Tuesday, September 2, 2014

Heart Rate and Recovery... and Heart Rate Recovery (HRR)

by Larry Creswell, M.D.

November's theme at Endurance Corner was recovery. We heard about a variety of issues related to both workout recovery and off-season recovery.

As endurance athletes, we’re interested in measures of recovery -- and particularly those measures that are quantifiable and might help guide our training schedules. Two such measures are the resting heart rate and heart rate recovery (HRR).

The human heart is an amazing pump. Just think about it: at 60 beats per minute, that’s 3,600 beats per hour, 86,000 beats per day, about 2.5 million beats per month, and more than a whopping 30 million beats per year! And that’s without any exercise to speed things up.

Although each heartbeat gets generated all by itself without our conscious control, the heart rate is actually under very fine control in a balance between the sympathetic (which increases the heart rate) and parasympathetic (which decreases the heart rate) nervous systems that influence the heart.

Resting Heart Rate
The resting heart rate is simply the heart rate at rest. One good way to measure the resting heart rate is to count your pulse when you awake in the morning, before rising from bed. Alternatively, it could be measured when you first stand up in the morning (and the value will be slightly higher). To be most useful for establishing a trend, it should be measured the same way each day.

Ample evidence has shown that the resting heart rate decreases over time with endurance training. This reduction in the resting heart rate stems from development of the parasympathetic nervous system in endurance athletes. Other, related adaptive changes in the heart’s physiology include: decreased resting blood pressure, increased cardiac output (the amount of blood the heart pumps each minute) and increased stroke volume (the amount of blood ejected by the heart with each heart beat).

There is much individual-to-individual variability in the resting heart rate, so trends for a given athlete rather than comparisons between athletes are most valuable. It’s also important to keep in mind that, even in a single athlete, the day-to-day variation in resting heart rate -- without any particular cause -- can be as much as several beats per minute.

That said, measurements of the resting heart rate, over time, can be very useful:

  1. The resting heart rate will gradually decrease during a training cycle
  2. The resting heart rate will gradually increase during a period of absolute or relative recovery
  3. An “unexplained” increase in the resting heart rate during a training cycle may be an indication of poor recovery

Heart Rate Recovery (HRR)
Heart rate recovery (HRR) is the rate at which the heart rate returns to baseline after a period of exercise.

Complete recovery of the heart rate may take an hour after light activity, several hours after long-duration aerobic exercise, and perhaps 24 hours after intense exercise. One easy way to measure HRR is to measure the change in heart rate during the first minute after submaximal exercise: a drop in heart rate of 15-20 beats per minute might be typical and a value less than 12 would be unfavorable.

We’ve known in medical circles for nearly 20 years that HRR is a useful index of cardiovascular fitness. The whole area of HRR and its clinical implications is a subject of current investigation, but it is well established that HRR is a strong predictor of both cardiovascular-related and all-cause mortality in healthy adults.

The typical endurance athlete will be aware of HRR, at least informally, and particularly how it manifests during an interval workout. With a heart rate monitor, it’s easy to get a general sense of how quickly the heart rate returns to baseline after a period of submaximal or maximal exercise. It’s only in recent years, though, that investigators have begun to study HRR rigorously as it relates to endurance athletes and recovery.

A 2010 report by Lambert and colleagues at the University of Cape Town formalized the use of HRR in a study of well-trained cyclists. They used an HRR measurement protocol that consisted of a 15-minute period of cycling on a trainer (6 minutes at 60% max heart rate, 6 minutes at 80% max heart rate, and 3 minutes at 90% max heart rate) and HRR was defined as the change in heart rate during the first minute after stopping exercise.

The investigators made several important observations about HRR:

  1. A slight increase in HRR accompanies fitness gain during a training cycle
  2. An unexpected increase in HRR may indicate fatigue due to training
  3. A decrease in HRR during a training cycle may indicate overtraining

As you can see, HRR may well be a physiologic parameter that can be used to gauge the effects of training as well as the readiness to race. You can expect to hear more about HRR and endurance athletes in the years ahead.


Reference

Lamberts RP, Swart J, Capostagno B, Noakes TD, Lambert MI. Heart rate recovery as a guide to monitor fatigue and predict changes in performance parameters. Scand J Med Sci Sports 2010: 20; 449-457.


Larry Creswell, M.D., is a cardiac surgeon and Associate Professor of Surgery at the University of Mississippi Medical Center in Jackson, Mississippi. In addition to his regular column on Endurance Corner, he maintains The Athlete's Heart blog to offer information about athletes and heart disease in an informal way and to encourage exchange and discussion that will help athletes build a heart-healthier lifestyle. You can contact him at lcreswell@umc.edu.
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