Day and Night, Night or Day?

This week's New York Times Thursday Styles section included an short piece, "Ready to Exercise? Check Your Watch" written buy a runner-writer Gina Kolata. Kolata and her running buddy assumed that they ran better in the morning than the evening. One day, after taking an evening spin class, they discovered that their heart rates were higher but their perceived rate of exertion (RPE) was lower. They observed that their heart rates were always higher, by 10-15 bpm, in the evening.

Is an evening workout better than the same workout done in the morning?

Here is the implied reasoning in the article:

1. If my RPE is higher in the morning and
2. If my heart rate is always lower during the morning than in the evening, by 10-15 beats
3. Then since my RPE is lower for the same higher heart rate it follows that late-day workouts are more effective at improving my overall fitness than morning workouts

Kolata's is right that there is limited research on the effectiveness of morning training versus later-day training, but places the wrong emphasis on using heart rate as a marker for fitness She probably should have asked

When is the best time to train and when is the best time to compete?

Research shows that the best performances are frequently seen during afternoons and evenings. This seems to be due to natural circadian rhythms (that can be trained and adapted!) We can use the results of these studies added to what we know about the specificity principle of training:

Train in conditions as close as possible to those that you'll find at a race.

Kolata may be confusing training with competition and judging her fitness improvement by subjective measures from a particular workout and not over the long run.

We should be asking whether training in the late-day actually results better performance for early-day races?

Using heart rate as a consistent measure of fitness or effort is effective over the long-term but not short-term. For example, heart rate lags behind effort by several seconds, so for short sprints, the heart rate doesn't reach a maximum until after the effort is finished. You can find more information about this in Understanding Heart Rate and Exercise, Master's Athlete Physiology and Performance, Stephen Seiler, PhD. For this reason, we coaches tell our trained athletes to use heart rate and perceived exertion it as guidelines but not a true measure of day-to-day fitness.

I think that most of us train to do well in competitions and maybe finish on the podium. As committed athletes, we're taking whatever opportunity arises, that fits into our career, that allows us to improve our performance and to, well, just enjoy!

So, my advice is to make certain to train when it is safe, in conditions that will most likely be present during competition, when it is convenient and above all, fun.

References

Circadian Specificity in Exercise Training, David W. Hill; Kirk J. Cureton, Mitchell A. Collins, Physical Education Department, University of Georgia, Athens, Georgia.

Other Articles

The Best Time of Day to Walk and Exercise, About.com