The
Cycloergometer
as a System
for Studying
Exercise-induced
Asthma
Peyton
A. Eggleston,
M.D.
From the Department of Pediatrics, University of Virginia School of
Medicine, Charlottesville
ABSTRACT. Although bicycle exercise induces less asthma than does treadmill running, the cycloergometer offers definite advantages for quantitative testing of broncho-spastic response, extensive knowledge of normal responses, lack of training artifact, and ease of physiologic monitoring. Using maximal heart rate to tailor the exercise load to a given subject, reliable responses can be obtained from sub-jects as young as 7 years old. To obtain such results, diurnal variations in response to exercise, resting bronchial tone, and previous medication must be controlled, and pulmonary function measurements must be taken frequently after exercise. Pediatrics, 56 (suppi): 899-903, 1975.
Most of the early studies of human physiologic response to exercise were done using the bicycle ergometer, so when the abnormal airway response found in certain asthmatics began to be studied
seriously about ten years ago, the cycloergometer was naturally one of the first systems used. There are definite advantages to the system. First, the large
body of accumulated knowledge of cardiovascular and metabolic response of normal subjects, already mentioned, provides an invaluable base for
compari-son and experimental planning. The stereotyped use of large muscle masses required in cycling limits training artifact and increases work efficiency. Work output is easily quantitated, as will be discussed later. The major advantages, however, of the bicycle
ergometer are practical: the subject’s thorax and arms are stable during exercise so instrumentation
is easier; and the relative light weight and simplicity of certain types of cycloergometers makes them ideally suited for field work away from formal testing
laboratories.
The cycloergometer’s greatest disadvantage, its relative ineffectiveness in inducing asthma,1,2 will be
discussed in more detail elsewhere.
METhOD
Differences in cardiovascular and metabolic
re-sponse to cycloergometer and treadmill exercise may relate to induction of asthma, and must be accounted
for when using a cycloergometer. When exercising to
exhaustion on a treadmill, a subject’s maximum oxy-gen uptake is approximately 7% greater than at the
same limit on a cycloergometer; as shown in Table I,’ this is not reflected in a significantly higher rate
or in a higher serum lactate concentration. Following maximal treadmill exercise most subjects are breath-less, cyanotic, and dizzy, while most cycloergometer
tests were limited by thigh fatigue and pain. During submaximal exercise, lactate accumulation, shown in Figure I, tends to be much higher on the cycloer-gometer at a given percent age of maximum oxygen
uptake, while heart rate in Figure 2 progresses
identically with both types of exercise.’
Since the limiting factor in bicycle exercise is leg fatigue rather than generalized exhaustion, it is im-portant to try to maintain the subject in a position
allowing for maximal comfort and for efficient use of the legs when using a cycloergometer to induce post-exercise asthma. Handlebar height should be adjusted so that the subject’s trunk is inclined
for-ward and part of the weight is carried on the hands rather than on the ischial spines. Seat height is
ad-justed so that the legs are in full extension when the pedal is at the bottom of its arc. Pedaling frequency should be 60 cycles per minute for optimum perform-ance; higher and lower heart rates are very difficult
to maintain at high work loads, and the efficiency of the system suffers, as shown in Figure 3.’ Either a tachometer, as supplied with some cycloergometers, or a metronome is effective in letting the subject
maintain this rate.
Work load on the cycloergometer is quantitated by two systems, compared in Table II. The unit of work
watt, the power required to move a body with a
weight of 9.8 newtons and a mass of 1/kg/i ft/i sec. The other system generally used is based on the kilo-pond (or kilogram if the earth’s gravitational force
is considered unity and ignored). Gravitational force
is not ignored in the cgs system, so force and work are approximately one tenth that in the kilopond system. Since cgs power is expressed as work per second rather than per minute, power units are approxi-mately six times those in the kilopond system.
S #{149}
Step
c.---c
Bicycle
-
Treadmill
‘I
80
‘I60
‘I
40.
120.
‘IOU
20
30
40
50
607080
90
100
Intensity
of
Exercise
(%
Aerobic
Power)
TABLE I
RESULTS OF EXERCISE*
Exercise VO2max.
(liters/mm)
Pulse Bate (beats/mm)
Lactate (mg/100 ml) Treadmill
Mean (i SD) 3.81 i 0.76 190 i 5 122 ± 21
Range 2.54 ± 5.84 178 to 197 78 to 166
Bicycle
Mean(iSD) 3.56±0.71 187±9 112±15
Range 2.57 to 5.23 167 to 207 89 to 143
Step
Mean (i SD) 3.68 i 0.73 188 ± 6 105 ± 26
Range 2.66 to 5.99 170 to 195 45 to 165
*Reproduced with permission from Shephard et a).’
C
E
a-1)
0
a:
4-0
a;
TABLE II
Two SYSTEMS OF MEASUREMENT
Measure Definition
Kilopond (kp) Force acting on a mass of I kg at the normal acceleration of gravity (9.8 newtons)
Kilopond meter (kpm) Work required to move a body I meter against a force of I kp (9.8 Joules)
Kilopond meter/mm Power required to move a body 1 meter/mm against a force of
(kpm/min) 1 kp (0.16 watt)
TABLE III
PROTOCOL FOR CYCLOERGOMETER TESTING
Factors Data
Age 7to2oyr
Testing time 1 to 4 PM
Medication None for 6 to 8 hr before test
Symptoms No more than mild before test
Exercise
Load 500 kg/mm/sq m or load necessary for 180 beats/mm
Duration 5 mm
Pulmonary function FVC, FEV, before exercise and at 0, 5, 10, 15, and 20 mm after
80’
0
Treadmill
.
.
.
Bicycle
.
.
Step
Test
:: oo
E
00 0
.-
,
S0
‘-,
40’
Lii
SI.-<
‘
0S
_i20
SS 0
6
0“
0
25
‘45
T65
‘85
WHO
8O6
%
Aerobic
Power
SUSJ(CT S.W. .5 LITERS
1.0
I#{163}X(RCISE .5,;
I’O 20beatsmjn
2OO-1’
180j.
Vmin
,Putmonory
ventitation
200
17!
150
. . .
Oxygen
uptake
1mun
5.6
5.4
5.2
5.0W
40
50
60
70
80
rpm
FIG. 3. Heart rate, minute volume, and oxygen uptakes at maximal exercise using different pedaling frequencies on a cycloergometer. (Reproduced with permission from
Hermansen and Saltin.’)
The protocol shown in Table III has been used successfully at the University of Washington to eval-uate exercise asthma in children. In general, children under 7 cannot cooperate well enough to give re-liable results, and the recommended heart rate
response is higher than would be appropriate for anyone over 20 years of age. Although there is little
supporting data it is generally felt that exercise-in-duced asthma varies diurnally like bronchial tone; so all exercise testing should be carried out at the same time of the day, preferably in the afternoon.
Subjects are asked to exclude bronchodilators for six to eight hours before testing, and any subject with
more than minimal symptoms is tested on another
day.
The children were exercised on a Quinton
cyclo-ergometer (model 844),* but the Collins Pedal-Mode ergometer should be comparable. A work load of
500 kg/mm/sq m was based on the data of Gumming
*Quinton Instruments, 3051 44th Avenue, West, Seattle,
Washington.
tWarren E. Collins, Inc., 220 Wood Road, Braintree, Massachusetts.
FIG. 4. Percent fall in FEV, at 5, 10, 15, and 20 minutes after exercise in a single subject exercising on four separate days.
(Adapted with permission from Pierson et al’)
and Danzinger,’ showing that such a work load gen-erally resulted in a stress that raised oxygen con-sumption to 85% to 90% of maximum in children.
At this stage, there is still a linear relationship be-tween oxygen consumption and heart rate but sub-jects are invariably stressed beyond their aerobic threshold.’
Relating work load to body surface area
compen-sates for mass to a certain extent, but heart rate must be monitored continuously during exercise to relate the work load to physiologic stress experienced by children who are more or less physically fit. Any
well-grounded three-lead electrocardiograph is sufficiently accurate, although a telemetric cardio-tachometer is safer and more convenient.
Tachy-cardia is usually maximal after one or two minutes exercise at 500 kg/mm/sq m. If heart rate is not at least 180 beats per minute at this work load after one or two minutes, work is increased appropriately
and another test is performed with the higher work load. Although there are no comparable studies on the cycloergometer, it has been shown on the tread-mill that exercise periods of five to six minutes are
optimal and that airway response decreases fol-lowing both longer and shorter work periods.
Spirometry is measured frequently after exercise and the point of maximal fall is compared. The vary-ing forced expiratory volume in one second (FEy1) response at four different runs with a single
sub-ject is shown in Figure 4 as an extreme example to illustrate how maximal fall may occur at various times following exercise. If spirometry were only
measured at a fixed interval following exercise, the variability of the individual’s response would be
exaggerated.
FEV1 RESPONSE 1’O
CYCLOERGOMETER EXERCISE
MEAN ± S.E.M.
Pi.rson, et ol.#{149}
969
2.0.LtTERS
.5.
I
EXEROSEMINUTES
1. Anderson SD, Connolly NM, Godfrey 5: Comparison of
I bronchoconstriction. Thorax 26:396, 1971.
5 0 IS 20
.
.
. . . .2. Fitch KD, Morton AR: Specificity of exercise in exercise-induced asthma. Br Med I4:577, 1971.
3. Shephard RJ, Allen C, Benade AJS, et al: The maximum Ftc. 5.Mean FEy values and SE for 15 subjects using
cycloergometer exercise. (Reproduced with permission
RESULTS
from Pierson et al’)
Using this protocol, 15 children were studied by Pierson et al.’ They were included in this study after previously demonstrating a greater than 20% fall in FEV1 following free-range running. Each subject
exercised four times except for one who only exer-cised twice. Means and standard error for FEy,
re-sponses in all 58 runs by these 15 subjects are shown in Figure 5. Maximal fall was 24% at ten minutes. The coefficient of variation of FEV, response was 43%
for individual subjects it ranged from 13% to 79%
with lower values in older, more coordinated chil-dren. Four of the children showed little or no bron-chospasm on any run.
dren. Four of the children showed little or no
bron-chospasm on any run.
In summary, the advantages of the cycloergometer are its portability, low cost, patient monitoring
facil-ity, and the lack of training artifact in physiologic response. The single disadvantage is a serious one-the low degree of bronchospasm produced by this
stress. Therefore, the cycloergometer is ideally suited to field studies where portability is critical and to experiments where many or complex physio-logic measurements are to be made. It is less suited
to the study of drug effects, unless subjects are care-fully selected for reactive airways, or for studies of incidence of exercise-induced asthma. In all studies,
adequate standardization data must be included to insure comparability of data.
REFERENCES
oxygen intake: An international reference standard ofcardiorespiratory fitness. Bull WHO 38:757, 1968. 4. Shephard RJ, et al: Standardization of submaximal
exer-cise tests. Bull WHO 38:765, 1968.
5. Hermansen L, Saltin B: Oxygen uptake during maximal treadmill and bicycle exercise. J Appl Physiol 26:31, 1969.
6. Cumming GR, Danzinger R: Bicycle ergometer studies in children: 11. Correlation of pulse rate with oxygen consumption. Pediatrics 32:202, 1963.
7. Silverman M, Anderson SD: Standardizations of exer-cise in asthmatic children. Arch Dis Child 47:883,
1972.
8. Pierson WE, Bierman CW, Stamm 5): Cycloergometer-induced bronchospasm. J Allergy 43:136, 1969.
ACKNOWLEDGMENT
The technical help of Patricia Beasley, RN., and Jerome Miller, B.S., is gratefully acknowledged as is the invaluable statistical advice of Jules I. Levine, Ph.D.
