Yesterday, I came across a paper focusing specifically on power lifters and how their muscle fiber compositions compare to sedentary counterparts. The study took vastus lateralis biopsy samples from 5 competitive power lifters, and 5 sedentary participants. Muscle fiber compositions were determined using MTPase histochemical analysis. Interestingly, it was found that sedentary participants expressed 12% type 2B fibers, while power lifters expressed an 11-percent decrease to 1% type 2B. Conversely, power lifters expressed 45% type 2A fibers compared to the sedentary group’s 33%.
Recently in class, I had the opportunity to present on another paper that studied the correlation between muscle fiber composition and obesity. The results found that there was a positive correlation between muscle type 2B fibers and BMI. Obese patients expressed 18% type 2B fibers, significantly more than their lean counterparts. The apparent increase in fiber type 2B expression in obese people compared to an apparent decrease in expression of type 2B in power lifters engenders questions as to the reasons behind the shifts.
This seems to communicate that the training, genetic make-up, or both of the competitive power lifters population appears to encourage more type 2A fast-twitch fibers compared to type 2B. The study was limited to groups of n=5, and would likely be greatly informed with an increased sample size. Additionally, a longitudinal study following the muscle fiber composition of individuals proceeding from novice to competitive power lifting could help isolate the effects of training of relative fiber type2A/B compositions.
References for further reading:
- Fry, A. C. et al. Muscle fiber characteristics of competitive power lifters. J. Strength Cond. Res. 17, 402–410 (2003).
- Tanner, C. J. et al. Muscle fiber type is associated with obesity and weight loss. Am. J. Physiol. Metab. 282, E1191–E1196 (2002).