Effects of skim milk and isotonic drink consumption before exercise on fluid homeostasis and time-trial performance in cyclists: a randomized cross-over study

Abstract

Background: Hydration status affects endurance performance. Pre-exercise hydration recommendations target the consumption of high carbohydrate and sodium beverages. Milk, due to its carbohydrate and sodium content, may be considered an effective pre-exercise hydration beverage. Purpose: In a randomized cross-over trial, we compared the effects of an isotonic sport drink (SPD) with skim milk (SM) consumption before a race, on fluid homeostasis and time-trial performance in road cyclists. Methods: Male road cyclists (n = 9; age, 26.8 ± 4.78 years) with 10.8 ± 8.56 years of experience in national competitions, consumed either SPD or SM in doses of 350 mL at 3 h and 350 mL at 1.5 h before a 18.6 km time-trial race. Measurements of body mass, urine specific gravity (USG), urine color and time-trial were compared between drinks (group; g) before and after the race (time; t). Results: The two-way ANOVA showed no differences between SPD and SM in body mass (t, p < 0.0001; g, p = 0.89; t × g, p = 0.54), USG (t, p = 0.01; g, p = 0.63; t × g, p = 0.29) and urine color (t, p = 0.01; g, p = 0.54; t × g, p = 0.28) before or after race. Furthermore, no differences on water consumption during the race (p = 0.55) or time-trial performance (p = 0.84) were observed between trials. Conclusion: Current results may help athletes with different beverages preferences to increase their options of hydration strategies.

Impact of hydration with beverages containing free sugars or xylitol on metabolic and acute kidney injury markers after physical exercise

“…Interestingly, similar results were obtained in a study of elite soccer players from the Spanish La Liga (Barcelona FC), in this group fewer than 30% of the subjects were euhydrated prior to training sessions (Rollo et al, 2021). This finding is consistent with previous observations that many athletes are poorly hydrated before training sessions (García-Berger et al, 2020). In a study of recreational basketball players, an at all astonishing 17.5% of subjects reported that they did not drink before exercise (Bibiloni et al, 2018).…”

“…Hypohydration greater than 2% of body mass impairs performance during endurance exercise, decreases physical work capacity and has a negative impact on mood ( Sawka and Montain, 2000 ; Sawka et al, 2007 ; Seo et al, 2014 ; Bibiloni et al, 2018 ; García-Berger et al, 2020 ). The risk of rhabdomyolysis, exercise-associated hyponatremia and acute kidney injury (AKI) is increased in subjects with a body water deficit ( Krisher et al, 2020 ; Juett et al, 2021 ).…”

“…Energy expenditure is as high as 1,300–1,600 kcal ( Seo et al, 2014 ). It has been accepted by sports experts that it is appropriate to consume a drink comprising carbohydrates (CHO) and electrolytes ( Sawka et al, 2007 ; Marcos et al, 2014 ; García-Berger et al, 2020 ; Millard-Stafford et al, 2021 ). Players should consume 1–3 g of CHO/kg body mass 3–4 h before kick-off and it is recommended to consume 30–60 g CHO after the warm-up and again at half-time ( Collins et al, 2021 ).…”

The effects of fluid absorption and plasma volume changes in athletes following consumption of various beverages

“…Athletes usually drink water or sports drinks (SpD) to rehydrate during training and competition. This effect has been demonstrated in several studies [10,15,16]. Still, one can also hydrate with water alone or with an oral rehydration solution (ORS) containing water with traces of sugar, salt, sodium, and potassium.…”

Compositional Aspects of Beverages Designed to Promote Hydration Before, During, and After Exercise: Concepts Revisited

“…In addition, these formulations may increase fluid retention and have mild hypervolemic effects; therefore, they may ameliorate dehydration during exercise, without the risk of possible adverse effects often observed with other hyperhydration protocols. Unfortunately, most research on the pre-exercise period has focused on maximizing glycogen stores to ensure adequate fuel supply during exercise, with only a few food products, such as coconut water, skimmed milk, non-alcoholic beer, and soup being explored to improve pre-exercise hydration status [ 195 , 196 , 197 , 198 ]. A rationale for the type, volume, and timing of pre-exercise hydration is not always clear, and further research on well-designed CES compositions to improve fluid balance before exercise is warranted.…”