Very little research has investigated the effects of ultra-endurance exercise on the bioenergetic status of muscle. The primary objective of this case study was to characterize the changes that occur in skeletal muscle mitochondria in response to a 100-km ultramarathon in monozygotic twins. A second objective was to determine whether mitochondrial function is altered by consuming a periodized low-carbohydrate, high-fat diet (LCHFD) during training compared to a high-carbohydrate diet.
One pair of male monozygotic twins ran 100 km on treadmills following 4 weeks of training on either a high carbohydrate or periodized LCHFD. Muscle biopsies were collected 4 weeks prior to the run, as well as 4- and 52-hours post-run. Blood draws were also performed immediately before, as well as 4- and 52-hours post-run.
Four hours post-run, respiratory capacity, citrate synthase activity and mitochondrial complex protein content were decreased. Two days later, both twins showed signs of rapid recovery in several of these measures. Furthermore, blood levels of creatine phosphokinase, C-reactive protein, and aspartate transaminase were elevated 4 hours after the run, but partially recovered two days later.
Although there were some differences between the twins, the primary finding is that there is significant mitochondrial impairment induced by running 100 km, which rapidly recovers within 2 days. These results provide ample rationale for future investigations of the effects of ultra-endurance activity on mitochondrial function.

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