Athletic Performance, Circadian Rhythm, Exercise Performance, Sports Performance
Conditions
Keywords
Napping, Caffeine, Recovery Protocol, Chronotype, Sex Differences, Evening Performance, Crossover Trial, Randomised Controlled Trial, Brain-Derived Neurotrophic Factor, Heart Rate Variability, Reaction Time, Agility, Jump Performance
Brief summary
This study evaluated whether afternoon napping, caffeine ingestion, and a standardised active recovery and nutritional protocol could influence evening physical and cognitive performance in healthy university athletes. Participants completed five experimental conditions in a randomised crossover design: placebo without napping, napping with placebo, caffeine without napping, napping combined with caffeine, and napping combined with caffeine plus a standardised active recovery and nutritional protocol. The nap opportunity lasted 90 minutes and caffeine was administered at 5 mg/kg body mass. The main outcome was repeated agility performance. Additional outcomes included sprint performance, jumping performance, reaction time, subjective sleepiness, sleep characteristics during the nap opportunity, and selected physiological measures. The study also explored whether responses differed according to sex and chronotype.
Detailed description
This randomised, placebo-controlled crossover study examined the isolated and combined effects of afternoon napping, caffeine ingestion, and a standardised active recovery and nutritional protocol on evening athletic performance. Participants completed five experimental conditions in a counterbalanced Latin-square order, with at least 72 h between sessions: 1. PLA: placebo capsule at 18:00, without a nap opportunity. 2. NAP: 90-min nap opportunity from 13:00 to 14:30 plus placebo capsule at 18:00. 3. CAF: caffeine ingestion at 18:00 (5 mg/kg body mass) without a nap opportunity. 4. NAP+CAF: 90-min nap opportunity plus caffeine ingestion at 18:00. 5. NAP+CAF+REC: 90-min nap opportunity plus caffeine ingestion at 18:00 and a standardised active recovery and nutritional protocol from 18:45 to 19:00. The active recovery and nutritional protocol included a standardised lower-limb dynamic stretching routine followed by a carbohydrate-protein snack containing 20 g maltodextrin and 10 g whey isolate. The protocol was identical for all participants allocated to this condition. Participants were stratified by sex and chronotype before condition allocation. Capsule allocation was double-blinded: participants, outcome assessors, and the testing team were unaware of whether caffeine or placebo had been administered. Blinding of nap and active recovery components was not possible because of the nature of these interventions. The primary outcome was total time during the Repeated Modified Agility Test. Secondary performance outcomes included 20-m sprint time, countermovement jump height, squat jump height, simple reaction time, choice reaction time, and subjective sleepiness. Nap sleep characteristics were assessed using portable electroencephalographic monitoring. Physiological measures included heart-rate variability, salivary cortisol, plasma brain-derived neurotrophic factor, and blood lactate. All sessions were conducted under standardised sleep, dietary, and activity-control procedures. The study explored whether intervention responses differed by sex and chronotype.
Interventions
BEHAVIORALAfternoon Nap
A 90-min afternoon nap opportunity from 13:00 to 14:30 in a quiet, dimly lit, temperature-controlled room. Sleep was monitored using a portable EEG headband. Participants were provided with earplugs and eye masks, and nap sleep characteristics, including sleep stages, were recorded.
DIETARY_SUPPLEMENTCaffeine
Anhydrous caffeine (5 mg/kg body mass) was administered orally in an opaque capsule at 18:00. Placebo capsules contained microcrystalline cellulose and were matched for appearance, mass, colour, and odour. Capsule allocation was blinded to participants and outcome assessors.
COMBINATION_PRODUCTStandardised Active Recovery and Nutritional Protocol
A 15-min standardised active recovery and nutritional protocol performed from 18:45 to 19:00. It included lower-limb dynamic stretching exercises (forward/backward and lateral leg swings, walking lunges, high knees, and butt kicks; 10 repetitions per leg at a controlled pace), followed by ingestion of a carbohydrate-protein snack containing 20 g maltodextrin and 10 g whey isolate mixed with 200 mL water.
OTHERPlacebo
Microcrystalline cellulose was administered orally in an opaque capsule at 18:00. Placebo capsules were matched to caffeine capsules for appearance, mass, colour, and odour.
Sponsors
The Higher Institute of Sport and Physical Education of Sfax
Study design
Allocation
RANDOMIZED
Intervention model
CROSSOVER
Primary purpose
OTHER
Masking
TRIPLE (Subject, Investigator, Outcomes Assessor)
Masking description
Double-blind, placebo-controlled design. Participants and investigators conducting the testing battery are blinded to condition assignment. The researcher preparing the capsules and the statistician are separate from the testing team. Blinding is maintained until final data analysis.
Intervention model description
Randomised, counterbalanced crossover design with 5 experimental conditions. Each participant completes all conditions in a different order determined by Latin square randomisation. Washout period between conditions: at least 72 hours.
Eligibility
Sex/Gender
ALL
Age
18 Years to 25 Years
Healthy volunteers
Yes
Inclusion criteria
* Healthy university athletes aged 18-25 years. * Regular engagement in structured training, defined as at least 10 training sessions per week of approximately 2 h each, across team sports, judo, athletics, tennis, or swimming. * Non-habitual napping, defined as fewer than one nap per week. * Low habitual caffeine intake, defined as \<80 mg/day, assessed using a 7-day dietary recall. * Non-smoker and free from regular medication or recreational drug use. * No musculoskeletal injury during the preceding month. * Good self-reported sleep quality, defined as a Pittsburgh Sleep Quality Index score \<5. * Definite morning chronotype (MEQ score 59-86) or definite evening chronotype (MEQ score 16-41). * For female participants: self-reported regular menstrual cycles (26-32 days), no hormonal contraceptive use, and no self-reported history of menstrual disorders.
Exclusion criteria
* Intermediate chronotype (MEQ score 42-58). * Habitual napping (≥1 nap per week). * Habitual caffeine intake ≥80 mg/day. * Smoking, regular medication use, or recreational drug use. * Musculoskeletal injury during the preceding month. * Pittsburgh Sleep Quality Index score ≥5. * Self-reported irregular menstrual cycles, hormonal contraceptive use, or history of menstrual disorders in female participants. * Self-reported sleep disorder. * Inability or unwillingness to complete all five experimental conditions.
Design outcomes
Primary
| Measure | Time frame | Description |
|---|---|---|
| Repeated Modified Agility Test (RMAT) Total Time | At approximately 19:35 on each of the five experimental days | Total time (seconds) to complete 10 maximal 20-m sprints with four changes of direction (forward sprint, left shuffle, right shuffle, backward sprint). The test was conducted on an indoor hardwood court using dual-beam photocells (Brower Timing Systems, Salt Lake City, UT, USA) placed at the start/finish line. Participants started from a standing position 0.5 m behind the first photocell. Lower values indicate better repeated agility performance. This was the primary outcome measure used for sample size calculation. |
Secondary
| Measure | Time frame | Description |
|---|---|---|
| Squat Jump (SJ) Height | At approximately 19:25 on each of the five experimental days. | Maximum jump height (cm) from a static squat position with knees at approximately 90° flexion, hands on hips. Participants held the starting position for 2-3 seconds before jumping vertically without any countermovement. Three maximal attempts were performed with 2 minutes of rest between attempts; the highest jump height was retained for analysis. Calculated from flight time using h = g·t²/8. Measured using Optojump Next optical system (1000 Hz sampling frequency). Higher values indicate better explosive lower-limb performance without stretch-shortening cycle contribution. |
| 20-m Sprint Time | At approximately 19:45 on each of the five experimental days. | Best time (seconds) of two maximal 20-m sprints from a standing start, with 3 minutes of passive recovery between sprints. Participants started 0.5 m behind the start line. Sprint time was measured using dual-beam photocells (Brower Timing Systems, Salt Lake City, UT, USA) placed at the start (0 m) and finish (20 m) lines. Lower values indicate better linear sprint performance. |
| Simple Reaction Time (SRT) | At approximately 19:15 on each of the five experimental days. | Mean reaction time (milliseconds) across 15 recorded trials. A green circle appeared on a black background on a 15-inch laptop screen (60 Hz refresh rate), and participants pressed the space bar as quickly as possible. Inter-trial interval varied randomly between 1000 and 2000 ms. Measured using OpenSesame software (version 3.3). Lower values indicate faster simple reaction time and better cognitive processing speed. |
| Choice Reaction Time (CRT) | At approximately 19:20 on each of the five experimental days. | Mean reaction time (milliseconds) across 15 recorded trials. Either a red circle (press the left arrow key) or a blue square (press the right arrow key) appeared randomly on a 15-inch laptop screen (60 Hz refresh rate). Participants had to identify the stimulus and press the correct key as quickly as possible. Inter-trial interval varied randomly between 1000 and 2000 ms. Measured using OpenSesame software (version 3.3). Lower values indicate faster choice reaction time and better cognitive decision-making speed. |
| Heart Rate Variability (RMSSD and HF Power) | At 12:00, 18:00, and approximately 19:45 on each of the five experimental days. | Heart-rate variability was recorded during 5-min supine resting measurements with spontaneous breathing using a Polar H10 chest strap. RR intervals were analysed using Kubios HRV software after artefact correction. The main HRV variables were RMSSD (ms) and high-frequency power (0.15-0.40 Hz, normalised units). |
| Salivary Cortisol Concentration | At 12:00, 18:00, approximately 19:45, and 30 minutes after exercise on each of the five experimental days. | Salivary cortisol concentration (nmol/L) measured using Salivette cotton swabs (Sarstedt, Nümbrecht, Germany). Participants were instructed to avoid eating, drinking (except water), and brushing teeth for 30 minutes before each sample. Samples were centrifuged at 1500×g for 10 minutes at 4°C, and the supernatant was stored at -80°C until analysis. Cortisol concentration was measured in duplicate using a high-sensitivity enzyme-linked immunosorbent assay (ELISA, IBL International, Hamburg, Germany) with a detection limit of 0.05 ng/mL and intra- and inter-assay coefficients of variation \< 8%. Lower values indicate reduced hypothalamic-pituitary-adrenal (HPA) axis activity. |
| Plasma Brain-Derived Neurotrophic Factor (BDNF) | Measured at baseline and after completion of the evening testing battery on each experimental day. | BDNF concentration (pg/mL) measured in venous blood samples (5 mL) drawn from an antecubital vein. Blood was collected into EDTA tubes, immediately centrifuged at 1500×g for 15 minutes at 4°C, and plasma was stored at -80°C until analysis. BDNF concentration was quantified using a commercially available ELISA kit (R\&D Systems, Minneapolis, MN, USA; catalogue number DBD00) with a detection limit of 20 pg/mL and intra- and inter-assay CVs \< 6% and \< 9%, respectively. Higher values indicate greater neurotrophic activity. |
| Blood Lactate Concentration | At 18:55, 3 minutes after the Repeated Modified Agility Test, and 3 minutes after the 20-m sprint on each of the five experimental days. | Lactate concentration (mmol/L) measured in capillary blood samples (5 µL) collected from the fingertip using a Lactate Pro 2 analyzer (Arkray, Kyoto, Japan), which has a coefficient of variation \< 3%. Higher values indicate greater metabolic perturbation and glycolytic activation during high-intensity exercise. |
| Countermovement Jump (CMJ) Height | At approximately 19:20 on each of the five experimental days. | Maximum jump height (cm) calculated from flight time using the formula h = g·t²/8, where g = 9.81 m·s-². Participants started from an upright standing position, performed a rapid downward movement to approximately 90° knee flexion, and immediately jumped vertically, maintaining hands on hips throughout. Three maximal attempts were performed with 2 minutes of rest between attempts; the highest jump height was retained. Measured using an optical measurement system (Optojump Next, Microgate SRL, Bolzano, Italy) with a sampling frequency of 1000 Hz. Higher values indicate better explosive lower-limb performance. |
| Nap Architecture (EEG) | During the 90-minute nap opportunity from 13:00 to 14:30 on NAP, NAP+CAF, and NAP+CAF+REC condition days only. | Objective sleep parameters recorded using a validated dry-electrode portable EEG headband (Dreem 3, Paris, France) with six channels (F3, F4, C3, C4, O1, O2, referenced to linked mastoids). Sleep stages were automatically scored in 30-second epochs using the manufacturer's algorithm and visually corrected by a certified sleep technologist blinded to condition and participant. Parameters extracted: total sleep time (TST, minutes), sleep onset latency (SOL, minutes), time in N2 sleep (minutes), time in N3 slow-wave sleep (minutes), time in REM sleep (minutes), and sleep efficiency (TST/time in bed × 100, %). |
Countries
Tunisia
Contacts
PRINCIPAL_INVESTIGATORKais El Abed, Phd
University of Sfax, Tunisia
Outcome results
None listed