean and total hard running distances increased with precooling 12% compared with CONT (P < 0.05); specifically, WB was 6%-7% greater than HH (P = 0.02) and H (P = 0.001), respectively. No change was evident in mean voluntary or evoked force before to after exercise with WB and HH cooling (P > 0.05). WB and HH cooling reduced Tc by 0.1°C-0.3°C compared with other conditions (P < 0.05). WB Tsk was suppressed for the entire session (P = 0.001). HR responses after WB cooling were reduced (P = 0.05; d = 1.07) compared with CONT conditions during exercise. CONCLUSIONS A relationship between precooling volume and exercise performance seems apparent, as larger surface area coverage augmented subsequent free-paced exercise capacity, in conjunction with greater suppression of physiological load. Maintenance of maximal voluntary contraction with precooling despite increased work output suggests the role of centrally mediated mechanisms in exercise pacing regulation and subsequent performance.

Is recovery driven by central or peripheral factors? A role for the brain in recovery following intermittent-sprint exercise.

Prolonged intermittent-sprint exercise (i.e., team sports) induce disturbances in skeletal muscle structure and function that are associated with reduced contractile function, a cascade of inflammatory responses, perceptual soreness, and a delayed return to optimal physical performance. In this context, recovery from exercise-induced fatigue is traditionally treated from a peripheral viewpoint, with the regeneration of muscle physiology and other peripheral factors the target of recovery strategies. The direction of this research narrative on post-exercise recovery differs to the increasing emphasis on the complex interaction between both central and peripheral factors regulating exercise intensity during exercise performance. Given the role of the central nervous system (CNS) in motor-unit recruitment during exercise, it too may have an integral role in post-exercise recovery. Indeed, this hypothesis is indirectly supported by an apparent disconnect in time-course changes in physiological and biochemical markers resultant from exercise and the ensuing recovery of exercise performance. Equally, improvements in perceptual recovery, even withstanding the physiological state of recovery, may interact with both feed-forward/feed-back mechanisms to influence subsequent efforts. Considering the research interest afforded to recovery methodologies designed to hasten the return of homeostasis within the muscle, the limited focus on contributors to post-exercise recovery from CNS origins is somewhat surprising. Based on this context, the current review aims to outline the potential contributions of the brain to performance recovery after strenuous exercise.

Cold‐water immersion decreases cerebral oxygenation but improves recovery after intermittent‐sprint exercise in the heat

This study examined the effects of post‐exercise cooling on recovery of neuromuscular, physiological, and cerebral hemodynamic responses after intermittent‐sprint exercise in the heat. Nine participants underwent three post‐exercise recovery trials, including a control (CONT), mixed‐method cooling (MIX), and cold‐water immersion (10 °C; CWI). Voluntary force and activation were assessed simultaneously with cerebral oxygenation (near‐infrared spectroscopy) pre‐ and post‐exercise, post‐intervention, and 1‐h and 24‐h post‐exercise. Measures of heart rate, core temperature, skin temperature, muscle damage, and inflammation were also collected. Both cooling interventions reduced heart rate, core, and skin temperature post‐intervention (P < 0.05). CWI hastened the recovery of voluntary force by 12.7 ± 11.7% (mean ± SD) and 16.3 ± 10.5% 1‐h post‐exercise compared to MIX and CONT, respectively (P < 0.01). Voluntary force remained elevated by 16.1 ± 20.5% 24‐h post‐exercise after CWI compared to CONT (P < 0.05). Central activation was increased post‐intervention and 1‐h post‐exercise with CWI compared to CONT (P < 0.05), without differences between conditions 24‐h post‐exercise (P > 0.05). CWI reduced cerebral oxygenation compared to MIX and CONT post‐intervention (P < 0.01). Furthermore, cooling interventions reduced cortisol 1‐h post‐exercise (P < 0.01), although only CWI blunted creatine kinase 24‐h post‐exercise compared to CONT (P < 0.05). Accordingly, improvements in neuromuscular recovery after post‐exercise cooling appear to be disassociated with cerebral oxygenation, rather reflecting reductions in thermoregulatory demands to sustain force production.

Physiological, perceptual, and technical responses to on-court tennis training on hard and clay courts.

Abstract Reid, MM, Duffield, R, Minett, GM, Sibte, N, Murphy, AP, and Baker, J. Physiological, perceptual, and technical responses to on-court tennis training on hard and clay courts. J Strength Cond Res 27(6): 1487–1495, 2013—The aim of this study was to investigate the effect of court surface (clay vs. hard court) on technical, physiological, and perceptual responses to on-court tennis training. Four high-performance junior male players performed 2 identical training sessions on hard and clay courts, respectively. Sessions included both physical conditioning and technical elements as led by the coach. Each session was filmed for later notational analysis of stroke count and error rates. Furthermore, players wore a global positioning satellite device to measure distance covered during each session, while heart rate, countermovement jump distance, and capillary blood measures of metabolites were measured before, during, and after each session. Additionally, a respective coach and athlete rating of perceived exertion (RPE) were measured after each session. Total duration and distance covered during each session were comparable (p > 0.05; d < 0.20). Although forehand and backhands stroke volume did not differ between sessions (p > 0.05; d < 0.30), large effects for increased unforced and forced errors were present on the hard court (p > 0.05; d > 0.90). Furthermore, large effects for increased heart rate, blood lactate, and RPE values were evident on clay compared with hard courts (p > 0.05; d > 0.90). Additionally, although player and coach RPE on hard courts were similar, there were large effects for coaches to underrate the RPE of players on clay courts (p > 0.05; d > 0.90). In conclusion, training on clay courts results in trends for increased heart rate, lactate, and RPE values, suggesting that sessions on clay courts tend towards higher physiological and perceptual loads than hard courts. Furthermore, coaches seem effective at rating player RPE on hard courts but may underrate the perceived exertion of sessions on clay courts.

Does the technique employed for skin temperature assessment alter outcomes? A systematic review

Skin temperature is an important physiological measure that can reflect the presence of illness and injury as well as provide insight into the localised interactions between the body and the environment. The aim of this systematic review was to analyse the agreement between conductive and infrared means of assessing skin temperature which are commonly employed in in clinical, occupational, sports medicine, public health and research settings.Full-text eligibility was determined independently by two reviewers. Studies meeting the following criteria were included in the review: (1) the literature was written in English, (2) participants were human (in vivo), (3) skin surface temperature was assessed at the same site, (4) with at least two commercially available devices employed-one conductive and one infrared-and (5) had skin temperature data reported in the study.A computerised search of four electronic databases, using a combination of 21 keywords, and citation tracking was performed in January 2015. A total of 8,602 were returned.Methodology quality was assessed by two authors independently, using the Cochrane risk of bias tool.A total of 16 articles (n = 245) met the inclusion criteria.Devices are classified to be in agreement if they met the clinically meaningful recommendations of mean differences within  ±0.5 °C and limits of agreement of  ±1.0 °C.Twelve of the included studies found mean differences greater than  ±0.5 °C between conductive and infrared devices. In the presence of external stimulus (e.g. exercise and/or heat) five studies found exacerbated measurement differences between conductive and infrared devices.This is the first review that has attempted to investigate presence of any systemic bias between infrared and conductive measures by collectively evaluating the current evidence base. There was also a consistently high risk of bias across the studies, in terms of sample size, random sequence generation, allocation concealment, blinding and incomplete outcome data.This systematic review questions the suitability of using infrared cameras in stable, resting, laboratory conditions. Furthermore, both infrared cameras and thermometers in the presence of sweat and environmental heat demonstrate poor agreement when compared to conductive devices. These findings have implications for clinical, occupational, public health, sports science and research fields.

The Effect of Post-Match Alcohol Ingestion on Recovery From Competitive Rugby League Matches

Abstract Murphy, AP, Snape, AE, Minett, GM, Skein, M, and Duffield, R. The effect of post-match alcohol ingestion on recovery from competitive rugby league matches. J Strength Cond Res 27(5): 1304–1312, 2013—This study investigated the effects of alcohol ingestion on lower-body strength and power and physiological and cognitive recovery after competitive Rugby League matches. Nine male Rugby players participated in 2 matches, followed by 1 of 2 randomized interventions, a control or alcohol ingestion session. Four hours post-match, participants consumed either beverages containing a total of 1 g of ethanol per kilogram bodyweight (vodka and orange juice; ALC) or a caloric and taste-matched nonalcoholic beverage (orange juice; CONT). Before the match, immediately post-match, 2 hours post-, and 16 hours post-match measures of countermovement jump (CMJ); maximal voluntary contraction (MVC); voluntary activation (VA); and damage and stress markers of creatine kinase (CK), C-reactive protein (CRP), cortisol, and testosterone analyzed from venous blood collection; and cognitive function (modified Stroop test) were determined. Alcohol resulted in large effects for decreased CMJ height (−2.35 ± 8.14% and −10.53 ± 8.36% decrement for CONT and ALC, respectively; p = 0.15, d = 1.40), without changes in MVC (p = 0.52, d = 0.70) or VA (p = 0.15, d = 0.69). Furthermore, alcohol resulted in a significant slowing of total time in a cognitive test (p = 0.04, d = 1.59) while exhibiting large effects for detriments in congruent reaction time (p = 0.19, d = 1.73). Despite large effects for increased cortisol after alcohol ingestion during recovery (p = 0.28, d = 1.44), post-match alcohol consumption did not unduly affect testosterone (p = 0.96, d = 0.10), CK (p = 0.66, d = 0.70), or CRP (p = 0.75, d = 0.60). It seems that alcohol consumption during the evening after competitive rugby matches may have some detrimental effects on peak power and cognitive recovery the morning after a Rugby League match. Accordingly, practitioners should be aware of the potential associated detrimental effects of alcohol consumption on recovery and provide alcohol awareness to athletes at post-match functions.

Mixed-method pre-cooling reduces physiological demand without improving performance of medium-fast bowling in the heat

Abstract This study examined physiological and performance effects of pre-cooling on medium-fast bowling in the heat. Ten, medium-fast bowlers completed two randomised trials involving either cooling (mixed-methods) or control (no cooling) interventions before a 6-over bowling spell in 31.9±2.1°C and 63.5±9.3% relative humidity. Measures included bowling performance (ball speed, accuracy and run-up speeds), physical characteristics (global positioning system monitoring and counter-movement jump height), physiological (heart rate, core temperature, skin temperature and sweat loss), biochemical (serum concentrations of damage, stress and inflammation) and perceptual variables (perceived exertion and thermal sensation). Mean ball speed (114.5±7.1 vs. 114.1±7.2 km · h−1; P = 0.63; d = 0.09), accuracy (43.1±10.6 vs. 44.2±12.5 AU; P = 0.76; d = 0.14) and total run-up speed (19.1±4.1 vs. 19.3±3.8 km · h−1; P = 0.66; d = 0.06) did not differ between pre-cooling and control respectively; however 20-m sprint speed between overs was 5.9±7.3% greater at Over 4 after pre-cooling (P = 0.03; d = 0.75). Pre-cooling reduced skin temperature after the intervention period (P = 0.006; d = 2.28), core temperature and pre-over heart rates throughout (P = 0.01−0.04; d = 0.96−1.74) and sweat loss by 0.4±0.3 kg (P = 0.01; d = 0.34). Mean rating of perceived exertion and thermal sensation were lower during pre-cooling trials (P = 0.004−0.03; d = 0.77−3.13). Despite no observed improvement in bowling performance, pre-cooling maintained between-over sprint speeds and blunted physiological and perceptual demands to ease the thermoregulatory demands of medium-fast bowling in hot conditions.

Specificity and context in post-exercise recovery: it is not a one-size-fits-all approach

The concept of specificity of exercise prescription and training is a longstanding and widely accepted foundation of the exercise sciences. Simply, the principle holds that training adaptations are achieved relative to the stimulus applied. That is, the manipulation of training variables (e.g. intensity or loading, mode, volume and frequency) directly influences the acute training stimulus, and so the long-term adaptive response (Young et al., 2001; Bird et al., 2005). Translating this concept to practice then recommends that exercise be prescribed specific to the desired outcomes, and the more closely this is achieved, the greater the performance gain is likely to be. However, the cardiovascular and metabolic adaptations traditionally associated with long, slow distance training types, similarly achieved using high-intensity training methods (for a review see Gibala et al., 2012), highlights understanding of underlying physiology as paramount for effective training program design. Various other factors including illness, sleep and psychology also impact on the training stimulus (Halson, 2014) and must be managed collectively with appropriate post-exercise recovery to continue performance improvements and reduce overtraining and injury risks (Kentta and Hassmen, 1998).

Heat acclimation for protection from exertional heat stress

This is a protocol for a Cochrane Review (Intervention). The objectives are as follows: To assess the effects of heat acclimation interventions aimed at protecting health and performance from exertional heat stress.

Occupational cooling practices of emergency first responders in the United States: A survey

ABSTRACT Despite extensive documentation directed specifically toward mitigating thermal strain of first responders, we wished to ascertain the degree to which first responders applied cooling strategies, and what opinions are held by the various agencies/departments within the United States. An internet-based survey of first responders was distributed to the International Association of Fire Chiefs, International Association of Fire Firefighters, National Bomb Squad Advisory Board and the USA Interagency Board and their subsequent departments and branches. Individual first responder departments were questioned regarding the use of pre-, concurrent, post-cooling, types of methods employed, and/or reasons why they had not incorporated various methods in first responder deployment. Completed surveys were collected from 119 unique de-identified departments, including those working in law enforcement (29%), as firefighters (29%), EOD (28%) and HAZMAT technicians (15%). One-hundred and eighteen departments (99%) reported heat strain/illness to be a risk to employee safety during occupational duties. The percentage of departments with at least one case of heat illness in the previous year were as follows: fire (39%) HAZMAT (23%), EOD (20%) and law enforcement (18%). Post-cooling was the scheduled cooling method implemented the most (63%). Fire departments were significantly more likely to use post-cooling, as well as combine two types of scheduled cooling compared to other departments. Importantly, 25% of all departments surveyed provided no cooling whatsoever. The greatest barriers to personnel cooling were as follows – availability, cost, logistics, and knowledge. Our findings could aid in a better understanding of current practices and perceptions of heat illness and injury prevention in United States first responders. Abbreviations: EOD: explosive ordnance disposal; HAZMAT: hazardous materials