Abstract
Purpose: To investigate the effects of placebo (PLA), 20 min nap opportunity (N20), 5mg·kg−1 of caffeine (CAF), and their combination (CAF+N20) on sleepiness, mood and reaction-time after partial sleep deprivation (PSD; 04h30 of time in bed; study 1) or after normal sleep night (NSN; 08h30 of time in bed; study 2).Methods: Twenty-three highly trained athletes (study 1; 9 and study 2; 14) performed four test sessions (PLA, CAF, N20 and CAF+N20) in double-blind, counterbalanced and randomized order. Simple (SRT) and two-choice (2CRT) reaction time, subjective sleepiness (ESS) and mood state (POMS) were assessed twice, pre- and post-intervention.Results: SRT was lower (i.e., better performance) during CAF condition after PSD (pre: 336 ± 15 ms vs. post: 312 ± 9 ms; p < 0.001; d = 2.07; Δ% = 7.26) and NSN (pre: 350 ± 39 ms vs. post: 323 ± 32 ms; p < 0.001; d = 0.72; Δ% = 7.71) compared to pre-intervention. N20 decreased 2CRT after PSD (pre: 411 ± 13 ms vs. post: 366 ± 20 ms; p < 0.001; d = 2.89; Δ% = 10.81) and NSN (pre: 418 ± 29 ms vs. post: 375 ± 40 ms; p < 0.001; d = 1.23; Δ% = 10.23). Similarly, 2CRT was shorter during CAF+N20 sessions after PSD (pre: 406 ± 26 ms vs. post: 357 ± 17 ms; p < 0.001; d = 2.17; Δ% = 12.02) and after NSN (pre: 386 ± 33 ms vs. post: 352 ± 30 ms; p < 0.001; d = 1.09; Δ% = 8.68). After PSD, POMS score decreased after CAF (p < 0.001; d = 2.38; Δ% = 66.97) and CAF+N20 (p < 0.001; d = 1.68; Δ% = 46.68). However, after NSN, only N20 reduced POMS (p < 0.001; d = 1.05; Δ% = 78.65) and ESS (p < 0.01; d = 0.71; Δ% = 19.11).Conclusion: After PSD, all interventions reduced sleepiness and only CAF enhanced mood with or without napping. However, only N20 enhanced mood and reduced sleepiness after NSN. Caffeine ingestion enhanced SRT performance regardless of sleep deprivation. N20, with or without caffeine ingestion, enhanced 2CRT independently of sleep deprivation. This suggests a different mode of action of napping and caffeine on sleepiness, mood and reaction time.
Highlights
The post-lunch dip (PLD) is characterized by an endogenous increase of sleepiness, favorizing daytime sleep (Monk, 2005; Bes et al, 2009)
Recent evidence suggest that the PLD could be severer after partial sleep deprivation (PSD), yet, these effects were more disturbing after PSD caused by early awakening compared to PSD caused by late bedtime (Romdhani et al, 2019)
Thirty-three participants were screened to be included in both studies, where four participants failed to fulfill the inclusion criteria
Summary
The post-lunch dip (PLD) is characterized by an endogenous increase of sleepiness (e.g., higher sleep propensity and shorter sleep onset latency), favorizing daytime sleep (Monk, 2005; Bes et al, 2009). It is common for athletes to compete or to train during this time of the day (Bes et al, 2009; Romdhani et al, 2019). PSD is common among athletes prior to major competition (Juliff et al, 2015), constantly associated with physical and cognitive performance degradation (Waterhouse et al, 2007; Romdhani et al, 2019, 2020, 2021b). It has been suggested that the decrease in performances maybe secondary to the PSD-induced decreased mood and cognitive functions (Waterhouse et al, 2007; Romdhani et al, 2019, 2021b)
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