Impact of Topical Capsaicin Cream on Thermoregulation and Perception While Walking in the Cold.

INTRODUCTION: Capsaicin, a chili pepper extract, can stimulate increased skin blood flow (SkBF) with a perceived warming sensation on application areas. Larger surface area application may exert a more systemic thermoregulatory response. Capsaicin could assist with maintaining heat transport to the distal extremities, minimizing cold weather injury risk. However, the thermoregulatory and perceptual impact of topical capsaicin cream application prior to exercise in the cold is unknown. METHODS: Following application of either a 0.1% capsaicin or control cream to the upper and lower extremities (10 g total, ∼40-50% body surface area), 11 participants in shorts and a t-shirt were exposed to 30 min of cold (0 °C, 40% relative humidity). Exposures comprised of 5 min seated rest, 20 min walking (1.6 m·s-1, 5% grade), and 5 min seated rest. Temperature (skin, core), SkBF, skin conductivity, heart rate, thermal sensation, and thermal comfort were measured throughout. RESULTS: The capsaicin treatment did not differ from the control treatment in skin temperature (treatment mean: 30.0 ± 2.5, 30.1 ± 2.4 °C, respectively, p = 0.655), core temperature (treatment mean: 37.3 ± 0.5, 37.4 ± 0.4 °C, respectively, p = 0.113), SkBF (treatment mean: -8.4 ± 10.0, -11.1 ± 10.7 A.U., respectively, p = 0.492), skin conductivity (treatment mean: -0.7 ± 5.1, 0.4 ± 6.4 µS, respectively, p = 0.651), or heart rate (treatment mean: 83 ± 29, 85 ± 28 beats·minute-1, respectively, p = 0.234). The capsaicin and control treatments also did not differ in thermal sensation (p = 0.521) and thermal comfort (p = 0.982), with perceptual outcomes corresponding with feeling "cool" and "just uncomfortable," respectively. CONCLUSIONS: 0.1% topical capsaicin application to exposed limbs prior to walking in a cold environment does not alter whole-body thermoregulation or thermal perception.

Influence of topical menthol gel on thermoregulation and perception while walking in the heat.

PURPOSE: Menthol is known to elicit opposing thermoregulatory and perceptual alterations during intense exercise. The current purpose was to determine the thermoregulatory and perceptual effects of topical menthol application prior to walking in the heat. METHODS: Twelve participants walked (1.6 m s-1, 5% grade) for 30 min in the heat (38 °C, 60% relative humidity) with either a 4% menthol or control gel on the upper (shoulder to wrist) and lower (mid-thigh to ankle) limbs. Skin blood flow (SkBF), sweat (rate, composition), skin conductivity, heart rate, temperature (skin, core), and thermal perception were measured prior to and during exercise. RESULTS: Skin conductivity expressed as time to 10, 20, 30, and 40 µS was delayed due to menthol (559 ± 251, 770 ± 292, 1109 ± 301, 1299 ± 335 s, respectively) compared to the control (515 ± 260, 735 ± 256, 935 ± 300, 1148 ± 298 s, respectively, p = 0.048). Sweat rate relative to body surface area was lower due to menthol (0.55 ± 0.16 L h-1 m(2)-1) than the control (0.64 ± 0.16 L h-1 m(2)-1, p = 0.049). Core temperature did not differ at baseline between the menthol (37.4 ± 0.3 °C) and control (37.3 ± 0.4 °C, p = 0.298) but was higher at 10, 20, and 30 min due to menthol (37.5 ± 0.3, 37.7 ± 0.2, 38.1 ± 0.3 °C, respectively) compared to the control (37.3 ± 0.4, 37.4 ± 0.3, 37.7 ± 0.3 °C, respectively, p < 0.05). The largest rise in core temperature from baseline was at 30 min during menthol (0.7 ± 0.3 °C) compared to the control (0.4 ± 0.2 °C, p = 0.004). Overall, the menthol treatment was perceived cooler, reaching "slightly warm" whereas the control treatment reached "warm" (p < 0.001). CONCLUSION: Menthol application to the limbs impairs whole-body thermoregulation while walking in the heat despite perceiving the environment as cooler.

The isolated effects of local cold application on proteolytic and myogenic signaling.

Post-exercise cooling studies reveal inhibitory effects on markers of skeletal muscle growth. However, the isolated effect of local cold application has not been adequately addressed. It is unclear if the local cold or the combination of local cold and exercise is driving negatively altered skeletal muscle gene expression. The purpose was to determine the effects of a 4 h local cold application to the vastus lateralis on the myogenic and proteolytic response. Participants (n = 12, 27 ± 6 years, 179 ± 9 cm, 82.8 ± 13.0 kg, 18.4 ± 7.1 %BF) rested with a thermal wrap placed on each leg with either circulating cold fluid (10 °C, COLD) or no fluid circulation (room temperature, RT). Muscle samples were collected to quantify mRNA (RT-qPCR) and proteins (Western Blot) associated with myogenesis and proteolysis. Temperatures in COLD were lower than RT at the skin (13.2 ± 1.0 °C vs. 34.8 ± 0.9 °C; p < 0.001) and intramuscularly (20.5 ± 1.3 °C vs. 35.6 ± 0.8 °C, p < 0.001). Myogenic-related mRNA, MYO-G and MYO-D1, were lower in COLD (p = 0.001, p < 0.001, respectively) whereas myogenic-mRNA, MYF6, was greater in COLD (p = 0.002). No other myogenic associated genes were different between COLD and RT (MSTN, p = 0.643; MEF2a, p = 0.424; MYF5, p = 0.523; RPS3, p = 0.589; RPL3-L, p = 0.688). Proteolytic-related mRNA was higher in COLD (FOXO3a, p < 0.001; Atrogin-1, p = 0.049; MURF-1, p < 0.001). The phosphorylation:total protein ratio for the translational repressor of muscle mass, 4E-BP1Thr37/46, was lower in COLD (p = 0.043), with no differences in mTORser2448 (p = 0.509) or p70S6K1Thr389 (p = 0.579). Isolated local cooling over 4 h exhibits inhibited myogenic and higher proteolytic skeletal muscle molecular response.

The independent effects of local heat application on muscle growth program associated mRNA and protein phosphorylation.

The development and maintenance of skeletal muscle is crucial for the support of daily function. Recent evidence suggests that genes coded for proteins associated with the human muscle growth program (myogenic and proteolytic genes) are sensitive to local heat application. Therefore, the purpose of this investigation was to determine the effect of 4 h of local heat application to the vastus lateralis at rest on acute phosphorylation (mTORSer2448, p70-S6K1Thr389, and 4E-BP1Thr47/36) and gene expression changes for proteins associated with the muscle growth program. Intramuscular temperature of the HOT limb was 1.2 ± 0.2 °C higher than CON limb after 4 h of local heating. However, this local heat stimulus did not influence transcription of genes associated with myogenesis (MSTN, p = 0.321; MYF5, p = 0.445; MYF6, p = 0.895; MEF2a, p = 0.809; MYO-G, p = 0.766; MYO-D1, p = 0.118; RPS3, p = 0.321; and RPL-3L, p = 0.577), proteolysis (Atrogin-1, p = 0.573; FOXO3a, p = 0.452; MURF-1, p = 0.284), nor protein phosphorylation (mTORSer2448, p = 0.981; P70-S6K1Thr389, p = 0.583; 4E-BP1Thr37/46, p = 0.238) associated with the muscle growth program. These findings suggest little to no association between the local application of heat, at rest, and the activation of the observed muscle growth program-related markers.

Influence of topical capsaicin cream on thermoregulation and perception during acute exercise in the heat.

PURPOSE: Determine if topical capsaicin, a transient receptor potential vanilloid heat thermoreceptor activator, alters thermoregulation and perception when applied topically prior to thermal exercise. METHODS: Twelve subjects completed 2 treatments. Subjects walked (1.6 m s-1, 5% grade) for 30 min in the heat (38 °C, 60% relative humidity) with either a capsaicin (0.025% capsaicin) or control cream applied to the upper (shoulder to wrist) and lower (mid-thigh to ankle) limbs covering ∼50% body surface area. Skin blood flow (SkBF), sweat (rate, composition), heart rate, temperature (skin, core), and perceived thermal sensation were measured prior to and during exercise. RESULTS: The relative change in SkBF was not different between treatments at any time point (p = 0.284). There were no differences in sweat rate between the capsaicin (1.23 ± 0.37 L h-1) and control (1.43 ± 0.43 L h-1, p = 0.122). There were no differences in heart rate between the capsaicin (122 ± 38 beats·min-1) and control (125 ± 39 beats·min-1, p = 0.431). There were also no differences in weighted surface (p = 0.976) or body temperatures (p = 0.855) between the capsaicin (36.0 ± 1.7 °C, 37.0 ± 0.8 °C, respectively) and control (36.0 ± 1.6 °C, 36.9 ± 0.8 °C, respectively). The capsaicin treatment was not perceived as hotter than the control treatment until minute 30 of exercise (2.8 ± 0.4, 2.5 ± 0.5, respectively, p = 0.038) CONCLUSIONS: Topical capsaicin application does not alter whole-body thermoregulation during acute exercise in the heat despite perceiving the treatment as hotter late in exercise.

Independent effects of acute normobaric hypoxia and hypobaric hypoxia on human physiology.

The purpose of this study was to examine the effects of acute normobaric (NH, decreased FiO2) and hypobaric (HH, 4200 m ascent) hypoxia exposures compared to sea level (normobaric normoxia, NN). Tissue oxygenation, cardiovascular, and body fluid variables measured during rest and a 3-min step-test following 90-min exposures (NH, HH, NN). Muscle oxygenated hemoglobin (O2Hb) decreased, and muscle deoxygenated hemoglobin (HHb) increased environmentally independent from rest to exercise (p < 0.001). During exercise, brain O2Hb was lower at HH compared to NN (p = 0.007), trending similarly with NH (p = 0.066), but no difference between NN and NH (p = 0.158). During exercise, HR at NH (141 ± 4 beats·min-1) and HH (141 ± 3 beats·min-1) were higher than NN (127 ± 44 beats·min-1, p = 0.002), but not each other (p = 0.208). During exercise, stroke volume at HH (109.6 ± 4.1 mL·beat-1) was higher than NH (97.8 ± 3.3 mL·beat-1) and NN (99.8 ± 3.9 mL·beat-1, p ≤ 0.010) with no difference between NH and NN (p = 0.481). During exercise, cardiac output at NH (13.8 ± 0.6 L) and HH (15.5 ± 0.7 L) were higher than NN (12.6 ± 0.5 L, p ≤ 0.006) with HH also higher than NH (p = 0.001). During acute hypoxic stimuli, skeletal muscle maintains oxygenation whereas the brain does not. These differences may be mediated by environmentally specific cardiovascular compensation. Thus, caution is advised when equating NH and HH.

Influence of Local Muscle Cooling on Mitochondrial-Related Gene Expression at Rest.

The purpose of this study was to determine the impact of localized cooling of the skeletal muscle during rest on mitochondrial related gene expression. Thermal wraps were applied to the vastus lateralis of each limb of 12 participants. One limb received a cold application (randomized) (COLD), while the other did not (RT). Wraps were removed at the 4 h time point and measurements of skin temperature, blood flow, and intramuscular temperature were taken prior to a muscle biopsy. RT-qPCR was used to measure expression of genes associated with mitochondrial development. Skin and muscle temperatures were lower in COLD than RT (p < 0.05). Femoral artery diameter was lower in COLD after 4 h (0.62 ± 0.05 cm, to 0.60 ± 0.05 cm, p = 0.018). Blood flow was not different in COLD compared to RT (259 ± 69 mL·min-1 vs. 275 ± 54 mL·min-1, p = 0.20). PGC-1α B and GABPA expression was higher in COLD relative to RT (1.57-fold, p = 0.037 and 1.34-fold, p = 0.006, respectively). There was no difference (p > 0.05) in the expression of PGC-1α, NT-PGC-1α, PGC-1α A, TFAM, ESRRα, NRF1, GABPA, VEGF, PINK1, PARK 2, or BNIP3-L. The impact of this small magnitude of difference in gene expression of PGC-1α B and GABPA without alterations in other genes are unknown. There appears to be only limited impact of local muscle cooling on the transcriptional response related to mitochondrial development.

Septuagenarians Approach 4 Times the Basal Metabolic Rate During Race Across America.

BACKGROUND: Previous data have demonstrated that Tour de France riders maintain total daily energy expenditure (TDEE) between 3.5 and 5.5 times the basal metabolic rate (×BMR). In contrast, TDEE for healthy male septuagenarians has been reported to average 1.3 to 2.0 ×BMR. PURPOSE: Measure the TDEE and water efflux during ultraendurance work in an older population during the cross-continent cycling Race Across America. METHODS: A 4-man septuagenarian team (70 [1.6] y, 72.0 [5.1] kg) received an oral dose of doubly labeled water prior to completing the Race Across America (4817 km, 51,816 m of climbing) for TDEE calculation. Nude body weight measures were coupled with collected urine samples. RESULTS: The race was completed in approximately 6.5 days (official time: 6 d, 13 h, and 13 min) with an average speed of 30.6 (0.7) km·h-1 (age-group course record). Body weight remained unchanged (prerace: 70.4 [5.8] kg, postrace: 70.0 [5.3] kg). TDEE was calculated over 3 race segments. TDEE varied between individual riders and segments throughout the continuous event (24.7 [4.2] MJ·24 h-1, 5900 [1015] kcals·24 h-1, 3.4 [0.5] ×BMR). Water efflux averaged 10.2 (0.8) L·24 h-1 resulting in a total turnover of 45.3 (3.9) L amounting to 1.5 (0.2) times initial total body water during the race. CONCLUSIONS: Highly active septuagenarians maintain body weight prerace to postrace, suggesting near energy balance when TDEE approaches 4 ×BMR. These values exceed twice those of previously observed healthy but less active septuagenarian men and are comparable to professional riders during portions of the Tour de France. Advanced age and high metabolic output are not mutually exclusive.

Deterioration of Lipid Metabolism Despite Fitness Improvements in Wildland Firefighters.

OBJECTIVE: Determine serum lipid and general health/fitness alterations following a 5-month wildfire suppression season. METHODS: We recruited 100 wildland firefighters (WLFFs) to a 5-month pre- to post-season observational study. Nude body mass, blood pressure (BP), grip strength, and steptest heart rate (HR) were recorded. Blood samples were collected for lipid panel analysis (total cholesterol, high density lipoproteins (HDL)-cholesterol, low density lipoproteins-cholesterol, very low density lipoproteinscholesterol, triglycerides, triglyceride:HDL-cholesterol ratio). Two-tailed dependent t tests determined statistical significance (P < 0.05). RESULTS: There were pre- to post-season changes in nude body mass (+2 ±â€Š4%, P  = 0.001), systolic BP (-2 ±â€Š10%, P  = 0.01), step-test HR (-5 ±â€Š10%, P  < 0.001), and all serum lipids (total cholesterol: +5 ±â€Š14%, P  = 0.02, HDL-cholesterol: = 1 ±â€Š17%, P  = 0.04, low density lipoproteins-cholesterol: +8 ±â€Š22%, P  = 0.02, very low density lipoproteins-cholesterol: +31 ±â€Š49%, P  < 0.001, triglycerides: +30 ±â€Š49%, P  < 0.001, triglyceride:HDL-cholesterol ratio: +37 ±â€Š58%, P  < 0.001). Pre- to post-season diastolic BP (P = 0.12) and grip strength (P = 0.60) remained stable. CONCLUSIONS: WLFFs demonstrate maladaptive serum lipids and body mass alterations despite subtle aerobic fitness improvements.

Workshift Changes in Hydration Status During Wildfire Suppression.

OBJECTIVE: Document wildland firefighters (WLFFs) hydration status during a singular workshift (13.7 ±â€Š1.4 hours). METHODS: WLFF researchers documented real-time WLFF (n = 71) urine metrics and fluid consumption. Body weight and blood samples (n = 25) were also collected. Two-tailed dependent t tests determined statistical significance (P < 0.05). RESULTS: Body weight significantly decreased (-0.3 ±â€Š1.1%, P > 0.05). Fluid consumption totaled 6.2 ±â€Š2.3 L including food and 5.0 ±â€Š2.1 L without food. Morning versus afternoon urine frequency (2.6 ±â€Š1.3, 3.1 ±â€Š1.9 voids), urine volume (1.2 ±â€Š0.7, 1.3 ±â€Š0.8 L), urine volume per void (440 ±â€Š157, 397 ±â€Š142 mL), and urine specific gravity (1.010 ±â€Š0.007, 1.010 ±â€Š0.007) were not significantly different (P > 0.05). Pre- to post-workshift serum chloride (103.2 ±â€Š1.9, 101.4 ±â€Š1.7 mM) and blood glucose (5.2 ±â€Š0.4, 4.5 ±â€Š0.7 mM) significantly decreased (P < 0.05), while serum sodium (141.5 ±â€Š2.4, 140.8 ±â€Š2.0 mM) and serum potassium (4.3 ±â€Š0.3, 4.2 ±â€Š0.3 mM) remained stable (P > 0.05). CONCLUSIONS: WLFFs can ingest fluid and food amounts that maintain workshift euhydration and electrolyte status.

Influence of Fluid Delivery Schedule and Composition on Fluid Balance, Physiologic Strain, and Substrate Use in the Heat.

INTRODUCTION: Wildfire suppression is characterized by high total energy expenditure and water turnover rates. Hydration position stands outline hourly fluid intake rates. However, dose interval remains ambiguous. We aimed to determine the effects of microdosing and bolus-dosing water and microdosing and bolus-dosing carbohydrate-electrolyte solutions on fluid balance, heat stress (physiologic strain index [PSI]), and carbohydrate oxidation during extended thermal exercise. METHODS: In a repeated-measures cross-over design, subjects completed four 120-min treadmill trials (1.3 m·s-1, 5% grade, 33°C, 30% relative humidity) wearing a US Forest Service wildland firefighter uniform and a 15-kg pack. Fluid delivery approximated losses calculated from a pre-experiment familiarization trial, providing 22 doses·h-1 or 1 dose·h-1 (46±11, 1005±245 mL·dose-1). Body weight (pre- and postexercise) and urine volume (pre-, during, and postexercise) were recorded. Heart rate, rectal temperature, skin temperature, and steady-state expired air samples were recorded throughout exercise. Statistical significance (P<0.05) was determined via repeated-measures analysis of variance. RESULTS: Total body weight loss (n=11, -0.6±0.3 kg, P>0.05) and cumulative urine output (n=11, 677±440 mL, P>0.05) were not different across trials. The micro-dosed carbohydrate-electrolyte trial sweat rate was lower than that of the bolus-dosed carbohydrate-electrolyte, bolus-dosed water, and microdosed water trials (n=11, 0.8±0.2, 0.9±0.2, 0.9±0.2, 0.9±0.2 L·h-1, respectively; P<0.05). PSI was lower at 60 than 120 min (n=12, 3.6±0.7 and 4.5±0.9, respectively; P<0.05), with no differences across trials. The carbohydrate-electrolyte trial's carbohydrate oxidation was higher than water trial's (n=12, 1.5±0.3 and 0.8±0.2 g·min-1, respectively; P<0.05), with no dosing style differences. CONCLUSIONS: Equal-volume diverse fluid delivery schedules did not affect fluid balance, PSI, or carbohydrate oxidation during extended thermal work.