Ergonomic Evaluation of an Alternative Tool for Cake Decorating

Abstract

Cake decorating involves several hand intensive steps with high grip force during the application of icing. The purpose of this laboratory study was to evaluate forearm muscle activity, discomfort, productivity, and usability of a new device for cake decorating compared to the traditional piping bag method. Subjects (N=17) performed two hours of cake decorating tasks using two different devices. Muscle activity from three forearm muscles, posture, subjective hand and arm fatigue, and usability of each device were assessed. Outcome measures were evaluated using binomial, Wilcoxin Signed Rank test, and the paired t-test. Mean median (APDF 50%) muscle activity were significantly less for the new device across all three muscles, and posture analysis showed significantly less wrist extension. Subjects rated the new device superior for refill and comfort, and the traditional method better for accuracy. The new device significantly reduced grip force and awkward wrist posture, two important risk factors for distal upper extremity pain and disorders. However, the new device did not receive the best overall rating because of problems with accuracy and overflow, especially with smaller decorating tips.

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DOI: 10.1177/1071181311551459 2011 55: 988Proceedings of the Human Factors and Ergonomics Society Annual Meeting
Carisa Harris, Bingyune Chen, Ira janowitz and David Rempel
Ergonomic Evaluation of an Alternative Tool for Cake Decorating
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Ergonomic Evaluation of an Alternative Tool for Cake Decorating.
by Carisa Harris, PhD, PT, Bingyune Chen, MSPH, Ira janowitz, CPE, David Rempel, MD, MPH
Cake decorating involves several hand intensive steps with high grip force during the application of icing.
The purpose of this laboratory study was to evaluate forearm muscle activity, discomfort, productivity, and usability
of a new device for cake decorating compared to the traditional piping bag method. Subjects (N=17) performed two
hours of cake decorating tasks using two different devices. Muscle activity from three forearm muscles, posture,
subjective hand and arm fatigue, and usability of each device were assessed. Outcome measures were evaluated
using binomial, Wilcoxin Signed Rank test, and the paired t-test. Mean median (APDF 50%) muscle activity were
significantly less for the new device across all three muscles, and posture analysis showed significantly less wrist
extension. Subjects rated the new device superior for refill and comfort, and the traditional method better for
accuracy. The new device significantly reduced grip force and awkward wrist posture, two important risk factors for
distal upper extremity pain and disorders. However, the new device did not receive the best overall rating because
of problems with accuracy and overflow, especially with smaller decorating tips.
INTRODUCTION
The task of decorating edible items such as
baked goods, candy, and ice cream cakes is a hand
intensive task that is associated with high rates of
hand and arm musculoskeletal disorders, including
carpal tunnel syndrome (Osorio 1994). The
California Department of Health and Services
reported 84 cases of work-related carpal tunnel
syndrome among cake decorators between 1992 and
2002. Cake decorators (COC code 688 - food
batchmakers) had the second highest rate of carpal
tunnel syndrome of any occupation (310/100,000
workers compared to overall rate across all
occupations of 36/100,000) (unpublished, Dr. Robert
Harrison) and is addressed in the OSHA draft
guidelines for Retail Grocery Stores (OSHA 2006).
There are approximately 166,000 bakers in the U.S.
in 2004 (BLS, 2004).
Workplace epidemiological studies have
demonstrated an association between upper extremity
musculoskeletal disorders, such as carpal tunnel
syndrome, wrist tendonitis, and epicondylitis, and
several biomechanical factors such as high grip or
pinch force, sustained awkward wrist postures, and
high repetition of hand and finger motions (NRC
2001; Bernard 1999; Armstrong 1987; Descatha,
2007; Silverstein, 1986). Forceful exertions over 100
N have been related to elbow pain and wrist pain
(Burgdorf, 1997). Repetitive motions, defined by
tasks with exertions less than every 30 seconds, are
associated with increased prevalence of distal upper
extremity (hand and wrist) discomfort and injury
(Silverstein, 1986; Silverstein, 1987). When
combined, these risk factors have been shown to act
synergistically (Silverstein,1986; Moore, 1995)
Cake decorating traditionally involves several
hand intensive steps including coating the cake with a
thin layer of icing then applying a decorative pattern
of icing to the top and sides of the cake with a piping
bag, a cloth or paper cone, filled with icing and
squeezed with one hand to expel icing through a
dispenser tip. The other hand may turn the cake or
hold the item being decorated. The process involves
applying a high force grip to the bag while decorating
with precision. The task may require sustained
awkward wrist, shoulder, and neck postures. The
grip force required is influenced by a number of
factors such as bag size, stiffness of icing (e.g.,
temperature and ingredients), and dispenser tip size.
The purpose of this laboratory study was to
compare a new cake decorating device to the
traditional method. The new device was designed to
decrease the grip force and awkward postures
associated with cake decorating. The study evaluated
the forearm muscle activity, wrist and shoulder
postures, discomfort, productivity and usability of
experienced cake decorators while using each device
for one hour. METHODS
Participants
Seventeen experienced cake decorators
participated in this laboratory study. Subjects were a
sample of convenience recruited from local bakeries
and ice cream cake stores. Participants were required
to be 18 years or older and to have more than one
year of experience as a paid cake decorator. Subjects
completed a brief questionnaire which collected data
on age, current upper body pain, cake decorating
experience, and ethnicity. The study was approved
by the University of California at San Francisco
Committee on Human Research.
Tasks
Subjects performed a one hour trial of cake
decorating with each device. The order of device
testing was block randomized. Cake decorating was
Copyright 2011 by Human Factors and Ergonomics Society, Inc. All rights reserved DOI 10.1177/1071181311551459
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performed on round or rectangular Styrofoam blocks
that are commonly used for cake décor training.
Three cake designs requiring easy, medium, and
difficult decorative techniques were shown to the
subjects. The smallest tip had a round 1.5 mm
diameter. Subjects decorated in the order of easy,
medium, and hard and repeated the order until 60
minutes had passed. The icing was a standard butter
cream icing (BakeMark, Los Angeles, California)
maintained at room temperature (20° C). The work
surface height was set to 88 cm but the participants
could place the cake on top of a 10 cm high round
Styrofoam block, if preferred. Cake decorating was
done while sitting except for the basket weave and
writing activities which were done while standing.
Subjects rested for approximately 20 minutes
between trials.
Measures
Intervention
Subjects performed cake decorating using two
devices, the traditional piping bag (12” or 14”)
(Figure 1) and the new device (Figure 2). The new
device (Easy Piper, Dittmar Development, Coeur
d’Alene, Idaho) utilizes a pump to transfer icing from
an 8-quart disposable bag into an elastic tube,
‘charging’ and inflating the tube with icing under
pressure. The tube is then detached from the pump.
At the other end of the tube, a hand-held applicator
trigger is used to dispense icing. Subjects were
required to use their dominant hand to dispense the
icing and could use their non-dominant hand to guide
the tool. When empty, the new device weighed 217g
and the traditional piping bag weighed 55g. Both
devices weighed approximately the same (612g)
when fully loaded with icing, however, the new
device could dispense 396g of icing and the
traditional piping bag could dispense 41% more
(559g). Grip force for the two methods was
estimated by applying force to the bag or switch with
a digital force dynamometer to achieve a flow
rate typical for decorating (approximately 5g
icing/6s).Prior to testing subjects were instructed on
refill and tip change technique for the new device and
were allowed up to 30 minutes of practice time.
Figure 1. Traditional piping bag.
Figure 2. Alternative device.
Outcome Measures
Bipolar surface electrodes were placed over the
extensor digitorum (ED), abductor pollicis
longus(APL), and the flexor digitorum superficialis
(FDS) muscles of the dominant forearm using
recommended anatomical placement (Perotto 2006).
Circular Ag/AgCl electrodes with an active diameter
of 8 mm and a center-to-center distance of 21 mm
were used. Data was recorded using a four channel
amplifier and data logger (Telemyo 2400T, Noraxon,
Scottsdale, Arizona). Raw electromyography signal
was recorded at 1500 Hz. Confirmation of muscle
activity was confirmed by manual muscle testing of
each muscle. Maximum voluntary contractions
(MVCs) were collected by having the subjects resist
a motion involving the muscle, performing a
maximum grip at five different grip spans, and a
lateral pinch force for 3 seconds. Each contraction
was repeated three times. An MVC was the highest
value of each muscle, calculated from the RMS
signal using a 1 second moving window, and used to
normalize subsequent values.
Three video cameras (Pan/tilt/zoom, Vanguard)
were positioned to capture subject shoulder and wrist
postures; one overhead, one from the right and one
from front. Images from the three cameras were
captured simultaneously to computer at 30 frames per
second (Quad Processor, Grand Magic Guard II)
(Winters 2006). Electromyography and video data
were recorded over the entire 60-minute trial.
At the end of the trials, subjects completed a
questionnaire that assessed hand and arm fatigue
using an RPR scale (0 to 11), usability of each device
and recommendations for design modifications.
Data Analysis
Raw electromyography data was converted to
RMS using a 100ms time constant. The signal for
each muscle was normalized to percent MVC and
summary measures for each trial and muscle were
calculated for the amplitude probability distribution
for median (APDF 50%) values (Jonsson, 1982).
Wrist and shoulder postures were measured from a
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random sample of 100 video frames per trial using
MVTA software (Yen, 2007). Productivity was
assessed by counting the number of cakes completed
during each 60-minute trial. Outcome measures were
compared between devices using a paired t-test
(posture) or the Wilcoxin Signed Rank test (e.g.,
subject ranking, APDF, productivity, fatigue).
RESULTS
The traditional piping bag required an average
estimated grip force of 9.7kg (SD=0.52) while the
new device required only 1.14kg (SD=0.11) of grip
force to dispense icing at a rate typical for decorating.
Subject demographic characteristics are presented in
Table 1. All but one subject was right handed. The
levels of median (Figure 3) muscle activity were less
for the new device than the piping bag across all
muscle groups. Posture analysis showed no
significant difference between shoulder flexion
(p=0.059), shoulder abduction(p=0.383) or wrist
radial deviation (p=0.522), however there was
significantly less wrist extension (p=0.045) with the
new device (Table 2).
Subjective ratings of fatigue were similar to the
electromyography findings (Table 3). Across all
body regions, subjects reported less fatigue with the
new device than the piping bag. This difference was
significant in the shoulder (p=0.017), forearm
(p=0.003), and hand (p=0.001) regions.
Subjects rated the new device superior to the
piping bag for refill, speed and setup (Table 3).
However, they rated the traditional piping bag
method better for accuracy and consistency of work
and rated the traditional method best overall. Open-
ended comments were solicited on likes, dislikes and
suggestions for improving the device design.
Recurring features that were liked about the new
device were the refill method, the ease of dispensing,
the ease of changing tips, and the cleanliness.
Recurring dislikes for the new device were overflow,
air pockets in the icing, lack of control with finer
décor, and weight/balance (too heavy). When using
the new device, especially with small tips, the icing
continued to exude from the tip even after the trigger
was released, leading to problems with accuracy and
poor quality of work. Participants suggested that the
overflow problem be addressed, the tool made
lighter, and the trigger sensitivity be improved. For
the traditional piping bag, subjects recommended
improving the refill method.
Productivity was slightly, but not significantly
(p=0.463), improved with the new device in
comparison to the piping bag method.
DISCUSSION
The new cake decorating device required less
than average muscle force across all three muscles
tested. These findings were matched by the lower
subjective ratings of fatigue with the new device in
comparison to the traditional method. Additionally,
awkward posture of wrist was significantly reduced.
These are important findings since cake decorating
involves high force and awkward posture of the wrist
for sustained durations, depending on the type and
number of cakes being decorated. The combination
of awkward posture, high force and high repetition
has been shown to have a synergistic effect than
either risk factor alone, so reducing excessive and
awkward postures is an important strategy to
reducing the overall risk of developing carpal tunnel
syndrome, tenosynovitis, or other musculoskeletal
disorders. With the high rate of hand and wrist
musculoskeletal disorders in this population,
particularly the high rate of carpal tunnel syndrome,
all reductions in force, awkward posture, or repetition
could have an impact on the incidence of future
injuries.
The new device did not receive the best overall
rating, primarily because of problems with overflow
and accuracy. With the smaller tips, the charge used
to expel the icing was too great causing oozing of the
icing even when trigger had been released.
Additionally, the air pockets in the icing were
problematic and would splatter icing on the cake with
no warning, requiring the cake decorator to start the
design over. Another problem identified was the
awkwardness of the weight of the tool. The icing
formed a large ball that did not rest on the hand but
rather over the wrist area. This caused it feel off
balance and more difficult to control. However, the
participants in the study decorate elaborate cakes
(e.g., wedding or special event cakes) and less
production or flat cakes. The new device may have
done better among decorators who specialize in
production cakes with more simple designs.
Several limitations of the study should be
acknowledged. The study was conducted in a
laboratory setting without the distractions or pressure
of a bakery; real work demands may increase muscle
loading. The icing tested was not one with a high
viscosity (e.g., German Chocolate) and was at room
temperature. In many bakeries the icing is
refrigerated before use which would require higher
grip forces. Cooler icing may have reduced the
overflow problem, but would likely have increased
overall grip force for both methods. Subjects had
little exposure to the new device prior to testing. It is
likely that with more exposure, the productivity and
usability ratings of the new device would improve.
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These study limitations would not be expected to
alter the conclusions of the study. Finally, the
electromyography values for some muscles were
higher than expected. This may be due to an
inadequate effort during the MVC or to cross-talk
from other muscles. Again, this would not be
expected to alter the study conclusions.
CONCLUSION
Feedback from experienced cake decorators
suggests that the manufacturer of the new cake
decorating device address the overflow problem to
improve its accuracy and associated impact on
quality of work. From the perspective of preventing
musculoskeletal disorders, the new device
significantly reduced grip force and awkward wrist
posture, thereby reducing the risk of developing
upper extremity pain and musculoskeletal disorders.
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Winters, J., Rempel, D., Story, M., Lemke, M., Barr,
A., Campbell, S., Danturthi, S. The Mobile Usability Lab
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ACKNOWLEDGEMENTS
Thank you to NIOSH for providing partial funding for this
study.
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Table 1. Demographic characteristics of participants
(N=17).
Mean (S.D.)
Gender
Female 13
Male 4
Age (years) 46.2 (14.3)
Ethnicity
African American 4
Asian 1
Hispanic 1
White 10
Work experience
Hrs/wk of work 36.2 (14.3)
Hrs/wk cake decorating
17.1 (12.8)
Years cake decorating 15.0 (9.7)
Discomfort level (0-5) during the past
4 months
Neck 2.6 (2.9)
Shoulders 2.8 (3.0)
Forearm 1.7 (2.1)
Wrist 3.1 (2.5)
Hand 3.2 (2.1)

Table 2. Upper extremity posture of dominant hand.
Average ROM (
°
) Piping
Bag Altern.
Tool p-value
Shoulder Flexion 29.2 28.5 0.586
Shoulder Abduction 23.2 24.0 0.383
Wrist Extension 35.8 33.5 0.045
Wrist Radial Deviation 6.8 7.6 0.522

Figure 3. Summary of median (APDF 50%) muscle
activity for three forearm muscles for each of the cake
decorating devices. Error bars are SD (N=17).
Table 3: Comparison Data-Subjective ratings of fatigue and usability using the Wilcoxin Sign Rank Test.
Exertion/Fatigue Summary
(0-11) Piping Bag New Tool P value
Neck 1.11 (1.28) 0.62 (0.97) 0.082
Shoulders 1.79 (2.15) 0.89 (1.08) 0.017
Forearms 2.63 (2.3) 0.81 (1.12) 0.003
Hands 3.72 (2.89) 1.01 (1.28) 0.001
Thumb 2.38 (3.13) 1.21 (1.43) 0.229
Digits 2-5 2.1 (2.98) 0.95 (1.17) 0.182
Tool Preference/ Comparison
Summary
(# of participants) Piping Bag New Tool
No
Prefer-
ence P-value
Better set up 8 9 0 0.500
Better refill 2 15 0 0.001
Easier tip change 4 4 9 0.637
Better accuracy 15 2 0 0.001
Faster work speed 7 10 0 0.315
Better consistency of work 14 1 2 0.000
Best overall 10 5 2 0.151
Productivity Piping Bag New Tool P-value
mean # cakes/hr 4.17 (1.73) 4.41 (1.65) 0.463
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