Thesis (M.Sc.)--University of the Witwatersrand, Faculty of Medicine, 1998. / During graded exercise, an intensity is reached where a subjects
ability to remove lactate lags behind the rate of lactace
production. The influence of body fluid shifts, during exercise
of increasing intensity, on the pattern of the blood lactate
response was studied.
The maximal oxygen uptake (V02 max) was measured using a
treadmill, on eleven subjects. Subsequently, lactate
accumulation in venous blood was measured, in triplicate, up to
an oxygen consumption greater than 90% V02max. During all
exercise, oxygen consumption was measured using an online system.
In addition, the blood samples at each workload were used to
determine haematocrit (Hct) and haemoglobin (Hb) levels.
The Hct and Hb values were used to calculate lactate accumulation
(corrected for body fluid shifts) as opposed to the absolute or
total lactate levels. The correction for body fluid shifts was
done using two techniques. The one using haematocrit only and the
other using both haematocrit and haemoglobin. The total and
accumulated lactate levels were related to %V02max using two
different models. Firstly, a lactate threshold (LT) was
determined using the classic lactate turning point (LTP) concept,
(ie. two straight lines fitted to the data points) . These Tines
iii
were computer generated. The intercept of the two lines (LT) was
compared for total lactate against accumulated lactate
(calculated using Hct alone and secondly Hct in combination with
Hb. In the latter cases, both the LT intercepts were shifted
slightly to the right (ie. to a higher % of V02max) . The average
difference in LT when adjusting with Hb and Hct was 0,519 of
%V02max (0,72% change) and when adjusting with Hct only was 1,17
of %V02 max (1,65% change).
Secondly, an exponential curve was fitted by regression to the
data (r=0.989+/-0.018). A substantial shift in the curve, both
down and to the right, was obtained when adjusting total lactate
to accumulated lactate. The %V02 max at a lactate concentration
of 4 mmol/I was used to define the position of the curve. The
difference when using Hct alone to calculate accumulated lactate
corrected for fluid shift was - 9,20% of V02max (p<0.05), and
when using Hb and Hct in combination, -8,71% of V02max (p<0,05) .
It is concluded that expressing the lactate curve as an
accumulated curve (corrected for body fluid shifts), rather than
in absolute terms, significantly alters the construction of the
curve during the exercise protocol used in this study. This is
especially relevant when using the exponential model,
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/14109 |
| Date | 25 June 1999 |
| Creators | Castleman, Barbara Ann |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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