In comparing a well-trained male subject and an untrained female subject as well

Question

In comparing a well-trained male subject and an untrained female subject as well as using the information given in the following table how did the resting metabolic rate (RMR) and exercise energy expenditure values compare in the two subjects? Discuss the physiological factors that might explain inter-subject differences in energy expenditure



Male

Time (min)        RER    Energy Expenditure (kcal/min)


Rest
1
2
3                     0.72                  3.48

Exercise
1                     0.75                      6.35
2                     0.75                      10.99
3                     0.80      11.38
4                     0.85                      10.99
5                     0.86                      11.75
6                     0.86                      11.85
7                     0.83                      11.22
8                     0.87                      12.12

Female

Time (min)        RER        Energy Expenditure (kcal/min)


Rest
1
2
3                     0.79                      3.54

Exercise
1                     0.73                      6.32
2                     0.96                      11.60
3                     1.00                      11.96
4                     0.99                      11.38
5                     0.99                      12.13
6                     0.96                      12.15
7                     0.96                      11.60
8                     0.95                      12.36

Explanation / Answer

physiological factors The major factor determining basal metabolic rate (BMR) is fat-free mass (FFM) (1–3), with some studies finding an additional contribution of fat mass (FM) (4, 5), but others failing to find such an effect (6, 7). Even when these factors are known, however, substantial residual variation remains. Understanding the physiologic nature of this variability is important because it has been implicated in the obesity epidemic in 2 separate ways. First, low BMR (after mass effects are removed) may be a predisposing risk factor for the development of obesity (8–10), and cross-sectional studies often report that formerly obese subjects have BMRs that are 3–5% lower than expected (11). However, although some long-term studies have indicated that variation in BMR is associated with subsequent weight gain (12), other longitudinal studies have failed to replicate this effect (13, 14). Second, BMR may show an adaptive response to caloric restriction, which may predispose individuals to subsequent weight regain. Many studies have called into question whether such changes reflect metabolic adaptation or simply disproportional losses of metabolically active FFM (15–18). Whatever the role of variations in BMR in the etiology of obesity, or the responses to caloric restriction, it is the largest component of the daily energy budget in westernized societies (19, 20). As such, manipulating BMR may provide a route toward treatment or prevention of obesity. A primary conclusion of The International Dietary Energy Consultancy Group workshop on energy and protein requirements in 1994 (20) was that "There is a need to investigate the causes of the relatively large inter-individual variations in BMR." Despite this need being identified a decade ago, however, little progress has been made. Leptin is an adipokine produced predominantly by adipose tissue (21). The role of leptin as a signaling molecule indicating the level of body fatness or historical levels of energy balance is well established (22, 23). Despite the broad correlation between body fatness and circulating leptin concentrations, this relation shows tremendous individual variability (24, 25), which may drive individual differences in residual BMR. Previous studies addressing the relation between circulating leptin and BMR have, however, produced confused results, with some studies finding positive associations (26–28), but others finding negative (29, 30) or no significant association (31–34). Some of these differences may reflect problems accounting for the confounding effects of FM on both BMR and leptin concentrations (35).

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