Ja. Zoladz et al., CHANGES IN ACID-BASE STATUS OF MARATHON RUNNERS DURING AN INCREMENTALFIELD-TEST - RELATIONSHIP TO MEAN COMPETITIVE MARATHON VELOCITY, European journal of applied physiology and occupational physiology, 67(1), 1993, pp. 71-76
Four top-class runners who regularly performed marathon and long-dista
nce races participated in this study. They performed a graded field te
st on an artificial running track within a few weeks of a competitive
marathon. The test consisted of five separate bouts of running. Each p
eriod lasted 6 min with an intervening 2-min rest bout during which ar
terialized capillary blood samples were taken. Blood was analysed for
pH, partial pressure of oxygen and carbon dioxide (PO2 and PCO2) and l
actate concentration ([la-]b). The values of base excess (BE) and bica
rbonate concentration ([HCO3-]) were calculated. The exercise intensit
y during the test was regulated by the runners themselves. The subject
s were asked to perform the first bout of running at a constant heart
rate f(c) which was 50 beats . min -1 below their own maximal f(c). Ev
ery subsequent bout, each of which lasted 6 min, was performed with an
increment of 10 beats . min -1 as the target f(c). Thus the last, the
fifth run, was planned to be performed with f(c) amounting to 10 beat
s . min -1 less than their maximal f(c). The results from these runner
s showed that the blood pH ranged very little in the bouts performed a
t a running speed below 100% of mean marathon velocity (v(m)BAR). Howe
ver, once v(m)BAR was exceeded, there were marked changes in acid-base
status. In the bouts performed at a velocity above the v(m)BAR there
was a marked increase in [la-]b and a significant decrease in pH, [HCO
3-], BE and PCO2. The average marathon velocity (v(m)BAR) was 18.46 (S
D 0.32) km . h -1. The [la -]b at a mean running velocity of 97.1 (SD
0.8) % of v(m)BAR was 2.33 (SD 1.33) mmol . l -1 which, compared with
a value at rest of 1.50 (SD 0.60) mmol . l -1, was not significantly h
igher. However, when running velocity exceeded the v(m) by only 3.6 (S
D 1.9) %, the [la - ]b increased to 6.94 (SD 2.48) mmol . l -1 (P < 0.
05 vs rest). We concluded from our study that the highest running velo
city 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 incr
ease significantly above the value at rest is a sensitive indicator of
capacity for marathon running.