Volume 6, Spring 2008 - Saddleback College

34
Saddleback Journal of Biology
Spring 2008
Fall 2007 Biology 3A Abstracts
lactic acid may challenge certain memory inhibition
(Gibbs, et al., 2007).
This study hopes to resolve some of the
confusion by providing a measure of the memory
capabilities at varied levels of lactate, across a small
sample population. Our hypothesis for this experiment
is: there is a significant difference in the memory
capability between resting and elevated levels of
lactate.
Materials and Methods
Subjects:
Ten test subjects (N = 10) were selected from
male and female individuals of ages 17 to 50 years in
age, and levels of fitness from semi-sedentary to
athletic. Minimum standards were observed in that all
subjects were adults and capable of 30 minutes of
sustained exercise, on a stationary bike, at moderate
levels.
Design of the study:
The measure of memory capability across
increasing levels of lactate involved a small sample
population of 10 individual adults with clean bills of
health. Lactate was generated by exercise at a heart rate
in the anaerobic range appropriate for the individual’s
age and relative fitness as following formula:
Max Heart Rate (Male) = 210 - Age * 0.8
Max Heart Rate (Female) = 205 - Age * 0.7
Target Heart Rate = (Max Heart Rate - Resting
Heart Rate) * Anaerobic Threshold %
Memory capability was measured by recall of a
number of items from a computer image viewed by the
test subject for two seconds. Measurement at multiple
levels of lactate including resting levels provided
adequate measures to differentiate memory tests. The
full test session consisted of the following:
Take resting lactate and heart rate
measurements
Test memory
10 minute warm-up,
Increase effort to reach target heart rate for
anaerobic exercise (based upon age, sex and
resting heart rate, see formulae above)
1 minute at target heart rate,
Take lactate measurement and record heart
rate
Test memory
5 minute recovery period at very low heart
rate
We do realize that there were many different
people being tested with many different fitness levels
so intensity of exercise was defined according to
Lactate Threshold (LT) to normalize any stress to
subjects (Farina et al., 2004).
Measurement of anaerobic activity:
Subjects wore an Xplorer GLX PasPort PS
2002 with Exercise Heart Rate sensor PS 2129 Polar
T31 wireless chest band heart rate monitor to measure
the subject’s heart rate over the test interval.
Measurement of lactate in blood:
Subjects’ lactate was measured through a
blood sample tested using a Lactate Scout portable
lactate measuring device. The samples were taken
using antiseptic technique, cleaning and sterilizing the
area to be lanced.
Measurement of cognitive ability:
Cognitive ability was determined using two
pictures, one each for the before and after test. The
pictures contain a variety of items, 20 items in each
picture, and were shown to the subject for two seconds
and then removed. Subjects then were asked to name
the items from the picture that they remember.
Data analysis:
The data collected was comprised of a lactate
measurement paired with a cognitive value for the
number of items remembered from the picture. The
paired values for resting and exercising states will be
compared to assess the impact of lactate on cognitive
ability.
Statistical analysis:
The statistical software in Excel (Microsoft®
version 2003) was used for all statistical analyses.
Comparisons between responses were made using
Student t-Test. Statistical significance was accepted at
5%. Results are presented as means ± standard error
(SE), unless stated otherwise.
Results
As can be seen in Table One, five subjects
scored slightly better on memory test one (low lactate)
than on memory test two (elevated lactate). Four
subjects scored the same on tests one and two. One
subject scored better on memory test two than on
memory test one.
Figure One shows the average scores, out of
twenty, for the two memory tests. Memory test one
yielded a mean score of 5.2 ± 0.47 (S.E.M.). Memory
test two yielded a mean score of 4.7 ± 0.45 (S.E.M.).
There is a small difference in the average scores on the
two memory tests. A one-tailed t-Test assuming
unequal variances was run, p = 0.22, p>0.05 therefore
there is no significant difference in the cognitive
abilities at baseline or elevated lactate levels.
Baseline lactate levels ranged from 2.0
mmol/L to 5.3 mmol/L. The elevated lactate levels
ranged from 8.1 mmol/L to 22.6 mmol/L.