Subjective Estimates of Exercise Ability: Comparison to Objective Measurements

Although not well validated, physicians frequently use subjective estimates of exercise ability to assess clinical status and therapeutic results. This study employed a standardized questionnaire and cardiopulmonary exercise test to compare the results of subjective estimates by 211 patients (mean age 13.9 yrs) with objective measurements of exercise ability. Questionnaire data correlated with measured maximal oxygen consumption. Individuals thought to be below average had a maximal oxygen consumption of 21±6 ml/kg/min. Those thought to have average fitness had a maximal oxygen consumption of 26±8 ml/kg/min, and those thought to be above average had a maximal oxygen consumption of 30±7 ml/kg/min. There was a great degree of overlap and scatter of these data, however, such that questionnaire data significantly overestimated exercise ability in 67% and underestimated it in 3% of the subjects. In only 30% of the subjects did the subjective estimate of exercise ability correspond with objectively measured exercise ability. It was concluded that subjective estimates are unreliable and should not be used in assessing the functional status of an individual patient, but subjective estimates may give some idea of objective capabilities in large population studies.