Changes in acid-base status of marathon runners during an incremental field test. Relationship to mean competitive marathon velocity
Zoladz, J.A.; Sargeant, A.J.; Emmerich, J.; Stoklosa, J.; Zychowski, A.
European Journal of Applied Physiology and Occupational Physiology 67(1): 71-76
1993
ISSN/ISBN: 0301-5548 PMID: 8375370 Document Number: 418423
Four top-class runners who regularly performed marathon and long-distance races participated in this study. They performed a graded field test on an artificial running track within a few weeks of a competitive marathon. The test consisted of five separate bouts of running. Each period lasted 6 min with an intervening 2-min rest bout during which arterialized capillary blood samples were taken. Blood was analysed for pH, partial pressure of oxygen and carbon dioxide (PO-2 and PCO-2) and lactate concentration ((la-)-b). The values of base excess (BE) and bicarbonate concentration ((HCO-3-)) were calculated. The exercise intensity during the test was regulated by the runners themselves. The subjects were asked to perform the first bout of running at a constant heart rate f-c which was 50 beats cntdot min-1 below their own maximal f-c. Every subsequent bout, each of which lasted 6 min, was performed with an increment of 10 beats cntdot min-1 as the target f-c. Thus the last, the fifth run, was planned to be performed with f-c amounting to 10 beats cntdot min-1 less than their maximal f-c. The results from these runners showed that the blood pH changed very little in the bouts performed at a running speed below 100% of mean marathon velocity ( hivin nu-m). However, once hivin nu-m was exceeded, there were marked changes in acid-base status. In the bouts performed at a velocity above the hivin nu-m there was a marked increase in (la-)-b and a significant decrease in pH, (HCO-3-), BE and pCO-2. The average marathon velocity ( hivin nu-m) was 18.46 (SD 0.32) km cntdot h-1. The (la-)-b at a mean running velocity of 97.1 (SD 0.8) % of hivin nu-m was 2.33 (SD 1.33) mmol cntdot l-1 which, compared with a value at rest of 1.50 (SD 0.60) mmol cntdot l-1, was not significantly higher. However, when running velocity exceeded the hivin nu-m by only 3.6 (SD 1.9) %, the (la-)-b increased to 6.94 (SD 2.48) mmol cntdot l-1 (P lt 0.05 vs rest). We concluded from our study that the highest running velocity at which the blood pH still remained constant in relation to the value at rest and the speed of the run at which (la-)-b began to increase significantly above the value at rest is a sensitive indicator of capacity for marathon running.