Effect of Carbohydrate-Protein Beverage on Glycogen Resynthesis and Muscle Damage Induced By Eccentric Resistance Exercise

This study examined effects of carbohydrate (C), carbohydrate-protein (CP), or placebo (P) beverages following eccentric resistance exercise on muscle damage by serum creatine kinase (CK), muscle protein breakdown by urinary 3-methylhistidine (3MH), muscle soreness, isokinetic muscle strength, muscle glycogen resynthesis, and serum hormones. Untrained males (N=26) underwent a 9-day controlled meat-free diet and 24 hr urine collections. To reduce glycogen, subjects cycled for 40 min at 70% of VO_2peak followed by 5 cycling sprints on day 4 evening. On day 5, fasted subjects performed 100 eccentric leg flexions at 120% of 1-RM and drank C (n=8, 1.25 g C/kg), CP (n=9, 0.875 g C/kg, 0.375 g protein/kg), or P (n=9) beverages immediate post-exercise (IPE) and 2 hr later. Muscle biopsies were taken IPE on day 5, and days 6 and 8 mornings. Blood was obtained days 4-10 fasted plus IPE, 3 hr, and 6 hr post-exercise on day 5. At 3 hr on day 5, insulin was higher for CP (24.6 ( 15.5 &#181;IU/ml) and C (17.2 +/- 10.9 &#181;IU/ml) than P (5.3 +/- 0.4 &#181;IU/ml, p<.05). Glycogen was low on day 5, partially recovered on day 6, and normal by day 8 (p<.01) with no difference among groups. Isokinetic quadriceps peak torque at 60^o/s decreased 24% on day 6 and remained depressed by 21% on d 8 (p<.01) for all groups. Soreness peaked on day 7 and CK on day 8 (p<.01) with no differences by group. CK increased (p<.01) over day 5 (delta CP 24.6 +/- 19.1, delta P 39.2 +/- 71.6, delta C 70.8 +/- 60.4 U/L) and was highest for C (p<.05). On day 5, CP had lowest 3MH (193.0 +/- 13.8 &#181;mol/d) versus C (251.1 +/- 22.5 &#181;mol/d, p<.05). Testosterone at 3 hr on day 5 was lower for C (4.2 +/- 0.3 ng/ml) and CP (4.3 +/- 0.3 ng/ml) versus P (5.1 +/- 0.2 ng/ml, p<.05). In summary, glycogen, muscle strength and soreness were unaffected by beverage. However, a CP beverage may be beneficial for reducing muscle damage and protein breakdown on the day of eccentric resistance exercise.