Is there a diurnal variation in 4-km cycling time-trial performance, conducted in an environmental chamber where a standardised approach has been employed?

Figures & data

Table 1. Checklist of considerations in chronobiological studies on humans and sporting performance for participant (1–3), methodological and equipment (4–8) and environmental (9) considerations and general comments and insights into decision for our study.

Consideration	General comments and insights into decision for out study.
Sample Size Estimation and rationale	A-priori test completed with power levels of 80%, p = 0.05 and meaningful effect size given – either from Cohen d tables or past literature with the reference for the research. This should be reported in the methods, in the statistical analysis section. It has been suggested that authors should report the full range of information required to enable the sample size estimation and rationale to be examined. This includes software used, the exact inputs to calculations, a rationale for those inputs, stopping rules and the statistical tests used to test a hypothesis or estimate a population parameter (Abt et al. 2020) – we conducted this and adopted the most stringent sample size estimation allowing recruitment above this for participant drop out.
Population	Biological sex: The combination of male and female data adds complexity to the interpretation of results and for the protocol we used add months to the data collection timeframe. Chronotype and sleep habits should be reported and interpreted (Barton et al. 1990; Walsh et al. 2021) – for our study where there is disagreement in a diurnal variation, we sought to limit variation in our population and used male, intermediate participants whose sleeping habits were like that of the protocol. Categorising fitness (such as by McKay et al. 2021) and markers of fitness should be done to help define the populations such as $\dot{\mathrm{V}}$O2 max/peak or Wingate tests. This information helps with further analysis depending on the distance of the time-trial and contribution of anaerobic or aerobic pathways - we used the methods of (McKay et al. 2021) and reported both $\dot{V}$O2 max/peak or Wingate tests.
Inclusion/Exclusion criteria to reduce confounding variables in studies.	Inclusion: No diagnosed sleep disorders; have not completed shift work or travelled outside the local time-zone in the past month; injury-free; habitually train at any time of day; habitual total sleep time appropriate to age and retiring and protocol waking times within that of the participants normal hygiene; not receiving pharmacological treatment (including NSAIDs); a habitual caffeine “low” consumption, hence <150 mg per day assessed by the caffeine consumption questionnaire (Landrum 1992; Drust et al. 2005; Yousefzadehfard et al. 2022) – we included these points in the method section.
Allocation of IDs to sessions	Either randomly allocated to groups (randomised) and then the order of sessions for groups counterbalanced in order of administration to minimise any potential learning effects (Monk and Leng 1982). This is sometimes referred to as cross over design or a cyclic Latin design (Drust et al. 2005). Or, allocated into two groups (named 1 and 2) equally based on physical ability for first and second session allocation. Practically entails stacking the performance measure for the last familiarisation session from fastest to slowest in Microsoft Excel, then pasting the words 1 or 2 respectively so the first cell (fastest participant) was 1 and next was 2 all the way down the column - we included these points in the method section.
Timing of sessions and Time between sessions	Being as close to the body temperature minimum and maximum as possible to maximise the chance of finding a rhythm (04:00 and 16:00 h respectively), but not so early as to cause sleep deprivation in the morning or be beyond the opening hours of the research facility; so 06:00–07:30 h in the morning and 17:00–19:00 h in the evening timings are normally chosen for diurnal studies - we followed this logic.
Familiarisation of participants to the performance test.	The rational for the number of familiarisations should be given as well as random and systematic bias of the last and penultimate given in the method section. This then quantifies the level of learning in the population of the research under investigation. Furthermore, familiarisation is an important experimental methodological consideration for sport and exercise scientists, since it may influence both the number of experimental trials needed in a study, and the sensitivity of the exercise performance criteria. It is therefore potentially very useful to know the test-retest reliability of performance measurements that are used in this manner - we followed this logic.
Diet (timing/content) and Timing of food consumption relative to the session.	The macro and micro-diet weekly habits given with normal caffeine consumption given. Participants recorded the type, amount, and timing of the food they ate for the period of 24 h before the day of the first session and were asked to replicate this diet for the days before the second experimental condition. Morning participants tend to come in fasted and evening not having eaten 4-h prior (Drust et al. 2005). Where is the difference in food intake is 3–4 h between overnight fast and evening fasting - we adopted a pragmatic approach where there was no consensus and having a breakfast or not in the morning had no effect on a range of performance measures (Bougard et al. 2009).
Method of temperature measurement for core body temperature and Ergometers chosen for the time-trial	The hierarchy for the measurement site of “core” temperature being Oesophageal, gut, rectal, intra-aural and oral sites for rest, with only oesophageal, gut, rectal sites used at during exercise (Waterhouse et al. 2005a). The factory error associated with the ergometer given as well as laboratory internal calibration checks. Consideration such as can the system measure distance or do they make approximate assumptions should be given - we followed this logic and used rectal as the site, Watbike Pro has a ±1% error in measuring distance and power. We originally were going to use the Excalibur Lode cycle ergometer but its accuracy for measuring distance is unknown.
Time of year and season given. Laboratory conditions	Inclusion of season(s) and range of time of dawn and dust hence total daylight hours should be given. Also, information on exposure to light in the morning session, both in the laboratory and before should be recorded. The range of ambient lighting, dry temperature, relative humidity, and barometric pressure should be given in method section - we followed this logic.

Figure 1. Schematic of the research design and protocol for conditions undertaken in the morning (07:00 h) or evening (17:00 h). Rectal and skin (Tr and Tsk) temperature and ratings of perceive exertion (RPE) were measured after the participants had reclined for 30-in at the start of the protocol and after the warm-up. Tr and tsk, RPE and HR values were also measured prior to taken every 1-km and the 4 km-time trial in the environmental chamber; with pacing asked every 2-km. Black dotted lines indicate blood taken. * indicates sleep questionnaires administered. BOP =Bridget’s optimal pacing scale.

Table 2. Mean (SD) values for morning (M) and evening (E) for resting or resting and post warm-up. Significance (P-value) for main effects for time of day (DV), pre-post warmup (WUP) and the interaction (DV x WUP) are given. Statistical significance (p < 0.05) is indicated in bold. * indicates a significant DV.

Variable	Morning (M)	Evening (E)	Significance (P-value) DV	Significance (P-value) WUP	Significance (P-value) DV x WUP
Rectal temperature (°C)	37.0 ± 0.2	37.5 ± 0.2 *	F1, 25 = 73.202, p < 0.0005	F1, 25 = 1.577, p = 0.221	F1, 9 = 2.769, p = 0.109
Mean skin temperature (°C)	37.6 ± 0.4	37.9 ± 0.4	F1, 25 = 3.417, p < 0.076	F1, 25 = 0.410, p = 0.841	F1, 25 = 2.247, p = 0.146
Mean body temperature (°C)	36.1 ± 1.0	36.4 ± 0.9 *	F1, 25 = 61.554, p < 0.0005	F1, 25 = 0.910, p = 0.349	F1, 25 = 2.518, p = 0.125
Pulse Oximetry (SpO2,%)	98 ± 2	98 ± 2	F1, 25 = 0.157, p = 0.697	F1, 25 = 2.942, p = 0.106	F1, 25 = 2.618, p = 0.141
Muscle Oxygen (SmO2,%)
Forearm (%)	58 ± 12	56 ± 14	F1, 25 = 0.638, p = 0.436	F1, 25 = 1.793, p = 0.199	F1, 25 = 1.160, p = 0.297
Thigh (%)	65 ± 17	66 ± 19	F1, 25 = 0.149, p = 0.704	F1, 25 = 7.571, p = 0.014	F1, 25 = 0.003, p = 0.960
Calf (%)	58 ± 14	63 ± 13	F1, 25 = 3.311, p = 0.088	F1, 25 = 0.274, p = 0.608	F1, 25 = 0.788, p = 0.388
Mood state – Vigour	5.7 ± 2.1	7.6 ± 3.2 *	F1, 25 = 13.069, p = 0.001
Mood state – Anger	1.0 ± 2.2	0.8 ± 1.6	F1, 25 = 0.224, p = 0.640
Mood state – Tension	1.6 ± 3.3	1.4 ± 3.4	F1, 25 = 0.039, p = 0.845
Mood state – Calm	7.8 ± 4.0	7.9 ± 3.7	F1, 25 = 0.004, p = 0.951
Mood state – Happiness	7.5 ± 2.9	7.8 ± 3.2	F1, 25 = 0.278, p = 0.603
Mood state – Confusion	0.8 ± 1.5	0.8 ± 1.6	F1, 25 = 0.007, p = 0.936
Mood state – Depression	0.7 ± 1.4	0.6 ± 1.4	F1, 25 = 0.189, p = 0.667
Mood state – Fatigue	5.5 ± 3.3	4.0 ± 2.9 *	F1, 25 = 4.279, p = 0.049
Sleep questionnaire
Ease to sleep	0.2 ± 2.7	−0.1 ± 1.7	F1, 25 = 0.130, p = 0.721
Time to sleep	−0.7 ± 1.9	0.1 ± 1.1	F1, 25 = 2.815, p = 0.106
How well slept	−0.3 ± 1.4	0.1 ± 1.5	F1, 25 = 0.696, p = 0.412
Waking time	−1.7 ± 1.4	−1.3 ± 1.5	F1, 25 = 2.606, p = 0.119
Alertness 30-min of waking	−0.2 ± 1.7	−0.1 ± 1.8	F1, 25 = 0.025, p = 0.876

Figure 2. Individual and mean (±95% CI) values for the finishing times in the evening and morning for a 4 km time-trial.

Figure 3. Mean (SD) values for pacing (s), power output (W), heart rate (BPM) and rating of perceived exertion (RPE) every 1-km for the 07:30 and 17:30 h for a 4-km time-trial.

Table 3. Mean (SD) values for morning (M) and evening (E) for pre-post or during the 4 km TT. Significance (P-value) for main effects for time of day (DV), distance or pre-post and the interaction of (DV x distance or DV x pre-post) are given. Statistical significance (p < 0.05) is indicated in bold * indicates a significant DV. Where RPE = rating of perceived exertion and TC = thermal comfort.

Variable	Morning (M)	Evening (E)	Significance (P-value) DV	Significance (P-value) Distance or pre-post	Significance (P-value) DV x distance (or PP)
Time-trial
Finishing time (s)	384.0 ± 29.6	374.1 ± 29.6 *	F1, 25 = 14.805, p = 0.001
Split times (s)	96.9 ± 0.4	95.4 ± 0.6 *	F1, 25 = 14.812, p = 0.001	F1.8, 45.3 = 6.091, p = 0.006	F1.9, 48.6 = 0.155, p=0.223
Power output (W)	217 ± 10	226 ± 8 *	F1, 25 = 7.135, p = 0.013	F1.5, 37.9 = 11.394, p < 0.0005	F 1.9, 48.6 = 0.149, p=0.856
RPE (6–20)	15.4 ± 0.2	15.4 ± 0.4	F1, 25 = 2.436, p = 0.131	F 2.0, 49.5 = 213.612, p < 0.0005	F2.5, 62.0 = 1.338, p=0.271
TC (1–10)	7.0 ± 1.2	7.3 ± 1.3	F1, 25 = 0.485, p = 0.492	F 2.6, 63.8 = 93.681, p < 0.0005	F2.6, 65.2 = 0.766, p=0.514
Effort (0–10 cm VAS)	7.7 ± 0.5	7.7 ± 0.2	F1, 25 = 0.031, p = 0.862	F 2.0, 49.4 = 96.563, p < 0.0005	F1.8, 44.6 = 0.061, p=0.925
Heart rate (BPM)	176 ± 5	176 ± 5	F1, 25 = 1.134, p = 0.297	F2.1, 25 = 74.240, p < 0.0005	F2.0, 50.9 = 0.335, p = 0.721
Rectal temperature (°C)	37.4 ± 0.3	37.7 ± 0.3 *	F1, 25 = 33.604, p < 0.0005	F1.4, 35.5 = 86.417, p < 0.0005	F1.5, 37.6 = 0.743, p = 0.447
Mean skin temperature (°C)	33.6 ± 2.8	33.7 ± 3.2	F1, 25 = 0.129, p = 0.723	F1.2, 30.7 = 0.008, p = 0.955	F1.8, 45.8 = 0.279, p = 0.739
Mean body temperature (°C)	36.6 ± 0.7	36.9 ± 0.7 *	F1, 25 = 26.712, p < 0.0005	F1.2, 31.3 = 47.819, p < 0.0005	F1.8, 44.4 = 1.003, p = 0.367
Pulse Oximetry (SpO2, %)	96 ± 3	97 ± 3	F1, 25 = 0.196, p = 0.694	F2.7, 42.9 = 3.825, p = 0.020	F2.2, 34.8 = 1.641, p = 0.207
Muscle Oxygen (SmO2, %)
Forearm (%)	49 ± 17	41 ± 20	F1, 16 = 2.455, p = 0.137	F1.4, 23.3 = 11.683, p = 0.001	F2.1, 33.8 = 0.954, p = 0.400
Thigh (%)	44 ± 22	44 ± 21	F1, 16 = 0.019, p = 0.893	F1.1, 17.6 = 4.480, p = 0.046	F1.9, 30.6 = 0.107, p = 0.891
Calf (%)	48 ± 16	50 ± 19	F1, 16 = 0.157, p = 0.697	F1.8, 28.26 = 5.029, p = 0.017	F1.9, 30.6 = 0.210, p = 0.798
BOP pacing (−5 to +5)	0.2 ± 1.5	0.5 ± 1.2	F1, 25 = 0.000, p = 1.000	F1, 25 = 1.464, p = 0.238	F1, 25 = 0.038, p = 0.847
Blood lactate (mmol.L)	6.6 ± 5.6	7.3 ± 6.3	F1, 25 = 16.255, p < 0.0005	F1, 25 = 1103.275, p < 0.0005	F1, 25 = 7.371, p = 0.012
Urine (Osmol)	703 ± 264	691 ± 245	F1, 25 = 0.076, p = 0.786	F1, 25 = 7.375, p = 0.012	F1, 25 = 1.084, p = 0.308

Figure 4. Mean (SD) values for forearm, calf, thigh muscle oxygenation (SmO₂, %) and peripheral oxygen saturation (SpO_2, %) every 1-km for the 07:30 and 17:30 h for a 4-km time-trial.

Table 4. Comparison of current study and other authors to the check list for consideration for diurnal variation (DV) studies (table 1), only studies whose participants were male, used a time-trial where distance was set and were undertaken in a thermoneutral environment were included in this comparison. FT = finishing time, PO = power output and CT = core temperature. * indicates contacted authors for information.

	Participant considerations			Methodological and equipment considerations				Environment considerations		Outcome
Author/Variable	Sample size/Sex/Age a priori sample test/	Training status/$\dot{\mathrm{V}}$O2peak/Performance info/	Habitual sleep times/daily preferences for exercise/Chronotype/	Distance and mode of TT/ Time between sessions/TOD of sessions/	Familiarisation to TT/ Allocation of IDs to sessions/	Diet (timing/content) on day of testing/	Core temp site (CT)/kit Ergometers chosen for the time-trial/	Time of year/Sunrise and sunset from start to study end/	Laboratory Dry temp/Humidity/BP/	DV in FT/ DV in PO/ DV in CT/
Current study	26/Males/18-28y/a priori =18 or 22 for one and two tailed t-test.	Recreationally-trained 3xWeek@1h/day, 11 years cycling experience/48.5±7.8 mL.kg.min^−1 , 30s peak PO from a Wingate test of 950±150W.	23:30–07:30 h/Did not have one/Chronotype score=34 ± 4 [28–39] Intermediate types.	4-km cycle ergometry/72 h/ 07:30 h and 17:30 h.	3 sessions, 3^rd vs 2^nd session, CV= 2.71%, p>0.05 ~0.4% difference in FT/ Allocated to groups due to familiarisation finish time then Counterbalanced.	Fasting before AM, eat immediately after, then 12h hence 4h before PM session. Replicated previous 24 h intake.	Rectal/Squirrel 1000 Series, Grant/Wattbike Pro. UK.	October to December (UK Autumn to Winter)/Sunrise-set range from start to end of experiment = 07:29 to 08:01 h and 18:01 to 19:50 h.	19°C/35–45%/750–760 mmHg.	FT:10s, Δ2.59%; p=0.001 PO: 9.1W, p=0.013 CT: ↑0.5°C in evening p<0.05.
Fiedler et al. 2022	15/Males/18+1y/Not given.	Recreationally trained 3xWeek@1h/day/Not given.	Not given/No given/Not given.	3-km run/36 h/07–08 h and 19–20 h.	Not given/Randomly allocated, cross over design.	Not given.	Not given/400m outdoor running track.	Not given/Not given.	Not given/Not given/Not given.	FT:7s, p=0.228 PO and CT not given.
Souissi et al. (2021)	12/Males/Not given/a priori =12.	Physically trained 4xWeek@3h/day/58.3±7.7 mL.kg^−1.min^−1	Not given/trained in Am and PM/Intermediate types.	10-km cycle ergometry/72 h/07–08 h and 17–18 h.	1 session/No data given/Randomly allocated.	Not given.	Intra-aural (ear), Braun, ThermoScan 6, France/Monark 874E, Sweden.	Not given/Not given.	20–21°C/40–45%/BP= Not given.	FT:19s, Δ2.3%; p=0.002. PO: p=0.16 CT: ↑0.33°C in evening p<0.05.
Zadow et al. (2020)	19/Males/39+11y/a priori =17.	Trained cyclists, Daily/62.1±8.7 mL.kg.min^−1	Not given/Not given/Intermediate types.	4-km cycle ergometry/48–84 h/08:30, 11:30, 14:30, 17:30, and 20:30 h.	1 session/Randomised and counterbalanced study design.	Not 3 h prior	Intra-aural (ear), Covidien Genius 2 UK/Wahoo KICKR Power Trainer, U.S.A..	Not given/Not given.	20.8+1.4°C/46.6+6.2%/BP= Not given.	FT: 1.1s, p=0.85 PO: 1.9W, p=0.78 ↑0.5°C in evening p<0.05.
Boyett et al. 2016	22/Males/18-44y/Not given.	11 trained (11 h a week) and 9 untrained cyclists (5h a week)/57±9 mL.kg.min^−1	Not given/Not given/Not given.	3-km/8h/06–10 h and 6–20 h.	Not given/Randomly allocated.	Fasted 7–10 h AM, 4 h for PM. Replicated previous 24 h intake.	Not given/Cycle Ergometer (Velotron, Racermate, U.S.A.).	Not given/Not given.	Not given/Not given/Not given.	FT: 2.9%, p>0.05. PO and CT not given.
Rae et al. 2015	18/Males/25–46y/Not given.	Masters’ swimmers, >2xWeek for 1 year/Not given.	Not given/Not given/9 Morning, 9 Intermediate types.	200 m Swimming/72 h/06:30 h and 18:30 h.	Not given/Randomised.	Fasted 12h AM, 4h for PM. 30 pre a 7% CHO drink.	Not given/Swimming pool (25m).	Not given/Not given.	Not given/Not given/Not given.	FT: 0.1s, p=0.902. PO and CT not given.
Fernandes et al. (2014)	9/Males/31+7y/a priori =6.	Recreational cyclists, 3xWeek@3-4h/day/49±7mL.kg.min^−1 , PPO of 253+52W.	Not given/4 Mod Morning, 5 Intermediate types.	1-km cycle ergometry/7 days/08 h and 18 h.	1 session/Randomised crossover design.	Overnight for AM and 8h for PM	Not given/Cycle-ergotrainer, Tacx T1680 Flow, Netherlands.	Not given/Not given.	19°C/35–45%/750–760 mmHg.	FT:6.5s, Δ6.9%; p=0.048. PO:39.3W, p>0.05 CT: Not given.
Edwards et al. (2008)	10/Males/26+6y/Not given.	Recreational runners, 3xWeek@3-4h/day/61.2±9.4 mL.kg.min^−1	*23:30–07:30h/*No preference/*Intermediate types.	10-km treadmill time-trial/48 h/02, 06, 10, 14, 18, 22 h.	3 sessions/Allocated to groups due to familiarisation finish time then Counterbalanced.	Not given.	Intra-aural (ear), Covidien Genius 2 UK/Woodway, ergo ELG 55, Germany.	Not given/Not given.	Not given/Not given/Not given.	Ft:10s, Δ2.59%; p=0.001, PO: 9.1W, p=0.013 Ct: ↑0.35°C, p<0.05.
Martin et al. (2007)	8/Sex not given/15-16y/Not given.	Competitive Swimmers, 5xWeek in AM and PM/Not given.	Not given/Not given/Intermediate types.	100 m swimming/48h/06:30–07:30 h and 06:30–18:30 h.	Not given/Randomised trial.	>3 h before testing.	Oral digital thermometer (Omron, UK)/Swimming pool (50m).	Not given/Not given.	Not given/Not given/Not given.	FT:1.7s, Δ2.6%; p=0.001. PO: Not given CT: ↑0.66°C in evening p<0.05.
Atkinson et al. (2005)	8/Males/24.9+3.5y/Not given.	Cyclists, 3xWeek@>45min/Not given.	Not given/Not given/ Chronotype score=39+6, Intermediate types.	16.1-km cycle ergometry/82 h/07:30 h and 17:30 h.	Not given/Randomly allocated, counterbalanced design.	06:00 h light breakfast, 12:00 h light lunch.	Intra-aural (ear) Genius 3000A, Sherwood Medical, UK/Kingcycle ergometer (EDS, Portaprompt Ltd, UK).	Not given/Not exposed to daylight as work Jan to Feb. Sunrise = 07:30–08:00 h.	Not given/Not given/Not given.	FT:156s, Δ3.6% p<0.05 PO: 56W p<0.05 CT: ↑0.5°C in evening p<0.05.

Abt G, Boreham C, Davison G, Jackson R, Nevill A, Wallace E, Williams M. 2020. Power, precision, and sample size estimation in sport and exercise science research. J Sports Sci. 38(17):1933–1935. doi: 10.1080/02640414.2020.1776002.

 PubMed Web of Science ®Google Scholar

Barton J, Folkard S, Smith LR, Spelten ER, Totterdell PA 1990. Standard shiftwork index manual. In: SAPU memo No: 1159 MRC/ESRC social and applied psychology unit. Sheffield: Department of Psychology, University of Sheffield; p. S10 2TN.

 Google Scholar

Walsh NP, Halson SL, Sargent C, Roach GD, Nédélec M, Gupta L, Leeder J, Fullagar HH, Coutts AJ, Edwards BJ, et al. 2021. Sleep and the athlete: consensus statement. Br J Sports Med. 55(7):356–368. doi: 10.1136/bjsports-2020-102025.

 Web of Science ®Google Scholar

McKay AK, Stellingwerff T, Smith ES, Martin DT, Mujika I, Goosey-Tolfrey VL, Sheppard J, Burke LM. 2021. Defining training and performance calibre: a participant classification framework. Int J Sport Physiol. 17(2):317–331. doi: 10.1123/ijspp.2021-0451.

 Web of Science ®Google Scholar

Landrum RE. 1992. College students’ use of caffeine and its relationship to personality. Coll Stud J. 26:151–155.

 Google Scholar

Drust B, Waterhouse J, Atkinson G, Edwards B, Reilly T. 2005. Circadian rhythms in sports performance—an update. Chronobiol Int. 22(1):21–44. doi: 10.1081/CBI-200041039.

 PubMed Web of Science ®Google Scholar

Yousefzadehfard Y, Wechsler B, DeLorenzo C. 2022. Human circadian rhythm studies: practical guidelines for inclusion/exclusion criteria and protocol. Neurobiol Sleep Circadian Rhythms. 13:1–18. ISSN 2451-9944. doi: 10.1016/j.nbscr.2022.100080.

 Google Scholar

Monk TH, Leng VC. 1982. Time of day effects in simple repetitive tasks: some possible mechanisms. Acta Psychol. 51(3):207–221. doi: 10.1016/0001-6918(82)90035-X.

 Web of Science ®Google Scholar

Bougard C, Bessot N, Moussay S, Sesboue B, Gauthier A. 2009. Effects of waking time and breakfast intake prior to evaluation of physical performance in the early morning. Chronobiol Int. 26(2):307–323. PMID: 19212843. doi: 10.1080/07420520902774532.

 PubMed Web of Science ®Google Scholar

Waterhouse J, Drust B, Weinert D, Edwards B, Gregson W, Atkinson G, Kao S, Aizawa S, Reilly T. 2005a. The circadian rhythm of core temperature: origin and some implications for exercise performance. Chronobiol Int. 22(2):207–226. PMID: 16021839. doi: 10.1081/cbi-200053477.

 PubMed Web of Science ®Google Scholar

Fiedler J, Altmann S, Chtourou H, Engel F, Neumann R, Woll A. 2022. Daytime fluctuations of endurance performance in young soccer players: a randomized cross-over trial. BMC Res Notes. 15:351. doi:10.1186/s13104-022-06247-1.

 PubMed Web of Science ®Google Scholar

Souissi W, Hammouda O, Ammar A, Ayachi M, Bardiaa Y, Daoud O, Hassen IB, Souissi M, Driss T. 2021. Higher evening metabolic responses contribute to diurnal variation of self-paced cycling performance. bs. 39(1):3–9. 102930. PMID: 35173357; PMCID: PMC8805356. doi: 10.5114/biolsport.2021.102930.

 Google Scholar

Zadow EK, Fell JW, Kitic CM, Han J, Wu SSX. 2020. Effects of time of day on pacing in a 4-km time trial in trained cyclists. Int J Sports Physiol Perform. 15:1455–1459. PMID: 33017804. doi: 10.1123/ijspp.2019-0952.

 PubMed Web of Science ®Google Scholar

Boyett JC, Giersch GE, Womack CJ, Saunders MJ, Hughey CA, Daley HM, Luden ND. 2016. Time of day and training status both impact the efficacy of caffeine for short duration cycling performance. Nutrients. PMID: 27754419. 8:639. doi: 10.3390/nu8100639.

 PubMed Web of Science ®Google Scholar

Rae DE, Stephenson KJ, Roden LC. 2015. Factors to consider when assessing diurnal variation in sports performance: the influence of chronotype and habitual training time-of-day. Eur J Appl Physiol. 115:1339–1349.

 PubMed Web of Science ®Google Scholar

Fernandes AL, Lopes-Silva JP, Bertuzzi R, Casarini DE, Arita DY, Bishop DJ, Lima-Silva AE, Shen W. 2014. Effect of time of day on performance, hormonal and metabolic response during a 1000-M cycling time trial. PloS One. 9(10):e109954. doi: 10.1371/journal.pone.0109954.

 PubMed Web of Science ®Google Scholar

Edwards BJ, Boyle B, Doran D, Waterhouse J, Reilly T. 2008. Effect of time of day on 10-km time-trial running performance. abstract for the E.C.S.S. 13^th annual congress. 9-12 July, 2008. Estoril, Portugal.

 Google Scholar

Martin L, Nevill AM, Thompson KG. 2007. Diurnal variation in swim performance remains, irrespective of training once or twice daily. Int J Sports Physiol Perform. 2:192–200. PMID: 19124906. doi: 10.1123/ijspp.2.2.192.

 PubMed Web of Science ®Google Scholar

Atkinson G, Todd C, Reilly T, Waterhouse J. 2005. Diurnal variation in cycling performance: influence of warm-up. J Sports Sci. 23:321–329. PMID: 15966350. doi: 10.1080/02640410410001729919.

 PubMed Web of Science ®Google Scholar