Low muscle glycogen concentration does not suppress the anabolic response to resistance exercise

We determined the effect of muscle glycogen concentration and postexercise nutrition on anabolic signaling and rates of myofibrillar protein synthesis after resistance exercise (REX). Sixteen young, healthy men matched for age, body mass, peak oxygen uptake (Vo(2peak)) and strength (one repetition maximum; 1RM) were randomly assigned to either a nutrient or placebo group. After 48 h diet and exercise control, subjects undertook a glycogen-depletion protocol consisting of one-leg cycling to fatigue (LOW), whereas the other leg rested (NORM). The next morning following an overnight fast, a primed, constant infusion of l-[ring-(13)C(6)] phenylalanine was commenced and subjects completed 8 sets of 5 unilateral leg press repetitions at 80% 1RM. Immediately after REX and 2 h later, subjects consumed a 500 ml bolus of a protein/CHO (20 g whey + 40 g maltodextrin) or placebo beverage. Muscle biopsies from the vastus lateralis of both legs were taken at rest and 1 and 4 h after REX. Muscle glycogen concentration was higher in the NORM than LOW at all time points in both nutrient and placebo groups (P < 0.05). Postexercise Akt-p70S6K-rpS6 phosphorylation increased in both groups with no differences between legs (P < 0.05). mTOR(Ser2448) phosphorylation in placebo increased 1 h after exercise in NORM (P < 0.05), whereas mTOR increased ~4-fold in LOW (P < 0.01) and ~11 fold in NORM with nutrient (P < 0.01; different between legs P < 0.05). Post-exercise rates of MPS were not different between NORM and LOW in nutrient (0.070 ± 0.022 vs. 0.068 ± 0.018 %/h) or placebo (0.045 ± 0.021 vs. 0.049 ± 0.017 %/h). We conclude that commencing high-intensity REX with low muscle glycogen availability does not compromise the anabolic signal and subsequent rates of MPS, at least during the early (4 h) postexercise recovery period.

Early time course of Akt phosphorylation after endurance and resistance exercise

PURPOSE

The aim of this study was to determine the early time course of exercise-induced signaling after divergent contractile activity associated with resistance and endurance exercise.

METHODS

Sixteen male subjects were randomly assigned to either a cycling (CYC; n = 8, 60 min, 70% V˙O2peak) or resistance (REX; n = 8, 8 x 5 leg extension, 80% one-repetition maximum, 3-min recovery) exercise group. Serial muscle biopsies were obtained from vastus lateralis at rest before, immediately after, and after 15, 30, and 60 min of passive recovery to determine early signaling responses after exercise.

RESULTS

There were comparable increases from rest in Akt(Thr308/Ser473) and mTOR(Ser2448) phosphorylation during the postexercise time course that peaked 30-60 min after both CYC and REX (P < 0.05). There were also similar patterns in p70S6K(Thr389) and 4E-BP1(Thr37/46) phosphorylation, but a greater magnitude of effect was observed for REX and CYC, respectively (P < 0.05). However, AMPK(Thr172) phosphorylation was only significantly elevated after CYC (P < 0.05), and we observed divergent responses for glycogen synthase(Ser641) and AS160 phosphorylation that were enhanced after CYC but not REX (P < 0.05).

CONCLUSIONS

We show a similar time course for Akt-mTOR-S6K phosphorylation during the initial 60-min recovery period after divergent contractile stimuli. Conversely, enhanced phosphorylation status of proteins that promote glucose transport and glycogen synthesis only occurred after endurance exercise. Our results indicate that endurance and resistance exercise initiate translational signaling, but high-load, low-repetition contractile activity failed to promote phosphorylation of pathways regulating glucose metabolism.

Short-term endurance training does not alter the oxidative capacity of human subcutaneous adipose tissue

Endurance training results in adaptations that enhance regulation of energy storage and expenditure at rest and during exercise. While processes involved in skeletal muscle oxidative remodelling are well described, it is unknown whether oxidative capacity of human subcutaneous white adipose tissue (WAT) is modified by endurance training. Since human WAT retains rudimentary characteristics required for upregulation of oxidative function, we hypothesised that 10 days of intense endurance training would promote changes in WAT that favour an increase in oxidative capacity. Eleven untrained males (age 22 +/- 1 years, body mass 81 +/- 5 kg, peak oxygen uptake (VO(2peak)) 3.7 +/- 0.2 l/min) undertook a 10-day endurance training protocol. Subcutaneous adipose tissue biopsies were taken from the abdomen prior to and 1 day after completion of training and analysed for fatty acid oxidative capacity, citrate synthase activity, and mitochondrial content via electron microscopy and gene expression analyses. There was a reduction in whole-body rates of carbohydrate oxidation, and concomitant increases in fat oxidation rate measured during 20-min of submaximal cycling (70% of pre-training VO(2peak)) and an increase in basal GLUT4 protein in skeletal muscle. Despite these training-induced adaptations, there were no changes in WAT of ex-vivo fat oxidation rate, maximal citrate synthase activity, mitochondrial volume or in selected genes involved in adipose tissue oxidative capacity. We conclude that 10 days training in previously untrained subjects results in adaptations in skeletal muscle but does not increase the oxidative capacity of WAT.