NEW YORK (Reuters Health) - When normal couch potatoes return from engaging in a little gardening, walking or some other physical activity, they may think that they have exerted more energy than they actually have, new study results suggest.

``Sedentary adults, who are unaccustomed to exerting themselves on a regular basis, tend to overestimate the intensity of their physical activities when they are asked to recall them,'' lead study author Dr. Glen E. Duncan, of the University of Florida, in Gainesville, told Reuters Health.

``This is important because the amount of energy expended in physical activity is related to overall mortality from cardiovascular disease,'' he said.

To investigate, Duncan and his colleagues studied 94 men and women who were enrolled in a 2-year exercise intervention. All of the subjects were healthy but most were moderately overweight and unfit.

The participants were asked to recall and to log the amount of time they spent sleeping and performing various activities--exercise, work-related activities, etc.--during the previous 7 days. Their recollection and log was then compared with the actual intensity and duration of their activity, as measured by heart rate monitors.

Forty-one percent of the subjects recalled engaging in moderate activity for at least 10 minutes, 3% said they had engaged in hard activity and 1.5% said they had engaged in very hard activity, the authors report in the July issue of the journal Preventive Medicine. According to their logs, 47%, 11% and 1.5% of the subjects spent at least 10 minutes in moderate, hard, and very hard activity, respectively.

Yet, heart rate monitor measurements revealed that only 15% of the individuals had engaged in moderate activity, 1.5% in hard activity, and none of the subjects had engaged in very hard activity, the report indicates.

The authors acknowledge, however, that unfit individuals may rate certain activities as more intense than fit individuals, and may generally have a more difficult time rating the intensity of activities since they are unaccustomed to regular physical exertion.

Further, the traditional scale used to measure vigorous activity may be inappropriate for sedentary adults, the researchers note.

``Our data support the notion that most sedentary middle-aged adults are not able to perform vigorous physical activities as defined by traditional means,'' they write.

In light of these findings, ``studies that use recall questionnaires to determine the intensity level at which sedentary adults perform their physical activity probably overestimate the actual intensity level,'' Duncan said

Duncan's study was supported by a grant from the National Heart, Lung, and Blood Institute.

SOURCE: Preventive Medicine 2001;33:18-26.

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