Maximal power, but not fatigability, is greater during repeated sprints performed in the afternoon

The clockwork of champions: Influence of circadian biology on exercise performance

Exercise physiology and circadian biology are distinct and long-standing fields. Recently they have seen increased integration, largely due to the discovery of the molecular components of the circadian clock and recognition of human exercise performance differences over time-of-day. Circadian clocks, ubiquitous in cells, regulate a daily tissue specific program of gene expression that contribute to temporal patterns of physiological functions over a 24-h cycle. Understanding how circadian clock function in skeletal muscle, as well as other tissues contribute to exercise performance is still in the very early stages. This review provides background on this emerging field with a review of early exercise and time-of-day studies in both human and animals. We then move into the role of the circadian clock and its daily program of gene expression in skeletal muscle with a focus on specific metabolic and physiological outputs that vary over time-of-day. Lastly, we discuss the recognition that the timing of exercise communicates with the skeletal muscle circadian clock to adjust its phase settings and why this maybe important for performance and health.

Timing Matters: Time of Day Impacts the Ergogenic Effects of Caffeine-A Narrative Review

Caffeine has attracted significant attention from researchers in the sports field due to its well-documented ergogenic effects across various athletic disciplines. As research on caffeine continues to progress, there has been a growing emphasis on evaluating caffeine dosage and administration methods. However, investigations into the optimal timing of caffeine intake remain limited. Therefore, this narrative review aimed to assess the ergogenic effects of caffeine administration at different times during the morning (06:00 to 10:00) and evening (16:00 to 21:00). The review findings suggest that circadian rhythms play a substantial role in influencing sports performance, potentially contributing to a decline in morning performance. Caffeine administration has demonstrated effectiveness in mitigating this phenomenon, resulting in ergogenic effects and performance enhancement, even comparable to nighttime levels. While the specific mechanisms by which caffeine regulates circadian rhythms and influences sports performance remain unclear, this review also explores the mechanisms underlying caffeine's ergogenic effects, including the adenosine receptor blockade, increased muscle calcium release, and modulation of catecholamines. Additionally, the narrative review underscores caffeine's indirect impact on circadian rhythms by enhancing responsiveness to light-induced phase shifts. Although the precise mechanisms through which caffeine improves morning performance declines via circadian rhythm regulation necessitate further investigations, it is noteworthy that the timing of caffeine administration significantly affects its ergogenic effects during exercise. This emphasizes the importance of considering caffeine intake timing in future research endeavors to optimize its ergogenic potential and elucidate its mechanisms.

Daily variation in performance measures related to anaerobic power and capacity: A systematic review

Numerous functional measures related to anaerobic performance display daily variation. The diversity of tests and protocols used to assess anaerobic performance related to diurnal effects and the lack of a standardized approach have hindered agreement in the literature. Therefore, the aim of the present study was to investigate and systematically review the evidence relating to time-of-day differences in anaerobic performance measures. The entire content of PubMed (MEDLINE), Scopus, SPORTDiscus® (via EBSCOhost) and Web of Science and multiple electronic libraries were searched. Only experimental research studies conducted in male adult participants aged ≥ 18 yrs before May 2021 were included. Studies assessing tests related to anaerobic capacity or anaerobic power between a minimum of two time-points during the day (morning vs evening) were deemed eligible. The primary search revealed that a total of 55 out of 145 articles were considered eligible and subsequently included. Thirty-nine studies assessed anaerobic power and twenty-five anaerobic capacity using different modes of exercise and test protocols. Forty-eight studies found several of their performance variables to display time-of-day effects, with higher values in the evening than the morning, while seven studies did not find any time-of-day significance in any variables which were assessed. The magnitude of difference is dependent on the modality and the exercise protocol used. Performance measures for anaerobic power found jump tests displayed 2.7 to 12.3% differences, force velocity tests ~8% differences, sprint tests 2.7 to 11.3% differences and 5-m multiple shuttle run tests 3.7 to 13.1% differences in favour of the evening. Performance measures for anaerobic capacity found Wingate test to display 1.8 to 11.7% differences and repeated sprint tests to display 3.4 to 10.2% differences. The only test not to display time-of-day differences was the running based anaerobic sprint test (RAST). Time-of-day variations in anaerobic performance has previously been partially explained by higher core-body and/or muscle temperature and better muscle contractile properties in the afternoon, although recent findings suggest that differences in methodology, motivation/arousal, habitual training times and chronotypes could provide additional explanations. There is a clear demand for a rigorous, standardised approach to be adopted by future investigations which control factors that specifically relate to investigations of time-of-day.

The effect of Ramadan fasting on the morning-evening difference in team-handball-related short-term maximal physical performances in elite female team-handball players

The combined effect of Ramadan fasting and the time of theday on the physical performance of team-handball players has not yet been fully investigated. This study investigated the effects of Ramadan fasting on the morning-evening difference in team-handball-related short-term maximal physical performance. With acounterbalanced study design, 15 elite female team-handball players underwent the hand grip (HG), ball throwing velocity (BTV), modified agility T-test (MAT), and repeated shuttle-sprint and jump ability (RSSJA) tests at 07:00 h and 17:00 h, one week before Ramadan (BR), and during thesecond (SWR) and fourth week of Ramadan (4WR). The oral temperature (OT) was monitored prior to exercise and the ratings of perceived exertion (RPE) scale were obtained after RSSJA. The results showed that the time of theday had an effect on OT under all conditions. The HG, BTV, and MAT test performances were higher in the evening than in the morning BR (P< .001, P< .05, and P< .001, respectively). However, the diurnal variation noted in the HG and MAT tests was reversed during the SWR and 4WR, while the BTV variation was blunted during the SWR and reversed during the 4WR. The best RSSJA performance was observed in the evening BR. However, for the best and mean sprint times, areversal of this diurnal variation was observed, which was blunted for the mean jump height and sprint time decrement during Ramadan. Moreover, RPE were influenced by the time of theday and the month of Ramadan. These findings suggest that the diurnal variation of team-handball-related short-term maximal physical performance may be reversed and/or blunted during Ramadan fasting.

Eat, Train, Sleep-Retreat? Hormonal Interactions of Intermittent Fasting, Exercise and Circadian Rhythm

The circadian rhythmicity of endogenous metabolic and hormonal processes is controlled by a complex system of central and peripheral pacemakers, influenced by exogenous factors like light/dark-cycles, nutrition and exercise timing. There is evidence that alterations in this system may be involved in the pathogenesis of metabolic diseases. It has been shown that disruptions to normal diurnal rhythms lead to drastic changes in circadian processes, as often seen in modern society due to excessive exposure to unnatural light sources. Out of that, research has focused on time-restricted feeding and exercise, as both seem to be able to reset disruptions in circadian pacemakers. Based on these results and personal physical goals, optimal time periods for food intake and exercise have been identified. This review shows that appropriate nutrition and exercise timing are powerful tools to support, rather than not disturb, the circadian rhythm and potentially contribute to the prevention of metabolic diseases. Nevertheless, both lifestyle interventions are unable to address the real issue: the misalignment of our biological with our social time.

Does circadian rhythm have an impact on anaerobic performance, recovery and muscle damage?

This study aimed to examine the effect of circadian rhythms (CR) on anaerobic performance and subsequent recovery, muscle damage, and respiratory muscle strength. Twenty diurnally active male football players (age, 22.20 ± 3.14 y) were asked to perform the Wingate anaerobic power test three times for 30 s each at 09:00, 14:00 and 19:00 h, with a minimum recovery period of 1 week between each testing day. Pretest oral temperature, respiratory muscle strength, oxygen saturation, and rating of perceived exertion were recorded at three different time of the day. To examine post-exercise recovery, heart rate (HR) and lactic acid (LA) levels were recorded before and after the tests. Blood samples were collected 20 min after each test to assess muscle damage. The body temperature taken at 19:00 h was the highest of the three (p < .01). After the tests, the LA value at 19:00 h was higher than that at 09:00 h (p < .05). According to CR, the HR values measured after anaerobic exercise were higher at 14:00 h (p < .05). The peak power value was higher at 14:00 h than at 19:00 h (p < .058). CR does not affect muscle damage and respiratory muscle strength. Further, at 14:00 h, anaerobic power was higher and recovery occurred faster compared to the other test times of 09:00 and 19:00 h. Therefore, it is recommended that anaerobic training should be performed early in the afternoon.

Reliability and time-of-day effect on measures of change of direction deficit in young healthy physical education students

This study aimed to examine the reliability and the time-of-day effect of the 505 change of direction (CoD), 10-m sprint, and change of direction deficit test (CoDD). At two different time of days, 39 young diurnally active physical education male students performed different physical tests: 505 CoD, and sprint tests. Measurements were taken at two separate testing sessions, i.e. in the morning (07:00-08:30 h) and early evening (17:00-18:30 h) in a randomized and counter-balanced setting on nonconsecutive days in 21 of them (21.5 ± 1.5 y of age). The results showed that the 505 CoD test, 10-m sprint, and CoDD performances were a reliable test, and performances were better in the evening the 505 CoD, 10-m sprint, and CoDD testing provided reliable and sensitive scores. In addition, phase 2 showed that CoD, speed, and CoDD are affected by the time of day.

Caffeine and Exercise Performance: Possible Directions for Definitive Findings

Caffeine is one of the most studied supplements in the world. Studies correlate its use to increased exercise performance in endurance activities, as well as its possible ergogenic effects for both intermittent and strength activities. Recent findings show that caffeine may increase or decrease exercise performance. These antagonist responses may occur even when using the same dosage and for individuals with the same characteristics, making it challenging to explain caffeine's impact and applicability. This review article provides an analytic look at studies involving the use of caffeine for human physical performance, and addresses factors that could influence the ergogenic effects of caffeine on different proposed activities. These factors subdivide into caffeine effects, daily habits, physiological factors, and genetic factors. Each variable has been focused on by discussions to research related to caffeine. A better understanding and control of these variables should be considered in future research into personalized nutritional strategies.

Effects of Time of Day on Pacing in a 4-km Time Trial in Trained Cyclists

CONTEXT

Time of day has been shown to impact athletic performance, with improved performance observed in the late afternoon-early evening. Diurnal variations in physiological factors may contribute to variations in pacing selection; however, research investigating time-of-day influence on pacing is limited.

PURPOSE

To investigate the influence of time-of-day on pacing selection in a 4-km cycling time trial (TT).

METHODS

Nineteen trained male cyclists (mean [SD] age 39.0 [10.7] y, height 1.8 [0.1] m, body mass 78.0 [9.4] kg, VO2max 62.1 [8.7] mL·kg-1·min-1) completed a 4-km TT on 5 separate occasions at 08:30, 11:30, 14:30, 17:30, and 20:30. All TTs were completed in a randomized order, separated by a minimum of 2 d and maximum of 7 d.

RESULTS

No time-of-day effects were observed in pacing as demonstrated by similar power outputs over 0.5-km intervals (P = .78) or overall mean power output (333.0 [38.9], 339.8 [37.2], 335.5 [31.2], 336.7 [35.2], and 334.9 [35.7] W; P = .45) when TTs were performed at 08:30, 11:30, 14:30, 17:30, and 20:30. Preexercise tympanic temperature demonstrated a time-of-day effect (P < .001), with tympanic temperature higher at 14:30 and 17:30 than at 08:30 and 11:30.

CONCLUSION

While a biological rhythm was present in tympanic temperature, pacing selection and performance when completing a 4-km cycling TT were not influenced by time of day. The findings suggest that well-trained cyclists can maintain a robust pacing strategy for a 4-km TT regardless of time of the day.

Caffeine and Exercise: What Next?

Caffeine is a widely utilized performance-enhancing supplement used by athletes and non-athletes alike. In recent years, a number of meta-analyses have demonstrated that caffeine's ergogenic effects on exercise performance are well-established and well-replicated, appearing consistent across a broad range of exercise modalities. As such, it is clear that caffeine is an ergogenic aid-but can we further explore the context of this ergogenic aid in order to better inform practice? We propose that future research should aim to better understand the nuances of caffeine use within sport and exercise. Here, we propose a number of areas for exploration within future caffeine research. These include an understanding of the effects of training status, habitual caffeine use, time of day, age, and sex on caffeine ergogenicity, as well as further insight into the modifying effects of genotype. We also propose that a better understanding of the wider, non-direct effects of caffeine on exercise, such as how it modifies sleep, anxiety, and post-exercise recovery, will ensure athletes can maximize the performance benefits of caffeine supplementation during both training and competition. Whilst not exhaustive, we hope that the questions provided within this manuscript will prompt researchers to explore areas with the potential to have a large impact on caffeine use in the future.

Circadian rhythms and exercise - re-setting the clock in metabolic disease

Perturbed diurnal rhythms are becoming increasingly evident as deleterious events in the pathology of metabolic diseases. Exercise is well characterized as a crucial intervention in the prevention and treatment of individuals with metabolic diseases. Little is known, however, regarding optimizing the timing of exercise bouts in order to maximize their health benefits. Furthermore, exercise is a potent modulator of skeletal muscle metabolism, and it is clear that skeletal muscle has a strong circadian profile. In humans, mitochondrial function peaks in the late afternoon, and the circadian clock might be inherently impaired in myotubes from patients with metabolic disease. Timing exercise bouts to coordinate with an individual's circadian rhythms might be an efficacious strategy to optimize the health benefits of exercise. The role of exercise as a Zeitgeber can also be used as a tool in combating metabolic disease. Shift work is known to induce acute insulin resistance, and appropriately timed exercise might improve health markers in shift workers who are at risk of metabolic disease. In this Review, we discuss the literature regarding diurnal skeletal muscle metabolism and the interaction with exercise bouts at different times of the day to combat metabolic disease.

Effects of caffeine ingestion on the diurnal variation of cognitive and repeated high-intensity performances

The purpose of this study was to evaluate the effects of caffeine ingestion on the daily variation of cognitive (i.e., reaction time (RT), attention) and repeated high-intensity exercise performances. Fifteen active males (age: 20 ± 1 years, height: 174.3 ± 4.3 cm, body-mass: 70.8 ± 3.5 kg) performed cognitive and physical tasks under two different circumstances [after a placebo or caffeine ingestion (6 mg/kg of body-mass)] at six different time-of-day (07 h00, 09 h00, 11 h00, 13 h00, 15 h00 and 17 h00) in a randomized double-blind balanced crossover design. During each session, RT, attention and 5-m multiple shuttles run test' performances were recorded. During both the placebo and the caffeine conditions, a significant diurnal variation was found with improvement of cognitive performances recorded at 11 h00 (e.g., RT: 0.37 ± 0.02-s and 0.36 ± 0.02-s for placebo and caffeine respectively) and 17 h00 (e.g., RT: 0.37 ± 0.02-s and 0.35 ± 0.03-s for placebo and caffeine respectively) compared to (i.e., worst performances) 07 h00 (e.g., RT: 0.41 ± 0.02-s and 0.38 ± 0.02-s for placebo and caffeine respectively) and 13 h00 (e.g., RT: 0.41 ± 0.02-s and 0.38 ± 0.02-s for placebo and caffeine respectively) (p < 0.05). For physical performance, improved values were recorded at 17 h00 (e.g., total distance: 730.00 ± 43.92-m and 733.93 ± 43.08-m for placebo and caffeine respectively) compared to 07 h00 (e.g., total distance: 698.14 ± 45.39-m and 709.21 ± 43.78-m for placebo and caffeine respectively) (p < 0.05). Compared to placebo, cognitive (e.g., RT: by 6.4% at 07 h00, 4.1% at 09 h00, 3.4% at 11 h00, 6.0% at 13 h00, 3.8% at 15 h00 and 3.8% at 17 h00) and physical (e.g., total distance: 1.6% at 07 h00, 0.9% at 09 h00, 0.1% at 11 h00 (p > 0.05), 0.5% at 13 h00, 1.0% at 15 h00 and 0.5% at 17 h00) performances increased at all time-of-day (p < 0.05). In conclusion, cognitive and physical performances are time-of-day dependent and caffeine is an effective ergogenic aid to improves both cognitive and physical performances especially at the moment of their lowest values.

Can caffeine supplementation reverse the effect of time of day on repeated-sprint exercise performance?

The aim of this study was to evaluate if caffeine can reduce the negative influence of diurnal variations on repeated-sprint performance, in addition to investigating if caffeine in the afternoon would potentiate performance compared with the morning. Thirteen physically active men took part in this randomized, double-blind, placebo-controlled and crossover study. All participants underwent a repeated-sprint ability test (10 × 6 s cycle sprints, with 30 s of rest) at 60 min after ingestion of either 5 mg·kg^-1 or placebo under 4 different conditions: morning with caffeine ingestion, morning with placebo ingestion, afternoon with caffeine ingestion, and afternoon with placebo ingestion. Total work, peak power (PP) and anaerobic power reserve (APR) were assessed. Oxygen uptake, heart rate, lactate concentration, and rating of perceived exertion were also measured during the repeated-sprint test. Total work (+8%, d = 0.2, small), PP (+6%, d = 0.2), and APR (+9%, d = 0.2) were significantly higher in the afternoon when compared with morning. However, physiological responses were not different between caffeine and placebo conditions. Repeated-sprint (10 × 6 s cycle sprint) performance was influenced by time of day, with lower performance in the morning compared with the afternoon. However, caffeine supplementation did not prevent the reduction in performance in the morning or improve performance in the afternoon.

The effect of air pollution on diurnal variation of performance in anaerobic tests, cardiovascular and hematological parameters, and blood gases on soccer players following the Yo-Yo Intermittent Recovery Test Level-1

This study aimed to investigate the effect of air pollution on diurnal variation of performance in anaerobic tests, cardiovascular and hematological parameters, and blood gases on soccer players following the Yo-Yo Intermittent Recovery Test Level-1 (YYIRT1). In a randomized order, 11 healthy soccer players (mean age: 21.8 [range: 20-24] years; height: 178.00 [range: 1.64-1.83] cm; body mass index [BMI]: 23.57 [range: 20.45-28.03] kg.m^-2) performed a YYIRT1 at two different times of day (TOD) (08:00 h and 18:00 h) in two areas (i.e. polluted (PA) and non-polluted (NPA)) with a recovery period of ≥ 72 h in between, to determine the maximal oxygen uptake (VO2max). In each test session: resting oral temperature is measured, anaerobic performances (pre- and post-YYIRT1) were performed, cardiovascular parameters and blood samples were collected at: rest, 3 min and 60 min after the YYIRT1, to assess blood gases and hematological parameters. Our results showed that, agility performance, VO2max, red blood cells (RBC), hemoglobin (Hb), pH, and bicarbonate levels (HCO3^-) decrease significantly (p < 0.001) following the YYIRT1 in PA compared to NPA. Likewise, the heart rate (HR), systolic blood pressure (SBP), platelets (PLT), white blood cells (WBC), neutrophiles (NEUT), lymphocytes (LYM), and partial pressure of CO2 levels (P_vCO2) were significantly higher (p < 0.001) in PA. This effect was slightly accentuated at 18:00 h for some parameters (i.e. Agility, HCO3^-, HR, P_vCO2, RBC, SBP). However, performances of sprint and Sargent jump test (SJT), oral temperature, rate of perceived exertion scales (RPE), partial pressure of O2 (P_vO2), diastolic blood pressure (DBP), and monocytes (MON) were not affected by pollution (p > 0.05). In conclusion, pollution seems to be critical for health stability and performance in response to YYIRT1 especially in the evening and the winter season. Therefore, coaches and athletes should draw attention to the potential importance of land use planning in their training sessions and competitions in the morning in polluted area to minimize the risk of pollution exposure.

Effects of time-of-day on oxidative stress, cardiovascular parameters, biochemical markers, and hormonal response following level-1 Yo-Yo intermittent recovery test

The aim of this study was to investigate the effect of time-of-day on oxidative stress, cardiovascular parameters, muscle damage parameters, and hormonal responses following the level-1 Yo-Yo intermittent recovery test (YYIRT). A total of 11 healthy subjects performed an intermittent test (YYIRT) at two times-of-day (i.e., 07:00 h and 17:00 h), with a recovery period of ≥36 h in-between, in a randomized order. Blood samples were taken at the rest (baseline) and immediately (post-YYIRT) after the YYIRT for measuring oxidative stress, biochemical markers, and hormonal response. Data were statistically analyzed using one-way and two-way repeated measures ANOVA and Bonferroni test at p < 0.05. Observed power (α = 0.05) and partial eta-squared were used. Our results showed that oxygen uptake (VO2max), maximal aerobic speed, and the total distance covered tended to be higher in the evening (17:00 h). There was also a main effect of time-of-day for cortisol and testosterone concentration, which were higher after the YYIRT in the morning (p < 0.05). The heart rate peak and the rating of perceived exertion scales were lower in the morning (p < 0.05). However, the plasma glucose (p < 0.01), malondialdehyde, creatine kinase (p < 0.01), lactate dehydrogenase (p < 0.05), high-density lipoprotein (p < 0.01), total cholesterol (p < 0.01), and triglycerides (p < 0.05) were higher after the YYIRT in the evening. Low-density lipoprotein, systolic blood pressure, diastolic blood pressure, and lactate levels (p > 0.05) were similar for the morning and evening test. In conclusion, our findings suggest that aerobic performance presents diurnal variation with great result observed in the evening accompanied by an improvement of hormonal, metabolic, and oxidative responses. These data may help to guide athletes and coaches and contribute to public health recommendations on exercise and muscle damage particularly in the competitive periods.

Ammonium Chloride Ingestion Attenuates Exercise-Induced mRNA Levels in Human Muscle

Minimizing the decrease in intracellular pH during high-intensity exercise training promotes greater improvements in mitochondrial respiration. This raises the intriguing hypothesis that pH may affect the exercise-induced transcription of genes that regulate mitochondrial biogenesis. Eight males performed 10x2-min cycle intervals at 80% V˙O2peak intensity on two occasions separated by ~2 weeks. Participants ingested either ammonium chloride (ACID) or calcium carbonate (PLA) the day before and on the day of the exercise trial in a randomized, counterbalanced order, using a crossover design. Biopsies were taken from the vastus lateralis muscle before and after exercise. The mRNA level of peroxisome proliferator-activated receptor co-activator 1α (PGC-1α), citrate synthase, cytochome c and FOXO1 was elevated at rest following ACID (P<0.05). During the PLA condition, the mRNA content of mitochondrial- and glucose-regulating proteins was elevated immediately following exercise (P<0.05). In the early phase (0–2 h) of post-exercise recovery during ACID, PGC-1α, citrate synthase, cytochome C, FOXO1, GLUT4, and HKII mRNA levels were not different from resting levels (P>0.05); the difference in PGC-1α mRNA content 2 h post-exercise between ACID and PLA was not significant (P = 0.08). Thus, metabolic acidosis abolished the early post-exercise increase of PGC-1α mRNA and the mRNA of downstream mitochondrial and glucose-regulating proteins. These findings indicate that metabolic acidosis may affect mitochondrial biogenesis, with divergent responses in resting and post-exercise skeletal muscle.

Sleep, circadian rhythms, and athletic performance

Sleep deprivation and time of day are both known to influence performance. A growing body of research has focused on how sleep and circadian rhythms impact athletic performance. This review provides a systematic overview of this research. We searched three different databases for articles on these issues and inspected relevant reference lists. In all, 113 articles met our inclusion criteria. The most robust result is that athletic performance seems to be best in the evening around the time when the core body temperature typically is at its peak. Sleep deprivation was negatively associated with performance whereas sleep extension seems to improve performance. The effects of desynchronization of circadian rhythms depend on the local time at which performance occurs. The review includes a discussion of differences regarding types of skills involved as well as methodological issues.

Prior low- or high-intensity exercise alters pacing strategy, energy system contribution and performance during a 4-km cycling time trial

We analyzed the influence of prior exercise designed to reduce predominantly muscle glycogen in either type I or II fibers on pacing and performance during a 4-km cycling time trial (TT). After preliminary and familiarization trials, in a randomized, repeated-measures crossover design, ten amateur cyclists performed: 1) an exercise designed to reduce glycogen of type I muscle fibers, followed by a 4-km TT (EX-FIB I); 2) an exercise designed to reduce glycogen of type II muscle fibers, followed by a 4-km TT (EX-FIB II) and; 3) a 4-km TT, without the prior exercise (CONT). The muscle-glycogen-reducing exercise in both EX-FIB I and EX-FIB II was performed in the evening, ∼12 h before the 4-km TT. Performance time was increased and power output (PO) was reduced in EX-FIB I (432.8±8.3 s and 204.9±10.9 W) and EX-FIB II (428.7±6.7 s and 207.5±9.1 W) compared to CONT (420.8±6.4 s and 218.4±9.3 W; P<0.01), without a difference between EX-FIB I and EX-FIB II (P>0.05). The PO was lower in EX-FIB I than in CONT at the beginning and middle of the trial (P<0.05). The mean aerobic contribution during EX-FIB I was also significantly lower than in CONT (P<0.05), but there was no difference between CONT and EX-FIB II or between EX-FIB I and EX-FIB II (P>0.05). The integrated electromyography was unchanged between conditions (P>0.05). Performance may have been impaired in EX-FIB I due a more conservative pacing at the beginning and middle, which was associated with a reduced aerobic contribution. In turn, the PO profile adopted in EX-FIB II was also reduced throughout the trial, but the impairment in performance may be attributed to a reduced glycolytic contribution (i.e. reduced lactate accumulation).

Effect of time of day on performance, hormonal and metabolic response during a 1000-M cycling time trial

The aim of this study was to determine the effect of time of day on performance, pacing, and hormonal and metabolic responses during a 1000-m cycling time-trial. Nine male, recreational cyclists visited the laboratory four times. During the 1^st visit the participants performed an incremental test and during the 2^nd visit they performed a 1000-m cycling familiarization trial. On the 3^rd and 4^th visits, the participants performed a 1000-m TT at either 8 am or 6 pm, in randomized, repeated-measures, crossover design. The time to complete the time trial was lower in the evening than in the morning (88.2±8.7 versus 94.7±10.9 s, respectively, p<0.05), but there was no significant different in pacing. However, oxygen uptake and aerobic mechanical power output at 600 and 1000 m tended to be higher in the evening (p<0.07 and 0.09, respectively). There was also a main effect of time of day for insulin, cortisol, and total and free testosterone concentration, which were all higher in the morning (+60%, +26%, +31% and +22%, respectively, p<0.05). The growth hormone, was twofold higher in the evening (p<0.05). The plasma glucose was ∼11% lower in the morning (p<0.05). Glucagon, norepinephrine, epinephrine and lactate were similar for the morning and evening trials (p>0.05), but the norepinephrine response to the exercise was increased in the morning (+46%, p<0.05), and it was accompanied by a 5-fold increase in the response of glucose. Muscle recruitment, as measured by electromyography, was similar between morning and evening trials (p>0.05). Our findings suggest that performance was improved in the evening, and it was accompanied by an improved hormonal and metabolic milieu.

The role of sense of effort on self-selected cycling power output

PURPOSE

We explored the effects of the sense of effort and accompanying perceptions of peripheral discomfort on self-selected cycle power output under two different inspired O2 fractions.

METHODS

On separate days, eight trained males cycled for 5 min at a constant subjective effort (sense of effort of '3' on a modified Borg CR10 scale), immediately followed by five 4-s progressive submaximal (sense of effort of "4, 5, 6, 7, and 8"; 40 s between bouts) and two 4-s maximal (sense of effort of "10"; 3 min between bouts) bouts under normoxia (NM: fraction of inspired O2 [FiO2] 0.21) and hypoxia (HY: [FiO2] 0.13). Physiological (Heart Rate, arterial oxygen saturation (SpO2) and quadriceps Root Mean Square (RMS) electromyographical activity) and perceptual responses (overall peripheral discomfort, difficulty breathing and limb discomfort) were recorded.

RESULTS

Power output and normalized quadriceps RMS activity were not different between conditions during any exercise bout (p > 0.05) and remained unchanged across time during the constant-effort cycling. SpO2 was lower, while heart rate and ratings of perceived difficulty breathing were higher under HY, compared to NM, at all time points (p < 0.05). During the constant-effort cycling, heart rate, overall perceived discomfort, difficulty breathing and limb discomfort increased with time (all p < 0.05). All variables (except SpO2) increased along with sense of effort during the brief progressive cycling bouts (all p < 0.05). During the two maximal cycling bouts, ratings of overall peripheral discomfort displayed an interaction between time and condition with ratings higher in the second bout under HY vs. NM conditions.

CONCLUSION

During self-selected, constant-effort and brief progressive, sub-maximal, and maximal cycling bouts, mechanical work is regulated in parallel to the sense of effort, independently from peripheral sensations of discomfort.

Oxygen uptake during repeated-sprint exercise

OBJECTIVES

Repeated-sprint ability appears to be influenced by oxidative metabolism, with reductions in fatigue and improved sprint times related to markers of aerobic fitness. The aim of the current study was to measure the oxygen uptake (VO₂) during the first and last sprints during two, 5 × 6-s repeated-sprint bouts.

DESIGN

Cross-sectional study.

METHODS

Eight female soccer players performed two, consecutive, 5 × 6-s maximal sprint bouts (B1 and B2) on five separate occasions, in order to identify the minimum time (trec) required to recover total work done (Wtot) in B1. On a sixth occasion, expired air was collected during the first and last sprint of B1 and B2, which were separated by trec.

RESULTS

The trec was 10.9 ± 1.1 min. The VO₂ during the first sprint was significantly less than the last sprint in each bout (p<0.001), and the estimated aerobic contribution to the final sprint (measured in kJ) was significantly related to VO₂max in both B1 (r=0.81, p=0.015) and B2 (r=0.93, p=0.001). In addition, the VO₂ attained in the final sprint was not significantly different from VO₂max in B1 (p=0.284) or B2 (p=0.448).

CONCLUSIONS

The current study shows that the VO₂ increases from the first to the last of 5 × 6-s sprints and that VO₂max may be a limiting factor to performance in latter sprints. Increasing V˙O₂max in team-sport athletes may enable increased aerobic energy delivery, and consequently work done, during a bout of repeated sprints.

Emotional pictures impact repetitive sprint ability test on cycle ergometre

This study investigated the interaction between emotion-eliciting pictures and power output during a repetitive supra-maximal task on a cycle ergometre. Twelve male participants (mean (±SD) age, height and weight: 28.58 ± 3.23 years, 1.78 ± 0.05 m and 82.41 ± 13.29 kg) performed 5 repeated sprint tests on a cycle ergometre in front of neutral, pleasant or unpleasant pictures. For each sprint, mechanical (peak power and work), physiological (heart rate) and perceptual (affective load) indices were analysed. Affective load was calculated from the ratings of perceived exertion, which reflected the amount of pleasant and unpleasant responses experienced during exercise. The results showed that peak power, work and heart rate values were significantly lower (P < 0.05) for unpleasant pictures (9.18 ± 0.20 W ∙ kg(-1); 47.69 ± 1.08 J ∙ kg(-1); 152 ± 4 bpm) when compared with pleasant ones (9.50 ± 0.20 W ∙ kg(-1); 50.11 ± 0.11 J ∙ kg(-1); 156 ± 3 bpm). Furthermore, the affective load was found to be similar for the pleasant and unpleasant sessions. All together, these results suggested that the ability to produce maximal power output depended on whether the emotional context was pleasant or unpleasant. The fact that the power output was lower in the unpleasant versus pleasant session could reflect a regulatory process aimed at maintaining a similar level of affective load for both sessions.

Is there a diurnal variation in repeated sprint ability on a non-motorised treadmill?

In active males, muscle force production and short-term (<6 s) anaerobic performance are significantly greater in the evening compared with the morning. This diurnal variation is attributed to motivational, peripheral and central factors, and possibly the higher core and muscle temperatures observed in the evening. However, little is known regarding whether diurnal variation on a treadmill also exists in team-sport specific tests of repeated sprint ability (RSA), as would be relevant to football, for example. A controlled laboratory protocol using a non-motorised treadmill has been used to investigate whether daily variation in RSA is present in highly motivated athletes. Twenty active males (mean ± SD: age, 21.0 ± 2.2 yrs; maximal oxygen uptake ([Formula: see text] max), 60.8 ± 4.8 ml kg min(-1); body mass, 77.02 ± 10.5 kg and height, 1.79 ± 0.07 m) volunteered and completed two sessions counterbalanced in order of administration (separated by >48 h): a morning (M, 07:30 h) and evening (E, 17:30 h) session. Both sessions included a 5-min active warm-up on a motorised treadmill at 10 km h(-1) followed by three task-specific warm-up sprints at 50%, 70% and 80%, respectively, on a non-motorised treadmill. During each trial, 10 × 3 s repeated sprints with 30 s recoveries were performed on the non-motorised treadmill. Rectal (Trec) and muscle temperature measurements (Tm) were taken after subjects had reclined for 30 min at the start of the protocol, and again after the active warm-up. Values of heart rate, thermal comfort (TC), rating of perceived exertion (RPE) and effort were measured throughout. Blood samples were taken at rest, after the sprints and 5-min post sprints. Data were analysed using a GLM with repeated measures. Trec and Tm values were higher at rest in the evening than the morning (0.46 °C and 0.57 °C, respectively, p < 0.05). Distance covered, peak power, average power, peak velocity and average velocity all showed significantly higher values in the evening compared with the morning (a range of 3.3-8.3%, p < 0.05), with peak power displaying a statistical trend (0.10 > p > 0.05). All subjects reported maximal values for "effort" for each sprint. There were significant positive correlations between Trec and Tm, Trec and RPE, TC and all measures of RSA performance. However, there was no correlation between fatigue index for peak power output or peak velocity and Trec. In summary, in this population of motivated subjects, time-of-day effects were seen in resting Trec and Tm values and all performance measures of RSA, in partial agreement with past research. The diurnal variation in Trec and Tm cannot fully explain time-of-day oscillations in RSA on a non-motorised treadmill. Although central temperature may provide some endogenous rhythm to human performance, the causal link seems to be due to a multiplicity of components and mechanisms.

Time-of-Day Effects on Psychomotor and Physical Performances in Highly Trained Cyclists

The aim of this study was to examine, in trained young cyclists, whether psychomotor performances were dependent on time of day and fluctuated similarly to changes in athletic performance. 14 highly trained male cyclists ( M age = 17.3 yr., SD = 1.6; M height = 179.0 cm, SD = 0.1; M body weight = 67.4 kg, SD = 4.5) voluntarily took part in 6 test sessions, at 08:30, 10:30, 12:30, 14:30, 16:30 and 18:30. Each test session comprised a maximal-intensity exercise consisting of 2 × 10-sec. sprints (all-out exercise) preceded by an attentional performance test including 4 fields of attention performed in a randomized order at different times throughout the same day, every 2 hr. between 08:30 and 18:30. The main results indicated that attentional and physical performances depended on the time of day, with an improvement in reaction times in phasic alertness, visual scanning, flexibility, Go/No-go, and an increase in maximum power throughout the day. This study shows the daily variations in physical performances and that fluctuations are reflected in psychomotor performances. These findings suggest that cyclists' training sessions cannot be programmed throughout the day without taking into consideration the effects of the time of day, with several practical applications for coaches and athletes.

Caffeine increases anaerobic work and restores cycling performance following a protocol designed to lower endogenous carbohydrate availability

The purpose this study was to examine the effects of caffeine ingestion on performance and energy expenditure (anaerobic and aerobic contribution) during a 4-km cycling time trial (TT) performed after a carbohydrate (CHO) availability-lowering exercise protocol. After preliminary and familiarization trials, seven amateur cyclists performed three 4-km cycling TT in a double-blind, randomized and crossover design. The trials were performed either after no previous exercise (CON), or after a CHO availability-lowering exercise protocol (DEP) performed in the previous evening, followed by either placebo (DEP-PLA) or 5 mg.kg(-1) of caffeine intake (DEP-CAF) 1 hour before the trial. Performance was reduced (-2.1%) in DEP-PLA vs CON (421.0±12.3 vs 412.4±9.7 s). However, performance was restored in DEP-CAF (404.6±17.1 s) compared with DEP-PLA, while no differences were found between DEP-CAF and CON. The anaerobic contribution was increased in DEP-CAF compared with both DEP-PLA and CON (67.4±14.91, 47. 3±14.6 and 55.3±14.0 W, respectively), and this was more pronounced in the first 3 km of the trial. Similarly, total anaerobic work was higher in DEP-CAF than in the other conditions. The integrated electromyographic activity, plasma lactate concentration, oxygen uptake, aerobic contribution and total aerobic work were not different between the conditions. The reduction in performance associated with low CHO availability is reversed with caffeine ingestion due to a higher anaerobic contribution, suggesting that caffeine could access an anaerobic "reserve" that is not used under normal conditions.

Effects of Ramadan on the Diurnal Variations of Repeated-Sprint Performance

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.

The effect of training at a specific time of day: a review

This article focuses on physical performances after training at a specific time of day. To date, although the effect of time of day on aerobic performances appears to be equivocal, during anaerobic exercises, the effect of time of day has been well established with early morning nadirs and peak performances in the late afternoon. These diurnal rhythms can be influenced by several factors such as the regular training at a specific time of day. Indeed, regular training in the morning hours may increase the lower morning performances to the same or even higher level as their normal diurnal peak typically observed in the late afternoon by a greater increase of performance in the evening. However, regular training in the evening hours may increase the morning-evening (i.e., amplitude of the rhythm) difference by a greater increase of performance in the late afternoon. Therefore, adaptations to training are greater at the time of day at which training is regularly performed than at other times. Nevertheless, although modifications in resting hormones concentrations could explain this time-of-day specific adaptations, precise information on the underlying mechanisms is lacking.

Diurnal variations in physical performances related to football in young soccer players

PURPOSE

This study investigated the effects of time-of-day on aerobic and anaerobic performances during the Yo-Yo, repeated sprint ability (RSA) and the Wingate tests in young soccer players.

METHODS

In a counterbalanced and a random order, twenty junior male soccer players completed the Yo-Yo, the RSA, and the Wingate tests at two different times-of-day: 07:00 and 17:00 h. During the Yo-Yo test, the total distance (TD) covered and the estimated maximal aerobic velocity (MAV) were determined. The peak power (PP) during each sprint, the percentage of decrement of PP (PD) and total work (Wtotal) during the RSA test were, also, measured. In addition, during the Wingate test, the peak (P(peak)) and mean (P(mean)) powers were recorded.

RESULTS

During the Wingate test, P(peak) and P(mean) were significantly higher at 17:00 than 07:00 h (P<0.05) with diurnal gains of 3.1±3.6 and 2.9±3.5% respectively. During the RSA test, PP during the first two sprints, Pdec and Wtotal were, also, higher in the evening (P<0.05) with amplitudes of 4.8±4.6, 3.1±3.0, 13.1±32.1, and 4.1±2.5% respectively. Likewise, TD and MAV during the Yo-Yo test were higher at 17:00 than 07:00 h with diurnal gains of 13.1±10.7 and 4.2±3.3 respectively.

CONCLUSIONS

The present study confirms the daily variations of both aerobic and anaerobic performances during the Yo-Yo, the RSA, and the Wingate tests in trained young Tunisian soccer players.

Diurnal variations of plasma homocysteine, total antioxidant status, and biological markers of muscle injury during repeated sprint: effect on performance and muscle fatigue--a pilot study

The aim of this study was (i) to evaluate whether homocysteine (Hcy), total antioxidant status (TAS), and biological markers of muscle injury would be affected by time of day (TOD) in football players and (ii) to establish a relationship between diurnal variation of these biomarkers and the daytime rhythm of power and muscle fatigue during repeated sprint ability (RSA) exercise. In counterbalanced order, 12 football (soccer) players performed an RSA test (5 x[6 s of maximal cycling sprint + 24 s of rest]) on two different occasions: 07:00-08:30 h and 17:00-18:30 h. Fasting blood samples were collected from a forearm vein before and 3-5 min after each RSA test. Core temperature, rating of perceived exertion, and performances (i.e., Sprint 1, Sprint 2, and power decrease) during the RSA test were significantly higher at 17:00 than 07:00 h (p < .001, p < .05, and p < .05, respectively). The results also showed significant diurnal variation of resting Hcy levels and all biological markers of muscle injury with acrophases (peak times) observed at 17:00 h. These fluctuations persisted after the RSA test. However, biomarkers of antioxidant status' resting levels (i.e., total antioxidant status, uric acid, and total bilirubin) were higher in the morning. This TOD effect was suppressed after exercise for TAS and uric acid. In conclusion, the present study confirms diurnal variation of Hcy, selected biological markers of cellular damage, and antioxidant status in young football players. Also, the higher performances and muscle fatigue showed in the evening during RSA exercise might be due to higher levels of biological markers of muscle injury and lower antioxidant status at this TOD.

Repeated-sprint ability - part I: factors contributing to fatigue

Short-duration sprints (<10 seconds), interspersed with brief recoveries (<60 seconds), are common during most team and racket sports. Therefore, the ability to recover and to reproduce performance in subsequent sprints is probably an important fitness requirement of athletes engaged in these disciplines, and has been termed repeated-sprint ability (RSA). This review (Part I) examines how fatigue manifests during repeated-sprint exercise (RSE), and discusses the potential underpinning muscular and neural mechanisms. A subsequent companion review to this article will explain a better understanding of the training interventions that could eventually improve RSA. Using laboratory and field-based protocols, performance analyses have consistently shown that fatigue during RSE typically manifests as a decline in maximal/mean sprint speed (i.e. running) or a decrease in peak power or total work (i.e. cycling) over sprint repetitions. A consistent result among these studies is that performance decrements (i.e. fatigue) during successive bouts are inversely correlated to initial sprint performance. To date, there is no doubt that the details of the task (e.g. changes in the nature of the work/recovery bouts) alter the time course/magnitude of fatigue development during RSE (i.e. task dependency) and potentially the contribution of the underlying mechanisms. At the muscle level, limitations in energy supply, which include energy available from phosphocreatine hydrolysis, anaerobic glycolysis and oxidative metabolism, and the intramuscular accumulation of metabolic by-products, such as hydrogen ions, emerge as key factors responsible for fatigue. Although not as extensively studied, the use of surface electromyography techniques has revealed that failure to fully activate the contracting musculature and/or changes in inter-muscle recruitment strategies (i.e. neural factors) are also associated with fatigue outcomes. Pending confirmatory research, other factors such as stiffness regulation, hypoglycaemia, muscle damage and hostile environments (e.g. heat, hypoxia) are also likely to compromise fatigue resistance during repeated-sprint protocols.

Diurnal variation in Wingate-test performance and associated electromyographic parameters

The present study was designed to evaluate time-of-day effects on electromyographic (EMG) activity changes during a short-term intense cycling exercise. In a randomized order, 22 male subjects were asked to perform a 30-s Wingate test against a constant braking load of 0.087 kg·kg(-1) body mass during two experimental sessions, which were set up either at 07:00 or 17:00 h. During the test, peak power (P(peak)), mean power (P(mean)), fatigue index (FI; % of decrease in power output throughout the 30 s), and evolution of power output (5-s span) throughout the exercise were analyzed. Surface EMG activity was recorded in both the vastus lateralis and vastus medialis muscles throughout the test and analyzed over a 5-s span. The root mean square (RMS) and mean power frequency (MPF) of EMG were calculated. Neuromuscular efficiency (NME) was estimated from the ratio of power to RMS. Resting core temperature, P(peak), P(mean), and FI were significantly higher (p < .05) in the evening than morning test (e.g., P(peak): 11.6 ± 0.8 vs. 11.9 ± 1 W·kg(-1)). The results showed that power output decreased following two phases. During the first phase (first 20s), power output decreased rapidly and values were higher (p < .05) in the evening than in the morning. During the second phase (last 10s), power decreased slightly and appeared independent of the time of day of testing. This power output decrease was paralleled by evolution of the MPF and NME. During the first phase, NME and MPF were higher (p < .05) in the evening. During the second phase, NME and MPF were independent of time of day. In addition, no significant differences were noticed between 7:00 and 17:00 h for EMG RMS during the whole 30 s. Taken together, these results suggest that peripheral mechanisms (i.e., muscle power and fatigue) are more likely the cause of the diurnal variation of the Wingate-test performance rather than central mechanisms.