Relationship between total energy expenditure and physical activity

The measurements of TEE described above indicate that the measured TEE/pREE of the groups of subjects studied (mean ages 64-74 years) was higher than the current recommended value for the age group > 50 years. This may indicate that current recommendations for energy (FAO/WHO/UNU, 1985) underestimate the usual energy need of older adults. However, it is alternatively possible that the physical activity of the subjects in those studies was unusually high. The lack of standardization in reporting of physical activity hampers an assessment of this issue. Concerning the studies conducted in our own laboratory, the mean values for self-reported durations of strenuous activity were 29 and 48 min/day for men and women, respectively (Roberts et al, 1992; Sawaya et al, 1995). These values included means of 4 and 7 min/day, respectively, for activities with predicted energy expenditure of >5 × REE. Thus, these groups of subjects did not appear to be unusually active, indicating that the 1985 recommendations on energy requirements may indeed be lower than usual energy needs. However, further research is needed to confirm this suggestion. In the study of Reilly et al (1993), a mean duration of leisure time activity of 40 min/day was reported together with 87 min/day of walking. These mean activity data appear relatively high, in keeping with the high mean PAL index in this group (aTEE/pREE = 1.84).

Another factor to consider in the determination of recommended energy requirements for older individuals is the issue of normal vs desirable levels of physical activity. Physical activity is the major determinant of variability in TEE/PEE between individuals and can potentially have a major effect on energy requirements. Figure 1 illustrates the relationship between strenuous physical activity (defined as the sub-set of self-reported strenuous activity with an expected mean energy cost of >5 × REE) and TEE/pREE (equal to aTEE/pREE) in our population of older men. It can be seen that, as expected, high levels of reported strenuous activity were associated with increased TEE/pREE. Individuals who reported no strenuous physical activity had a mean value for TEE/pREE of 1.70 while those who reported 30 min/day of strenuous physical activity had a mean TEE/PEE ratio of 1.90. Although it is widely accepted that a sedentary existence is associated with increased morbidity and mortality (Paffenbarger et al, 1986; Blair et al, 1989; Helmrich et al, 1991; Paffenbarger et al, 1993), there is no general consensus over what levels and types of physical activity are optimal for long-term health (Paffenbarger et al, 1986; Blair et al, 1989; Helmrich et al, 1991; Paffenbarger et al, 1993). For this reason, it is appropriate to continue to make recommendations for different levels of physical activity, and also to recommend a minimum activity level that makes allowance for some strenuous physical activity for cardiovascular maintenance.