|Would be interesting to compare sunlight and artificial light in future studies.|
Bright (>4000 lux), preferable blue (at least having a blue component) light has repeatedly been shown to increase athletic performance. Studies like Kantermann et al. (2012) show, however, that the efficacy of bright light exposure significantly depends on the chronotype of an athlete.
In said study, the athletes were exposed to 4420 lux for 120 min before and right before a 40-min time trial. Significant performance increases were observed only for those subjects, though, who were performing ∼14.8 h after their midpoint of sleep on free days (MSFsc). Subjects who trained "earlier" on their internal clock (in this case ∼11.8 h after the MSFsc), on the other hand, did not record any benefits.
Back in the day, Kantermann et al. speculated that a short(er) exposure or mudaltion of light intensity and/or timing could likewise have affected their results. Thus, the hypothesis Knaier et al. used in their 2015 contribution to the "light for performance" research was to that different bright light (BL) exposure regimes prior to and during a time-trial applied during the “sensitive” phase of the circadian rhythm result in a dose dependent increase of time-trial power output - meaning: longer exposure and brighter light = maximal performance benefits.
To test this hypothesis the scientists assigned young (25.1 ± 3.1 years) men to three groups with two different light intensities (A = BL, 4420 lx vs. B = ML, 230 lx) for all three randomly chosen exposure times (2h pre + exercise time, 2HEX | 1h pre + exercise time 1HEX | 1h pre 1H).
|Figure 1: Study protocol for 2HEX, 1HEX, and 1H. Time-trial: 40 min in duration; bright light/moderate light (BL/ML): continuous randomized exposure (slightly rearranged version of a figurr from Knaier. 2015).|
|Figure 2: Total work (in kJ) during the 40-minute time-trial to exhaustion (Knaier. 2015).|
- Total work performed during the time-trial in kJ in the 2HEX group was significantly higher in the BL setting (527 kJ) than in ML (512 kJ) (P = 0.002), but not in 1HEX (BL: 485 kJ; ML: 498 kJ) or 1H (BL: 519 kJ; ML: 514 kJ) (P = 0.770; P = 0.485).
- There was a significant (P = 0.006) positive dose–response relationship between the duration of light exposure and the work performed over the three doses of light exposure.
Whether and to which extent the "more light equals more performance" equation will hold with (a) even longer or (b) even more intense light, however, is something that will have to be investigated in future dose-response studies. Studies like O'Brien et al. (2000) which has already proven that shortening the exposure time (in this case to 20 minutes only during exercise) will reduce the effects of bright light exposure on cycling performance to zero.
- Kantermann, Thomas, et al. "The stimulating effect of bright light on physical performance depends on internal time." PloS one 7.7 (2012): e40655.
- Knaier, R., et al. "Dose–response relationship between light exposure and cycling performance." Scandinavian journal of medicine & science in sports (2015).
- Nelson, Arnold G., Joke Kokkonen, and Megan Mickenberg. "Acute short-term dim light exposure can lower muscle strength endurance." Journal of Sport and Health Science 4.3 (2015): 270-274.
- O'Brien, Patrick M., and Patrick J. O'Conner. "Effect of bright light on cycling performance." Medicine & Science in Sports & Exercise (2000).
- Thompson, A., et al. "The effects of evening bright light exposure on subsequent morning exercise performance." International journal of sports medicine 36.02 (2015): 101-106.