Review articleCarbohydrate restriction: Friend or foe of resistance-based exercise performance?
Introduction
Glucose availability is important for muscular performance lasting >30s, and dietary carbohydrates are now considered the most important of the three macronutrients for fueling endurance sports [1]. However, before the late 19th century, athletes, coaches, and even some scientists believed protein was the major source of energy for muscular activity [2]. From a historical perspective, Zuntz [3], [4], Frentzel and Reach [5], and Krogh and Lindhard [6] demonstrated through a series of landmark experiments that carbohydrates and lipids fuel exercise, with the varying proportions of the two macronutrients in the diet and the intensity of work determining the proportions in which they were oxidized. In 1924, researchers from Harvard Medical School conducted experiments with runners from the Boston Marathon to investigate the role of carbohydrates on exercise performance [7]. It was observed that blood glucose levels were reduced in several Boston Marathon runners who crossed the finish line, thus establishing a relationship between blood glucose, carbohydrate consumption, and performance [7]. In the following year, many of these same athletes were supplemented with a large amount of carbohydrates the day before the race, and they were allowed to eat sugary candy before and during the event [8]. Blood glucose concentrations after completion of the marathon were sampled by researchers and they found that by normalizing blood glucose concentrations (before and during running), symptoms of fatigue and stupor were prevented and mental focus was increased [8]. This was one of the first studies to establish a causal link between carbohydrate consumption and sport performance. In the 1960s, it was demonstrated that high-carbohydrate diets improved endurance performance and carbohydrate feedings during exercise delayed fatigue [9], [10], [11]. Finally, in the 1970s, research revealed that manipulation of dietary carbohydrate levels from a carbohydrate-free diet, mixed diet, and high-carbohydrate diet increased muscle glycogen content and consequentially increased the time of moderate exercise to exhaustion [12]. The supra-cited effects of manipulation of carbohydrate ingestion leading to increased muscle glycogen content are currently known as carbohydrate loading [13], [14]. Those studies were essential to paving the road for the carbohydrate saga in sports nutrition.
It is now fully appreciated that adequate carbohydrate ingestion is necessary for optimal endurance performance, with recommendations well established in sports nutrition societies [15]. However, for strength- and physique-based athletes, sports nutrition recommendations have focused more on amino acid and protein ingestion [16], with much less attention given to carbohydrate requirements. In fact, the role of dietary carbohydrates in strength training performance and adaptation are currently under debate, with some researchers questioning whether dietary carbohydrates impart any ergogenic or adaptive benefit to strength training at all [17]. For strength- and physique-based athletes, carbohydrates are consumed for the following four main purposes:
- 1.
To maintain high muscle glycogen levels to sustain muscle contractions during high-intensity strength training sessions.
- 2.
To enhance muscle recovery and adaptation (via increasing protein synthesis and suppressing protein breakdown) between exercise sessions [18].
- 3.
To enhance aesthetics acutely, especially for physique competitions, whereby carbohydrate loading increases muscle glycogen and intermuscular water content leading to a more “muscular” appearance [19].
- 4.
To improve body composition via reductions in fat mass; however, in this case, most individuals reduce carbohydrate consumption in an attempt to mobilize more fatty acids from the adipose tissue [20].
In all four situations, carbohydrates are important (either in high/adequate amounts or low amounts) for strength training and the physique athlete, and are discussed in detail after a brief explanation of carbohydrate metabolism.
Section snippets
Carbohydrate metabolism
Ingested carbohydrates are degraded by extensive enzymatic systems in the body, initially found in saliva (salivary amylase), then in the pancreatic juice (pancreatic amylase), and finally by intestinal microvilli enzymes (maltase, lactase and sucrase). After being digested, they are absorbed as glucose or fructose in the intestine, via glucose/fructose transporters [21]. In sports nutrition, the choice of a given source of carbohydrates is extremely important for several reasons, from
Muscle contractions and glucose metabolism
Muscle contraction is a process dependent on intramuscular adenosine triphosphate (ATP) being replenished by bioenergetic systems [23]. During efforts lasting 30 to 180s, the ATP required for muscle contractions is mainly powered through glycolysis [27]. Glycolysis is a set of 10 step reactions generating two or three ATPs, depending on whether glucose or glycogen is the initial substrate, respectively [27]. During anaerobic exercises, when available, glycogen is the preferred source of energy
Metabolic demands of strength/power athlete training and physique athlete training
Resistance-training variable prescriptions (volume, intensity, rest between sets, repetition tempo, etc.) vary widely based on the desired outcome. Consequentially, metabolic demand and substrate utilization also will differ between resistance-training prescriptions. During the yearly training plan, strength and power athletes often divide their training into periods of general preparation, defined in part by performing higher volumes and lower intensities to optimize work capacity and
Muscle glycogen availability and dietary carbohydrate affect resistance-based muscular performance
Maintaining muscle glycogen via adequate carbohydrate consumption (4–7 g/kg daily) is recommended to optimize both acute strength performance (i.e., a power lifter who must execute three 1 RM attempts for the squat, bench press, and deadlift with 15–30 min of rest between attempts during competition) and supporting high weekly volumes of resistance training [63]. From a mechanistic perspective, it would appear that maintaining glycogen is indeed important for performance in both acute and
Dietary carbohydrate and muscle glycogen affect postresistance exercise adaptations
Insulin and insulin growth factor 1 (IGF-1) have been shown to play a major role in skeletal muscle anabolism and potentially more importantly, restricting protein breakdown. The receptors of insulin (IR) and IGF-1 (IGF-1 R) have a 45% to 65% homology between their ligand-binding domains and 60% to 85% homology in their tyrosine kinase substrate recruitment domains. It has been suggested that their respective genes have evolved from an ancestral gene that has been highly conserved in the
Effects of carbohydrate manipulation on body composition outcomes
When an organism consumes less calories than expended for a consistent period (i.e., >24–48 h) weight loss from reductions in body tissue occur; however, a variety of factors that affect eating behavior and activity will influence both the rate as well as the composition of the weight lost [107]. Given the risk for cardiovascular and metabolic diseases associated with excess adiposity, even in individuals with body mass index <25 kg/m2 [108], and the importance of maintaining muscle mass to
Effects of carbohydrate manipulation on aesthetic outcomes in competitive physique athletes
Physique athletes (i.e., bodybuilding, physique, figure, and bikini divisions) are assessed based on their presentation of an aesthetic appearance, defined by appropriate levels of muscularity, bilateral symmetry, aesthetic balance between various muscle groups, and a low body fat [115]. Ergo, although two athletes of similar stature and muscular development may present with differing body fat percentages, the athlete with the lower measured body fat percentage may not always win. As such,
Conclusions and Future Perspectives
The metabolic response to resistance training is distinct from endurance training and differs from high-intensity interval training because of longer time under tension and more prolonged eccentric contractions [46]. Moreover, variances in resistance training variable prescription, such as the differences in volume, intensity, and interset rest between typical strength and hypertrophy prescriptions, results in varying metabolic responses. Research examining the effects of varying levels of
References (129)
- et al.
Exercise metabolism: historical perspective
Cell Metab
(2015) - et al.
Exercise and regulation of carbohydrate metabolism
Prog Mol Biol Transl Sci
(2015) - et al.
Effect of acidosis on Ca2+ sensitivity of skinned cardiac muscle with troponin C exchange
Implications for myocardial ischemia. FEBS Lett
(1989) - et al.
Effects of carbohydrate and protein supplementation during resistance exercise on respiratory exchange ratio, blood glucose, and performance
J Clin Transl Endocrinol
(2015) Skeletal muscle hypertrophy and atrophy signaling pathways
Int J Biochem Cell Biol
(2005)- et al.
Search for the competitive edge: a history of dietary fads and supplements
J Nutr
(1997) About the role of sugar in animal metabolism
Arch Physiol
(1896)About the importance of different nutrients as producers of muscle power
Pflugers Arch
(1901)- et al.
Investigations on the source of muscle power
Pflugers Arch
(1901) - et al.
Relative value of fat and carbohydrate as source of muscular energy
Biochem J
(1920)
de M. Scriver, et al. Sugar content of the blood in runners following a marathon race
JAM
Muscle glycogen and muscle electrolytes during prolonged physical exercise
Acta Physiol Scand
Nutrition for maximal sports performance
JAMA
Muscle glycogen synthesis after exercise: an enhancing factor localized to the muscle cells in man
Nature
Diet, muscle glycogen, and endurance performance
J Appl Physiol
Something old and something new - very new
Nutr Today
Diet, muscle glycogen and physical performance
Acta Physiol Scand
The use of carbohydrates during exercise as an ergogenic aid
Sports Med
International Society of Sports Nutrition position stand: protein and exercise
J Int Soc Sports Nutr
Carbohydrate intake and resistance-based exercise: are current recommendations reflective of actual need?
Br J Nutr
Carbohydrate supplementation and resistance training
J Strength Cond Res
Early weight gain and glycogen-obligated water during nutritional rehabilitation
Hum Nutr Clin Nutr
Nutritional strategies of high level natural bodybuilders during competition preparation
J Int Soc Sports Nutr
Carbohydrate digestion and absorption. Role of the small intestine
N Engl J Med
Eating, exercise, and "thrifty" genotypes: Connecting the dots toward an evolutionary understanding of modern chronic diseases
J Appl Physiol
Glucose metabolism and regulation: beyond insulin and glucagon
Diabetes Spectrum
Through the looking glass: current and future perspectives on the role of hormonal interplay in glucose homeostasis
Diabetes Educ
The glucose-6-phosphatase system
Biochem J
Interaction among skeletal muscle metabolic energy systems during intense exercise
J Nutr Metab
The metabolic systems; carbohydrate metabolism. In: Farrell PA, Joyner MJ, Hartmann H, Wirth K, Keiner M, Mickel C, et al. Short-term Periodization Models: Effects on Strength and Speed-strength Performance
Sports Med
Regulation of endogenous fat and carbohydrate metabolism in relation to exercise intensity and duration
Am J Physiol
Biochemistry of exercise-induced metabolic acidosis
Am J Physiol Regul Integr Comp Physiol
Changes in muscle fiber conduction velocity indicate recruitment of distinct motor unit populations
J Appl Physiol
Phosphocreatine content in single fibers of human muscle after sustained submaximal exercise
Am J Physiol
Muscle glycogen depletion patterns in type I and subgroups of type II fibres during prolonged severe exercise in man
Acta Physiol Scand
Potential mechanisms for a role of metabolic stress in hypertrophic adaptations to resistance training
Sports Med
Skeletal muscle: A brief review of structure and function
Calcif Tissue Int
Skeletal muscle insulin resistance is the primary defect in type 2 diabetes
Diabetes Care
The effect of graded doses of insulin on total glucose uptake, glucose oxidation, and glucose storage in man
Diabetes
Exercise, GLUT4, and skeletal muscle glucose uptake
Physiol Rev
Signaling mechanisms in skeletal muscle: Acute responses and chronic adaptations to exercise
IUBMB Life
Hypoxia in Combination With Muscle Contraction Improves Insulin Action and Glucose Metabolism in Human Skeletal Muscle via the HIF-1 α Pathway
Diabetes
Glucose transport and glucose transporters in muscle and their metabolic regulation
Diabetes Care
Prevention of glycogen supercompensation prolongs the increase in muscle GLUT4 after exercise
Am J Physiol Endocrinol Metab
Short-term Periodization Models: Effects on Strength and Speed-strength Performance
Sports Med
Skeletal Muscle Hypertrophy: How important is Exercise Intensity?
J Trainology
Fatigue during High-Intensity Intermittent Exercise
Sport Med
Comparison of the acute Metabolic responses to traditional resistance, BW and Battling Rope Exercises
J Strength Cond Res
Energy cost of isolated resistance exercises across low- to high-intensities
PLoS One
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