No abstract

There is growing interest in the effect of exogenous ketone body supplementation on exercise responses and performance. The limited studies to date have yielded equivocal data, likely due in part to differences in dosing strategy, increase in blood ketones, and participant training status. Using a randomized, double-blind, counterbalanced design, we examined the effect of ingesting a ketone monoester (KE) supplement (600 mg/kg body mass) or flavour-matched placebo in endurance-trained adults (n=10 males, n=9 females; VO2peak=57±8 ml/kg/min). Participants performed a 30-min cycling bout at ventilatory threshold intensity (71±3% VO2peak), followed 15 min later by a 3 kJ/kg body mass time-trial. KE versus placebo ingestion increased plasma [β-hydroxybutyrate] before exercise (3.9±1.0 vs 0.2±0.3 mM, p<0.0001, dz=3.4), ventilation (77±17 vs 71±15 L/min, p<0.0001, dz=1.3) and heart rate (155±11 vs 150±11 beats/min, p<0.001, dz=1.2) during exercise, and rating of perceived exertion at the end of exercise (15.4±1.6 vs 14.5±1.2, p<0.01, dz=0.85). Plasma [β-hydroxybutyrate] remained higher after KE vs placebo ingestion before the time-trial (3.5±1.0 vs 0.3±0.2 mM, p<0.0001, dz=3.1), but performance was not different (KE: 16:25±2:50 vs placebo: 16:06±2:40 min:s, p=0.20; dz=0.31). We conclude that acute ingestion of a relatively large KE bolus dose increased markers of cardiorespiratory stress during submaximal exercise in endurance-trained participants. Novelty bullets: •Limited studies have yielded equivocal data regarding exercise responses after acute ketone body supplementation. •Using a randomized, double-blind, placebo-controlled, counterbalanced design, we found that ingestion of a large bolus dose of a commercial ketone monoester supplement increased markers of cardiorespiratory stress during cycling at ventilatory threshold intensity in endurance-trained adults.

This study investigated the effects of acute and chronic beetroot juice (BRJ) supplementation on submaximal exercise oxygen uptake (VO 2), time trial (TT) performance, and contractile properties of the plantar flexors in females. Study 1: Using a double blind, randomized, crossover design, 12 recreationally active females using hormonal contraceptives supplemented acutely (2.5 h) and chronically (8 days) with 280 mL BRJ/d (~26 mmoles nitrate [NO3−]) or a NO3−‐free placebo (PLA). On days 1 and 8, participants cycled for 10 min at 50% and 70% VO 2peak and completed a 4 kJ/kg body mass TT. Plasma [NO3−] and nitrite ([NO2 −]) increased significantly following BRJ supplementation versus PLA. There was no effect of BRJ supplementation on VO 2 at 50% or 70% VO 2peak, or TT performance. Study 2: 12 recreationally active females (n = 7 from Study 1) using hormonal contraceptives participated in a baseline visit and were supplemented acutely (2.5 h) and chronically (8 days) with 280 mL BRJ/d. Maximum voluntary strength (MVC) of the plantar flexors was assessed and a torque‐frequency curve performed. BRJ had no effect on MVC, voluntary activation, peak twitch torque, time to peak torque, or half relaxation time. Following both acute (46.6 ± 4.9% of 100 Hz torque) and chronic (47.2 ± 4.4%) supplementation, 10 Hz torque was significantly greater compared to baseline (32.9 ± 2.6%). In summary, BRJ may not be an effective ergogenic aid in recreationally active females as it did not reduce submaximal exercise VO 2 or improve aerobic TT performance despite increasing low frequency torque production.

The effects of mild dehydration during ice hockey are well-studied in males, but not females. In a randomized, crossover design 11 female varsity hockey players drank no fluid (1.7±0.3% body mass loss) or water to maintain hydration during simulated-hockey exercise. Core temperature (P<0.01) and perceived fatigue (P=0.02) were higher and sprint power lower (P<0.01) when mildly dehydrated. Thus, mild dehydration may impair hockey performance and thermoregulation while increasing perceived fatigue in females. • Female stop-and-go sport athletes may benefit their in-game sprint performance and thermoregulation by following personalized in-game hydration to prevent becoming mildly dehydrated.

Physiological strain during exercise is increased by mild dehydration (~1-3% body mass loss). This response may be sex-dependent but there are no direct comparative data in this regard. This review aimed to develop a framework for future research by exploring the potential impact of sex on thermoregulatory and cardiac strain associated with exercise-induced dehydration. Sex-based comparisons were achieved by comparing trends from studies that implemented similar experimental protocols but recruited males and females separately. This revealed a higher core temperature (Tc) in response to exercise-induced dehydration in both sexes, however it seemingly occurred at a lower percent body mass loss in females. Although less clear, similar trends existed for cardiac strain. The average female may have a lower body water volume per body mass compared to males, and therefore the same % body mass loss between the sexes may represent a larger portion of total body water in females potentially posing a greater physiological strain. Additionally, the rate which Tc increases at exercise onset might be faster in females and induce a greater thermoregulatory challenge earlier into exercise. The Tc response at exercise onset is associated with lower sweating rates in females, which is commonly attributed to sex-differences in metabolic heat production. However, a reduced sweat gland sensitivity to stimuli, lower fluid output per sweat gland, and sex hormones promoting fluid retention in females may also contribute. In conclusion, the limited evidence suggests sex-based differences exist in thermoregulatory and cardiac strain associated with exercise-induced dehydration, and this warrants future investigations.

During play, ice hockey goaltenders routinely dehydrate through sweating and lose ≥2% body mass, which may impair thermoregulation and performance. Purpose: This randomized, crossover study examined the effects of mild dehydration on goaltender on-ice thermoregulation, heart rate, fatigue, and performance. Methods: Eleven goaltenders played a 70-minute scrimmage followed by a shootout and drills to analyze reaction time and movements. On ice, they either consumed no fluid (NF) and lost 2.4% (0.3%) body mass or maintained body mass with water (WAT) or a carbohydrate–electrolyte solution (CES). Save percentage, rating of perceived exertion, heart rate, and core temperature were recorded throughout, and a postskate questionnaire assessed perceived fatigue. Results: Relative to NF, intake of both fluids decreased heart rate (interaction: P = .03), core temperature (peak NF = 39.0°C [0.1°C], WAT = 38.6°C [0.1°C], and CES = 38.5°C [0.1°C]; P = .005), and rating of perceived exertion in the scrimmage (post hoc: P < .04), as well as increasing save percentage in the final 10 minutes of scrimmage (NF = 75.8% [1.9%], WAT = 81.7% [2.3%], and CES = 81.3% [2.3%], post hoc: P < .04). In drills, movement speed (post hoc: P < .05) and reaction time (post hoc: P < .04) were slower in the NF versus both fluid conditions. Intake of either fluid similarly reduced postskate questionnaire scores (condition: P < .0001). Only CES significantly reduced rating of perceived exertion in drills (post hoc: P < .05) and increased peak movement power versus NF (post hoc: P = .02). Shootout save percentage was similar between conditions (P = .37). Conclusions: Mild dehydration increased physiological strain and fatigue and decreased ice hockey goaltender performance versus maintaining hydration. Also, maintaining hydration with a CES versus WAT may further reduce perceived fatigue and positively affect movements.

This study recorded the dietary intakes of young male ice hockey players (10–13 year (yr)) for 3 consecutive days while participating in a 5-day summer hockey camp. Players were categorized as older children (OC, n = 10; 10.7 ± 0.2 yr; 37.1 ± 1.5 kg; 147.9 ± 2.1 cm) and young adolescents (YA, n = 10; 12.9 ± 0.1 yr; 45.2 ± 1.5 kg; 157.0 ± 2.4 cm). Players consumed their usual daily intakes. Parents recorded food intake in the mornings and evenings, while the researchers recorded food intake at camp. Energy intake was higher in both groups when compared to data for age-matched young Canadian (CDN) males (OC, 2967 ± 211 vs. 2000 kcal/day; YA, 2773 ± 91 vs. 2250 kcal/day). Carbohydrate (CHO) (OC, 11.2 ± 0.8 vs. YO, 8.9 ± 0.5 g/kg body mass/day) and protein (OC, 3.2 ± 0.3; YO, 2.4 ± 0.1 g/kg/day) intakes were higher than reported for young CDN males (CHO, 3.6 and protein, 1.0 g/kg/day) and were within the Acceptable Macronutrient Distribution Range (AMDR; CHO, 56 ± 2.3; 57.4 ± 0.8%; protein, 16.1 ± 1.0; 15.7 ± 0.7%). Fat intake was also within the AMDR in both groups (OC, 29.8 ± 1.6%; YA, 28.3 ± 1.0%). Micronutrient intake was adequate except for Vitamin D intakes that were below the recommended 15 ug/day at 6.3 ± 0.7 (OC) and 5.0 ± 1.5 ug/day (YA). In summary, energy and macronutrient intakes of the OC (10–11 yr) and YA (12–13 yr) players were high and well above the age matched CDN norms. The older children had higher energy intakes/kg body mass than the young adolescents. Higher energy intakes allowed for micronutrients intakes to be met in these young active males, except for vitamin D intake.

Background: Rest between training sessions can be short for athletes. In these situations, consuming carbohydrate (CHO) postexercise replenishes glycogen stores, which is important for recovery and subsequent performance. Purpose: This study tested whether CHO intake during a 2-hour rest between exercise bouts improved performance in the subsequent bout. Methods: In a randomized, single-blinded, crossover design, 10 recreationally active participants (23 [4] y, 70.8 [6.6] kg, 47.0 [5.4] mL·O2·min−1·kg·body·mass−1) arrived at the lab postprandial and completed 2 exercise bouts separated by a 2-hour rest. Bouts included 5 × 4-minute intervals at ∼80% peak oxygen consumption separated by 2 minutes at ∼40% peak oxygen consumption and ended with an endurance trial to voluntary exhaustion at ∼90% peak oxygen consumption. During intervals 1 and 4 in each bout, expired gases were collected and O2 deficit was estimated. Immediately following bout 1, either a CHO (1.2 g CHO·kg·body·mass−1) or placebo solution was consumed. Results: Endurance trial duration decreased in bout 2 versus 1 in both conditions (P < .01) but was ∼35% longer in bout 2 with CHO versus placebo (interaction, P = .03; post hoc, P = .03). Oxygen uptake increased during interval 4 versus 1 in both bouts (P < .01) but was unaffected by CHO (P ≥ .58). O2 deficit was unaffected by CHO (P = .93), bout, or interval (P ≥ .15). Perceived exertion was higher in bout 2 versus 1 (P < .001) and reduced in intervals 2 and 4 in CHO (P ≤ .01). Conclusions: When rest between training sessions is 2 hours, athletes may improve subsequent performance by consuming CHO during recovery.