Maximal Aerobic Power and Functional Independence in Older Adults
Len Kravitz, Ph.D.
Article reviewed:
Shephard, R. J. (2008). Maximal oxygen intake and independence in old age. British Journal of Sports Medicine, published online April 10, 2008, Doi:10.1136/bjsm.2007.044800
Introduction
Maximal aerobic power is a useful, meaningful and motivational physiological measurement fitness professionals and personal trainers utilize to track progress with their clients. It is also associated with the performance of vigorous bouts of exercise in competitive cardiorepiratory events. From a clinical perspective, increased cardiovascular fitness is associated with decreased risk of disease. As well, maximal aerobic power is 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 to functional independence has 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. This review by Roy J. Shephard, Ph.D. examined existing studies on aging and aerobic capacity in elders to determine the known relationships between independent living and maximal aerobic capacity.
VO2 max 101: What is Maximal Aerobic Capacity?
Maximal oxygen consumption (also called maximal oxygen uptake, maximal aerobic power, aerobic capacity, functional aerobic capacity, or simply VO2 max) 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 VO2 max represents the volume used per minute (in scientific notation, a dot (sometimes) appears over the V to indicate “per unit of time”). VO2 max is usually expressed in relative (uptake relative to body weight) terms 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.
What is the Association of VO2 Max and Aging in Males and Females?
Shephard (2008) summarizes that 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 to about 25 ml/kg/min at the age of 60 years. With inactive females, Shepard notes that aerobic power begins to decline at the age of 35 years from values just about 38 ml/kg/min to roughly 25 ml/kg/min at the age of 60. This approximates a 44% and 34% loss in aerobic power in males and females, respectively. The decreases in VO2 max with age are extremely variable, but may be attributed to a decline 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.
Wait! Why is there a Gender Difference in VO2 Max?
The gender differences in VO2 max have generally been explained by differences in body composition and heart size. Sedentary adult women (&Mac179; 55 yr) generally average about 30% body fat, whereas inactive men (&Mac179; 55 yr) average 16% body fat (Heyward, 2006). Therefore, when VO2 max 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 effects oxygen delivery to working muscle (Hutchinson, Cureton, Outz & Wilson, 1991). These differences in heart size and body composition account for almost 99% of the gender-specific differences between men and women in maximal aerobic capacity (Hutchinson, Cureton, Outz & Wilson, 1991).
When Do Low VO2 Max Values Affect Functional Independence?
From 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 autonomously complete activities of daily living. Shephard continues that independent living seniors tend to have VO2 max values of at least 18 ml/kg/min (in men) and 15 ml/kg/min (in women).
How Trainable is VO2 Max in Older Adults?
In a commendable review of the published literature since 1990, Shephard stratified published VO2 max research with seniors in 8-10 week, 12-18 week and 24-52 week comparisons. Analysis indicates that a 12.9% increase in VO2 max can be realized within 8-10 weeks of aerobic training as compared to an increase of 14.1% in 12-18 weeks and 16.9% in 24-52 weeks of aerobic conditioning. Clearly, personal trainers and fitness professionals can help prevent or even reverse the age-related decrease and functional independence with progressive aerobic conditioning in senior populations. From 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. Shephard continues that higher intensities with seniors lead to even greater gains. An increase of 25% in VO2 max (about 6 ml/kg/min) is equivalent to gaining back an estimated 12 years of vigor to one's lifestyle.
What Strategies Should Fitness Professionals and Personal Trainers Use to Get Older Adults More Active?
The updated physical activity guidelines by the American College of Sports Medicine and American Heart Association (ACSM/AHA, 2007) recommend that adults over age 65 meet or exceed 30 minutes of moderate intense physical activity on most days of the week. Moderate physical activity is defined as activity such as brisk walking or other physical activities that reasonably accelerate heart rate. This is comparable to a walking speed of 3 to 4 miles per hour, or walking a distance of 2 miles in 30 to 40 minutes. 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 10-minute or more intermittent bouts of exercise and physical activity throughout the course of the day. The 2007 updated ACSM/AHA recommendations for older adults involve a combination of structured and non-structured approaches to increasing physical movement in hopes of reducing the deleterious effects of inactivity.
The unstructured approach to physical activity, referred to as functional health, involves developing ways to be more active in one's daily life. These include suggestions such as 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 break), doing more energetic house work (such as vacuuming), using stairs in place of elevators, and doing more mall walking while shopping. Many of these recommendations are weight bearing due to the fact that diminishing leg strength 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 the regular participation in this component of fitness will definitely help to 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, with whom minor reductions in fitness translate into significant reductions in level of independence and quality of life.
Take Home Message
The progressive deterioration of health associated with inactivity is a modifiable occurrence in older adult populations. Personal trainers and 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.
Additional references:
Heyward, V. (2006). Advanced Fitness Assessment and Exercise Prescription (5th ed.). Champaign, Ill.: Human Kinetics.
Hutchinson, P.L., Cureton, K.J., Outz, H., & Wilson, G. (1991). Relationship of cardiac size to maximal oxygen uptake and body size in men and women. International Journal of Sports Medicine, 12, 369-373.
ACSM. Updated Physical Activity Guidelines Released Today
http://www.acsm.org/AM/Template.cfm?Section=Home_Page&TEMPLATE=/CM/HTMLDisplay.cfm&CONTENTID=7764
Accessed November 20, 2008
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