The Effects of Obesity on Skeletal Muscle Contractile FunctionMonday, July 16, 2018
Given that obesity has profound effects on all organ systems, it is not surprising that excess body fat is also associated with a decrease in muscle function.
The complex biology of the molecular, structural, and functional changes that have been associated with obesity are now extensively discussed in a review article by James Tallin and colleagues, published in the Journal of Experimental Biology.
Without going into the molecular details here, suffice it to say that there is considerable evidence to show and explain why muscular function is impaired in both animal models and humans with excess body fat. (For e.g. at a cellular level, the dominant effects of obesity are disrupted calcium signalling and 5′-adenosine monophosphate-activated protein kinase (AMPK) activity. As a result, there is a shift from slow to fast muscle fibre types. There is also evidence for an impairment in myogenesis resulting from disruption of muscle satellite cell activation. Furthermore, muscle function is affected by insulin resistance and decreased adiponectin levels generally associated with obesity).
Although individuals with obesity will often have a larger muscle mass and may well be stronger than “normal-weight” individuals, when corrected for the amount of extra muscle, it is evident that the muscles are less efficient.
In fact, many of the biochemical and structural changes that occur in obesity are very similar to those found with aging. Not surprisingly, when aging meets obesity, things get even worse.
Although the paper does not discuss the reversibility of these changes with weight loss (or obesity treatment in general), I am aware of other data showing that much of the loss of muscle contractile function associated with obesity can be reversed with weight loss.
A clinical correlate of this is the fact that, following weight loss, individuals often find that it takes far more exercise to burn the same number of calories than before (this is not just because the person is now carrying less weight).
Given the increased recognition that lean body mass is an important determinant of overall health and function, clearly this topic is of continuing interest.