24 h Hydration profile of collegiate soccer players training once versus twice per day in the heat.

This study examined 24-h hydration parameters among collegiate, male soccer players (n = 17) during twice (X2) and once (X1) per day practice schedules in the heat. Urine specific gravity (USG) and body mass were measured before morning practices, afternoon practice (X2)/team meeting (X1), and the next morning practices. Fluid intake, sweat losses, and urinary losses were assessed during each 24-h window. Pre-practice body mass or USG did not differ among the timepoints. Sweat losses differed among all practices (p < 0.05) and averaged approximately 2.181±0.693 (X2AM) 1.710±0.474 (X2PM), and 3.361±0.956 L (X1AM), but players averaged replacing >50% of sweat losses with fluid intake every practice. Fluid intake during and between practices from practice 1 to the afternoon practice for X2 resulted in a positive fluid balance for X2 (+0.446±0.916 L). However, higher sweat loss during the initial morning practice and lower relative fluid intake prior to the afternoon team meeting the following morning resulted in a negative fluid balance (-0.304±0.675 L; p < 0.05: Cohen's d = 0.94) over the same time period for X1. By the start of the next morning practice sessions, both X1 (+0.664±1.051 L) and X2 (+0.446±0.916 L) were in positive fluid balance, respectively. Ample fluid consumption opportunities, scaled down practice intensities during X2, and potentially intentional greater relative fluid intake during X2 training resulted in no difference in fluid shift versus an X1 schedule before the start of practices. The majority of players maintained fluid balance drinking ad libitum regardless of practice schedule.

Assessment of Metabolic Flexibility by Substrate Oxidation Responses and Blood Lactate in Women Expressing Varying Levels of Aerobic Fitness and Body Fat.

ABSTRACT: Waldman, HS, Bryant, AR, Knight, SN, Killen, LG, Davis, BA, Robinson, MA, and O'Neal, EK. Assessment of metabolic flexibility by substrate oxidation responses and blood lactate in women expressing varying levels of aerobic fitness and body fat. J Strength Cond Res 37(3): 581-588, 2023-Collection of substrate oxidation responses during exercise is proposed as a noninvasive means for assessing metabolic flexibility in male subjects. However, because of hormonal and metabolic differences between sexes, this method may not be applicable to female subjects. This study assessed metabolic flexibility through indirect calorimetry across female subjects with different maximal oxidative capacities. Thirty-eight (18-45 years) eumenorrheic female subjects were stratified ( p < 0.05) based on V̇ o2 peak (mL·kg -1 ·min -1 ) into (1) endurance-trained (ET, n = 12, 42.6 ± 5.3), (2) recreationally active (RA, n = 13, 32.3 ± 1.6), or (3) overweight female subjects (OW, n = 13, 21.0 ± 4.0). Subjects completed the same 5-stage graded exercise test with intensities of 30, 45, 60, 75, and 90 W. Lactate [La - ], carbohydrate (CHOox), and fat (FATox) oxidation rates were assessed during the last min of each 5-minute stage. Subjects then cycled to exhaustion to determine V̇ o2 peak. Endurance-trained and RA female subjects expressed significantly ( p ≤ 0.05) higher absolute rates and rates scaled to fat-free mass of CHOox and FATox compared with OW female subjects during multiple stages. [La - ] failed to consistently differentiate the 3 groups with higher [La - ] for OW only found during stage 4; however, RER differed by 0.09 units or more at each stage for OW vs. ET. It seems that RER was more sensitive to cohort characteristics than [La - ] contrasting recent findings in male cohorts. In conclusion, indirect calorimetry is a practical and noninvasive method for assessing metabolic flexibility in eumenorrheic female subjects of varying aerobic fitness levels.