The Concept of CMR

Physical activity and energy expenditure

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Regular physical activity is an excellent way to maintain a healthy body weight and a low-risk metabolic profile. There is a wealth of data proving that physical activity generates cardiovascular and metabolic benefits beyond what can be explained by related energy expenditure.

Regular physical activity can increase resting metabolic rate (RMR), which increases total daily energy expenditure. Sjodin et al. (6) measured the RMR of 8 athletes and compared it to sedentary individuals matched for sex and fat-free mass. They found that for any given amount of fat-free mass, the RMR of athletes was significantly higher than that of sedentary controls. Although the subject is still open to debate, it is generally believed that regular exercise/physical activity can help maintain energy expenditure by having a positive effect on lean body mass (mostly skeletal muscle) (7). Physical activity also regulates key enzymes involved in energy metabolism. For example, it has been shown that exercise decreases β-adrenoreceptors in the heart while increasing these receptors in skeletal muscle (8). Physical activity also tends to increase post-exercise β-adrenergic stimulation, thereby increasing energy expenditure by boosting lipid oxidation (9). Moreover, by improving insulin sensitivity, exercise also lowers plasma insulin and glucose levels (10). Lipoprotein lipase (LPL) is a key enzyme involved in the lipoprotein-lipid metabolism that regulates fat storage in adipose tissue (11). Exercise reduces LPL activity in adipose tissue but activates LPL activity in skeletal muscle, helping it oxidize more fuel (12). Exercise also has an impact on LPL response to insulin. For instance, trained athletes are known to have heightened adipose tissue LPL response, which allows them to efficiently replenish adipose tissue lipid stores between exercise bouts (13).

Reference

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6. Sjodin AM, Forslund AH, Westerterp KR, et al. The influence of physical activity on BMR. Med Sci Sports Exerc 1996; 28: 85-91.

7. Speakman JR and Selman C. Physical activity and resting metabolic rate. Proc Nutr Soc 2003; 62: 621-34.

8. Pouliot MC, Després JP, Lemieux S, et al. Waist circumference and abdominal sagittal diameter: best simple anthropometric indexes of abdominal visceral adipose tissue accumulation and related cardiovascular risk in men and women. Am J Cardiol 1994; 73: 460-8.

9. Yoshioka M, Doucet E, St-Pierre S, et al. Impact of high-intensity exercise on energy expenditure, lipid oxidation and body fatness. Int J Obes Relat Metab Disord 2001; 25: 332-9.

10. Bjorntorp P, De Jounge K, Sjostrom L, et al. The effect of physical training on insulin production in obesity. Metabolism 1970; 19: 631-8.

11. Eckel RH. Lipoprotein lipase. A multifunctional enzyme relevant to common metabolic diseases. N Engl J Med 1989; 320: 1060-8.

12. Ladu MJ, Kapsas H and Palmer WK. Regulation of lipoprotein lipase in muscle and adipose tissue during exercise. J Appl Physiol 1991; 71: 404-9.

13. Mauriège P, Prud'homme D, Marcotte M, et al. Regional differences in adipose tissue metabolism between sedentary and endurance-trained women. Am J Physiol 1997; 273: E497-506.

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