The purpose of the heart is to pump blood from the venous system into the arterial system. The total output of that pump is called cardiac output. It’s measured in volume of blood per minute. Your heart rate is the main means by which you increase the circulation of blood.
From low heart rates to intermediate heart rates, the heart is able to increase the circulation by increasing the stroke volume – the amount of blood ejected by the heart into the arterial system each time the heart beats.
Up to 90 beats a minute, you’re getting a strong assist from the stroke-volume increase. After 90, this influence is less and less.
After 130, if you’re not in good shape, the circulation is increased by heart rate alone. At a heart rate of 130 or higher, the heart is beating so fast that it doesn’t have time to fill any greater volume, so the amount of blood the heart puts out varies in direct proportion to the number of beats per minute. It’s a lot more efficient for the heart to have both systems, the stroke-volume increases and the pulse-rate increases, working to increase its output.
Now the effects of conditioning become apparent. If you’re well conditioned, you can extend this contribution of stroke volume up to 140 beats a minute because of the more efficient coordination of the fibers of the heart. If the heart is in poor condition, then stroke-volume contribution may quit at 120 beats a minute.
Take it to the Limit
Beyond 170 to 180 beats a minute, cardiac output doesn’t increase even if your heart beats faster. You’ve reached the limit of venous return to the heart.
The heart may go above 200 beats a minute. Heartbeats as high as 230 have been recorded during exercise. Each person has his own maximum. It’s not important that you can get your heart rate up to 220 and I can get mine only to 210 or that someone else can get his only to 190. Many top athletes can’t get their heart rates above 190.
Maximum heart rate is not an index of physical fitness. Long-term training may have no effect at all on increasing your maximum heart rate. Maximum heart rate lowers as you age; studies of a large population in Sweden have demonstrated that the average maximum heart rate drops about one beat per minute each year. The reason why it decreases with age isn’t well understood, but it has no bearing on your capacity to function, in any case.
For large adult populations, the average maximum heart rate is approximately 220 beats a minute minus the person’s age. This isn’t an ideal figure, or a goal, or one to put into competition. It’s a theoretical estimate of maximum exercise pulse at various ages.