The influence of age, gender, and training on exercise efficiency.

OBJECTIVES: The aim of this study was to determine whether changes in oxygen efficiency occur with aging or exercise training in healthy young and older subjects.
BACKGROUND: Exercise capacity declines with age and improves with exercise training. Whether changes in oxygen efficiency, defined as the oxygen cost per unit work, contributes to the effects of aging or training has not yet been defined.
METHODS: Sixty-one healthy subjects were recruited into four groups of younger women (ages 20 to 33 years, n = 15), younger men (ages 20 to 30 years, n = 12), older women (ages 65 to 79 years, n = 16), and older men (ages 65 to 77 years, n = 18). All subjects underwent cardiopulmonary exercise testing to analyze aerobic parameters before and after three to six months of supervised aerobic exercise training.
RESULTS: Before training, younger subjects had a much higher exercise capacity, as shown by a 42% higher peak oxygen consumption (VO2) (ml/kg/min, p < 0.0001). This was associated with an 11% lower work VO2/W (p = 0.02) and an 8% higher efficiency than older subjects (p = 0.03). With training, older subjects displayed a larger increase in peak W/kg (+29% vs. +12%, p = 0.001), a larger decrease in work VO2/W (-24% vs. -2%, p < 0.0001), and a greater improvement in exercise efficiency (+30% vs. 2%, p < 0.0001) compared to the young.
CONCLUSIONS: 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. These age-related changes are reversed with exercise training, which improves efficiency to a greater degree in the elderly than in the young.