The importance of salt in the athlete’s diet

Sodium Ingestion Improves Groundstroke Performance in Nationally-Ranked Tennis Players: A Randomized, Placebo-Controlled Crossover Trial

This study examined the dose-response effects of ingesting different sodium concentrations on markers of hydration and tennis skill. Twelve British nationally-ranked tennis players (age: 21.5 ± 3.1 years; VO_2peak: 45.5 ± 4.4 ml^.kg^.min^-1) completed four identical in-door tennis training sessions in a cluster randomized, single-blind, placebo-controlled, crossover design. Twenty-minutes prior to each training session, participants consumed a 250 ml sodium-containing beverage (10, 20, 50 mmol/L) or a placebo (0 mmol/L), and continued to consume 1,000 ml of the same beverage at set periods during the 1-h training session. Tennis groundstroke and serve performance, agility, urine osmolality, fluid loss, sodium sweat loss and perceptual responses (rating of perceived exertion (RPE), thirst, and gastrointestinal (GI) discomfort) were assessed. Results showed that ingesting 50 mmol/L sodium reduced urine osmolality (-119 mOsmol/kg; p = 0.037) and improved groundstroke performance (5.4; p < 0.001) compared with placebo. This was associated with a reduction in RPE (-0.42; p = 0.029), perception of thirst (-0.58; p = 0.012), and GI discomfort (-0.55; p = 0.019) during the 50 mmol/L trial compared with placebo. Linear trend analysis showed that ingesting greater concentrations of sodium proportionately reduced urine osmolality (β = -147 mOsmol/kg; p = 0.007) and improved groundstroke performance (β = 5.6; p < 0.001) in a dose response manner. Perceived thirst also decreased linearly as sodium concentration increased (β = -0.51; p = 0.044). There was no evidence for an effect of sodium consumption on fluid loss, sweat sodium loss, serve or agility performance (p > 0.05). In conclusion, consuming 50 mmol/L of sodium before and during a 1-h tennis training session reduced urine osmolality and improved groundstroke performance in nationally-ranked tennis players. There was also evidence of dose response effects, showing that ingesting greater sodium concentrations resulted in greater improvements in groundstroke performance. The enhancement in tennis skill may have resulted from an attenuation of symptomologic distracters associated with hypohydration, such as RPE, thirst and GI discomfort.

Nutritional Intake, Sports Nutrition Knowledge and Energy Availability in Female Australian Rules Football Players

This study aimed to assess nutritional intake, sports nutrition knowledge and risk of Low Energy Availability (LEA) in female Australian rules football players. Victorian Football League Women’s competition (VFLW) players (n = 30) aged 18–35 (weight: 64.5 kg ± 8.0; height: 168.2 cm ± 7.6) were recruited from Victoria, Australia. Nutritional intake was quantified on training days using the Automated 24 h Dietary Assessment Tool (ASA24-Australia), and sports nutrition knowledge was measured by the 88-item Sports Nutrition Knowledge Questionnaire (SNKQ). The risk of LEA was assessed using the Low Energy Availability in Females Questionnaire (LEAF-Q). Daily mean carbohydrate intake in the current investigation was 3 g⋅kg⁻¹⋅d⁻¹, therefore, below the minimum carbohydrate recommendation for moderate exercise of approximately one hour per day (5–7 g⋅kg⁻¹⋅d⁻¹) and for moderate to intense exercise for 1–3 h per day (6–10 g⋅kg⁻¹⋅d⁻¹) for 96.3% and 100% of players, respectively. Daily mean protein intake was 1.5 g⋅kg⁻¹⋅d⁻¹, therefore, consistent with recommendations (1.2–2.0 g⋅kg⁻¹⋅d⁻¹) for 77.8% of players. Daily mean calcium intake was 924.8 mg⋅d⁻¹, therefore, below recommendations (1000 mg⋅d⁻¹) for 65.5% of players, while mean iron intake was 12.2 mg⋅d⁻¹, also below recommendations (18 mg⋅d⁻¹) for 100% of players. Players answered 54.5% of SNKQ questions correctly, with the lowest scores observed in the section on supplements. Risk of LEA was evident in 30% of players, with no differences in carbohydrate (p = 0.238), protein (p = 0.296), fat (p = 0.490) or energy (p = 0.971) intakes between players at risk of LEA and those not at risk. The results suggest that female Australian rules football players have an inadequate intake of carbohydrate and calcium and low sports nutrition knowledge. Further investigation to assess the risk of LEA using direct measures is required.

Validity and reliability of the Horiba C-122 compact sodium analyzer in sweat samples of athletes

Accurate sodium replacement during prolonged exercise is possible when sweat rate and sweat sodium content are directly measured. Few athletes have access to sweat sodium content measurement, as the equipment needed to perform such analyzes is costly, laboratory-based or requires technical skills. Using 70 sweat samples collected in 24 athletes from 3 anatomical sites, this study determined the reliability [single-trial and inter-day (7 samples over 3 days)] and validity (instrument error) of a pocket-sized, easy-to-use and low cost sodium analyzer (Horiba C-122, Kyoto, Japan) against reference values of an ion chromatograph, the 883 Basic IC plus (Metrohm AG, Herisau, Switzerland). The Horiba C-122 showed high single-trial reliability with an intraclass correlation coefficient (ICC) of 0.997, a typical error of measurement (EM) of 1.77 mmol/L and a coefficient of variation (CV) of 3.73%. As expected, the reliability of the 883 Basic IC plus was superior to that of the Horiba C-122 (ICC: 0.999; typical EM: 0.70 mmol/L; CV: 1.52%). The Horiba’s C-122 inter-day reliability was high (ICC: 1.00; typical EM: 0.35 mmol/L). An ICC of 0.975 indicates there was a strong relationship between results provided by both analyzers. Compared with reference values, the Horiba C-122 demonstrated a mean bias of 1.71 mmol/L, a pure EM of 7.52 mmol/L and 68% limits of agreement ranging from -5.81 to 9.23 mmol/L. We propose that the Horiba C-122 is sufficiently reliable to be used under field conditions where some degree of imprecision is acceptable, but not for research purposes where high accuracy is required.

Body composition and nutritional profile of male adolescent tennis players

In this cross-sectional study, we evaluated the body composition and dietary intake of 44 adolescent tennis players. After being divided into two groups (age 10-13 years and age 14-18), the players had their weight, height, and sexual maturation assessed. Dual-energy X-ray absorptiometry was used to assess body composition. Food intake was obtained from a non-consecutive 4-day food record. The data were analysed using the Virtual Nutri v.1.0 software and compared with the present recommendations for adolescent athletes or dietary reference intakes. Body mass index and body fat for tennis practice were adequate for 89% and 71% of the tennis players respectively, regardless of age group. A calorie deficit greater than 10% of energy expenditure was observed in 32% of the sample. Fifty percent of the athletes consumed carbohydrates in accordance with recommended values. Protein and lipid intakes were above recommended values, while fibre, calcium, potassium, magnesium, and folic acid intakes were below recommendation for 98%, 80%, 100%, 100%, and 98% of the tennis players respectively. The observed nutritional deficiencies represent an additional barrier for adolescents engaged in competitive sports to achieve an optimum nutrition to maintain growth, health, and performance.

Biobehavior of the human love of salt

We are beginning to understand why humans ingest so much salt. Here we address three issues: The first is whether our salt appetite is similar to that in animals, which we understand well. Our analysis suggests that this is doubtful, because of important differences between human and animal love of salt. The second issue then becomes how our predilection for salt is determined, for which we have a partial description, resting on development, conditioning, habit, and dietary culture. The last issue is the source of individual variation in salt avidity. We have partial answers to that too in the effects of perinatal sodium loss, sodium loss teaching us to seek salt, and gender. Other possibilities are suggested. From animal sodium appetite we humans may retain the lifelong enhancement of salt intake due to perinatal sodium loss, and a predisposition to learn the benefits of salt when in dire need. Nevertheless, human salt intake does not fit the biological model of a regulated sodium appetite. Indeed this archetypal 'wisdom of the body' fails us in all that has to do with behavioral regulation of this most basic need.