A heat acclimation protocol for team sports

Background: It is well documented that heat acclimation of 6 or more sessions of at least 60 min duration prolongs the time to exhaustion during endurance walking, cycling and running in the heat. However, this type of acclimation is not specific to team sport activity and the effect of acclimation on prolonged high intensity intermittent running has not yet been investigated. Objective: To assess the impact of an intermittent acclimation protocol on distance run during team sport activity. Methods: The impact of 4 short heat acclimation sessions (30 – 45 min of the Loughborough Intermittent Shuttle Test; LIST) on high-intensity intermittent running capacity (LIST) in the heat (30oC, 27% RH), was examined. Seventeen female welltrained games players were split into 3 groups; an acclimation group (30oC, 24% RH), a moderate training group (18oC, 41% RH), and a control group who did not complete any training between the main trials (pre- and post-acclimation). The pre- (A) and post-acclimation (B) trials were separated by 28 days to control for menstrual phase and verified using hormonal analysis. The 4 acclimation or moderate training sessions utilising the LIST were completed with one or two rest days interspersed between each session in a 10-day period prior to the post-acclimation trial (B). Results: In the post-acclimation trial distance run was increased by 33% in the acclimation group (A: 7703 ± 1401 vs B: 10215 ± 1746m; interaction group x trial P<0.05), but was unchanged in the moderate and control groups. The acclimation group had a lower rectal temperature (interaction group x trial x time P<0.01) due to a lower rate of rise, and an increase in thermal comfort [1] after acclimation (End A: 7 ± 2 vs 6 ± 2; interaction group x trial P<0.01). There was no difference in serum 3 progesterone, aldosterone or cortisol concentrations following acclimation or between groups. Conclusion: Four 30-45 min sessions of intermittent exercise induced acclimation, and resulted in an improvement in intermittent running exercise capacity in female games players. A lower rectal temperature and a concomitant rise in thermal comfort may be partly responsible for the improvement in exercise capacity

Match Analysis of U9 and U10 English Premier League Academy Soccer Players Using a Global Positioning System

The purpose of this study was to examine the match activity profile of U9 and U10 elite soccer players and to establish if there were any differences between players who were subsequently retained or released by their clubs. Such information should prove valuable in the design of training programs for these very young players and in the talent identification and development process. A Global Positioning System was used to analyze 2-4 inter-academy 6-a-side matches of English Premier League Academy players (U9: N=22 and U10: N=12) who trained three times a week (4.5 h). Speed zones were created based on 5 and 10m sprint times and an independent sample t-test was employed for a statistical analysis. Both squads covered ~4000 m in total or ~4700 m·h-1 during a match (NS between squads), with the U10s tending to cover a greater distance at moderate (p = 0.10) and high speeds (p=0.08) than the U9s. Retained group covered a greater distance than released group (retained vs. released: 4478±513 m vs. 4091±462 m, p<0.05) during a match and covered a greater distance during low speed running in absolute (1226±259 m vs. 1005±221 m, p<0.05) and relative (1325±235 m·h-1 vs. 1132±210 m·h-1, p<0.05) terms. Thus, U9 and U10 players cover over 4000 m in match play and those players who are retained by academies cover a greater distance in total and at low speeds (2.1-3.1 m·s-1). This information may support the preparation of squad training programs and the talent identification and development process

Influence of biological maturity on the match performance of 8 to 16 year old elite male youth soccer players

The aim of this study was to examine the influence of biological maturity on match performance in elite youth male soccer players. The participants were 80 Premier League Academy outfield players (8-16 years old). Biological maturity was determined by calculating estimated chronological age at peak height velocity. The U9 and U10 squads played 6-a-side and the U11-U16 squads played 11-a-side inter-academy matches. All matches were analyzed using a 1 Hz Global Positioning System (SPI elite, GPSport, Australia) with squad specific speed zones which were calculated based on 5 m flying sprint speed in the last 5 m of 10 m sprint test. In the U9/U10s, earlier maturers were given a longer pitch time by coaches (~4 min per match, p = 0.029) and covered a greater total distance (~9%, ~400 m, p = 0.037) and a greater distance by walking (~13%, ~100 m, p = 0.024) and jogging (~12%, ~200 m, p = 0.014) during a match compared to later maturers. In the U13/U14s, earlier maturers covered a greater distance per hour of a match by high speed running compared to later maturers (~25%, ~130 m, p = 0.028) and spent a longer percentage of time in high speed running during a match compared to later maturers (3.4% vs. 2.7%, p = 0.034). Thus, coaches should take care to provide all players with a similar pitch-time and should be aware in the talent identification and development process, particularly with the U13/U14 age group, that maturity can influence high speed match running performance

Motion analysis of U11 to U16 elite English Premier League Academy players

This study examined: 1) the distances and speeds covered during match play for U11 to U16 English Premier League Academy players; 2) the differences in match performance between retained and released players; and 3) the effect of calculating speed zones in different ways when analysing match performance. Eighty-one Academy outfield players (10 to 16 years old), competing in 11-a-side matches, were analysed using a 1 Hz Global Positioning System with three speed zones (absolute, squad, individual). Pitch dimensions were: 78.7 x 54.1 m (U11 and U12); 88.0 x 64.2 m (U13); and 100.8 x 68.2 m (U14-U16). Match durations were: 20 min x 2 + 15 min x 2 or 25 min x 3 (U11); 25 min x 3 (U12 and U13); and 40 min x 2 (U14-U16). The matches were part of the regular series of inter-academy matches between Premier League Academies during a season. Completion of at least a half of the duration of a match in two separate matches (mean ± SD = 3.1 ± 0.8 matches: range: 2-4 matches) was the criterion for inclusion in the study. Total match running distance increased with age from ~5700 m·h-1 (U11) to ~6700 m·h-1 (U15) (p 6.0 m∙s-1) distance covered with age (U11: 29 m·h-1, U16: 164 m·h-1, p<0.01). Using the squad speed zones it was possible to discern differences between retained and released players in the U11/U12s (moderate speed running) and in the U15/U16s (walking, jogging and low speed running) (p<0.01). Thus, total and high intensity running distances increase with age and walking, jogging, low speed running and moderate speed running distances are greater in retained than released players and these differences are best identified through the use of absolute and squad speed zones, respectively

The accumulation of exercise and postprandial endothelial function in boys

The purpose of this study was to investigate the effect of accumulating 60 min of exercise on endothelial function and triacylglycerol concentrations following the ingestion of a high-fat breakfast and lunch in fourteen adolescent boys (aged 12 to 14 years). Two, 2-day main trials (control and exercise) were completed in a counter-balanced, cross-over design. Participants were inactive on day 1 of the control trial but on day 1 of the exercise trial completed 6 x 10 min runs at 70% of peak oxygen uptake, spread over the day. On day 2 triacylglycerol concentrations and flow-mediated dilation (FMD) were measured prior to, and following, ingestion of the high-fat meals. In the control trial FMD was reduced by 30% and 33% (P0.05). These results support the concept of accumulating physical activity for health in adolescents as the accumulated exercise attenuated the decline in FMD seen following the consumption of high-fat meals

The effects of a mid-morning bout of exercise on adolescents' cognitive function

The aim of the present study was to examine the effects of a mid-morning bout of exercise on adolescents’ cognitive function in a randomised crossover design where each participant completed two experimental trials. Forty-five adolescents (13.3±0.3 years old), undertook a bout of exercise (ten repeats of level one of the multi-stage fitness test, 30s rest between repeats; exercise trial) or continued to rest (resting trial). A battery of cognitive function tests assessing visuo-motor speed, executive function and working memory (visual search test, Stroop test and Sternberg paradigm, respectively) was completed 30 min before and 45 min following the exercise. Average heart rate during exercise was 172±17 beats/min. On the visual search test, there was a greater improvement in response times across the morning on the exercise trial (t=2.6, p=0.009). However, this improvement in response times was combined with a greater decrease in accuracy on the exercise trial (z=2.0, p=0.044). On the Sternberg paradigm there was a greater improvement in response times across the morning following exercise when compared to resting (t=2.6, p=0.010). The mid-morning bout of exercise did not affect Stroop test performance. These improvements in response times are most likely the result of a general speeding up of responses across several cognitive domains, because response times were improved similarly across two different domains and across all test complexity levels, rather than being restricted to the specific high cognitive load levels. Accordingly, exercise in school settings may help to improve cognitive function in adolescents during the school morning

Longitudinal development of match-running performance in elite male youth soccer players [forthcoming]

This study longitudinally examined age-related changes in the match-running performance of retained and released elite youth soccer players aged 8-18 years. The effect of playing position on age-related changes was also considered. Across three seasons 263 elite youth soccer players were assessed in 1-29 competitive matches (988 player-matches). For each player-match, total distance and distances covered at age-group-specific speed zones (low-speed, high-speed, sprinting) were calculated using 1 Hz or 5 Hz GPS. Mixed modelling predicted that match-running performance developed non-linearly, with age-related changes best described with quadratic age terms. Modelling predicted that playing position significantly modified age-related changes (p<0.05) and retained players covered significantly more low-speed distance compared to released players (p<0.05), by 75 ± 71 m.h-1 (mean ± 95% CI) (effect size ± 95% CI: 0.35 ± 0.34). Model intercepts randomly varied, indicating differences between players in match-running performance unexplained by age, playing position or status. These findings may assist experts in developing training programmes specific to the match-play demands of players of different ages and playing positions. Although retained players covered more low-speed distance than released players, further study of the actions comprising low-speed distance during match-play is warranted to better understand factors differentiating retained and released players

Breakfast glycaemic index and cognitive function in adolescent school children

It has been suggested that a low-glycaemic index (GI) breakfast may be beneficial for some elements of cognitive function (e.g. memory and attention), but the effects are not clear, especially in adolescents. Thus, the aim of the present study was to examine the effects of a low-GI breakfast, a high-GI breakfast and breakfast omission on cognitive function in adolescents. A total of fifty-two adolescents aged 12–14 years were recruited to participate in the study. Participants consumed a low-GI breakfast, a high-GI breakfast or omitted breakfast. A battery of cognitive function tests was completed 30 and 120 min following breakfast consumption and capillary blood samples were taken during the 120 min postprandial period. The findings show that there was a greater improvement in response times following a low-GI breakfast, compared with breakfast omission on the Stroop (P=0·009) and Flanker (P=0·041) tasks, and compared with a high-GI breakfast on the Sternberg paradigm (P=0·013). Furthermore, accuracy on all three tests was better maintained on the low-GI trial compared with the high-GI (Stroop: P=0·039; Sternberg: P=0·018; Flanker: P=0·014) and breakfast omission (Stroop: P<0·001; Sternberg: P=0·050; Flanker: P=0·014) trials. Following the low-GI breakfast, participants displayed a lower glycaemic response (P<0·001) than following the high-GI breakfast, but there was no difference in the insulinaemic response (P=0·063) between the high- and low-GI breakfasts. Therefore, we conclude that a low-GI breakfast is most beneficial for adolescents' cognitive function, compared with a high-GI breakfast or breakfast omission

Sex differences in adolescents' glycaemic and insulinaemic responses to high and low glycaemic index breakfasts: a randomised control trial

During puberty young people undergo significant hormonal changes which affect metabolism and, subsequently, health. Evidence suggests there is a period of transient pubertal insulin resistance, with this effect greater in girls than boys. However, the response to everyday high and low glycaemic index (GI) meals remains unknown. Following ethical approval, forty adolescents consumed a high GI or low GI breakfast, in a randomised cross-over design. Capillary blood samples were taken during a 2-h postprandial period, examining the glycaemic and insulinaemic responses. Maturity offset and homoeostatic model assessment (HOMA) were also calculated. The glycaemic response to the breakfasts was similar between boys and girls, as shown by similar peak blood glucose concentrations and incremental AUC (IAUC) following both high and low GI breakfasts (all P> 0·05). Girls exhibited a higher peak plasma insulin concentration 30 min post-breakfast following both high GI (P=0·043, g=0·69) and low GI (P =0·010, g =0·84) breakfasts, as well as a greater IAUC following high GI (P=0·041, g =0·66) and low GI (P =0·041, g =0·66) breakfasts. HOMA was positively correlated with the insulinaemic responses (all P<0·0005) and maturity offset (P =0·037). The findings of the present study suggest that pubertal insulin resistance affects the postprandial insulinaemic responses to both high and low GI meals. Specifically, girls exhibit a greater insulinaemic response than boys to both meals, despite similar glycaemic responses. This study is the first to report the glycaemic and insulinaemic responses to everyday meals in boys and girls, supporting the recommendation for young people to base their diet on low GI carbohydrates