March 13, 2006 — Although older individuals have lower exercise efficiency than do younger individuals, training improves efficiency more in older than in younger individuals, according to the results of a study reported in the March 7 issue of the Journal of the American College of Cardiology.

"Little is known about the potential role of exercise efficiency in the decline of exercise capacity with aging, female gender, or the untrained state," write J. Susie Woo, MD, from the University of Washington in Seattle, and colleagues. "The purpose of this study was to determine whether a reduction in exercise efficiency occurs with aging, whether exercise efficiency differs in men versus women, and whether increases in exercise capacity from several months of supervised exercise training would be associated with improvements in exercise efficiency."

Of the 61 healthy subjects recruited for this study, 15 were younger women aged 20 to 33 years, 12 were younger men aged 20 to 30 years, 16 were older women aged 65 to 79 years, and 18 were older men aged 65 to 77 years. All participants underwent cardiopulmonary exercise testing before and after 3 to 6 months of supervised aerobic exercise training.

Before training, younger subjects had a much higher exercise capacity than did older subjects, with 42% higher peak oxygen consumption (VO₂; mL/kg per minute; P < .0001), 11% lower work VO₂/W (P = .02), and 8% higher efficiency (P = .03). With training, older subjects had a larger increase in peak W/kg (+29% vs +12%; P = .001), a larger decrease in work VO₂/W (-24% vs -2%; P < .0001), and a greater improvement in exercise efficiency (+30% vs 2%; P < .0001) than did younger subjects.

"Older age is associated with a decreased exercise efficiency and an increase in the oxygen cost of exercise, which contribute to a decreased exercise capacity," the authors write. "These age-related changes are reversed with exercise training, which improves efficiency to a greater degree in the elderly than in the young."

Study limitations include adjustment of oxygen consumption and watts for weight but not for fat-free mass; possibly inaccurate reflection of the wide variability in how efficiently individual people exercise; lack of data on stroke volume, cardiac output, and biochemical or muscle biopsy data; and lack of subjects aged 30 to 65 years.

"Our findings suggest that the decline in aerobic capacity seen with older age is associated with a decreased exercise efficiency, an increased oxygen cost of exercise and O₂ debt, and slower recovery kinetics," the authors conclude. "Exercise training results in an improvement in these parameters, likely by inducing increased O₂ delivery through increased stroke volume and muscle capillarization, as well as improved O₂ utilization from an increase in mitochondrial enzyme activity.... Even with relatively low levels of exercise training, our subjects made significant improvements in efficiency, oxygen debt, and recovery VO₂/W that were even greater in the elderly subjects than in the young."

In an accompanying editorial, Edward G. Lakatta, MD, and Paul D. Chantler, PhD, from the National Institute on Aging in Baltimore, Md, note that metabolic debts associated with the performance of dynamic exercise increase with aging.

"The physiological significance of this metabolic debt incurred during exercise is that its underlying factors collectively reduce exercise capacity, with all the attendant health and performance drawbacks of such a reduction," Drs. Lakatta and Chantler write. "The good news is that all of these age-associated deficits can be substantially reduced by regular exercise (i.e., physical conditioning)!"

J Am Coll Cardiol. 2006;47:1049-1059