Aging and the Physical Demands of Running

Resting heart rate (RHR), the number of heartbeats per minute at rest, stays fairly constant through adulthood, provided that fitness level stays fairly constant. (Resting heart rate generally reflects fitness level.) Sedentary adults have resting heart rates of 60 to 100 beats per minute compared to 40 to 60 beats per minute for very active adults. This is because the cardiovascular systems of active adults are more efficient than those of sedentary adults.

Clearly, however, running increases your need for oxygen. To get enough of it, your heart must pump blood more quickly. When you run fast or race, your heart rate approaches maximum levels. Unlike RHR, maximum heart rate (MHR) - the highest number of heartbeats per minute (BPM) experienced at the end of a race or in maximal exercise - decreases with age. Whether you are sedentary or active, MHR declines about one beat per minute each year, or about 40 beats per minute between the ages of 20 and 60. A simple method to calculate your MHR, accurate to within about 10 beats per minute, is the formula 220 minus your age. For example, if you are 34, your predicted MHR is 186 BPM, or 220 minus 34.

Frankly, few masters runners from Liberty Athletic Club, where I coach, base their efforts on heart rate, relying more on pace per mile or perceived exertion or both. That said, if you are pacing your runs according to percentage of maximum heart rate and incorporating intense sprints at an effort above 95 percent of your maximum heart rate, check with your doctor first if you have health issues. That intensity challenges the heart, joints, and muscles. I've also seen many masters runners who race distances from the 5K and up limit the intensity of their hard days to 90 percent of maximum heart rate, and they're posting excellent results.

For an accurate measure of your maximum heart rate, take a 10- to 20-minute stress test at a qualified facility, such as a hospital or fitness testing center. During the test you will exercise to your limit - often on a treadmill while someone periodically increases its speed or slope - while you're attached to a heart rate monitor or electrocardiogram (ECG). One or the other will show your maximum heart rate during the final moments of maximal exertion.

Like heart rate, respiration rate - the number of breaths taken per minute - increases with running. As you know, when you run you breathe faster and deeper to supply your heart, lungs, and muscles with oxygen. While respiration rate remains fairly constant with age, it's harder for older runners to extract as much oxygen with each breath than it is for younger runners.

And what about blood pressure? That's also affected by running. Blood pressure refers to the pressure of the circulating blood on blood vessel walls and is divided into systolic and diastolic pressure. Systolic pressure refers to the force in the arteries when the heart beats, pumping out blood. Diastolic pressure refers to the force in the arteries when the heart relaxes between beats. In healthy adults, blood pressure remains the same through the decades. Normal blood pressure is 120 over 80, and ideally less than 120 for systolic and less than 80 for diastolic pressure. You may, however, be among those 20 percent of adults or the almost half of adults over 65 who have slightly elevated blood pressure. In any case, running raises not your diastolic, but your systolic blood pressure. Like other kinds of exercise that involve intensity, running can cause normal blood pressure to increase to 200 over 80 and as high as 300 over 80. These readings are dangerously high, indicating too much pressure on the blood vessel walls. The bottom line is that your blood pressure should be checked before you start a training program, and clearance from your doctor is important.

If you're at risk for developing high blood pressure, you can take routine measures in your training to moderate it. A warm-up before and cool-down after running help your blood pressure adjust gradually to different levels of stress. Warm up by walking or jogging slowly for at least 10 minutes. Cool down by walking or jogging for at least 10 minutes. (Stopping too suddenly after your run can cause a sharp drop in blood pressure, resulting in lightheadedness and cramping.) Don't hold your breath while running because that can raise blood pressure. In terms of diet, limit your salt intake and avoid caffeine, which can raise blood pressure before and during a run.

Body temperature stays constant throughout life, but a strenuous run can raise it. In addition, running in hot and humid conditions can raise core temperature in any runner, and masters are more affected by humid conditions than open runners. Middle-aged bodies are less efficient at sweating, a cooling mechanism for the body. Masters runners are also more sensitive to cold. Their skin is less likely to constrict (shiver) to preserve body heat, and their metabolism is generally slower.

VV̇O₂max, the single best measure of overall cardiovascular performance or fitness level, also declines. V represents volume, O₂ represents oxygen, and max is maximum. VV̇O₂max is usually expressed in relative terms, as milliliters of oxygen consumed per kilogram of body weight per minute (ml/kg/min). Essentially, VV̇O₂max is the greatest amount of oxygen that can be used at the cellular level by the entire body during physical activity. A high VV̇O₂maxgenerally correlates with high endurance performance.

How much does VV̇O₂max decline with aging? In terms of percentages, it declines by an average of about 10 percent per decade in sedentary adults after ages 25 to 30. As an example, a 10 percent decline per decade translates to the equivalent of adding 30 seconds to a 10K personal best each year (or adding 5 minutes in 10 years). Despite the general decline in VV̇O₂max, though, continued vigorous training can slow the rate of decline per decade from 10 to 5 percent (Joyner 1993; Marti and Howald 1990). One 22-year longitudinal study found that while continued training can lower that decline to 5 to 7 percent, two exceptional elite male runners had declines of as little as 2 percent per decade between ages 22 and 46 (Trappe et al. 1996; Marti and Howald 1990).

Some studies of masters athletes have shown that this decline accelerates at certain times, from the mid-50s to mid-60s, and then again in the mid-70s. One study of 2,599 masters runners by Dr. Vonda Wright, orthopedic surgeon at the University of Pittsburgh, pointed to an unusually sharp decline at age 75 (Wright and Perricelli 2008).

Having watched women from their 20s to 70s run weekly quarter- and half-mile intervals over 20 years, I can see this decline clearly on the track. Here's just one example of two national-class middle-distance masters runners (with aliases) that shows how the decline can accelerate from the mid-50s to the mid-60s. At 52, Sarah typically ran 5 to 6 seconds behind 40-year-old Linda on half-mile (800 m) intervals. Both trained similarly and were equally talented. On those same intervals 12 years later, with similar continued training, Sarah, in her mid-60s, was 15 to 16 seconds behind Linda, then in her early 50s.

So what can you do to mitigate the decline in VV̇O₂max? Granted, some things are out of your control. You can't control genetics, which accounts for 25 to 50 percent of variance in VV̇O₂max. You can't always control disease, which lowers VV̇O₂max. And you obviously can't control aging. But you can gradually raise your level of activity - distance or speed - and you can control the quality of your diet. Excess fat lowers VV̇O₂max(So and Choi 2010). So take heart (and make the most of it)!