HEART RATE ZONES

Age formulas are convenient and frequently wrong by ten to twenty beats. If you are healthy and used to hard efforts, a field test is far better.

A simple max HR test

• Warm up thoroughly — at least 15 minutes with a few hard accelerations.
• Find a steady climb or set a firm resistance on the trainer.
• Ride 3 minutes hard but controlled, then 3 minutes at the hardest pace you can hold.
• In the final 30 seconds, sprint until you have nothing left.
• Your highest recorded beat, typically a few seconds after you stop, is close to your max.

If you have any cardiac history, high blood pressure, or have not trained in years, get medical clearance first. A max HR test is the single hardest thing you can ask of yourself on a bike.

• Lag. Heart rate needs 30-90 seconds to catch up, so it is useless for controlling intervals shorter than about three minutes.
• Cardiac drift. On a long ride, the same power produces a higher heart rate as you dehydrate and heat up — expect 5-10 beats over a couple of hours.
• Heat. A hot room adds beats at any wattage. This is why indoor riders need a fan more than they need a new trainer.
• Caffeine, stress and sleep. All shift the numbers by several beats in either direction.
• Suppression when fatigued. Deeply tired riders often cannot raise their heart rate at all — a useful warning sign.

None of this makes heart rate useless. It makes it a measure of strain rather than output. Use power to set the effort and heart rate to interpret it.

It works perfectly well if you follow two rules: control long steady rides by keeping heart rate under your zone 2 ceiling, and control short hard efforts by perceived effort instead, accepting that the heart rate trace will lag behind. For everything in between, watch the average over the interval rather than the number at any instant.