Damien Fournet

Body mapping of cutaneous wetness perception across the human torso during thermo-neutral and warm environmental exposures

Sensing skin wetness is linked to inputs arising from cutaneous cold-sensitive afferents. As thermosensitivity to cold varies significantly across the torso, we investigated whether similar regional differences in wetness perception exist. We also investigated the regional differences in thermal pleasantness and whether these sensory patterns are influenced by ambient temperature. Sixteen males (20 ± 2 yr) underwent a quantitative sensory test under thermo-neutral [air temperature (Tair) = 22°C; relative humidity (RH) = 50%] and warm conditions (Tair = 33°C; RH = 50%). Twelve regions of the torso were stimulated with a dry thermal probe (25 cm(2)) with a temperature of 15°C below local skin temperature (Tsk). Variations in Tsk, thermal, wetness, and pleasantness sensations were recorded. As a result of the same cold-dry stimulus, the skin-cooling response varied significantly by location (P = 0.003). The lateral chest showed the greatest cooling (-5 ± 0.4°C), whereas the lower back showed the smallest (-1.9 ± 0.4°C). Thermal sensations varied significantly by location and independently from regional variations in skin cooling with colder sensations reported on the lateral abdomen and lower back. Similarly, the frequency of perceived skin wetness was significantly greater on the lateral and lower back as opposed to the medial chest. Overall wetness perception was slightly higher under warm conditions. Significantly more unpleasant sensations were recorded when the lateral abdomen and lateral and lower back were stimulated. We conclude that humans present regional differences in skin wetness perception across the torso, with a pattern similar to the regional differences in thermosensitivity to cold. These findings indicate the presence of a heterogeneous distribution of cold-sensitive thermo-afferent information.

Mild evaporative cooling applied to the torso provides thermoregulatory benefits during running in the heat

We investigated the effects of mild evaporative cooling applied to the torso, before or during running in the heat. Nine male participants performed three trials: control‐no cooling (CTR), pre‐exercise cooling (PRE‐COOL), and during‐exercise cooling (COOL). Trials consisted of 10‐min neutral exposure and 50‐min heat exposure (30 °C; 44% humidity), during which a 30‐min running protocol (70% VO2max) was performed. An evaporative cooling t‐shirt was worn before the heat exposure (PRE‐COOL) or 15 min after the exercise was started (COOL). PRE‐COOL significantly lowered local skin temperature (Tsk) (up to −5.3 ± 0.3 °C) (P < 0.001), mean Tsk (up to −2 ± 0.1 °C) (P < 0.001), sweat losses (−143 ± 40 g) (P = 0.002), and improved thermal comfort (P = 0.001). COOL suddenly lowered local Tsk (up to −3.8 ± 0.2 °C) (P < 0.001), mean Tsk (up to −1 ± 0.1 °C) (P < 0.001), heart rate (up to −11 ± 2 bpm) (P = 0.03), perceived exertion (P = 0.001), and improved thermal comfort (P = 0.001). We conclude that the mild evaporative cooling provided significant thermoregulatory benefits during exercise in the heat. However, the timing of application was critical in inducing different thermoregulatory responses. These findings provide novel insights on the thermoregulatory role of Tsk during exercise in the heat.

Tactile cues significantly modulate the perception of sweat-induced skin wetness independently of the level of physical skin wetness

Humans sense the wetness of a wet surface through the somatosensory integration of thermal and tactile inputs generated by the interaction between skin and moisture. However, little is known on how wetness is sensed when moisture is produced via sweating. We tested the hypothesis that, in the absence of skin cooling, intermittent tactile cues, as coded by low-threshold skin mechanoreceptors, modulate the perception of sweat-induced skin wetness, independently of the level of physical wetness. Ten males (22 yr old) performed an incremental exercise protocol during two trials designed to induce the same physical skin wetness but to induce lower (TIGHT-FIT) and higher (LOOSE-FIT) wetness perception. In the TIGHT-FIT, a tight-fitting clothing ensemble limited intermittent skin-sweat-clothing tactile interactions. In the LOOSE-FIT, a loose-fitting ensemble allowed free skin-sweat-clothing interactions. Heart rate, core and skin temperature, galvanic skin conductance (GSC), and physical (w(body)) and perceived skin wetness were recorded. Exercise-induced sweat production and physical wetness increased significantly [GSC: 3.1 μS, SD 0.3 to 18.8 μS, SD 1.3, P < 0.01; w(body): 0.26 no-dimension units (nd), SD 0.02, to 0.92 nd, SD 0.01, P < 0.01], with no differences between TIGHT-FIT and LOOSE-FIT (P > 0.05). However, the limited intermittent tactile inputs generated by the TIGHT-FIT ensemble reduced significantly whole-body and regional wetness perception (P < 0.01). This reduction was more pronounced when between 40 and 80% of the body was covered in sweat. We conclude that the central integration of intermittent mechanical interactions between skin, sweat, and clothing, as coded by low-threshold skin mechanoreceptors, significantly contributes to the ability to sense sweat-induced skin wetness.

Can body-mapped garments improve thermal comfort for sport in the cold?

Body maps of the human body have been developed regarding distribution of sweat production [1] and skin temperature [2]. However it has rarely been explored how body-mapped clothing (textile properties adjusted locally according to body mappings) impact thermal responses and perceptions. The present study investigates the question for exercising in the cold, manipulating skin temperatures by various distributions of clothing. It was hypothesized that covering naturally cold regions would make skin temperature more uniform and be beneficial for thermal comfort.

Decreasing the tactile interaction between skin, sweat and clothing significantly reduces the perception of wetness independently of the level of physical skin wetness during moderate exercise.

Although the ability to sense skin wetness and humidity is critical for behavioural and autonomic adaptations, humans are not provided with specific skin receptors for sensing wetness [1]. We have recently demonstrated that humans perceive the wetness experienced when the skin is in contact with a wet surface through a multisensory integration of thermal and tactile inputs generated by the interaction between skin and moisture [2]. To further the understanding on the neurophysiology of human skin wetness perception, here we tested the hypothesis that the perception of sweat-induced skin wetness can be significantly manipulated, independently from the level of physical skin wetness.

Assessment of Sport Garments Using Infrared Thermography

Sport garments and their properties directly influence the heat exchanges occurring at the interface between the human skin and the environment. Active skin cooling or warming through innovative apparel is more and more developed in training and competition. Infrared thermography can provide original insights into the patterns of skin temperature distribution during exercise that can then be used for clothing design using a bodymapping approach.