Effects of bright and blue light on acoustic reaction time and maximum handgrip strength in male athletes: a randomized controlled trial

Abstract

Purpose

To assess which type of evening light exposure has the greatest effect on reaction time and maximum handgrip strength. These were pre-specified secondary outcomes in a trial which primarily investigated the influence of light on cycling performance.

Methods

Seventy-four male athletes were allocated at random to either bright light (BRIGHT), monochromatic blue light (BLUE), or a control condition (CONTROL). Light exposure lasted for 60 min and started 17 h after the individual midpoint of sleep. Reaction time, handgrip strength, and melatonin levels were measured before and after the light exposure. We used analysis of covariance to compare the groups with respect to the investigated outcomes.

Results

Two participants had to be excluded retrospectively. The remaining 72 participants had a median age of 23 years. The adjusted difference in reaction time was −1 ms [95% confidence interval (CI) −8, 6] for participants in BRIGHT and 2 ms (95% CI −5, 9) for participants in BLUE, both relative to participants in CONTROL. The adjusted difference in handgrip strength was 0.9 kg (95% CI −1.5, 3.3) for participants in BRIGHT and −0.3 kg (95% CI −2.7, 2.0) for participants in BLUE, both relative to participants in CONTROL. After the light exposure, 17% of participants in BRIGHT, 22% in BLUE, and 29% in CONTROL showed melatonin concentrations of 2 pg/ml or higher.

Conclusions

The results suggest that bright light might reduce melatonin levels but neither bright nor blue light exposure in the evening seem to improve reaction time or handgrip strength in athletes.

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