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Lara A. Carlson, Kaylee M. Pobocik, Michael A. Lawrence, Daniel A. Brazeau and Alexander J. Koch

/anterior hypothalamus, which has been shown to initiate sleep. 12 Exercise can elicit acute and delayed changes in melatonin secretion, although the direction of exercise-induced changes varies with the time of day exercise was performed. 13 , 14 Furthermore, studies investigating the impact of exercise on melatonin

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Hichem Souissi, Anis Chaouachi, Karim Chamari, Mohamed Dogui, Mohamed Amri and Nizar Souissi

The purpose of this study was to examine the time-of-day effects on short-term performances in boys. In a balanced and randomized study design, 20 boys performed four anaerobic tests of strength and power (grip strength, Squat-Jump, Five-jump and cycle Wingate tests) at 08:00, 14:00 and 18:00 hr on separate days. The results showed a time-of-day effect on oral temperature. Analysis of variance revealed a significant time-of-day effect for short-term performances for strength, cycle, and jump tests. The post hoc analysis revealed that performances improved significantly from morning to afternoon but no significant differences were noticed between 14:00 and 18:00 hr. The differences between the morning and the afternoon (the highest value measured either at 14:00 or at 18:00 hr) reached 5.9% for grip strength, 3.5% for the squat jump test, 5% for the five jump test, and 5.5% for Ppeak and 6% for Pmean during the Wingate test. A significant positive correlation was found between temperature and short-term performances. In conclusion, a time-of-day effect in the child’s maximal short-term exercise performances exists in relation with core temperature. Such variations would have pronounced effects when expressed in training programs and competitions.

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Katriona J.M O’Donoghue, Paul A. Fournier and Kym J. Guelfi

Although the manipulation of exercise and dietary intake to achieve successful weight loss has been extensively studied, it is unclear how the time of day that exercise is performed may affect subsequent energy intake. The purpose of the current study was to investigate the effect of an acute bout of exercise performed in the morning compared with an equivalent bout of exercise performed in the afternoon on short-term energy intake. Nine healthy male participants completed 3 trials: morning exercise (AM), afternoon exercise (PM), or control (no exercise; CON) in a randomized counterbalanced design. Exercise consisted of 45 min of treadmill running at 75% VO2peak. Energy intake was assessed over a 26-hr period with the participants eating ad libitum from a standard assortment of food items of known quantity and composition. There was no significant difference in overall energy intake (M ± SD; CON 23,505 ± 6,938 kJ, AM 24,957 ± 5,607 kJ, PM 24,560 ± 5,988 kJ; p = .590) or macronutrient preferences during the 26-hr period examined between trials. Likewise, no differences in energy intake or macronutrient preferences were observed at any of the specific individual meal periods examined (i.e., breakfast, lunch, dinner) between trials. These results suggest that the time of day that exercise is performed does not significantly affect short-term energy intake in healthy men.

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Andrea K. Chomistek, Eric J. Shiroma and I-Min Lee

Background:

Physical activity is important for maintaining healthy weight. The time of day when exercise is performed—a highly discretionary aspect of behavior—may impact weight control, but evidence is limited. Thus, we examined the association between the timing of physical activity and obesity risk in women.

Methods:

A cross-sectional analysis was conducted among 7157 Women’s Health Study participants who participated in an ancillary study begun in 2011 that is measuring physical activity using accelerometers. The exposure was percentage of total accelerometer counts accumulated before 12:00 noon and the outcome was obesity.

Results:

Mean (±SD) BMI among participants was 26.1 (±4.9) kg/m2 and 1322 women were obese. The mean activity counts per day was 203,870 (±95,811) of which a mean 47.1% (±11.5%) were recorded in the morning. In multivariable-adjusted models, women who recorded < 39% (lowest quartile) of accelerometer counts before 12:00 noon had a 26% higher odds of being obese, compared with those recording ≥ 54% (highest quartile) of counts before noon (P trend = 0.02).

Conclusions:

These study findings—that women who are less active during morning hours may be at higher risk of obesity—if confirmed can provide a novel strategy to help combat the important health problem of obesity.

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Chris Brogden, Kelly Marrin, Richard Page and Matt Greig

of movement screening is fundamental to the subsequent design of prehabilitation and injury management strategies. Circadian rhythm is a term used to describe variations in many human physiological variables 8 and factors influencing athletic performance, relative to time of day. 9 , 10 It has been

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Huan Zhao, Xiao-Qiu Chu, Xiao-Qing Lian, Ze-Mu Wang, Wei Gao and Lian-Sheng Wang

Purpose:

Exercise leads to a lower risk of coronary artery disease (CAD). However, whether time of day physical exercise has effects on CAD is still unclear. The present study is to investigate the relationship between time of day physical exercise and angiography determined CAD in a Chinese population.

Subjects:

A total of 1,129 consecutive participants who underwent coronary angiography for the first time were enrolled in our study. Participants were divided into non-CAD group and CAD group according to the result of coronary angiography. We used a predesigned questionnaire—the work-related activity, leisure-time activity, and physical exercise information were recorded in the form of self-reporting.

Results:

Doing physical exercise was associated with a reduced risk of CAD, after adjusting the established and potential confounders, with an adjusted odds ratio (OR) of 0.48 (95% CI, 0.35–0.67) compared with those who did not any physical exercise. Moreover, the risk of CAD could linearly decrease with increase of intensity, duration and frequency of exercise. Further stratification analysis revealed that the protective effects of exercise were more significant in the afternoon and evening group than in the morning and forenoon group. The adjusted ORs of doing physical exercise in morning, forenoon, afternoon, and evening groups were 0.53 (0.36–0.78), 0.51(0.27–0.96), 0.46(0.25–0.85), 0.43(0.28–0.66), respectively, compared with nonexerciser (p < .05).

Conclusions:

Doing physical exercise can decrease the risk of CAD, and exercising in the afternoon or evening may have more significant effects on the prevention of CAD than in other time of day.

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Hichem Souissi, Hamdi Chtourou, Anis Chaouachi, Mohamed Dogui, Karim Chamari, Nizar Souissi and Mohamed Amri

The aim of this study was to assess the effect of time-of-day-specific training on the diurnal variations of short-term performances in boys. Twenty-four boys were randomized into a morning-training-group (07:00–08:00h; MTG), an evening training-group (17:00–18:00h; ETG) and a control-group (CG). They performed four tests of strength and power (unilateral isometric maximal voluntary contraction of the knee extensor muscles, Squat-Jump, Counter-Movement-Jump and Wingate tests) at 07:00 and 17:00h just before (T0) and after 6 weeks of resistance training (T1). In T0, the results revealed that short-term performances improved and oral temperature increased significantly from morning to afternoon (amplitudes between 2.36 and 17.5% for both oral temperature and performances) for all subjects. In T1, the diurnal variations of performances were blunted in the MTG and persisted in the ETG and CG. Moreover, the training program increase muscle strength and power especially after training in the morning hours and the magnitude of gains was greater at the time-of-day-specific training than at other times. In conclusion, these results suggest that time-of-day-specific training increases the child’s anaerobic performances specifically at this time-of-day. Moreover, the improvement of these performances was greater after morning than evening training.

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Louise Martin, Alan M. Nevill and Kevin G. Thompson

Purpose:

Fast swim times in morning rounds are essential to ensure qualification in evening finals. A significant time-of-day effect in swimming performance has consistently been observed, although physical activity early in the day has been postulated to reduce this effect. The aim of this study was to compare intradaily variation in race-pace performance of swimmers routinely undertaking morning and evening training (MEG) with those routinely undertaking evening training only (EOG).

Methods:

Each group consisted of 8 swimmers (mean ± SD: age = 15.2 ± 1.0 and 15.4 ± 1.4 y, 200-m freestyle time 132.8 ± 8.4 and 136.3 ± 9.1 s) who completed morning and evening trials in a randomized order with 48 h in between on 2 separate occasions. Oral temperature, heart rate, and blood lactate were assessed at rest, after a warm-up, after a 150-m race-pace swim, and after a 100-m time trial. Stroke rate, stroke count, and time were recorded for each length of the 150-m and 100-m swims.

Results:

Both training groups recorded significantly slower morning 100-m performances (MEG = +1.7 s, EOG = +1.4 s; P < .05) along with persistently lower morning temperatures that on average were –0.47°C and –0.60°C, respectively (P < .05). No differences were found in blood-lactate, heart-rate, and stroke-count responses (P > .05). All results were found to be reproducible (P > .05).

Conclusions:

The long-term use of morning training does not appear to significantly reduce intradaily variation in race-pace swimming or body temperature.

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Asma Aloui, Anis Chaouachi, Hamdi Chtourou, Del P. Wong, Monoem Haddad, Karim Chamari and Nizar Souissi

Purpose:

This study examined the effects of Ramadan on cycling repeated-sprint ability (RSA) and corresponding diurnal variations.

Methods:

Twelve active men performed an RSA test (5 × 6-s maximal sprints interspersed with 24 s passive recovery) during morning and afternoon sessions 1 wk before Ramadan (BR), during the second (R2) and the fourth (R4) weeks of Ramadan, and 2 wk after Ramadan (AR). Maximal voluntary contraction was assessed before (MVCpre), immediately after (MVCpost), and 5 min after the RSA test (MVCpost5). Moreover, hematocrit, hemoglobin, and plasma sodium and potassium (K+) concentrations were measured at rest and after the RSA test and MVCpost.

Results:

Overall, peak power (Ppeak) during the RSA test decreased throughout the 5 sprints. Ppeak measured in the first sprint and MVCpre were lower during Ramadan than BR in the afternoon (P < .05) and higher in the afternoon than the morning BR and AR (P < .05). However, this diurnal rhythmicity was not found for the last 4 sprints’ Ppeak, MVCpost, and MVCpost5 in all testing periods. Furthermore, the last 4 sprints’ Ppeak, MVCpost, MVCpost5, and morning MVCpre were not affected by Ramadan. [K+] measured at rest and after the RSA test and MVCpost were higher during Ramadan than BR in the afternoon (P < .05) and higher in the afternoon than the morning during Ramadan (P < .05).

Conclusions:

Fatigability is higher in the afternoon during Ramadan, and, therefore, training and competition should be scheduled at the time of day when physical performance is less affected.

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Olivier Hue, Roland Monjo, Marc Lazzaro, Michelle Baillot, Philippe Hellard, Laurent Marlin and A. Jean-Etienne

The authors tested the effect of cold water ingestion during high-intensity training in the morning vs the evening on both core temperature (TC) and thermal perceptions of internationally ranked long-distance swimmers during a training period in a tropical climate. Nine internationally ranked long-distance swimmers (5 men and 4 women) performed 4 randomized training sessions (2 in the evening and 2 in the morning) with 2 randomized beverages with different temperatures for 3 consecutive days. After a standardized warm-up of 1000 m, the subjects performed a standardized training session that consisted of 10 × 100 m (start every 1′20″) at a fixed velocity. The swimmers were then followed for the next 3000 m of the training schedule. Heart rate (HR) was continuously monitored during the 10 × 100 m, whereas TC, thermal comfort, and thermal sensation (TS) were measured before and after each 1000-m session. Before and after each 1000 m, the swimmers were asked to drink 190 mL of neutral (26.5 ± 2.5°C) or cold (1.3 ± 0.3°C) water packaged in standardized bottles. Results demonstrated that cold water ingestion induced a significant effect on TC, with a pronounced decrease in the evening, resulting in significantly lower mean TC and lower mean delta TC in evening cold (EC) than in evening neutral (EN), concomitant with significantly lower TS in EC than in EN and a significant effect on exercise HR. Moreover, although TC increased significantly with time in MN, MC, and EN, TC was stabilized during exercise in EC. To conclude, we demonstrate that a cold beverage had a significant effect on TC, TS, and HR during training in high-level swimmers in a tropical climate, especially during evening training.