Margherita Raccuglia

Human wetness perception of fabrics under dynamic skin contact

This experiment studied textile (surface texture, thickness) and non-textile (local skin temperature changes, stickiness sensation and fabric-to-skin pressure) parameters affecting skin wetness perception under dynamic interactions. Changes in fabric texture sensation between WET and DRY states and their effect on pleasantness were also studied. The surface texture of eight fabric samples, selected for their different structures, was determined from surface roughness measurements using the Kawabata Evaluation System. Sixteen participants assessed fabric wetness perception, at high pressure and low pressure conditions, stickiness, texture and pleasantness sensation on the ventral forearm. Differences in wetness perception (p < 0.05) were not determined by texture properties and/or texture sensation. Stickiness sensation and local skin temperature drop were determined as predictors of wetness perception (r2 = 0.89), and although thickness did not correlate with wetness perception directly, when combined with stickiness sensation it provided a similar predictive power (r2 = 0.86). Greater (p < 0.05) wetness perception responses at high pressure were observed compared with low pressure. Texture sensation affected pleasantness in DRY (r2 = 0.89) and WET (r2 = 0.93). In WET, pleasantness was significantly reduced (p < 0.05) compared to DRY, likely due to the concomitant increase in texture sensation (p < 0.05). In summary, under dynamic conditions, changes in stickiness sensation and wetness perception could not be attributed to fabric texture properties (i.e. surface roughness) measured by the Kawabata Evaluation System. In dynamic conditions thickness or skin temperature drop can predict fabric wetness perception only when including stickiness sensation data.

Human wetness perception in relation to textile water absorption parameters under static skin contact

Skin wetness perception (WP) greatly affects thermal and sensorial discomfort in clothing and as such is of great interest to the clothing industry. Following neurophysiological studies of WP, this study looks at textile parameters affecting WP. Twenty-four fabrics varying in thickness, fiber type and absorption capacity were studied. Using 12 participants (males/females), the WP induced was studied in four wetness states: 1. Dry; 2. absolute (ABS), all having the same absolute water content of 2400 µL per sample (=0.24 µL mm−2); 3. 100REL, saturated with water to their individual absorption capacity; 4. 50REL, to 50% of the value in 3. As total absorption capacity was highly correlated (r = 0.99) to fabric thickness, conditions 3 and 4 were equivalent to having the same water content per volume of textile, i.e. 0.8 and 0.4 µL mm−3, respectively. Samples were applied to the upper back statically to minimize the contribution of surface roughness/friction. WP was highly correlated to drop in skin temperature induced by the wet fabric, and increased with application pressure of the fabric. No effect of fiber type was observed. In REL, with equal µL mm−3, WP showed a positive correlation to total fabric water-content-per-area (µL mm−2), and thus also to thickness, given the correlation between the latter two, with saturation above 1.5 µL mm−2. In ABS, on the other hand, with equal µL mm−2, and thus with relative water content (µL mm µL mm−3) inversely proportional to thickness, WP was also inversely proportional to thickness. Thus WP showed opposing responses depending on the wetting type, indicating that the methodology of manipulating water content should be selected in relation to the product end-use.

Clothing comfort during physical exercise – Determining the critical factors

Clothing comfort is determined by multiple material and design factors. Wetness at the skin-clothing interface mainly impacts wear comfort. The current study investigated the combined effect of fabric contact area, fabric absolute sweat content and fabric moisture saturation percentage on wetness and stickiness sensations, during exercise. Moreover, factors causing wear (dis)comfort during exercise were identified. Higher fabric saturation percentage induced greater stickiness sensation, despite lower fabric contact area and absolute sweat content (typically associated with lower stickiness). Wetness perception did not change between fabrics with different saturation percentages, contact areas and sweat contents. Therefore, fabric saturation percentage mainly affects stickiness sensation of wet fabrics, overruling the impact of fabric contact area and absolute sweat content. No overall model of wear discomfort across all data could be developed, however, models for different time points were produced, with texture and stickiness sensations being the best predictors of wear discomfort at baseline and during exercise, respectively. This suggests that the factors determining clothing (dis)comfort are dynamics and alter importance during exercise activity.

Anchoring biases affect repeated scores of thermal, moisture, tactile and comfort sensations in transient conditions

In this study, we addressed potential biases which can occur when sensorial scores of temperature, wetness and discomfort are repeatedly reported, in transient exercise conditions. We pointed out that, when repeatedly reported, previous sensorial scores can be set by the participants as reference values and the subsequent score may be given based on the previous point of reference, the latter phenomenon leading to a bias which we defined as ‘anchoring bias’. Indeed, the findings shown that subsequent sensorial scores are prone to anchoring biases and that the bias consisted in a systematically higher magnitude of sensation as compared to when reported a single time only. As such, the study allowed recognition, quantification and mitigation of the identified bias which can improve the methodological rigour of research studies involving assessments of sensorial data in transient conditions.

Localized and systemic variations in central motor drive at different local skin and muscle temperatures

This study investigated the ability to sustain quadriceps central motor drive while subjected to localized heat and metaboreceptive feedback from the contralateral leg. Eight active males each completed two counter-balanced trials, in which muscle temperature (Tm) of a single-leg (TEMP-LEG) was altered to 29.4°C (COOL) or 37.6°C (WARM), while the contralateral leg (CL-LEG) remained thermoneutral: 35.3°C and 35.2°C Tm in COOL and WARM, respectively. To activate metaboreceptive feedback, participants first performed one 120-s isometric maximal voluntary contraction (MVC) of the knee extensors in the TEMP-LEG, immediately followed by postexercise muscle ischemia (PEMI) via femoral blood flow occlusion. To assess central motor drive of a remote muscle group immediately following PEMI, another 120-s MVC was subsequently performed in the CL-LEG. Voluntary muscle activation (VA) was assessed using the twitch interpolation method. Perceived mental effort and limb discomfort were also recorded. In a cooled muscle, a significant increase in mean force output and mean VA (force, P < 0.001; VA, P < 0.05), as well as a significant decrease in limb discomfort (P < 0.05) occurred during the sustained MVC in the TEMP-LEG. However, no differences between Tm were observed in mean force output, mean VA, or limb discomfort during the sustained MVC in the CL-LEG (force, P = 0.33; VA, P > 0.68; and limb discomfort, P = 0.73). The present findings suggest that elevated local skin temperature and Tm can increase limb discomfort and decrease central motor drive, but this does not limit systemic motor activation of a thermoneutral muscle group.

The interaction between cooling and hypoxia on the rate of peripheral and central fatigue development of the knee extensors

High altitude often comprises hypobaric hypoxia and cold ambient temperatures. However, research examining human performance during these stressors in combination is sparse [1]. Previous findings have reported that the rate of fatigue additively increases when hypoxia and cold are combined [2]. However this study investigated small muscle groups (forearm flexors) using a fixed duration (closed) exercise protocol. Thus, the present study sought to examine whether volitional exhaustion or task failure (during an open protocol) of the larger knee extensor muscles would result in a similar additive effect during combined hypoxic-cold exposure.

The use of optimised heating trousers and the role of the blood flow on the reduction in muscle temperature post warm up

Activities that are highly dependent on power output can benefit from increases in muscle temperature (Tm) in terms of work done and skeletal muscle power output. When athletes experience a significant delay between active warm up and performance, Tm declines. Previous studies have demonstrated that using heated trousers during a period of inactivity can attenuate this decline, with a greater peak power output as result [1,2]. However, in these studies, the reduction in Tm was not completely eliminated. Thus, in the current study we aimed to optimise the heating procedure, in order to eliminate the reduction in Tm post-warm up. Furthermore, to understand the reason of this reduction, the effect of the blood flow in the cooling process of the leg was studied.