Why does maximum heart rate drop with age?

Researchers at the University of Colorado have new insight into the age-old question of why maximum heart rate (maxHR) decreases with age. This decrease in maxHR not only limits the performance of aging athletes but it is also a leading cause for nursing home admittance for otherwise-healthy elderly individuals who no longer have the physical capacity required for independent living. We say we're just getting old and slowing down, but exactly what is it that is slowing down?

Everybody knows that aerobic capacity decreases with age. You know that chart in your gym that shows your target decreasing as you get older? Well, that's not a senior discount to let the elderly get off easy on their treadmill workouts. It's because older hearts simply can't beat as fast as younger hearts. So the older person who's doing 120 beats per minute is probably working harder—at a higher percentage of maximum heart rate—than the younger person who is at 150 beats per minute.

A new study by a group led by Catherine Proenza, PhD and Roger Bannister, PhD from the University of Colorado School of Medicine reports that one of the reasons for the age-dependent reduction in maximum heart rate is that aging depresses the spontaneous electrical activity of the heart's natural pacemaker, the sinoatrial node.

A dissertation from Eric D. Larson, a graduate from Proenza's lab in the Department of Physiology and Biophysics, is described in the article. Larson said, "I utilized a method to record ECGs from conscious and found that maximum heart rate was slower in older mice, just as it is in older people. This result wasn't unexpected. But what was completely new was that the slower maxHR was because the individual pacemaker cells—called sinoatrial myocytes, or 'SAMs'—from old mice just couldn't beat as fast as SAMs from young mice."

The researchers recorded the tiny electrical signals from the isolated cells and found that SAMs from old mice beat more slowly, even when they were fully stimulated by the fight-or-flight response which can be observed in these individual cells. The slower beating rate was due to a limited set of changes in the action potential waveform, the electrical signal that is generated by the cells. The changes were caused by altered behavior of some in the membranes of the older cells. (Ion channels are proteins that conduct electricity across the cell membrane. Imagine a balloon with little tiny pinholes that open and close to let the air in and out; ion channels are like the pinholes.)

Like most initial discoveries in basic science, this study opens many more questions and avenues for further research. But the significance of the study is that it raises the possibility that sinoatrial ion channels and the signaling molecules that regulate them could be novel targets for drugs to slow the loss of aerobic capacity with age. In the meanwhile, Proenza notes that "although goes down for everybody equally, regardless of physical conditioning, people can improve and maintain their at all ages by exercising."

This study will be published in the Oct. 14 Proceedings of the National Academy of Sciences.

More information: Depressed pacemaker activity of sinoatrial node myocytes contributes to the age-dependent decline in maximum heart rate, www.pnas.org/cgi/doi/10.1073/pnas.1308477110

Related Stories

Understanding the role of IKACh in cardiac function

Jul 15, 2013

Researchers have uncovered a previously unknown role for the acetylcholine-activated inward-rectifying potassium current (IKACh) in cardiac pacemaker activity and heart rate regulation, according to a st ...

Rhythm is it: Ion channels ensure the heart keeps time

Sep 09, 2011

The heartbeat is the result of rhythmic contractions of the heart muscle, which are in turn regulated by electrical signals called action potentials. Action potentials result from the controlled flow of ions into heart muscle ...

Recommended for you

Student seeks to improve pneumonia vaccines

7 hours ago

Almost a million Americans fall ill with pneumonia each year. Nearly half of these cases require hospitalization, and 5-7 percent are fatal. Current vaccines provide protection against some strains of the ...

Seabed solution for cold sores

8 hours ago

The blue blood of abalone, a seabed delicacy could be used to combat common cold sores and related herpes virus following breakthrough research at the University of Sydney.

Better living through mitochondrial derived vesicles

Aug 19, 2014

(Medical Xpress)—As principal transformers of bacteria, organelles, synapses, and cells, vesicles might be said to be the stuff of life. One need look no further than the rapid rise to prominence of The ...

Zebrafish help to unravel Alzheimer's disease

Aug 19, 2014

New fundamental knowledge about the regulation of stem cells in the nerve tissue of zebrafish embryos results in surprising insights into neurodegenerative disease processes in the human brain. A new study by scientists at ...

User comments

Adjust slider to filter visible comments by rank

Display comments: newest first

EnricM
1.4 / 5 (10) Oct 15, 2013
Several questions:
1) What has the study in old mice to do with humans?
2) Why is maxHR related to nursing?
3) Has this been measured in athletes or in sedentary humans and if so how does it apply to athletes?

A side note: I am an athlete, thus not new to HR training and my fair share of sports physiology (hence my interest)