Should I be concerned about my HR?

There are many misconceptions about heart rates in athletes. For many elite athletes, max heart rate is a focus, and when I’ve trained Olympian track athletes particularly they are frustrated that during aquatic cross training, their HR is significantly lower causing them to believe they aren’t getting a good workout. The job of the heart is to pump blood. It has two mechanisms to do that during exercise: increasing heart rate and increasing stroke volume (the amount of blood pumped during each contraction.) Our heart rates have a biological range which decreases its max with age. We typically start our lives with ± 220 MHR, but by age 70 or so, that is significantly lower as a HRmax. A typical stroke volume is around 40 cc/beat, so with a typical HR of 60, about 2400 ml/min cardiac output. With max exercise training, that stroke volume is able to nearly double, and from a cardiac efficiency standpoint, increasing stroke volume is much more efficient than increasing heart rate. Aquatic immersion by itself increases stroke volume by about 30%, so there is an automatic increase in cardiac output even with sedentary immersion, and aquatic immersed exercise typically produces a HR about 12-15% lower than land-based exercise of similar intensity.

So a resting HR of 45 might be a concern in an emergency room, but is a frequent point of pride in an elite athlete. The brain, which is very sensitive to reduced cardiac output is still getting sufficient blood flow to function perfectly when one’s HR is low but stroke volume is high and total cardiac output is normal. The body is amazing well calibrated to maintain healthy cerebral blood flow. Simple aquatic immersion, and immersed exercise on a treadmill produces a 10-15% increase in cerebral blood flow, so as aquatic exercisers, we are doing our brains a real favor by increasing cerebral blood flow and cerebral oxygen supply!!

Bruce E. Becker, MD, MS

There are many misconceptions about heart rates in athletes. For many elite athletes, max heart rate is a focus, and when I’ve trained Olympian track athletes particularly they are frustrated that during aquatic cross training, their HR is significantly lower causing them to believe they aren’t getting a good workout. The job of the heart is to pump blood. It has two mechanisms to do that during exercise: increasing heart rate and increasing stroke volume (the amount of blood pumped during each contraction.) Our heart rates have a biological range which decreases its max with age. We typically start our lives with ± 220 MHR, but by age 70 or so, that is significantly lower as a HRmax. A typical stroke volume is around 40 cc/beat, so with a typical HR of 60, about 2400 ml/min cardiac output. With max exercise training, that stroke volume is able to nearly double, and from a cardiac efficiency standpoint, increasing stroke volume is much more efficient than increasing heart rate. Aquatic immersion by itself increases stroke volume by about 30%, so there is an automatic increase in cardiac output even with sedentary immersion, and aquatic immersed exercise typically produces a HR about 12-15% lower than land-based exercise of similar intensity.

So a resting HR of 45 might be a concern in an emergency room, but is a frequent point of pride in an elite athlete. The brain, which is very sensitive to reduced cardiac output is still getting sufficient blood flow to function perfectly when one’s HR is low but stroke volume is high and total cardiac output is normal. The body is amazing well calibrated to maintain healthy cerebral blood flow. Simple aquatic immersion, and immersed exercise on a treadmill produces a 10-15% increase in cerebral blood flow, so as aquatic exercisers, we are doing our brains a real favor by increasing cerebral blood flow and cerebral oxygen supply!!

Bruce E. Becker, MD, MS