When it comes to muscle fiber-types, you’ve got your fast-twitch for sprinting and slow-twitch for distance running performance, right? Well, not so fast. Researchers have recently published results online in the Journal of Applied Physiology that suggest it might not be so black and white, after all.
Looking at a group of highly trained distance runners, researchers at the Human Performance Laboratory at Ball State University in Indiana have found that long term endurance training may affect both slow- and fast-twitch muscle fibers. This, in turn, suggests fast-twitch fibers could play a role in long distance performance.
The researchers collected muscle biopsies from the gastrocnemius (calf) muscles of 8 male collegiate varsity cross country runners and 8 (4 male, 4 female) recreationally active controls to study the contractile properties of the muscle fibers at the cellular level. By looking at samples taken from highly trained athletes, they hoped to learn more about the effects of long term training on both slow- and fast-twitch fibers that could lend insights into athletic performance.
In the study, they found that the muscle diameters of both fast- and slow- twitch muscle fibers and the contraction velocity of both muscle fiber types was greater in the endurance runners than in the recreationally active control group. These two factors led to greater power in both types of muscle fibers in the cross country runners.
The results suggest that it is not only slow-twitch muscle fibers that respond to endurance training, but also fast-twitch fibers normally associated with sprinting. In their discussion, the authors wonder if this enhancement of fast-twitch fibers then contributes to high running performance in trained distance athletes. So, when it comes to muscle function, it could be more complex than just slow-twitch for the long haul and fast-twitch for short bursts of speed.
Photo credit: Brian Sawyer
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