On the existence of a lactate threshold during incremental
exercise; a systems analysis.
Cabrera, Marco E., and Howard J. Chizeck.
Departments of Biomedical Engineering and Systems Engineering, and
Department of Pediatrics, Division of Pediatric Cardiology, Case
Western Reserve University, Cleveland, Ohio 44106
APStracts 2:0557A, 1995.
The relationship between blood lactate concentration (LA) and oxygen
uptake (O2) during incremental exercise remains controversial: does
LA increase smoothly as a function of O2 (Continuous Model) or does
it begin to increase abruptly above a particular metabolic rate
(Threshold Model)? The dynamic characteristics of the underlying
physiological system are investigated here using system
identification analysis techniques. A multivariate deterministic time
series model of the LA and O2 response to incremental changes in work
rate was fitted to simulated and experimental data. Time-varying
system response parameters were determined through the application of
a weighted recursive least-squares algorithm. The model, using the
identified time varying parameters, provided a good fit to the data.
The variation of these parameters over time was then examined. Two
major transitions in the parameters were found to occur, at intensity
levels equivalent to 53+/-8% O2max and 77+/-9% O2max (experimental
data). These changes in the model parameters indicate that the best
linear dynamic model that fits the observed system behavior has
changed. This implies that the system has changed its operation in
some way, either by altering its structure or by moving to a
different operating region. The identified parameter changes over
time suggest that the exercise intensity range (from rest to O2max)
is divided into three main intensity domains, each with distinct
dynamics. Further study of this three-phase system may help in the
understanding of the underlying physiological mechanisms that affect
the dynamics of LA and O2 during exercise.
Received 26 January 1994; accepted in final form 11 December
1995.
APS Manuscript Number A86-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 23 December 95