Abstract
Many sports competitions take place during television prime time, a time of the day when many athletes have already exceeded their time of peak performance. We assessed the effect of different light exposure modalities on physical performance and melatonin levels in athletes during prime time. Seventy-two young, male elite athletes with a median (interquartile range) age of 23 (21; 29) years and maximum oxygen uptake (VO2max) of 63 (58; 66) ml/kg/min were randomly assigned to three different light exposure groups: bright light (BRIGHT), blue monochromatic light (BLUE), and control light (CONTROL). Each light exposure lasted 60 min and was scheduled to start 17 h after each individual's midpoint of sleep (median time: 9:17 pm). Immediately after light exposure, a 12-min time trial was performed on a bicycle ergometer. The test supervisor and participants were blinded to the light condition each participant was exposed to. The median received light intensities and peak wavelengths (photopic lx/nm) measured at eye level were 1319/545 in BRIGHT, 203/469 in BLUE, and 115/545 in CONTROL. In a multivariate analysis adjusted for individual VO2max, total work performed in 12 min did not significantly differ between the three groups. The amount of exposure to non-image forming light was positively associated with the performance gain during the time trial, defined as the ratio of the work performed in the first and last minute of the time trial, and with stronger melatonin suppression. Specifically, a tenfold increase in the exposure to melanopic light was associated with a performance gain of 8.0% (95% confidence interval: 2.6, 13.3; P = 0.004) and a melatonin decrease of −0.9 pg/ml (95% confidence interval: −1.5, −0.3; P = 0.006). Exposure to bright or blue light did not significantly improve maximum cycling performance in a 12-min all-out time trial. However, it is noteworthy that the estimated difference of 4.1 kJ between BRIGHT and CONTROL might represent an important performance advantage justifying further studies. In conclusion, we report novel evidence that evening light exposure, which strongly impacts the human circadian timing system, enables elite athletes to better maintain performance across a 12-min cycling time trial.
Highlights
Many athletes reach their peak endurance performance between the afternoon and the early evening (Reilly and Waterhouse, 2009) depending on their chronotype (Facer-Childs and Brandstaetter, 2015)
Three participants had to be excluded from the analysis of the primary outcome due to invalid measurement of maximum oxygen uptake (VO2max), no exhaustion during the cardiorespiratory fitness test and premature termination of the time trial, respectively
In the multivariate analysis adjusted for the prespecified potential confounder VO2max, the difference in work performed during the time trial was 4.1 kJ (95% confidence interval [CI] −4.5, 12.7; P = 0.346) for participants in bright light (BRIGHT) and −1.2 kJ for participants in blue light (BLUE), both relative to participants in control light (CONTROL) (Table 3)
Summary
Many athletes reach their peak endurance performance between the afternoon and the early evening (Reilly and Waterhouse, 2009) depending on their chronotype (Facer-Childs and Brandstaetter, 2015). Can shift circadian melatonin rhythms (Gronfier et al, 2004; Wirz-Justice et al, 2004; Revell et al, 2006), acutely lower melatonin levels, increase alertness (Cajochen, 2007), and improve mood (Hoffmann et al, 2008a) The extent of these effects depends on intensity (Zeitzer et al, 2000; Hoffmann et al, 2008a), wavelength (Cajochen et al, 2005; Vandewalle et al, 2007; Hoffmann et al, 2008a,b; Smith et al, 2009; Chellappa et al, 2011; Rüger et al, 2013), individual light-dark history (Hébert et al, 2002), duration (Chang et al, 2012), and time of day of light exposure (Cajochen, 2007). Blue light with a wavelength of 460–480 nm activates the non-image forming system with strong effects on alertness, melatonin, and thermoregulation (Cajochen et al, 2005)
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