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Flatwater kayaking requires upper-body muscle strength and a lean body composition. This case study describes a nutrition intervention with a 19-year-old male elite sprint kayaker to increase muscle mass and improve recovery posttraining. Before the intervention, average daily energy intake was 13.6 ± 2.5 MJ (M ± SD; protein, 1.8 g/kg; carbohydrate, 3.6 g/kg), and the athlete was unable to eat sufficient food to meet the energy demands of training. During the 18-month intervention period, the athlete’s daily energy intake increased to 22.1 ± 3.8 MJ (protein, 3.2 g/kg; carbohydrate, 7.7 g/kg) by including milk-based drinks pre- and posttraining and before bed and an additional carbohydrate-based snack midmorning. This simple dietary intervention, along with a structured strength and conditioning program, resulted in an increase of 10 kg body mass with minimal change in body fat percentage. Adequate vitamin D status was maintained without the need for supplementation during the intervention period. In addition, the athlete reported the milk-based drinks and carbohydrate snacks were easy to consume, and no adverse side effects were experienced. This was the first time the athlete was able to maintain weight during intensive phases of the training cycle.

We propose that there is a link between muscle protein synthesis and breakdown that is regulated, in part, through maintenance of the free intracellular pool of essential amino acids. For example, we propose that muscle protein breakdown is paradoxically elevated in the anabolic state following resistance exercise in part because the even greater stimulation of synthesis would otherwise deplete this pool. Thus, factors regulating muscle protein breakdown must be evaluated in the context of the prevailing rate of muscle protein synthesis. Further, the direct effect of factors on breakdown may depend on the physiological state. For example, local hyperinsulinemia suppresses accelerated muscle protein breakdown after exercise, but not normal resting breakdown. Thus, factors regulating muscle protein breakdown in human subjects are complex and interactive.

During postexercise recovery, optimal nutritional intake is important to replenish endogenous substrate stores and to facilitate muscle-damage repair and reconditioning. After exhaustive endurance-type exercise, muscle glycogen repletion forms the most important factor determining the time needed to recover. Postexercise carbohydrate (CHO) ingestion has been well established as the most important determinant of muscle glycogen synthesis. Coingestion of protein and/or amino acids does not seem to further increase muscle glycogensynthesis rates when CHO intake exceeds 1.2 g · kg⁻¹ · hr⁻¹. However, from a practical point of view it is not always feasible to ingest such large amounts of CHO. The combined ingestion of a small amount of protein (0.2–0.4 g · (0.2−0.4 g · kg⁻¹ · hr⁻¹) with less CHO (0.8 g · kg⁻¹ · hr⁻¹) stimulates endogenous insulin release and results in similar muscle glycogen-repletion rates as the ingestion of 1.2 g · kg⁻¹ · hr⁻¹ CHO. Furthermore, postexercise protein and/or amino acid administration is warranted to stimulate muscle protein synthesis, inhibit protein breakdown, and allow net muscle protein accretion. The consumption of ~20 g intact protein, or an equivalent of ~9 g essential amino acids, has been reported to maximize muscle protein-synthesis rates during the first hours of postexercise recovery. Ingestion of such small amounts of dietary protein 5 or 6 times daily might support maximal muscle protein-synthesis rates throughout the day. Consuming CHO and protein during the early phases of recovery has been shown to positively affect subsequent exercise performance and could be of specific benefit for athletes involved in multiple training or competition sessions on the same or consecutive days.

This study tests the hypotheses that (a) a mixture of whey protein, amino acids (AA), and carbohydrates (CHO) stimulates net muscle protein synthesis to a greater extent than isoenergetic CHO alone after resistance exercise; and (b) that the stimulatory effect of a protein, AA, and CHO mixture will last beyond the 1 st hour after intake. Eight subjects participated in 2 trials. In one (PAAC), they ingested 77.4 g CHO, 17.5 g whey protein, and 4.9 g AA 1 hr after resistance exercise. In the other (CON), 100 g CHO was ingested instead. They received a primed constant infusion of L-[²H₅]-phenylalanine, and samples from femoral artery and vein, and biopsies from vastus lateralis were obtained. The area under the curve for net uptake of phenylalanine into muscle above pre-drink value was 128 ±42 mg • leg^-1 (PAAC) versus 32 ± 10 mg - leg^-1 (CON) for the 3 hr after the drink (p = .04). The net protein balance response to the mixture consisted of two components, one rapid immediate response, and a smaller delayed response about 90 min after drink, whereas in CON only a small delayed response was seen. We conclude that after resistance exercise, a mixture of whey protein, AA, and CHO stimulated muscle protein synthesis to a greater extent than isoenergetic CHO alone. Further, compared to previously reported findings, the addition of protein to an AA + CHO mixture seems to extend the anabolic effect.

Skeletal muscle proteins are constantly being synthesized and degraded, and the net balance between synthesis and degradation determines the resultant muscle mass. Biochemical pathways that control protein synthesis are complex, and the following must be considered: gene transcription, mRNA splicing, and transport to the cytoplasm; specific amino acyl-tRNA, messenger (mRNA), ribosomal (rRNA) availability; amino acid availability within the cell; the hormonal milieu; rates of mRNA translation; packaging in vesicles for some types of proteins; and post-translational processing such as glycation and phosphorylation/dephosphorylation. Each of these processes is responsive to the need for greater or lesser production of new proteins, and many states such as sepsis, uncontrolled diabetes, prolonged bed-rest, aging, chronic alcohol treatment, and starvation cause marked reductions in rates of skeletal muscle protein synthesis. In contrast, acute and chronic resistance exercise cause elevations in rates of muscle protein synthesis above rates found in nondiseased rested organisms, which are normally fed. Resistance exercise may be unique in this capacity. This chapter focuses on studies that have used exercise to elucidate mechanisms that explain elevations in rates of protein synthesis. Very few studies have investigated the effects of aging on these mechanisms; however, the literature that is available is reviewed.