This study examined effects of carbohydrate (CHO), milk-based carbohydrate-protein (CHO-PRO), or placebo (P) beverages on glycogen resynthesis, muscle damage, inflammation, and muscle function following eccentric resistance exercise. Untrained males performed a cycling exercise to reduce muscle glycogen 12 hours prior to performance of 100 eccentric quadriceps contractions at 120% of 1-RM (day 1) and drank CHO (n = 8), CHO-PRO (n = 9; 5 kcal/kg), or P (n = 9) immediately and 2 hours post-exercise. At 3 hours post-eccentric exercise, serum insulin was four times higher for CHO-PRO and CHO than P (p < .05). Serum creatine kinase (CK) increased for all groups in the 6 hours post-eccentric exercise (p < .01), with the increase tending to be lowest for CHO-PRO (p < .08) during this period. Glycogen was low post-exercise (33 ± 3.7 mmol/kg ww), increased 225% at 24 hours, and tripled by 72 hours, with no group differences. The eccentric exercise increased muscle protein breakdown as indicated by urinary 3-methylhistidine and increased IL-6 with no effect of beverage. Quadriceps isokinetic peak torque was depressed similarly for all groups by 24% 24 hours post-exercise and remained 21 % lower at 72 hours (p < .01). In summary, there were no influences of any post-exercise beverage on muscle glycogen replacement, inflammation, or muscle function.
Janet R. Wojcik, Janet Walberg-Rankin, Lucille L. Smith and F.C. Gwazdauskas
Harry E. Routledge, Jill J. Leckey, Matt J. Lee, Andrew Garnham, Stuart Graham, Darren Burgess, Louise M. Burke, Robert M. Erskine, Graeme L. Close and James P. Morton
Invasive team sports such as soccer, 1 , 2 rugby league, 2 and Australian Football (AF) 2 , 3 are characterized by high-intensity (>19.8 km/h) intermittent activity profiles. Given the duration of activity (ie, 80–120 min) and high-intensity intermittent profiles, muscle glycogen is considered
Laís Monteiro Rodrigues Loureiro, Caio Eduardo Gonçalves Reis and Teresa Helena Macedo da Costa
& Clarke, 2016 ) exercises. After cessation of endurance exercise, muscle glycogen is typically restored to preexercise concentrations within 24 hr when sufficient amounts of high-glycemic-index carbohydrates (CHOs) (≥1.0 g/kg) are immediately ingested ( Burke et al., 2016 ). However, for athletes involved
Samuel G. Impey, Kelly M. Hammond, Robert Naughton, Carl Langan-Evans, Sam O. Shepherd, Adam P. Sharples, Jessica Cegielski, Kenneth Smith, Stewart Jeromson, David L. Hamilton, Graeme L. Close and James P. Morton
adopted an experimental design whereby male cyclists completed a nonexhaustive training session in which glycogen remained within an absolute concentration (i.e., pre- and postexercise concentrations of <350 and >100 mmol/kg·dry weight (dw), respectively) considered representative of train-low conditions
David R. Lamb, Ann C. Snyder and Thomas S. Baur
This study compared two high carbohydrate (CHO) diets in 14 male runners for effects on muscle glycogen deposition, endurance, and sensations of gastrointestinal discomfort. Muscle glycogen was measured in the vastus lateralis at rest and run time to exhaustion at 75 % VO2max was measured following 3-1/2 days on a 50% CHO diet. After 14 days the subjects consumed a 20% CHO diet and continued training to reduce glycogen. During the next 3-1/2 days, subjects ran less and consumed a 90% CHO diet emphasizing pasta and rice (Pasta, n=7) or lesser amounts of pasta and rice supplemented by a maltodextrin beverage (Supplement, n=7). Glycogen was again measured, followed by a second run to exhaustion. Compared to the 50% CHO diet, Pasta increased muscle glycogen by 27.1 ± 12.2 mmoles/kg muscle (M±SE; p < 0.05) and run time by 15.7±5.9 min; Supplement increased glycogen by 43.2 ± 13.5 mmoles/kg (p < 0.05) and run time by 29.0 ± 7.4 min (p < 0.05). Total glycogen concentrations and run times were not significantly different for Pasta versus Supplement. Subjects reported less gastrointestinal discomfort and greater overall preference for Supplement than for Pasta. Thus, glycogen loading can be accomplished at least as effectively and more comfortably by substituting a maltodextrin drink for some of the pasta and rice in a glycogen loading diet.
Robert A. Robergs
During the initial hours of recovery from prolonged exhaustive lower body exercise, muscle glycogen synthesis occurs at rates approximating 1-2 mmol·kg−1 wet wt·
Michelle Smith Rockwell, Janet Walberg Rankin and Helen Dixon
This study investigated the effect of initial muscle glycogen on performance of repeated sprints and some potential mechanisms for an effect of glycogen on fatigue. Eight subjects performed 2 cycling trials (repeated 60-s sprints) following consumption of either a high carbohydrate (HC) or a low carbohydrate (LC) diet. Muscle biopsies and blood samples were collected at baseline, following a 15% (15% fatigue) and a 30% decline in sprint performance (30% fatigue), when exercise was terminated. Baseline muscle glycogen levels [346 ± 19 HC (SEM) vs. 222 ± 19 mmol/kg dw LC] and total exercise time to 30% fatigue were higher following HC than LC (57.5 ± 10.0 vs. 42.0 ± 3.6 min; p < .05). Similar significant (p < .05) decreases over the entire exercise bout were seen in muscle glycogen (43%), creatine phosphate (CP; 35%), and sarcoplasmic reticu-lum (SR) Ca2+-uptake in isolated homogenized muscle (56%) for both trials (p > .05 between trials). The percentage decline in SR Ca2+-release was less for HC than LC (36% and 53%, respectively), but this was not statistically different. In summary, HC delayed fatigue during repeated sprints. As the reductions in muscle glycogen, CP, and SR function during exercise were not different by dietary treatment, these data do not support a link between whole muscle glyco-gen and SR function or CP reduction during repeated sprint exercise.
Christian Åkermark, Ira Jacobs, Margareta Rasmusson and Jan Karlsson
The effects of carbohydrate (CHO) loading on physical characteristics including muscle fiber distribution, muscle glycogen concentration, and physical performance were studied in two top Swedish ice hockey teams. Players were randomly allocated to two groups: those consuming a CHO-enriched diet (CHO group) and those consuming a mixed diet (controls). Biopsies from the vastus lateralis muscle were taken three times: after Game 1, before Game 2, and after Game 2. Muscle fiber distribution averaged 50 ± 2% slow twitch fibers (mean ± 1SEM). Muscle glycogen concentrations (measured in mmol glucose units · kg−1 wet muscle) were as follows: after Game 1, 43 ± 4 (ail players); before Game 2,99 ± 7 (CHO group) and 81 ± 7 (controls); and after Game 2, 46 ± 6 (CHO group) and 44 ± 5 (controls). Distance skated, number of shifts skated, amount of time skated within shifts, and skating speed improved with CHO loading. It was concluded that individual differences in performance could be related to muscle glycogen metabolism.
Michael J. Cramer, Charles L. Dumke, Walter S. Hailes, John S. Cuddy and Brent C. Ruby
A variety of dietary choices are marketed to enhance glycogen recovery after physical activity. Past research informs recommendations regarding the timing, dose, and nutrient compositions to facilitate glycogen recovery. This study examined the effects of isoenergetic sport supplements (SS) vs. fast food (FF) on glycogen recovery and exercise performance. Eleven males completed two experimental trials in a randomized, counterbalanced order. Each trial included a 90-min glycogen depletion ride followed by a 4-hr recovery period. Absolute amounts of macronutrients (1.54 ± 0.27 g·kg-1 carbohydrate, 0.24 ± 0.04 g·kg fat-1, and 0.18 ± 0.03g·kg protein-1) as either SS or FF were provided at 0 and 2 hr. Muscle biopsies were collected from the vastus lateralis at 0 and 4 hr post exercise. Blood samples were analyzed at 0, 30, 60, 120, 150, 180, and 240 min post exercise for insulin and glucose, with blood lipids analyzed at 0 and 240 min. A 20k time-trial (TT) was completed following the final muscle biopsy. There were no differences in the blood glucose and insulin responses. Similarly, rates of glycogen recovery were not different across the diets (6.9 ± 1.7 and 7.9 ± 2.4 mmol·kg wet weight- 1·hr-1 for SS and FF, respectively). There was also no difference across the diets for TT performance (34.1 ± 1.8 and 34.3 ± 1.7 min for SS and FF, respectively. These data indicate that short-term food options to initiate glycogen resynthesis can include dietary options not typically marketed as sports nutrition products such as fast food menu items.
Jeffrey J. Zachwieja, David L. Costill and William J. Fink
To determine the effect of carbohydrate feeding on muscle glycogen resynthesis, 8 male cyclists pedaled for 2 hrs on a cycle ergometer at 70% of VO2max while consuming either a 10% carbohydrate solution (CHO) or a nonnutritive sweet placebo (No CHO). Muscle biopsies were obtained from the vastus lateralis prior to, immediately postexercise, and at 2,4, and 24 hrs of recovery. Blood samples were taken before and at the end of exercise, and at specified times during recovery. During both trials food intake was withheld for the first 2 hrs of recovery, but at 2 hrs postexercise a 24% carbohydrate solution was ingested. The rate of muscle glycogen resynthesis during the first 2 hrs of recovery was similar for the CHO and No CHO trials. Following ingestion of the 24% carbohydrate supplement, the rates of muscle glycogen resynthesis increased similarly in both trials. These similar rates of resynthesis following ingestion of the carbohydrate supplement were obtained despite significantly greater serum glucose and insulin levels during the No CHO trial. The results indicate that the carbohydrate feedings taken during exercise had little effect on postexercise muscle glycogen resynthesis.