Failure to Repeatedly Supercompensate Muscle Glycogen Stores in Highly Trained Men PATRICK MCINERNEY 1 , SARAH J. LESSARD 1 , LOUISE M. BURKE 2 , VERNON G. COFFEY 1 , SONIA L. LO GIUDICE 1 , ROBERT J. SOUTHGATE 1 , and JOHN A. HAWLEY 1 1 Exercise Metabolism Group, School of Medical Sciences, RMIT University, Victoria, AUSTRALIA; and 2 School of Health Sciences, Deakin University, Burwood, Victoria, AUSTRALIA ABSTRACT MCINERNEY, P., S. J. LESSARD, L. M. BURKE, V. G. COFFEY, S. L. LO GIUDICE, R. J. SOUTHGATE, and J. A. HAWLEY. Failure to Repeatedly Supercompensate Muscle Glycogen Stores in Highly Trained Men. Med. Sci. Sports Exerc., Vol. 37, No. 3, pp. 404 – 411, 2005. Purpose: It is not known whether it is possible to repeatedly supercompensate muscle glycogen stores after exhaustive exercise bouts undertaken within several days. Methods: We evaluated the effect of repeated exercise-diet manipulation on muscle glycogen and triacylglycerol (IMTG) metabolism and exercise capacity in six well-trained subjects who completed an intermittent, exhaustive cycling protocol (EX) on three occasions separated by 48 h (i.e., days 1, 3, and 5) in a 5-d period. Twenty-four hours before day 1, subjects consumed a moderate (6 g·kg -1 )-carbohydrate (CHO) diet, followed by 5 d of a high (12 g·kg -1 ·d -1 )-CHO diet. Muscle biopsies were taken at rest, immediately post-EX on days 1, 3, and 5, and after 3 h of recovery on days 1 and 3. Results: Compared with day 1, resting muscle [glycogen] was elevated on day 3 but not day 5 (435  57 vs 713  60 vs 409  40 mmol·kg -1 , P  0.001). [IMTG] was reduced by 28% (P  0.05) after EX on day 1, but post-EX levels on days 3 and 5 were similar to rest. EX was enhanced on days 3 and 5 compared with day 1 (31.9  2.5 and 35.4  3.8 vs 24.1  1.4 kJ·kg -1 , P  0.05). Glycogen synthase activity at rest and immediately post-EX was similar between trials. Additionally, the rates of muscle glycogen accumulation were similar during the 3-h recovery period on days 1 and 3. Conclusion: We show that well-trained men cannot repeatedly supercompensate muscle [glycogen] after glycogen-depleting exercise and 2 d of a high-CHO diet, suggesting that the mechanisms responsible for glycogen accumulation are attenuated as a consequence of successive days of glycogen-depleting exercise. Key Words: CARBOHYDRATE, GLYCOGEN SYNTHESIS, MUSCLE TRIACYLGLYCEROL, GLYCOGEN SYNTHASE A lmost 40 years ago, Swedish investigators described an extreme regimen involving submaximal exercise to exhaustion, a period of restricted carbohydrate (CHO) intake, and subsequent consumption of large quan- tities of dietary CHO to increase the stores of muscle and liver glycogen (2). This exercise-diet regimen dramatically elevated or “supercompensated” muscle glycogen levels and prolonged submaximal exercise time to exhaustion, com- pared with ingestion of a low-CHO diet (1). The positive relationship between the preexercise levels of muscle (and liver) glycogen and the improvement in exercise capacity led to subsequent experiments designed to determine the optimal methods for maximally increasing glycogen stores before glycogen-depleting exercise (14,18,29). Depending on the extent of glycogen depletion, and pro- vided that adequate CHO is consumed and the individual reduces his or her exercise training, the complete restoration of muscle glycogen can occur within 24 h after prolonged, continuous submaximal exercise (1). Whereas exercise-diet interventions to achieve supercompensated muscle glycogen stores and their effect on a variety of single exercise tasks have been well described (14), these procedures do not address the problem of athletic competitions that require repeated maximal efforts: athletes in many events often have to undertake prolonged, submaximal, and/or intermit- tent high-intensity exercise bouts on successive days for several weeks (19). In this case, the restoration of glycogen stores after exhaustive exercise is probably the single most important factor determining the time needed to recover before intense activity can be continued or resumed (5). Presently, it is not known whether trained individuals can supercompensate their muscle glycogen stores after bouts of glycogen-depleting exercise that are undertaken in rapid (48 h) succession. Whereas much attention has focused on determinants of postexercise glycogen accumulation (18), less is known about muscle triacylglycerol (IMTG) metabolism during recovery. Kiens and Richter (20) reported that during the postexercise recovery period, muscle glycogen synthesis has such high metabolic priority that IMTG is broken down at Address for correspondence: John A. Hawley, PhD., Exercise Metabolism Group, School of Medical Sciences, RMIT University, PO Box 71, Bun- doora, Victoria 3083, Australia; E-mail: john.hawley@rmit.edu.au. Submitted for publication July 2004. Accepted for publication November 2004. 0195-9131/05/3703-0404 MEDICINE & SCIENCE IN SPORTS & EXERCISE ® Copyright © 2005 by the American College of Sports Medicine DOI: 10.1249/01.MSS.0000155699.51360.2F 404