Bright Light Exposure Improves Your Workouts Sign. (~8%)

Would be interesting to compare sunlight and artificial light in future studies.

You will remember the circadian rhythm series in which I have previously discussed the relevance of light exposure as a means to set, reset and entrain your internal clock in order to reap all sorts of health and performance benefits.

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.

Learn more about the health effects of correct / messed up circadian rhythms

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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).

As Figure 1 illustrates we are thus dealing with a total of three trials and their moderate light counter parts which are not illustrated in Figure 1. Thanks to the use of a cross-over design this means that all subjects were exposed to either bright light (BL, 4420 lux) or moderate light (ML, 230 lx).

Figure 2: Total work (in kJ) during the 40-minute time-trial to exhaustion (Knaier. 2015).

The scientists' analyses of the studies results and the normalization of the results according to the subjects' individual chronotype (estimated based on the Munich Chronotype Questionnaire) yielded the following two primary study outcomes:

• 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. 

Overall, the study does therefore confirm that "[a] long duration light exposure is an effective tool to increase total work in a medium length timetrial" - what's new (compared to the previously referenced Kantermann study is the observation that this advantage holds, even if the results are normalized for the subjects' individual chronotype.

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.

Bottom line: While one hour of bright or 2h of medium intensity light appears to allow for too little 'light accumulation' to have physiologically relevant affects, long duration of exposure to bright light is, as Knaier et al. point out "an effective tool to increase total work at least for the initial phase of a medium length time-trial" (Knaier. 2015); and what's important, the performance increase of ~8% which was observed not just in the Knaier study, but also in a differently designed trial by Thomson, et al. (2015 | cf. Figure 3), is large enough to be relevant for any competing athlete.

Figure 3: A study by Thompson, et al. (2015) suggests that pre-bed exposition to bright light (30 min) can increase the time-trial performance of athletes on the subsequent morning. Since this will also suppress the melatonin levels of practitioners this is yet a strategy that should not be employed regular (competition only).

The results of Knaier are thus in contrast to a similarly recent study by Nelson et al. (2015) who found that acute short-term dim light exposure can actually lower muscle strength endurance (-18%, albeit with high inter-individual variability). Against that background it should be obvious that, even though, bright light exposure is indeed "likely to increase alertness and reduce sleepiness and help athletes to compensate for disadvantages in competitions at unfavorable times and improve performance" (Knaier. 2015). And don't forget - the scientists from the University of Basel are right: "The ideal duration of expo sure to increase performance and simultaneously interfere as little as possible with athletes’ routine still needs to be found" (Knaier. 2015). In fact, even timing and strategies like the pre-evening light exposure that increased the time trial performance in Thomson et al. (2015 | see Figure 3) must be tested as alternatives | Comment on Facebook!

References:

• 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.