Go Away Groundhog!
No matter how much I appreciate indoor training tools like the CompuTrainer and ErgVideo, the bicycle is designed for riding outdoors and not strapped to a trainer. And even here in the Great White North, winter seems to be oh so gradually fading away into spring, allowing more opportunities for getting the rubber onto the road.
I don’t know about you, but the first rides of spring are always brutal. Part of it comes from simply not being in prime fighting shape. Coupled with that, the highly variable pace of outdoor solo and group riding, as opposed to the generally steady prolonged pace of intervals done indoors, exerts a higher level of neuromuscular stress and fatigue on the body. And of course, part of it comes from the continuing cold, damp, and windy spring weather that seems to cut through all my various layers of clothes.
Here Comes the Sun
Counteracting all that, though, is the gradually warmer and sunnier weather. After a winter riding under indoor lighting, even a little glimpse of sunshine is a psychological godsend and is ludicrously addictive. Little by little, day by day, the little rolling hills become seemingly flatter and the sluggishness fades away.
On one level, such a sensation is rather strange for somebody like me. That’s because I tend to have a fairly stable fitness level throughout the entire year. One reason is that I tend to be much more consistent and systematic in my training over the winter, whereas travel for research and family during the summer often leaves me off the bike for prolonged stretches.
Being a scientist means a curiosity about nearly everything under the sun. So this just makes me wonder – is it just my imagination or does greater sunshine or light exposure actually provide an ergogenic effect on exercise performance?
See the Light
Light level and performance isn’t as trivial an idea as it may initially sound. Humans have a strong circadian (daily) rhythm in a variety of physiological measures, including hormones such as melatonin and growth hormone. This plays out in strong patterns in body temperature, with core temperature dropping by about 0.5-1 degree Celsius during night-time whether sleep occurs or not, then gradually rising from morning over the course of the day. Light exposure seems to play a major role in these patterns, with decreased light in the evening stimulating the production of melatonin and the drop in temperature. Arousal, which plays a major role in exercise capacity, is also strongly tied to light exposure.
A research group at the University of Georgia explored the effects of light intensity on exercise capacity. The main research context focused on the effects of extremely bright lights, as often used for adjusting circadian rhythms following travel across multiple time zones. Such bright lights have also been used therapeutically to combat the depression associated with Seasonal Affective Disorder and lack of exposure to natural sunlight.
Light it Up
• 12 competitive (Cat 2, 3, and college) cyclists were recruited, with average age of 24 were recruited. During an initial familiarization 20 min TT, average wattage was 256W.
• During the three experimental sessions, the actual test was a 20 min self-paced time trial, where the subjects were asked to complete as much work as possible (i.e. sustain the highest average wattage possible).
• In all trials, the ambient light was at ~12,000 lux of full-spectrum light from a light box positioned in front of the subject. The amount of light actually reaching the subjects was manipulated by wearing sunglasses of different darknesses.
• Overall, the light intensity reaching the retina were: 1,320, 2,640, and 6,000 lux. By comparison, complete darkness is obviously 0 lux, typical room lighting is approximately 400-600 lux, and extremely bright sunshine can approach 100,000 lux.
• To eliminate bias, not only was the external lighting similar, but subjects were not informed of the true purpose of the study. Rather, they were told they were testing the effects of different colour eyewear on psychological and physiological responses to exercise. My personal view of this is that the additional deception probably wasn’t of much use, as there isn’t really much of a difference for the subjects between thinking about different lens colour versus different light levels, which kind of go hand in hand.
• Continuous feedback of cadence, heart rate, power, and time were provided during the test, although summary data was not provided until all trials were completed. I would have preferred that no data or feedback, except for time, be provided so that subjects were truly blinded to their performance and didn’t have the potential for a learning effect over the course of the experiment.
At the end of the day, the primary finding by the authors was a nonsignificant effect of light intensity on all parameters tested.
• Average power output was about 275 +/- 5W for each of the 1,320 and 2,640 lux conditions, and 271 +/-5W for the 6,000 lux trial.
• The pattern of voluntary pace selection was similar across light conditions, with all trials gradually increasing average power over the course of the 20 min.
• No difference in subjective ratings of perceived exertion or local leg pain either overall or during the course of the 20 min.
• No difference in mood or alertness ratings either overall or during the course of the 20 min.
Light of my Life
The average power data is a classic example of statistical versus practical significance. In this case, statistics would conclude that light makes no difference to performance. However, the average 4.6W lower in the 6,000 lux condition would translate, at 275W average pace, to a 180 m shorter distance covered. Or for a 13.3 km, this would equal a 16-s time gap. While that may be small potatoes for weekend warriors, this can get you on or off the podium at the elite ranks.
Overall, I’m not a complete fan of the research design, in that I would not have given the subjects any feedback during the tests except for time. Also, as the authors rightly pointed out, ultimately their range of light intensities is big when compared to room lighting, it is quite narrow when you consider the large differences that can be seen naturally outdoors depending on clouds and time of day.
How, then, to use the data? As you can guess, firm conclusions are difficult to make directly from this single experiment. But if the trend for slightly lower power outputs at higher light intensities does hold, it might support other research that suggests that maximal power outputs and muscular strength occurs at the early evening period, where body temperature and arousal are generally highest. So if you’re trying to set a personal best in a field test, you might want to time it later in the afternoon once the blazing sun (and the higher temperatures) start to recede.
Have fun and ride safe!
O’Brien, P.M. and P.J. O’Connor. Effect of bright light on cycling performance. Medicine and Science in Sport and Exercise. 32:439-447, 2000.
Stephen Cheung is a Canada Research Chair at Brock University, with a research specialization in the effects of thermal stress on human physiology and performance. He can be reached for comments at firstname.lastname@example.org .