Kevin Currell

Validity, reliability and sensitivity of measures of sporting performance

Performance testing is one of the most common and important measures used in sports science and physiology. Performance tests allow for a controlled simulation of sports and exercise performance for research or applied science purposes. There are three factors that contribute to a good performance test: (i) validity; (ii) reliability; and (iii) sensitivity. A valid protocol is one that resembles the performance that is being simulated as closely as possible. When investigating race-type events, the two most common protocols are time to exhaustion and time trials. Time trials have greater validity than time to exhaustion because they provide a good physiological simulation of actual performance and correlate with actual performance. Sports such as soccer are more difficult to simulate. While shuttle-running protocols such as the Loughborough Intermittent Shuttle Test may simulate physiology of soccer using time to exhaustion or distance covered, it is not a valid measure of soccer performance. There is a need to include measures of skill in such protocols. Reliability is the variation of a protocol. Research has shown that time-to-exhaustion protocols have a coefficient of variation (CV) of >10%, whereas time trials are more reliable as they have been shown to have a CV of <5%. A sensitive protocol is one that is able to detect small, but important, changes in performance. The difference between finishing first and second in a sporting event is <1%. Therefore, it is important to be able to detect small changes with performance protocols. A quantitative value of sensitivity may be accomplished through the signal : noise ratio, where the signal is the percentage improvement in performance and the noise is the CV.

Superior endurance performance with ingestion of multiple transportable carbohydrates.

INTRODUCTION The aim of the present study was to investigate the effect of ingesting a glucose plus fructose drink compared with a glucose-only drink (both delivering carbohydrate at a rate of 1.8 g.min(-1)) and a water placebo on endurance performance. METHODS Eight male trained cyclists were recruited (age 32 +/- 7 yr, weight 84.4 +/- 6.9 kg, .VO(2max) 64.7 +/- 3.9 mL.kg(-1).min(-1), Wmax 364 +/- 31 W). Subjects ingested either a water placebo (P), a glucose (G)-only beverage (1.8 g.min(-1)), or a glucose and fructose (GF) beverage in a 2:1 ratio (1.8 g.min(-1)) during 120 min of cycling exercise at 55% Wmax followed by a time trial in which subjects had to complete a set amount of work as quickly as possible (approximately 1 h). Every 15 min, expired gases were analyzed and blood samples were collected. RESULTS Ingestion of GF resulted in an 8% quicker time to completion during the time trial (4022 s) compared with G (3641 s) and a 19% improvement compared with W (3367 s). Total carbohydrate (CHO) oxidation was not different between GF (2.54 +/- 0.25 g.min(-1)) and G (2.50 g.min(-1)), suggesting that GF led to a sparing of endogenous CHO stores, because GF has been shown to have a greater exogenous CHO oxidation than G. CONCLUSION Ingestion of GF led to an 8% improvement in cycling time-trial performance compared with ingestion of G.

Effect of beverage glucose and sodium content on fluid delivery.

BackgroundRapid fluid delivery from ingested beverages is the goal of oral rehydration solutions (ORS) and sports drinks.ObjectiveThe aim of the present study was to investigate the effects of increasing carbohydrate and sodium content upon fluid delivery using a deuterium oxide (D2O) tracer.DesignTwenty healthy male subjects were divided into two groups of 10, the first group was a carbohydrate group (CHO) and the second a sodium group (Na). The CHO group ingested four different drinks with a stepped increase of 3% glucose from 0% to 9% while sodium concentration was 20 mmol/L. The Na group ingested four drinks with a stepped increase of 20 mmol/L from 0 mmol/L to 60 mmol/l while glucose concentration was 6%. All beverages contained 3 g of D2O. Subjects remained seated for two hours after ingestion of the experimental beverage, with blood taken every 5 min in the first hour and every 10 min in the second hour.ResultsIncluding 3% glucose in the beverage led to a significantly greater AUC 60 min (19640 ± 1252 δ‰ vs. VSMOW.60 min) than all trials. No carbohydrate (18381 ± 1198 δ‰ vs. VSMOW.60 min) had a greater AUC 60 min than a 6% (16088 ± 1359 δ‰ vs. VSMOW.60 min) and 9% beverage (13134 ± 1115 δ‰ vs. VSMOW.60 min); the 6% beverage had a significantly greater AUC 60 min than the 9% beverage. There was no difference in fluid delivery between the different sodium beverages.ConclusionIn conclusion the present study showed that when carbohydrate concentration in an ingested beverage was increased above 6% fluid delivery was compromised. However, increasing the amount of sodium (0–60 mmol/L) in a 6% glucose beverage did not lead to increases in fluid delivery.

Plasma deuterium oxide accumulation following ingestion of different carbohydrate beverages

Optimal fluid delivery from carbohydrate solutions such as oral rehydration solutions or sports drinks is essential. The aim of the study was to investigate whether a beverage containing glucose and fructose would result in greater fluid delivery than a beverage containing glucose alone. Six male subjects were recruited (average age (+/-SD): 22 +/- 2 y). Subjects entered the laboratory between 0700 h and 0900 h after an overnight fast. A 600 mL bolus of 1 of the 3 experimental beverages was then given. The experimental beverages were water (W), 75 g glucose (G), or 50 g glucose and 25 g fructose (GF); each beverage also contained 3.00 g of D2O. Following administration of the experimental beverage subjects remained in a seated position for 180 min. Blood and saliva samples were then taken every 5 min in the first hour and every 15 min thereafter. Plasma and saliva samples were analyzed for deuterium enrichment by isotope ratio mass spectrometry. Deuterium oxide enrichments were compared using a 2-way repeated measures analysis of variance. The water trial (33 +/- 3 min) showed a significantly shorter time to peak than either G (82 +/- 40 min) or GF (59 +/- 25 min), but the difference between G and GF did not reach statistical significance. There was a significantly greater AUC for GF (55 673 +/- 10 020 delta per thousand vs. Vienna Standard Mean Ocean Water (VSMOW).180 min) and W (60 497 +/- 9864 delta per thousand vs. VSMOW.180 min) compared with G (46 290 +/- 9622 delta per thousand vs. VSMOW.180 min); W and GF were not significantly different from each other. These data suggest that a 12.5% carbohydrate beverage containing glucose and fructose results in more rapid fluid delivery in the first 75 min than a beverage containing glucose alone.

IOC Consensus Statement: Dietary Supplements and the High-Performance Athlete

Nutrition usually makes a small but potentially valuable contribution to successful performance in elite athletes, and dietary supplements can make a minor contribution to this nutrition programme. Nonetheless, supplement use is widespread at all levels of sport. Products described as supplements target different issues, including (1) the management of micronutrient deficiencies, (2) supply of convenient forms of energy and macronutrients, and (3) provision of direct benefits to performance or (4) indirect benefits such as supporting intense training regimens. The appropriate use of some supplements can benefit the athlete, but others may harm the athlete’s health, performance, and/or livelihood and reputation (if an antidoping rule violation results). A complete nutritional assessment should be undertaken before decisions regarding supplement use are made. Supplements claiming to directly or indirectly enhance performance are typically the largest group of products marketed to athletes, but only a few (including caffeine, creatine, specific buffering agents and nitrate) have good evidence of benefits. However, responses are affected by the scenario of use and may vary widely between individuals because of factors that include genetics, the microbiome and habitual diet. Supplements intended to enhance performance should be thoroughly trialled in training or simulated competition before being used in competition. Inadvertent ingestion of substances prohibited under the antidoping codes that govern elite sport is a known risk of taking some supplements. Protection of the athlete’s health and awareness of the potential for harm must be paramount; expert professional opinion and assistance is strongly advised before an athlete embarks on supplement use.

Utilizing small nutrient compounds as enhancers of exercise-induced mitochondrial biogenesis

Endurance exercise, when performed regularly as part of a training program, leads to increases in whole-body and skeletal muscle-specific oxidative capacity. At the cellular level, this adaptive response is manifested by an increased number of oxidative fibers (Type I and IIA myosin heavy chain), an increase in capillarity and an increase in mitochondrial biogenesis. The increase in mitochondrial biogenesis (increased volume and functional capacity) is fundamentally important as it leads to greater rates of oxidative phosphorylation and an improved capacity to utilize fatty acids during sub-maximal exercise. Given the importance of mitochondrial biogenesis for skeletal muscle performance, considerable attention has been given to understanding the molecular cues stimulated by endurance exercise that culminate in this adaptive response. In turn, this research has led to the identification of pharmaceutical compounds and small nutritional bioactive ingredients that appear able to amplify exercise-responsive signaling pathways in skeletal muscle. The aim of this review is to discuss these purported exercise mimetics and bioactive ingredients in the context of mitochondrial biogenesis in skeletal muscle. We will examine proposed modes of action, discuss evidence of application in skeletal muscle in vivo and finally comment on the feasibility of such approaches to support endurance-training applications in humans.

Postexercise High-Fat Feeding Suppresses p70S6K1 Activity in Human Skeletal Muscle

PURPOSE This study aimed to examine the effects of reduced CHO but high postexercise fat availability on cell signaling and expression of genes with putative roles in regulation of mitochondrial biogenesis, lipid metabolism, and muscle protein synthesis. METHODS Ten males completed a twice per day exercise model (3.5 h between sessions) comprising morning high-intensity interval training (8 × 5 min at 85% V˙O2peak) and afternoon steady-state (SS) running (60 min at 70% V˙O2peak). In a repeated-measures design, runners exercised under different isoenergetic dietary conditions consisting of high-CHO (HCHO: 10 g·kg CHO, 2.5 g·kg protein, and 0.8 g·kg fat for the entire trial period) or reduced-CHO but high-fat availability in the postexercise recovery periods (HFAT: 2.5 g·kg CHO, 2.5 g·kg protein, and 3.5 g·kg fat for the entire trial period). RESULTS Muscle glycogen was lower (P < 0.05) at 3 h (251 vs 301 mmol·kg dry weight) and 15 h (182 vs 312 mmol·kg dry weight) post-SS exercise in HFAT compared with HCHO. Adenosine monophosphate-activated protein kinase α2 activity was not increased post-SS in either condition (P = 0.41), although comparable increases (all P < 0.05) in PGC-1α, p53, citrate synthase, Tfam, peroxisome proliferator-activated receptor, and estrogen-related receptor α mRNA were observed in HCHO and HFAT. By contrast, PDK4 (P = 0.003), CD36 (P = 0.05), and carnitine palmitoyltransferase 1 (P = 0.03) mRNA were greater in HFAT in the recovery period from SS exercise compared with HCHO. Ribosomal protein S6 kinase activity was higher (P = 0.08) at 3 h post-SS exercise in HCHO versus HFAT (72.7 ± 51.9 vs 44.7 ± 27 fmol·min·mg). CONCLUSION Postexercise high-fat feeding does not augment the mRNA expression of genes associated with regulatory roles in mitochondrial biogenesis, although it does increase lipid gene expression. However, postexercise ribosomal protein S6 kinase 1 activity is reduced under conditions of high-fat feeding, thus potentially impairing skeletal muscle remodeling processes.

A–Z of nutritional supplements: dietary supplements, sports nutrition foods and ergogenic aids for health and performance – Part 28

Part 28 includes a supplement purported to combat fatigue and enhance growth hormone (ornithine); a well-known ingredient (phenylalanine) of a well-known sweetener (aspartame); a possible energy enhancer via 2,3 diphosphoglycerate (phosphate); and a rather dubious supplement purported in the early 1940s to have a wide range of medicinal effects (pangamic acid). Of these, only phosphate appears to have some credible evidence to support the claims of an ergogenic effect. ### K Currell Ornithine is an amino acid which plays a key role in the urea cycle, facilitating the disposal of ammonia. Ammonia is produced during intense exercise and may be one of the causes of fatigue. There is some evidence that L-ornithine hydrochloride supplementation prior to high-intensity exercise may prevent fatigue and improve performance by modulating the metabolism of ammonia.1 At present, the evidence is far from conclusive with a need to conduct more research using valid measures of performance. It has been suggested that ornithine supplementation will promote the secretion of growth hormone within humans.2 However, research has not been conducted to show whether this may enhance the adaptation to training and ultimately lead to an improvement in the performance. One potential avenue of future research is ornithine-α-ketoglutarate. This has been shown to improve the recovery of individuals from burns, trauma and in the postoperative state. It may also be a precursor of nitric oxide.2 At present, there is not enough evidence to support the use of ornithine in sport performance. However, further research should be conducted to investigate its use. ### DR Moore Phenylalanine is …

A–Z of nutritional supplements: dietary supplements, sports nutrition foods and ergogenic aids for health and performance–Part 20

As usual, the alphabet throws together a mixture of supplements with different levels of popularity and scientific support. Part 20 covers some rarely reported, studied and/or little used supplements in sport: glycine, histidine and inosine. The majority of human studies of supplementation with the essential amino acid histidine has involved clinical work. In terms of athletic performance, there is current interest in supplementation strategies to increase muscle content of the histidine-containing dipeptide (HCD), carnosine. Despite some interest in the use of a chicken breast extract (CBEX) described in this article, most of the focus in this area involves β-alanine supplementation (covered in part 5). There was some interest in inosine as an ergogenic aid in the 1990s but it appears not to have been studied since then. Meanwhile, there appears little role for glycine supplementation in sport although some interest in glycine-containing compounds is possible. β-Hydroxymethyl β-butyrate (HMB) is much more well known, with marketing usually targeting bodybuilders. ### K Currell Glycine is the smallest amino acid; it is non-essential and can be synthesised from serine. Glycine is present in most proteins and is particularly highly concentrated in collagen. Consequently, one of the highest food sources of glycine is gelatin. Glycine is also one of the three amino acid components of glutathione, which is a key component of the bodys defences against oxidative stress; however, it is thought that glycine availability is not the limiting step in glutathione synthesis. Glycine ingestion increases plasma concentrations of insulin in a similar way to other amino acids.1 Glycine is also an inhibitory neurotransmitter. There is little research on supplementation with glycine. Research has looked at its potential role in decreasing inflammation.2 Sport specific research has focused on combining glycine with other nutrients. Glycine-propionyl-L-carnitine (GPLC) has been shown to influence exercise performance,3 decrease oxidative …

A–Z of nutritional supplements: dietary supplements, sports nutrition foods and ergogenic aids for health and performance—part 12

This part of our A–Z series contains five articles on a wide variety of topics. For the sake of continuity, some topics in the alphabetical listing have been moved further down: curcumin, which will appear collectively with flavonoids; docosahexanoic acid and eicosapentanoic acid, which will now come under the umbrella of fatty acids. The compounds covered in part 12 range considerably in their composition and their physiological roles in the body. However, they do share some common characteristics, which might be seen as a generic description of most of the supplements marketed to athletes. Each has a mechanism by which it is proposed that supplementation might improve sports performance, based on the enhancement of an existing biochemical or hormonal pathway that is considered limiting. The marketing credibility of each of these supplements, and others, is boosted from time to time by anecdotal reports of use by a successful athlete or popularity within a certain sporting population. For example, dehydroepiandrosterone achieved notoriety in sporting circles when American baseball player, Mark McGwire, provided testimonials regarding its use during the 1998 season in which he broke the league record for hitting home runs. Alternatively, dimethylglycine has enjoyed the mystique among Western athletes of being used by athletes from Eastern Bloc countries. However, the most important characteristic is that each product has received only minor attention from sports scientists, in terms of involvement in well-conducted, randomised, controlled trials, specific to sport. ### K Currell, A Syed Cysteine is a non-essential amino acid and, together with glycine and glutamate, is an important precursor of the tripeptide glutathione. Glycine and glutamate are readily available within the body and it is thought that the limiting step in the synthesis of glutathione is the availability of cysteine.1 Glutathione is one of the key antioxidants within the body2 and is an essential …