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“How vigorously are you able to work out? The answer may predict how long you will live.” ~RealAge Tip of the Day (www.RealAge.com)
Exercise Capacity and Longevity—in Women
Several years back I wrote about a Stanford University study of 6213 men, which found that “each increase of 1 MET in exercise capacity conferred a 12 percent improvement in survival.” (Greater Fitness/Longer Life, #91, Health & Fitness) Simply put, the harder you are able to exercise, the longer you’re likely to live. A new study published in The New England Journal of Medicine (August 4, 2005) found a similar striking correlation in women.
The goal of the study was two fold: first, to establish a nomogram or graphic presentation for predicting exercise capacity on the basis of age, and second, to assess the predictive value of age-related exercise capacity for survival. Such a prognostic nomogram had been developed for men, but not for women. “Few studies have evaluated exercise capacity in women,” the researchers led by Martha Gulati, MD, Northwestern University, Bluhm Cardiovascular Institute, wrote, “and to date, no standard for age-related declines in physical fitness has been established for women.”
The researchers studied 5721 healthy women and 4471 that had been referred for evaluation of suspected heart disease. The healthy women (referred to as “asymptomatic”) had an average age of 52 (35-86) and the referral subjects (“symptomatic”) an average age of 61 (34-93). Exercise capacity was measured for both groups using a standard treadmill stress test. Results were calculated in metabolic equivalents (METs) based on speed and grade at the time of maximum exertion. One MET is equal to the amount of energy, measured in oxygen consumption, a person uses at rest. Two METs is oxygen uptake walking on a level surface at less than 2 mph, five METS is oxygen uptake walking 4 mph, and eight METS is the oxygen uptake running at 6 miles per hour.
In addition, members of the healthy group were divided into two categories, sedentary or active, based on their response to one question: Do you have a regular (exercise) training program? The result was: 866 “active” and 4643 “sedentary.” In other words, only 15% of the healthy group exercised regularly, which sounds about right for women in general.
The healthy group and the referral group were followed for an average of 8.4 years and 5.3 years, respectively. The National Death Index was used to determine deaths and causes during the follow-up periods. In the healthy group 180 died, 58 due to cardiac causes. In the referral group of symptomatic women 537 died, 45 from heart problems.
As you would expect, the healthy (asymptomatic) women had a higher exercise capacity and a lower death rate than the referral group of women with cardiovascular symptoms (symptomatic). Moreover, the active subgroup had the highest exercise capacity in either population.
Here are the particulars. They’re a little heavy. Stick with me.
The asymptomatic group had an average peak exercise capacity of 8 METs, with a low of 1.4 and a high of 20; the symptomatic group averaged 6.9 METs, with a range of 1.2 to 17.4.
Exercise capacity and age were found to be directly related in the asymptomatic (healthy) group of 5721 women; exercise capacity declined with age. Significantly, the 866 active members of that group had a higher overall exercise capacity for their age than the 4643 sedentary members of the group. (My interpretation: Exercise capacity usually declines with age, but regular exercise can slow or stop (even reverse) the decline; see “The Competitive Edge,” # 26c, The Age Factor category on this website.)
The linear relationship between exercise capacity and age made it possible for the researchers to create equations for predicting exercise capacity based on age for the entire asymptomatic group, and for the active and sedentary members of that group (three equations).
“[For all 5721 healthy or asymptomatic women,] regression analysis of exercise capacity for age yielded the following equation: predicted MET = 14.7 – (0.13 x age),” the researchers wrote. “For the active subgroup of 866 women, the regression equation was as follows: predicted MET = 17.9 – (0.16 x age).”
(I will not burden you with the equation for the sedentary subgroup because, as you would expect, it was almost the same as for the entire asymptomatic population. The sedentary subgroup, of course, constituted 85% of the asymptomatic group. No equation was developed for the referral or symptomatic women.)
As you can see, the predicted capacity for the asymptomatic group as a whole is lower at any given age than for the active subgroup. For example, average predicted exercise capacity for a healthy 60-year-old women would be 6.9 METs [14.7 – (0.13 x 60) = 6.9 METs], and 8.3 METs for an active women of the same age [17.9 – (0.16 x 60) = 8.3 METs]. In short, exercise capacity for the active subgroup of women was 20% higher on average.
Using the two equations, graphs or nomograms were constructed where “a line drawn from the patient’s age on the lefthand scale to the MET value [for that patient] on the righthand scale will cross the percentage line at the point corresponding to the patient’s percentage of predicted exercise capacity for age.” In other words, one nomogram gave the percentage of predicted exercise capacity for each subject in the asymptomatic group and the other nomogram for those in the active subgroup.
Using the nomogram constructed using the first equation, for the entire asymptomatic group, the researchers determined the percentage of predicted exercise capacity achieved for each participant in both populations (asymptomatic and symptomatic). The results ranged from 20 percent to 150 percent of the predicted value for age.
As you’ll see, greater exercise capacity at all ages shows up loud and clear in the survival numbers.
“The risk of death [from all causes] among asymptomatic [healthy] women whose exercise capacity was less than 85 percent of the predicted value was twice that among women whose exercise capacity was at least 85 percent of the age-predicted value,” the researchers reported. “[The] hazard ratio for death from cardiac causes” was even greater, almost two and one half times greater for the women below 85% of the predicted value than for those at 85% or better. “Results were similar in the cohort of symptomatic [referral] women.”
In short, greater exercise capacity was predictive of longer life for both cohorts of women, asymptomatic and symptomatic; more so when death was caused by heart problems.
The advantage was even greater for the women whose exercise capacity exceeded the predicted value.
In the healthy group of women, “as compared with women whose exercise capacity exceeded the age-predicted value by more than three MET,” the risk of death from any cause was 2.63 times greater for those whose exercise capacity was found to be less than predicted, and 4.27 times greater for death from cardiac causes; for women with heart symptoms (the referral group), the ratio was 3.28 and 3.80, respectively.
The last ratio, 3.80, is interesting. It seems strange that the risk of death from cardiac causes would be higher for healthy women with less than predicted fitness than for women with cardiovascular symptoms with less than predicted fitness. The researchers offered no explanation. I suppose it’s just a statistical glitch. Nevertheless, below predicted exercise capacity in all categories was found to substantially increase the risk of death.
Finally, the least fit women were found to be most at risk.
For example, symptomatic women under 55 with exercise capacity 2 or more METs below expectations and women over 70 from 0 to 2 METs below expectations had the highest mortality ratios.
Bottom line: In women as well as men, exercise capacity is a powerful predictor of longevity.
Intervals for Life
“Boost your exercise capacity—and your longevity—with internal training by adding short bursts of more intense activity to your workout,” says the RealAge Tip of the Day (www.RealAge.com), commenting on the study we’ve been discussing.
Makes perfect sense, doesn’t it? To improve exercise capacity, you must go beyond your comfort zone from time to time; exercise physiologists call this overload. Intervals are a great way to introduce overload into your training. Intervals make you work harder and, as a consequence, become stronger and fitter. Intervals build exercise capacity, and exercise capacity adds life to your years and years to your life.
Real Age recommends “jogging a few minutes once or twice here and there during a long walk” or increasing the resistance occasionally on your exercise bike. That’s good advice. If you’re healthy and willing, however, more frequent and intense intervals would be even better, as explained in our article # 152, “Sprints Build Endurance” (Fitness & Health category).
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