The effect of a six-day ski-hike on plasma catecholamine concentrations and on their response to submaximal exercise.

Plasma catecholamine concentrations and dopamine-beta-hydroxylase activities were studied in 29 participants of a six-day cross-country ski-hike (260 km) to elucidate the adaptive responses of the sympatho-adrenal system to prolonged heavy exercise. Immediately after skiing on the first skiing day plasma noradrenaline concentrations appeared to be over twice as high as in the morning. On the morning of the fourth day noradrenaline levels had increased significantly when compared to those of the first morning. Concentrations after skiing on the fourth day were, however, about the same as in the first evening. After a submaximal ergometer test performed immediately after the skiing concentrations were still raised and the relative enhancement by this short-term exercise was about the same magnitude (40--60 %) on every test day. On the sixth day noradrenaline concentrations were about the same level as on the fourth day. Eleven days after the hike the basal noradrenaline levels were still about 25 % higher than before it. The changes of plasma adrenaline concentrations were in the same direction although not as striking as those of noradrenaline. Dopamine alterations were negligible. A significant but reversible decrease in plasma dopamine-beta-hydroxylase activities and cholesterol concentrations was found during the hike. The present results show that the sympatho-adrenal system is activated during the first few days of a ski-hike type prolonged exercise. A plateau developed in about four days. There were no signs of a decreased sympatho-adrenal response to a short-term heavy load.