The stimulating effect of bright light on physical performance depends on internal time.

PLoS One 2012 11;7(7):e40655. Epub 2012 Jul 11.

Centre for Behaviour and Neurosciences, University of Groningen, Groningen, The Netherlands.

The human circadian clock regulates the daily timing of sleep, alertness and performance and is synchronized to the 24-h day by the environmental light-dark cycle. Bright light exposure has been shown to positively affect sleepiness and alertness, yet little is known about its effects on physical performance, especially in relation to chronotype. We, therefore, exposed 43 male participants (mean age 24.5 yrs ± SD 2.3 yrs) in a randomized crossover study to 160 minutes of bright (BL: ≈ 4.420 lx) and dim light (DL: ≈ 230 lx). During the last 40 minutes of these exposures, participants performed a bicycle ergometer test. Time-of-day of the exercise sessions did not differ between the BL and DL condition. Chronotype (MSF(sc), mid-sleep time on free days corrected for oversleep due to sleep debt on workdays) was assessed by the Munich ChronoType Questionnaire (MCTQ). Total work was significantly higher in BL (median 548.4 kJ, min 411.82 kJ, max 875.20 kJ) than in DL (median 521.5 kJ, min 384.33 kJ, max 861.23 kJ) (p = 0.004) going along with increased exhaustion levels in BL (blood lactate (+12.7%, p = 0.009), heart rate (+1.8%, p = 0.031), and Borg scale ratings (+2.6%, p = 0.005)) in all participants. The differences between total work levels in BL and DL were significantly higher (p = 0.004) if participants were tested at a respectively later time point after their individual mid-sleep (chronotype). These novel results demonstrate, that timed BL exposure enhances physical performance with concomitant increase in individual strain, and is related not only to local (external) time, but also to an individual's internal time.

Download full-text PDF

Source
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0040655PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3394763PMC
January 2013
8 Reads

Publication Analysis

Top Keywords

physical performance
12
bright light
8
total work
8
internal time
8
time
5
mctq total
4
86123 0004
4
work higher
4
higher median
4
questionnaire mctq
4
chronotype questionnaire
4
workdays assessed
4
assessed munich
4
munich chronotype
4
median 5484
4
5484 min
4
87520 median
4
median 5215
4
38433 max
4
5215 min
4

References

(Supplied by CrossRef)
Alerting effects of light.
C Cajochen et al.
Sleep Med Rev 2007
Circadian rhythms in man.
J Aschoff et al.
Science 1965
Two decades of circadian time.
MH Hastings et al.
J Neuroendocrinol 2008
Epidemiology of the human circadian clock.
T Roenneberg et al.
Sleep Med Rev 2007
Entrainment concepts revisited.
T Roenneberg et al.
J Biol Rhythms 2010
The art of entrainment.
T Roenneberg et al.
J Biol Rhythms 2003

Similar Publications