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).
I’m not even sure what to say here to explain the opposite outcome we expected for muscle fiber composition. A larger study group is definitely needed. I was gonna say it would have something to do when how long they were powerlifting, but the average was ten years.
The fact that there were less Type 2b fibers in experienced powerlifters is surprising. I just researched an article on ethnicity and muscle fiber types for the sports gene so I would make a statement that they should have included ethnicity in the study. Other than that I would guess that maybe the reason for this is that powerlifting workouts require more muscular endurance than the name suggests and that maybe the workouts performed by powerlifters actually do more for muscular endurance than muscular power or both. Type 2b fibers rely more on glycolytic pathways whereas type 2a fibers are geared more towards oxidative. This would lead me to believe that chronic adaptations to powerlifting affect oxidative pathways more than glycolytic.
This has also been observed with (olympic) weightlifters. Only super heavy lifters had plenty of 2B, supposedly because they had lots of fat. I heard this from person who worked in Andy Galpin’s lab in one of the Stronger by Science podcasts.
Seem that to be physically active and lean is to say good bye to 2B fibers. I don’t know if sprinters, throwers or jumpers display more 2B fibers (and how much that is due to genetic talent unhindered by training program and lean bodymass), but in the world of strength it surely seems that only way to have plenty of 2Bs is to be obese. But then again super heavies are not particularly powerful, they tend to lift less relative to their bodyweight compared to lighter weight classes so obsessing about 2Bs might be counterproductive.