Science on the Run
Linking current research to running
By Nikki Reiter
Runners have long been admired for their well-sculpted calves, which is perhaps why a group of researchers from James Madison University investigated the effect of marathon training on the calf musculature of recreational runners. All fun aside, they found that running really can modify the architecture of the calf muscle.
Two leg muscles highly involved in running were investigated (see picture). The lateral gastrocnemius (LG) is a very powerful, mainly fast-twitch muscle involved in the push-off of the running stride. The vastus lateralis (VL) is one of the quadriceps muscles of the thigh, and works to extend (straighten) the leg when bent and provide knee stability.
The variables of interest were muscle fibre length, thickness and pennation angle. Pennation angle refers to the orientation of the muscle fibers that dictate how much force is required to contract a muscle.
Here’s how it went. A 12-week marathon-training program was administered to 16 recreational runners. Running was at a self-selected pace and weekly volume was increased from 24 km to approximately 60 km over four runs per week, including a long run of 29 km by week 12. LG and VL muscle fibre length and pennation angles were measured using ultrasonography at rest, both at the start and end of the training program. The researchers did not measure changes during running, as this would be highly difficult given the laboratory equipment used.
The result? After the training program, big changes were discovered for the LG, but not the VL. While no increase in LG thickness was found, LG muscle fibre length decreased 10%, while the pennation angle increased 17%.
What does this mean? Well, a reduced fascicle length requires less energy for contraction, and also results in an overall greater mechanical stiffness of the muscle relative to the Achilles tendon, which may play into energy storage capabilities and resulting increases in running efficiency. Although statistically non-significant, running economy increased by 3% in this study, which supports this idea. Increased pennation angle allows for the muscle to work ‘less hard’ to achieve its required force production for distance running.
A final comment: Calf musculature is different in sprinters than in distance runners. The structure of a distance runner’s calves allows for more fatigue-resistance when running and uses less energy for force production. However, what they makeup for in endurance, they lack in power. The way the muscle fibres orient themselves is reflective of these characteristics.
Nikki Reiter is the Laboratory Coordinator in the School of Health and Exercise Sciences at the University of British Columbia Okanagan in Kelowna, BC, Canada. With a master’s degree in Biomechanics and as a trained exercise physiologist, she ensures students are taking the scientific approach to training through their lab experiences. Additionally, Nikki offers online gait analysis through Run Right Gait Analysis. Visit her website www.run-right.ca for more information.