Sweat distribution and perceived wetness across the human foot: the effect of shoes and exercise intensity

Ingesting carbonated water post-exercise in the heat transiently ameliorates hypotension and enhances mood state

The objective was to assess if post-exercise ingestion of carbonated water in a hot environment ameliorates hypotension, enhances cerebral blood flow and heat loss responses, and positively modulates perceptions and mood states. Twelve healthy, habitually active young adults (five women) performed 60 min of cycling at 45% peak oxygen uptake in a hot climate (35°C). Subsequently, participants consumed 4°C carbonated or non-carbonated (control) water (150 and 100 mL for males and females regardless of drink type) at 20 and 40 min into post-exercise periods. Mean arterial pressure decreased post-exercise at 20 min only (P = 0.032) compared to the pre-exercise baseline. Both beverages transiently (∼1 min) increased mean arterial pressure and middle cerebral artery mean blood velocity (cerebral blood flow index) regardless of post-exercise periods (all P ≤ 0.015). Notably, carbonated water ingestion led to greater increases in mean arterial pressure (2.3 ± 2.8 mmHg vs. 6.6 ± 4.4 mmHg, P < 0.001) and middle cerebral artery mean blood velocity (1.6 ± 2.5 cm/s vs. 3.8 ± 4.1 cm/s, P = 0.046) at 20 min post-exercise period compared to non-carbonated water ingestion. Both beverages increased mouth exhilaration and reduced sleepiness regardless of post-exercise periods, but these responses were more pronounced with carbonated water ingestion at 40 min post-exercise (mouth exhilaration: 3.1 ± 1.4 vs. 4.7 ± 1.7, P = 0.001; sleepiness: -0.7 ± 0.91 vs. -1.9 ± 1.6, P = 0.014). Heat loss responses and other perceptions were similar between the two conditions throughout (all P ≥ 0.054). We show that carbonated water ingestion temporarily ameliorates hypotension and increases the cerebral blood flow index during the early post-exercise phase in a hot environment, whereas it enhances mouth exhilaration and reduces sleepiness during the late post-exercise phase.

Effect of Wetsuit Use on Body Temperature and Swimming Performance During Training in the Pool: Recommendations for Open-Water Swimming Training With Wetsuits

PURPOSE

Open-water swimmers need to train with wetsuits to get familiar with them; however, body core temperature (Tcore) kinetics when using wetsuits in swimming-pool training remains unclear. The present study assessed the effects of wetsuit use in pool training on Tcore, subjective perceptions, and swimming performance to obtain suggestions for wearing wetsuits in training situations.

METHODS

Four elite/international-level Japanese swimmers (2 female, age 24 [1] y) completed two 10-km trials with (WS) and without wetsuit (SS) in the swimming pool (Tw: 29.0 °C). During the trial, swimmers were allowed to remove their wetsuit if they could no longer tolerate the heat. Tcore was continuously recorded via ingestible temperature sensors. Swimming speed was estimated from every 100-m lap time.

RESULTS

Tcore increased by distance in both trials in all swimmers. Tcore when swimmers removed their wetsuit in the WS (distance: 3800 [245] m, time: 2744 [247] s) was higher than that at the same distance in the SS in all swimmers. Rating of perceived exertion was higher in the SS than the WS, and swimming speed was slower in the WS than the SS in all swimmers.

CONCLUSION

Wetsuit use during pool training increases Tcore and decreases swimming performance. Although wearing wetsuits in training situations is important for familiarization, for the safety of the swimmers, it is recommended that they remove their wetsuit if they feel too hot.

Influence of changes in foot morphology and temperature on bruised toenail injury risk during running

Despite runners frequently suffering from dermatologic issues during long distance running, there is no compelling evidence quantitatively investigating their underlying injury mechanism. This study aimed to determine the foot morphology and temperature changes during long distance running and reveal the effect of these alterations on the injury risk of bruised toenail by measuring the subjective-perceived hallux comfort and gap length between the hallux and toebox of the shoe. Ten recreational runners participated in the experimental tests before (baseline), immediately after 5 and 10 km of treadmill running (12 km/h), in which the foot morphology was measured by a 3D foot scanner, the foot temperature was detected by an infrared camera, the perceived comfort was recorded by a visual analogue scale, and the gap length in the sagittal plane was captured by a high-speed camera. Ball width became narrower (106.39 ± 6.55 mm) and arch height (12.20 ± 2.34 mm) was reduced greatly after the 10 km run (p < 0.05). Foot temperature increased significantly after 5 and 10 km of running, and the temperature of dorsal hallux (35.12 ± 1.46 °C), dorsal metatarsal (35.92 ± 1.59 °C), and medial plantar metatarsal (37.26 ± 1.34 °C) regions continued to increase greatly from 5 to 10 km of running (p < 0.05). Regarding hallux comfort, the perceived scores significantly reduced after 5 and 10 km of running (2.10 ± 0.99, p < 0.05). In addition, during one running gait cycle, there was a significant increase in gap length at initial contact (39.56 ± 6.45 mm, p < 0.05) for a 10 km run, followed by a notable decrease upon reaching midstance (29.28 ± 6.81 mm, p < 0.05). It is concluded that the reduced ball width and arch height while increased foot temperature during long-distance running would exacerbate foot-shoe interaction, potentially responsible for bruised toenail injuries.

Thermal Sensation After the 10-km Open-Water Swimming in Cool Water Depends on the Skin's Thermal Sensitivity Rather Than Core Temperature

PURPOSE

To assess the core temperature fluctuations during 10-km open-water swimming (OWS) in cool water and the relationship between thermal sensation (TS) after 10-km OWS, core temperature, and local skin thermal sensitivity.

METHODS

Nine highly trained OWS swimmers (4 female; age 22 [3] y) completed a single 10-km trial in cool water (22.3 °C) wearing swimsuits for OWS. During the trial, core temperature was continuously recorded via ingestible temperature sensors, and TS after trial was also measured. Then, local skin warm/cool sensitivity was measured in the forearm.

RESULTS

All swimmers completed the 10-km OWS. Mean swimming speed for males and females were 1.39 (1.37-1.42 m/s) and 1.33 m/s (1.29-1.38 m/s), respectively. Core temperature increased in 8 out of 9 swimmers during 10-km OWS (P = .047), with an average increase of 0.8 °C. TS after 10-km OWS varied among swimmers. There were no correlations between post-OWS TS and post-OWS core temperature (P = .9333), whereas there was a negative correlation between post-OWS TS and local skin cool sensitivity (P = .0056).

CONCLUSION

These results suggest that core temperature in elite swimmers might not decrease during 10-km OWS in the cool water temperature of official OWS. In addition, individual differences in TS after 10-km OWS may be related to skin cool sensitivity rather than core temperature.

Physiological effects of exercise in heat while wearing a polyester versus cotton T-shirt in physically active men with obesity: a pilot study

BACKGROUND

Obesity may impair evaporation especially during exercising in heat. Polyester sportwear is proposed to improve the evaporation but its effectiveness remains overlooked. We investigated physiological effects of exercise in heat while wearing a polyester versus cotton T-shirt on thermoregulation, perspiration, and cardiovascular regulations.

METHODS

Physically active men with obesity (N.=7; 21.7±1.7 years old; VO2peak 36.8±8.7 mL/kg/min; body fat percentage 34.7±4.3%) performed two randomized, crossover walking sessions for 30 mins (27 °C; 12% relative humidity) while wearing a polyester or cotton T-shirt, separated by a 7-day wash out period. Thermoregulation was assessed by measuring tympanic, torso (back and chest), and peripheral (forehead and forearm) skin temperatures. Perspiration rate was estimated as the difference in body weight (pre minus post walking). Heart rate was measured by a Polar heart rate monitor. Systolic and diastolic blood pressure were measured by a sphygmomanometer. All measurements were performed pre, during, and post each session. Two-way ANOVA examined main effects of time, fabric type, and their interactions on the study's outcomes.

RESULTS

Back and chest temperatures increased (∆=1.6 °C and 0.9 °C, respectively) while forehead and forearm temperatures decreased (∆=-0.5 °C and -1.6 °C, respectively) over time (P<0.05 for all). Only forehead temperature had an interaction effect for time by fabric type where greater decrease was observed during the polyester T-shirt session compared to the cotton T-shirt session (∆=-0.1 vs. -0.8 °C; P=0.016). Heart rate (∆=27.8 beat/min) and systolic blood pressure (∆=7.5 mmHg) increased while diastolic blood pressure (∆=-5.0 mmHg) decreased over time (P<0.05 for all). No difference observed for perspiratory rate (P>0.05).

CONCLUSIONS

The current findings do not support the superiority of polyester or cotton sportwear for better thermoregulatory, perspiratory, and cardiovascular regulations in physically active men with obesity. Future research should examine the effectiveness of other alternative fabrics of sportwear for better physiological responses when exercising in the heat, particularly in adults with obesity.

Thermoregulation in Two Models of Trail Run Socks with Different Fabric Separation

BACKGROUND

Trail running socks with the same fibers and design but with different separations of their three-dimensional waves could have different thermoregulatory effects. Therefore, the objective of this study was to evaluate the temperatures reflected on the sole of the foot after a mountain race with the use of two models of socks with different wave separations.

MATERIAL AND METHODS

In a sample of 34 subjects (twenty-seven men and seven women), the plantar temperature was analyzed with the thermal imaging camera Flir E60bx® (Flir systems, Wilsonville, OR, USA) before and after running 14 km in mountainous terrain at a hot temperature of 27 °C. Each group of 17 runners ran with a different model of separation between the waves of the tissue (2 mm versus 1 mm). After conducting the post-exercise thermographic analysis, a Likert-type survey was conducted to evaluate the physiological characteristics of both types of socks.

RESULTS

There was a significant increase in temperature in all areas of interest (p < 0.001) after a 14 km running distance with the two models of socks. The hallux zone increased in temperature the most after the race, with temperatures of 8.19 ± 3.1 °C and 7.46 ± 2.1 °C for the AWC 2.2 and AWC 3, respectively. However, no significant differences in temperature increases were found in any of the areas analyzed between the two groups. Runners perceived significant differences in thermal sensation between AWC 2.2 socks with 4.41 ± 0.62 points and AWC 3 with 3.76 ± 1.03 points (p = 0.034).

CONCLUSION

Both models had a similar thermoregulatory effect on the soles of the feet, so they can be used interchangeably in short-distance mountain races. The perceived sensation of increased thermal comfort does not correspond to the temperature data.

A modelling framework for local thermal comfort assessment related to bicycle helmet use

Thermal discomfort due to accumulated sweat increasing head skin wettedness may contribute to low wearing rates of bicycle helmets. Using curated data on human head sweating and helmet thermal properties, a modelling framework for the thermal comfort assessment of bicycle helmet use is proposed. Local sweat rates (LSR) at the head were predicted as the ratio to the gross sweat rate (GSR) of the whole body or by sudomotor sensitivity (SUD), the change in LSR per change in body core temperature (Δt_re). Combining those local models with Δt_re and GSR output from thermoregulation models, we simulated head sweating depending on the characteristics of the thermal environment, clothing, activity, and exposure duration. Local thermal comfort thresholds for head skin wettedness were derived in relation to thermal properties of bicycle helmets. The modelling framework was supplemented by regression equations predicting the wind-related reductions in thermal insulation and evaporative resistance of the headgear and boundary air layer, respectively. Comparing the predictions of local models coupled with different thermoregulation models to LSR measured at the frontal, lateral and medial head under bicycle helmet use revealed a large spread in LSR predictions predominantly determined by the local models and the considered head region. SUD tended to overestimate frontal LSR but performed better for lateral and medial head regions, whereas predictions by LSR/GSR ratios were lower and agreed better with measured frontal LSR. However, even for the best models root mean squared prediction errors exceeded experimental SD by 18-30%. From the high correlation (R > 0.9) of skin wettedness comfort thresholds with local sweating sensitivity reported for different body regions, we derived a threshold value of 0.37 for head skin wettedness. We illustrate the application of the modelling framework using a commuter-cycling scenario, and discuss its potential as well as the needs for further research.

Nonwoven/Nanomembrane Composite Functional Sweat Pads

Sweat is a natural body excretion produced by skin glands, and the body cools itself by releasing salty sweat. Wetness in the underarms and feet for long durations causes itchiness and an unpleasant smell. Skin-friendly reusable sweat pads could be used to absorb sweat. Transportation of moisture and functionality is the current challenge that many researchers are working on. This study aims to develop a functional and breathable sweat pad with antimicrobial and quick drying performance. Three layered functional sweat pads (FSP) are prepared in which the inner layer is made of an optimized needle-punched coolmax/polypropylene nonwoven blend. This layer is then dipped in antimicrobial ZnO solution (2, 4, and 6 wt.%), and super absorbent polymer (SAP) is embedded, and this is called a functional nonwoven (FNW1) sheet. Electrospun nanofiber-based nanomembranes of polyamide-6 are optimized for bead-free fibers. They are used as a middle layer to enhance the pad's functionality, and the third layer is again made of needle-punched optimized coolmax/polypropylene nonwoven sheets. A simple nonwoven-based sweat pad (SSP) is also prepared for comparison purposes. Nonwoven sheets are optimized based on better comfort properties, including air/water vapor permeability and moisture management (MMT). Nonwoven webs having a higher proportion of coolmax show better air permeability and moisture transfer from the inner to the outer layer. Antimicrobial activity of the functional nonwoven layer showed 8 mm of bacterial growth, but SSP and FSP showed only 6 mm of growth against Staphylococcus aureus. FSP showed superior comfort and antibacterial properties. This study could be a footstone toward highly functional sweat pads with remarkable comfort properties.

Effects of textile-fabricated insole on foot skin temperature and humidity for enhancing footwear thermal comfort

Traditional insole materials which trap heat and moisture inside footwear cause discomfort to the wearer. Here, a novel textile-fabricated insole material with a 3D structure that offers good porosity and breathability for improving the footwear microclimate is proposed. Changes in foot skin temperature and humidity when wearing the textile-fabricated insole throughout treadmill walking are collected from 21 female subjects (age: 25.5 ± 4.5) and compared with traditional and 3D printed insoles. Subjective assessment of their perceived thermal comfort with various insole conditions is also conducted. In comparison to polyurethane, 3D printed thermoplastic polyurethane and leather insoles, textile-fabricated insoles show no significant changes in foot skin temperature. Nevertheless, a significant reduction of the relative humidity of the skin of the sole (3.21%) and heel (24.41%) is found. The findings are a valuable reference for the fabrication of insoles with higher wear comfort.

Influence of Upper Footwear Material Properties on Foot Skin Temperature, Humidity and Perceived Comfort of Older Individuals

Studying the in-shoe microclimate of older individuals is important for enhancing their foot comfort and preventing foot diseases. However, there is a lack of scientific work that explores the thermo-physiological wear comfort of older individuals with different footwear. This study aims to examine the effects of upper footwear materials on changes and distributions in the foot skin temperature and relative humidity for older individuals. Forty older individuals are recruited to perform sitting and walking activities under four experimental conditions in a conditioning chamber. The findings indicate that footwear upper constructed of highly permeable mesh fabric with large air holes shows fewer changes in foot skin temperature (ranging from 1.3 to 3.3 °C) and relative humidity (ranging from -13.3 to 5.7%) throughout the entire foot during dynamic walking, as well as higher subjective ratings on perceived thermal comfort when compared to footwear made of synthetic leather and composite layers. The findings serve to enhance current understanding of designing footwear with optimum comfort for older adults.

Footwear microclimate and its effects on the microbial community of the plantar skin

The association between the footwear microclimate and microbial community on the foot plantar skin was investigated by experiments with three participants. Novel methods were developed for measuring in-shoe temperature and humidity at five footwear regions, as well as the overall ventilation rate inside the footwear. Three types of footwear were tested including casual shoes, running shoes, and perforated shoes for pairwise comparison of footwear microclimate and corresponding microbial community on the skin. The major findings are as follows: (1) footwear types make a significant difference to in-shoe temperature at the instep region with the casual shoes sustaining the warmest of all types; (2) significant differences were observed in local internal absolute humidity between footwear types, with the casual shoes sustaining the highest level of humidity at most regions; (3) the perforated shoes provided the highest ventilation rate, followed by running and casual shoes, and the faster the gait, the larger the discrepancy in ventilation rate between footwear types; (4) the casual shoes seemed to provide the most favorable internal environment for bacterial growth at the distal plantar skin; and (5) the bacterial growth at the distal plantar skin showed a positive linear correlation with the in-shoe temperature and absolute humidity, and a negative linear correlation with the ventilation rate. The ventilation rate seemed to be a more reliable indicator of the bacterial growth. Above all, we can conclude that footwear microclimate varies in footwear types, which makes contributions to the bacterial growth on the foot plantar skin.

Body mapping of regional sweat distribution in young and older males

Purpose

Given the pressing impact of global warming and its detrimental effect on the health of older populations, understanding age-related changes in thermoregulatory function is essential. Age differences in regional sweat distribution have been observed previously, but given the typically small measurement areas assessed, the development of whole body sweat maps for older individuals is required. Therefore, this study investigated age-related differences in regional sweat distribution in a hot environment (32 °C/50%RH) in young and older adults, using a body mapping approach.

Methods

Technical absorbent pads were applied to the skin of 14 young (age 24 ± 2 years) and 14 older (68 ± 5 years) males to measure regional sweat rate (RSR) at rest (30 min) and during exercise (30 min), at a fixed heat production (200 W m⁻²). Gastrointestinal (T_gi) and skin temperature (T_sk), heart rate, thermal sensation, and thermal comfort were also measured.

Results

Whole body sweat maps showed that despite equal heat production, healthy older males had significantly lower gross sweat loss (GSL) than the young and significantly lower RSR at almost all body regions at rest and at the hands, legs, ankles, and feet during exercise. The lower sweat loss in the older group coincided with a greater increase in T_gi and a consistently higher T_sk at the legs, despite subjectively feeling slightly cooler than younger individuals.

Conclusion

These findings support the evidence of age-related deterioration in both autonomic and subjective responses in the heat and highlight the lower extremities as the most affected body region.

Electronic supplementary material

The online version of this article (10.1007/s00421-020-04503-5) contains supplementary material, which is available to authorized users.