Maximal Aerobic Power and Functional Independence in Older Adults

Shephard, R.J.2008. Maximal oxygen intake and independence in old age. British Journal of Sports Medicine, published online Apr. 10, 2008; doi:10.1136/bjsm.2007.044800

Maximal aerobic power is a useful, meaningful and motivational physiological measurement that all types of fitness professionals use to track their clients’ progress. It is also associated with the performance of vigorous bouts of exercise in competitive cardiorespiratory events.

From a clinical perspective, increased cardiovascular fitness is associated with decreased risk of disease. It is also related to the functional independence of seniors in the execution of their activities of daily living. However, the rate of deterioration in aerobic power and its association with functional independence have not been fully investigated. The progress that can be made to improve aerobic capacity in the later stages of life is only starting to be explained. Roy J. Shephard, PhD, examined existing studies on aging and aerobic capacity in older adults to determine the known relationships between independent living and maximal aerobic capacity.

Maximal oxygen consumption (also called maximal oxygen uptake, maximal aerobic power, aerobic capacity, functional aerobic capacity or simply VO₂max) is regarded as the criterion measure of cardiorespiratory fitness. It is the highest rate at which oxygen can be consumed during exercise, or the maximal rate at which oxygen can be taken in, distributed and used by the body during physical activity. The “V” in VO₂max represents the volume used per minute (in scientific notation, a dot sometimes appears over the V to indicate “per unit of time”). VO₂max is usually expressed in relative terms (uptake relative to body weight) as milliliters of oxygen consumed per kilogram of body weight per minute (ml O₂/kg/min or ml/kg/min). Significant factors that influence maximal oxygen consumption in healthy adults are age, gender, heredity, body composition, state of training and mode of exercise. In addition, a number of diseases—such as heart disease, chronic obstructive pulmonary disease, diabetes, cancer and bone-related diseases (such as osteoporosis)—can markedly impair maximal aerobic capacity.

According to Shephard, cross-sectional research indicates that aerobic power decreases fairly steadily in sedentary males, with average values in the region of 45 ml/kg/min around the age of 20 years dropping to about 25 ml/kg/min at the age of 60. With inactive females, Shephard notes, aerobic power begins to decline at the age of 35 from values at about 38 ml/kg/min to roughly 25 ml/kg/min at the age of 60. These figures point to losses in aerobic power of approximately 44% and 34% in males and females, respectively, although decreases in VO₂max with age are extremely variable. These decreases may be attributed to declines in maximal heart rate, stroke volume (blood pumped per beat), fat-free mass and extraction of oxygen at the cell (referred to as arteriovenous oxygen difference). Physiological losses in aerobic capacity occur as a natural consequence of aging but are clearly enhanced by an inactive lifestyle.

The gender differences in VO₂max have generally been explained by differences in body composition and heart size. Sedentary adult women (≥ 55 years) generally average about 30% body fat, whereas inactive
men (≥ 55 years) average 16% body fat (Heyward 2006). Therefore, when VO₂max is expressed relative to body mass (ml/
kg/min), women generally have about 20% lower aerobic capacities than their male counterparts. However, expressing aerobic capacity in terms of fat-free (muscle) mass balances out the gender difference. Women also tend to have smaller hearts, which profoundly affects oxygen delivery to working muscle (Hutchinson et al. 1991). These differences in heart size and body composition account for almost 99% of the gender-specific differences in maximal aerobic capacity between men and women (Hutchinson et al. 1991).

From an analysis of existing research, Shephard suggests that older adults whose maximal aerobic power has dropped to approximately 12–15 ml/kg/min often become very challenged to complete activities of daily living autonomously. Shephard goes on to state that seniors living independently tend to have VO₂max values of at least 18 ml/kg/min (in men) or 15 ml/kg/min (in women).

In a commendable review of the literature published since 1990, Shephard stratified VO₂max research on seniors into training programs lasting 8–10 weeks, 12–18 weeks and 24–52 weeks. His analysis indicates that a 12.9% increase in VO₂max can be realized within 8–10 weeks of aerobic training; a 14.1% increase can be realized within 12–18 weeks of training; and a 16.9% increase can be realized within 24–52 weeks of training. Clearly, with progressive aerobic conditioning personal trainers and other fitness professionals can help prevent or even reverse the age-related decrease in functional abilities in senior populations. From a review of the data, Shephard suggests that gradually increasing aerobic training can boost the aerobic power of the elderly by at least 10 ml/kg/min, potentially delaying the loss of independence by as much as 20 years. He concludes that using higher intensities with seniors leads to even greater gains: exercising on a cycle ergometer for 30 minutes 3 days per week at 70%–80% VO₂ peak for just 3 months increased subjects’ VO₂max by almost 25% (about 6 ml/kg/min)—equivalent to gaining back an estimated 12 years of vigor to their lifestyle.

Strategies to Get Older Adults More Active

The updated physical activity guidelines released by the American College of Sports Medicine and the American Heart Association (ACSM/AHA 2007) recommend that adults over age 65 meet or exceed 30 minutes of moderate-
intensity physical activity on most days of the week. Moderate physical activity is defined as brisk walking or other physical activities that reasonably accelerate heart rate. Therefore, walking a distance of 2 miles in 30–40 minutes—a walking speed of 3–4 miles per hour—would meet the requirement. For less fit adults, the physical activity guidelines are much easier to attain now that recommendations also encourage the “accumulation” of somewhat hard physical activity in
intermittent bouts of exercise and physical activity lasting 10 minutes or longer throughout the course of the day. The 2007 updated ACSM/AHA guidelines for older adults involve a combination of structured and unstructured approaches to increasing physical movement, in hopes of reducing the deleterious effects of inactivity (see Figure 1).

The unstructured approach to physical activity, referred to as functional health, involves developing ways to be more active in one’s daily life. Activities that fall into this category include taking a family walk after dinner, walking the dog frequently, walking more briskly when doing errands, parking the car in the back of the parking lot, taking walking breaks instead of coffee breaks (or with the coffee breaks), doing more energetic housework (such as vacuuming), using stairs in place of elevators and doing more mall walking while shopping. Shephard notes that many of these recommendations are weight bearing owing to the fact that diminishing leg strength (which effects walking speed, stride and lower-extremity function) is one of the strongest predictors of disability in older adults.

In contrast to unstructured physical activity, structured physical activity and exercise is most commonly described as purposeful, planned, repetitive bodily movement performed at sufficient intensity to improve or maintain physical fitness. The spectrum of aerobic exercise options is limitless, and regular participation in this component of fitness will definitely help combat fatigue, undue injury and the diseases of inactivity. As Shephard highlights in his review, nowhere is consistent aerobic activity more important than in the older-adult population, for whom minor reductions in fitness translate into significant reductions in independence and quality of life.

The progressive deterioration of health associated with inactivity is a modifiable occurrence in older-adult populations. Personal trainers and other fitness professionals should enthusiastically encourage older adults to create lives full of physical activity in order to enjoy the benefits of longer-lasting functional health and chronic-disease prevention.