Cory L. Butts

Cooling Effectiveness of a Modified Cold-Water Immersion Method After Exercise-Induced Hyperthermia

CONTEXT  Recommended treatment for exertional heat stroke includes whole-body cold-water immersion (CWI). However, remote locations or monetary or spatial restrictions can challenge the feasibility of CWI. Thus, the development of a modified, portable CWI method would allow for optimal treatment of exertional heat stroke in the presence of these challenges. OBJECTIVE  To determine the cooling rate of modified CWI (tarp-assisted cooling with oscillation [TACO]) after exertional hyperthermia. DESIGN  Randomized, crossover controlled trial. SETTING  Environmental chamber (temperature = 33.4°C ± 0.8°C, relative humidity = 55.7% ± 1.9%). PATIENTS OR OTHER PARTICIPANTS  Sixteen volunteers (9 men, 7 women; age = 26 ± 4.7 years, height = 1.76 ± 0.09 m, mass = 72.5 ± 9.0 kg, body fat = 20.7% ± 7.1%) with no history of compromised thermoregulation. INTERVENTION(S)  Participants completed volitional exercise (cycling or treadmill) until they demonstrated a rectal temperature (Tre) ≥39.0°C. After exercise, participants transitioned to a semirecumbent position on a tarp until either Tre reached 38.1°C or 15 minutes had elapsed during the control (no immersion [CON]) or TACO (immersion in 151 L of 2.1°C ± 0.8°C water) treatment. MAIN OUTCOME MEASURE(S)  The Tre, heart rate, and blood pressure (reported as mean arterial pressure) were assessed precooling and postcooling. Statistical analyses included repeated-measures analysis of variance with appropriate post hoc t tests and Bonferroni correction. RESULTS  Before cooling, the Tre was not different between conditions (CON: 39.27°C ± 0.26°C, TACO: 39.30°C ± 0.39°C; P = .62; effect size = -0.09; 95% confidence interval [CI] = -0.2, 0.1). At postcooling, the Tre was decreased in the TACO (38.10°C ± 0.16°C) compared with the CON condition (38.74°C ± 0.38°C; P < .001; effect size = 2.27; 95% CI = 0.4, 0.9). The rate of cooling was greater during the TACO (0.14 ± 0.06°C/min) than the CON treatment (0.04°C/min ± 0.02°C/min; t15 = -8.84; P < .001; effect size = 2.21; 95% CI = -0.13, -0.08). These differences occurred despite an insignificant increase in fluid consumption during exercise preceding CON (0.26 ± 0.29 L) versus TACO (0.19 ± 0.26 L; t12 = 1.73; P = .11; effect size = 0.48; 95% CI = -0.02, 0.14) treatment. Decreases in heart rate did not differ between the TACO and CON conditions (t15 = -1.81; P = .09; effect size = 0.45; 95% CI = -22, 2). Mean arterial pressure was greater at postcooling with TACO (84.2 ± 6.6 mm Hg) than with CON (67.0 ± 9.0 mm Hg; P < .001; effect size = 2.25; 95% CI = 13, 21). CONCLUSIONS  The TACO treatment provided faster cooling than did the CON treatment. When location, monetary, or spatial restrictions are present, TACO represents an effective alternative to traditional CWI in the emergency treatment of patients with exertional hyperthermia.

Physiologic and Perceptual Responses to Cold-Shower Cooling After Exercise-Induced Hyperthermia.

CONTEXT Exercise conducted in hot, humid environments increases the risk for exertional heat stroke (EHS). The current recommended treatment of EHS is cold-water immersion; however, limitations may require the use of alternative resources such as a cold shower (CS) or dousing with a hose to cool EHS patients. OBJECTIVE To investigate the cooling effectiveness of a CS after exercise-induced hyperthermia. DESIGN Randomized, crossover controlled study. SETTING Environmental chamber (temperature = 33.4°C ± 2.1°C; relative humidity = 27.1% ± 1.4%). PATIENTS OR OTHER PARTICIPANTS Seventeen participants (10 male, 7 female; height = 1.75 ± 0.07 m, body mass = 70.4 ± 8.7 kg, body surface area = 1.85 ± 0.13 m(2), age range = 19-35 years) volunteered. INTERVENTION(S) On 2 occasions, participants completed matched-intensity volitional exercise on an ergometer or treadmill to elevate rectal temperature to ≥39°C or until participant fatigue prevented continuation (reaching at least 38.5°C). They were then either treated with a CS (20.8°C ± 0.80°C) or seated in the chamber (control [CON] condition) for 15 minutes. MAIN OUTCOME MEASURE(S) Rectal temperature, calculated cooling rate, heart rate, and perceptual measures (thermal sensation and perceived muscle pain). RESULTS The rectal temperature (P = .98), heart rate (P = .85), thermal sensation (P = .69), and muscle pain (P = .31) were not different during exercise for the CS and CON trials (P > .05). Overall, the cooling rate was faster during CS (0.07°C/min ± 0.03°C/min) than during CON (0.04°C/min ± 0.03°C/min; t16 = 2.77, P = .01). Heart-rate changes were greater during CS (45 ± 20 beats per minute) compared with CON (27 ± 10 beats per minute; t16 = 3.32, P = .004). Thermal sensation was reduced to a greater extent with CS than with CON (F3,45 = 41.12, P < .001). CONCLUSIONS Although the CS facilitated cooling rates faster than no treatment, clinicians should continue to advocate for accepted cooling modalities and use CS only if no other validated means of cooling are available.

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

Abstract 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.

Effect of hypohydration on thermoregulatory responses in men with low and high body fat exercising in the heat

It is unclear whether men with low body fat (LO-BF) have impaired thermoregulation during exercise heat stress compared with those with high body fat (HI-BF) when euhydration (EU) is maintained. Furthermore, in LO-BF individuals, hypohydration (HY) impairs thermoregulatory responses during exercise heat stress, but it is unknown whether this occurs in HI-BF counterparts. The purpose of this study was to test the hypotheses that men with HI-BF have impaired thermoregulatory responses to exercise heat stress and that HY further exacerbates these impairments vs. LO-BF. Men with LO-BF [n = 11, body mass (BM) 73.9 ± 8.5 kg, BF% 13.6 ± 3.8] and HI-BF (n = 9, BM 89.6 ± 6.9 kg, BF% 30.2 ± 4.1), in a randomized crossover design, performed 60 min of upright cycling in a hot environment (40.3 ± 0.4°C, relative humidity 32.5 ± 1.9%) at a metabolic heat production rate of 6 W/kg BM and finished exercise either euhydrated (EU; 0.3 ± 1.2 vs. 0.3 ± 0.9% BM loss) or HY (-2.5 ± 1.1 vs. -1.7 ± 1.5% BM loss). Changes in rectal temperature (ΔTrec), local sweat rate (ΔLSR), and cutaneous vascular conductance (ΔCVC; %max) were measured throughout. When EU, LO-BF and HI-BF had similar CVC and LSR responses (P > 0.05); however, LO-BF had a lower ΔTrec vs. HI-BF (0.92 ± 0.35 vs. 1.31 ± 0.32°C, P = 0.021). Compared with EU, HY increased end-exercise ΔTrec in LO-BF (0.47 ± 0.37°C, P < 0.01) but not in HI-BF (-0.06 ± 0.29°C, P > 0.05). HY, compared with EU, did not affect ΔLSR and ΔCVC in either group (P > 0.05). We conclude that, when euhydrated, men with HI-BF have a greater increase in Trec vs. LO-BF but similar CVC and LSR. HY exacerbates increases in Trec in LO-BF but not HI-BF. NEW & NOTEWORTHY This is the first known investigation to compare thermoregulatory responses to exercise heat stress between men with high and low body fat (BF) in a physiologically uncompensable environment while simultaneously examining the confounding influence of hydration status. Both groups demonstrated similar sweating and cutaneous vasodilatory responses when euhydrated, despite vast differences in rectal temperature. Furthermore, in contrast to low BF, individuals with high BF demonstrated similar increases in core body temperature when either euhydrated or hypohydrated.

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

ABSTRACT 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.

Renal stress and kidney injury biomarkers in response to endurance cycling in the heat with and without ibuprofen

Exercise, especially in the heat, can contribute to acute kidney injury, which can expedite chronic kidney disease onset. The additional stress of ibuprofen use is hypothesized to increase renal stress. OBJECTIVES To observe the effects of endurance cycling in the heat on renal function. Secondarily, we investigated the effect of ibuprofen ingestion on kidney stress. DESIGN Randomized, placebo controlled and observational methods were utilized. METHODS Forty cyclists (52±9y, 21.7±6.5% body fat) volunteered and completed an endurance cycling event (5.7±1.2h) in the heat (33.2±5.0°C, 38.4±10.7% RH). Thirty-five participants were randomized to ingest a placebo (n=17) or 600mg ibuprofen (n=18) pre-event. A blood sample was drawn before and following the event. Serum creatinine was assessed by colorimetric assay. An ELISA was used to measure serum neutrophil gelatinase-associated lipocalin. Fractional excretion of sodium was calculated after urinary and serum electrolyte analyses. RESULTS Placebo versus ibuprofen groups contributed no significant difference in any variable (p>0.05). Serum creatinine significantly increased from pre- (0.52±0.14mg/dL) to post-event (0.88±0.21mg/dL; p<0.001). Serum neutrophil gelatinase-associated lipocalin significantly increased (pre: 68.51±17.54ng/mL; post: 139.12±36.52ng/mL; p<0.001) and fractional excretion of sodium was significantly reduced from pre- (0.52±0.24%) to post-event (0.27±0.18%; p<0.001). CONCLUSIONS Changes in renal biomarkers suggest mild acute kidney injury and reduced kidney function during a single bout of endurance cycling in the heat, without influence from moderate ibuprofen ingestion.

Effectiveness of Ice-Sheet Cooling Following Exertional Hyperthermia

BACKGROUND The procedure of wrapping a heat casualty in ice-water soaked bed sheets to reduce core temperature has received little investigation, despite the practice and recommendation for its use in some military settings. Thus, the purpose of this study was to investigate the cooling efficacy of ice-sheet cooling (ISC) following exertional hyperthermia. METHODS 13 (11 males, 2 females) participants (age = 23 ± 3 years, height = 176.5 ± 10.3 cm, mass = 78.6 ± 15.3 kg, body fat = 19.6 ± 8.6%, and body surface area = 1.95 ± 0.22 m2) volunteered to complete 2 randomized, crossover design trials on an outdoor recreation field (34.4 ± 1.4°C, 54.4 ± 4.1% relative humidity). Each trial consisted of exercise (self-paced 400-m warm-up, 1,609-m run, and 100-m sprints) followed by 15 minutes of either lying supine in the shade with no treatment (control [CON]) or being treated with ice-water soaked sheets wrapped around their body (ISC). Physiological (rectal temperature [Tre], heart rate, mean-weighted skin temperature) and perceptual measures (thermal sensation, rating of perceived exertion) were assessed after each exercise protocol, every 3 minutes during treatment, and every 5 minutes during recovery. FINDINGS By design, there were no differences during exercise between ISC and CON for Tre (p = 0.16), skin temperature (p = 0.52), heart rate (p = 0.62), thermal sensation (p = 0.89), or rating of perceived exertion (p = 0.99). There were greater decreases in Tre at 3 (ISC 0.33 ± 0.26°C vs. CON 0.03 ± 0.30°C, p = 0.01) and 6 minutes (ISC 0.47 ± 0.27°C vs. CON 0.30 ± 0.19°C, p = 0.05) of treatment; however, the overall rate of cooling was not different between trials (CON 0.05 ± 0.02°C/min vs. ISC 0.06 ± 0.02°C/min, p = 0.72). Skin temperature (Tsk) was significantly reduced from 3 minutes (ISC 34.4 ± 1.7°C vs. CON 36.6 ± 0.5°C, p = 0.007) through 15 minutes (ISC 32.4 ± 1.5 vs. CON 36.1 ± 0.4°C, p < 0.001) of treatment. There was a trend for lower heart rate with ISC (p = 0.051). Thermal sensation was reduced from 3 minutes of treatment (ISC 3.5 ± 0.9 vs. CON 4.5 ± 0.6, p = 0.002) through 15 minutes (ISC 2.8 ± 1.0 vs. CON 3.9 ± 0.4, p = 0.005). DISCUSSION ISC does not provide effective reduction in Tre following exertional hyperthermia compared to no treatment. However, perceptual benefits may warrant the use of ISC in settings where rapid reductions in core temperature are not a concern (i.e., recovery from exercise). Thus, clinicians should continue to utilize validated techniques (i.e., cold-water immersion) for the treatment of exertional heat illnesses.

Carotid baroreflex control of heart rate is enhanced, while control of mean arterial pressure is preserved during whole-body heat stress in young healthy men.

Whole body heat stress (WBH) results in numerous cardiovascular alterations that ultimately reduce orthostatic tolerance. While impaired carotid baroreflex (CBR) function during WBH has been reported as a potential reason for this decrement, study design considerations may limit interpretation of previous findings. We sought to test the hypothesis that CBR function is unaltered during WBH. CBR function was assessed in 10 healthy male subjects (age: 26 ± 3; height: 185 ± 7 cm; weight: 82 ± 10 kg; BMI: 24 ± 3 kg/m2; means ± SD) using 5-s trials of neck pressure (+45, +30, and +15 Torr) and neck suction (-20, -40, -60, and -80 Torr) during normothermia (NT) and passive WBH (Δ core temp ∼1°C). Analyses of stimulus response curves (four-parameter logistic model) for CBR control of heart rate (CBR-HR) and mean arterial pressure (CBR-MAP), as well as separate two-way ANOVA of the hypotensive and hypertensive stimuli (factor 1: thermal condition, factor 2: chamber pressure), were performed. For CBR-HR, maximal gain was increased during WBH (-0.73 ± 0.11) compared with NT (-0.39 ± 0.04, mean ± SE, P = 0.03). In addition, the CBR-HR responding range was increased during WBH (33 ± 5) compared with NT (19 ± 2 bpm, P = 0.03). Separate analysis of hypertensive stimulation revealed enhanced HR responses during WBH at -40, -60, and -80 Torr (condition × chamber pressure interaction, P = 0.049) compared with NT. For CBR-MAP, both logistic analysis and separate two-way ANOVA revealed no differences during WBH. Therefore, in response to passive WBH, CBR control of heart rate (enhanced) and arterial pressure (no change) is well preserved.

Obesity, but not hypohydration, mediates changes in mental task load during passive heating in females

Background The independent effects of hypohydration and hyperthermia on cognition and mood is unclear since the two stresses often confound each other. Further, it is unknown if obese individuals have the same impairments during hyperthermia and hypohydration that is often observed in non-obese individuals. Methods The current study was designed to assess the independent and combined effects of mild hypohydration and hyperthermia on cognition, mood, and mental task load in obese and non-obese females. Twenty-one healthy females participated in two passive heating trials, wherein they were either euhydrated or hypohydrated prior to and throughout passive heating. Cognition (ImPACT), mental task load (NASA-TLX), and mood (Brunel Mood Scale; BRUMS) were measured before and after a 1.0 °C increase in core temperature (TC). Results After a 1.0 °C TC elevation, hypohydration resulted in greater (p < 0.05) body mass loss (−1.14 ± 0.48 vs −0.58 ± 0.48 kg; hypohydrated and euhydrated, respectively) and elevation in serum osmolality (292 ± 4 vs 282 ± 3 mOsm; p < 0.05) versus euhydration. Hypohydration, independent of hyperthermia, did not affect mental task load or mood (p > 0.05). Hyperthermia, regardless of hydration status, impaired (∼5 A.U) measures of memory-based cognition (verbal and visual memory), and increased mental task load, while worsening mood (p < 0.05). Interestingly, obese individuals had increased mental task load while hyperthermic compared to the non-obese individuals (p < 0.05) even while euhydrated. Hypohydration did not exacerbate any heat-related effects on cognition between obese and non-obese females (p > 0.05). Conclusion These data indicate that hyperthermia independently impairs memory-based aspects of cognitive performance, mental task load, and leads to a negative mood state. Mild hypohydration did not exacerbate the effects of hyperthermia. However, obese individuals had increased mental task load during hyperthermia.

Effects of a phase change cooling garment during exercise in the heat

Abstract The purpose of our study was to examine the physiological, perceptual, and performance effects of wearing a phase change cooling garment (CG) during an interval exercise routine in the heat. Sixteen male participants (age 23 ± 3 years, ht 1.76 ± 0.11 m; wt 78.5 ± 11.2 kg; body fat 15.2 ± 5.8%) completed two trials (one with phase change inserts, CG, and one control without inserts) consisting of two submaximal exercise portions separated by 5-minute seated rest, and a final maximal effort performance bout. Each submaximal bout involved 30 seconds or 1 minute of muscular endurance and agility exercises and 5 minutes of treadmill jogging and step-ups. The performance bout included 30 seconds or 1 minute of muscular endurance and agility exercises, with participants completing as many repetitions as possible, followed by a 15-minute recovery (active and passive). Rectal temperature (Tre) and heart rate were not different between trials, however change in Tre from baseline was improved during 10 and 15 minutes of recovery with the CG (P < .05). Mean skin temperature was lower using the CG vs control throughout the trial (P < .05). Thermal sensation was lower when using the CG compared to control (P < .001). There were no differences in any outcomes of the performance exercises (P > .05). These findings indicate that the continuous use of a CG during an interval style workout in the heat provides improvements in thermal sensation, however, only minimal thermophysiological benefits, and no performance augmentation.