Comparison of plasma Cortisol sampling sites for rock climbing

Aim. Blood samples for the determination of plasma Cortisol concentration are generally obtained via venipuncture or capillary sampling at the fingertip. During rock climbing the upper body, forearms and fingertips are subject to continual loading and gripping making sampling at these sites problematic. The purpose of this study was to examine differences in plasma Cortisol concentrations from capillary samples taken at the fingertip and first (big) toe in a rock climbing context. Methods. Nine (8 males, 1 female) climbers completed a succession of climbing bouts at three different angles (91°,100° and 110°). Capillary blood samples were taken simultaneously from the fingertip and first toe pre and post climb at each angle. Plasma samples were collected via centrifugation and subsequently analysed for Cortisol using an Enzyme-Linked Immunosorbent Assay (ELISA) kit. All standards and samples were analysed in duplicate. Intra assay coeffiecients of variation (CV%) were 5.91% and 7.94% for finger and toe respectively. Results. A limits of agreement plot revealed all data points to be well within upper and lower bounds of the 95% population confidence interval. Paired samples t-tests (for finger and toe) indicated there were no significant differences between sample sites. Subsequent regression analysis revealed a strong relationship (R²=0.78, y=1.031x - 2.079) between fingertip and first toe capillary plasma cortisol concentrations. Conclusion. Findings suggest that the first toe offers a valid alternative sampling site for plasma cortisol concentration in a rock climbing context.