JOURNAL OF
APPLIED
BEHAVIOR ANALYSIS
1992)25,671-679
NUMBER
3 (FAu 1992)
EFFECTS OF A VARIABLE-RATIO REINFORCEMENT SCHEDULE WITH
CHANGING CRITERIA ON EXERCISE IN OBESE AND NONOBESE BOYS
RAYLEEN V. DE LucA AND STEPHEN W. HOLBORN
UNIVERSITY OF MANITOBA
The effects of a variable-ratio schedule of reinforcement on pedaling a stationary exercise bicycle
were examined. Three obese and three nonobese 11-year-old boys were individually tested five times
weekly for approximately 12 weeks. A changing-criterion design was used in which each successive
criterion was increased over mean performance rate in the previous phase by approximately 15%.
The contingencies of the successive criteria resulted in systematic increases in rate of exercise for all
children. Final variable-ratio rates were higher than those under fixed ratios found in previous
research, with rates for 2 of the 3 obese boys approximating those of the nonobese.
DESCRIPTORS: obesity, exercise, changing criterion design, variable-ratio schedule, children
Childhood obesity is a prevalent problem (Aristimuno, Foster, Voors, Srinivasan, & Berenson,
1984) that has been demonstrated to cause physiological (e.g., Mann, 1974; Mayer, 1970; Mobbs,
1970) as well as psychological problems (e.g., Israel
& Stolmaker, 1980). Although behavioral treatment approaches for childhood obesity have been
explored recently (e.g., Epstein, Wing, Koeske, &
Valoski, 1987), Epstein and Wing (1987) asserted
that "additional research on exercise's role is needed" (p. 336). Because research has indicated that
obesity is often associated with physical inactivity
(e.g., Bullen, Reed, & Mayer, 1964; Cohen, Gelfand, Dodd, Jensen, & Turner, 1980; Johnson,
Burke, & Mayer, 1956; Mayer, 1968; Rony, 1940;
Stefanik, Heald, & Mayer, 1959), exercise appears
to be an important focus for research.
The benefits of behavioral principles of reinforcement to increase physical activity with obese
children have been demonstrated in recent studies
conducted by De Luca and Holborn (1985, 1990).
Applying a fixed-interval (FI) schedule of reinforcement to exercising in obese and nonobese boys,
De Luca and Holborn (1985) demonstrated that
reinforcement schedules can be a powerful tool to
increase exercise duration. In an attempt to increase
The authors express appreciation to Gloria Eldridge and
Randy Atkinson for assistance with the equipment as well
as for their suggestions and support throughout the study.
This research was supported by the Manitoba Mental Health
Research Foundation. Reprints may be obtained from Rayleen V. De Luca, Department of Psychology, University of
Manitoba, Winnipeg, Manitoba R3T 2N2, Canada.
response rate, De Luca and Holborn (1990) examined the effects of a fixed-ratio (FR) schedule,
matched to the reinforcement frequency of an F1
1-min schedule, with obese and nonobese children
pedaling on a stationary exercise bicyde. After the
initial F1 phase, when the schedule was changed to
FR, all children showed an increased rate of exercising, and the duration of exercising was maintained at maximum during all contingency phases.
The present research was designed to examine
whether variable-ratio (VR) schedules would increase and maintain even higher rates of exercising
than FR and F1 schedules do.
A single-case changing-criterion design (Hartmann & Hall, 1976; Kazdin, 1982) was used. The
changing-criterion design has been demonstrated to
be effective in shaping behavior (Hartmann & Hall,
1976). Brownell (1984) recommended that "one
key to exercise instruction is to begin at the patient's
level" (p. 412). Using a changing-criterion design,
the initial criterion is based on the subject's own
baseline performance and is increased via small,
successive increments. In this manner, high rates
of exercise can be approached gradually and systematically.
METHOD
Subjects and Setting
Six male 11-year-old children, whose parents
consented to their participation in a study involving
exercise on a stationary bicycle, were chosen as
subjects. Half of the subjects were obese and half
671
672
62RYLEEN V. DE LUCA and STEPHEN W. HOLBORN
were of normal weight (as defined by age, height,
and weight norms, Demirjian, 1980, and skin-fold
thickness, Seltzer & Mayer, 1965). To qualify, obese
children had to be at least 20% above average body
weight for their age, sex, and height (Demirjian,
1980), had no medical problems that contraindicated exercise, were not taking medication that
would affect body weight, and were not involved
in a formal weight control program. The obese boys
were at least at the 97th percentile for weight and
ranged from 32% to 161.4% over the acceptable
range for percentage body fat. All obese subjects
were classified as "overfat" (Canadian Department
of Health and Welfare [CDHW], 1984). The nonobese boys were at, or slightly below, the 50th
percentile for weight. Two nonobese boys were
within the acceptable range for percentage body fat
for boys, and 1 was 5.5% over the acceptable range
for percentage body fat and was dassified as "undesirable" (CDHW, 1984). The heights of all boys
were within the normal range. All testing was conducted in the nurse's room of an elementary school
in Winnipeg, Manitoba.
Apparatus
A CCM stationary exercise bicyde was programmed to ring a bell and to illuminate a red
light simultaneously after each variable number
(VR) of responses during the contingency phases.
Lehigh Valley and BRS electromechanical modules
were used for programming stimulus events and
for recording responses and reinforcements. The bell
and light were programmed via electromechanical
timers and relay circuitry. Each wheel revolution
constituted a response and was recorded on magnetic counters. Folding 183-cm partitions were used
to obscure the equipment panels from the subject's
view. A 7-W red light was mounted on the front
middle panel of the bicyde in the subject's line of
vision. Throughout the study, the tension of the
bicyde was set at moderately low resistance (2.27
kg) for all subjects.
Experimental Design
A single-case changing-criterion design was employed (see Hartmann & Hall, 1976; Kazdin,
1982). Baseline data were taken for 3 obese and
3 nonobese boys for eight sessions until behavior
appeared stable to visual inspection, after which
the initial VR schedule was introduced. Eight sessions later, when responding was stable, the second
VR subphase was introduced. Following another
eight sessions, when stability was reached, the third
VR subphase ensued for eight sessions. To exhibit
fuiher control, a three-session return-to-baseline
phase was followed by a final VR subphase at the
previous criterion, which lasted for five sessions.
Procedure
Throughout the study, subjects were individually
tested daily from Monday to Friday over approximately 12 weeks. The instructions given at the
beginning of each session were identical for all subjects: "Exercise as long as you like." No further
encouragement was given. Recording began when
the subject began pedaling the bicyde. The experimenter was seated behind the equipment panels
out of the subject's view. Sessions terminated when
the subject dismounted from the bicyde or when
30 min had elapsed, whichever occurred first.
Baseline. Prior to the first session, each child
was asked if he would like to exercise five times
weekly on the stationary bicyde. During the first
session, following the consent of each subject to
participate in the exercise program, the instructions
"exercise as long as you like" were given. No stimulus changes occurred, nor was reinforcement administered during baseline. After eight sessions, the
point system was introduced.
Reinforcement survey. Reinforcement surveys
(Cautela, 1977) were individually administered to
each child during the first week of baseline. Ten
items from the preferred categories were selected as
back-up reinforcers. Subjects rated on a scale of 1
to 10 how much they liked each item. Higher costs
were then assigned to the items with higher preference ratings.
VR (first subphase). The VR schedule of reinforcement was implemented during the ninth session, after a stable baseline had been achieved. The
mean number of revolutions per minute during the
baseline was calculated for each subject. A separate
VR REINFORCEMENT SCHEDULE
ratio value was assigned to each subject during the
initial VR phase on the basis of approximately a
15% increase over mean responding during baseline. For example, the obese subject who pedaled
a mean of 60 revolutions per minute during baseline received a VR 70 schedule; the schedule for
the nonobese subject, who pedaled a mean of 70
revolutions per minute during baseline, was VR
80. This manipulation ensured that the shifts in
density of reinforcement would be similar for subjects and that the first criterion would not be overly
stringent. Prior to beginning the first session of this
phase, subjects were allowed to examine the 10
back-up reinforcers, tagged with the number of
points necessary for purchase. Reinforcers induded
a hand-held battery-operated game, kite, bicyde
bell, flashlight, model car, model plane, puzzle,
adventure book, and comic books. Subjects were
advised that they could earn points by exercising
on the bicyde to "buy" the items that they liked
best. They were told that each time the bell rang
and the light went on, they would earn a point.
At the end of each session, the subject received a
tally of the number of points he had earned during
the session and the cumulative total to date.
VR (second subphase). The second VR schedule
of reinforcement was implemented during the 17th
session, after stability had been achieved in the first
VR subphase. A separate ratio value was assigned
to each subject on the basis of a 15% increase over
mean responding during the previous subphase. In
other words, a different criterion for performance
was specified for each subject, based on his performance in the previous subphase.
VR (third subphase). The third VR schedule
of reinforcement was implemented when stability
was achieved for the second VR subphase. Again,
a separate ratio value was assigned to each subject
during the third subphase on the basis of a 15%
increase over mean responding during the previous
subphase.
Return to baseline. To provide further evidence
of experimental control, the return-to-baseline phase
was implemented after eight sessions on the third
VR subphase, when stability in responding had
occurred, and was continued for three sessions.
673
Return to VR third subphase. The subjects were
returned to their individual third subphase schedules for the last five sessions, which coincided with
the last 5 days of school prior to summer vacation.
Social validation. Each subject, as well as parents and homeroom and physical education teachers, completed a social validation questionnaire at
the end of the program. Questionnaires employed
a 7-point rating scale with higher numbers reflecting increased social validation. Questionnaires ascertained consumer satisfaction with the treatment
program as well as perceived improvements in
physical activity and appearance of the children.
RESULTS
The dependent measures were (a) the overall
rate of responding per session (which was calculated
by dividing the total number of revolutions per
session by the total number of minutes spent exercising) and (b) the total time spent exercising per
session.
Figure 1 illustrates the response rates for all
subjects. During baseline there was some fluctuation in response rate, with a gradual decline for 2
of the nonobese boys, Shawn and Steve. The response rate for the remaining nonobese boy, Scott,
was relatively stable throughout the baseline phase.
The nonobese boys responded at a mean of 71.9
revolutions per minute during baseline. For the
obese boys, there was an initial increase in response
rate from the first to the second session, followed
by generally stable responding for Peter and Paul
during baseline.
The performance of the remaining obese subject,
Perry, continued to accelerate until the third session,
when there was a sharp decrement followed by
stable responding. The obese boys responded at a
mean of 59.2 revolutions per minute during baseline, which was 12.8 revolutions per minute slower
than their slimmer counterparts. Upon implementation of the initial VR schedules, response rates
for all subjects increased. Performance was consistently above the criterion for all boys (criterion was
set at approximately 15% over each individual subject's baseline performance). The mean rate of re-
674
RAYLEEN V. DE LUCA and STEPHEN W. HOLBORN
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Figure 1. Mean revolutions pedaled per minute during baseline, VR 1 (VR range, 70 to 85), VR 2 (VR range, 90 to
115), VR 3 (VR range, 100 to 130), return to baseline, and return to VR 3 phases for obese and nonobese subjects.
VR REINFORCEMENT SCHEDULE
sponding during the first VR subphase was 98.89
revolutions per minute for the nonobese boys and
85.51 revolutions per minute for the obese boys.
The change in criterion in the second VR subphase produced an increase in response rate for all
subjects. The mean rate of responding during the
second VR subphase for nonobese boys was 114.2,
whereas the obese boys' rate was somewhat slower
at 101.2 revolutions per minute. However, unlike
performance during the first VR subphase, each
boy's response rate was initially slightly slower than
the set criterion. Of course, falling below criterion
still produced substantial reinforcement on the VR
schedule, due to variability in the ratios required
for reinforcement (i.e., some of the ratios fell below
80 responses per minute).
There was an initial increase in performance for
all boys upon implementation of the third VR
subphase. One nonobese and 2 obese boys performed at or above the criterion throughout this
subphase. The remaining subjects performed at approximately the criterion rate. The mean response
rate for the nonobese subjects was 130.0 revolutions
per minute, whereas the obese boys pedaled a mean
of 117.0 revolutions per minute.
Implementation of the return-to-baseline phase
produced a reduction in response rate for all boys.
The mean response rate of 95.3 for nonobese boys
was higher than the obese boys' mean rate of 83.6
revolutions per minute.
Reintroduction of the token economy produced
substantial increases in all subjects' response rates.
Both nonobese and obese subjects achieved their
highest response rates during this subphase. The
mean rate of responding during the final VR subphase was 138.7 revolutions per minute for nonobese boys, whereas the obese boys performed at
the mean rate of 123.6 revolutions per minute.
During the final subphase of the program, 3 nonobese and 2 obese boys consistently performed well
above the criterion, and upward trends were evident. The response rate for the remaining obese
child, Perry, was relatively stable (M = 98.9)
throughout the phase, and he performed slightly
above the criterion during the last session.
675
Figure 2 shows the total time spent riding the
exercise bicyde by all subjects. (Data points are
absent for Perry for eight sessions because he was
absent from school.) It can be seen that during
baseline there was a general decline over sessions
in the duration of exercise for all subjects. Nonobese
boys exercised a mean of 15.2 min per session,
whereas obese boys spent slightly less time pedaling
(M = 12.9 min). The implementation of a reinforcement program produced a substantial increase
in the amount of time spent exercising by all subjects. Although 1 obese subject, Paul, did not exercise for the entire allotted period of time during
the first session, performance of all subjects stabilized at the maximum of 30 min. All boys exercised
the full 30 min during all contingency phases. Introduction of the return-to-baseline phase produced
decreases in the time spent exercising for all nonobese and obese boys. Nonobese boys exercised a
mean of 11.2 min per session during the returnto-baseline phase, whereas the obese children pedaled a mean of 13.3 min per session. The reintroduction ofreinforcement increased performance once
again, and all subjects exercised- the maximum of
30 min per session for the duration of the program.
Responses to the social validation questionnaire
from the children, parents, and teachers were uniformly positive. With respect to satisfaction with
the treatment procedures, the modal rating for all
groups was 7 (the highest possible score on the
7-point rating scale). Ratings of improvements in
physical activity and appearance were also extremely high (mode = 7).
DISCUSSION
The results of the present study indicated that
the rate of exercise, as measured by the speed of
bicyde pedaling, can be increased using a VR schedule of reinforcement. As expected, the introduction
of the initial VR subphase of the changing-criterion
design produced marked increases in the rate of
exercise for all subjects. The outcome is an extension
of De Luca and Holbom's (1990) findings that
high rates of exercise were established during a ratio
676
.
RAYLEEN V. DE LUCA and STEPHEN W. HOLBORN
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VR 100
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SESSIONS
Figure 2. Total number of minutes spent exercising during baseline, VR I (VR range, 70 to 85), VR 2 (VR range,
90 to 115), VR 3 (VR range, 100 to 130), return to baseline, and return to VR 3 phases for obese and nonobese subjects.
VR REINFORCEMENT SCHEDULE
(FR) schedule of reinforcement. It is noteworthy
that the highest rates achieved under VR by both
obese and nonobese boys in the present study were
generally greater than the most accelerated rates
under the FR in the earlier De Luca and Holbom
(1990) research. High rates of responding with
infrequent pausing are typically produced with humans and animals on VR schedules (e.g., Lowe,
1979; Orlando & Bijou, 1960). In addition, further
support is provided for the view that VR schedules
can attenuate past history differences (Baron & Galizio, 1983; Kaufman, Baron, & Kopp, 1966). In
particular, the obese subjects' histories of reduced
rates of responding were eventually overcome by
successively increasing levels of the VR schedule.
For 2 of the obese subjects (Peter and Paul), the
final levels of exercise approximated those of the
nonobese boys. Perry's final VR performance was
lower, but he was absent for much of the training.
Another contributing factor to the higher rates
may have been use of a changing-criterion design.
In the present study, the rate of exercise generally
improved in increments to match or exceed the
criterion specified. An exception to this occurred
with 1 obese and 1 nonobese boy who did not
meet the criterion during the third subphase. In
many studies, not meeting the criterion would have
negated reinforcement (Kazdin, 1982); however,
in the present study, because of the variable nature
of the schedule it resulted only in reduced amounts
of reinforcement. The 2 children's behavior came
under control of the criterion in the following phase,
and their exercise behavior accelerated as they attempted to "catch up" in points to their peers.
The results also corroborate De Luca and Holbom's (1985, 1990) findings that exercise duration
can be increased using behavioral principles of reinforcement with children. The introduction of a
token economy produced increases in duration of
exercise to the maximum 30 min. Control was
evident in the children's duration of bicyde pedaling. When the children received reinforcement for
biking, they continued for the maximum allotted
time; when they did not receive reinforcement, their
pedaling rapidly decreased. When reinforcement
677
was withdrawn and the bicyde's bell and light no
longer signaled points, the boys reduced their time
spent pedaling and complained about no longer
being able to collect points.
Turning to indices of social validity, the questionnaire data for the children, their parents, and
their teachers uniformly indicated maximum or dose
to maximum ratings of satisfaction with both treatment procedures and outcome. Also, there were
other anecdotal indicators of consumer satisfaction
that are equally compelling. For example, in relation to satisfaction with treatment procedures, on
a number of occasions boys in the program asked
if their friends could participate. Many times when
the 30 min were over, the children asked if they
could bicyde for a longer time to "get more points."
Parents of all of the boys reported that their sons
had spoken positively about the program, with one
parent of an obese boy stating "that's all he talked
about for weeks." Each of the obese boys convinced
their parents to purchase a new bicyde for him
during the course of the study. The boys daimed
that although each had ridden bicydes in the past,
they really had not cared much for biking.
In relation to satisfaction with treatment outcome, the convergence of a variety of anecdotal
observations proved persuasive of positive effect.
Every subject participated in the school's track and
field events. The nonobese boys participated in running events, and the obese boys participated in ball
throwing, long jumping, and high jumping. Two
of the obese boys received ribbons of achievement
for the first time in these events. Although all of
the nonobese boys received ribbons at the track and
field meet, 2 of them (Shawn and Steve) went on
to compete in the 200-m and 400-m runs in the
citywide track and field meet. Shawn won an award
for his division. Shawn's mother reported that she
felt her son's participation in the biking program
improved his stamina, enabling him to compete in
a larger meet for the first time.
Reduced girth measurements were most noticeable for Peter. He was excited that he could now
wear his stepfather's pants (Size 32) rather than
the Size 36 he had previously wom. The vice-
678
RAYLEEN V. DE LUCA and STEPHEN W. HOLBORN
principal ofthe school commented that "Peter looks
like a new boy. He looks terrific." Peter's mother
reported that when he went for a physical examination prior to going to camp, the doctor complimented Peter on his improved appearance and fitness. Playing soccer and swimming became frequent
activities for Peter.
All parents were very supportive of the program
and felt their sons had benefited from it. The parents of 1 obese boy stated that they had been
initially hesitant about the program, but were "very
thrilled" with the outcome and their son's "changed
attitude" about participating in physical activity.
Peter's mother asked if her younger son could also
be involved in the program. Teachers stated that
the program was very beneficial for all students.
However, changes in physical activity were noticed
particularly for the obese boys, who they felt had
particularly benefited from the program.
A number of interesting areas remain for future
research. Primary among these should be the design
of experiments to assess and program for generalization of trained exercise behaviors to the natural
environment. Because there are more overweight
girls than boys (Manitoba Department of Education, 1978), it will be important to indude obese
girls, as well as boys, in future research. Although
the results of the present study are promising, further research on curtailment of obesity at an early
age is crucial, if enduring life-style changes are to
prevent obese youngsters from becoming obese
adults.
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VR REINFORCEMENT SCHEDULE
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ReceivedJuly 9, 1990
Initial editorial decision September 13, 1990
Revisions received December 13, 1990; April 29, 1991;
July 21, 1991
Final acceptance August 23, 1991
Action Editor, Charles R. Greenwood