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Mechanical models of cycling time-trial performance have indicated adverse effects of variations in external power output on overall performance times. Nevertheless, the precise influences of the magnitude and number of these variations over different distances of time trial are unclear. A hypothetical cyclist (body mass 70 kg, bicycle mass 10 kg) was studied using a mathematical model of cycling, which included the effects of acceleration. Performance times were modelled over distances of 4-40 km, mean power outputs of 200-600 W, power variation amplitudes of 5-15% and variation frequencies of 2-32 per time-trial. Effects of a "fast-start" strategy were compared with those of a constant-power strategy. Varying power improved 4-km performance at all power outputs, with the greatest improvement being 0.90 s for ± 15% power variation. For distances of 16.1, 20 and 40 km, varying power by ± 15% increased times by 3.29, 4.46 and 10.43 s respectively, suggesting that in long-duration cycling in constant environmental conditions, cyclists should strive to reduce power variation to maximise performance. The novel finding of the present study is that these effects are augmented with increasing event distance, amplitude and period of variation. These two latter factors reflect a poor adherence to a constant speed.

The activity records of five groups of healthy or ill subjects have been measured for 4-26 days by an accelerometer placed on the nondominant wrist. These data, together with a record of times retiring to/rising from bed, have been used to produce a series of dichotomy indices for comparing the amounts of activity when in bed and out of bed. Reliable differences between individuals were found, with healthy subjects showing a greater degree of dichotomy than one subject with delayed sleep phase syndrome or three subjects with colorectal cancer. The method is convenient for extended data collection and offers the possibility of describing an individual's activity profile in a variety of circumstances.

Population data indicate that 14–28% of workers are involved in a shift work schedule which includes some time spent working at night. Shift workers predominate in heavy industries and emergency services, but they are also increasingly found in finance, ‘E-commerce,’ and service industries. Shift work-related sleep disorder is characterized by excessive sleepiness at work and insomnia during scheduled times for sleep. Data from epidemiological studies also suggest that shift workers, and especially those engaged in night work, are generally more prone to gastro-intestinal problems, obesity, heart disease, and cancer than day workers. Disruption of circadian rhythms during shift work is thought to be important in explaining these increased health problems. Nevertheless, differences between shift workers and day workers in lifestyle factors, including participation in physical activity, have been generally under-researched. Evaluated treatments for shift work-related sleep problems include light exposure, melatonin ingestion, hypnotics, caffeine, and central nervous stimulants or other agents influencing sleepiness. Most studies show positive results, although most have involved a simulation of shift work in the laboratory rather than actual shift work which is associated with a multitude of biological and socio-behavioral stressors. Modafinil and armodafinil are two of the few substances which have been studied in randomized controlled trials involving patients with diagnosed shift work sleep disorder. Both substances were found to improve sleepiness during the work period and sleep quality in rest periods. It seems as though there are no randomized controlled trials which have tested the efficacy of lifestyle-based interventions on such outcomes in patients with diagnosed shift work type sleep disorder.

It has recently been reported how to quantify inter-individual differences in the response to an exercise intervention using the standard deviation of the change scores, as well as how to appraise these differences for clinical relevance. In a parallel-group randomised controlled trial, the key trigger for further investigation into inter-individual responses is when the standard deviation of change in the intervention sample is substantially larger than the same standard deviation derived from a suitable comparator sample. ‘True’ and clinically relevant inter-individual differences in response can then be plausibly expected, and potential moderators and mediators of the inter-individual differences can be explored. We now aim to critically review the research on the inter-individual differences in response to exercise training, focusing on maximal oxygen uptake (VO2max). A literature search through the relevant bibliographic databases resulted in the identification of six relevant studies that were published prior to the influential HEalth, RIsk factors, exercise Training And GEnetics (HERITAGE) Family Study. Only one of these studies was found to include a comparator arm. Re-analysis of the data from this study, accounting for random within-subjects variation, revealed an absence of clinically important inter-individual differences in the response of VO2max to exercise training. The standard deviation of change was, in fact, larger (±5.6 mL/kg/min) for the comparator than the intervention group (±3.7 mL/kg/min). We located over 180 publications that resulted from the HERITAGE Family Study, but we could not find a comparator arm in any of these studies. Some authors did not explain this absence, while others reasoned that only inter-individual differences in exercise response were of interest, thus the intervention sample was investigated solely. We also found this absence of a comparator sample in on-going studies. A perceived high test–retest reliability is offered as a justification for the absence of a comparator arm, but the test–retest reliability analysis for the HERITAGE Family Study was over a much shorter term than the length of the actual training period between baseline and follow-up measurements of VO2max. We also scrutinised the studies in which twins have been investigated, resulting in concerns about how genetic influences on the magnitude of general within-subjects variability has been partitioned out (again in the absence of a comparator no-training group), as well as with the intra-class correlation coefficient approach to data analysis. Twin pairs were found to be sometimes heterogeneous for the obviously influential factors of sex, age and fitness, thereby inflating an unadjusted coefficient. We conclude that most studies on inter-individual differences in VO2max response to exercise training have no comparator sample. Therefore, true inter-individual differences in response cannot be quantified, let alone appraised for clinical relevance. For those studies with a comparator sample, we found that the inter-individual differences in training response were not larger than random within-subjects variation in VO2max over the same time period as the training intervention.

We aimed to provide the first quantitative synthesis of derived static allometric coefficients ( b ) used for scaling maximal oxygen uptake (VO 2max ) to whole-body mass and fat-free mass in human samples. Eight electronic databases were searched for relevant peer-reviewed articles. Inclusion criteria comprised human cardiorespiratory fitness data; cross-sectional study designs; an empirical derivation of the exponent; reported precision statistics; and reported information regarding participant sex, age and sports background, VO 2max protocol, body composition protocol and line-fitting methods. Thirty-seven studies, involving 7,851 participants, met the eligibility criteria and were dichotomized into two main domains relevant to whole-body mass (n=28) and fat-free mass (n=16), respectively. The pooled allometric exponent (95% CL) was found to be 0.71 (0.65 to 0.77) for body mass and 0.91 (0.83 to 0.98) for fat-free mass. The among-studies heterogeneity was substantial for both whole-body mass and fat-free mass (τ =±0.15). Participant sex explained 33% of the between-study variability in the whole body mass exponent, but only 5% of the variability in the fat-free mass exponent. While the body mass exponent was substantially lower in women ( b =0.52; 95% CL: 0.41 to 0.64) than for men ( b =0.77; 95% CL: 0.71 to 0.83), the fat-free mass exponent was similar for both sexes. None of the identified moderator variables was statistically significant. The body mass exponent estimate encompassed both ⅔- and ¾-power laws. Conversely, the fat-free mass exponent was substantially larger and more generalisable due to the heterogeneity of body composition in human samples. We conclude that the scaling of VO 2max in humans is consistent with the allometric cascade model, with an estimated pooled exponent that precludes ⅔- and ¾-power scaling.

Low cardiorespiratory fitness (VO 2max ) is an important risk factor for diabetes, cardiovascular disease and some cancers, making lifestyle interventions especially relevant. There is purported to be substantial inter-individual differences in how VO 2max responds to lifestyle/exercise interventions. Recently, we described the appropriate approach for quantifying these inter-individual differences. Therefore, we aimed to apply this approach to quantify inter-individual differences in the responses of VO 2max . We re-analysed data from the influential ‘Activity Counselling Trial’ (ACT), which was designed to determine the effects of general lifestyle assistance as well as formal counselling on physical activity and VO 2max in 479 men and 395 women. Importantly, an appropriate comparator group was also present in order to quantify ‘true’ inter-individual differences in VO 2max response. For women, the ‘true’ inter-individual responses in VO 2max (expressed as a SD) were found to be±129 (95% Confidence interval: −40 to 187) ml/min in the general lifestyle assistance group and±93 (−91 to 160) ml/min in the formal lifestyle counselling group. For men, true individual differences in response were±116 (95%CI: −130 to 210) ml/min and±148 (−105 to 234) ml/min in the assistance and counselling groups, respectively. Although the mean increase in VO 2max was greater in women, this increase corresponded to a trivial effect size. This application of the appropriate analyses to the ACT dataset indicate that, on average, the effects of activity counselling on VO 2max were small, although there were moderate ‘true’ inter-individual differences in the VO 2max response in women (0.34 SD) and small ‘true’ inter-individual differences in men (0.27 SD). Further genotype investigation may therefore be warranted in order to determine the mediators of this observed heterogeneity in response.

Tolerance time to a standardized orthostatic stressor is markedly reduced in normotensive individuals in the morning. However, the physiological mechanisms that underpin this phenomenon are unknown. The purpose of this study was to examine the role of α(1)-adrenergic activity on orthostatic tolerance and associated cardiorespiratory and cerebrovascular responses, and to determine whether its endogenous modulation is important in the diurnal variation of orthostatic tolerance. In a four-trial, randomized placebo-controlled crossover experiment, 12 normotensive volunteers (aged 25 ± 1 yrs; mean ± SE) completed a 60° head-upward tilt (HUT; 15 min or until onset of presyncope) at 06:00 and 16:00 h, 90 min after the administration of either α(1)-blockade (prazosin, 1 mg/20 kg body weight) or placebo. Continuous beat-to-beat measurements of middle cerebral blood flow velocity (transcranial Doppler), blood pressure (Finometer), heart rate, stroke volume, cardiac output, and end-tidal carbon dioxide were obtained. Independent of time-of-day, α(1)-blockade markedly reduced the ability to tolerate a 15-min 60° HUT; tolerance time was 229% shorter compared with the placebo condition (p ≤ .0001). Moreover, a marked diurnal variation in orthostatic tolerance was evident following α(1)-adrenergic blockade; e.g., tolerance time in the morning (176 ± 30 s) was lower than in the afternoon (354 ± 75 s; p = .04). These findings highlight an important role of α(1)-sympathetic vasoconstrictor activity in acutely regulating blood pressure and offsetting syncope, especially in the early morning.

Although vascular function is lower in the morning than afternoon, previous studies have not assessed the influence of prior sleep on this diurnal variation. The authors employed a semiconstant routine protocol to study the contribution of prior nocturnal sleep to the previously observed impairment in vascular function in the morning. Brachial artery vascular function was assessed using the flow-mediated dilation technique (FMD) in 9 healthy, physically active males (mean ± SD: 27 ± 9 yrs of age), at 08:00 and 16:00 h following, respectively, 3.29 ± .37 and 3.24 ± .57 h prior sleep estimated using actimetry. Heart rate and systolic and diastolic blood pressures were also measured. The data of the experimental sleep condition were compared with the data of the "normal" diurnal sleep condition, in which FMD measurements were obtained from 21 healthy individuals who slept only during the night, as usual, before the morning test session. The morning-afternoon difference in FMD was 1 ± 4% in the experimental sleep condition compared with 3 ± 4% in the normal sleep condition (p = .04). This difference was explained by FMD being 3 ± 3% lower in afternoon following the prior experimental sleep (p = .01). These data suggest that FMD is more dependent on the influence of supine sleep than the endogenous circadian timekeeper, in agreement with our previous finding that diurnal variation in FMD is influenced by exercise. These findings also raise the possibility of a lower homeostatic "set point" for vascular function following a period of sleep and in the absence of perturbing hemodynamic fluctuation.

Objective Women with polycystic ovary syndrome (PCOS) demonstrate an increased prevalence of cardiovascular disease (CVD) risk factors. Previous researchers have compared flow-mediated dilation (FMD), an early marker of CVD, in women with and without PCOS. Evidence for a PCOS-mediated reduction in FMD remains equivocal, potentially because of study differences in cohort-matching and measurement approaches. The aims of this systematic review and meta-analysis were to examine to what extent FMD is impaired in PCOS and to explore the influence of potential moderators of FMD reduction, such as age and BMI. Design A systematic review and meta-analysis of published observational studies comparing FMD in PCOS with control women. Patients Twenty-one published studies were included (PCOS, n = 908; controls, n = 566). A subanalysis, using tighter inclusion criteria, involved seven studies (PCOS, n = 402; control, n = 251). Measurements Mean differences in FMD between PCOS and controls were synthesized. The subanalysis was delimited to the inclusion of age and BMI-matched controls. These factors were then explored as moderators using meta-regression. Results The pooled mean FMD was 3·4% (95% CI=1·9, 4·9) lower in PCOS compared with control women, with substantial heterogeneity between studies. In the subanalysis, the PCOS-mediated reduction in FMD was 4·1% (95% CI=2·7, 5·5). Heterogeneity remained substantial (I2=81%). Subsequent meta-regression indicated that the magnitude of FMD difference was not influenced by BMI (P = 0·17) nor age (P = 0·38). Conclusions This systematic research synthesis indicates that endothelial function is compromised in PCOS women, even if they are young and nonobese.

Contains fulltext : 110649.pdf (Publisher’s version ) (Closed access) Individuals with a spinal cord injury (SCI), especially with tetraplegia, experience poor sleep quality, and this may be related to impaired control of circadian rhythmicity. Here, we examined the evening onset of melatonin secretion, an important hormone for the initiation of sleep, in people with a complete cervical (tetraplegia) and thoracic (paraplegia) SCI, and age- and sex-matched able-bodied control participants. Multiple samples of salivary melatonin were obtained during the evening hours and analyzed by ELISA methods in 10 control partcipants, 9 individuals with paraplegia, and 6 individuals with tetraplegia. Sleep quality was assessed using questionnaires. Interactive effects of group and time were found for melatonin levels (P=0.022). In the control and paraplegia groups, the mean melatonin level increased significantly from 2.59 +/- 1.04 and 4.28 +/- 3.28 pg/ml at 7 PM to 10.62 +/- 4.59 and 13.10 +/- 7.39 pg/ml at 11 PM, respectively (P0.05). Decreased sleep quality was more prevalent in individuals with tetraplegia (83%) and paraplegia (75%) compared with controls (20%; P=0.02). Unlike in the control and paraplegia groups, the evening increase in melatonin concentration was completely absent in the tetraplegia group. This provides biological insight into sleep regulation in humans and provides better understanding of the poor sleep quality in people with tetraplegia. 01 juli 2012

Strenuous exercise is associated with an immediate decrease in endothelial function. Repeated bouts of ischemia followed by reperfusion, known as remote ischemic preconditioning (RIPC), is able to protect the endothelium against ischemia-induced injury beyond the ischemic area. We examined the hypothesis that RIPC prevents the decrease in endothelial function observed after strenuous exercise in healthy men. In a randomized, crossover study, 13 healthy men performed running exercise preceded by RIPC of the lower limbs (4 × 5-min 220-mmHg bilateral occlusion) or a sham intervention (sham; 4 × 5-min 20-mmHg bilateral occlusion). Participants performed a graded maximal treadmill running test, followed by a 5-km time trial (TT). Brachial artery endothelial function was examined before and after RIPC or sham, as well as after the 5-km TT. We measured flow-mediated dilation (FMD), an index of endothelium-dependent function, using high-resolution echo-Doppler. We also calculated the shear rate area-under-the-curve (from cuff deflation to peak dilatation; SRAUC). Data are described as mean and 95% confidence intervals. FMD changed by 0.30). In the sham trial, FMD changed from 5.1 (4.4–5.9) to 3.7% (2.6–4.8) following the 5-km TT ( P = 0.02). In the RIPC trial, FMD changed negligibly from 5.4 (4.4–6.4) post-IPC and 5.7% (4.6–6.8) post 5-km TT ( P = 0.60). Baseline diameter, SRAUC, and time-to-peak diameter were all increased following the 5-km TT ( P < 0.05), but these changes did not influence the IPC-mediated maintenance of FMD. In conclusion, these data indicate that strenuous lower-limb exercise results in an acute decrease in brachial artery FMD of ∼1.4% in healthy men. However, we have shown for the first time that prior RIPC of the lower limbs maintains postexercise brachial artery endothelium-dependent function at preexercise levels.

Three investigations were carried out to examine the concurrent validity and the reliability of a portable dynamometer (Takei Kiki Kogyo) for the measurement of back and leg strength. First, leg extension strength of 19 subjects was measured using the Takei dynamometer and compared to the isometric knee extension strength of the dominant (right) leg measured using a computer-controlled dynamometer (Lido Active, Davis, CA). The back extension strength of 18 subjects was also compared between the two dynamometers. Second, back and leg strengths of 36 subjects, aged 19-30 years, were measured twice using the Takei dynamometer. Six days separated the test and retest. Third, back and leg strengths of four subjects, aged 21-30 years, were measured at six different times of the solar day. Significant relations (p0.001) were obtained between the Takei and Lido dynamometers for leg strength (r = 0.90) and back strength (r = 0.79). Significant test-retest correlations (p0.001) were found for leg strength (r = 0.80) and back strength (r = 0.91). Group mean (+/- SD) leg strength values of test (1450.4 +/- 428.6 N) and retest (1432.8 +/- 449.1 N) did not differ ((p0.05). A small (4.5%) but significant difference was found between the test (1057.2 +/- 309.9 N) and retest (1106.2 +/- 334.4 N) mean values for back strength (p0.05). A time of day effect was evident for back and leg strength (p0.05); on average the peak times occurred at 16:53 h and 18:20 h, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

The purpose of this study was to establish if provision of CHO altered the mucosal immune and salivary cortisol responses to intermittent exercise in the heat. In a double-blind design, 10 males undertook soccer-specific intermittent exercise on a motorized treadmill on 2 occasions, each over 90 min and separated by 1 week. During CHO and placebo trials, subjects were given either a carbohydrate solution (3 ml · kg (-1) body weight) or placebo drink, 5 min before the commencement of exercise, at 15, 30 min, at half time, 60 and 75 min into exercise. Salivary flow rate increased throughout the placebo trial and decreased throughout the CHO treatment; the difference between conditions neared statistical significance (P=0.055). Neither s-IgA concentration nor s-IgA to osmolality ratio was affected by 2 conditions or differed at any time-point post-exercise (P>0.05). The s-IgA secretion rate increased, s-IgA to protein ratio decreased post-exercise and salivary cortisol decreased 24 h post-exercise (P

Purpose The study’s purposes were to 1) assess changes in cardiorespiratory fitness (CRF) from 1998 to 2010, controlling for decimal age and body mass index (BMI), and 2) repeat the analysis in cohorts from 2005 to 2010, controlling for maturation, deprivation, and BMI. Methods : A total of 27,942 (n= 14,247 boys) 9- to 10.9-yr-old participants from one UK city were included in this serial cross-sectional study from 1998–1999 to 2009–2010. An indices of multiple deprivation (IMD) score was assigned to each participant on the basis of home postcode. Stature, sitting stature, and body mass were estimated. BMI and somatic maturity were calculated. Performance on the 20-m multistage shuttle run test (20mSRT) was used to estimate CRF (total shuttles). One-way ANCOVAs were completed to assess temporal trends in CRF, separately by sex. Model 1 assessed changes from 1998 to 2010 and included decimal age and BMI as covariates. Model 2 assessed changes from 2005 to 2010 and included maturity, IMD, and BMI as covariates. Results : Results indicate that 20mSRT performance has declined in UK schoolchildren. An annual decline of 1.34% and 2.29% was observed in boys and girls, respectively. In model 1, for boys, the baseline cohort performed better than all other groups with the exception of the 1999–2000 group. For girls, declines in 20mSRT performance were observed from 2003 onward. In model 2, for boys, the 2007–2008 and 2008–2009 cohorts completed fewer 20mSRT shuttles than all other groups. For girls, the 2007–2008 and 2008–2009 cohorts also performed worse than all other years. Conclusions : The decline in CRF suggests children in the more recent SportsLinx cohorts may be at an increased risk of car-diometabolic illness in comparison with earlier cohorts. The promotion of vigorous physical activity is urged to promote CRF in children.

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 (P0.0005). Further covariate-adjusted analysis revealed that those competitors who consumed carbohydrate the day before the race at a quantity of7 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 consumed7 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.

Early morning reduction in endothelium-dependent, flow-mediated dilation (FMD) may contribute to the high incidence of sudden cardiac death at this time of day. The mechanisms underpinning diurnal variation in FMD are unclear, but potentially relate to a circadian rhythm in sympathetic nerve activity. We hypothesized that blockade of α1-mediated sympathetic nerve activity would act to attenuate the diurnal variation in FMD. In a randomized and placebo-controlled design, we measured brachial artery FMD in 12 participants (mean age = 26 yr, SD = 3) at 0600 and 1600 after ingestion of an α1-blocker (prazosin, 1 mg/20 kg body mass) or placebo. Arterial diameter and shear rate were assessed using edge-detection software. Heart rate and blood pressure were also measured. Data were analyzed using linear mixed modeling. Following placebo, FMD was 8 ± 2% in the morning compared with 10 ± 3% in the afternoon ( P = 0.04). Blockade with prazosin led to a slight but nonsignificant increase in morning FMD ( P = 0.24) and a significant ( P = 0.04) decrease in afternoon FMD, resulting in no diurnal variation ( P = 0.20). Shear rate did not differ in the morning or afternoon under either condition ( P > 0.23). Blood pressure was lower following prazosin compared with placebo ( P < 0.02), an effect that was similar at both times of day ( P > 0.34). Heart rate and norepinephrine levels were higher in the afternoon following prazosin. These data indicate that α1-adrenoreceptor activity does not explain lower morning endothelium-dependent FMD.

reply: We would like to thank Mc Loughlin and Mc Loughlin (4a) for their response and for bringing attention to the appropriate selection of transducer operating frequency for flow-mediated dilation investigations. We agree that employing a transducer with a higher central frequency (i.e., 12 MHz) will yield a greater detail resolution in the axial plane when interrogating vessels such as the brachial artery, and this would provide a greater sensitivity in detecting small changes in flow-evoked vasodilatation. However, in our review (8), we discussed not only the brachial artery but also the common femoral (9), profunda femoris (12), superficial femoral (1, 2, 10, 12), popliteal (5, 6, 11), and posterior tibial (3, 7) arteries. When these lower-limb vessels are insonated at an optimal region in terms of flow conditions, for example, at a distance where entrance effects are minimized, the artery depth is often greater than that expected for a typical brachial artery. Given that the average attenuation coefficient is 0.5 dB·cm−1·MHz−1 (4), there is considerable degradation of image quality when employing a high-frequency probe while imaging a deeper lying vessel. This can render the image unusable when combined with automated analysis software. The subsequent trade-off between detail resolution and depth penetration is a further consideration for researchers when performing flow-mediated dilation investigations; however, the minimum transducer recommended is 7.5 MHz for all peripheral arteries so as to maintain adequate detail resolution. Certainly, we advocate the use of higher transducer frequencies (i.e., 12 MHz) when investigating more superficial vessels such as the brachial and radial arteries.

Endothelial dysfunction is an early atherosclerotic event that precedes clinical symptoms and may also render established plaque vulnerable to rupture. Noninvasive assessment of endothelial function is commonly undertaken using the flow-mediated dilation (FMD) technique. Some studies indicate that FMD possesses independent prognostic value to predict future cardiovascular events that may exceed that associated with traditional risk factor assessment. It has been assumed that this association is related to the proposal that FMD provides an index of endothelium-derived nitric oxide (NO) function. Interestingly, placement of the occlusion cuff during the FMD procedure alters the shear stress stimulus and NO dependency of the resulting dilation: cuff placement distal to the imaged artery leads to a largely NO-mediated response, whereas proximal cuff placement leads to dilation which is less NO dependent. We used this physiological observation and the knowledge that prognostic studies have used both approaches to examine whether the prognostic capacity of FMD is related to its role as a putative index of NO function. In a meta-analysis of 14 studies (>8300 subjects), we found that FMD derived using a proximal cuff was at least as predictive as that derived using distal cuff placement, despite the latter being more NO dependent. This suggests that, whilst FMD is strongly predictive of future cardiovascular events, this may not solely be related to its assumed NO dependency. Although this finding should be confirmed with more and larger studies, we suggest that any direct measure of vascular (endothelial) function may provide independent prognostic information in humans.

Moving rapidly from a supine to a standing posture is a common daily activity, yet a significant physiological challenge. Syncope can result from the development of initial orthostatic hypotension (IOH) involving a transient fall in systolic/diastolic blood pressure (BP) of40/20 mm Hg within the first 15 s, and/or a delayed orthostatic hypotension (DOH) involving a fall in systolic/diastolic BP of20/10 mm Hg within 15 min of posture change. Although epidemiological data indicate a heightened syncope risk in the morning, little is known about the diurnal variation in the IOH and DOH mechanisms associated with postural change. The authors hypothesized that the onset of IOH and DOH occurs sooner, and the associated cardiorespiratory and cerebrovascular changes are more pronounced, in the early morning. At 06:00 and 16:00 h, 17 normotensive volunteers, aged 26 ± 1 yrs (mean ± SE), completed a protocol involving supine rest, an upright stand, and a 60° head-up tilt (HUT) during which continuous beat-to-beat measurements of middle cerebral artery velocity (MCAv), mean arterial BP (MAP), heart rate, and end-tidal Pco(2) (P(ET)co(2)) were obtained. Mean MCAv was ∼12% lower at baseline in the morning (p ≤ .01) and during the HUT (p .01), despite a morning elevation in P(ET)co(2) by ∼2.2 mm Hg (p = .01). The decline in MAP during initial standing (morning vs. afternoon: 50% ± 4% vs. 49% ± 3%) and HUT (39% ± 3% vs. 38% ± 3%) did not vary with time-of-day (p .30). In conclusion, although there is a marked reduction in MCAv in the morning, there is an absence of diurnal variation in the onset of and associated physiological responses associated with IOH and DOH. These responses, at least in this population, are unlikely contributors to the diurnal variation in orthostatic tolerance.

Item does not contain fulltext Endothelial dysfunction is now considered an important early event in the development of atherosclerosis, which precedes gross morphological signs and clinical symptoms. The assessment of flow-mediated dilation (FMD) was introduced almost 20 years ago as a noninvasive approach to examine vasodilator function in vivo. FMD is widely believed to reflect endothelium-dependent and largely nitric oxide-mediated arterial function and has been used as a surrogate marker of vascular health. This noninvasive technique has been used to compare groups of subjects and to evaluate the impact of interventions within individuals. Despite its widespread adoption, there is considerable variability between studies with respect to the protocols applied, methods of analysis, and interpretation of results. Moreover, differences in methodological approaches have important impacts on the response magnitude, can result in spurious data interpretation, and limit the comparability of outcomes between studies. This review results from a collegial discussion between physiologists with the purpose of developing considered guidelines. The contributors represent several distinct research groups that have independently worked to advance the evidence base for improvement of the technical approaches to FMD measurement and analysis. The outcome is a series of recommendations on the basis of review and critical appraisal of recent physiological studies, pertaining to the most appropriate methods to assess FMD in humans.

Athletes ingest melatonin in an attempt to improve sleep quality or alleviate symptoms of jet lag after transmeridian travel. It is not known whether there are residual effects of this hormone on physical performance in fit subjects. After a sample size estimation involving a meaningful effect on performance of 5%, five milligrams of melatonin or placebo were ingested by twelve physically-active subjects before sleep in a double-blind experiment. The following morning, subjective sleep quality (latency and maintenance) were measured together with intra-aural temperature, grip strength of the left and right hands, and time to complete a 4 km time trial on a cycle ergometer. The subjects also rated perceived exertion during the latter test. The null hypothesis of no effect of melatonin on either subjective sleep quality or physical performance measured the morning after administration could not be rejected on the basis of our observations (P > 0.30). The mean differences between treatments were less than 1% for the strength tests and time trial performance. The confidence intervals for these differences for left and right grip strength and the cycling test were - 2.1 to 2.8 kg, - 3.1 to 2.7 kg and -3.0 to 4.5 s, respectively. In conclusion, it is unlikely that 5 mg of melatonin would have any meaningful effects on physical performance in the morning after fit subjects ingest the hormone. There was also little evidence that it improves sleep quality in this population. Further research is needed concerning the effects of daytime and nighttime admistration of melatonin on performance, in both situations of normal and disturbed sleep.

Background:Active video games (exergames) increase energy expenditure (EE) and physical activity (PA) compared with sedentary video gaming. The physiological cost and enjoyment of exergaming in adolescents, and young and older adults has not been documented, nor compared with aerobic exercise. This study compared the physiological cost and enjoyment of exergaming on Wii Fit with aerobic exercise in 3 populations.Methods:Cardiorespiratory and enjoyment measurements were compared in 14 adolescents, 15 young adults, and 13 older adults during handheld inactive video gaming, Wii Fit activities (yoga, muscle conditioning, balance, aerobics), and brisk treadmill walking and jogging.Results:For all groups EE and heart rate (HR) of Wii Fit activities were greater than handheld gaming (P < .001) but lower than treadmill exercise (P ≤ .001). Wii aerobics elicited moderate intensity activity in adolescents, young adults, and older adults with respective mean (SD) metabolic equivalents of 3.2 (0.7), 3.6 (0.8), and 3.2 (0.8). HR during Wii aerobics fell below the recommended intensity for maintaining cardiorespiratory fitness. Group enjoyment rating was greater for Wii balance and aerobics compared with treadmill walking and jogging (P ≤ .05).Conclusions:Wii Fit appears an enjoyable exergame for adolescents and adults, stimulating light-to-moderate intensity activity through the modification of typically sedentary leisure behavior.

The cerebrovasculature dilates or constricts in response to acute blood pressure changes to stabilize cerebral blood flow across a range of blood pressures. It is unclear, however, whether such dynamic cerebral autoregulation (dCA) is equally effective in responding to falling versus rising blood pressure. In this study we applied a pharmacological approach to evaluate dCA gain to transient hypotension and hypertension and compared this method with 2 established indices of dCA that do not explicitly differentiate between dCA efficacy and falling versus rising blood pressure. Middle cerebral arterial velocity and blood pressure recordings were made in 26 healthy volunteers randomized to 2 protocols. In 10 subjects, dCA gain to transient hypotension induced with intravenous nitroprusside was compared with dCA gain to transient hypertension induced with intravenous phenylephrine. In 16 subjects, dCA gain to transient hypotension induced with intravenous nitroprusside was compared with the rate of regulation and autoregulatory index derived from transient hypotension induced with the thigh cuff deflation technique. dCA gain to transient hypotension induced with intravenous nitroprusside was unrelated to dCA gain to transient hypertension induced with intravenous phenylephrine ( r =0.06; P =0.87) and was consistently greater than dCA gain to transient hypertension induced with intravenous phenylephrine (0.57±0.16 versus 0.31±0.20 cm/s per millimeter of mercury; P r =−0.52; P =0.037) and autoregulatory index ( r =−0.66; P =0.005). These data indicate that, under our laboratory conditions, dCA appears to be inherently nonlinear with disparate efficacy against rising and falling blood pressure, and dCA gain derived from pharmacologically induced transient hypotension correlates with established nonpharmacological indices of dCA.

Approximately 10% of employees undertake night work, which is a significant predictor of weight gain, possibly because responses to activity and eating are altered at night. It is known that the appetite-related hormone, acylated ghrelin, is suppressed after an acute bout of exercise during the day, but no researcher has explored whether evening exercise alters acylated ghrelin and other appetite-related outcomes during a subsequent night shift. Six healthy men (mean +/- SD: age 30 +/- 8 yrs, body mass index 23.1 +/- 1.1 kg/m(2)) completed two crossover trials (control and exercise) in random order. Participants fasted from 10:00 h, consumed a test meal at 18:00 h, and then cycled at 50% peak oxygen uptake or rested between 19:00-20:00 h. Participants then completed light activities during a simulated night shift which ended at 05:00 h. Two small isocaloric meals were consumed at 22:00 and 02:00 h. Venous blood samples were drawn via cannulation at 1 h intervals between 19:00-05:00 h for the determination of acylated ghrelin, leptin, insulin, glucose, triglyceride, and non-esterified fatty acids concentrations. Perceived hunger and wrist actimetry were also recorded. During the simulated night shift, mean +/- SD acylated ghrelin concentration was 86.5 +/- 40.8 pg/ml following exercise compared with 71.7 +/- 37.7 pg/ml without prior exercise (p = 0.015). Throughout the night shift, leptin concentration was 263 +/- 242 pg/ml following exercise compared with 187 +/- 221 pg/ml without prior exercise (p = 0.017). Mean levels of insulin, triglyceride, non-esterified fatty acids, and wrist actimetry level were also higher during the night shift that followed exercise (p0.05). These data indicate that prior exercise increases acylated ghrelin and leptin concentrations during a subsequent simulated night shift. These findings differ from the known effects of exercise on acylated ghrelin and leptin during the day, and therefore have implications for energy balance during night work.

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.

A single bout of exercise lowers blood pressure (BP) for up to 24 h afterwards. The magnitude of this post-exercise hypotension (PEH) has been reported to be correlated most strongly to pre-exercise BP, and this apparent relationship has influenced position statements about the value of exercise in arterial hypertension. Nevertheless, this correlation could be adversely affected by mathematical coupling and regression-to-the-mean artefacts. Therefore, we aimed to examine the degree to which BP status moderates PEH while, for the first time, controlling for these statistical artefacts. A total of 32 participants, with pre-exercise mean arterial pressures of 65-110 mm Hg, cycled for 30 min at 70% peak oxygen uptake. Systolic BP and diastolic BP were measured (Portapres) before exercise and for 20 min after exercise. Changes in BP were regressed against pre-exercise values, and against the mean of pre- and post-exercise BP, among other indices that are also known not to be prone to artefacts. Correlations between pre-exercise BP and the exercise-mediated reductions were typical of those previously reported (r=0.37-0.62, P0.05), but not large enough to rule out spuriousness (P0.05). Artefact-free indices of BP status (pre- and post-exercise mean as well as an earlier independent measurement) did not correlate with reductions in BP (P0.05), which were moderated more by peak oxygen uptake and time of day (P0.05). These data indicate that, if statistical artefacts are not controlled for, the influence of BP status on the degree of PEH can be spuriously exaggerated to the extent that other more important moderators of BP change are masked.

Sudden cardiac and cerebral events are most common in the morning. A fundamental question is whether these events are triggered by the increase in physical activity after waking, and/or a result of circadian variation in the responses of circulatory function to exercise. Although signaling pathways from the master circadian clock in the suprachiasmatic nuclei to sites of circulatory control are not yet understood, it is known that cerebral blood flow, autoregulation and cerebrovascular reactivity to changes in CO(2) are impaired in the morning and, therefore, could explain the increased risk of cerebrovascular events. Blood pressure (BP) and the rate pressure product (RPP) show marked 'morning surges' when people are studied in free-living conditions, making the rupture of a fragile atherosclerotic plaque and sudden cardiac event more likely. Since cerebral autoregulation is reduced in the morning, this surge in BP may also exacerbate the risk of hemorrhagic and ischemic strokes in the presence of other acute and chronic risk factors. Increased sympathetic activity, decreased endothelial function, and increased platelet aggregability could also be important in explaining the morning peak in cardiac and cerebral events but how these factors respond to exercise at different times of day is unclear. Evidence is emerging that the exercise-related responses of BP and RPP are increased in the morning when prior sleep is controlled. We recommend that such 'semi-constant routine' protocols are employed to examine the relative influence of the body clock and exogenous factors on the 24-h variation in other circulatory factors.

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.

Chronobiological investigations into core temperature during and after exercise can involve ambulatory measurements of intestinal temperature during actual competitions, esophageal temperature measurements in laboratory simulations, or rectal temperature, which can be measured in both the field and laboratory. These sites have yet to be compared during both morning and afternoon exercise and subsequent recovery. At 08:00 and 17:00 h, seven recreationally active males exercised at 70% peak oxygen uptake for 30 min and then recovered passively for 30 min. During the experiment, esophageal, rectal, intestinal, and skin temperatures, plus sweat loss, heart rate, and ratings of perceived exertion (RPE), were monitored. We found that the diurnal variation in intestinal temperature responses (0.45+/-0.32 degrees C; mean+/-SD) was significantly larger compared with rectal (0.33+/-0.24 degrees C) and, particularly, esophageal temperature responses (0.21+/-0.20 degrees C; p= 0.019). This reflected a greater difference of 0.25-0.40 degrees C between the esophagus and the other two sites in the afternoon, compared to inter-site differences of only 0.13-0.16 degrees C in the morning. Diurnal variation was small for skin temperature, heart rate, sweat loss, and RPE responses during exercise (p0.05). Our data suggest that the relative differences between intestinal, rectal, and esophageal temperature during exercise and subsequent recovery depend on time of day to the extent that inferences from studies on experimental and applied chronobiology will be affected.

Understanding the 'human operator' is a central concern of both ergonomists and sport and exercise scientists. This cutting-edge collection of international research papers explores the interface between physical, cognitive and occupational ergonomics and sport and exercise science, illuminating our understanding of 'human factors' at work and at play. Drawing on a wide diversity of disciplines, including applied anatomy, biomechanics, physiology, engineering, psychology and design, the book explores themes of central importance within contemporary ergonomics and sport and exercise science, such as performance, health, environment, technology and special populations. Contemporary Sport, Leisure and Ergonomics establishes important methodological connections between the disciplines, advancing the research agenda within each. It is essential reading for all serious ergonomists and human scientists.

Recently, we reported that circadian variation exists in the response of blood pressure (BP) following a bout of uninterrupted exercise. The usual phenomenon of post-exercise hypotension was absent or reversed when such exercise was performed between 04:00-08:00 h. Nevertheless, research examining BP changes following bouts of intermittent exercise at different times of the day is scarce, even though this type of activity is probably more popular. Therefore, we aimed to compare post-exercise BP reductions of continuous (CONT) and intermittent (INT) exercise protocols performed at 08:00 h and 16:00 h. At both of these times of day, eight normotensive males completed 30 min of continuous cycling in the CONT and three 10 min bouts of cycling separated by 10 min of rest in the INT protocol. The exercise intensity was set at 70% (.)VO(2peak) during both protocols. Heart rate, systolic (S) and diastolic (D) BP, and mean arterial pressure (MAP) were measured 5 min before and 20 min after exercise. Changes from pre-exercise baseline were analyzed using linear mixed modeling. MAP was 8+/-1 mm Hg lower following INT compared with CONT exercise (p0.05). SBP and DBP were also significantly lower following INT compared with CONT exercise (p0.05). Diurnal variation in MAP was evident, with attenuated hypotension being observed after morning exercise (p0.05), although this diurnal variation was less marked following INT compared with CONT exercise (p0.05). We conclude that intermittent exercise mediates greater post-exercise hypotension compared with a single continuous bout of equivalent work and that this protocol-dependent difference is greatest in the afternoon. Therefore, a bout of afternoon exercise that is occasionally interrupted with short rest periods is recommended for lowering BP acutely.

Summary Background: 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). Methods: 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% CIs) for uppermost versus 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 7,873 incident cases, were identified. For colon cancer, there were inverse associations with LT-PA for men (RR 0.80; 95% CIs 0.67 to 0.96) and women (0.86; 0.76 to 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. Interpretation: 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.

Contains fulltext : 80072thijssen.pdf (Publisher’s version ) (Closed access) It has been deemed important to normalize flow-mediated dilation (FMD), a marker of endothelial function, for between-subject differences in the eliciting shear rate (SR) stimulus. Conventionally, FMD is divided by the area under the curve of the SR stimulus. In the context of a cross-sectional comparison across different age cohorts, we examined whether this ratio approach adhered to established statistical assumptions necessary for reliable normalization. To quantify brachial artery FMD and area under the curve of SR, forearm cuff inflation to suprasystolic pressure was administered for 5 min to 16 boys aged 10.9 yr (SD 0.3), 48 young men aged 25.3 yr (SD 4.2), and 15 older men aged 57.5 yr (SD 4.3). Mean differences between age groups were statistically significant (P < 0.001) for nonnormalized FMD [children: 10.4% (SD 5.4), young adults: 7.5% (SD 2.9), older adults: 5.6% (SD 2.0)] but not for ratio-normalized FMD (P = 0.10). Moreover, all assumptions necessary for reliable use of ratio-normalization were violated, including regression slopes between SR and FMD that had y-intercepts greater than zero (P < 0.05), nonlinear and unstable relations between the normalized ratios and SR, skewed data distributions, and heteroscedastic variance. Logarithmic transformation of SR and FMD before ratio calculation improved adherence to these assumptions and resulted in age differences similar to the nonnormalized data (P = 0.03). In conclusion, although ratio normalization of FMD altered findings about age differences in endothelial function, this could be explained by violation of statistical assumptions. We recommend that exploration of these assumptions should be routine in future research. If the relationship between SR and FMD is generally found to be weak or nonlinear or variable between samples, then ratio normalization should not be applied.

Recently, we found that the reactivity of ambulatory blood pressure (BP) to everyday physical activities is highest in the morning. All participants in that study slept normally at night and freely chose their activity levels, which did not allow a separation of any circadian influence on the BP response from the effects of sleep per se. Therefore, the aims of the present study were to investigate whether there is circadian variation in the BP response to a controlled bout of exercise, and whether or not such variation is explained by the residual masking effects of nocturnal sleep. Following 4 h of nocturnal sleep, six normotensive males exercised on a cycle ergometer at 04:00, 06:00, 08:00, and 10:00 h. On a separate day, participants also slept for 4 h in the afternoon and then exercised at 16:00, 18:00, 20:00, and 22:00 h. Mean arterial BP, cardiac output (CO), heart rate (HR), and total peripheral resistance (TPR) were measured for 5 min before and 5, 10, 15, and 20 min after each exercise bout. Post-exercise data were subtracted from pre-exercise baselines and analyzed using general linear modeling with repeated measures. Fifteen min after exercise at 04:00 h, mean arterial BP was 8-14 mm Hg higher (p0.05) than it was after the corresponding post-exercise time at the other clock-hour trials, including the 16:00 h bout that immediately followed daytime sleep. Significantly (p0.05) greater responses of TPR and HR were also found after the 04:00 h exercise bout. We conclude that mean arterial BP shows highest reactivity to a controlled bout of exercise when performed in the morning. This phenomenon cannot be attributed simply to the residual effects of sleep, as it was not observed when participants exercised after a period of daytime sleep.

The reactivity of ambulatory blood pressure following a given change in everyday physical activities is highest in the morning. Whether the acute response of blood pressure following a controlled bout of steady-state exercise is influenced by time of day is examined in this study. After 45 min of supine rest, 12 male normotensives completed 30 min of cycling at 70% $$ \dot V{\text{O}}_{{2{\text{peak}}}} $$ which began at either 0800 or 1600 hours. Arterial blood pressure, cardiac output, total peripheral resistance, cutaneous blood flow and temperature were determined before, and up to 90 min after, exercise. Mean ± SE arterial pressure, averaged over the acute (20-min) period, reduced by 7 ± 2 mmHg following exercise at 1600 hours but increased by 3 ± 3 mmHg following exercise at 0800 hours (P = 0.03). Total peripheral resistance fell by 4.2 ± 0.8 mmHg l−1 min−1 after exercise at 1600 hour, but increased slightly by 0.1 ± 0.5 mmHg l−1 min−1 after morning exercise (P = 0.02). We conclude that the acutely hypotensive effects following 30 min of steady state exercise are less marked in the morning, probably because the exercise-mediated decrease in peripheral resistance is not as apparent at this time of day.

A questionnaire was administered to elite athletes from Australia, Canada, the UK, and the USA representing 10 Olympic sports in order to explore knowledge and understanding of over-the-counter (OTC) medication since the removal of many of these substances from the World Anti-Doping Agency (WADA) Prohibited List, in 2004. Athletes demonstrated limited knowledge and understanding. Around half (50.5 %) knew the penalty incurred following a doping violation involving a banned OTC stimulant. The terms Monitoring Program and Specified Substance List were understood by 43.3 % and 67.5 % of respondents, respectively. Overall, the status of substances in relation to the Prohibited List was correctly identified in just 35.1 % of cases. As a whole, athletes were of the opinion that OTC stimulants posed a risk to health, were performance enhancing and that their use was against the spirit of sport. They were undecided as to whether these drugs should be returned to the Prohibited List. Elite athletes require targeted education programmes that will enable them to make informed decisions on the potential of OTC medications for therapeutic or performance enhancing purposes.

The thermoregulatory responses to morning exercise after exposure to different schedules of bright light were examined. At 07:00 h, six males ran on two occasions in an environmental chamber (temperature = 31.4 +/- 1.0 degrees C, humidity = 66 +/- 6 %) for 40 min at 60 % of maximal oxygen uptake. Participants were exposed to bright light (10,000 lux) either between 22:00 - 23:00 h (BT (low)) or 06:00 - 07:00 h (BT (high)). Otherwise, participants remained in dim light (< 50 lux). It was hypothesized that BT (low) attenuates core temperature during morning exercise via the phase-delaying properties of evening bright light and by avoiding bright light in the morning. Evening bright light in BT (low) suppressed (p = 0.037) the increase in melatonin compared to dim light (1.1 +/- 11.4 vs. 15.2 +/- 19.7 pg x ml (-1)) and delayed (p = 0.034) the core temperature minimum by 1.46 +/- 1.24 h. Core temperature was 0.20 +/- 0.17 degrees C lower in BT (low) compared to BT (high) during the hour before exercise (p = 0.036), with evidence (p = 0.075) that this difference was maintained during exercise. Conversely, mean skin temperature was 1.0 +/- 1.7 degrees C higher during the first 10 min of exercise in BT (low) than in BT (high) (p = 0.030). There was evidence that the increase in perceived exertion was attenuated in BT (low) (p = 0.056). A chronobiologically-based light schedule can lower core temperature before and during morning exercise in hot conditions.

We examined variations in dart-throwing performance during the daytime in 12 participants. Two distances from the dartboard were investigated - the normal distance (short throws) and another 50% further away than this (long throws). Intra-aural temperature and subjective fatigue were measured, and errors in performance were assessed as the radial distances of throws from the bulls-eye and the standard deviation of these distances. Long-distance throws improved significantly throughout the daytime and correlated positively with intra-aural temperature (r= -0.49, P=0.002 and r= -0.49, P=0.002 for errors and standard deviation of errors, respectively), but not with subjective fatigue (r= -0.10, P=0.56 and r= -0.05, P=0.74 for errors and standard deviation of errors, respectively). Short-distance throws were associated less with intra-aural temperature (r= -0.46, P= 0.005 and r= -0.17, P=0.31 for errors and standard deviation of errors, respectively), and worsened with fatigue (r=+0.34, P= 0.040 for errors). Compared with the short-distance throws, the long-distance throws were performed significantly less well than could be accounted for by the increased distance (mean errors were increased 1.67-2.78 times and standard deviation of errors of errors 1.58-3.68 times), supporting the concept of a trade-off between force of contraction and accuracy of performance. Throwing darts can be used as a model for investigating factors that influence motor performance, and our results indicate that the effects of time of day upon performance depend upon the relative importance of force and accuracy.

Failure to recover fully between sessions has been suggested to cause immunodepression. Therefore, the cumulative effects of soccer-specific intermittent exercise undertaken on different days 48 h apart on salivary IgA, cortisol and total protein concentration were investigated. Nine male subjects completed two trials of soccer-specific intermittent exercise 48 h apart on a motorised treadmill. Timed unstimulated saliva samples were collected immediately before and after exercise, and 24 and 48 h post-exercise. Salivary IgA concentration (EX (1): 215 +/- 160 to 335 +/- 246 and EX (2): 144 +/- 93 to 271 +/- 185 mg . l (-1), p = 0.007), osmolality (p = 0.001) and total protein (p = 0.001) increased immediately following exercise in both trials and decreased 24 h afterwards, whereas saliva flow rate decreased significantly (p = 0.015) before returning to pre-exercise values 24 h postexercise. The IgA secretion rate, IgA to osmolality ratio, IgA to total protein, solute secretion rate, total protein secretion rate, and cortisol did not differ between the time-points. The results suggest that performing two bouts of moderate intensity soccer-specific intermittent exercise 48 h apart does not suppress resting salivary IgA concentration significantly although a small progressive reduction in salivary IgA was observed. These findings may not extend to successive competitive soccer games when vulnerable players might experience clinically relevant reductions in s-IgA.

Summary The number of travellers undertaking long-distance flights has continued to increase. Such flights are associated with travel fatigue and jet lag, the symptoms of which are considered here, along with their similarities, differences, and causes. Difficulties with jet lag because of sleep loss and decreased performance are emphasised. Since jet lag is caused mainly by inappropriate timing of the body clock in the new time zone, the pertinent properties of the body clock are outlined, with a description of how the body clock can be adjusted. The methods, both pharmacological and behavioural, that have been used to alleviate the negative results of time-zone transitions, are reviewed. The results form the rationale for advice to travellers flying in different directions and crossing several time zones. Finally, there is an account of the main problems that remain unresolved.

Previous researchers have identified significant differences between laboratory and road cycling performances. To establish the ecological validity of laboratory time-trial cycling performances, the causes of such differences should be understood. Hence, the purpose of the present study was to quantify differences between laboratory- and road-based time-trial cycling and to establish to what extent body size [mass (m) and height (h)] may help to explain such differences. Twenty-three male competitive, but non-elite, cyclists completed two 25 mile time-trials, one in the laboratory using an air-braked ergometer (Kingcycle) and the other outdoors on a local road course over relatively flat terrain. Although laboratory speed was a reasonably strong predictor of road speed (R2 = 69.3%), a significant 4% difference (P0.001) in cycling speed was identified (laboratory vs. road speed: 40.4 +/- 3.02 vs. 38.7 +/- 3.55 km x h(-1); mean +/- s). When linear regression was used to predict these differences (Diff) in cycling speeds, the following equation was obtained: Diff (km x h(-1)) = 24.9 - 0.0969 x m - 10.7 x h, R2 = 52.1% and the standard deviation of residuals about the fitted regression line = 1.428 (km . h-1). The difference between road and laboratory cycling speeds (km x h(-1)) was found to be minimal for small individuals (mass = 65 kg and height = 1.738 m) but larger riders would appear to benefit from the fixed resistance in the laboratory compared with the progressively increasing drag due to increased body size that would be experienced in the field. This difference was found to be proportional to the cyclists' body surface area that we speculate might be associated with the cyclists' frontal surface area.

We review the literature on whether exercise is a synchroniser of human circadian rhythms, and highlight the specific methodological problems that are associated with this topic. In applied research, exercise has been investigated as a treatment for jet lag and shift-work problems. In these studies, there have been difficulties in controlling the characteristics of the exercise bout, the athletic status of research participants and exposure to other confounding synchronisers. Therefore, it is unclear at present whether exercise can help mitigate the problems associated with transmeridian travel and shift-work. In laboratory-based experiments, participants have exercised at various times of the day and the change in phase of various circadian rhythms has been measured. Although it is difficult to control for the considerable masking effects of exercise on these estimates of circadian timing, it is clear that nocturnal exercise can induce phase delays in the onset of melatonin. Reports of exercise-induced phase advances of the melatonin rhythm are rarer, as are any phase-shifting effects at all on the body temperature rhythm. In practical terms, the substantial levels of activity needed to obtain phase shifts may not be attainable by the majority of people. In mechanistic terms, the lack of agreement with the phase-shifting effects of bright light suggests that exercise is not exerting its effects via photic entrainment pathways. An alternative explanation may involve exercise-induced hyperthermia. Moreover, it is perplexing why exercise should have a different phase response curve to light, given that humans are diurnally active.

Objective Athletes frequently train with a short time recovery between sessions. The present aim was to establish how salivary IgA is altered following two soccer-specific intermittent exercise bouts performed on the same day. Design Ten males participated in two experimental trials (single session, double session) 1 week apart, in a counterbalanced design. One trial entailed afternoon exercise only (PMEX), in which participants completed soccer-specific intermittent exercise starting at 14:30 h. On the other occasion, participants performed two bouts of exercise [starting at 10:30 h (AMEX 1 ) and at 14:30 h (PMEX 2 )]. Timed unstimulated saliva samples were collected before and immediately after exercise. Results Mean salivary IgA levels increased significantly immediately post-exercise in the single afternoon trial (PMEX). Performance of a second soccer-specific exercise bout in 1 day elicited an increase in heart rate and perceived exertion, compared with the single session, but did not appear to suppress salivary IgA outcomes. Performing soccer-specific exercise at these different times of day did not affect the salivary IgA concentration and secretion rate or salivary cortisol in the short term. Conclusions These findings suggest that, two 90-min exercise sessions performed at a moderate intensity with a 2.25 h rest in between do not necessarily have adverse effects on salivary IgA levels.

Purpose: Evidence supporting cardiac fatigue following prolonged endurance exercise remains equivocal. The purpose of this meta-analysis was to quantify all data fulfilling the specified inclusion criteria, examining the short-term effect of prolonged endurance exercise on left ventricular function. Methods: A random effects meta-analysis of the weighted mean change in ejection fraction (EF), systolic blood pressure/end systolic volume (SBP/ESV) ratio, and early-to-late diastolic filling (E/A) was conducted on 23 studies using the SE of the between-subjects SD. HR, SBP, and left ventricular internal diameter during diastole (LVIDd) were also analyzed. Studies were coded according to exercise duration and training status: moderate duration trained (MDt) and untrained (MDu), 60-150 min; long duration (LD), 166-430 min; and ultra duration (UD), 640-1440 min. Relationships were assessed via Pearson's product-moment correlation. Results: A significant (P < 0.05) overall decrease in EF (mean, confidence interval (CI): -1.95%, -1.03 to -2.88%), SBP/ESV (mean, CI: -0.8, -0.63 to -0.97), and E/A (mean, CI: -0.45, -0.39 to -0.51) was observed. Only UD and MDu subgroups demonstrated a reduction in EF. All subgroups demonstrated significant (P < 0.05) decreases in E/A. Alterations in LVIDd and SBP were related to respective decreases in EF and SBP/ESV, but not to E/A. Conclusion: The decrease in EF and SBP/ESV observed in UD and MDu indicates a reduction in systolic function, partially explained by altered cardiac loading. A decrease in E/A in all subgroups, unrelated to changes in loading, suggests an intrinsic impairment of left ventricular relaxation. Future investigators should employ load-independent indices of cardiac function and attempt to uncover the mechanisms of this phenomenon

Some factors influencing food intake and subjective responses to meals were assessed in 2 groups (n=40 and n=36) of healthy university students. Both groups were studied for 6 days and included both "structured" and "unstructured" times. A questionnaire was completed by all subjects at 3 h intervals while awake. The questionnaires asked the subjects to state the factors that led them to choose to eat or not to eat a meal in the previous 3 h. If they ate a meal, they were required to describe the type of meal eaten and their responses to it-their hunger before it, their enjoyment of the meal itself, and their degree of satisfaction afterwards. Subjects were also asked to describe the type of meal that they would like to have eaten (the desired meal) in the absence of any restraints due to time pressure, cost, and so on. In the first group, 3 "structured" (working) and 3 "unstructured" (rest) days were chosen. Consistant with our previous studies, structured days, as compared to unstructured days, were associated with smaller meals and less positive subjective responses to them. Also, the meals that were eaten were often smaller than those that were desired, or were even missed altogether, due to time pressure. Not only were the meals eaten on unstructured days larger and rated, to by the subjects more positively, but also there was an additional positive effect if the meal played a social role. In the second group, 6 days were chosen, during which there were structured and unstructured 3 h periods. Many of the findings (with regard to reasons for eating or not eating a meal, and the effect of meal size upon subjective responses to it, for example) were the same as in the first group. However, the effect of structured vs. unstructured 3 h periods was significantly less marked than the effect of structured vs. unstructured days that had been found in the first group, and effects due to social factors and time pressure were less reliably present. The results indicate that food intake is affected by whether the whole or only part of the day is "structured" or "unstructured." These findings might be relevant to some problems faced by the workforce, in general, and by night workers, in particular.

Twelve healthy participants were studied in an Isolation Unit. For the first 7 (control) days, subjects lived on UK time. Then the clock was advanced by 8 h, mimicking an eastward time-zone transition, and for days 8 to 12, participants lived on this new local time. Two constant routines (participants were not allowed to sleep, were restricted in movement, and ate regular, identical snacks) were undertaken, during the control days (days 3 to 4) and at the end of the experiment (days 11 to 12). Rectal temperature and activity were measured throughout, with activity used to correct the measured temperatures for the direct (masking) effects of the sleep-wake cycle. Phase changes of the temperature rhythm between the constant routines were assessed by cross-correlation and cosinor analysis. During days 8 to 10, the measured temperatures and those that had been corrected (purified) for masking were assessed by the same two methods, and the shifts were extrapolated to predict the values expected during the second constant routine. Individuals differed widely in the phase shifts of the temperature rhythm, but the correlations between the changes measured by constant routines and those estimated by the purification methods were high (r=0.771 to 0.903), and the differences between them were not significantly different from zero (p0.24). Phase shifts of the measured (masked) temperature rhythm were poorer predictors of the shift obtained from the constant routines (ror=0.605; mean+/-SD of differences3+/-4.5 h). Limitations of the methods due to the variability of results are discussed, but we conclude that the mean phase shifts obtained from purified, but not raw, temperature data show acceptable agreement with those found using our version of the constant routine.

We examined the effects of a single 2.5-mg dose of melatonin on the thermoregulatory and circulatory responses to intermittent exercise at a room temperature of 27.2+/-0.4 degrees C (mean+/-S.D.), a relative humidity of 55+/-3% (mean+/-S.D.), and a light intensity of 200-300 lux. In a double-blind cross-over study, six male participants ingested either melatonin or placebo at 11:45 hr. Participants then rested in a semi-supine position for 75 min and completed an intermittent running protocol for 66 min at alternating intensities of 40, 60 and 80% of maximal oxygen uptake. Rectal and mean skin temperature, heart rate, blood pressure, skin blood flow, subjective alertness and sleepiness, ratings of perceived exertion (RPE) and thermal strain were recorded. No effects of melatonin were found on these variables measured during the resting period (P>0.10). During exercise, melatonin was found to moderate the increase in rectal temperature by approximately 0.25 degrees C (P=0.050) and magnify the increase in skin blood flow (P=0.047). Postexercise systolic blood pressure was 7.8+/-2.5 mmHg (mean+/-S.D.) lower than before the exercise in the melatonin trial; a change which differed significantly to that in the placebo trial (P=0.018). Melatonin did not influence subjective alertness and sleepiness before or after exercise and did not change the responses of mean skin temperature, RPE and thermal strain during the exercise (P>0.10). In summary it is apparent that a 2.5-mg dose of melatonin has hypothermic, but not soporific, effects during 66 min of intermittent exercise performed under moderate heat stress. Whether such effects improve endurance athletic performance in hot conditions remains to be confirmed. Our data also suggest that postexercise systolic hypotension is more marked after ingestion of melatonin.