The Importance Of Moderate Training Intensity

By Dan Carey, Phd., Univ. of St. Thomas

The “no pain no gain” mindset of competitive athletes probably detracts from performance rather than enhances it. As a physiologist, I would like to explain the importance of “easy” training days.

One of the oldest and probably still most respected training philosophies is “hard-easy.” Physiologically the body needs to recover from a hard day. Intense training depletes glycogen stores. It takes approximately 48 hours to completely replenish glycogen (carbohydrate) stores. This is why 2 consecutive hard days are difficult to maintain.

In addition, hydration needs to be restored. A simple way to monitor your hydration status is with a bathroom scale. Large fluctuations in weight from day to day are the result of hydration status and not fat gain/loss.

Joel Friel, author of “The Cyclist’s Training Bible”, stated “Of frequency, intensity and duration, the one most important to get correct is intensity.” In addition to allowing the body to restore glycogen and water levels, easy days also train the body to metabolize fat better.

For endurance events of one hour or longer, burning fat allows the body to store glycogen for the next hard day. While I believe some advice given about “the fat burning zone” is very misleading, it is still true that a moderate intensity of training optimizes fat metabolism. This is both an acute and chronic effect.

In my research on the “fat burning zone” to be presented at a local sports medicine conference, optimal fat burning occurs at 59-76% of maximal heart rate. While this intensity is indeed moderate, it overlaps the low end of the target heart rate zone for improved aerobic endurance established by the American College of Sports Medicine (70-85% maximal heart rate).

A final point is that all of the desired changes in fitness occur when the body is at rest, not when the stress of exercise is applied. If the body is not rested, it cannot optimize these changes. A good example of this is tapering, which is a reduction in training volume/intensity for 10-21 days prior to an important race. Tapering has been shown to enhance performance 3-5%. While this may seem small, it may be the difference between an average and good performance.

While a training schedule will fluctuate from week to week, depending on the training period, I think a good program has at least 2 days of moderate training per week. I believe one of the primary benefits of training with a heart rate monitor is not in ensuring that you are in your “threshold” or “anaerobic zone.” Rather the best use of these monitors is for “holding back” your intensity and forcing yourself to stay within this moderate aerobic zone.