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Protein, protein hydrolysates, and amino acids have become popular ingredients in sports nutrition. The use of protein, protein hydrolysates, and amino acid mixtures has multiple applications when aiming to improve post exercise recovery. After exhaustive endurance-type exercise, muscle glycogen repletion is the most important factor determining the time needed to recover. Coingestion of relatively small amounts of protein and/or amino acids with carbohydrate can be used to augment postprandial insulin secretion and accelerate muscle glycogen synthesis rates. Furthermore, it has been well established that ingesting protein, protein hydrolysates, and amino acid can stimulate protein synthesis and inhibit protein breakdown and, as such, improve net muscle protein balance after resistance- or endurance-type exercise. The latter has been suggested to lead to a more effective adaptive response to each successive exercise bout. To augment net muscle protein accretion, athletes involved in resistance-type exercise generally ingest both protein and carbohydrate during post exercise recovery. However, carbohydrate ingestion after resistance-type exercise does not seem to be warranted to further stimulate muscle protein synthesis or improve whole-body protein balance when ample protein has already been ingested. Because resistance-type exercise is also associated with a substantial reduction in muscle glycogen content, it would be preferred to coingest some carbohydrate when aiming to accelerate glycogen repletion. More research is warranted to assess the impact of ingesting different proteins, protein hydrolysates, and/or amino acids on muscle protein accretion after exercise.

Six days of dietary nitrate supplementation in the form of beetroot juice (~0.5 L/d) has been reported to reduce pulmonary oxygen uptake (VO₂) during submaximal exercise and increase tolerance of high-intensity work rates, suggesting that nitrate can be a potent ergogenic aid. Limited data are available regarding the effect of nitrate ingestion on athletic performance, and no study has investigated the potential ergogenic effects of a small-volume, concentrated dose of beetroot juice. The authors tested the hypothesis that 6 d of nitrate ingestion would improve time-trial performance in trained cyclists. Using a double-blind, repeated-measures crossover design, 12 male cyclists (31 ± 3 yr, VO_2peak = 58 ± 2 ml · kg⁻¹ · min⁻¹, maximal power [W_max] = 342 ± 10 W) ingested 140 ml/d of concentrated beetroot (~8 mmol/d nitrate) juice (BEET) or a placebo (nitrate-depleted beetroot juice; PLAC) for 6 d, separated by a 14-d washout. After supplementation on Day 6, subjects performed 60 min of submaximal cycling (2 × 30 min at 45% and 65% W_max, respectively), followed by a 10-km time trial. Time-trial performance (953 ± 18 vs. 965 ± 18 s, p < .005) and power output (294 ± 12 vs. 288 ± 12 W, p < .05) improved after BEET compared with PLAC supplementation. Submaximal VO₂ was lower after BEET (45% W_max = 1.92 ± 0.06 vs. 2.02 ± 0.09 L/min, 65% W_max 2.94 ± 0.12 vs. 3.11 ± 0.12 L/min) than with PLAC (main effect, p < .05). Wholebody fuel selection and plasma lactate, glucose, and insulin concentrations did not differ between treatments. Six days of nitrate supplementation reduced VO₂ during submaximal exercise and improved time-trial performance in trained cyclists.

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.

Mitogen-activated protein kinase (MAPK) pathways are activated in skeletal muscle during endurance exercise, but the upstream molecular events are incompletely resolved. As an increase in plasma nonesterified fatty acids (NEFA) is a common feature of long-lasting exercise, the authors tested the hypothesis that NEFA contribute to the activation of MAPK during endurance exercise. Acipimox was used before and during endurance exercise to prevent the elevation of plasma NEFA levels in healthy subjects and patients with diabetes. In 2 separate studies, healthy subjects cycled for 2 hr and patients with diabetes for 1 hr at 50% W_max. In control conditions, plasma NEFA concentrations increased from 0.35 to 0.90 mM during exercise in healthy subjects and from 0.55 to 0.70 mM in patients with diabetes (p < .05). Phosphorylation states of extracellularly regulated kinase 1 and 2 (ERK1/2), p38, and c-Jun NH₂-terminal kinases (JNK) were significantly increased after exercise in the vastus lateralis in both groups. Acipimox blocked the increase in plasma NEFA concentrations and almost completely repressed any rise in ERK1/2 and p38 but not in JNK. In conclusion, the data support a role for plasma NEFA in the activation of p38 and ERK1/2 in skeletal-muscle tissue of healthy and diabetic subjects during endurance exercise. Further investigation will be required to determine the molecular link between NEFA and MAPK activation during exercise in human skeletal muscle.

With the increasing knowledge about the role of nutrition in increasing exercise performance, it has become clear over the last 2 decades that amino acids, protein, and protein hydrolysates can play an important role. Most of the attention has been focused on their effects at a muscular level. As these nutrients are ingested, however, it also means that gastrointestinal digestibility and absorption can modulate their effcacy significantly. Therefore, discussing the role of amino acids, protein, and protein hydrolysates in sports nutrition entails holding a discussion on all levels of the metabolic route. On May 28–29, 2007, a small group of researchers active in the field of exercise science and protein metabolism presented an overview of the different aspects of the application of protein and protein hydrolysates in sports nutrition. In addition, they were asked to share their opinions on the future progress in their fields of research. In this overview, an introduction to the workshop and a short summary of its outcome is provided.

Although beetroot juice, as a nitrate carrier, is a popular ergogenic supplement among athletes, nitrate is consumed through the regular diet as well. We aimed to assess the habitual dietary nitrate intake and identify the main contributing food sources in a large group of highly trained athletes. Dutch highly trained athletes (226 women and 327 men) completed 2–4 web-based 24-hr dietary recalls and questionnaires within a 2- to 4-week period. The nitrate content of food products and food groups was determined systematically based on values found in regulatory reports and scientific literature. These were then used to calculate each athlete’s dietary nitrate intake from the web-based recalls. The median[IQR] habitual nitrate intake was 106[75–170] mg/d (range 19–525 mg/d). Nitrate intake correlated with energy intake (ρ = 0.28, p < .001), and strongly correlated with vegetable intake (ρ = 0.78, p < .001). In accordance, most of the dietary nitrate was consumed through vegetables, potatoes and fruit, accounting for 74% of total nitrate intake, with lettuce and spinach contributing most. When corrected for energy intake, nitrate intake was substantially higher in female vs male athletes (12.8[9.2–20.0] vs 9.4[6.2–13.8] mg/MJ; p < .001). This difference was attributed to the higher vegetable intake in female vs male athletes (150[88–236] vs 114[61–183] g/d; p < .001). In conclusion, median daily intake of dietary nitrate in highly trained athletes was 106 mg, with large interindividual variation. Dietary nitrate intake was strongly associated with the intake of vegetables. Increasing the intake of nitrate-rich vegetables in the diet might serve as an alternative strategy for nitrate supplementation.