Regional and Time Course Differences in Sweat Cortisol and Glucose During Steady State Exercise

Abstract

The ability to use sweat as a biofluid for noninvasive sampling and diagnostics is a popular area of innovation. However, body mapping for local sweat metabolites is lacking and collection methods are inconsistent. To determine regional and time course differences in sweat cortisol and glucose concentrations we collected sweat with absorbent patches (3MTMTegaderm+PAD) from eight, non-acclimatized, euhydrated (USG 1.012±0.008) subjects (24-44 y; 80.2±10.2 kg; V̇O2 max 52.2 ±6.4 mL/kg/min) at the following sites: right dorsal forearm (RDF), right triceps (RT), right scapula (RS) and forehead (FH) at 0-25 (25), 30-55 (55), and 60-85 (85) min during 90 min of cycling (82% HR max) in a heated chamber (32°C, 50% RH). ELISA was used for the detection of cortisol (Invitrogen, ThermoFisher Scientific) and glucose (Caymen Chemical Co.) concentrations. Data are presented as mean±SD or median±IQR for data that were not normally distributed. One-way ANOVA or Kruskal-Wallis were used to test differences among groups. Dunn's test for multiple comparisons was used for post-hoc analysis. Excretion rates (ER) were calculated as the product of concentration and local sweat rate (LSR). Whole body sweat rate was 0.85±0.09 mg/cm2/min. LSR was significantly different among sites (FH 4.1±2.3 > RS 1.6±0.6, RDF 1.4±0.9 > RT 0.8±0.5 mg/cm2/min; p<0.0001). LSR was the same across time for FH, whereas RDF (p=0.04), RS (p=0.01), and RT (p=0.01) varied. RS LSR at 55 (p=0.02) and 85 (p=0.02) were greater than 25 min. RT LSR at 55 was higher than 25 min (p=0.01). RDF LSR had no specific differences. Cortisol concentrations were similar across sites (FH 2.7±3.1, RDF 2.2±2.1, RS 2.2±2.2, RT 1.9±1.5 ng/mL). FH cortisol concentrations varied across time (1.8±1.6, 2.9±2.2, 4.9±9.6 ng/mL at 25, 55, and 85 min, respectively; p=0.02), with specific differences between 25 and 85 min (p=0.02). RDF cortisol concentrations also varied across time (1.3±1.6, 2.9±1.7, 3.5±6.3 ng/mL at 25, 55, and 85 min, respectively; p=0.01), with specific differences between RDF 25 and 85 min (p=0.01). RT and RS cortisol concentrations were similar across time. Cortisol ER was 4.3±6.2 pg/cm2/min and varied across sites (FH 9.8±14.8, RDF 3.7±4.9, RS 4.0±3.1, RT 2.2±2.2 pg/cm2/min (p<0.0001)). FH cortisol ER was greater than all other sites (RDF p=0.004, RS p=0.006, RT p<0.0001). FH (p=0.02) and RDF (p=0.01) cortisol ERs varied across time points, where 85 was greater than 25 min (FH p=0.02, RDF p=0.01). RT and RS cortisol ERs were similar across time. Glucose concentrations (0.2±0.5 mg/dL) were similar across sites and between time points within the same site. Glucose ER across all sites was 5.2±9.1 ng/cm2/min and differed across sites (FH 5.4±22.4, RDF 6.2±9.9, RS 7.0±8.6, RT 2.8±4.1 ng/cm2/min; p=0.04), where FH was greater than RT (p=0.03). Glucose ER did not differ between time points within each location. In summary, cortisol concentration and ER increase as exercise time progresses on the FH and RDF, but not the RS or RT. This study demonstrates that the site and time point selection for sweat sampling is a necessary consideration for future research.