Pre-race dietary carbohydrate intake can independently influence sub-elite marathon running performance

We examined whether selected anthropometric and nutritional factors influenced field-based marathon running performance. An internet-based data collection tool allowed competitors in the 2009 London Marathon (n=257, mean ± SD age: 39 ± 8 years, finish time: 273.8 ± 59.5 min) to record a range of anthropometric, training and nutritional predictors. Multivariate statistical methods were used to quantify the change in running speed mediated by a unit change in each predictor via the 95% confidence interval for each covariate-controlled regression slope ( B). Gender ( B=1.22 to 1.95 km/h), body mass index ( B=-0.14 to -0.27 km/h), training distance ( B=0.01 to 0.04 km/h) and the amount of carbohydrate consumed the day before the race ( B=0.08 to 0.26 km/h) were significant predictors, collectively accounting for 56% of the inter-individual variability in running speed (P<0.0005). Further covariate-adjusted analysis revealed that those competitors who consumed carbohydrate the day before the race at a quantity of >7 g/kg body mass had significantly faster overall race speeds (P=0.01) and maintained their running speed during the race to a greater extent than with those who consumed <7 g/kg body mass (P=0.02). We conclude that, in addition to gender, body size and training, pre-race day carbohydrate intake can significantly and independently influence marathon running performance.

Diurnal variation in time to presyncope and associated circulatory changes during a controlled orthostatic challenge

Epidemiological data indicate that the risk of neurally mediated syncope is substantially higher in the morning. Syncope is precipitated by cerebral hypoperfusion, yet no chronobiological experiment has been undertaken to examine whether the major circulatory factors, which influence perfusion, show diurnal variation during a controlled orthostatic challenge. Therefore, we examined the diurnal variation in orthostatic tolerance and circulatory function measured at baseline and at presyncope. In a repeated-measures experiment, conducted at 0600 and 1600, 17 normotensive volunteers, aged 26 ± 4 yr (mean ± SD), rested supine at baseline and then underwent a 60° head-up tilt with 5-min incremental stages of lower body negative pressure until standardized symptoms of presyncope were apparent. Pretest hydration status was similar at both times of day. Continuous beat-to-beat measurements of cerebral blood flow velocity, blood pressure, heart rate, stroke volume, cardiac output, and end-tidal Pco2 were obtained. At baseline, mean cerebral blood flow velocity was 9 ± 2 cm/s (15%) lower in the morning than the afternoon ( P < 0.0001). The mean time to presyncope was shorter in the morning than in the afternoon (27.2 ± 10.5 min vs. 33.1 ± 7.9 min; 95% CI: 0.4 to 11.4 min, P = 0.01). All measurements made at presyncope did not show diurnal variation ( P > 0.05), but the changes over time (from baseline to presyncope time) in arterial blood pressure, estimated peripheral vascular resistance, and α-index baroreflex sensitivity were greater during the morning tests ( P < 0.05). These data indicate that tolerance to an incremental orthostatic challenge is markedly reduced in the morning due to diurnal variations in the time-based decline in blood pressure and the initial cerebral blood flow velocity “reserve” rather than the circulatory status at eventual presyncope. Such information may be used to help identify individuals who are particularly prone to orthostatic intolerance in the morning.

Match-to-match variability of high-speed activities in premier league soccer

The aim of the present investigation was to determine the between-match variability of high-speed running activities completed by a large sample of elite players over an extended period of time. A further aim of the study was to determine the influence of playing position on the magnitude of this variability. Observations on individual match performance measures were undertaken on 485 outfield players (median of 10 games per player; range=2-57) competing in the English Premier League from 2003/2004 to 2005/2006 using a computerised tracking system (Prozone, Leeds, England). High-speed activities selected for analysis included total high-speed running distance (THSR), high-speed running (HSR), total sprint distance (TSD) and the total number of sprints undertaken. Total high-speed running distance in possession and without possession of the ball was also analysed. Match-to-match variability was generally high across all variables with a mean CV of 16.2+/-6.4% (95% CI=15.6-16.7%) and 30.8+/-11.2% (95% CI=29.9-31.7%) reported for HSR and TSD covered during a game. This variability was generally higher for central players (midfielders and defenders) and lower for wide midfielders and attackers. Greater variability was also noted when the team were in possession of the ball (approximately 30%) than when they did not have possession (approximately 23%). The findings of the present study indicate that match-to-match variability in performance characteristics of elite soccer players is high. This inherent variability means that research requires large sample sizes in order to detect real systematic changes in performance characteristics.

Lifestyle factors and colorectal cancer risk (2): a systematic review and meta-analysis of associations with leisure-time physical activity

OBJECTIVE

Increased physical activity may decrease the risk of colorectal cancer. As a prerequisite to the determination of lifestyle attributable risks, we performed a systematic review and meta-analysis of prospective observational studies to quantify gender-specific risk associated with increased leisure-time physical activity (LT-PA).

METHOD

We searched MEDLINE and EMBASE (to December 2007), and other sources, selecting reports based on strict inclusion criteria. We used random-effects meta-analyses to estimate summary risk ratios (RR) and 95% confidence intervals (95% CI) for uppermost vs lowermost categories of physical activity. To investigate dose-response, we explored risks ratios as a function of cumulative percentiles of physical activity distribution.

RESULTS

Fifteen datasets from 14 articles, including 7873 incident cases, were identified. For colon cancer, there were inverse associations with LT-PA for men (RR: 0.80; 95% CI: 0.67-0.96) and women (0.86; 0.76-0.98). LT-PA did not influence risk of rectal cancer. The dose-response analysis was consistent with linear pattern reductions in risk of colon cancer in both genders. There was evidence of moderate between-study heterogeneity but summary estimates were broadly consistent across potential confounding factors.

CONCLUSION

Increased LT-PA is associated with a modest reduction in colon but not rectal cancer risk; a risk reduction, which previously may have been overstated. LT-PA only interventions in public health cancer prevention strategies are unlikely to impact substantially on colorectal cancer incidences.

Prior exercise lowers blood pressure during simulated night-work with different meal schedules

BACKGROUND

Shift-work and a sedentary lifestyle are risk factors for raised blood pressure (BP). Exercise can reduce BP in diurnally-active individuals, but it is unknown whether postexercise hypotension persists when people are active and eating at night. We present the first investigation into the acute effects of exercise on BP monitored during simulated night-work.

METHODS

Nine normotensive participants, aged 20-42 years, completed at least two crossover trials beginning at 1800 hours. Between 1900 and 2000 hours, participants either rested or exercised at 50% peak oxygen uptake (VO(2peak)) and then remained awake throughout the night, completing various tasks until 0515 hours. Six participants completed a total of four trials in which they exercised or rested, whereas either one standardized (60 kJ/kg) meal at 2200 hours or two smaller (30 kJ/kg) meals at 2200 and 0200 hours were eaten. Systolic and diastolic BP, mean arterial pressure (MAP), heart rate (HR), and wrist activity were recorded every 30 min.

RESULTS

Following exercise, MAP was significantly (P < 0.0005) lower throughout the night-shift compared with no prior exercise (95% confidence limits for reduction: 4-7 mm Hg). The postexercise reductions in systolic BP and MAP were not moderated by diet, but the reduction in diastolic BP was slightly greater when only one meal was eaten (P < 0.0005). BP was lower even though wrist activity and HR were significantly higher following exercise (P < 0.0005).

CONCLUSIONS

These data indicate that prior exercise lowers BP throughout a subsequent 8-h night-shift in healthy individuals within the normotensive range. Therefore, regular low-intensity exercise might moderate the well-known association between shift-work participation and raised BP.

Lifestyle factors and colorectal cancer risk (1): systematic review and meta-analysis of associations with body mass index

OBJECTIVE

Excess body weight, defined by body mass index (BMI), may increase the risk of colorectal cancer. As a prerequisite to the determination of lifestyle attributable risks, we undertook a systematic review and meta-analysis of prospective observational studies to quantify colorectal cancer risk associated with increased BMI and explore for differences by gender, sub-site and study characteristics.

METHOD

We searched MEDLINE and EMBASE (to December 2007), and other sources, selecting reports based on strict inclusion criteria. Random-effects meta-analyses and meta-regressions of study-specific incremental estimates were performed to determine the risk ratio (RR) and 95% confidence intervals (CIs) associated with a 5 kg/m(2) increase in BMI.

RESULTS

We analysed 29 datasets from 28 articles, including 67,361 incident cases. Higher BMI was associated with colon (RR 1.24, 95% CIs: 1.20-1.28) and rectal (1.09, 1.05-1.14) cancers in men, and with colon cancer (1.09, 1.04-1.12) in women. Associations were stronger in men than in women for colon (P < 0.001) and rectal (P = 0.005) cancers. Associations were generally consistent across geographic populations. Study characteristics and adjustments accounted for only moderate variations of associations.

CONCLUSION

Increasing BMI is associated with a modest increased risk of developing colon and rectal cancers, but this modest risk may translate to large attributable proportions in high-prevalence obese populations. Inter-gender differences point to potentially important mechanistic differences, which merit further research.

Relationships between leisure-time energy expenditure and individual coping strategies for shift-work

A total of 13 to 14% of European and North American workers are involved in shift work. The present aim is to explore the relationships between coping strategies adopted by shift workers and their leisure-time energy expenditure. Twenty-four female and 71 male shift workers (mean +/- SD age: 37 +/- 9 years) completed an adapted version of the Standard Shift-work Index (SSI), together with a leisure-time physical activity questionnaire. Predictors of age, time spent in shift work, gender, marital status and the various shift-work coping indices were explored with step-wise multiple regression. Leisure-time energy expenditure over a 14-d period was entered as the outcome variable. Gender (beta = 7168.9 kJ/week, p = 0.023) and time spent in shift work (beta = 26.36 kJ/week, p = 0.051) were found to be predictors of energy expenditure, with the most experienced, male shift workers expending the most energy during leisure-time. Overall 'disengagement' coping scores from the SSI were positively related to leisure-time energy expenditure (beta = 956.27 kJ/week, p = 0.054). In males, disengagement of sleep problems (beta = -1078.1 kJ/week, p = 0.086) was found to be negatively correlated to energy expenditure, whereas disengagement of domestic-related problems was found to be positively related to energy expenditure (beta = 1961.92 kJ/week, p = 0.001). These relations were not found in female shift workers (p = 0.762). These data suggest that experienced male shift workers participate in the most leisure-time physical activity. These people 'disengage' more from their domestic-related problems, but less from their sleep-related problems. It is recommended that physical activity interventions for shift workers should be designed with careful consideration of individual domestic responsibilities and perceived disruption to sleep.

Analysis of high intensity activity in Premier League soccer

The aim of the present investigation was to provide a detailed analysis of the high intensity running activity completed by elite soccer players during match-play. A further aim of the study was to evaluate the importance of high intensity running activity to overall team success. Observations on individual match performance measures were undertaken on 563 outfield players (median of 8 games per player; range=1-57) competing in the English Premier League from 2003/2004 to 2005/2006 using a computerised tracking system (Prozone, Leeds, England). High intensity activities selected for analysis included total high intensity running distance (THIR), total sprint distance (TSD) and the number and type of sprints undertaken. Total high intensity running distance in possession and without possession of the ball was also analysed. The THIR was dependant upon playing position with wide midfield (1,049+/-106 m) and central defenders (681+/-128 m) completing the highest and lowest distance respectively (p<0.001). High intensity activity was also related to team success with teams finishing in the bottom five (919+/-128 m) and middle ten (917+/-143 m) league positions completing significantly more THIR compared with teams in the top five (885+/-113 m) (p=0.003). The THIR and TSD also significantly declined during the 2nd half with the greatest decrements observed in wide midfield and attacking players (p<0.05). Both positional differences in high intensity activity and the observed change in activity throughout the game were also influenced by team success (p<0.05). The results of the present study indicate that high intensity activity in elite soccer match-play is influenced by both playing position and previous activity in the game. These activity patterns are also dependant upon success of the team. This may indicate that overall technical and tactical effectiveness of the team rather than high levels of physical performance per se are more important in determining success in soccer.