Training decreases muscle glycogen turnover during exercise

Abstract

The present study was undertaken to determine the effects of endurance training on glycogen kinetics during exercise. A new model describing glycogen kinetics was applied to quantitate the rates of synthesis and degradation of glycogen. Trained and untrained rats were infused with a 25% glucose solution with 6-3H-glucose and U-14C-lactate at 1.5 and 0.5 microCi x min(-1) (where 1 Ci=3.7 x 10(10) Bq), respectively, during rest (30 min) and exercise (60 min). Blood samples were taken at 10-min intervals starting just prior to isotopic infusion, until the cessation of exercise. Tissues harvested after the cessation of exercise were muscle (soleus, deep, and superficial vastus lateralis, gastrocnemius), liver, and heart. Tissue glycogen was quantitated and analyzed for incorporation of 3H and 14C via liquid scintillation counting. There were no net decreases in muscle glycogen concentration from trained rats, whereas muscle glycogen concentration decreased to as much as 64% (P < 0.05) in soleus in muscles from untrained rats after exercise. Liver glycogen decreased in both trained (30%) and untrained (40%) rats. Glycogen specific activity increased in all tissues after exercise indicating isotope incorporation and, thus, glycogen synthesis during exercise. There were no differences in muscle glycogen synthesis rates between trained and untrained rats after exercise. However, training decreased muscle glycogen degradation rates in total muscle (i.e., the sum of the degradation rates of all of the muscles sampled) tenfold (P < 0.05). We have applied a model to describe glycogen kinetics in relation to glucose and lactate metabolism during exercise in trained and untrained rats. Training significantly decreases muscle glycogen degradation rates during exercise.

Glycogen storage and muscle glucose transporters (GLUT-4) of mice selectively bred for high voluntary wheel running

“…Even when faced with an exogenous glucose infusion [final concentration 25% (w/w)], both trained and untrained rats experience significant hepatic glycogenolysis during exercise (Azevedo et al, 1998). In our study, although all three phenotypes showed a net glycogenesis in liver from 16:00 h to 07:00 h (Table 2), there was a negative relationship between the number of revolutions at 02:00 h and glycogen concentration in liver (Fig.…”

“…Moreover, the observed increase in [glycogen] from 16:00 h to 07:00 h (particularly evident for liver of all mice, for gastrocnemius of HR normal and for soleus of HR mini; Table 2) implies that a net glycogen deposition occurs concomitantly with the period of active wheel running in these mice. Although the classic theory of glycogen metabolism is that complete activation of glycogen phosphorylase through phosphorylation is coupled with the complete inactivation of glycogen synthase (Stryer, 1995), several studies of glycogen kinetics in vivo have shown that simultaneous glycogen synthesis and degradation occurs both in liver and muscle during exercise in rats (Constable et al, 1984;David et al, 1990;Azevedo et al, 1998) and humans (Magnusson et al, 1994;Price et al, 1994).…”

Effects of macamides on endurance capacity and anti-fatigue property in prolonged swimming mice

“…Increase in glycogen consumption has been related to elevated fatigue (Ren et al 2011). By contrast, increase in fatty acid metabolism during exercise, leads to a decreased glycogen depletion rate and enhanced endurance exercise performance (Azevedo et al 1998;Favier & Koubi 1988). The enhanced availability of free fatty acids is thought to cause greater fat mobilisation in the active muscles (Oh & Ohta 2003).…”

Effects of Astaxanthin Supplementation on Exercise-Induced Fatigue in Mice

“…15) Therefore, increased fatty acid utilization is thought to be important for endurance performance. These increases are associated with enhanced lipolysis and sparing of stored glycogen, resulting in a delay of complete glycogen depletion by increasing circulating catecholamines.…”