Living, training and playing in the heat: challenges to the football player and strategies for coping with environmental extremes

Different humidity environments do not affect the subsequent exercise ability of college football players after aerobic high-intensity interval training

Previous studies have explored the effect of differing heat and relative humidity (RH) environments on the performance of multiple anaerobic high-intensity interval training (HIIT). Still, its impact on physiological responses and performance following aerobic HIIT has not been well studied. This study examined the effects of differing RH environments on physiological responses and performance in college football players following HIIT. Twelve college football completed HIIT under four different environmental conditions: (1) 25 °C/20% RH (Control group); (2) 35 °C/20% RH (H20 group); (3) 35 °C/40% RH (H40 group); (4) 35 °C/80% RH (H80 group). The heart rate (HR), mean arterial pressure (MAP), lactate, tympanic temperature (TT), skin temperature (TS), thermal sensation (TS), and rating of perceived exertion (RPE) were recorded continuously throughout the exercise. The heart rate variability (HRV): including root mean squared differences of the standard deviation (RMSSD)、standard deviation differences of the standard deviation (SDNN)、high frequency (HF), low frequency (LF), squat jump height (SJH), cycling time to exhaustion (TTE), and sweat rate (SR) were monitored pre-exercise and post-exercise. The HR, MAP, lactate, TT, Ts, TS, and RPE in the 4 groups showed a trend of rapid increase, then decreased gradually. There was no significant difference in HR, MAP, TT, or RPE between the 4 groups at the same time point (p > 0.05), in addition to this, when compared to the C group, the lactate, Ts, TS in the other 3 groups significant differences were observed at the corresponding time points (p < 0.05). The RMSSD, SDNN, HF, and LF levels in the 4 groups before exercise were not significantly different. The RMSSD and HF in the H40 and H80 groups were significantly decreased and other HRV indicators showed no significant difference after exercise. In sports performance measurement, the SJH and TTE were significantly decreased, but there was no significant difference in the 4 groups. The SR was no significant difference in the 4 groups after exercise. In conclusion, heat and humidity environments elicited generally greater physiological effects compared with the normal environment but did not affect sports performance in college football players.

Perspectives on Player Performance during FIFA World Cup Qatar 2022: A Brief Report

Changing the date of the FIFA World Cup Qatar 2022 may represent a factor to consider for the expected performance of participating players. This was due to fixture congestion at the start of the season and expected weather conditions during the competition. Thus, the main purpose of this brief report was to critically analyze the potential impact of changing the competition date and weather conditions on players' performance. In addition, a brief description about the performance during the World Cup is also provided. For the research, the Web of Science, PubMed and SPORTDiscus databases were accessed using the primary keywords FIFA World Cup and World Soccer Cup associated with the secondary keywords match running performance, fixture congestion, fatigue and weather conditions. After applying inclusion and exclusion criteria, 52 articles were considered for analysis. The results seem to indicate that although changes were expected due to the modifications made (i.e., the competition date and scheduling congestion), the performance of the players seems not to have been affected in terms of the analyzed indicators. Furthermore, it seems possible to identify some patterns in the behavior of the teams that reached the most advanced stages of the competition.

Is there meaningful influence from situational and environmental factors on the physical and technical activity of elite football players? Evidence from the data of 5 consecutive seasons of the German Bundesliga

The study aimed to identify the effects of situational (match location, match outcome and strength of team/opponent team) and environmental (ambient temperature, relative humidity, WBGT, ground and weather condition) factors on the physical and technical activity of elite football on individual playing positions. Physical and technical activity were collected from 779 football players competing in the German Bundesliga during 5 domestic seasons, from 2014/2015 to 2018/2019, totalling 1530 matches. The data on players' physical and technical activity was taken from the IMPIRE AG system. Based on the available data, 11 variables were selected to quantify the match activity profiles of players. The results showed that situational variables had major effects on the technical performance (especially number of passes performed) but minor effects on physical performance. In turn, among the analysed environmental factors, temperature is the most sensitive, which affects the Total Distance and Sprint Efforts of players in all five positions. This investigation demonstrated that, given that passing is a key technical activity in modern football, players and training staff should be particularly aware that passing maybe affected by situational variables. Professional players are able to react and adapt to various environmental conditions, modifying physical activity depending on the needs in German Bundesliga. These results could help coaches and analysts to better understand the influences of situational and environmental variables on individual playing positions during the evaluation of players' physical and technical performance.

Is temperature an important variable in recovery after mild traumatic brain injury?

With nearly 42 million mild traumatic brain injuries (mTBIs) occurring worldwide every year, understanding the factors that may adversely influence recovery after mTBI is important for developing guidelines in mTBI management. Extensive clinical evidence exists documenting the detrimental effects of elevated temperature levels on recovery after moderate to severe TBI. However, whether elevated temperature alters recovery after mTBI or concussion is an active area of investigation. Individuals engaged in exercise and competitive sports regularly experience body and brain temperature increases to hyperthermic levels and these temperature increases are prolonged in hot and humid ambient environments. Thus, there is a strong potential for hyperthermia to alter recovery after mTBI in a subset of individuals at risk for mTBI. Preclinical mTBI studies have found that elevating brain temperature to 39°C before mTBI significantly increases neuronal death within the cortex and hippocampus and also worsens cognitive deficits. This review summarizes the pathology and behavioral problems of mTBI that are exacerbated by hyperthermia and discusses whether hyperthermia is a variable that should be considered after concussion and mTBI. Finally, underlying pathophysiological mechanisms responsible for hyperthermia-induced altered responses to mTBI and potential gender considerations are discussed.

Genetic biomarkers in non-contact muscle injuries in elite soccer players

PURPOSE

Damage to skeletal muscle necessitates regeneration to maintain proper muscle form and function. Interindividual differences in injury severity, recovery time, and injury rate could be explained by the presence of single nucleotide polymorphisms (SNPs) in genes involved in the reparation and regeneration of connective tissue . We wished to identify new genetic biomarkers that could help to prevent or minimize the risk of non-contact muscle injuries and are associated with a predisposition to developing muscle injuries.

METHODS

Using allelic discrimination techniques, we analysed 12 SNPs in selected genes from the genomic DNA of 74 elite soccer players.

RESULTS

SNPs in the hepatocyte growth factor (HGF) gene showed evidence of a statistically significant association with injury incidence, severity, and recovery time. SNPs in the SOX15 gene showed evidence of a statistically significant association with injury incidence. SNPs in the GEFT and LIF genes showed evidence of a statistically significant association with recovery time.

CONCLUSIONS

Genetic profile could explain why some elite soccer players are predisposed to suffer more injuries than others and why they need more time to recover from a particular injury. SNPs in HGF genes have an important role as biomarkers of biological processes fragility within muscle injuries related to injury rate, severity, and long recovery time.

Evidence for β-adrenergic modulation of sweating during incremental exercise in habitually trained males

The aim of the present study was to determine the β-adrenergic contribution to sweating during incremental exercise in habitually trained males. Nine habitually trained and 11 untrained males performed incremental cycling until exhaustion (20 W/min). Bilateral forearm sweat rates (ventilated capsule) were measured at two skin sites that were transdermally administered via iontophoresis with either 1% propranolol (Propranolol, a nonselective β-adrenergic receptor antagonist) or saline (Control). The sweat rate was evaluated as a function of both relative (percentage of maximum workload) and absolute exercise intensities. The sweat rate at the Propranolol site was lower than the control during exercise at 80 (0.57 ± 0.21 and 0.45 ± 0.19 mg·cm−2·min−1 for Control and Propranolol, respectively) and 90% (0.74 ± 0.22 and 0.65 ± 0.17 mg·cm−2·min−1, respectively) of maximum workload in trained males (all P < 0.05). By contrast, no between-site differences in sweat rates were observed in untrained counterparts (all P > 0.05). At the same absolute intensity, higher sweat rates on the control site were observed in trained males relative to the untrained during exercise at 160 (0.23 ± 0.20 and 0.04 ± 0.05 mg·cm−2·min−1 for trained and untrained, respectively) and 180 W (0.40 ± 0.20 and 0.13 ± 0.13 mg·cm−2·min−1, respectively) (all P < 0.05), whereas this between-group difference was not observed at the Propranolol site (all P > 0.05). We show that the β-adrenergic mechanism does modulate sweating during exercise at a submaximal high relative intensity in habitually trained males. The β-adrenergic mechanism may in part contribute to the greater sweat production in habitually trained males than in untrained counterparts during exercise.

NEW & NOTEWORTHY We demonstrated for the first time that the β-adrenergic mechanism does modulate sweating (i.e., β-adrenergic sweating) during exercise using a localized β-adrenoceptor blockade in humans in vivo. β-Adrenergic sweating was evident in habitually trained individuals during exercise at a submaximal high relative intensity (80–90% maximal work). This observation advances our understanding of human thermoregulation during exercise and of the mechanism that underlies sweat gland adaptation to habitual exercise training.

Comparison of density and output of sweat gland in tropical Africans and temperate Koreans

Modification of sweating could be due to changes in activated sweat gland density (ASGD) and/or activated sweat gland output (ASGO). The present study determined regional and inter-ethnic differences in ASGD and ASGO during passive heating between tropical natives (African, n=22) and temperate natives (Republic of Korean, n=25). Heat load was carried out by immersing the half body into a hot water bath for 30min. Tympanic temperature (Tty) and skin temperature (Ts) were measured. Mean body temperature (mTb) was calculated. Sudomotor activities including sweat onset time, sweat rate, ASGD, and ASGO were examined in eight regions of the skin. Africans had smaller increase in mTb during passive heating than Koreans. The onset time of sweating was much more delayed in Africans compared to Koreans. In response to thermal load, ASGD and ASGO differed between body regions in Africans and Koreans. In most skin regions, ASGD and ASGO were lower in tropical Africans compared to those in temperate Koreans. Trunk portion including chest, upper back, lower back, abdomen had greater swear rate, ASGD, and ASGO compared to peripheral segments including upper arm, forearm, leg, and thigh in both ethnic groups. Distribution patterns of ASGD over the body appeared to be similar in both Africans and Koreans at the peak of thermal loading. In conclusion, the present study demonstrates that sudomotor activity in tropical Africans is reduced with lower ASGD and ASGO over the body surface compared to temperate Koreans.

Physical activity profile of 2014 FIFA World Cup players, with regard to different ranges of air temperature and relative humidity

The present study attempts to assess changes in soccer players' physical activity profiles under the simultaneous influence of the different combinations of ambient temperature and relative humidity characterising matches of the 2014 FIFA World Cup hosted by Brazil. The study material consisted of observations of 340 players representing 32 national teams taking part in the tournament. The measured indices included total distances covered; distances covered with low, moderate, or high intensity; numbers of sprints performed, and peak running speeds achieved. The analysis was carried out using FIFA official match data from the Castrol Performance Index system. Ultimately, consideration was given to a combination of three air temperature ranges, i.e. below 22 °C, 22-28 °C, and above 28 °C; and two relative humidity ranges below 60 % and above 60 %. The greatest average distance recorded (10.54 ± 0.91 km) covered by players at an air temperature below 22 °C and a relative humidity below 60 %, while the shortest (9.83 ± 1.08 km) characterised the same air temperature range, but conditions of relative humidity above 60 % (p ≤ 0.001). Two-way ANOVA revealed significant differences (p ≤ 0.001) in numbers of sprints performed by players, depending on whether the air temperature range was below 22 °C (40.48 ± 11.17) or above 28 °C (30.72 ± 9.40), but only where the relative humidity was at the same time below 60 %. Results presented indicate that the conditions most comfortable for physical activity on the part of players occur at 22 °C, and with relative humidity under 60 %.

Influence of Environmental Conditions on Performance and Heart Rate Responses to the 30-15 Incremental Fitness Test in Rugby Union Athletes

Natera, AOW, Jennings, J, Oakley, AJ, and Jones, TW. Influence of environmental conditions on performance and heart rate responses to the 30-15 incremental fitness test in rugby union athletes. J Strength Cond Res 33(2): 486-491, 2019-The purpose of this study was to examine the differences in performance and heart rate (HR) responses between a high heat outdoor condition (34.0° C, 64.1% humidity) and a temperate indoor condition (22.0° C, 50.0% humidity) during the 30-15 intermittent fitness test (30-15IFT). Eight highly trained Rugby Union players (28.1 ± 1.5 years, 181.4 ± 8.8 cm, 88.4 ± 13.3 kg) completed the 30-15IFT in 2 different temperature conditions. Dependent variables recorded and analyzed included: final running speed of the 30-15IFT, HR at rest (HR rest), maximum HR (Max HR), HR recovery, average HR (HR ave), and submaximal HR corresponding to 25, 50, and 75% of final test speed (HR 25%, HR 50%, and HR 75%) and HR at 13 km·h (HR 13 km·h). Greater running speeds were achieved when the test was conducted indoors (19.4 ± 0.7 km·h vs. 18.6 ± 0.6 km·h, p = 0.002, d = 1.67). Average HR and HR 13 km·h were greater when the test was conducted outdoors (p ≤ 0.05, d > 0.85). Large effect sizes were observed for the greater HR at submaximal intensities (d > 0.90). The results of this study highlight the influence of temperature on 30-15IFT performance and cardiac responses. It is recommended that prescription of training based on 30-15IFT results reflects the temperature that the training will be performed in and that practitioners acknowledge that a meaningful change in assessment results can be the result of seasonal temperature change rather than training-induced change.

Energy expenditure in caving

The aim of this study was to determine the energy expenditure of a group of cavers of both genders and different ages and experience during a 10 hour subterranean exploration, using portable metabolimeters. The impact of caving activity on body composition and hydration were also assessed through bioelectrical impedance, and nutritional habits of cavers surveyed. During cave activity, measured total energy expenditure (TEE) was in the range 225-287 kcal/h for women-men (MET = 4.1), respectively; subjects had an energy intake from food in the range 1000-1200 kcal, thus inadequate to restore lost calories. Bayesian statistical analysis estimated the effect of predictive variables on TEE, revealing that experienced subjects had a 5% lower TEE than the less skilled ones and that women required a comparatively larger energy expenditure than men to perform the same task. BIVA (bioelectrical impedance vector analysis) showed that subjects were within the range of normal hydration before and after cave activity, but bioelectrical changes indicated a reduction of extracellular water in men, which might result in hypo-osmolal dehydration in the case of prolonged underground exercise. All these facts should be considered when planning cave explorations, preparing training programs for subjects practising caving, and optimizing a diet for cavers. Further, information gathered through this study could be of value to reduce accidents in caves related to increase in fatigue.

Improved sweat gland function during active heating in tennis athletes

BACKGROUND

Relatively few studies on the peripheral sweating mechanisms of trained tennis athletes have been conducted. The purpose of this study was to compare the sweating capacities of tennis athletes against untrained subjects (controls).

METHODS

Thirty-five healthy male volunteers participated including 15 untrained subjects and 20 trained tennis athletes (nationally ranked). Active heat generation was performed for 30 min (running at 60% VO 2 max ) in a climate chamber (temperature, 25.0°C ± 0.5°C; relative humidity, 60% ± 3%, termed active heating). Sweating data (local sweat onset time, local sweat volume, activated sweat glands, sweat output per gland, whole body sweat loss volume) were measured by the capacitance hygrometer-ventilated capsule method and starch-iodide paper. Mean body temperature was calculated from tympanic and skin temperatures.

RESULTS

Local sweat onset time was shorter for tennis athletes (p < 0.001). Local sweat volume, activated sweat glands of the torso and limbs, sweat output per gland, and whole body sweat loss volume were significantly higher for tennis athletes than control subjects after active heating (p < 0.001). Tympanic and mean body temperatures were lower among tennis athletes than controls (p < 0.05).

CONCLUSION

These results indicate that tennis athletes had increased regulatory capacity of their sweat gland function.

Evaluation of 2 Heat-Mitigation Methods in Army Trainees

CONTEXT

 Heat injury is a significant threat to military trainees. Different methods of heat mitigation are in use across military units. Mist fans are 1 of several methods used in the hot and humid climate of Fort Benning, Georgia.

OBJECTIVES

 To determine if (1) the mist fan or the cooling towel effectively lowered participant core temperature in the humid environment found at Fort Benning and (2) the mist fan or the cooling towel presented additional physiologic or safety benefits or detriments when used in this environment.

DESIGN

 Randomized controlled clinical trial.

SETTING

 Laboratory environmental chamber.

PATIENTS OR OTHER PARTICIPANTS

 Thirty-five physically active men aged 19 to 35 years.

INTERVENTION(S)

 (1) Mist fan, (2) commercial cooling towel, (3) passive-cooling (no intervention) control. All treatments lasted 20 minutes. Participants ran on a treadmill at 60% V̇o₂max.

MAIN OUTCOME MEASURE(S)

 Rectal core temperature, heart rate, thermal comfort, perceived temperature, perceived wetness, and blood pressure.

RESULTS

 Average core temperature increased during 20 minutes of cooling (F_1,28 = 64.76, P < .001, η_p² = 0.70), regardless of group (F_1,28 = 3.41, P = .08, η_p² = 0.11) or condition (F_1,28 < 1.0). Core temperature, heart rate, and blood pressure did not differ among the 3 conditions. Perceived temperature during 20 minutes of cooling decreased (F_1,30 = 141.19, P < .001, η_p² = 0.83) regardless of group or condition. Perceived temperature was lower with the mist-fan treatment than with the control treatment (F_1,15 = 7.38, P = .02, η_p² = 0.32). The mist-fan group perceived themselves to be cooler even at elevated core temperatures.

CONCLUSIONS

 The mist fan and cooling towel were both ineffective at lowering core temperature. Core temperature continued to increase after exercise in all groups. The mist fan produced feelings of coolness while the core temperature remained elevated, possibly increasing the risk of heat illness.

Hydration: The New FIFA World Cup's Challenge for Referee Decision Making?

Various continental sporting events have exposed team sports referees to different environmental conditions. Several studies have focused on strategies to prevent athlete performance impairment induced by heat or warm (or both) conditions, but few authors have investigated the effect of heat on referees' performance. In a thermoneutral environment, referees' physical activity induced mild 2.0% dehydration, which was responsible for reductions in physical, psychomotor, and cognitive performances. Therefore, the hydration status of referees should be taken into account to reduce referees' errors and misjudgments in the heat.

Short-term heat acclimation training improves physical performance: a systematic review, and exploration of physiological adaptations and application for team sports

BACKGROUND

Studies have demonstrated that longer-term heat acclimation training (≥8 heat exposures) improves physical performance. The physiological adaptations gained through short-term heat acclimation (STHA) training suggest that physical performance can be enhanced within a brief timeframe.

OBJECTIVE

The aim of this systematic review was to determine if STHA training (≤7 heat exposures) can improve physical performance in healthy adults.

DATA SOURCES

MEDLINE, PubMed, and SPORTDiscus™ databases were searched for available literature.

STUDY SELECTION

Studies were included if they met the following criteria: STHA intervention, performance measure outcome, apparently healthy participants, adult participants (≥18 years of age), primary data, and human participants.

STUDY APPRAISAL

A modified McMaster critical appraisal tool determined the level of bias in each included study.

RESULTS

Eight papers met the inclusion criteria. Studies varied from having a low to a high risk of bias. The review identified aerobic-based tests of performance benefit from STHA training. Peak anaerobic power efforts have not been demonstrated to improve.

LIMITATIONS

At the review level, this systematic review did not include tolerance time exercise tests; however, certain professions may be interested in this type of exercise (e.g. fire-fighters). At the outcome level, the review was limited by the moderate level of bias that exists in the field. Only two randomized controlled trials were included. Furthermore, a limited number of studies could be identified (eight), and only one of these articles focused on women participants.

CONCLUSIONS

The review identified that aerobic-based tests of performance benefit from STHA training. This is possibly through a number of cardiovascular, thermoregulatory, and metabolic adaptations improving the perception of effort and fatigue through a reduction in anaerobic energy release and elevation of the anaerobic threshold. These results should be viewed with caution due to the level of available evidence, and the limited number of papers that met the inclusion criteria of the review. STHA training can be applied in the team-sport environment during a range of instances within the competitive season. A mixed high-intensity protocol may only require five sessions with a duration of 60 min to potentially improve aerobic-based performance in trained athletes.

Seasonal Acclimatization in Summer versus Winter to Changes in the Sweating Response during Passive Heating in Korean Young Adult Men

We investigated the sweating response during passive heating (partial submersion up to the umbilical line in 42±0.5℃ water, 30 min) after summer and winter seasonal acclimatization (SA). Testing was performed in July during the summer, 2011 [summer-SA; temp, 25.6±1.8℃; relative humidity (RH), 82.1±8.2%] and in January during the winter, 2012 (winter-SA; temp, -2.7±2.9℃; RH, 65.0±13.1%) in Cheonan (126°52'N, 33.38'E), Republic of Korea. All experiments were carried out in an automated climatic chamber (temp, 25.0±0.5℃: RH, 60.0±3.0%). Fifteen healthy men (age, 23.4±2.5 years; height, 175.0±5.9 cm; weight, 65.3±6.1 kg) participated in the study. Local sweat onset time was delayed during winter-SA compared to that after summer-SA (p< 0.001). Local sweat volume, whole body sweat volume, and evaporative loss volume decreased significantly after winter-SA compared to those after summer-SA (p<0.001). Changes in basal metabolic rate increased significantly after winter-SA (p< 0.001), and tympanic temperature and mean body temperature were significantly lower after summer-SA (p<0.05). In conclusion, central sudomotor acitivity becomes sensitive to summer-SA and blunt to winter-SA in Rebubic of Korea. These results suggest that the body adjusts its temperature by economically controlling the sweating rate but does not lower the thermal dissipation rate through a more effective evaporation scheme after summer-SA than that after winter-SA.

Sauna-induced body mass loss in young sedentary women and men

The aim of the study was to evaluate the relationship between body mass index (BMI) and body mass loss (BML) induced by thermal stress in a dry sauna. The study was conducted on a group of 674 sedentary students, 326 women and 348 men aged 19-20. The correlations between BMI scores and BML were determined. The subjects were placed in supine position in a dry sauna for two sessions of 10 minutes each with a 5-minute break. The influence of BMI on the amount of BML in the sauna was determined by nonlinear stepwise regression. The smallest BML was noted in underweight subjects; students with normal weight lost more weight, whereas the greatest BML was reported in overweight and obese subjects. Persons with a high BMI are at higher risk of dehydration, and they should pay particular attention to replenishing fluids during a visit to the sauna. The proposed equations for calculating BML based on a person's BMI can be useful in estimating the amount of fluids that should be replenished by both men and women during a visit to a dry sauna.

Perda hidrica e pratica de hidratacao em atletas de futebol

INTRODUÇÃO: Atletas de futebol sofrem grande estresse fisiológico durante os treinos. As características da atividade associadas às condições climáticas desfavoráveis podem provocar desidratação intensa resultando em redução de desempenho físico. OBJETIVO: Estimar o percentual de desidratação de atletas futebolistas durante sessões de treino na cidade de Cuiabá-MT, Brasil. MÉTODOS: Os dados foram coletados nas instalações do centro de treinamento da equipe. Participaram do estudo 17 atletas profissionais do sexo masculino (idade = 21,53 ± 1,19 anos; peso=71,99±7,66 kg; estatura=1,76±0,08m; IMC=23,31±1,69kg/m²). Foram analisadas as pesagens de pré e pós-treino em dois dias não consecutivos de treino (A e B) e pela perda de peso ocorrida, obteve-se a diferença de massa corporal (ΔMC); também se anotou toda a ingestão de líquidos. Os dados registrados foram aplicados às fórmulas específicas para análise. RESULTADOS: O ΔMC entre a medida inicial e a medida final do treino A foi de 1,08 ± 0,45 kg, já a do treino B foi de 0,85 ± 0,47kg, representando 1,5 ± 0,63% e 1,19 ± 0,59% de desidratação, respectivamente. O volume de líquido ingerido foi de 2.591 ± 440 ml no treino A e de 926 ± 356 ml no treino B. A prática do futebol reduziu a massa corporal dos atletas após o treino, indicando que houve desidratação. CONCLUSÃO: Apesar da oferta constante de água aos jogadores, observamos que a reposição hídrica ad libitum não foi suficiente para manter o estado eu-hidratado de todos os atletas.

Single nucleotide polymorphisms associated with non-contact soft tissue injuries in elite professional soccer players: influence on degree of injury and recovery time

BACKGROUND

The biological mechanisms involved in non-contact musculoskeletal soft tissue injuries (NCMSTI) are poorly understood. Genetic risk factors may be associated with susceptibility to injuries, and may exert marked influence on recovery times.

METHODS

Data on type and degree of injury and recovery time were collected in 73 male professional soccer players (43 White, 11 Black Africans and 19 Hispanics) who suffered total of 242 injuries (203 muscle, 24 ligament, and 15 tendon injuries). One single nucleotide polymorphism (SNPs) in the following genes were analyzed: Elastin (ELN); Titin (TTN); SRY-related HMG-box (SOX15); Insulin-like growth factor 2 (IGF2); Chemokine, CC motif, ligand 2 (CCL2); Collagen type 1 alpha 1(COL1A1); Collagen type 5 alpha 1 (COL5A1), and Tenascin C (TNC).

RESULTS

There was evidence of a statistically significant association between the degree of injury and the IGF2 genotype (P = 0.034). In addition, there was evidence of a statistically significant association between the degree of muscle injury and CCL2 (P = 0.026) Finally, there was evidence of a statistically significant association between ELN and degree of injury (p = 0.009) and recovery time (P = 0.043). There was no evidence of a statistically significant association between any of the genes studied and degree of injury or recovery time for tendon injuries.

CONCLUSION

SNPs in the IGF2, CCL2, and ELN genes may be associated to the degree and recovery time of NCMSTI.

The evaporative requirement for heat balance determines whole-body sweat rate during exercise under conditions permitting full evaporation

Although the requirements for heat dissipation during exercise are determined by the necessity for heat balance, few studies have considered them when examining sweat production and its potential modulators. Rather, the majority of studies have used an experimental protocol based on a fixed percentage of maximum oxygen uptake (% ). Using multiple regression analysis, we examined the independent contribution of the evaporative requirement for heat balance (Ereq) and % to whole-body sweat rate (WBSR) during exercise. We hypothesised that WBSR would be determined by Ereq and not by % . A total of 23 males performed two separate experiments during which they exercised for 90 min at different rates of metabolic heat production (200, 350, 500 W) at a fixed air temperature (30°C, n = 8), or at a fixed rate of metabolic heat production (290 W) at different air temperatures (30, 35, 40°C, n = 15 and 45°C, n = 7). Whole-body evaporative heat loss was measured by direct calorimetry and used to calculate absolute WBSR in grams per minute. The conditions employed resulted in a wide range of Ereq (131-487 W) and % (15-55%). The individual variation in non-steady-state (0-30 min) and steady-state (30-90 min) WBSR correlated significantly with Ereq (P < 0.001). In contrast, % correlated negatively with the residual variation in WBSR not explained by Ereq, and marginally increased (∼2%) the amount of total variability in WBSR described by Ereq alone (non-steady state: R(2) = 0.885; steady state: R(2) = 0.930). These data provide clear evidence that absolute WBSR during exercise is determined by Ereq, not by % . Future studies should therefore use an experimental protocol which ensures a fixed Ereq when examining absolute WBSR between individuals, irrespective of potential differences in relative exercise intensity.

Metabolic limitations of performance and fatigue in football

Football participation requires considerable utilization of both aerobic and anaerobic energy systems to match the high energetic demands of the sport. The consequent stresses imposed on the physiological and metabolic systems carries players to the threshold of exhaustion during match-play, from which they are required to recover in preparation for the subsequent game. A high number of players experience fatigue during the high-intensity bouts and a consequent decline in their performance towards the end of the game is a likely outcome during match-play. The current review aims to establish the current understanding that relates to metabolic limitations of performance and the associated mechanisms for the onset of fatigue that may be instrumental in further development of evidence-based nutritional and training interventions in this event.

Risk management: FIFA's approach for protecting the health of football players

BACKGROUND

Sport and exercise have long-term health benefits, but there is also a risk that participants will sustain injuries and/or ill health from these activities. For this reason, international sports governing bodies have a responsibility to identify the risks that exist within their sport and to provide guidance to participants and other stakeholders on how these risks can be controlled within acceptable levels.

PURPOSE

To demonstrate how Fédération Internationale de Football Association (FIFA), as football's governing body, uses a risk management framework to identify, quantify, mitigate and communicate the risks of injury and ill health in football for men, women and children in all environments.

METHOD

All the research papers published by FIFA's Medical Assessment and Research Centre (F-MARC) during the period 1994 to 2011 were reviewed and categorised according to an established sport-related risk management framework.

CONCLUSIONS

F-MARC investigated and mitigated 17 areas of risk to footballers' health in a coherent and consistent approach through the process of risk management.

Physiological and performance adaptations to an in-season soccer camp in the heat: associations with heart rate and heart rate variability

The aim of the present study was to examine the associations between adaptive responses to an in-season soccer training camp in the heat and changes in submaximal exercising heart rate (HRex, 5-min run at 9  km/h), postexercise HR recovery (HRR) and HR variability (HRV). Fifteen well-trained but non-heat-acclimatized male adult players performed a training week in Qatar (34.6 ± 1.9°C wet bulb globe temperature). HRex, HRR, HRV (i.e. the standard deviation of instantaneous beat-to-beat R-R interval variability measured from Poincaré plots SD1, a vagal-related index), creatine kinase (CK) activity, plasma volume (PV) changes, and post-5-min run rate of perceived exertion (RPE) were collected at six occasions in temperate environmental conditions (22°C). Players also performed the yo-yo intermittent recovery test level 1 (Yo-Yo IR1) in the same environmental conditions (22°C), both at the beginning and at the end of the training week. Throughout the intervention, HRex and HRV showed decreasing (P < 0.001) and increasing (P < 0.001) trends, respectively, while HRR remained unaffected (P = 0.84). Changes in HRex [-0.52, 90% confidence limits (-0.64; -0.38), P < 0.001] and SD1 [0.35 (0.19; 0.49), P < 0.001] were correlated with those in PV. There was no change in RPE (P = 0.92), while CK varied according to training contents (P < 0.001), without association with HR-derived measures. Yo-Yo IR1 performance increased by 7 ± 9% (P = 0.009), which was correlated with changes in HRex [-0.64 (-0.84; -0.28), P = 0.01]. In conclusion, we found that an in-season soccer training camp in the heat can significantly improve PV and soccer-specific physical performance; both of which are associated with changes in HRex during a 5-min submaximal run.