ERGONOMIC ANALYSIS OF MODERN DAY KITCHEN KNIVES
Richard T. Stone, Ph.D.; Olivia Janusz MS; Thomas Schnieders Ph.D Candidate
Industrial and Manufacturing Systems Engineering
Iowa State University
The focus of this study was on how different knife characteristics affect the consumer’s ability to slice
vegetables. The aim of this study was to investigate if there is a difference in cutting between a chef knife
and a santoku knife, a ceramic knife and a stainless-steel knife, and a sharp and dull knife in terms of muscle
activation, body part discomfort, time, and slice performance. The results show for the consumer that knife
characteristics do not affect the user’s performance.
Every day, millions of Americans spend time at home
preparing food to eat or to serve their household. In 2014, the
US Department of labor reported 56.3% of the population
engaged in food preparation and cleanup, averaging 1.04
hours daily spent on this activity (Bureau of Labor Statistics,
2014). While the younger population might have no trouble
completing kitchen tasks, those who are aging or have other
physical disabilities might have problems using certain kitchen
tools to prepare food the way they want to (Gustafsson, 2002).
Cooking in the kitchen is a necessity for many people, and
making tools and tasks easier or less time consuming can have
a significant effect on the person’s ability to complete them
(Ritzel & Donelson, 2001& Bowers, 2000).
Arthritis and old age can greatly affect the task of food
preparation (Reisine, Goodenow, & Grady, 1987 & U, 1996).
One study interviews 48 older people between the ages of 60
and 90 about food preparation. Of the participants, 19 percent
had trouble completing tasks related to food preparation, or
had modifications for ways they could accomplish tasks. One
of the participants felt pain while peeling and chopping, and
another said she didn’t have enough strength in her hands to
be able to do certain food preparation tasks. An alternative
suggestion was buying prepared meals or pre-sliced vegetables
instead of doing the work yourself (Maguire et al., 2014). This
is an unfortunate substitute when “older people often find it
personally rewarding to continue with familiar kitchen
routines and skills known throughout their lives” (Maguire et
al., 2014, p. 77). When aging, cooking is the last thing a
person wants to give up (Shanas, 1968).
Much of past human factors and ergonomics work in the
kitchen has focused on the layout and creating universally
designed kitchen tools (Mitchell, n.d.). Sam Farber started
OXO in 1990, when his wife suffering from arthritis found
kitchen tools increasingly harder to use. He did not want to
make a special needs product, so universal design became the
philosophy of OXO (Coleman, 2007). OXO is now one of the
leading companies in kitchen tools and their approach has
been identifying what tools hurt to use and how can they be
made more comfortable (“Simply better design,” 2008). Many
of their products feature a comfortable power grip. A power
grip wraps the finger and thumb around the tool and gives the
user strength to perform the task (Konz, 1974). While it is
important to create tools for everyone to use, there are other
areas of food preparation to study (Williamson, 2012). Slicing
vegetables is one task a power grip cannot easily be applied to.
Slicing vegetables with a knife is a tiring activity, and
there are no easy short cuts or ways to complete the task
(Lang, 2000). Although there are many different variables in
the knife market (type of knife, material, and sharpness being
the three main ones) there is no research done on the consumer
level to see if these variables affect the user’s ability. This
study concentrates on the kitchen task of slicing vegetables,
specifically carrots and potatoes, in the home setting.
Commercial operations have workers cutting for extended
lengths of time. Studies have been done to examine fields such
as meatpacking, where the risk of cumulative trauma is 30
times greater than the average for all other industries
(McGorry, Dowd, & Dempsey, 2005). Professional chefs
spend years learning the skills that give them the precision and
expertise they need (Trotter, Wareing, Hill, & Hall, 2008).
Consumers, on the other hand, will not be using a knife for a
long length of time when preparing a meal and are not going
to dedicate a period of time to learning the proper way to cut
each type of food with accuracy. The focus of this study was
on how different types of knives, materials, and levels of
sharpness affect the user while slicing carrots and potatoes.
The user was outfitted with electromyography (EMG) sensors,
and the percent of their maximum voluntary contraction
(MVC) was used as a metric. The other dependent variables
were body part discomfort, the duration of the task, and slice
performance, tested from a sampling of their vegetable slices.
There are many types of knives serving different
purposes. There are two multipurpose knives recommended
for slicing vegetables, the chef knife and the santoku knife.
The chef knife is the all-purpose knife most people know and
use. It’s used for chopping, slicing, dicing, and mincing most
food. This knife is “wide enough to give you plenty of knuckle
clearance when you’re working on a cutting board; long
enough to cut large items efficiently and small items precisely;
and curved enough to let you rock the blade as you chop” (Jay
& Sur La Table, 2008, p. 21). Another knife, that has gained
popularity in recent years, is the santoku knife. This is a
Japanese utility knife and translates to the “knife of three
virtues.” There are three different theories for what the three
virtues are. The first is the ability to cut fish, vegetables, and
meat. The second is that the knife excels in slicing, mincing,
and chopping. And the final theory is the ability to use “the tip
of the knife for fine work, the cutting edge for general duty,
and the heel of the knife for heavy-duty chopping” (Ward &
Regan, 2008, p. 49). These two knives were selected for this
study due to their wide range of uses and popularity in the
home. Most home cooks are likely to own versatile knives and
not ones for specific uses.
One debate about knives is what material is better to
use, stainless steel or ceramic. Stainless steel knives have been
around for a long time. They’re strong, durable, and easily
sharpened. New metals are being used and mixed to optimize
the knife; for instance, sharp brittle carbon steel is placed
between flexible stainless-steel, giving the user the sharp
brittle metal in the middle, and softer metal surrounding it to
keep it in good condition. In the last 25 years, ceramic knives
have entered the market. The ceramic blade is 50% stronger
than steel, it’s sharp, and stays sharp. It makes for a light
knife, but it is brittle and cannot be sharpened at home. This
knife can do most of the daily tasks, but with hard foods it
might not stand up to the challenge (Jay & Sur La Table,
2008). The third knife variable investigated was how
sharpness affects the user. Sharp knives are believed to be
safer to use than dull knives. A butcher explained that when
you have dull knife it takes more cuts to cut through than with
a sharp knife. The more cuts made, the more likely it is to
have the knife slip and have the person cut themselves
(Christensen, 2011). In a study focusing on commercially
cutting meat it was found that sharper blades required
significantly less cutting moments and grip forces than the dull
blade (McGorry, Dowd, & Dempsey, 2003). Another study
found for professional de-boners that there were significantly
less muscle activation for the flexor digitorum superficialis,
biceps branchii, triceps branchii, anterior deltoids, and the
upper trapezius muscles (Claudon & Marsot, 2006).
In this study, the hypotheses being tested were: (1) The
ceramic knife will result in a lower amount of muscle
activation, lower task time, higher slice performance, and
lower body part discomfort than the stainless-steel knife. (2)
The sharp knife will result in a lower amount of muscle
activation, lower task time, higher slice performance, and
lower body part discomfort than the dull knife. (3) The chef
knife will result in a lower amount of muscle activation, lower
task time, higher slice performance, and lower body part
discomfort than the santoku knife.
METHODS AND MATERIALS
There were 50 participants comprised of 11 females and
39 males. The average female age was 21 years old with a
range from 19 to 28. The average male age was 21 years old
with a range from 19 to 32.
The participants were required to test two knives,
each on a different day. The study had four different knives,
with two paired together. The first pair was a sharp JA
Henckels International chef knife and a dull JA Henckels
International chef knife. The knives were the same, but one
was dulled. The second pair was a sharp JA Henckels
International santoku knife and a sharp KitchenAid ceramic
chef knife. Both JA Henckels International chef knives and the
JA Henckels International santoku knife had the same handle.
A ceramic knife with the same grip was not available, so
another brand and design was used. This knife has a soft grip
to it, while the JA Henckels brand knives were hard. The order
of the paired knives was balanced among the participants.
To maintain the same level of sharpness an EST
K100 Knife Edge Sharpness Tester was used. A tolerance
zone was developed to ensure the sharp knife remained at the
same sharpness, and the dull knife remained at the same
dullness (Edge On Up, n.d.).
EMG was used to capture the muscle activity during
the study. The activity of four muscles was recorded: the
extensor digitorum, carpi radialis, biceps branchii, and triceps
branchii. Maximum voluntary contractions (MVC) were
found, and the average muscle activity over the task were used
to find the percent MVC reached. Participants were given a
body part discomfort survey before and after the study. The
participants were asked to rate how much discomfort they
were experiencing in their thumb, fingers, lower arm, upper
arm, and shoulder for their dominant arm. The scale went
from 1 to 10, 1 being no discomfort and 10 being the
maximum discomfort. The change in discomfort was recorded
for each body part.
The time it took to complete the task was recorded
from the EMG software. The last metric for the study was the
slice performance, where a random sample of slices was tested
for size. For carrots, ten slices were tested on the tolerance
zone of +/- 1/8” on the 1/2” slice. For potatoes, five slices
were tested to see if they met the tolerance zone of +/- 1/8” on
the 1/2” slice.
There were two different procedures followed for the
two vegetables sliced. Both carrots and potatoes were chosen
to cut because they provide resistance and required a certain
amount of strength to cut through.
When the participant arrived, they were given the
informed consent and an overview of the study. Having given
their consent, the participant was shown a video on how to
slice carrots or potatoes. The video “How to Slice a Carrot”
shared the key point of keeping your knife tip on the cutting
board (mahalodotcom, 2011). The video “How to Slice
Potatoes” showed the participant how to effectively slice a
Figure 1: (a) Chef knife, (b) Santoku knife, (c) Ceramic
potato (MonkeySee, n.d.). After watching the video and
confirming their understanding, the participant was given a
body part discomfort form to fill out. EMG sensors were
places on the participant and MVCs were collected.
Participants were given verbal feedback to encourage them to
put in their maximal effort (Jung & Hallbeck, 2004).
The participant was introduced to the testing
environment consisting of a counter top at the standard height
of 36” and a cutting board (Crews & Zavotka, 2006). The
participant was given the knife they would be using and the
carrots or potatoes they would be slicing. Each participant was
given two pounds of carrots to slice, which represents the
upper end of a recipe one might follow at home (“Apricot
Glazed Carrots Recipe,” n.d.). They were told to cut the
carrots in 1/2” slices using only their dominant hand on the
knife. The participants slicing the potatoes were given two
pounds of potatoes to slice into 1/2” slices using only their
dominant hand (O'Sullivan, n.d.). There was a diagram given
to them to show the desired size of the slices. They were given
a bin to move the slices into. With no further questions, the
participant started and the EMG recording software was
started. Once the participant sliced all the carrots or potatoes,
the EMG data was stopped and saved. The participant was
given another body part discomfort survey to fill out. The time
taken was noted from the EMG file.
The results for the average percent of MVC reached for
the extensor digitorum, carpi radialis, biceps branchii, and
tricps branchii are shown in Figures 2-5. A series of inferential
statistical test was performed for each muscle. With the large
amounts of variation between participants, there was no
statistical significance for any of the muscles while cutting
either carrots or potatoes. The type of knife, material of the
knife, and the sharpness of the knife, did not affect the percent
of the MVC reached or the amount of energy required to
complete the slicing.
Figure 2: % MVC for the Extensor Digitorum
Figure 3: % MVC for the Carpi Radialis
Figure 4: % MVC for the Biceps Branchii
Figure 5: % MVC for the Triceps Branchii
Body Part Discomfort
Participants found the most discomfort in the fingers
and lower arms, while they felt minimal discomfort in the
shoulder. A series of inferential statistical tests were
performed, and there was no statistical significance between
the different knives tested. The type of knife, material of the
knife, and the sharpness of the knife, did not affect the
discomfort the participants felt from the task of slicing carrots
Average % MVC
Average % MVC-Extensor Digitorum
Average % MVC
Average % MVC-Carpi Radialis
Averae % MVC
Average % MVC-Biceps Branchii
Avergae % MVC
Average % MVC- Triceps Branchii
A series of inferential statistical tests were performed
and there was no statistical difference between the knives for
slicing performance. The type of knife, material of the knife,
and the sharpness of the knife, did not affect slicing
performance for either the carrots or potatoes.
A series of inferential statistical test were performed
and there was no statistically significant difference in the time
it took to complete the task for the four knives. The type of
knife, material of the knife, and the sharpness of the knife, did
not affect the time it took to complete the task for either the
carrots of potatoes.
From the electromyography results it was shown that for
the four muscles tested: the extensor digitorum, carpi radialis,
biceps branchii, and triceps branchii, there were no
statistically significant differences between the knife
characteristics tested. It was expected that the dull chef knife
would require more muscle activation to complete the task that
using the sharp chef knife. This did not prove true; there was
no trend or significant difference between the sharp and dull
knife for either vegetable sliced. The difference between the
chef and santoku knife was hypothesized to be that the chef
knife would require less muscle activation. The lack of a
statically significant difference resulted in there being no
difference in muscle activation between the two types of
knives. The last expectation was that the ceramic knife would
perform better than the stainless-steel knife. Since there was
no statistically significant difference between the two, the
results show these knives require the same muscle activation
The body part discomfort survey covered five different
body parts: the fingers, thumb, lower arm, upper arm, and
shoulder. For each of these body parts there were no
statistically significant differences between the different knife
characteristics tested. The hypothesis the dull chef knife
would result in less body part discomfort than the sharp chef
knife was rejected, along with the other two hypotheses being
the ceramic would result in less than the stainless steel, and
the chef would result in less than the santoku.
The last two metrics, slice performance and time also
proves to be statistically insignificant for the different knives.
All three hypotheses were rejected that said the dull knife
would take longer and have worse slice performance than the
sharp knife, the stainless knife would take longer and have
worse slice performance than the ceramic knife, and the
santoku knife would take longer and have worse slice
performance than the chef knife.
All the results showed there was no statistically
significant differences between the knife characteristics. This
means that for the short time a consumer is cooking at home it
does not matter what type of knife they use in terms of muscle
activation, body part discomfort, time, and slice performance.
For all of the metrics tested: electromyography, body
part discomfort, time, and slice performance, there were no
significant differences between the different knives tested for
slicing carrots or potatoes. These results show for the
consumer it does not make a difference what knife they use for
a short cutting task. This lead to the conversation of what
would make a difference to the consumer cutting task. Options
brainstormed for future work were cutting other types of food,
using a different grip on the knife, picking a different type of
knife task, trying other knife materials, and redesigning the
LIMITATIONS AND ASSUMPTIONS
One limitation for this study was it only consisted of
cutting carrots and potatoes. These foods are similar in cutting
style and are only two examples of foods that are sliced with a
knife. Different foods require different forces, and meat might
be a food that having a sharp knife is important (Brown,
James, & Purnell, 2005). For this study it was not economical
to cut meat, and it would also have been a biohazard in the lab
to have raw meat. The participants were all from the college
population and not older adults were used as participants. If
the duration of the task had been longer, there might have
been more time for a difference to appear, but it was decided
to keep the task to be realistic for the consumer. Another
limitation was the grip of the ceramic knife was different than
the handles of the other knives.
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