How long after maximal physical exertion should baseline computerized neurocognitive testing and symptom assessment be administered?

Objective: Prior research suggests maximal physical exertion (MPE) may negatively affect the reliability and validity of computerized neurocognitive testing (CNT); the purpose of this study was to identify aclinically relevant recovery interval following MPE for the administration of baseline CNT.Design: Random-crossover.Participants: Thirty (M = 21.87 ± 2.29 y), moderately-active,healthy participants, without history of ADHD, learning disabilities, psychological disorders or concussion (within the last six months).Intervention: Participants completed four randomly ordered experimental trials. Except for the control trial, CNT was administered following MPE with assigned recovery intervals [Immediate, 10-minutes,or 20-minutes]. Aseries of repeated measures analysis of variance (ANOVAs) were performed on CNT composite and total symptom scores.Results: Total symptom scores were significantly greater (p < .01) at the immediate, 10-minute,and 20-minuterecovery intervals compared to the control trial. Processing speed was significantly faster at the 20-minuterecovery interval compared to the control trials. Visual memory, verbal memory, or reaction time did not differ across recovery intervals.Conclusions: Clinicians should wait more than 20 minutes before assessing baseline concussion symptoms following about of MPE.

Adequacy of Daily Fluid Intake Volume Can Be Identified From Urinary Frequency and Perceived Thirst in Healthy Adults.

Objective: Achieving and maintaining an optimal level of hydration has significant implications for both acute and chronic health, yet many hydration assessments are not feasible for the general public. Urinary frequency (UF) is a reliable method to self-assess hydration status in healthy individuals, and thirst can provide additional sensory information on adequacy of daily fluid intake volume (DFI). However, threshold values for these indices to detect optimal hydration have not been determined. In this study, we sought to determine threshold values for 24-hour UF and perceived thirst that could accurately distinguish between optimal and suboptimal hydration states.Methods: Thirty-two healthy adults (age 22 ± 3 years, body mass index 24.9 ± 4.1 kg/m2) collected urine over 24 hours on four separate occasions, where UF was recorded as well as thirst at each void using a numbered perceptual scale. Using urine osmolality as the criterion standard, all samples were either classified as representing an optimal (≤500 mOsm·kg-1) or suboptimal hydration status (>500 mOsm·kg-1).Results: A 24-hour UF ≤6 was able to detect suboptimal hydration with good accuracy (area under the curve [AUC] 0.815) and a 24-hour average perceived thirst rating > 3 ("a little thirsty") could detect it with reasonable accuracy (AUC 0.725). In addition, a UF ≤4 had a considerably higher positive likelihood ratio to detect suboptimal hydration versus a UF ≤6 (9.03 versus 2.18, respectively).Conclusions: These analyses suggest that individuals with a 24-hour UF ≤6 or perceiving themselves to be, on average, "a little thirsty" throughout the day are likely to be suboptimally hydrated and thus underconsuming an adequate DFI.

Examining the links between hydration knowledge, attitudes and behavior.

PURPOSE: This study aimed to examine the psychological factors (knowledge, barriers and facilitators) that can contribute to hydration-related behaviors (i.e., fluid intake) in the general population and how these relate to physical health. METHODS: A structured survey was developed to examine the links between hydration knowledge (29 items), attitudes about hydration (80 items), and fluid intake behavior (8 items) among US adults. Survey data from Phase 1 (n =301, US adults) psychometrically evaluated the items via item analysis (knowledge and fluid behavior) and factor analysis (attitudes). Phase 2 survey data (n =389, US adults and college students) refined and validated the new 16-item hydration knowledge measure, 4-item fluid intake behavior index, and 18-item attitude measure (barriers and facilitators of hydration-related behaviors) alongside indices of physical health (BMI and exercise behaviors). RESULTS: Participants had a moderate level of hydration knowledge (Phase 1: 10.91 ± 3.10; Phase 2: 10.87 ± 2.47). A five-factor measure of attitudes which assessed both facilitators (social pressure and attention to monitoring) and barriers (lack of effort, physical barriers and lack of a fluid container) to hydration demonstrated strong internal consistency (αs from 0.75 to 0.90). Attitudes about hydration-most notably barriers to hydration-were associated with indicators of health and with fluid intake behaviors, whereas hydration knowledge was not. CONCLUSIONS: Increasing hydration knowledge may be necessary for people who hold inaccurate information about hydration, but attitudes about hydration are likely to have a larger impact on fluid intake behaviors and health-related outcomes.

Effects of a 14-Day Hydration Intervention on Individuals with Habitually Low Fluid Intake.

BACKGROUND: Debate continues over whether or not individuals with low total water intake (TWI) are in a chronic fluid deficit (i.e., low total body water) [1]. When women with habitually low TWI (1.6 ± 0.5 L/day) increased their fluid intake (3.5 ± 0.1 L/day) for 4 days 24-h urine osmolality decreased, but there was no change in body weight, a proxy for total body water (TBW) [2]. In a small (n = 5) study of adult men, there were no observable changes in TBW, as measured by bioelectrical impedance, after increasing TWI for 4 weeks [3]. However, body weight increased and salivary osmolality decreased indicating that the study may have been underpowered to detect changes in TBW. Further, no studies to date have measured changes in blood volume (BV) when TWI is increased. OBJECTIVES: Therefore, the purpose of this study was to identify individuals with habitually low fluid intake and determine if increasing TWI, for 14 days, resulted in changes in TBW or BV. METHODS: In order to identify individuals with low TWI, 889 healthy adults were screened. Participants with a self-reported TWI less than 1.8 L/day (men) or 1.2 L/day (women), and a 24-h urine osmolality greater than 800 mOsm were included in the intervention phase of the study. For the intervention phase, 15 participants were assigned to the experimental group and 8 participants were assigned to the control group. The intervention period lasted for 14 days and consisted of 2 visits to our laboratory: one before the intervention (baseline) and 14 days into the intervention (14-day follow-up). At these visits, BV was measured using a CO-rebreathe procedure and deuterium oxide (D2O) was administered to measure TBW. Urine samples were collected immediately prior, and 3-8 h after the D2O dose to allow for equilibration. Prior to each visit, participants collected 24-h urine to measure 24-h hydration status. After the baseline visit, the experimental group increased their TWI to 3.7 L for males and 2.7 L for females in order to meet the current Institute of Medicine recommendations for TWI. RESULTS: Twenty-four-hour urine osmolality decreased (-438.7 ± 362.1 mOsm; p < 0.001) and urine volume increased (1,526 ± 869 mL; p < 0.001) in the experimental group from baseline, while there were no differences in osmolality (-74.7 ± 572 mOsm; p = 0.45), or urine volume (-32 ± 1,376 mL; p = 0.89) in the control group. However, there were no changes in BV (Fig. 1a) or changes in TBW (Fig. 1b) in either group. CONCLUSIONS: Increasing fluid intake in individuals with habitually low TWI increases 24-h urine volume and decreases urine osmolality but does not result in changes in TBW or BV. These findings are in agreement with previous work indicating that TWI interventions lasting 3 days [2] to 4 weeks [3] do not result in changes in TBW. Current evidence would suggest that the benefits of increasing TWI are not related changes in TBW.

Mild hypohydration impairs cycle ergometry performance in the heat: A blinded study.

The aim of the present study was to observe the effect of mild hypohydration on exercise performance with subjects blinded to their hydration status. Eleven male cyclists (weight 75.8 ± 6.4 kg, VO2peak : 64.9 ± 5.6 mL/kg/min, body fat: 12.0 ± 5.8%, Powermax : 409 ± 40 W) performed three sets of criterium-like cycling, consisting of 20-minute steady-state cycling (50% peak power output), each followed by a 5-km time trial at 3% grade. Following a familiarization trial, subjects completed the experimental trials, in counter-balanced fashion, on two separate occasions in dry heat (30°C, 30% rh) either hypohydrated (HYP) or euhydrated (EUH). In both trials, subjects ingested 25 mL of water every 5 minutes during the steady-state and every 1 km of the 5-km time trials. In the EUH trial, sweat losses were fully replaced via intravenous infusion of isotonic saline, while in the HYP trial, a sham IV was instrumented. Following the exercise protocol, the subjects' bodyweight was changed by -0.1 ± 0.1% and -1.8 ± 0.2% for the EUH and HYP trial, respectively (P < 0.05). During the second and third time trials, subjects averaged higher power output (309 ± 5 and 306 ± 5 W) and faster cycling speed (27.5 ± 3.0 and 27.2 ± 3.1 km/h) in the EUH trial compared to the HYP trial (Power: 287 ± 4 and 276 ± 5 W, Speed: 26.2 ± 2.9 and 25.5 ± 3.3 km/h, all P < 0.05). Core temperature (Tre ) was higher in the HYP trial throughout the third steady-state and 5-km time trial (P < 0.05). These data suggest that mild hypohydration, even when subjects were unaware of their hydration state, impaired cycle ergometry performance in the heat probably due to greater thermoregulatory strain.

Tolerance to a haemorrhagic challenge during heat stress is improved with inspiratory resistance breathing.

NEW FINDINGS: What is the central question of this study? Does inspiratory resistance breathing improve tolerance to simulated haemorrhage in individuals with elevated internal temperatures? What is the main finding and its importance? The main finding of this study is that inspiratory resistance breathing modestly improves tolerance to a simulated progressive haemorrhagic challenge during heat stress. These findings demonstrate a scenario in which exploitation of the respiratory pump can ameliorate serious conditions related to systemic hypotension. ABSTRACT: Heat exposure impairs human blood pressure control and markedly reduces tolerance to a simulated haemorrhagic challenge. Inspiratory resistance breathing enhances blood pressure control and improves tolerance during simulated haemorrhage in normothermic individuals. However, it is unknown whether similar improvements occur with this manoeuvre in heat stress conditions. In this study, we tested the hypothesis that inspiratory resistance breathing improves tolerance to simulated haemorrhage in individuals with elevated internal temperatures. On two separate days, eight subjects performed a simulated haemorrhage challenge [lower-body negative pressure (LBNP)] to presyncope after an increase in internal temperature of 1.3 ± 0.1°C. During one trial, subjects breathed through an inspiratory impedance device set at 0 cmH2 O of resistance (Sham), whereas on a subsequent day the device was set at -7 cmH2 O of resistance (ITD). Tolerance was quantified as the cumulative stress index. Subjects were more tolerant to the LBNP challenge during the ITD protocol, as indicated by a > 30% larger cumulative stress index (Sham, 520 ± 306 mmHg min; ITD, 682 ± 324 mmHg min; P < 0.01). These data indicate that inspiratory resistance breathing modestly improves tolerance to a simulated progressive haemorrhagic challenge during heat stress.

Spot Sample Urine Specific Gravity Does Not Accurately Represent Small Decreases in Plasma Volume in Resting Healthy Males.

BACKGROUND: Urine specific gravity (USG) is often used to assess hydration status, particularly around athletic competition, but it is unknown whether high USG is indicative of plasma volume (PV) reduction (i.e., hypohydration). We tested the hypothesis that if high USG is reflective of reduced PV, subsequent fluid ingestion would increase PV. PURPOSE: The purpose of this study was to examine 24-hour changes in USG and PV in individuals presenting with high and low spot USG. METHODS: Nineteen healthy males were provided food and water over 24 hours with a total water volume of 35 ml·kg-1 body mass. Absolute PV and blood volume (BV), measured using the CO-rebreathe technique, along with USG were measured before and after a 24-hour intervention period. Based on a preintervention morning spot USG, subjects were post hoc assigned to groups according to USG (≤1.020 or >1.020; low and high USG, respectively). RESULTS: Despite presenting with an elevated spot USG (1.026 ± 0.004), subsequent fluid ingestion over 24 hours did not lead to changes (∆) in PV (-75 ± 234 ml) or BV (-156 ± 370 ml) in the high USG group (p > 0.05). However, a spot USG after the 24-hour intervention in this group decreased (p = 0.018) to a level indicating improved hydration status (1.017 ± 0.007). In the low USG group, there were no changes in PV (-39 ± 274 ml), BV (-82 ± 396 ml), or USG (0.003 ± 0.007) over the 24-hour fluid intervention (all p > 0.05). CONCLUSIONS: Despite a high preintervention USG and subsequent decrease after 24-hour fluid intake, measures of PV and BV were not indicative of this seemingly improved hydration status. This suggests that a highly concentrated spot sample USG and subsequent changes are not accurately representative of PV or BV.

Prolonged standing increases lower limb arterial stiffness.

PURPOSE: Standing workstations have recently been promoted as a healthy alternative to sitting. However, it is unknown how prolonged standing affects arterial stiffness, a prognostic indicator of cardiovascular health. The purpose of this study was twofold: to observe changes in arterial stiffness, as assessed by pulse wave velocity (PWV), with a 2-h bout of standing, and to determine if short, intermittent walking bouts provide a comparative advantage to standing alone. METHODS: Nineteen adults had arterial stiffness assessed by pulse wave velocity. Central (CPWV), upper peripheral (UPWV), and lower peripheral (LPWV) PWV were assessed before (supine), during standing (min 10, 60, and 120), and after (supine) the 2-h standing bout. In one trial, the participants stood at a standing desk immobile for 2 h. In the other trial, participants performed 5-min walking breaks after every 25 min of standing. RESULTS: After 2-h of standing, supine (85.8 ± 90.1 cm/s) and standing (303.4 ± 390.2 cm/s), LPWV increased independent of trial (i.e., main effect of time; p < 0.001). Walking breaks during 2 h of standing did not significantly attenuate these changes. In addition, standing CPWV decreased over time (- 38.5 ± 61.5 cm/s; p = 0.04). Yet, UPWV, standing or supine, did not change over the course of standing (p > 0.05). CONCLUSIONS: These findings indicate that prolonged standing increases the measures of arterial stiffness and there is no evidence that walk breaks attenuate this response.

Postsynaptic cutaneous vasodilation and sweating: influence of adiposity and hydration status.

INTRODUCTION: Obesity and hypohydration independently affect postsynaptic endothelial function, but it is unknown if hypohydration affects lean and obese individuals differently. PURPOSE: To examine the effect of hypohydration on postsynaptic cutaneous vasodilation and sweating in men with high and low adiposity (HI- and LO-BF, respectively). METHODS: Ten males with LO-BF and ten with HI-BF were instrumented for forearm microdialysis when euhydrated and hypohydrated. Changes in cutaneous vascular conductance (CVC) with intradermal infusion of sodium nitroprusside (SNP) and methacholine chloride (MCh) were assessed. Local sweat rate (LSR) was simultaneously assessed at the MCh site. At the end of the last dose, maximal CVC was elicited by delivering a maximal dose of SNP for 30 min to both sites with simultaneous local heating at the SNP site. The concentration of drug needed to elicit 50% of the maximal response (EC50) was compared between groups and hydration conditions. RESULTS: When euhydrated, EC50 of MCh-induced CVC was not different between LO- vs. HI-BF [- 3.04 ± 0.12 vs. - 2.98 ± 0.19 log (MCh) M, P = 0.841]. EC50 of SNP-induced CVC was higher in euhydrated HI- vs. LO-BF (- 1.74 ± 0.17 vs. - 2.13 ± 0.06 log (SNP) M, P = 0.034). Within each group, hydration status did not change MCh- or SNP-induced CVC (P > 0.05). LSR was not different between groups or hydration condition (P > 0.05). CONCLUSIONS: These data suggest reduced sensitivity of endothelium-independent vasodilation in individuals with high adiposity when euhydrated. However, hypohydration does not affect cutaneous vasodilation or local sweat rate differently between individuals with low or high adiposity.

Examining the Influence of Exercise Intensity and Hydration on Gastrointestinal Temperature in Collegiate Football Players.

DeMartini-Nolan, JK, Martschinske, JL, Casa, DJ, Lopez, RM, Stearns, RL, Ganio, MS, and Coris, E. Examining the influence of exercise intensity and hydration on gastrointestinal temperature in collegiate football players. J Strength Cond Res 32(10): 2888-2896, 2018-Debate exists regarding the influence of intensity and hydration on body temperature during American football. The purpose of this study was to observe body core temperature responses with changes in intensity and hydration. Twenty-nine male football players (age = 21 ± 1 year, height = 187 ± 9 cm, mass = 110.1 ± 23.5 kg, body mass index [BMI] = 31.3 ± 5.0, and body surface area [BSA] = 2.34 ± 0.27 m) participated in 8 days of practice in a warm environment (wet bulb globe temperature: 29.6 ± 1.6° C). Participants were identified as starters (S; n = 12) or nonstarters (n = 17) and linemen (L; n = 14) or nonlinemen (NL; n = 15). Variables of interest included core body temperature (T), hydration status, and physical performance characteristics as measured by a global positioning system. Intensity measures of average heart rate (138 ± 9 bpm), low-velocity movement (4.2 ± 1.7%), high-velocity movement (0.6 ± 0.6%), and average velocity (0.36 ± 0.10 m·s) accounted for 42% of the variability observed in T (38.32 ± 0.34° C, r = 0.65, p = 0.01). Hydration measures (percent body mass loss = -1.56 ± 0.80%, urine specific gravity [Usg] = 1.025 ± 0.006, and urine color [Ucol] = 6 ± 1) did not add to the prediction of T (p = 0.83). Metrics of exercise intensity accounted for 39% of the variability observed in maximum T (38.83 ± 0.42° C, r = 0.62, p = 0.02). Hydration measures did not add to this prediction (p = 0.40). Low-velocity movement, high-velocity movement, average velocity, BMI, and BSA were significantly different (p = 0.002, p < 0.001, p = 0.02, p < 0.001, p < 0.001, respectively) between L vs. NL. Heart rate and T were not different between L and NL (p > 0.05). Exercise intensity primarily accounted for the rise in core body temperature. Although L spent less time at higher velocities, T was similar to NL, suggesting that differences in BMI and BSA added to thermoregulatory strain.

Effect of a Cooling Kit on Physiology and Performance Following Exercise in the Heat.

CONTEXT: Exercising in the heat leads to an increase in body temperature that can increase the risk of heat illness or cause detriments in exercise performance. OBJECTIVE: To examine a phase change heat emergency kit (HEK) on thermoregulatory and perceptual responses and subsequent exercise performance following exercise in the heat. DESIGN: Two randomized crossover trials that consisted of 30 minutes of exercise, 15 minutes of treatment (T1), performance testing (5-10-5 pro-agility test and 1500-m run), and another 15 minutes of treatment (T2) identical to T1. SETTING: Outdoors in the heat (wet-bulb globe temperature: 31.5°C [1.8°C] and relative humidity: 59.0% [5.6%]). PARTICIPANTS: Twenty-six (13 men and 13 women) individuals (aged 20-27 y). INTERVENTIONS: Treatment was performed with HEK and without HEK (control, CON) modality. MAIN OUTCOME MEASURES: Gastrointestinal temperature, mean skin temperature, thirst sensation, and muscle pain. RESULTS: Maximum gastrointestinal temperature following exercise and performance was not different between trials (P > .05). Cooling rate was faster during T1 CON (0.053°C/min [0.049°C/min]) compared with HEK (0.043°C/min [0.032°C/min]; P = .01). Mean skin temperature was lower in HEK during T1 (P < .001) and T2 (P = .05). T2 thirst was lower in CON (P = .02). Muscle pain was lower in HEK in T2 (P = .03). Performance was not altered (P > .05). CONCLUSIONS: HEK improved perception but did not enhance cooling or performance following exercise in the heat. HEK is therefore not recommended to facilitate recovery, treat hyperthermia, or improve performance.

Effect of hypohydration on postsynaptic cutaneous vasodilation and sweating in healthy men.

Hypohydration decreases cutaneous vasodilation and sweating during heat stress, but it is unknown if these decrements are from postsynaptic (i.e., sweat gland/blood vessel) alterations. The purpose of this study was to determine if hypohydration affects postsynaptic cutaneous vasodilation and sweating responses. Twelve healthy men participated in euhydrated (EU) and hypohydrated (HY) trials, with hypohydration induced via fluid restriction and passive heat stress. Changes in cutaneous vascular conductance (CVC; %max) in response to incremental intradermal infusion of the endothelium-independent vasodilator sodium nitroprusside (SNP) and the endothelium-dependent vasodilator methacholine chloride (MCh) were assessed by laser Doppler flowmetry. Local sweat rate (LSR) was simultaneously assessed at the MCh site via ventilated capsule. At the end of the last dose, maximal CVC was elicited by delivering a maximal dose of SNP (5 × 10-2 M) for 30 min to both sites with simultaneous local heating (~44°C) at the SNP site. The concentration of drug needed to elicit 50% of the maximal response (log EC50) was compared between hydration conditions. The percent body mass loss was greater with HY vs. EU (-2.2 ± 0.7 vs. -0.1 ± 0.7%, P < 0.001). Log EC50 of endothelium-dependent CVC was lower with EU (-3.62 ± 0.22) vs. HY (-2.93 ± 0.08; P = 0.044). Hypohydration did not significantly alter endothelium-independent CVC or LSR (both P > 0.05). In conclusion, hypohydration attenuated endothelium-dependent CVC but did not affect endothelium-independent CVC or LSR responses. These data suggest that reductions in skin blood flow accompanying hypohydration can be partially attributed to altered postsynaptic function.

Effect of passive heat stress and exercise in the heat on arterial stiffness.

PURPOSE: Prior evidence indicates that acute heat stress and aerobic exercise independently reduce arterial stiffness. The combined effects of exercise and heat stress on PWV are unknown. The purpose of this study was to determine the effects of heat stress with passive heating and exercise in the heat on arterial stiffness. METHODS: Nine participants (n = 3 females, 47 ± 11 years old; 24.1 ± 2.8 kg/m2) completed four trials. In a control trial, participants rested supine (CON). In a passive heating trial (PH), participants were heated with a water-perfusion suit. In two other trials, participants cycled at ~50% of [Formula: see text] in a hot (~40 °C; HC trial) or cool (~15 °C; CC trial) environment. Arterial stiffness, measured by PWV, was obtained at baseline and after each intervention (immediately, 15, 30, 45, and 60 min post). Central PWV (C PWV) was assessed between the carotid/femoral artery sites. Upper and lower peripheral PWV was assessed using the radial/carotid (U PWV) and dorsalis pedis/femoral (L PWV) artery sites. The mean body temperature (T B) was calculated from the skin and rectal temperatures. RESULTS: No significant changes in T B were observed during the CON and CC trials. As expected, the PH and HC trials elevated T B 2.69 ± 0.23 °C and 1.67 ± 0.27 °C, respectively (p < 0.01). PWV did not change in CON, CC, or HC (p > 0.05). However, in the PH trial, U PWV was reduced immediately (-107 ± 81 cm/s) and 15 min (-93 ± 82 cm/s) post-heating (p < 0.05). CONCLUSIONS: Heat stress via exercise in the heat does not acutely change arterial stiffness. However, passive heating reduces U PWV, indicating that heat stress has an independent effect on PWV.

Exertional Hyponatremia and Serum Sodium Change During Ultraendurance Cycling.

INTRODUCTION: Exertional hyponatremia (EH) during prolonged exercise involves all avenues of fluid-electrolyte gain and loss. Although previous research implicates retention of excess fluid, EH may involve either loss, gain, or no change of body mass. Thus, the etiology, predisposing factors, and recommendations for prevention are vague-except for advice to avoid excessive drinking. PURPOSE: This retrospective field study presents case reports of two unacquainted recreational cyclists (LC, 31y and AM, 39 years) who began exercise with normal serum electrolytes but finished a summer 164-km ride (ambient, 34±5°C) with a serum [Na+] of 130 mmol/L. METHODS: To clarify the etiology of EH, their pre- and post-exercise measurements were compared to a control group (CON) of 31 normonatremic cyclists (mean ± SD; 37±6 years; 141±3 mmol Na+/L). RESULTS: Anthropomorphic characteristics, exercise time, and post-exercise ratings of thermal sensation, perceived exertion and muscle cramp were similar for LC, AM and CON. These two hyponatremic cyclists consumed a large and similar volume of fluid (191 and 189 ml/kg), experienced an 11 mmol/L decrease of serum [Na+], reported low thirst sensations; however, LC gained 3.1 kg (+4.3% of body mass) during 8.9 hr of exercise and AM maintained body mass (+0.1kg, +0.1%, 10.6h). In the entire cohort (n = 33), post-event serum [Na+] was strongly correlated with total fluid intake (R2 = 0.45, p < .0001), and correlated moderately with dietary sodium intake (R2=0.28, p = .004) and body mass change (R2 = 0.22, p = .02). Linear regression analyses predicted the threshold of EH onset (<135 mmol Na+/L) as 168 ml fluid/kg. CONCLUSIONS: The wide range of serum [Na+] changes (+6 to -11 mmol/L) led us to recommend an individualized rehydration plan to athletes because the interactions of factors were complex and idiosyncratic.

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.

Effect of Caffeine on Perceived Soreness and Functionality Following an Endurance Cycling Event.

Caldwell, AR, Tucker, MA, Butts, CL, McDermott, BP, Vingren, JL, Kunces, LJ, Lee, EC, Munoz, CX, Williamson, KH, Armstrong, LE, and Ganio, MS. Effect of caffeine on perceived soreness and functionality following an endurance cycling event. J Strength Cond Res 31(3): 638-643, 2017-Caffeine can reduce muscle pain during exercise; however, the efficacy of caffeine in improving muscle soreness and recovery from a demanding long-duration exercise bout has not been established. The purpose of this study was to investigate the effects of caffeine intake on ratings of perceived muscle soreness (RPMS) and perceived lower extremity functionality (LEF) following the completion of a 164-km endurance cycling event. Before and after cycling RPMS (1-to-6; 6 = severe soreness) and LEF (0-to-80; 80 = full functionality) were assessed by questionnaires. Subjects ingested 3 mg/kg body mass of caffeine or placebo pills in a randomized, double-blind fashion immediately after the ride and for the next 4 mornings (i.e., ∼800 hours) and 3 afternoons (i.e., ∼1200 hours). Before each ingestion, RPMS and LEF were assessed. Afternoon ratings of LEF were greater with caffeine ingestion the first day postride (65.0 ± 6.1 vs. 72.3 ± 6.7; for placebo and caffeine, respectively; p = 0.04), but at no other time points (p > 0.05). The caffeine group tended to have lower overall RPMS in the afternoon versus placebo (i.e., main effect of group; 1.1 ± 0.2 vs. 0.5 ± 0.2; p = 0.09). Afternoon RPMS for the legs was significantly lower in the caffeine group (main effect of caffeine; 1.3 ± 0.2 vs. 0.5 ± 0.3; p = 0.05). In conclusion, ingesting caffeine improved RPMS for the legs, but not LEF in the days following an endurance cycling event. Athletes may benefit from ingesting caffeine in the days following an arduous exercise bout to relieve feelings of soreness and reduced functionality.

No Change in 24-Hour Hydration Status Following a Moderate Increase in Fluid Consumption.

PURPOSE: To investigate changes in 24-hour hydration status when increasing fluid intake. METHODS: Thirty-five healthy males (age 23.8 ± 4.7 years; mass 74.0 ± 9.4 kg) were divided into 4 treatment groups for 2 weeks of testing. Volumes of 24-hour fluid ingestion (including water from food) for weeks 1 and 2 was 35 and 40 ml/kg body mass, respectively. Each treatment group was given the same proportion of beverages in each week of testing: water only (n = 10), water + caloric cola (n = 7), water + noncaloric cola (n = 10), or water + caloric cola + noncaloric cola + orange juice (n = 8). Serum osmolality (Sosm), total body water (TBW) via bioelectrical impedance, 24-hour urine osmolality (Uosm), and volume (Uvol) were analyzed at the end of each 24-hour intervention. RESULTS: Independent of treatment, total beverage consumption increased 22% from week 1 to 2 (1685 ± 320 to 2054 ± 363 ml; p < 0.001). Independent of beverage assignment, the increase in fluid consumption between weeks 1 and 2 did not change TBW (43.4 ± 5.2 vs 43.0 ± 4.8 kg), Sosm (292 ± 5 vs 292 ± 5 mOsm/kg), 24-hour Uosm (600 ± 224 vs 571 ± 212 mOsm/kg), or 24-hour Uvol (1569 ± 607 vs 1580 ± 554 ml; all p > 0.05). CONCLUSIONS: Regardless of fluid volume or beverage type consumed, measures of 24-hour hydration status did not differ, suggesting that standard measures of hydration status are not sensitive enough to detect a 22% increase in beverage consumption.

Effects of mild hypohydration on cooling during cold-water immersion following exertional hyperthermia.

PURPOSE: We investigated the effects of mild hypohydration compared to euhydration on the cooling efficacy of cold-water immersion (CWI). METHODS: Fourteen participants (eight male, six female; age 26 ± 5 years; ht 1.77 ± 0.08 m; wt 72.2 ± 8.8 kg; 20.6 ± 7.4 % body fat) completed one euhydrated (EU) trial followed by one hypohydrated trial (HY; via 24 h fluid restriction) in an environmental chamber (33.6 ± 0.9 °C, 55.8 ± 1.7 % RH). Volitional exercise was performed in a manner that matched end-exercise rectal temperature (T re) through repeating exercise mode and intensity. Participants were then immersed in ice water (2.0 ± 0.8 °C) until T re reached 38.1 °C or for a maximum of 15 min. T re, heart rate (HR), skin blood flux (SBF) and mean skin temperature (T sk) were monitored continuously during cooling. RESULTS: Pre-cooling body mass was decreased in the HY trial (-2.66 ± 1.23 % body mass) and maintained in the EU trial (-0.66 ± 0.44 %) compared to baseline mass (P < 0.001). Cooling rates were faster when EU (0.14 ± 0.05 °C/min) compared to HY (0.11 ± 0.05 °C/min, P = 0.046). HR, SBF, and T sk were not different between EU and HY trials (P > 0.05), however, all variables significantly decreased with immersion independent of hydration status (P < 0.001). CONCLUSION: The primary finding was that hypohydration modestly attenuates the rate of cooling in exertionally hyperthermic individuals. Regardless of hydration status, the cooling efficacy of CWI was preserved and should continue to be utilized in the treatment of exertional hyperthermia.

Pro- and anti-inflammatory cytokine responses to a 164-km road cycle ride in a hot environment.

PURPOSE: The purpose of this study was to examine the circulating cytokine response to a recreational 164-km road cycling event in a high ambient temperature and to determine if this response was affected by self-paced exercise time to completion. METHODS: Thirty-five men and five women were divided into tertiles based on time to complete the cycling event: slowest (SLOW), moderate (MOD), and fastest (FAST) finishers. Plasma samples were obtained 1-2 h before (PRE) and immediately after (IP) the event. A high-sensitivity multiplex assay kit was used to determine the concentration of plasma anti-inflammatory cytokines (IL-4, IL-5, IL-10, IL-13) and pro-inflammatory cytokines (IL-1ß, IL-2, IL-6, IL-7, IL-8, IL-12, GM-CSF, IFN-γ, and TNF-α). RESULTS: The concentration of plasma IL-10 increased significantly (p < 0.05) in FAST and MOD groups and had no change in the SLOW group in response to a 164-km cycling event in the hot environment. Other cytokine responses were not influenced by the Time to completion. Pro-inflammatory cytokines IL-1ß, IL-2, GM-CSF, and TNF-α decreased; whereas, IL-6 and IL-8 increased from PRE to IP. Additionally, anti-inflammatory cytokines IL-4 and IL-13 decreased. CONCLUSIONS: Completion of a 164-km cycling event induced substantial changes in circulating pro- and anti-inflammatory cytokine concentrations. Time to completion appears to have a greater influence on the systemic IL-10 response than the environmental condition; however, it is possible that a threshold for absolute intensity must be reached for environmental conditions to affect the IL-10 response to exercise. Thus, cyclists from the FAST/MOD groups appear more likely to experience an acute transient immune suppression than cyclists from the SLOW group.

Fluid Balance of Adolescent Swimmers During Training.

Swimming, either competitively or leisurely, is a unique activity that involves prolonged exercise while immersed in stable water temperatures. This environment could have an influence on the hydration status of swimmers independently of fluid balance. Forty-six healthy adolescent swimmers (26 males and 20 females; 12.8 ± 2.3 years; 50.6 ± 13.4 kg) were studied during a typical training session in an indoor swimming pool. First morning, prepractice and postpractice urine samples were tested for osmolality and specific gravity, whereas all athletes consumed fluids ad libitum. Sixty-seven percent of the athletes were hypohydrated (urine osmolality [Uosm] ≥700 mmol·kg(-1)) based on their first morning urine sample, which increased to 78% immediately before training. During the 2-hour swimming practice, the minimal sweat loss (0.39 ± 0.27 L) combined with ad libitum fluid availability resulted in unchanged body weight (0.1 ± 0.3 kg). Additionally, thirst was similar (before practice: 46 ± 26, after practice: 55 ± 33 mm on a 100-mm visual analog scale) at pretraining and posttraining time points (p > 0.05). Interestingly, postpractice Uosm was reduced significantly compared with the prepractice value (630 vs. 828 mmol·kg(-1); p = 0.001), without any significant change in body weight (0.1 ± 0.3 kg; p > 0.05). In conclusion, the present data indicated that more than two-thirds of the young swimmers appeared in their practice suboptimally hydrated. Although no changes in body mass were observed during the swimming practice, the decrease in urine hydration markers after swimming might less accurately reflect hydration state.