A study recently published (2019) in PLOS ONE, conducted by Serrano et al, examined the muscle phenotype of twenty-one World/Olympic and National-caliber weightlifters. The researchers aimed to establish an understanding of the
UNDERSTANDING FIBER TYPES
A quick and dirty explanation of muscle
Three fiber types exist, each one expressing a single isoform (MHC l, lla, llx) and several hybrids, expressing a combination of isoforms. This creates a continuum of speeds, from slow to fast, with each fiber type displaying different metabolic, morphologic, and contractile properties. The relative quantity of each fiber type in a given muscle is often highly correlated with performance.
The sample for this study included six World/Olympic-caliber females, nine national-calibre females, and six national-calibre men. The athletes were considered “World-caliber” if they had competed on the most recent Olympic or World team and at the most recent national event. Athletes were considered National-caliber if they had competed at the 2017 American Open Finals and placed top five but were never on an Olympic or World team. Participants held over twenty-five national records and had earned more than 170 national/international medals at the time of the study. The table below gives descriptive information of the athletes, including age, body mass, years competing, snatch relative 1RM, and clean and jerk relative 1RM. Relative 1RM here refers to the lift divided by the athlete’s body mass
A muscle biopsy of the vastus lateralis (quadricep muscle) was completed, the tissue samples were gathered, and two distinct fiber type techniques were used to differentiate the fibers: homogenate composition and single fiber distribution. For single fiber, individual fibers were mechanically separated under a light microscope. This approach is the most accurate for calculating fiber type % in a muscle sample. For homogenate, the samples were hand homogenized and diluted. This approach allows the researcher to quantify the percent area occupied by each fiber type.
“Thus, SF indicates how frequently each isoform exists but cannot address how much area each FT occupies within the muscle. HG addresses the latter, but cannot delineate hybrids, therefore inaccurately quantifying FT%.” (p 4)
How should these results shape our training? Well, it really should not. The authors concluded that fiber type % is more influenced by years competing/training and athlete caliber rather than sex, seeing as there was no difference between male and females when looking at number of fast-twitch muscle fibers. The training that produces great weightlifters tends to also produce a particular muscle phenotype, at least in the quadriceps. Body mass also influences distribution of fiber types within a muscle, showing variations in the number of MHC lla/llx fibers between bodyweight categories, expressing a correlation supported by other research. I guess where we go from here is back to the lab. More participants and more biopsies would help us understand the differences between sports and fiber type %, teasing out the influences of training styles and, subsequently, varied adaptations.
Pette, D., & Staron, R. S. (2000). Myosin isoforms, muscle fiber types, and transitions. Microscopy Research and Technique, 50(6), 500–509.
Serrano N, Colenso-Semple LM, Lazauskus KK, Siu JW, Bagley JR, Lockie RG, et al. (2019). Extraordinary fast-twitch fiber abundance in elite weightlifters. PLoS ONE, 14(3): e0207975.