Sex differences in the effects of inorganic nitrate supplementation on exercise economy and endurance capacity in healthy young adults.

Dietary nitrate (NO3-) is a widely used supplement purported to provide beneficial effects during exercise. Most studies to date include predominantly males. Therefore, the present study aimed to investigate if there is a sex-dependent effect of NO3- supplementation on exercise outcomes. We hypothesized that both sexes would exhibit improvements in exercise economy and exercise capacity following NO3- supplementation, but males would benefit to a greater extent. In a double-blind, randomized, crossover study, twelve females (24 ± 4 yr) and fourteen males (23 ± 4 yr) completed two 4-min moderate-intensity (MOD) exercise bouts followed by a time-to-exhaustion (TTE) task after following 3 days of NO3- supplementation (beetroot juice or BRJ) or NO3--depleted placebo (PL). Females were tested during the early follicular phase of the menstrual cycle. During MOD exercise, BRJ reduced the steady-state V̇o2 by ∼5% in males (M: Δ -87 ± 115 mL·min-1; P < 0.05) but not in females (F: Δ 6 ± 195 mL·min-1). Similarly, BRJ extended TTE by ∼15% in males (P < 0.05) but not in females. Dietary NO3- supplementation improved exercise economy during moderate-intensity exercise and exercise capacity during severe-intensity TTE in males but not in females. These differences could be related to estrogen levels, antioxidant capacity, nitrate-reducing bacteria, or a variety of known physiologic differences such as skeletal muscle calcium handling, and/or fiber type. Overall, our data suggests the ergogenic benefits of oral NO3- supplementation found in studies predominantly on male subjects may not be applicable to females.NEW & NOTEWORTHY While inorganic nitrate (NO3-) supplementation has increased in popularity as an ergogenic aid to improve exercise performance, the role of sex in NO3- supplementation on exercise outcomes is lacking despite known physiological differences during exercise between sex. This study revealed that males, but not females, improved exercise economy during submaximal exercise and exercise capacity during exercise within the severe-intensity domain following NO3- supplementation.

The effects of inorganic nitrate supplementation on exercise economy and endurance capacity across the menstrual cycle.

Oral inorganic nitrate (NO3-) supplementation has been shown to increase bioavailable NO and provide potential ergogenic benefits in males; however, data in females is scarce. Estrogen is known to increase endogenous NO bioavailability and to fluctuate throughout the menstrual cycle (MC), being lowest in the early follicular (EF) phase and highest during the late follicular (LF) phase. This study examined the effects of oral NO3- supplementation on exercise economy, endurance capacity, and vascular health in young females across the MC. Ten normally menstruating females' MCs were tested in a double-blinded, randomized design during both the EF and LF phases of the MC. Participants consumed ∼13 mmol NO3-, in the form of 140 mL beetroot juice (BRJ) or an identical NO3--depleted placebo (PL) for ∼3 days before lab visits and 2 h before testing on lab visits. Plasma nitrate, nitrite, and estradiol were assessed, as was blood pressure and pulse wave velocity. Moderate-intensity exercise economy and severe intensity time to exhaustion (TTE) were tested on a cycle ergometer. As expected, plasma estradiol was elevated in the LF phase, and plasma nitrite and nitrate were elevated in the BRJ condition. Exercise economy was unaltered by BRJ or the MC, however TTE was significantly worsened by 48 s (∼10%) after BRJ supplementation (P = 0.04), but was not different across the MC with no interaction effects. In conclusion, NO3- supplementation did not affect exercise economy or vascular health and worsened aerobic endurance capacity (TTE), suggesting healthy females should proceed with caution when considering supplementation with BRJ.NEW & NOTEWORTHY Although inorganic nitrate (NO3-) supplementation has increased in popularity as a means of improving exercise performance, data in females at different phases of the menstrual cycle are lacking despite known interactions of estrogen with NO. This study revealed neither NO3- supplementation nor the menstrual cycle influenced exercise economy or vascular health in healthy young naturally menstruating females, while NO3- supplementation significantly worsened endurance capacity (10%) independent of the menstrual cycle phase.

The impact of elevated body core temperature on critical power as determined by a 3-min all-out test.

Critical power (CP) delineates the heavy and severe exercise intensity domains, and sustained work rates above CP result in an inexorable progression of oxygen uptake to a maximal value and, subsequently, the limit of exercise tolerance. The finite work capacity above CP, W', is defined by the curvature constant of the power-duration relationship. Heavy or severe exercise in a hot environment generates additional challenges related to the rise in body core temperature (Tc) that may impact CP and W'. The purpose of this study was to determine the effect of elevated Tc on CP and W'. CP and W' were estimated by end-test power (EP; mean of final 30 s) and work above end-test power (WEP), respectively, from 3-min "all-out" tests performed on a cycle ergometer. Volunteers (n = 8, 4 female) performed the 3-min tests during a familiarization visit and two experimental visits (thermoneutral vs. hot, randomized crossover design). Before experimental 3-min tests, the subjects were immersed in water (thermoneutral: 36°C for 30 min; hot: 40.5°C until Tc was ≥38.5°C). Mean Tc was significantly greater in the hot condition than in the thermoneutral condition (38.5 ± 0.0°C vs. 37.4 ± 0.2°C; means ± SD, P < 0.01). All 3-min tests were performed in an environmental chamber [thermoneutral: 18°C, 45% relative humidity (RH); hot: 38 °C, 40% RH]. EP was similar between thermoneutral (239 ± 57 W) and hot (234 ± 66 W; P = 0.55) conditions. WEP was similar between thermoneutral (10.9 ± 3.0 kJ) and hot conditions (9.3 ± 3.6; P = 0.19). These results suggest that elevated Tc has no significant impact on EP or WEP.NEW & NOTEWORTHY The parameters of the power-duration relationship (critical power and W') estimated by a 3-min all-out test were not altered by elevated body core temperature as compared with a thermoneutral condition.