Genetic differences govern the elite levels of athletic performance. However, it is also evident that no matter your level of competition – from local high school athlete to professional all-star– speed endurance training can be significantly improved by following a consistent training plan.
Fascinating new research has found that with speed endurance training and reduced training volume, it is possible to adapt “fast-twitch” muscle fibers as “slow-twitch.”
Speed endurance training effect
Researchers found that speed endurance training improves running economy by 2% in normal conditions and 3.2% in a muscle glycogen-depleted condition.
In the muscle glycogen-depleted condition, 10km performance is improved by 3.9%. VO2max is the same after and before the intervention, but vVO2max is 2% higher after than before. As a result, muscle fibers’ adaptation is related to energy-consuming processes in primarily ST muscle fibers.
It is interesting to note that the VO2max was the same after and before the intervention, but vVO2max was 2% higher after than before. This may indicate that this training improved running economy by increasing it at greater speeds than measured in the 10km test.
Plasticity of muscle fibers
According to a review of muscle fiber plasticity, The two primary types of muscle fibers, Type I (slow-twitch) and Type II (fast-twitch), are shown to have different rates of growth, regeneration, and fatigue.
Type II fibers are broken down to a greater degree after a workout, which may increase fatigue. At the same time, anaerobic exercise can also decrease mitochondrial density and function in Type II fibers.