2017 ACSM PINES session: 10 questions 10 experts
Tuesday May 30, 2017, Denver, Colorado, USA
By Nancy Clark MS, RD
Each year prior to the annual meeting of the American College of Sports Medicine (ACSM), PINES organizes a session with 10 Questions and 10 Experts. The topic of this year’s session was Research that Changed Sports Nutrition. Ten PINES experts volunteered to report on an influential paper they deemed had an impact on sports nutrition practice. Each expert explained why he or she selected the study, why the research made an impact, and any greater insights the expert now has regarding the study. Here is what they had to say:
#1. Ron Maughan, University of St. Andrews, Scotland
Bergstrom J, Hultman E. Muscle glycogen synthesis after exercise: an enhancing factor localized to the muscle cells in man. Nature 1966; 210:309-310.
This clever study had just two subjects – the authors. These subjects did one-legged cycling to exhaustion, then ate a high carbohydrate diet for 3 days. By the use of muscle biopsy, they compared muscle glycogen content of the rested and exercised legs and showed that exercise caused glycogen depletion in the exercise leg but not in the resting leg. Glycogen was restored to normal after 24 h in the exercised leg and then increased to supra-normal levels over the next 2 days: there was no change in the glycogen content of the resting leg, even though both legs were exposed to the same diet.
Maughan respects the study because it continued the tradition of self-experimentation in human physiology established by Krogh, Haldane and others, the methodological innovations of using one-leg cycling and collecting human muscle tissue by needle biopsy, and how this one experiment with only two subjects opened the doors to extensive research on the effects of manipulation of carbohydrate availability on exercise performance.
#2. Louise Burke PhD. Australian Institute of Sport and Australian Catholic University, Melbourne
Karlsson J, Saltin B. Diet, muscle glycogen, and endurance performance J Appl Physiol 1971; 31:203-6.
This crossover study was with 10 male runners who did glycogen depleting exercise, and then carbo-loaded by eating either a high carb, a low-carb, or a mixed diet for three days prior to a 30 Km time trial or actual race. The carbo-loaded runners completed the 30 Km event in less time because they were able to maintain their pace (not because carbo-loading enabled them to run faster).
Burke respects this study because it provided evidence-based recommendations that could be applied to real-life practice in elite athletes. It showed the importance of doing research not just in the lab, but also in the field. Although we now know the depletion aspect of the study is not necessary, today’s endurance athletes still “carbo-load.”
#3. Barry Braun, PhD, Colorado State University
Coyle E, Coggan A, Hemmert R, Ivy J. Muscle glycogen utilization during prolonged strenuous exercise when fed carbohydrate. 1986; J Appl Physiol 61:165-72.
In this study, the 7 male cyclists exercised for one hour longer when fed CHO during exercise as compared to when they consumed no carbs during exercise. Both groups had the same level of muscle glycogen depletion at three hours, suggesting that consuming carbs did not slow the rate of muscle glycogen depletion but rather provided an alternative fuel that powered the last hour of exercise. Providing carbs during exercise also lowered perceived exertion.
Braun likes this study because it shows that consuming carbs during exercise delays fatigue but NOT by slowing the rate of muscle glycogen use. It also raised the question of whether providing carbohydrate has effects on the perception of fatigue, a critical insight that led to novel ideas such as whether using carbohydrate mouth rinses could offer performance benefits.
#4. Trent Stelligwerff PhD, Canadian Sport Institute Pacific
Jeukendrup A, Jones D. Effect of carbohydrate mouth rinse on 1-h cycle time trial performance. Med Sci Sports Exerc. 2004; 36 (12):2107-11.
In this study, 9 cyclists completed two 40-Km time trials. In one trieal, they swished (and spat out) 25 ml of a sports drink for 5 seconds (only about 1.6g of CHO per 25ml) about every 8min of a 1-hour time trial. By mouthwashing with CHO they had a 2-minute improvement in time trial performance compared to when they swished and spat plain water.
Trent likes this area of research, as further studies taught us that that taste and glucose receptors can “light up” the brain’s pleasure centers, with the benefit of lowering ratings of perceived exertion. Although Trent was initially surprised that mouth rinsing “works,” he acknowledged that evidence now shows that 10 out of 13 CHO mouthwashing studies have now shown a performance benefit.
#5. Lawrence Spriet PhD, University of Guelph
Harvel R, Pernow B, Jones N. Uptake and release of free fatty acids and other metabolites in the legs of exercising men J Appl Physiol 1967; 23:90-9.
This study with 4 males directly measured free fatty acid (FFA) uptake, oxidation and release from exercising muscles during 90-120 minutes of low to moderate intensity cycling, during which 60% of the energy came from fat and 40% from carbohydrate. The researchers identified the importance of fat as fuel for contracting muscles.
Lawrence likes this study because it allowed us to partition where the fat fuel was coming from during exercise. Both fat from outside the muscles (delivered in the blood) and inside the muscles (stored fat) was used during exercise. Also, this study identified that the important fat source in the blood was free fatty acid, and not the triglyerides that circulate in the blood.
#6. Melinda Manore PhD RD, Oregon State University
Bullough R, Gillette C, Harris M, Melby C. Interaction of acute changes in exercise energy expenditure and energy intake on resting metabolic rate. Am J Clin Nutr 1995; 61:473-81.
This study with 8 male athletes measured resting metabolic rate on a day preceeded by 90 minutes of cycling at 75% VO2max (“high training days” with or without adequate energy intake) and compared it to the RMR on a day with no prior exercise for two days (“rest days” with and without adequate calories). The researchers compared the results to 8 untrained men who did no exercise, and showed that exercise, energy intake and training status affected resting metabolic rate (RMR).
Melinda likes this study because is it shows the impact that exercise has on energy metabolism and raised the question: When should we measure RMR, given exercise has extended metabolic effects?
#7. Enette Larson-Meyer PhD RD, University of Wyoming
Spellerberg A. Increase of athletic effectiveness by systematic ultraviolet irradiation. Strahlentherapie. 1952; 88:567-70. (translated from a German journal)
This article describes how German sports medicine staff reduced chronic pain and soreness in injured athletes by exposing them to a sun lamp. The article did not mention the number of athletes, not did the authors do any statistics, other than to report the sun treatment had a “convincing effect.”
Enette likes the study because it suggests sunlight anti-inflammatory and other has healing properties. Did the sun lamp improve vitamin D status? (D was not measured.) This is the first study to document that repeated “exposure to ultra-violet light might impact both athletes’ performance and treatment of injuries.
#8. Andrew Bosch MSc PhD University of Cape Town
Mosora F, Lefebvre P, Pirnay F, Lacroix M, Luyckx A, Duchesne J. Quantitative Evaluation of the Oxidation of an Exogenous Glucose Load Using Naturally Labeled 13c-Glucose. Metabolism 25 (12), 1575-1582.
Andrew chose to highlight research that has taught us how to quantify carbohydrate oxidation rates using naturally labeled C-13 stable isotopes. By consuming labeled glucose, researchers are able to determine how much carbohydrate a muscle uses during exercise, as well as the fate of the carbohydrate (e.g., converts to lactate, gets stored in the liver). Stable isotopes help researchers obtain a good understanding of the fate of glucose during exercise.
#9. Kevin Tipton PhD, University of Stirling
Rennie M, Edwards R, Halliday D, Matthews D, Wolman S, Millward D. Muscle protein synthesis measured by stable isotope techniques in man: the effects of feeding and fasting. Clin Sci 1982; 63:519-23.
This study was the first to measure muscle protein metabolism following feeding in humans. When fed, the subjects’ increase in whole body protein synthesis was largely reflection of increased skeletal muscle protein synthesis (as compared to protein in other parts of the body).
Kevin likes this study because it set the stage for today’s research on the role of exercise in muscle protein synthesis.
#10. Graeme Close PhD, John Moores University, Liverpool
Khassaf M, McArdle A, Esanu C, et al. Effect of vitamin C supplements on antioxidant defence and stress proteins in human lymphocytes and skeletal muscle. J Physiol 2003; 549:645-52
In this study, the athletes took high doses (500mg/day) of vitamin C, with hopes of improving health and performance, only to learn that superloading antioxidants has a negative effect on recovery from exercise. The body expresses protective enzymes when exposed to the stress of reactive oxygen species (ROS) generated during exercise. If vitamin C reduces these enzymes, the body does not get stressed, and that can dampen the adaptations that improve recovery.
Graeme likes this study because it changed our understanding of free radicals and exercise. We now know that athletes should not use supplements during training, but rather eat plenty of fruits and vegetables. However, he mentioned there may be a case for Vitamin C supplements during competitions, a time when the athlete is looking for speedy recovery and not adaptations.
Author
Nancy Clark MS RD CSSD, Nancy has a sports nutrition practice in the Boston-area. She is author of Nancy Clark’s Sports Nutrition Guidebook and has an online workshop.
