The Effects of Detraining on Muscle Mitochondria and Performance in Mice

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Periods of training cessation (i.e. detraining), commonly occur during illness, injury, or travel. While it is well established that detraining can lead to a decline in mitochondrial capacity and subsequent endurance performance little is know about the timing of these events in mice. PURPOSE: The purpose of this study was to determine the effects of various periods of detraining on the decline in mitochondrial and performance related training adaptations in mice. METHODS: Male CD-1 mice were randomly assigned to either an untrained (UT) control group or a detraining time-point (0wks, 2wks, or 4wks). Prior to beginning the assigned detraining period, all mice completed 8wks of treadmill running (6 d/wk, 1hr/d at 25m/min and 5% grade). At each detraining time point mice performed a treadmill run to fatigue (RTF) test at 25m/min and 5% grade. Fatigue was recorded as the time at which the mouse could no longer keep pace with the treadmill despite one minute of continuous hand prodding. Additional mice were sacrificed at each detraining time point and the soleus (sol) muscle, and heart was harvested. Heart and body weight ((HW), (BW)) was measured and the sol was analyzed for gene expression (mRNA) of PGC-1alpha and mitochondrial DNA (mtDNA) using RT-PCR. Data was analyzed using a one-way ANOVA with significance set at P<0.05. RESULTS: HW expressed as a percentage of BW, was significantly greater at the end of training (0 wks) and at 2 wks and 4 wks of detraining, compared with UT mice (P<0.05). At 0 wk mice ran significantly longer than UT mice in the RTF test (P<0.05), however these training effects were lost following 2wks and 4wks of detraining. Expression of PGC-1alpha and mtDNA in the sol was elevated at 0wks and 2wks of detraining and had declined to UT values by 4wks. CONCLUSIONS: These results show that training cessation causes a rapid decline in mitochondrial related training adaptations in mice that is associated with decreased endurance performance. These findings illuminate the need for determining strategies, either nutritionally or physically, to prevent these effects during unavoidable breaks in training. Supported by a Student grant from ACSM.