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Clark Cotton


Skeletal muscle phenotypes can change based on individual training and diet. Expression of fast twitch, glycolytic muscle fibers (type IIB) fibers, can be upregulated through fast paced, explosive movements. Expression of slow twitch, oxidative muscle fibers (type I) fibers, can be upregulated by low intensity endurance training. In addition to low intensity, endurance training, studies have suggested that a high fat diet can also prompt upregulation of oxidative muscle type I fibers (Hoppeler et al. 2011). In this study we aim to see whether or not the combination of a high fat diet and endurance exercise would increase expression of more slow twitch, oxidative fiber types with longer contraction and relaxation times combined with increased fatigue resistance. We started with 21 mice broken into three groups: A control group (normal diet / no exercise), high fat group (high fat diet / no exercise), and an exercise group (high fat diet / exercise). After thirty days on the specified diet and exercise regimens, we measured twitch contraction strength, contraction time, relaxation time, and fatigue time using isolated tibialis anterior muscles. . We found that mean mean contraction time was significantly higher for mice in the exercise group when compared to the control group. Although not significant, we also found changes in mean relaxation times consistent with an increase in more slow, oxidative fiber types. We did not observe any changes in contraction strength or fatigue resistance. Future studies using more sophisticated in vitro techniques combined with muscle fiber typing may more accurately reveal the potential effects of a high fat, endurance training regimen on expressed muscle fiber-type.