Effects of Acute Hypoxia on
the Estimation of Lactate Threshold from Ventilatory Gas
Exchange Indices During an Incremental Exercise Test
O. OZCELIK, H. KELESTIMUR
Firat University, Department of Physiology, Faculty of Medicine,
Received October 15, 2003
Accepted January 26, 2004
The purpose of this study was to investigate the validity of
non-invasive lactate threshold estimation using ventilatory and
pulmonary gas exchange indices under condition of acute hypoxia.
Seven untrained males (21.41.2 years) performed two incremental
exercise tests using an electromagnetically braked cycle
ergometer: one breathing room air and other breathing 12 % O2.
The lactate threshold was estimated using the following
parameters: increase of ventilatory equivalent for O2 (VE/VO2)
without increase of ventilatory equivalent for CO2 (VE/VCO2). It
was also determined from the increase in blood lactate and
decrease in standard bicarbonate. The VE/VO2 and lactate
increase methods yielded the respective values for lactate
threshold: 1.910.10 l/min (for the VE/VO2) vs. 1.890.1 l/min
(for the lactate). However, in hypoxic condition, VE/VO2 started
to increase prior to the actual threshold as determined from
blood lactate response: 1.670.1 l/min (for the lactate) vs.
1.370.09 l/min (for the VE/VO2) (P=0.0001), i.e. resulted in
pseudo-threshold behavior. In conclusion, the ventilatory and
gas exchange indices provide an accurate lactate threshold.
Although the potential for pseudo-threshold behavior of the
standard ventilatory and gas exchange indices of the lactate
threshold must be concerned if an incremental test is performed
under hypoxic conditions in which carotid body chemosensitivity
Exercise • Hypoxia • Lactate threshold