Let's look at four ways to use your heart-rate monitor effectively to improve your cycling performance.
1. Measure your heart rate during easy rides to safeguard against overtraining
The purpose of your easy ride is to recover from the stress of hard training and racing. If you do these rides too hard (as many cyclists do), you will become overtrained, with staleness eventually setting in. You can avoid this problem by tracking your heart rate on your easy days. Let's say you typically ride 20 miles in 60 minutes at a heart rate of 155 beats per minute (bpm). One day, however, you find your heart rate is 165 bpm during your regular one-hour ride. That is most likely a sign that you should back off for a couple of days before doing your next hard workout or race. You may be overtrained or fighting a bug.
2. Don't use a formula to determine your maximal heart rate
You need to know your maximal heart rate (MHR) to set correct training levels. Several formulas exist to predict MHR; all have flaws. The formulas were developed using regression equations, which means that if 100 cyclists estimate their MHR using a formula, the average will be just about right; the MHR for an individual, however, could be off by up to 20 bpm.
Recently, a 30-year-old cyclist came to me for a training program. His estimated MHR, based on the 220-minus-age formula, was 190 bpm. But when he rode twice for four minutes hard uphill, his heart rate went up to 197 bpm 7 bpm higher than the formula predicted. Formulas also can overestimate MHR, as in the case of a 20-year-old cyclist who could only get his heart rate up to 191 bpm.
3. Don't select your heart rate for racing based on measurements taken during training
Two studies from an international conference on the use of heart-rate monitors, published in the Journal of Sports Sciences, reported that heart rate during racing is substantially higher than during training at the same pace. One study, from the Sports Science Institute of South Africa, found heart rates measured during a 10K running race to be 20 bpm higher than while training at the same speed; during a marathon the rates were 19 bpm higher than when training at marathon race pace.
The researchers write, "The heart rate difference could not be explained by differences in terrain or added psychological stress."
Several researchers speculate that increased psychological arousal in the races can account for the difference. This suggests that the excitement of racing accounts, at least in part, for the higher heart rates.
The upshot is that using training heart rates to select race paces will lead to slower-than-anticipated race times. As a result, you could end up racing several miles per hour slower than your pace at the same heart rate during training and that could turn into a much slower pace, let's say in a time trial! This phenomenon in reverse can work against you too. For example, if you base your heart rate for tempo rides on your heart rate during a 10-mile race, you may end up doing your tempo rides too fast.
4. Remember that your heart rate increases as you become dehydrated
This phenomenon, called cardiac drift, occurs because dehydration causes a drop in blood volume, which means less blood is pumped with each heartbeat. A study published in the Journal of Applied Physiology found that heart rate increases seven beats per minute for each 1 percent loss in body weight due to dehydration.
Cycling for one hour in 70-degree heat can result in a loss of 1.5 to 3 pounds. That's a 1 percent to 2 percent weight loss for a 150-pound cyclist, which would increase heart rate by seven to 14 bpm.
If this cyclist is planning a tempo ride at a heart rate of 150 to 155 bpm, she should account for the fact that her pace will slow during the ride, and allow her heart rate to increase to about 160 to 175 bpm by the end.