STRESS RESPONSES TO A 50 KM NORDIC SKI-RACE

Abstract

Introduction: There is very limited information on the physiological responses to exhaustive cross-country ski-racing in elite athletes. Therefore the primary purpose of this study was to examine the leukocyte and hormonal responses related to a 50K World Cup ski-race. Subsequently, we wanted to compare these findings with existing data from marathon races of similar intensity and duration, but typically involving less muscle mass. A subsidiary objective was to examine if the observed perturbations in the blood compartment could indicate any health risk associated with exhaustive cross-country skiing in elite athletes. Methods: Ten elite male athletes from the Norwegian cross-country ski team, age: 23–32 years and VO2 max: 81–92 ml kg−1min−1, participated. They followed usual pre-race routines with breakfast 3 h before race start at 11.30 AM and liberal consumption of a CHO-electrolyte sports drink. During the 50 km race, all athletes drank 1.0–1.51 of the same drink. Pre-race blood samples were taken between 10:00-10:30 AM, and post-race samples were obtained within 1 min after the finish. Mean race time was 142 min (135–146 min). Leukocyte counts were performed on a Sysmex K-1000 and the lymphocyte sub-counts on a FACS-scan flow-cytometer. Epinephrine (EPI) and norepinephrine (NE) were analyzed using a HPLC method. Cortisol (Cort), testosterone (Testo), growth hormone (GH) and insulin (Ins) were measured with a RIA method. Plasma glucose (Glu) was determined on a Tecnicon Chem I analyzer and free fatty acids (FFA) concentrations were determined ezymatically. Wilcoxon's Signed rank test was used for statistical analysis. Means, SD and exact p-values are given. Results: From pre- to post race, we observed significant increases in concentrations of leukocytes (pre:5.0 ± 0.9; post:21.4 ± 2.9 ×103/mm3; p = 0.005), granulocytes (pre:2.7 ± 1.0; post: 18.0 ± 3.7 ×103/mm3; p = 0.005), lymphocytes (pre:1.9 ± 0.4; post: 3.1 ± 1.4 ×103/mm3; p = 0,005), NK-cells (pre:0.43 ± 0.12; post: 1.09 ± 0.54×103/mm3, p = 0.005), B-cells (pre:0.19 ± 0.08; post: 0.35 ± 0.16 ×103/mm3; p = 0.005), but not in concentrations of monocytes, CD3+, CD4+ and CD8+ cells. We also observed significant increases in EPI (pre: 0.4 ± 0.2; post: 4.6 ± 2.7 nmol/1; p = 0.005), NE (pre: 3.7 ± 1.3; post:19.7 ± 6.0 nmol/l; p = 0.005), Cort (pre:462 ± 114; post: 957 ± 154 nmol/l; p = 0.005), GH (pre:1.2 ± 2.2; post:27.1 ± 13 mIE/1; p = 0.005), Glu (pre: 5.4 ± 1.0; post: 7.2 ± 1.8 mmol/1; p = 0.01) and FFA (pre: 0.2 ± 0.06; post: 0.7 ± 0.2 mmol/1; p = 0.005) while Testo levels were unchanged, and Ins decreased (pre:299 ± 168; post:59 ± 20 pmol/1; p = 0.005). Discussion: Both the absolute values and percentage changes in total leucocytes, granulocytes, catecholamines, growth hormone, insulin and glucose were more pronounced after a 50 km ski race compared with what has been observed during marathon races (Nieman et al.). Previously, an augmented catecholamine and glucose response has been found when arm work was added to an on-going leg exercise and this effect was ascribes to increased amounts of muscle mass (Kjaer et al.). We suggest that cross-country skiing at high intensity involving activation of a large proportion of total body muscle mass may require higher concentrations of catecholamines compared with running at the same aerobic intensity. This increased catecholamine surge subsequently mobilizes more leukocytes into circulation and leads to a more pronounced insulin and glucose response. No indication of health risk was found. Acknowledgements: Sponsored by The Norwegian Federation of Sports and Olympic Committee