More Muscle Means Less Fat

More Muscle Equals Lower Intramuscular Fat

In a previous article posted titled, “Weight Training Beats Cardio for Reducing Belly Fat in Older Adults”, researchers reported that when activity levels over a 12-year period was examined in older men, those who increased the amount of time spent in weight training by 20 minutes a day had less gain in their waistline (-0.67 cm) compared with men who similarly increased the amount of time they spent on moderate-to-vigorous aerobic exercise (-0.33 cm), and yard work or stair climbing (-0.16 cm). The researchers found that resistance training was associated with a lower waist circumference in a cohort of male health professionals with a mean age of 55 years. This means that weight training was associated with lower body fat compared to aerobic training.

New research published in the European Journal of Applied Physiology has reported that more muscle is associated with less intramuscular fat. So not only does resistance exercise lower fat in the abdominal area, but it also lowers fat in the skeletal muscle. We once thought that fat was just this empty slap of fat, but we now know that fat is very active. Once thought to be an inert storage depot for excess calories, important only to energy homeostasis, we now know that adipose tissue expresses and secretes a multitude of hormones and pro-inflammatory cytokines thereby acting in an autocrine, paracrine, and endocrine manner signaling the heart, musculoskeletal, central nervous, and metabolic systems. Skeletal muscles of older individuals have a larger amount of intramuscular adipose tissue than those of younger individuals. Intramuscular fat (or Intramuscular triglycerides) is located throughout skeletal muscle. If you have ever looked at a slap of beef and found that white marbling in between the red meat, that’s intramuscular fat. Furthermore, older adults with increased Intramuscular fat levels in their muscles are known to experience increased levels of muscle weakness, decreased mobility function, and are at increased risk of diabetes and insulin resistance. It is not understood how aging affects the intramuscular adipose tissue content of individual muscles of the thigh. Researchers examined the relationship between intramuscular adipose tissue content and skeletal muscle, biochemical blood profiles, and physical activity. At the end of the study, intramuscular adipose tissue content in quadriceps, hamstrings, and adductor for the older group was significantly higher than in the younger group, but the interesting finding was that the more muscle a person had, the less intramuscular fat the person had in muscle.

Fifteen older and 15 younger men and women participated in this study. Magnetic resonance imaging of the right thigh was taken to measure intramuscular adipose tissue content and skeletal muscle for the legs and subcutaneous adipose tissue cross sectional area of the thigh. At the end of the study, intramuscular adipose tissue content in quadriceps, hamstrings, and adductor for the older group was significantly higher than in the younger group, but the interesting finding was that the more muscle a person had, the less intramuscular fat the person had in muscle. So basically, the older men had less muscle than the younger men. These results suggest that skeletal muscle size could be a major determinant of intramuscular adipose tissue content regardless of age.

Here is another study showing the benefits of resistance training for older adults. Increased intramuscular fat in older adults is associated with increased levels of muscle weakness, decreased mobility function, and are at increased risk of diabetes and insulin resistance. More muscle is associated with lower intramuscular fats, so the study points to the benefits of resistance exercise for lowering intramuscular fat.

Akima H, Yoshiko A, Hioki M, Kanehira N, Shimaoka K, Koike T, Sakakibara H, Oshida Y. Skeletal muscle size is a major predictor of intramuscular fat content regardless of age. Eur J Appl Physiol. 2015Aug;115(8):1627-35.

M. Visser, B. H. Goodpaster, S. B. Kritchevsky et al., “Muscle mass, muscle strength, and muscle fat infiltration as predictors of incident mobility limitations in well-functioning older persons,” Journals of Gerontology A, vol. 60, no. 3, pp. 324–333, 2005.

L. J. Tuttle, D. R. Sinacore, and M. J. Mueller, “Intermuscular adipose tissue is muscle specific and associated with poor functional performance,” Journal of Aging Research, vol. 2012.