Training with heart rate

Once the effort is long enough for the number to settle, however, heart rate becomes very useful. Particularly when you have a power meter as well.

For instance, a comparison I like is the decoupling rate. In a long ride where you hold a steady power, it is possible to see what your heart rate does in response. Early in a long ride the two should sit in a fairly stable relationship. Later, heart rate often climbs while power stays consistent. That rise — heart rate decoupling from power — is helpful information.

Over months, a smaller drift at the same sort of ride is one sign that fitness is moving the right way. In contrast, a drift that is bigger than usual for you could potentially signal fatigue or illness. Recent work on long rides has tied the same drift to something more specific than a vague sense of fading. As heart rate climbs against a steady power, the power you can still hold at an easy-to-steady endurance intensity tends to fall with it. The goalposts move during the ride. Heart rate is often the first thing that demonstrates this.

Do not read every rise as fitness, fatigue or illness, though. Heat, dehydration and a poor night's sleep can push heart rate up at the same power. So could a normal long effort in its own right. The rate of decoupling number (PWR:HR), therefore, is a prompt to look at the rest of the picture, not a diagnosis on its own.

If you do not have a power meter, heart rate is still super helpful. In fact, I would really encourage you to get comfortable using heart rate, power and perceived effort as interchangeable. When they agree, you can be confident. When they do not, that disagreement itself is useful information.

During 5-minute plus intervals, though, it is possible to use heart rate in a similar way to how you would use power and power training zones. Put simply, is your heart rate in the right range during the interval to stress the energy system you are looking to target with that interval. For this to work, of course, you need to know your heart rate zones and the ranges within which your heart rate must settle to be correctly hitting the right energy system. The starting point for this is gauging your threshold heart rate.

The field test I tend to use the most is a 30-minute time trial on a turbo, or an outside 10-mile time trial if you can persuade an athlete to sign up to a local race.

Ensure you use a heart rate strap rather than a wrist or arm strap. Optical heart rate monitors used by watches and wrist monitors are useful for tracking long-term patterns but, IMO, useless when you need accurate workout-based numbers. Heart rate straps are still the gold standard. On the date of writing this article, I completed a tempo run and during a 5-minute 5k-paced effort, there was a 20 bpm difference between the data from my chest strap and the optical heart rate monitor on my watch.

Warm up properly — at least 10 minutes, with some accelerations to get the fast-twitch muscle fibres going. Then ride 30 minutes as hard as you can genuinely sustain. We ignore the first 10 minutes and take the average heart rate across the final 20 minutes, minus 6 bpm, to give us a rough threshold heart rate.

A lab review of the 30-minute test, in cyclists and triathletes, found the last-20-minute heart rate repeatable, and also a little generous: on average it sat about six beats above a laboratory lactate threshold. Hence, we minus 6 bpm from the 20-minute average.

Knowing the number is the start. The useful part is using threshold heart rate and heart rate zones alongside whatever else you have. Power, if you have it. Perceived effort, always.

For instance, my threshold heart rate usually sits around 156 bpm. If I am into the 160s, I know I am working my VO2max. If I then go above about 165, I know I am shifting into the anaerobic systems. It really is as simple as that. Your numbers will not be the same as mine, but the habit should be the same: know what "around threshold" feels like, know what "a few beats over" means, etc.

The same anchor works for long events. These are my numbers, against a threshold of around 156 bpm.

There is an important practical point here for our triathletes. In training, hold the power and let heart rate tell you what the effort is becoming. In a long race, cap the heart rate and let the power come down. Defending a power number while heart rate climbs through the zones is how a good ride becomes a bad run.

Heart rate should also be an important factor in deciding whether today's session should happen as written.

A common picture: the warm-up feels awful. The legs are heavy. Perceived effort is higher than it should be for the work in front of you. Then you look at heart rate. If it is much higher than normal for that effort or power, or much lower, something is up. The mismatch is the signal, not the direction of it.

If you have earned that fatigue — a big block, short sleep, sessions stacked up — scale the day down. Intensity, duration, or both. If you should not be that tired, because you have just had a recovery day or a run of easier sessions, it can be the first sign you are coming down with something. Heat, dehydration and a bad night can also influence the picture. The point is not to diagnose yourself from a warm-up, but the point is also not to force the session when heart rate and effort have both told you the day is different.