United States
Environmental Protection
Agency
Health Effects
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S1 -86/006 Dec. 1986
Project Summary
Effects of 60-Hz Fields on
Human Health Parameters
Mary R. Cook, Carl M. Maresh, and Harvey D. Cohen
Research on the effects of exposure
to 60-Hz electric and magnetic fields
has provided contradictory evidence for
both increases and decreases in physio-
logical and metabolic functioning, and
specific results have often been difficult
to replicate. If biological responses to
powerline fields occur, they are un-
doubtedly subtle, and research strate-
gies must be specifically designed to
enhance and clarify subtle effects.
The study reported here used quanti-
tative exercise testing techniques to
evaluate whether increases in
metabolism, caused by moderate
steady-state exercise prior to exposure
to real or sham fields, would clarify po-
tential field effects.
This research showed that physical
recovery processes following moderate
steady-state exercise were the same in
real and sham fields. Of the variables
examined, only heart rate (cardiac in-
terbeat interval) was altered by 2 hr of
field exposure. A small, statistically sig-
nificant decrease in heart rate (3 beats/
min) was found when subjects were ex-
posed to the real field after sitting
quietly prior to exposure. This repli-
cates our earlier research, in which
heart rate showed a similar decrease
after a total of 6 hr of field exposure.
The results suggest that future studies
should examine a broader range of the
continuum of human arousal and phys-
iological activation.
This Project Summary was devel-
oped by EPA's Health Effects Research
Laboratory, Research Triangle Park, NC,
to announce key findings of the re-
search project that is fully documented
in a separate report of the same title
(see Project Report ordering informa-
tion at back).
Introduction
Public concern has been expressed
about possible health risks arising from
exposure to the electric and magnetic
fields generated by overhead power
transmission lines. Previous research
results have often been contradictory
and difficult to replicate, suggesting
that field effects, if real, are subtle. Fur-
thermore, the literature suggests that
60-Hz fields might interact with neural
mechanisms important in the control of
levels of arousal. Research strategies.
specifically designed to elucidate subtle
effects are needed, and such strategies
should be used to directly investigate
the effects of field exposure over the
continuum of human arousal.
Quantitative exercise testing tech-
niques have been quite helpful in im-
proving the understanding of mecha-
nisms associated with adaptation to
other environmental conditions. Con-
trolled exercise can be used to raise
physiological and metabolic function to
a higher level; at this higher level, sub-
tle changes in function may be more ap-
parent and therefore more easily mea-
sured. This research was based on the
idea that exercise testing methods
might be particularly promising in re-
search on 60-Hz field effects, since re-
sults of previous studies on the effects
of field exposure have provided support
for both increases and decreases in
physiological functioning, as well as for
a dampening or shifting of normal circa-
dian variations.
The research reported here had two
objectives: to evaluate the efficacy of
the approach by determining the feasi-
bility of combining exercise and field
exposure techniques; and to evaluate
whether increases in metabolism.
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caused by moderate steady-state exer-
cise prior to exposure to real or sham
fields, would clarify potential field ef-
fects.
Procedures
Experimental Design
Each of eleven subjects participated
in a maximal exercise test, one familiar-
ization session, and four experimental
sessions. During the four experimental
sessions, which were held at weekly in-
tervals, four conditions were presented
in counterbalanced order: (1) exercise
on a bicycle ergometer at 50% of VO2
max for 45 min, followed by exposure to
sham fields for 2 hr; (2) exercise fol-
lowed by exposure to real fields (9 kV/
m, 16 A/m) for 2 hr; (3) sitting quietly for
45 min, followed by exposure to sham
fields for 2 hr; and (4) sitting quietly fol-
lowed by exposure to real fields. All four
sessions were conducted under double-
blind conditions.
Measure of cardiac activity, rectal
temperature, and biochemistry were
obtained at the end of a 30-min equili-
bration period and during the 45-min
pre-exposure period (exercise or sitting
quietly). Ratings of perceived exertion
also were collected at 2-min intervals
during exercise. All measures except
rectal temperature and perceived exer-
tion were obtained during recovery in
the real and sham fields. In addition,
continuous dosimetry measures were
taken throughout exposure. At the end
of each session, both the experimenter
and the subject judged whether the real
or sham fields had been presented.
Exposure Facility and Double-
Blind Control System
The exposure room is positioned in-
side a parallel plate system. A set of ca-
pacitively coupled, copper gradient
rings is located behind the walls to in-
crease field uniformity. The magnetic
field is generated by six Helmholtz coils,
surrounding the room in both the verti-
cal and horizontal axes. Dedicated
equipment is used to maintain ambient
temperature and relative humidity at
controlled levels, and the exposure area
is continuously monitored from two ad-
jacent control rooms via closed-circuit
television and audio intercommunica-
tion equipment. Uniform electric and
magnetic fields can be generated in the
subject test area (0-16 kV/m, ± 5.6%; 0-
32 A/m, ± 4.8%). The vertical axis of the
magnetic field is in phase with the elec-
tric field, and the horizontal axis is
phase shifted 90° with the electric field.
Additional equipment provides continu-
ous monitoring of electric and magnetic
field status, and individual short circuit
current (Isc) throughout the exposure
period. During exposure periods in this
study the E field was set at 9 kV/m and
the magnetic field components set at 16
A/m.
The double-blind experimental con-
trol system allows presentation of real
and sham fields without either the sub-
ject or the experimenters being aware
of which field condition is in effect at
any given time. Experimenters are kept
unaware of exposure conditions
through a system of hardware and soft-
ware interlocks under the control of a
master computer program. The inter-
locks blank, mask, or disguise all field-
related cues in the control room equip-
ment.
Our previous research indicated that
subjects could often perceive the fields
when they raised their hands in the air.
The double-blind system was designed
to counteract this major perceptual cue.
It uses the continuous Isc monitoring
circuit to detect arm and hand move-
ment. Whenever continuous Isc ex-
ceeds an individually set reference
value, the strength of the electric field is
immediately decreased by 75% for 30
sec, and then gradually returns to the
original 9 kV/m level. When the original
level is attained, the Isc comparison is
again made. If the hands are still raised,
field strength again decreases; if Isc is
below the reference value, field
strength continues to be maintained at
9 kV/m. Once an experimental session is
started, operation of the double-blind
system is completely automatic.
Subjects
Twelve men between 21 and 29 years
of age volunteered to participate in the
study, but only 11 subjects completed
all of the experimental sessions. All
were in good health and had not partic-
ipated during the past year in a formal
aerobic conditioning program. Each
subject's daily activity pattern remained
consistent throughout the duration of
the study. After a complete and accurate
verbal description of the procedures,
risks, and benefits associated with the
study, each subject provided written in-
formed consent. Subjects were paid for
their participation.
Maximal Exercise Test
In addition to measuring each sub-
ject's aerobic power, the maximal exer-
cise test was designed to determine the
workload and heart rate that most
closely corresponded with 50% of the
VO2 max. Metabolic measurements
were assessed using a breath-by-breath
system. The subject wore a Hans-
Rudolph respiratory mask (Hans
Rudolph, Incorporated) connected to a
Medical Graphics Wave-Form analyzer
(Medical Graphics Corporation); 02 and
C02 percentages were determined
using a Perkin-Elmer MGA 1100 mass
spectrometer.
The subject cycled continuously on a
bicycle ergometer (Monark A.B.) at 60
rpm beginning with a 2-min workload of
0 kgm-min~1 followed by incremental
increases of 180 kgnvmin"1 every 3 min
until volitional exhaustion. To ascertain
that V02 max had been attained, each
subject was required to meet at least
three of the following criteria: (1) no fur-
ther increase in oxygen uptake, despite
an increase in workload (plateau crite-
rion); (2) attainment of the age-
predicted maximal heart rate; (3) a res-
piratory exchange ratio (VC02/VO2)
greater than 1.10; and (4) a blood lactic
acid value of at least 8 mM-L~1 at 4 min
after exercise.
Experimental Sessions
When a subject arrived at the labora-
tory, he changed into a sweatsuit and
cotton socks. Electrodes for recording
heart rate were attached, a rectal tem-
perature probe inserted, and a 20-gauge
cannula maintained patent with a hep-
arin lock inserted into a forearm vein.
After a 30-min equilibration period, a
blood sample was drawn; the standard-
ized 45-min exercise/no-exercise period
then began. Under the no-excercise
condition, the subject sat quietly read-
ing for the remainder of the period.
Under exercise conditions, the subject
cycled continuously (60 rpm) at appro-
priately adjusted workload settings to
maintain the desired 50% of his previ-
ously determined V"O2 max. Heart rate
and core temperature were monitored,
and differentiated ratings of perceived
exertion were recorded every 5 min. A
3-mL blood sample was drawn via the
cannula after 30 min of exercise for
measurement of lactic acid. Prior to con-
clusion of the exercise test, another
blood sample was drawn for measure-
ment of all blood variables. Identical
physiological and biochemical meas-
ures were obtained under the no-
exercise condition, except that the 30-
min lactate sample was not required.
After the exercise period, the subject
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immediately entered the exposure facil-
ity. The rectal probe and the subject's
shoes were removed, the subject put
the sweatshirt back on, and the electric
field dosimetry "ground" was attached
to both ankles. This transition required
approximately 2 min. The real or sham
field was then activated by initiating the
computer program. Cardiac measures
were obtained continuously during the
exposure period. Blood pressure and
blood samples for all blood variables
were obtained at 10, 30, 60, 90, and 120
min after exercise. Approximately 2 min
of field deactivation was required each
time blood pressure readings and blood
samples were obtained.
Results
The first goal of statistical analysis
was to verify that the conditions speci-
fied in the experimental design were
met. No difference in temperature or
humidity was found between real and
sham exposure days. Subjects were un-
able to distinguish between real and
sham conditions at better than chance
levels. All subjects met criteria for max-
imal exercise tests, and increased
metabolic steady-state was associated
with the 45-min exercise regimen.
Analysis of Experimental
Variables
Each dependent measure was sub-
mitted to three analyses. The first ad-
dressed the question of whether exer-
cise, as compared to sitting quietly,
altered the measure significantly. The
other two analyses examined exercise
and no-exercise conditions separately
to determine whether exposure to 60-Hz
fields had a significant effect. This strat-
egy was chosen since a major hypothe-
sis was that any field effects observed
would show higher levels of statistical
significance after exercise. Data at 10,
30, 60, 90, and 120 min from the end of
the exercise or resting period were used
for these analyses. An effect was
considered to be statistically significant
if probability was .05 or less. The
Greenhouse-Geisser correction was
used to adjust for inflated degrees of
freedom due to repeated measures.
Although exercise produced the ex-
pected changes in the physiological and
biochemical measures, the variables
were not different under real and sham
field conditions subsequent to exercise.
However, when subjects rested quietly
prior to exposure, heart rate was slower
during exposure to the real fields than
during exposure to sham fields. Com-
parison between heart rate at the end of
the first 10 min of exposure and after
120 min of exposure indicated that, on
real field exposure days, subjects
showed a significant decrease in heart
rate, while on sham exposure days no
change was found. This decrease in
heart rate associated with exposure to
the real fields occurred for 9 of the 11
subjects; the magnitude of the change
was correlated with total exposure to
the electric field as measured with short
circuit current (r = .49, df 9, p < .10). No
other differences in response between
real and sham field exposure were
found.
Conclusions and
Recommendations
The feasibility of the methods and
procedures used was clearly estab-
lished. Exercise at 50% of maximal oxy-
gen uptake produced the expected
changes in plasma volume and in hor-
mone, electrolyte, and lactic acid levels.
When subjects were subsequently ex-
posed to real and sham fields, the
double-blind control procedures used
were effective in preventing the sub-
jects from distinguishing between the
two conditions at better than chance
levels. If subjects sat quietly instead of
exercising during the preexposure pe-
riod, heart rate significantly decreased
during subsequent exposure to the real
fields. This phenomenon was also ob-
served in our previous study of field ex-
posure effects. However, the use of
moderate, steady-state exercise prior to
exposure did not serve to clarify field
effects. The recovery process was the
same under real versus sham exposure
conditions.
These results suggest that future
work should focus on evaluation of the
effects of 60-Hz fields on the entire proc-
ess of exercise-induced activation and
recovery (pre-exercise, exercise, and re-
covery). Ideally, such studies should:
(1) contrast exercise results with results
obtained after periods of very low phys-
iological arousal; (2) vary the duration
of exposure to fields before exercise;
and (3) examine the effects of different
intensities of exercise in the fields.
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MaryR. Cook, Carl M. Maresh, and Harvey D. Cohen are with Midwest Research
Institute, Kansas City. MO 64110.
Carl F. Blackman is the EPA Project Officer (see below).
The complete report, entitled "Effects of 60-Hz Fields on Human Health
Parameters," (Order No. PB 86-231 297/AS; Cost: $ 11.95. subject to change)
will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Health Effects Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for EnviroRrffSntal Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S1-86/006
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