Anterior cerebral blood velocity and end-tidal CO2 responses to exercise differ in children and adults.

Little is known about the response of the cerebrovasculature to acute exercise in children and how these responses might differ with adults. Therefore, we compared changes in middle cerebral artery blood velocity (MCAVmean), end-tidal Pco2 ([Formula: see text]), blood pressure, and minute ventilation (V̇e) in response to incremental exercise between children and adults. Thirteen children [age: 9 ± 1 (SD) yr] and thirteen sex-matched adults (age: 25 ± 4 yr) completed a maximal exercise test, during which MCAVmean, [Formula: see text], and V̇e were measured continuously. These variables were measured at rest, at exercise intensities specific to individual ventilatory thresholds, and at maximum. Although MCAVmean was higher at rest in children compared with adults, there were smaller increases in children (1-12%) compared with adults (12-25%) at all exercise intensities. There were alterations in [Formula: see text] with exercise intensity in an age-dependent manner [F(2.5,54.5) = 7.983, P < 0.001; η2 = 0.266], remaining stable in children with increasing exercise intensity (37-39 mmHg; P > 0.05) until hyperventilation-induced reductions following the respiratory compensation point. In adults, [Formula: see text] increased with exercise intensity (36-45 mmHg, P < 0.05) until the ventilatory threshold. From the ventilatory threshold to maximum, adults showed a greater hyperventilation-induced hypocapnia than children. These findings show that the relative increase in MCAVmean during exercise was attenuated in children compared with adults. There was also a weaker relationship between MCAVmean and [Formula: see text] during exercise in children, suggesting that cerebral perfusion may be regulated by different mechanisms during exercise in the child.NEW & NOTEWORTHY These findings provide the first direct evidence that exercise increases cerebral blood flow in children to a lesser extent than in adults. Changes in end-tidal CO2 parallel changes in cerebral perfusion in adults but not in children, suggesting age-dependent regulatory mechanisms of cerebral blood flow during exercise.

Urine color as an indicator of urine concentration in pregnant and lactating women.

AIM: Urine concentration measured via osmolality (U OSM) and specific gravity (U SG) reflects the adequacy of daily fluid intake, which has important relationships to health in pregnant (PREG) and lactating (LACT) women. Urine color (U COL) may be a practical, surrogate marker for whole-body hydration status. PURPOSE: To determine whether U COL was a valid measure of urine concentration in PREG and LACT, and pair-matched non-pregnant, non-lactating control women (CON). METHODS: Eighteen PREG/LACT (age 31 ± 1 years, pre-pregnancy BMI 24.3 ± 5.9 kg m-2) and eighteen CON (age 29 ± 4 years, BMI 24.1 ± 3.7 kg m-2) collected 24-h and single-urine samples on specified daily voids at five time points (15 ± 2, 26 ± 1, and 37 ± 1 weeks gestation, 3 ± 1 and 9 ± 1 weeks postpartum during lactation; CON visits were separated by similar time intervals) for measurement of 24-h U OSM, U SG, and U COL and single-sample U OSM and U COL. RESULTS: Twenty-four-hour U COL was significantly correlated with 24-h U OSM (r = 0.6085-0.8390, P < 0.0001) and 24-h U SG (r = 0.6213-0.8985, P < 0.0001) in all groups. A 24-h U COL ≥ 4 (AUC = 0.6848-0.9513, P < 0.05) and single-sample U COL ≥ 4 (AUC = 0.9094-0.9216, P < 0.0001) indicated 24-h U OSM ≥ 500 mOsm kg-1 (representing inadequate fluid intake) in PREG, LACT, and CON. CONCLUSIONS: Urine color was a valid marker of urine concentration in all groups. Thus, PREG, LACT, and CON can utilize U COL to monitor their daily fluid balance. Women who present with a U COL ≥ 4 likely have a U OSM ≥ 500 mOsm kg-1 and should increase fluid consumption to improve overall hydration status.

Precision, Accuracy, and Performance Outcomes of Perceived Exertion vs. Heart Rate Guided Run-training.

Johnson, EC, Pryor, RR, Casa, DJ, Ellis, LA, Maresh, CM, Pescatello, LS, Ganio, MS, Lee, EC, and Armstrong, LE. Precision, accuracy, and performance outcomes of perceived exertion vs. heart rate guided run-training. J Strength Cond Res 31(3): 630-637, 2017-The purpose of this investigation was to compare run-prescription by heart rate (HR) vs. rating of perceived exertion (RPE) during 6 weeks to determine which is superior for consistent achievement of target intensities and improved performance. Forty untrained men participated in this laboratory-controlled and field-controlled trial. Participants were divided into heart rate (HRTG) and rating of perceived exertion training groups (RPETG). All underwent maximal-graded exercise testing and a 12-minute run test before and after training. Intensity was prescribed as either a target HR or RPE that corresponded to 4 relative intensity levels: 45, 60, 75, and 90% V[Combining Dot Above]O2 reserve (V[Combining Dot Above]O2R). Mean exercise intensity over the 6 weeks did not differ between HRTG (65.6 ± 7.2%HRR) and RPETG (61.9 ± 9.0%HRR). V[Combining Dot Above]O2max (+4.1 ± 2.5 ml·kg·min) and 12 minutes run distance (+240.1 ± 150.1 m) improved similarly in HRTG and RPETG (p > 0.05). HRTG displayed lower coefficients of variation (CV) (5.9 ± 4.1%, 3.3 ± 3.8%, and 3.0 ± 2.2%) and %error (4.1 ± 4.7%, 2.3 ± 4.1% and 2.6 ± 3.2%) at 45, 60, and 75% V[Combining Dot Above]O2R compared with RPETG (CV 11.1 ± 5.0%, 7.7 ± 4.1% and 5.6 ± 3.2%; all p < 0.005) %error (15.7 ± 9.2%, 10.6 ± 9.2% and 6.7 ± 3.2%; all p < 0.001), respectively. Overall, HR-prescribed and RPE-prescribed run-training resulted in similar exercise intensity and performance outcomes over 6 weeks. Differences in the CV and %error suggest use of HR monitoring for individuals that are new to running as it improves precision and accuracy but does not increase performance improvements across 6 weeks.

The Effects of Nitrate-Rich Supplementation on Neuromuscular Efficiency during Heavy Resistance Exercise.

OBJECTIVE: Nitrate-rich (NR) supplements can enhance exercise performance by improving neuromuscular function and the aerobic cost of exercise. However, little is known about the effects of nitrate on dynamic, multijoint resistance exercise. METHODS: Fourteen resistance-trained men (age, 21.1 ± 0.9 years; height, 173.2 ± 2.9 cm: body mass, 77.6 ± 4.3 kg; squat one-repetition maximum [1RM], 127.5 ± 18.8 kg) participated in a randomized, double-blind, crossover experiment. Subjects consumed an NR or nitrate-poor (NP) supplement for 3 days, performed a bout of heavy resistance exercise, completed a washout, and then repeated the procedures with the remaining supplement. Before, during, and after exercise, individual and gross motor unit efficiency was assessed during isometric and dynamic muscle contractions. In addition, we compared physical performance, heart rate, lactate, and oxygen consumption (VO2). RESULTS: Nitrate-rich supplementation resulted in lower initial muscle firing rates at rest and lower mean and maximum firing rates over the course of fatiguing exercise. Nitrate-poor supplementation was accompanied by increased mean and maximum firing rates by the end of exercise and lower initial firing rates. In addition, NR supplementation resulted in higher mean peak electromyography (EMG) amplitudes. Heart rate, lactate, and physical performance did not differ by treatment, but oxygen consumption increased more frequently when the NP supplement was consumed. CONCLUSION: Supplementation with an NR beetroot extract-based supplement provided neuromuscular advantages during metabolically taxing resistance exercise.

Urine colour change as an indicator of change in daily water intake: a quantitative analysis.

PURPOSE: Urine colour (U Col) is simple to measure, differs between low-volume and high-volume drinkers, and is responsive to changes in daily total fluid intake (TFI). However, to date, no study has quantified the relationship between a change in TFI and the resultant change in U Col. This analysis aimed to determine the change in TFI needed to adjust 24-h U Col by 2 shades on an 8-colour scale, and to evaluate whether starting U Col altered the relationship between the change in TFI and change in U Col. METHODS: We performed a pooled analysis on data from 238 healthy American and European adults (50 % male; age, 28 (sd 6) years; BMI 22.9 (sd 2.6) kg/m(2)), and evaluated the change in TFI, urine volume (U Vol), and specific gravity (U SG) associated with a change in U Col of 2 shades. RESULTS: The mean [95 % CI] change in TFI and U Vol associated with a decrease in U Col by 2 shades (lighter) was 1110 [914;1306] and 1011 [851;1172] mL/day, respectively, while increasing U Col by 2 shades (darker) required a reduction in TFI and U Vol of -1114 [-885;-1343] and -977 [-787;-1166] mL/day. The change in U Col was accompanied by changes in U SG (lighter urine: -.008 [-.007;-.010]; darker urine: +.008 [.006;.009]). Starting U Col did not significantly impact the TFI change required to modify U Col by 2 shades. CONCLUSIONS: Our results suggest a quantifiable relationship between a change in daily TFI and the resultant change in U Col, providing individuals with a practical means for evaluating and adjusting hydration behaviours.

Endurance Cyclist Fluid Intake, Hydration Status, Thirst, and Thermal Sensations: Gender Differences.

This field investigation assessed differences (e.g., drinking behavior, hydration status, perceptual ratings) between female and male endurance cyclists who completed a 164-km event in a hot environment (35 °C mean dry bulb) to inform rehydration recommendations for athletes. Three years of data were pooled to create 2 groups of cyclists: women (n = 15) and men (n = 88). Women were significantly smaller (p < .001) than men in height (166 ± 5 vs. 179 ± 7 cm), body mass (64.6 ± 7.3 vs. 86.4 ± 12.3 kg), and body mass index (BMI; 23.3 ± 1.8 vs. 26.9 ± 3.4) and had lower preevent urinary indices of hydration status, but were similar to men in age (43 ± 7 years vs. 44 ± 9 years) and exercise time (7.77 ± 1.24 hr vs. 7.23 ± 1.75 hr). During the 164-km ride, women lost less body mass (-0.7 ± 1.0 vs. -1.7 ± 1.5 kg; -1.1 ± 1.6% vs. -1.9 ± 1.8% of body weight; p < .005) and consumed less fluid than men (4.80 ± 1.28 L vs. 5.59 ± 2.13 L; p < .005). Women consumed a similar volume of fluid as men, relative to body mass (milliliters/kilogram). To control for performance and anthropomorphic characteristics, 15 women were pair-matched with 15 men on the basis of exercise time on the course and BMI; urine-specific gravity, urine color, and body mass change (kilograms and percentage) were different (p < .05) in 4 of 6 comparisons. No gender differences were observed for ratings of thirst, thermal sensation, or perceived exertion. In conclusion, differences in relative fluid volume consumed and hydration indices suggest that professional sports medicine organizations should consider gender and individualized drinking plans when formulating pronouncements regarding rehydration during exercise.

Effects of Three Oral Nutritional Supplements on Human Hydration Indices.

Urine color (Ucol) as a hydration assessment tool provides practicality, ease of use, and correlates moderately to strongly with urine specific gravity (Usg) and urine osmolality (Uosm). Indicative of daily fluid turnover, along with solute and urochrome excretion in 24-hr samples, Ucol may also reflect dietary composition. Thus, the purpose of this investigation was to determine the efficacy of Ucol as a hydration status biomarker after nutritional supplementation with beetroot (880 mg), vitamin C (1000 mg), and riboflavin (200 mg). Twenty males (Mean ± SD; age, 21 ± 2 y; body mass, 82.12 ± 15.58 kg; height, 1.77 ± 0.06 m) consumed a standardized breakfast and collected all urine voids on one control day (CON) and 1 day after consuming a standardized breakfast and a randomized and double-blinded supplement (SUP) over 3 weeks. Participants replicated exercise and diet for one day before CON, and throughout CON and SUP. Ucol, Usg, Uosm, and urine volume were measured in all 24-hr samples, and Ucol and Usg were measured in all single samples. Ucol was a significant predictor of single sample Usg after all supplements (p < .05). Interestingly, 24-hr Ucol was not a significant predictor of 24-h Usg and Uosm after riboflavin supplementation (p = .20, p = .21). Further, there was a significant difference between CON and SUP 24-h Ucol only after riboflavin supplementation (p < .05). In conclusion, this investigation suggests that users of the UCC (urine color chart) should consider riboflavin supplementation when classifying hydration status and use a combination of urinary biomarkers (e.g., Usg and Ucol), both acutely and over 24 hr.

Effect of cycling in the heat for 164 km on procoagulant and fibrinolytic parameters.

PURPOSE: We assessed the impact of completing the Hotter'n Hell Hundred (HHH), an annual 164 km road cycling event performed in a hot environment, on hemostatic balance in men. METHODS: Sixteen men who completed the ride in <6 h were included in this study. Plasma samples were collected on that morning of the ride (PRE) and immediately on the completion of the ride (IP). Primary hemostasis was assessed by platelet count and von Willebrand factor antigen (vWF:Ag). Coagulation was assessed by measuring prothrombin fragment 1 + 2 (PTF 1 + 2) and thrombin-antithrombin complex (TAT), whereas fibrinolysis was assessed by plasminogen activator inhibitor antigen (PAI-1 Ag), tissue plasminogen activator (tPA Ag), and D-Dimer analyses. RESULTS: Compared to PRE, increases (p < 0.001) were observed at IP for platelets (39 %), vWF:Ag (65 %), PTF 1 + 2 (47 %), TAT (81 %), tPA Ag (231 %), PAI-1 Ag (148 %), and D-Dimer (54 %). PRE PAI-1 Ag concentrations were directly related to BMI and waist circumference (p < 0.05). D-Dimer concentrations at IP correlated positively with age (p < 0.05). CONCLUSIONS: Completing the HHH activated the coagulation and fibrinolytic systems in balance. Age was positively correlated with IP D-Dimer concentrations. Additionally, participants displaying a larger BMI and waist circumference exhibited a positive correlation with PRE PAI-1 Ag concentrations.

Ultraendurance cycling in a hot environment: thirst, fluid consumption, and water balance.

The purpose of this field investigation was to identify and clarify factors that may be used by strength and conditioning professionals to help athletes drink adequately but not excessively during endurance exercise. A universal method to accomplish this goal does not exist because the components of water balance (i.e., sweat rate, fluid consumed) are different for each athlete and endurance events differ greatly. Twenty-six male cyclists (mean ± SD; age, 41 ± 8 years; height, 177 ± 7 cm; body mass, 81.85 ± 8.95 kg) completed a summer 164-km road cycling event in 7.0 ± 2.1 hours (range, 4.5-10.4 hours). Thirst ratings, fluid consumed, indices of hydration status, and body water balance (ingested fluid volume - [urine excreted + sweat loss]) were the primary outcome variables. Measurements were taken before the event, at designated aid stations on the course (52, 97, and 136 km), and at the finish line. Body water balance during exercise was not significantly correlated with exercise time on the course, height, body mass, or body mass index. Thirst ratings were not significantly correlated with any variable. We also observed a wide range of total sweat losses (4.9-12.7 L) and total fluid intakes (2.1-10.5 L) during this ultraendurance event. Therefore, we recommend that strength and conditioning professionals develop an individualized drinking plan for each athlete, by calculating sweat rate (milliliter per hour) on the basis of body mass change (in kilograms), during field simulations of competition.

Diagnostic accuracy of urinary indices to detect mild dehydration in young men following acute riboflavin, Vitamin C or beetroot supplementation.

BACKGROUND: Individuals of all ages are encouraged to monitor their hydration status daily to prevent clinically severe fluid imbalances such as hyponatremia or dehydration. However, acute oral nutritional supplementation may alter urinary hydration assessments and potentially increase the likelihood of inappropriate clinical decisions or diagnosis. This investigation sought to examine the influence of three common over-the-counter nutritional supplements (beetroot, riboflavin, and Vitamin C) on urinary hydration assessments in physically active young men after a 2% exercise-induced dehydration. DESIGN: Eight males (Mean ± SD; age: 22 ± 3 yr; body mass index: 27 ± 5.0) consumed either a standard meal with supplementation (intervention) or a standard meal without supplementation (control). Participants performed a variety of aerobic or resistance exercises until reaching ≥2% body mass loss in a counter-balanced, double-blinded design. Following exercise participation, urine samples were collected for an 8 h observational period during which food consumption was replicated. Urine samples were analyzed for urine color, specific gravity, volume, and osmolality. Maintenance of ~2% body mass loss (2.6 ± 0.5%; range: 1.7-4.0%) was confirmed following the 8 h observational period. RESULTS: Statistically significant (p < 0.05) changes were noted in urine color following Vitamin C supplementation compared to control; however, the difference was not clinically meaningful. CONCLUSIONS: These findings indicate that urine color, specific gravity, and osmolality maintain clinical utility to detect moderate levels of dehydration in physically active men consuming commercially available doses of beetroot, riboflavin, or Vitamin C.

Stability in neurovascular function at 3800m.

Hypoxia-induced neurocognitive impairments have been of clinical interest for centuries. The mechanisms responsible for these neurocognitive impairments at altitude are unclear, but may relate to the uncoupling of local neural activity with appropriate changes in cerebral blood flow (CBF; i.e., functional hyperemia). At both sea level and following 3 and 7days at 3800m (Barcroft Research Lab, White Mountain, CA, USA), transcranial Doppler was used to index CBF during three separate tasks designed to evoke cerebral functional hyperemia in 11 healthy individuals (26.6±5.5yrs, 2 females). The tasks were: 1) Visual stimulation (VS), with measurement of anterior and posterior CBF; 2) Verbal fluency (VF), with measurement of bilateral CBF; and 3) Visuospatial task (VST), with measurement of bilateral CBF. The VS evoked an increase from baseline to percent peak response in both the posterior (15.2±7.7%, P<0.01) and anterior (7.6±3.5%, P<0.01) cerebral hemispheres; however, the percent peak response was higher in the posterior brain, where visual regions are localized (P=0.01). The left-sided task, VF, resulted in an increase in both the left (12.2±4.0%, P<0.01) and right (9.0±4.4%, P<0.01) cerebral hemispheres; however, the percent peak response was higher in the left brain, where language centers are located (P<0.01). The right-sided task, VST, evoked an increase in both the left (13.9±7.1%, P<0.01) and right (16.8±6.7%, P<0.01) cerebral hemispheres; however, the percent peak response was higher in the right brain, where visuospatial regions are located (P<0.01). Each cerebral functional hyperemia response for all three tasks was unaffected by high altitude exposure (P>0.05). Overall, at least at 3800m, neurovascular function is intact with exposure to 3 and 7days of high altitude and likely does not explain the previous reports of neurocognitive impairment.