The lack of standardization of methods and procedures have hindered agreement in the literature related to time-of-day effects on repeated sprint performance and needs clarification. Therefore, the aim of the present study was to investigate and systematically review the evidence relating to time-of-day based on performance measures in repeated-sprints. The entire content of PubMed (MEDLINE), Scopus, SPORTDiscus® (via EBSCOhost) and Web of Science was searched. Only experimental research studies conducted in male adult participants aged ≥18yrs, published in English before June 2019 were included. Studies assessing repeated-sprints between a minimum of two time-points during the day (morning versus evening) were deemed eligible. The primary search revealed that a total of 10 out of 112 articles were considered eligible and subsequently included. Seven articles were deemed strong and three moderate quality. Eight studies found repeated-sprint performance across the first, first few, or all sprints, to increase in favor of the evening. The magnitude of difference is dependent on the modality and the exercise protocol used. The non-motorized treadmill established an average 3.5–8.5% difference in distance covered, average and peak velocity, and average power, across all sprints in three studies and in peak power in two studies. In cycling, power output differed across all sprints by 6.0% in one study and 8.0% for the first sprint only in five studies. All four studies measuring power decrement values (i.e. rate of fatigue) established differences up to 4.0% and two out of five studies established total work to be significantly higher by 8.0%. Repeated-sprint performance is affected by time-of-day with greater performance in the late/early afternoon. The magnitude is dependent on the variable assessed and the mode of exercise. There is a clear demand for more rigorous investigations which control factors that specifically relate to investigations of time-of-day and are specific to the sport of individuals.

The present study investigated whether increasing morning rectal temperatures (T_rec) to resting.evening levels, or decreasing evening T_rec or muscle (T_m) temperatures to morning values, would influence repeated sprint (RS) performance in a causal manner. Twelve trained males underwent five sessions [age (mean ± SD) 21.8 ± 2.6 yr, peak oxygen uptake ( peak) 60.6 ± 4.6 mL kg min⁻¹, stature 1.78 ± 0.07 m and body mass 76.0 ± 6.3 kg]. These included a control morning (M, 07:30 h) and evening (E, 17:30 h) session (5-min warm-up), and three further sessions consisting of a warm-up morning trial (M_E, on a motorised treadmill) until T_rec reached evening levels; and two cool-down evening trials (in 16–17°C water) until T_rec (E_Mrec) or T_m (E_Mmuscle) values reached morning temperatures, respectively. All sessions included a 3 × 3-s task-specific warm-up followed by 10 × 3-s RS with 30-s recoveries performed on a non-motorised treadmill. T_rec and T_m measurements were taken at the start of the protocol and following the warm-up or cool-down period. Values for T_rec and T_m were higher in the evening compared to morning values (0.45°C and 0.57°C, P < 0.05). RS performance was lower in the M for distance covered (DC), average power (AP) and average velocity (AV) (9–10%, P < 0.05). Pre-cooling T_rec and T_m in the evening reduced RS performance to levels observed in the morning (P < 0.05). However, an active warm-up resulted in no changes in morning RS performance. Diurnal variation in T_rec and T_m is not wholly accountable for time-of-day oscillations in RS performance on a non-motorised treadmill; the exact mechanism(s) for a causal link between central temperature and human performance are still unclear and require more research.

The present study investigated whether increasing morning rectal temperatures (T_rec) to evening levels, or increasing morning and evening T_rec to an “optimal” level (38.5°C), resulting in increased muscle temperatures (T_m), would offset diurnal variation in repeated sprint (RS) performance in a causal manner. Twelve trained males underwent five sessions [age (mean ± SD) 21.0 ± 2.3 years, maximal oxygen consumption (V̇O₂max) 60.0 ± 4.4 mL.kg^–1 min^–1, height 1.79 ± 0.06 m, body mass 78.2 ± 11.8 kg]. These included control morning (M, 07:30 h) and evening (E, 17:30 h) sessions (5-min warm-up), and three further sessions consisting of a warm-up morning trial (M_E, in 39–40°C water) until T_rec reached evening levels; two “optimal” trials in the morning and evening (M_38.5 and E_38.5, in 39–40°C water) respectively, until T_rec reached 38.5°C. All sessions included 3 × 3-s task-specific warm-up sprints, thereafter 10 × 3-s RS with 30-s recoveries were performed a non-motorised treadmill. T_rec and T_m measurements were taken at the start of the protocol and following the warm-up periods. Values for T_rec and T_m at rest were higher in the evening compared to morning values (0.48°C and 0.69°C, p < 0.0005). RS performance was lower (7.8–8.3%) in the M for distance covered (DC; p = 0.002), average power (AP; p = 0.029) and average velocity (AV; p = 0.002). Increasing T_rec in the morning to evening values or optimal values (38.5°C) did not increase RS performance to evening levels (p = 1.000). However, increasing T_rec in the evening to “optimal” level through a passive warm-up significantly reduced DC (p = 0.008), AP (p < 0.0005) and AV (p = 0.007) to values found in the M condition (6.0–6.9%). Diurnal variation in T_rec and T_m is not wholly accountable for time-of-day oscillations in RS performance on a non-motorised treadmill; the exact mechanism(s) for a causal link between central temperature and human performance are still unclear and require more research.

Dual-energy X-ray absorptiometry (DXA) and adipose tissue percentage estimates (AT%) derived from regression based skinfold equations were compared. 35 Gaelic games players [20.9±1.7 years; 78.1±8.6 kg; 179.5±5.7 cm] underwent whole body fan beam DXA scans following a standardised protocol and assessment of skinfold thickness at 8 sites. Adipose tissue% from the sum of skinfolds and/or via body density were calculated for general and athlete specific equations (SKf-AT %). The relationship, i. e., proportional bias, fixed bias and random error (SEE) between DXA-AT% and AT% derived from the 6 skinfold equations were determined using least squares regression analysis. Skinfold AT% estimates were underestimated relative to DXA-AT% across all skinfold equations except that of Durnin and Wormersley [9] (D&W−∑_4AT%) (16.7±3.4 vs. 16.6±4.0%). All equations demonstrated 95% prediction intervals ranges exceeding ~10%. Each equation failed to predict AT% relative to DXA within an accepted±3.5% anthropometric error rate. It is recommended that the conversion of absolute skinfold thickness to an AT% is avoided and that the skinfold equations assessed herein are not utilised in Gaelic games players. Alternate ‘sum of skinfold’ approaches should be considered.

There is currently a lack of research into the energy demands and associated nutritional intakes of elite Gaelic football players during the pre-season period, which is a crucial time of year for physical development. The aim of the current study was to investigate the dietary intake and energy expenditure (EE) of elite Gaelic football players during a typical pre-season week. Over a seven-day period, which included four training days and three rest days, dietary intake (validated self-reported estimated food diary) and EE (Sensewear Pro armband) were recorded in 18 male players from a single elite inter-county Gaelic football team. Average energy intake (EI) (3283 ± 483 kcal) was significantly (p = 0.002) less than average EE (3743 ± 335 kcal), with a mean daily energy deficit of −460 ± 503 kcal. Training days elicited the greatest deficits between intake and expenditure. The mean carbohydrate (CHO) intake was 3.6 ± 0.7 g/kg/day, protein intake was 2.1 ± 0.5 g/kg/day, and fat intake was 1.6 ± 0.2 g/kg/day. These findings indicate that the dietary practices of the sampled players were inadequate to meet EE and CHO recommendations. Training days are of particular concern, with the players not altering energy and CHO intake to encounter increased energy demands. Education on nutritional strategies for elite Gaelic footballers should be considered in relation to training demands to avoid detriments to performance and health.