Heart rate

Decades ago a mathematical relationship between a person’s age and maximum heart rate was discovered: 220 – age. Subtract your age from 220 and you’ll get your maximum heart rate. This formula is in wide use today although more recent studies have modified it a bit. The original observation came from a small sample of adult athletes and is only roughly accurate. We have no idea to what degree this pertains to non-athletes or the elderly.

We commonly link heart rate with fitness. We set the treadmill to levels of difficulty based on a certain percentage of the presumed max heart rate. I want to talk a bit about the relationship of heart rate to fitness.

The purpose of the heart is to pump oxygen-carrying blood to the tissues and return carbon dioxide. The more fit you are, the better the heart does that. That would seem to imply that fitter a person is, the faster the heart pumps, but it doesn’t. Exactly the opposite occurs. Athletes have slower resting heart rates than the rest of us.

What we are really interested in is cardiac output – the amount of blood a heart can pump per minute – and that introduces the concept of stroke volume. That’s the amount of blood pushed out of the heart with each stroke. It’s easy to see, therefore, that a heart with a stroke volume of two cups only needs to beat half as fast as a heart pushing one cup with each stroke to push the same amount of blood per minute.

Athletes’ hearts are capable of higher stroke volumes to increase cardiac output and meet the oxygen demand of the body. Both heart rate and stroke volume increase as the athlete begins to run and achieve a plateau where the heart rate is constant. But an interesting thing happens when we compare the runner on the treadmill with the runner on an open track. Both can be running the same speed, but their heart rates differ. The heart of the open track runner beats faster and the cardiac output is higher.

Alternatively, we can run them both to the same heart rate, but the treadmill runner will achieve a higher speed. The reason for this is that the open track runner is actually moving weight from point A to point B. The treadmill runner is running in place and his body needs less energy. Here is where the treadmill becomes deceptive. You may be running 6-minute miles on the treadmill, but when you try to do that on the track, you can’t.

Even though your heart rate is up in the training range, say 85% of your max, your stroke volume is less than it would be if you were actually moving weight and burning oxygen to do it. This is because your heart rate is greatly influenced by sensors in your joints. The sensors tell the brain that you are moving and you are going to be needing more oxygen soon, so speed up the heart. The heart speeds up (this can be seen even in paraplegics by moving their limbs for them) but the stroke volume and cardiac output stay modest.

You think you’re training efficiently, but you’re not. You need to move weight to train and improve aerobic capacity. Sometimes a machine at a gym is all that’s available, but don’t believe you’re getting the same benefit as if you were actually running a track at the same speed or heart rate.

So if you can’t trust your heart rate to gauge whether you are training effectively or not, what can you rely on? A pretty good rule is that if you can talk, you’re not training. As few as three bursts of maximum effort – 100-yard-dashes for example – for as little as ten seconds two or three times a week will improve your aerobic fitness and burn more fat that an hour every day on the treadmill at so-called “fat burning” levels of difficulty.

You should be gasping for breath at the end of each wind sprint. If you do that, everything else – oxygen carrying capacity of the blood, capillary support, hemoglobin, energy production by mitochondria, buffering capacity, blood pressure and heart rate will move in a healthy direction. You don’t need to pay attention to heart rate.