Glycogen depletion patterns in trained rats adapted to a high-fat or high-carbohydrate diet.

Male Sprague-Dawley rats (n = 48, > 200 g) were progressively treadmill trained over 5 wk where they were running 60 min/d, 5 d/wk. One-half of the group consumed a high-fat diet (HF, 78.7% of energy), while one-half consumed a high-carbohydrate diet (HC, 68.7% of energy). On the day of the experiment, 6 rats per diet were run at 29 m/min, 8% grade for 0, 10, 20, or 60 min. Immediately post-exercise rats were anesthetized, and soleus (S), red vastus lateralis (RV), and white vastus lateralis (WV) muscles were removed. There were no significant differences between diets for S glycogen pre-, during, or post-exercise. RV glycogen (micromol x g(-1) wet wt) was lower (p < 0.05) at rest for the HF (27.5 +/- 3.9, Mean +/- SEM) vs the HC (37.6 +/- 3.5), but similar to HC at 60 min (11.0 +/- 1.9, HF; 8.6 +/- 1.3, HC). RV glycogen use rates (nmol x g(-1) x min(-1)) were lower for the HF (985 +/- 295, 356 +/- 61) than the HC (1593 +/- 144, 1055 +/- 272) for 0-10 and 11-20 min, respectively. Resting WV glycogen was lower for the HF (25.3 +/- 1.6) vs the HC (40.7 +/- 5.8), while post exercise values were similar (17.0 +/- 4.4, HF; 15.7 +/- 2.0, HC). WV glycogen use was negligible from 0-10 and 11-20 min in the HF compared to the HC (280 +/- 169 and 1601 +/- 177 nmol x g(-1) x min(-1), respectively). These data indicate that muscle glycogen is spared during the early stages of prolonged exercise in HF adapted rats and that the sparing occurs according to expected muscle recruitment patterns.