Mitochondrial Gene Expression In Well Trained Cyclists: Effects Of Low Glycogen Levels

Abstract

It has recently been shown that markers for mitochondrial biogenesis can be promoted when endurance training is undertaken twice every second day compared with daily training. The mechanisms underlying this adaptation are not fully understood but low muscle glycogen levels have been suggested to enhance the signalling pathways involved in mitochondrial biogenesis. PURPOSE: To study the acute effects of low glycogen on the exercise-induced molecular signalling of mitochondrial biogenesis in well trained cyclists. METHODS: Ten well trained cyclists (VO2max 65 ± 1 mL kg-1 min-1, Wmax 387 ± 8 W) cycled for 60 min at ∼ 66 % of VO2max with either low (LG: 166 mmol kg-1 dw) or close to normal (NG: 478 mmol kg-1 dw) muscle glycogen levels. Muscle biopsies were taken before and 3 h after exercise. RESULTS: The mRNA of peroxisome proliferator-activated receptor-γ coactivator-1 (PGC-1α), the master regulator of mitochondrial biogenesis, was enhanced to a greater extent after LG compared with NG (810 % vs. 250 %, P < 0.001). The mRNA of Cytochrome C oxidase subunit I (COX-I) was increased by 30 % after LG but decreased with 10 % after NG (P < 0.01, LG vs. NG). The mRNA of mitochondrial transcription factor A (Tfam) increased to the same extent after LG and NG (50 %, P < 0.01). CONCLUSION: Exercise undertaken with low glycogen levels induce a stronger stimulus on genes involved in mitochondrial biogenesis than exercise with normal glycogen levels. A low glycogen training strategy might therefore be beneficial for improving muscle oxidative capacity in well trained individuals. This study was supported by The Swedish National Centre for Research in Sports.