Effects of a carbohydrate-protein beverage on cycling endurance and muscle damage.
Saunders MJ, Kane MD, Todd MK.
School of Kinesiology and Recreation Studies, James Madison University, Harrisonburg, VA 22807, USA. saundemj@jmu.edu
INTRODUCTION: The purpose of this study was to determine whether endurance cycling performance and postexercise muscle damage were altered when consuming a carbohydrate and protein beverage (CHO+P; 7.3% and 1.8% concentrations) versus a carbohydrate-only (CHO; 7.3%) beverage. METHODS: Fifteen male cyclists (mean (.-)VO(2peak) = 52.6 +/- 10.3 mL x kg x min) rode a cycle ergometer at 75% (.-)VO(2peak) to volitional exhaustion, followed 12 - 15 h later by a second ride to exhaustion at 85% (.-)VO(2peak). Subjects consumed 1.8 mL x kg BW of randomly assigned CHO or CHO+P beverage every 15 min of exercise, and 10 mL x kg BW immediately after exercise. Beverages were matched for carbohydrate content, resulting in 20% lower total caloric content per administration of CHO beverage. Subjects were blinded to treatment beverage and repeated the same protocol seven to 14 d later with the other beverage. RESULTS: In the first ride (75% (.-)VO(2peak)), subjects rode 29% longer (P < 0.05) when consuming the CHO+P beverage (106.3 +/- 45.2 min) than the CHO beverage (82.3 +/- 32.6 min). In the second ride (85% (.-)VO(2peak)), subjects performed 40% longer when consuming the CHO+P beverage (43.6 +/- 12.5 min) than when consuming the CHO beverage (31.2 +/- 8.7 min). Peak postexercise plasma CPK levels, indicative of muscle damage, were 83% lower after the CHO+P trial (216.3 +/- 122.0 U x L) than the CHO trial (1318.1 +/- 1935.6 U x L). There were no significant differences in exercising levels of (.-)VO(2), ventilation, heart rate, RPE, blood glucose, or blood lactate between treatments in either trial. CONCLUSION: A carbohydrate beverage with additional protein calories produced significant improvements in time to fatigue and reductions in muscle damage in endurance athletes. Further research is necessary to determine whether these effects were the result of higher total caloric content of the CHO+P beverage or due to specific protein-mediated mechanisms.
Med Sci Sports Exerc. 2001 Jun;33(6):907-15
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Determinants of post-exercise glycogen synthesis during short-term recovery.
Jentjens R, Jeukendrup A.
Human Performance Laboratory, School of Sport and Exercise Sciences, University of Birmingham, Edgbaston, Birmingham, UK.
The pattern of muscle glycogen synthesis following glycogen-depleting exercise occurs in two phases. Initially, there is a period of rapid synthesis of muscle glycogen that does not require the presence of insulin and lasts about 30-60 minutes. This rapid phase of muscle glycogen synthesis is characterised by an exercise-induced translocation of glucose transporter carrier protein-4 to the cell surface, leading to an increased permeability of the muscle membrane to glucose. Following this rapid phase of glycogen synthesis, muscle glycogen synthesis occurs at a much slower rate and this phase can last for several hours. Both muscle contraction and insulin have been shown to increase the activity of glycogen synthase, the rate-limiting enzyme in glycogen synthesis. Furthermore, it has been shown that muscle glycogen concentration is a potent regulator of glycogen synthase. Low muscle glycogen concentrations following exercise are associated with an increased rate of glucose transport and an increased capacity to convert glucose into glycogen.The highest muscle glycogen synthesis rates have been reported when large amounts of carbohydrate (1.0-1.85 g/kg/h) are consumed immediately post-exercise and at 15-60 minute intervals thereafter, for up to 5 hours post-exercise. When carbohydrate ingestion is delayed by several hours, this may lead to ~50% lower rates of muscle glycogen synthesis. The addition of certain amino acids and/or proteins to a carbohydrate supplement can increase muscle glycogen synthesis rates, most probably because of an enhanced insulin response. However, when carbohydrate intake is high (> or =1.2 g/kg/h) and provided at regular intervals, a further increase in insulin concentrations by additional supplementation of protein and/or amino acids does not further increase the rate of muscle glycogen synthesis. Thus, when carbohydrate intake is insufficient (<1.2 g/kg/h), the addition of certain amino acids and/or proteins may be beneficial for muscle glycogen synthesis. Furthermore, ingestion of insulinotropic protein and/or amino acid mixtures might stimulate post-exercise net muscle protein anabolism. Suggestions have been made that carbohydrate availability is the main limiting factor for glycogen synthesis. A large part of the ingested glucose that enters the bloodstream appears to be extracted by tissues other than the exercise muscle (i.e. liver, other muscle groups or fat tissue) and may therefore limit the amount of glucose available to maximise muscle glycogen synthesis rates. Furthermore, intestinal glucose absorption may also be a rate-limiting factor for muscle glycogen synthesis when large quantities (>1 g/min) of glucose are ingested following exercise.
Int J Sports Med. 1998 Jun;19 Suppl 2:S142-5.
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Effects of liquid carbohydrate ingestion on markers of anabolism following high-intensity resistance exercise.
Thyfault JP, Carper MJ, Richmond SR, Hulver MW, Potteiger JA.
Department of Physiology, Brody School of Medicine, East Carolina University, Greenville, North Carolina 27858, USA. thyfaultj@mail.edu.edu
We examined the effects of liquid carbohydrate (CHO) supplementation on markers of anabolism following high-intensity resistance exercise. Nine resistance-trained men consumed either CHO or placebo (PLC) 10 minutes before and immediately following 2 resistance exercise sessions. Cortisol (CORT), insulin (INS), ammonia (AMM), and glucose (GLU) were measured before, immediately after, and 1.5 and 4 hours after exercise. Urinary nitrogen (NH(+3)) was measured 24 hours before and after exercise. There was a significant difference in INS levels immediately after exercise and 1.5 hours after exercise. No significant differences were observed for CORT, AMM, GLU, or NH(+3)between treatments. Significant within-group differences were found for the PLC group: CORT before compared with immediately after exercise; INS before compared with immediately after exercise and before compared with 1.5 hours after exercise; and AMM before compared with immediately after exercise and before compared with 1.5 hours after exercise. Significant within-group differences were found for the CHO group: CORT immediately after compared with 1.5 hours after exercise and immediately after compared with 4 hours after exercise; INS before compared with 1.5 hours after exercise; and AMM before compared with immediately after exercise. Liquid CHO ingestion leads to a more favorable anabolic environment immediately following a resistance exercise bout; however, our indirect measures of protein degradation were not altered by CHO ingestion.
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Nutrition for post-exercise recovery.
Burke LM.
Australian Institute of Sport, ACT, Australia.
Recovery after exercise poses an important challenge to the modern athlete. Important issues include restoration of liver and muscle glycogen stores, and the replacement of fluid and electrolytes lost in sweat. Rapid resynthesis of muscle glycogen stores is aided by the immediate intake of carbohydrate (I g.kg-1 BM each 2 hours), particularly of high glycemic index carbohydrate foods, leading to a total intake over 24 hours of 7-10 g.kg-1 BM. Provided adequate carbohydrate is consumed it appears that the frequency of intake, the form (liquid versus solid) and the presence of other macronutrients does not affect the rate of glycogen storage.
ul Toxicol Pharmacol. 2002 Apr;35(2 Pt 2):S1-93.
