Increased skin wetness independently augments cool-seeking behaviour during passive heat stress.

KEY POINTS: Skin wetness occurring secondary to the build-up of sweat on the skin provokes thermal discomfort, the precursor to engaging in cool-seeking behaviour. Associative evidence indicates that skin wetness stimulates cool-seeking behaviour to a greater extent than increases in core and mean skin temperatures. The independent contribution of skin wetness to cool-seeking behaviour during heat stress has never been established. We demonstrate that skin wetness augments cool-seeking behaviour during passive heat stress independently of differential increases in skin temperature and core temperature. We also identify that perceptions of skin wetness were not elevated despite increases in actual skin wetness. These data support the proposition that afferent signalling from skin wetness enhances the desire to engage in cool-seeking behaviour during passive heat stress. ABSTRACT: This study tested the hypothesis that elevations in skin wetness augments cool-seeking behaviour during passive heat stress. Twelve subjects (6 females, age: 24 ± 2 y) donned a water-perfused suit circulating 34 °C water and completed two trials resting supine in a 28.5 ± 0.4 °C environment. The trials involved a 20 min baseline period (26 ± 3% relative humidity (RH)), 60 min while ambient humidity was maintained at 26±3% RH (LOW) or increased to 67 ± 5% RH (HIGH), followed by 60 min passive heat stress (HS) where the water temperature in the suit was incrementally increased to 50 °C. Subjects were able to seek cooling when their neck was thermally uncomfortable by pressing a button. Each button press initiated 30 s of -20 °C fluid perfusing through a custom-made device secured against the skin on the dorsal neck. Mean skin (Tskin ) and core (Tcore ) temperatures, mean skin wetness (Wskin ) and neck device temperature (Tdevice ) were measured continuously. Cool-seeking behaviour was determined from total time receiving cooling (TTcool ) and cumulative button presses. Tskin and Tcore increased during HS (P < 0.01) but were not different between conditions (P ≥ 0.11). Wskin was elevated in HIGH vs. LOW during HS (60 min: by + 0.06 ± 0.07 a.u., P ≤ 0.04). Tdevice was lower in HIGH vs. LOW at 40-50 min of HS (P ≤ 0.01). TTcool was greater for HIGH (330 ± 172 s) vs. LOW (225 ± 167 s, P < 0.01), while the number of cumulative button presses was greater from 40-60 min in HS for HIGH vs. LOW (P ≤ 0.04). Increased skin wetness amplifies the engagement in cool-seeking behaviour during passive heat stress.

Skin wettedness is an important contributor to thermal behavior during exercise and recovery.

We tested the hypothesis that mean skin wettedness contributes to thermal behavior to a greater extent than core and mean skin temperatures. In a 27.0 ± 1.0°C environment, 16 young participants (8 females) cycled for 30 min at 281 ± 51 W·m2, followed by 120 min of seated recovery. Mean skin and core temperatures and mean skin wettedness were recorded continuously. Participants maintained a thermally comfortable neck temperature throughout the protocol using a custom-made device. Neck device temperature provided an index of thermal behavior. Linear regression was performed using individual minute data with mean skin wettedness and core and mean skin temperatures as independent variables and neck device temperature as the dependent variable. Standarized ß-coefficients were used to determine relative contributions to thermal behavior. Mean skin temperature differed from preexercise (32.6 ± 0.5°C) to 10 min into exercise (32.3 ± 0.6°C, P < 0.01). Core temperature increased from 37.1 ± 0.3°C preexercise to 37.7 ± 0.4°C by end exercise ( P < 0.01) and remained elevated through 30 min of recovery (37.2 ± 0.3°C, P < 0.01). Mean skin wettedness increased from preexercise [0.14 ± 0.03 arbitrary units (AU)] to 20 min into exercise (0.43 ± 0.09 AU, P < 0.01) and remained elevated through 80 min of recovery (0.18 ± 0.06 AU, P ≤ 0.05). Neck device temperature decreased from 26.4 ± 1.6°C preexercise to 18.5 ± 8.7°C 10 min into exercise ( P = 0.03) and remained depressed through 20 min of recovery (14.4 ± 11.2°C, P < 0.01). Mean skin wettedness (52 ± 24%) provided a greater contribution to thermal behavior compared with core (22 ± 22%, P = 0.06) and mean skin (26 ± 16%, P = 0.04) temperatures. Skin wettedness is an important contributing factor to thermal behavior during exercise and recovery.

Effect of acute fatigue and training adaptation on countermovement jump performance in elite snowboard cross athletes.

Countermovement jump performance was examined in response to acute neuromuscular (NM) fatigue (study I) and chronic training (study II) in elite snowboard cross (SBX) athletes, through both typical (countermovement jump [CMJ]-TYP) and alternative (CMJ-ALT) CMJ variables. Seven (4 men and 3 women) elite (Olympic-level) SBX athletes participated in study I, and 5 of the same athletes (2 men and 3 women) participated in study II. Countermovement jump variables relating to force, velocity, power, and time were measured during both eccentric and concentric jump phases, with CMJ-TYP variables reflecting CMJ output and CMJ-ALT variables reflecting CMJ mechanics. In study I, CMJ performance was assessed before and after a fatiguing lower-body exercise protocol, and in study II, CMJ performance was examined before and after a 19-week structured training block. Meaningful differences in CMJ performance were examined using the magnitude of change (effect sizes [ES]) for group and individual changes. Acute fatigue decreased peak force and eccentric function, while the duration of the jump increased. The structured training block increased peak force and eccentric function, while jump duration markedly decreased. In both study I and study II, the largest ES were associated with CMJ-ALT variables. The CMJ test seems a suitable monitoring tool in elite SBX athletes for the detection of both acute fatigue and training-adaptation. Compared with CMJ output, CMJ mechanics exhibits more marked and divergent changes after both acute NM fatigue and a structured training block. CMJ-ALT variables should therefore be incorporated into CMJ analysis.

Comparison of the Capacity of Different Jump and Sprint Field Tests to Detect Neuromuscular Fatigue.

Different jump and sprint tests have been used to assess neuromuscular fatigue, but the test with optimal validity remains to be established. The current investigation examined the suitability of vertical jump (countermovement jump [CMJ], squat jump [SJ], drop jump [DJ]) and 20-m sprint (SPRINT) testing for neuromuscular fatigue detection. On 6 separate occasions, 11 male team-sport athletes performed 6 CMJ, SJ, DJ, and 3 SPRINT trials. Repeatability was determined on the first 3 visits, with subsequent 3 visits (0-, 24-, and 72-hour postexercise) following a fatiguing Yo-Yo running protocol. SPRINT performance was most repeatable (mean coefficient of variation ≤2%), whereas DJ testing (4.8%) was significantly less repeatable than CMJ (3.0%) and SJ (3.5%). Each test displayed large decreases at 0-hour (33 of 49 total variables; mean effect size = 1.82), with fewer and smaller decreases at 24-hour postexercise (13 variables; 0.75), and 72-hour postexercise (19 variables; 0.78). SPRINT displayed the largest decreases at 0-hour (3.65) but was subsequently unchanged, whereas SJ performance recovered by 72-hour postexercise. In contrast, CMJ and DJ performance displayed moderate (12 variables; 1.18) and small (6 variables; 0.53) reductions at 72-hour postexercise, respectively. Consequently, the high repeatability and immediate and prolonged fatigue-induced changes indicated CMJ testing as most suitable for neuromuscular fatigue monitoring.

The Molecular Effect of Wearing Silver-Threaded Clothing on the Human Skin.

With growing awareness that what we put in and on our bodies affects our health and wellbeing, little is still known about the impact of textiles on the human skin. Athletic wear often uses silver threading to improve hygiene, but little is known about its effect on the body's largest organ. In this study, we investigated the impact of such clothing on the skin's chemistry and microbiome. Samples were collected from different body sites of a dozen volunteers over the course of 12 weeks. The changes induced by the antibacterial clothing were specific for individuals, but more so defined by gender and body site. Unexpectedly, the microbial biomass on skin increased in the majority of the volunteers when wearing silver-threaded T-shirts. Although the most abundant taxa remained unaffected, silver caused an increase in diversity and richness of low-abundant bacteria and a decrease in chemical diversity. Both effects were mainly observed for women. The hallmark of the induced changes was an increase in the abundance of various monounsaturated fatty acids (MUFAs), especially in the upper back. Several microbe-metabolite associations were uncovered, including Cutibacterium, detected in the upper back area, which was correlated with the distribution of MUFAs, and Anaerococcus spp. found in the underarms, which were associated with a series of different bile acids. Overall, these findings point to a notable impact of the silver-threaded material on the skin microbiome and chemistry. We observed that relatively subtle changes in the microbiome result in pronounced shifts in molecular composition. IMPORTANCE The impact of silver-threaded material on human skin chemistry and microbiome is largely unknown. Although the most abundant taxa remained unaffected, silver caused an increase in diversity and richness of low-abundant bacteria and a decrease in chemical diversity. The major change was an increase in the abundance of various monounsaturated fatty acids that were also correlated with Cutibacterium. Additionally, Anaerococcus spp., found in the underarms, were associated with different bile acids in the armpit samples. Overall, the impact of the silver-threaded clothing was gender and body site specific.

Exercise intensity independently modulates thermal behavior during exercise recovery but not during exercise.

We tested the hypothesis that thermal behavior is greater during and after high- compared with moderate-intensity exercise. In a 27°C, 20% relative humidity environment, 20 participants (10 women, 10 men) cycled for 30 min at moderate [53% (SD 6) peak oxygen uptake (V̇o2peak) or high [78% (SD 6) V̇o2peak] intensity, followed by 120 min of recovery. Mean skin and core temperatures and mean skin wettedness were recorded continuously. Participants maintained thermally comfortable neck temperatures with a custom-made neck device. Neck device temperature provided an index of thermal behavior. The weighted average of mean skin and core temperatures and mean skin wettedness provided an indication of the afferent stimulus to thermally behave. Mean skin and core temperatures were greater at end-exercise in high intensity (P < 0.01). Core temperature remained elevated in high intensity until 70 min of recovery (P = 0.03). Mean skin wettedness and the afferent stimulus were greater at 10-20 min of exercise in high intensity (P ≤ 0.03) and remained elevated until 60 min of recovery (P < 0.01). Neck device temperature was lower during exercise in high versus moderate intensity (P ≤ 0.02). There was a strong relation between the afferent stimulus and neck device temperature during exercise (high: R2 = 0.82, P < 0.01; moderate: R2 = 0.95, P < 0.01) and recovery (high: R2 = 0.97, P < 0.01; moderate: R2 = 0.93, P < 0.01). During exercise, slope (P = 0.49) and y-intercept (P = 0.91) did not differ between intensities. In contrast, slope was steeper (P < 0.01) and y-intercept was higher (P < 0.01) during recovery from high-intensity exercise. Thermal behavior is greater during high-intensity exercise because of the greater stimulus to behave. The withdrawal of thermal behavior is augmented after high-intensity exercise. NEW & NOTEWORTHY This is the first study to determine the effects of exercise intensity on thermal behavior. We show that exercise intensity does not independently modulate thermal behavior during exercise but is dependent on the magnitude of afferent stimuli. In contrast, the withdrawal of thermal behavior after high-intensity exercise is augmented. This may be a consequence of an attenuated perceptual response to afferent stimuli, which may be due to processes underlying postexercise hypoalgesia.

Thermal Behavior Differs between Males and Females during Exercise and Recovery.

INTRODUCTION: This study tested the hypothesis that females rely on thermal behavior to a greater extent during and after exercise, relative to males. METHODS: In a 24°C ± 1°C; (45% ± 10% RH) environment, 10 males (M) and 10 females (F) (22 ± 2 yr) cycled for 60 min (metabolic heat production: M, 117 ± 18 W·m; F, 129 ± 21 W·m), followed by 60-min recovery. Mean skin and core temperatures, skin blood flow and local sweat rates were measured continually. Subjects controlled the temperature of their dorsal neck to perceived thermal comfort using a custom-made device. Neck device temperature provided an index of thermal behavior and mean body temperature provided an index of the stimulus for thermal behavior. Data were analyzed for total area under the curve for exercise and recovery time points. To further isolate the effect of exercise on thermal behavior during recovery, data were also analyzed the minute mean body temperature returned to preexercise levels within a subject. RESULTS: There were no sex differences in metabolic heat production (P = 0.71) or body temperatures (P ≥ 0.10) during exercise. Area under the curve for neck device temperature during exercise was greater for F (-98.4°C·min ± 33.6°C·min vs -64.5°C·min ± 47.8°C·min, P = 0.04), but did not differ during recovery (F, 86.8°C·min ± 37.8°C·min; M, 65.6°C·min ± 35.9°C·min; P = 0.11). In M, mean skin (P = 0.90), core (P = 0.70) and neck device (P = 0.99) temperatures had recovered by the time that mean body temperature had returned to preexercise levels. However, in F, neck device temperature (P = 0.04) was reduced while core temperature remained elevated (P < 0.01). CONCLUSIONS: Females use thermal behavior during exercise to a greater extent than M. During recovery, thermal behavior may compensate for elevated core temperatures in F despite mean body temperatures returning to preexercise levels.

Thermal behavior alleviates thermal discomfort during steady-state exercise without affecting whole body heat loss.

We tested the hypothesis that thermal behavior resulting in reductions in mean skin temperature alleviates thermal discomfort and mitigates the rise in core temperature during light-intensity exercise. In a 27 ± 0°C, 48 ± 6% relative humidity environment, 12 healthy subjects (6 men, 6 women) completed 60 min of recumbent cycling. In both trials, subjects wore a water-perfused suit top continually perfusing 34 ± 0°C water. In the behavior trial, subjects maintained their upper body thermally comfortable by pressing a button to perfuse cool water (2.2 ± 0.5°C) through the top for 2 min per button press. Metabolic heat production (control: 404 ± 52 W, behavior: 397 ± 65 W; P = 0.44) was similar between trials. Mean skin temperature was reduced in the behavior trial (by -2.1 ± 1.8°C, P < 0.01) because of voluntary reductions in water-perfused top temperature (P < 0.01). Whole body (P = 0.02) and local sweat rates were lower in the behavior trial (P ≤ 0.05). Absolute core temperature was similar (P ≥ 0.30); however, the change in core temperature was greater in the behavior trial after 40 min of exercise (P ≤ 0.03). Partitional calorimetry did not reveal any differences in cumulative heat storage (control: 554 ± 229, behavior: 544 ± 283 kJ; P = 0.90). Thermal behavior alleviated whole body thermal discomfort during exercise (by -1.17 ± 0.40 arbitrary units, P < 0.01). Despite lower evaporative cooling in the behavior trial, similar heat loss was achieved by voluntarily employing convective cooling. Therefore, thermal behavior resulting in large reductions in skin temperature is effective at alleviating thermal discomfort during exercise without affecting whole body heat loss.NEW & NOTEWORTHY This study aimed to determine the effectiveness of thermal behavior in maintaining thermal comfort during exercise by allowing subjects to voluntarily cool their torso and upper limbs with 2°C water throughout a light-intensity exercise protocol. We show that voluntary cooling of the upper body alleviates thermal discomfort while maintaining heat balance through convective rather than evaporative means of heat loss.

Thermal Behavior Augments Heat Loss Following Low Intensity Exercise.

We tested the hypothesis that thermal behavior alleviates thermal discomfort and accelerates core temperature recovery following low intensity exercise. Methods: In a 27 0 C, 48 6% relative humidity environment, 12 healthy subjects (six females) completed 60 min of exercise followed by 90 min of seated recovery on two occasions. Subjects wore a suit top perfusing 34 ± 0 °C water during exercise. In the control trial, this water continually perfused throughout recovery. In the behavior trial, the upper body was maintained thermally comfortable by pressing a button to receive cool water (3 2 °C) perfusing through the top for 2 min per button press. Results: Physiological variables (core temperature, p ≥ 0.18; mean skin temperature, p = 0.99; skin wettedness, p ≥ 0.09; forearm skin blood flow, p = 0.29 and local axilla sweat rate, p = 0.99) did not differ between trials during exercise. Following exercise, mean skin temperature decreased in the behavior trial in the first 10 min (by -0.5 0.7 °C, p < 0.01) and upper body skin temperature was reduced until 70 min into recovery (by 1.8 1.4 °C, p < 0.05). Core temperature recovered to pre-exercise levels 17 31 min faster (p = 0.02) in the behavior trial. There were no differences in skin blood flow or local sweat rate between conditions during recovery (p ≥ 0.05). Whole-body thermal discomfort was reduced (by -0.4 0.5 a.u.) in the behavior trial compared to the control trial within the first 20 min of recovery (p ≤ 0.02). Thermal behavior via upper body cooling resulted in augmented cumulative heat loss within the first 30 min of recovery (Behavior: 288 92 kJ; Control: 160 44 kJ, p = 0.02). Conclusions: Engaging in thermal behavior that results in large reductions in mean skin temperature following exercise accelerates the recovery of core temperature and alleviates thermal discomfort by promoting heat loss.

Thermal behavior remains engaged following exercise despite autonomic thermoeffector withdrawal.

We tested the hypothesis that thermal behavior during the exercise recovery compensates for elevated core temperatures despite autonomic thermoeffector withdrawal. In a thermoneutral environment, 6 females and 6 males (22 ±â€¯1 y) cycled for 60 min (225 ±â€¯46 W metabolic heat production), followed by 60 min passive recovery. Mean skin and core temperatures, skin blood flow, and local sweat rate were measured continually. Subjects controlled the temperature of their dorsal neck to perceived thermal comfort using a custom-made neck device. Neck device temperature provided an index of thermal behavior. Mean body temperature, calculated as the average of mean skin and core temperatures, provided an index of the stimulus for thermal behavior. To isolate the independent effect of exercise on thermal behavior during recovery, data were analyzed post-exercise the exact minute mean body temperature recovered to pre-exercise levels within a subject. Mean body temperature returned to pre-exercise levels 28 ±â€¯20 min into recovery (Pre: 33.5 ±â€¯0.2, Post: 33.5 ±â€¯0.2 °C, P = 0.20), at which point, mean skin temperature had recovered (Pre: 29.6 ±â€¯0.4, Post: 29.5 ±â€¯0.5 °C, P = 0.20) and core temperature (Pre: 37.3 ±â€¯0.2, Post: 37.5 ±â€¯0.3 °C, P = 0.01) remained elevated. Post-exercise, skin blood flow (Pre: 59 ±â€¯78, Post: 26 ± 25 PU, P = 0.10) and local sweat rate (Pre: 0.05 ±â€¯0.25, Post: 0.13 ±â€¯0.14 mg/cm2 min-1, P = 0.09) returned to pre-exercise levels, while neck device temperature was depressed (Pre: 27.4 ±â€¯1.1, Post: 21.6 ±â€¯7.4 °C, P = 0.03). These findings suggest that thermal behavior compensates for autonomic thermoeffector withdrawal in the presence of elevated core temperatures post-exercise.

Alternative countermovement-jump analysis to quantify acute neuromuscular fatigue.

PURPOSE: To examine the reliability and magnitude of change after fatiguing exercise in the countermovement-jump (CMJ) test and determine its suitability for the assessment of fatigue-induced changes in neuromuscular (NM) function. A secondary aim was to examine the usefulness of a set of alternative CMJ variables (CMJ-ALT) related to CMJ mechanics. METHODS: Eleven male college-level team-sport athletes performed 6 CMJ trials on 6 occasions. A total of 22 variables, 16 typical (CMJ-TYP) and 6 CMJ-ALT, were examined. CMJ reproducibility (coefficient of variation; CV) was examined on participants' first 3 visits. The next 3 visits (at 0, 24, and 72 h postexercise) followed a fatiguing high-intensity intermittent-exercise running protocol. Meaningful differences in CMJ performance were examined through effect sizes (ES) and comparisons to interday CV. RESULTS: Most CMJ variables exhibited intraday (n = 20) and interday (n = 21) CVs of <10%. ESs ranging from trivial to moderate were observed in 18 variables at 0 h (immediately postfatigue). Mean power, peak velocity, flight time, force at zero velocity, and area under the force-velocity trace showed changes greater than the CV in most individuals. At 24 h, most variables displayed trends toward a return to baseline. At 72 h, small increases were observed in time-related CMJ variables, with mean changes also greater than the CV. CONCLUSIONS: The CMJ test appears a suitable athlete-monitoring method for NM-fatigue detection. However, the current approach (ie, CMJ-TYP) may overlook a number of key fatigue-related changes, and so practitioners are advised to also adopt variables that reflect the NM strategy used.

Analysis of jump performance of world-class mogul skiers over an Olympic quadrennial cycle: a case study.

This case study examines the longitudinal jump data of 1 male and 1 female world-class mogul skier over the course of a quadrennial leading to the 2010 Winter Olympics. Between-subjects standard deviation, smallest worthwhile enhancement, % coefficient of variance, and effect size (ES) were calculated from team jump testing taking place immediately preceding the 2010 Winter Olympics, as this was deemed the point in the quadrennial that the athlete group would be most likely near their best performance. These data were then used to characterize the progression of explosive power of elite mogul skiers over an Olympic quadrennial. Jump data for both the male and the female athlete showed trivial to large improvements in jump performance from Q1 (quadrennial year 1) to Q2, variable changes in performance from Q2 to Q4, and an overall improvement (small to large ES) from Q1 to Q4. Explosive power is a critical component of performance for moguls, and an analysis of the group data (Canadian athletes 2006-2010) shows that of all performance markers, jump testing is the variable that clearly delineates between World Cup and developmental athletes.