Fiber-specific responses of muscle glycogen repletion in fasted rats physically active during recovery from high-intensity physical exertion

Abstract

Mild physical activity performed immediately after a bout of intense exercise in fasting humans results in net glycogen breakdown in their slow oxidative (SO) muscle fibers and glycogen repletion in their fast twitch (FT) fibers. Because several animal species carry a low proportion of SO fibers, it is unclear whether they can also replenish glycogen in their FT fibers under these conditions. Given that most skeletal muscles in rats are poor in SO fibers (<5%), this issue was examined using groups of 24-h fasted Wistar rats (n=10) that swam for 3 min at high intensity with a 10% weight followed by either a 60-min rest (passive recovery, PR) or a 30-min swim with a 0.5% weight (active recovery, AR) preceding a 30-min rest. The 3-min sprint caused 61-79% glycogen fall across the muscles examined, but not in the soleus (SOL). Glycogen repletion during AR without food was similar to PR in the white gastrocnemius (WG), where glycogen increased by 71%, and less than PR in both the red and mixed gastrocnemius (RG, MG). Glycogen fell by 26% during AR in the SOL. Following AR, glycogen increased by 36%, 87%, and 37% in the SOL, RG, and MG, respectively, and this was accompanied by the sustained activation of glycogen synthase and inhibition of glycogen phosphorylase in the RG and MG. These results suggest that mammals with a low proportion of SO fibers can also replenish the glycogen stores of their FT fibers under extreme conditions combining physical activity and fasting.

Effect of Yeast-Derived Peptides on Skeletal Muscle Function and Exercise-Induced Fatigue in C2C12 Myotube Cells and ICR Mice

“…In addition, the composition of muscle fibers is closely correlated with glycogen stores and fast-twitch fibers are abundant in glycogen content. 50 However, the regulatory effects of YPLP on fasttwitch fibers in vitro were not positively correlated with the regulatory effects on glycogen content in vivo in the current study. This is probably because the composition of skeletal muscle fibers is various in different parts of the muscle tissue in vivo.…”

“…Calbet and MacLean reported that active peptides could also stimulate the secretion of insulin, promoting the generation of glycogen. In addition, the composition of muscle fibers is closely correlated with glycogen stores and fast-twitch fibers are abundant in glycogen content . However, the regulatory effects of YPLP on fast-twitch fibers in vitro were not positively correlated with the regulatory effects on glycogen content in vivo in the current study.…”

Progresses of the Past Decade on Factors Contributing to Skeletal Muscle Glycogen Synthase Regulation

“…One determinant of GS activity is the existing amount of glycogen within the muscle as well as muscle fiber type [77,78]. As demonstrated in rodents, low glycogen content was associated with decrease in GS phosphorylation and high glycogen content was associated with decrease in GS activation [79][80][81].…”

Respostas fisiológicas e moleculares de três modelos de treinamento de corrida com cargas equiparadas em ratos Wistar

“…Conforme relatado anteriormente, os estoques de glicogênio muscular desempenham papel importante no aporte energético durante uma sessão aguda de exercício de alta intensidade (Raja et al, 2008). Sendo assim, a recuperação dos estoques depletados durante um exercício ocorre, sobre condições favoráveis, preferencialmente em fibras de contração rápida (Raja et al, 2008).…”

“…Conforme relatado anteriormente, os estoques de glicogênio muscular desempenham papel importante no aporte energético durante uma sessão aguda de exercício de alta intensidade (Raja et al, 2008). Sendo assim, a recuperação dos estoques depletados durante um exercício ocorre, sobre condições favoráveis, preferencialmente em fibras de contração rápida (Raja et al, 2008). E, como mostrado por Sano et al (2012) uma sessão aguda de natação de alta intensidade e curta duração (8 x 20 segundos; 18% do peso corporal), em condições favoráveis de consumo de carboidrato, causa a supercompensação do glicogênio de forma similar ao que ocorre com um exercício de alto volume (3 horas sem carga adicional).…”