A common lament associated with the human condition is the lack of sustained energy required to adapt to changing living requirements. Historically, demands for nourishment and energy changed dramatically as society transitioned from hunter-gatherer to agrarian base and then to urban collections of masses of people attracted by the industrial age. This is also the case in the modern era for adults of all ages and, depending on life choices, can be a significant challenge to reaching a balance between energy creation and expenditure. For athletes of all levels the challenge is even greater, but sports nutrition science has provided tools and solutions.
Strength, performance and endurance demands are not new. As humans organized into societies, the creation of military organizations was accompanied by the establishment of athletic training and competitions. In fact, the original Olympic games of ancient Greece were demonstrations of human prowess in athletics. According to legend, the Olympics were first organized by Heracles (presumed son of Zeus), who went by the Roman name Hercules. The first Olympic competition for which any written records exist are from the year 776 BC. These exhibitions of extraordinary athletic performance lasted almost 12 centuries before the Roman Emperor Theodosius banned them. The games were “reborn” in 1894 through the efforts of Baron Pierre de Coubertin and started again in 1896.
With the 2020 Summer Olympics scheduled for later this year in Japan, once again the world will be treated to exhibitions of human endurance and excellence requiring focus, skill and expenditures of energy unimaginable to most “normal” folks. Perhaps those of us who are not Olympic-quality athletes can learn from the science of human energy creation and metabolism, which the elite trainers and athletes have at their training tables.
Glucose and Glycogen Fueling
The ability for athletes to train consistently depends largely on consuming adequate levels of nutrients associated with glycogen maintenance and restoration. Most high-expenditure exertion requires sufficient stores of glycogen—which the body places in striated muscle—to allow rapid muscle contraction and release during exertion. During prolonged physical activity, which is often intense, muscle glycogen particles are metabolized into glucose molecules that lead to the formation of adenosine triphosphate (ATP) through a process of oxidation.
The actual creation of energy for muscle firing involves the ATP-adenosine diphosphate (ADP) system, generating “energy” sources for fast-twitch and slow-twitch muscle fibers. This is a reflection of the fact that glycogen comprises several individual glucose molecules, wherein all glycogen particles are activated by glycogenin.1 The “particles” of glycogen are directly related to the proper functions of branching enzymes, which collect glucose particles and the enzyme glycogen synthase—both of which collect glucose into the resulting glycogen particle or “package” of energy-creating glucose.
The intensity of exercise is directly related to the rate of muscle glycogen degradation.2 Likewise, the duration of the exercise changes the mathematical equation of glycogen metabolism (e.g., a sprinter has different needs than a long-distance runner) and training programs are modified to not overload the system of one versus another. Consequently, recommended intake of carbohydrates, the primary dietary driver of glucose production, varies to reflect the system load from daily or periodic training.3
While most people have experienced muscle fatigue associated with glycogen store exhaustion, often through repetitive exercise utilizing one or more muscle groups, we seem to forget that glycogen is not just found in our musculature. In fact, the amount of glycogen stored in the human liver is staggering in both quantity and construct. This rich source of “energy” is stored in the body with three times its weight in water, which is often the reason for weight gain in those who have high carbohydrate intake, to prepare for exertion.4
Carbohydrate intake during periods of exercise helps regulate the stores of liver glycogen and may also spare glycogen in fast-twitch muscle cells. The type of muscle fibers one has as an athlete depends mostly on the nature of the activity. In the case of anaerobic, short-duration intense activity, the fast-twitch fibers will predominate. The slow-twitch fibers have higher concentrations of myoglobin and mitochondria and are often associated with long distance runners or athletic exertions of significant duration.5
People often take for granted that carbohydrates are required to help sustain energy, while others have defaulted to simple carbohydrates such as sugars or high fructose corn syrup to achieve those results. It wasn’t until the 1960s that research in Scandinavia turned to muscle biopsies to establish the impact of glycogen in muscle to endurance and performance.6,7 It is hard to imagine that prior to that time, no physical evidence linked carbohydrate ingestion to muscle glucose expenditure.
The best forms of foods delivering healthy levels of carbohydrates remain unprocessed fruits, grains and vegetables that provide a minimum of 20 g carbohydrates per serving, and deliver essential nutrients found generally lacking in modern American diets. Those are essential items such as dietary fiber, calcium, magnesium, potassium and the antioxidant vitamins A, C, E and D. Female athletes that are not menopausal should also consider supplementation with iron and choline, as well as a suite of B vitamins and folacin. These are often labeled as “gap nutrients,” which signifies that the average American diet does not achieve the minimal standards set by the U.S. government for these nutrients. Master athletes (those over age 55) have generally reported a longer time of recovery from endurance exercises such as long-distance biking, running or swimming. This suggests that restoration of muscle glycogen stores is slower in older adults; ingesting additional high-quality protein should assist stimulation of MPS.10,11
In summary, giving the human body the proper nutrients on a consistent basis plays a vital role in helping achieve maximum potential, especially as individuals learn how energy works for them, no matter the level of their athletic pursuits.
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Mark A. LeDoux is founder, chairman and chief executive officer of Natural Alternatives International Inc. an organization established in 1980 with facilities in the U.S. and Switzerland engaged in the research, design and manufacture of nutritional supplement programs and products for multinational clients. He is a proud member and leader of many industry organizations.
1 Smythe C, Cohen P. “The discovery of glycogenin and the priming mechanism for glycogen biogenesis.” European Journal of Biochemistry. 1991;200:625-631.
2 Hawley JA, Lackey JJ. “Carbohydrate dependence during prolonged, intense endurance exercise.” Sports Medicine. 2015;45(suppl 1):S5-12.
3 Thomas TD, Erdman KA, Burke LM. “Nutrition and Athletic Performance.” Med Sci Sports Exerc. 2016;48:543-568.
4 Kreitzman SN, Coxon AY, Szaz KF. “Glycogen storage; illusions of easy weight loss, excessive weight regain, and distortions in estimates of body composition.” Am J Clin Nutr. 1992;56(suppl 1):292-293.
5 De Bock K et. al. “Fiber type-specific muscle glycogen sparing due to carbohydrate intake before and during exercise.” Am J Physiol Endo Metab. 2016;311:E543-E553.
6 Bergstrom J, Hultman E. “Muscle glycogen synthesis after exercise: an enhancing factor localized to the muscle cells in man.” Nature. 1966;210:309-310.
7 Hultman E, Bergstrom J. “Muscle glycogen synthesis in relation to diet studied in normal subjects.” Acta Med Scand. 1967;182:129-139.
8 Betts JA, Williams C. “Short-term recovery from prolonged exercise; exploring the potential for protein ingestion to accentuate the benefits of carbohydrate supplements.” Sports Medicine. 2010;40:941-959.
9 Morton RW, McGlory C, Phillips SM. “Nutritional interventions to augment resistance training-induced skeletal muscle hypertrophy.” Front Physiol. 2015;6:245.
10 Ivy JL et al. “Early post-exercise muscle glycogen recovery is enhanced with a carbohydrate-protein supplement.” J. Appl. Physiol. 2002;93:1337-1344.
11 Doering TM et al. “Postexercise dietary protein strategies to maximize muscle repair and remodeling in masters endurance athletes; a review.” Int. J. Sports Nutr. Exerc. Metab. 2016;26:168-178.