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Hum Factors Man. 2020;1–16. wileyonlinelibrary.com/journal/hfm © 2020 Wiley Periodicals LLC
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Received: 18 October 2018
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Revised: 25 February 2020
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Accepted: 24 April 2020
DOI: 10.1002/hfm.20846
RESEARCH ARTICLE
Hand tool handle size and shape determination based on hand
measurements using a contour gauge
Ching‐Yi Wang
1
|Deng‐Chuan Cai
2
1
Department of Creative Product Design, Asia
University, Taichung, Taiwan
2
Department of Industrial Design, National
Yunlin University of Science and Technology,
Yunlin, Taiwan
Correspondence
Ching‐Yi Wang, Department of Creative
Product Design, Asia University, No. 500,
Lioufeng Rd., Wufeng, Taichung 41354,
Taiwan.
Email: catincar@gmail.com
Funding information
National Science Council, Taiwan,
Grant/Award Number: 106‐2813‐C‐036‐011‐E
Abstract
The purpose of this study is to provide a novel approach to tool handle design and
development based on measurements of hand shape using a contour gauge. In
general, traditional design techniques, designing based on anthropometric data, and
derived mathematical models do not incorporate enough subject data to design a
customized product. First, anthropometric measurements on the right hand of
60 participants were collected with a contour gauge to manufacture matching
handles. A curved handle fitting the human hand was constructed with common
computer‐aided design software, and cylindrical handles and elliptical handles were
added for comparison. All of the handles were used to record the participants' grip
force to evaluate the operating efficiency of the handles. Finally, the participants
completed a comfort‐rating questionnaire. The results show that contours based on
the hand provided the highest operating performance and the best overall comfort‐
rating compared to cylindrical handles and elliptical cylindrical handles. The newly
developed handles in the grip force tasks have the highest push performance and the
best comfort ratings compared to traditional cylindrical and elliptical handles. The
developed handles could provide the hand tool industry information on developing
and manufacturing many other similar handle designs (such as those for saws and
electric screwdrivers).
KEYWORDS
anthropometric measurement, computer‐aided design, ergonomics, hand tool, product design
1|BACKGROUND
Correct tool design is important for increasing performance and
subjective comfort and satisfaction, and for preventing upper‐
extremity musculoskeletal disorders (Moore, Wells, & Ranney,
1991). Regardless of the main function of the tool, the most im-
portant part of a manual tool is the handle in regard to ergonomics
(Das, Jongkol, & Ngui, 2005; Garneau & Parkinson, 2011;Kong&
Lowe, 2005; Motamedzade, Choobineh, Mououdi, & Arghami,
2007). This study investigated the comfort of the handles of power‐
driven hand tools (e.g., electric drills and electric screwdrivers).
Push force is one of the most important components in the opera-
tion of power hand tools (Das et al., 2005; Habes & Grant, 1997;
Kong & Lowe, 2005;Seo&Armstrong,2008). However, when
holding these power hand tools in push force, the hand may ex-
perience discomfort. Due to the nature of complex tasks, where the
grasp of a tool is necessary, the loads on the hand are high, which
can lead to discomfort, pain, and acute and cumulative trauma
disorders (ATDs; e.g., blisters, inflamed skin, and cramped muscles;
Garneau & Parkinson, 2011; Harih, 2014;Harih&Čretnik, 2013;
Harih & Dolšak, 2013; Kong & Lowe, 2005;Oh&Radwin,1993;Seo
& Armstrong, 2008). Therefore, good tool handle design may pre-
vent these injuries when power gripping the handle. Grip force
determines the optimal shape of the handle. Therefore, grip force
tasks to determine the correct shape of designed handles for
comfort of the hand are the main concern of this study.
Generally, traditional design techniques based on anthropometric
data are not sufficient to employ user data to design a suitable handle
for a specific target population (Harih & Dolšak, 2013). Many studies
have explored tool handle design in seeking to define the optimal size
and shape of the tool handle. Most studies focused on cylindrical‐
(Lemerle, Klinger, Cristalli, & Geuder, 2008;Putz‐Anderson, 1988;
Rossi, Berton, Grélot, Barla, & Vigouroux, 2012;Seo&
Armstrong, 2008; Welcome, Rakheja, Dong, Wu, & Schopper, 2004)
and elliptical‐shaped (Cochran & Riley, 1986;Seo&Armstrong,2011)
handles to provide guidelines for determining the optimal diameters to
increase finger‐force comfort, exertion, and contact area. However,
few studies considered the shape of the hand in the design process,
which could additionally improve the ergonomics of the handle. Many
studies suggested that handles should be designed with varying sizes
based on different hand lengths (Das et al., 2005;Ekşioğlu, 2004;Kong
&Lowe,2005;Seo&Armstrong,2008). Thus, handles with a shape
fitting the hand may reduce hand discomfort and the risk of hand
damage. Some studies considered the anatomical shape of the hand in
the optimal power grasp position based on medical imaging technology
and found that handles with more contact area are more comfortable
(Harih, 2013,2014;Harih&Čretnik, 2013;Harih&Dolšak, 2013;
Kaljun, 2014). For tool manufacturers, this advanced technology would
require significant cost to develop three‐dimensional (3D) models of
the hand. In the current study, physical measurement provides a
simple approach to construct tool handle shapes to best fit the human
hand. This process could also decrease cost to companies, and the
different sizes of handles could meet public needs. Harih and Dolšak
(2014) found that the handle shape had the greatest impact on the
participant's comfort ratings, and the customized handle was rated
more comfortable than the cylindrical handle for overall subjective
comfort ratings.
For comfort rating measurements, different studies used sub-
jective and objective criteria to determine the optimal handle. The
subjective comfort ratings included the comfort questionnaire hand
tools, which considered the various descriptors of comfort/dis-
comfort in using hand tools, and localized perceived discomfort
(LPD), which was measured using a detailed hand‐wrist map to
evaluate discomfort (Dianat, Nedaei, & Nezami, 2015; Groenesteijn,
Eikhout, & Vink, 2004; Harih & Dolšak, 2013,2014; Kuijt‐Evers
et al., 2004,2005,2007; Vink & van Eijk, 2007). The objective
comfort ratings involved different measurements based on different
tasks, including grip force and the push force, which assessed the
operational efficiency and performance of the handle (Harih &
Čretnik, 2013; Harih & Dolšak, 2013; Kalra, Rakheja, Marcotte,
Dewangan, & Adewusi, 2015; Welcome et al., 2004), and electro-
myography (EMG) for evaluating hand‐arm muscle activity and
loading (Barański & Kozupa, 2014; Das et al., 2005; Kong &
Freivalds, 2003; Kong & Lowe, 2005; Kuijt‐Evers et al., 2007;
Li, 2003; Lin, McGorry, Chang, & Dempsey, 2007).
Some studies demonstrated that push force and comfort/dis-
comfort were highly correlated (Das et al., 2005; Eikhout,
Bronkhorst, & Grinten, 2001; Kuijt‐Evers et al., 2005,2007). When
the handle is comfortable to use, the user can produce higher push
forces. Radwin, Vanbergeijk, and Armstrong (1989) assessed the
fastener‐driving procedure and discovered that the forearm muscle
activity torque accumulation is greater than that of the user holding
and supporting the tool while operating the power tool. The re-
lationship between push force and discomfort was found in evalua-
tions of hacksaws and scrapers (Das et al., 2005; Kuijt‐Evers
et al., 2005,2007). For hacksaw studies, Das et al. (2005) and
Kuijt‐Evers et al. (2007) found higher push force with a hacksaw that
was subjectively evaluated as better. Moreover, the artist believes
that reducing the scraping action of the scraper can significantly
reduce discomfort in the upper limbs (Eikhout et al., 2001; Rempel,
Harrison, & Barnhart, 1992).
Several studies on the comfortable handle for gripping focused
on the hand contact pressure and hand distribution (Harih &
Dolšak, 2013,2014; Harih & Tada, 2015; Lemerle et al., 2008; Rossi
et al., 2012; Sanders & McCormick, 1993; Seo & Armstrong, 2011).
Harih and Dolšak (2013) proved that greater contact area can be
obtained by lowering the overall and local contact pressure. In ad-
dition, a high contact area handle can decrease the torsional strength
by vibration and increase gripping stability when operating the power
tool (Harih & Dolšak, 2013). However, their designed asymmetric
handles limited the use of the handle by a broad population and wide
range of tasks. Further research by Harih (2014) further modified a
symmetrical and smooth tool‐handle, which can be used by a wider
target population. This symmetrical design leads to better control of
the tool handle. Moreover, Rossi et al. (2012) demonstrated that the
palm was the major contributor to handle force, and the intensity of
the force distributions was transferred to thumb force when the
handle diameter increased. Harih and Tada (2015) found that the
largest difference in peak contact pressure was between different
fingertips. These arguments on contact pressure distributions might
involve the different sizes of hand length. This study considers that
the handle fits a participant's hand length for consistency of the
power contribution of the hand.
However, the handle performed to the maximum push force and
also produced the largest grip force. Welcome et al. (2004) proved
that the handle size, push, and grip forces determined the handle
contact force (Aldien, Welcome, Rakheja, Dong, & Boileau, 2005).
Contact pressure in high push and grip force can cause hand dis-
comfort, especially in the thenar eminence of the thumb muscles
(Aldien et al., 2005). The hand‐shaped handle evenly distributes the
hand pressure, reducing the local contact pressure caused by un-
suitable handles that cause the hands to experience discomfort and
pain. The purpose of this study was to improve the performance of
the push force and reduce the pressure on the hand grip. This study
suggested that the higher the performance of the push force, the
higher the comfort of the previous assessment (Das et al., 2005;
Kuijt‐Evers et al., 2005,2007) although the supporting data were still
insufficient. Measuring the push performance and hand pressure
could fully prove the comfort and design quality of the handle.
This study included designing a tool handle to fit the human hand
based on hand measurements using a contour gauge. Three different
types of 3D models of tool handles, including curved handles,
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WANG AND CAI
cylindrical handles, and elliptical handles, were constructed by
computer‐aided design software. The newly developed handle was
compared to traditional cylindrical and elliptical handles using push
and grip forces for evaluation of the handle and subjective comfort
ratings of the hand.
2|EXPERIMENT 1: PUSH FORCE
2.1 |Hand anthropometric measurements
Sixty adult participants (mean age = 31.2 years; SD =4.4years),in-
cluding 30 males (mean age = 33.7 years; SD = 4.6 years) and
30 females (mean age = 28.7 years; SD = 4.2 years), participated in the
experiment. Hand anthropometric measurements were obtained with
the participant's right hand using calipers and a contour gauge (25‐cm
long, 1mm‐wide pins). As shown in Figure 1a, the A, B, C, and D di-
mensions were measured with the calipers. The contour gauge was
used to record the profile of the E, F, and G hand surfaces. The contour
gauge is a series of tightly packed pins that retain the topographical
image of the profile when depressed onto a surface (McCormick, 1994).
2.2 |Definition of push force direction
The push force direction is determined according to the biodynamic
hand‐coordinate system defined in Dong et al. (2015), in which the
z‐axis passes proximally through the third metacarpal bone when
gripping (Figure 1b). The x‐axis of the system is approximately normal
to the palm of the hand, projecting anteriorly from the origin when
the hand lies open in the normal anatomical position, that is, palms
facing forward. The axis parallel to the x and z‐axes and passing
through the center of the handle circle were used as the reference x
and z‐axis. When the wrist is in a neutral position, the angle between
the forearm axis and the wrist is approximately 30° (Dong
et al., 2015). The positioning line was marked for aligning at the
centerline of the handle when the handle was being held.
The finger position was according to Harih and Dolšak (2013),
where the tip of the thumb overlaps with the fingertips of the index
and medium fingers when acquiring the optimal diameters for each
finger. Table 1presents the anthropometric data of the participants
with large, medium, and small hands. The percentiles of hand lengths
for the large, medium, and small hands were determined by sugges-
tions of Kong and Lowe (2005) for hand length that were the best fit
for different populations: small (5th–30th percentile), medium
(30th–75th percentile), and large (75th–95th percentile) hand lengths.
The averages of the hand lengths for these three sizes were based on
the anthropometric measurements of the Taiwanese population
25–34 years old (Wang, Wang, & Lin, 2002;Table2). The one‐sample
t‐test found that the hand length and hand breadth of this study were
not significantly different from the anthropometrical data of Wang
et al. (t[59] = 1.92; p= .06 and t[59]= −1.63; p=.11, respectively), in-
dicating that these three sizes corresponded to Taiwanese hand size.
The anthropometric data of the participants with large, medium, and
small hands were used to determine the dimensions of small, medium,
and large handles. A further independent‐sample t‐test found a sig-
nificant difference between hand length and gender (t[58] = 11.60;
p< .0001), indicating that gender affects hand length.
2.3 |Two‐dimensional hand data acquisition
As shown in Figure 2, the grasp posture was used in the measure-
ment of the hand as follows: (a) First, the participants were asked to
FIGURE 1 The definitions of the human hand dimension measurements: (a) A, B, C, and D dimensions were measured with calipers. The
contour gauge was used to record the profile of the E, F, and G curves. (b) The grip gesture was determined by the biodynamic hand coordinate
system defined in ISO 8727 (1997)
WANG AND CAI
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make a hand gesture that looked like holding a handlebar (Figure 2a).
Four adhesive markers were affixed on each hand of each participant
to ensure that the correct gripping hand was aligned with the re-
ference axis. The marker on the hand was aligned with the marker on
the contour gauge to ensure that a consistent hand grip orientation
was achieved. (b) Then, the contour gauge with red and black color
was used to press the plastic pins against the hand's curved surface
(Figure 2b). (c) The pins conforming to the hand shape and the profile
of the hand were then drawn on graph paper (Figure 2c). (d) Finally,
using these profiles, the handle shape was constructed and
dimensioned (Figure 2d).
The hand must be in a holding position and measured with a
contour gauge. It is important to minimize the changes in the muscles
held by the hand when measuring. When measuring E, F, and G hand
surfaces, four fingers or thumbs are used to open a measurable space
with a limited amount and maintain a holding posture for measure-
ment. For example, while measuring the E‐curve (Figure 2b), the
thumb is tilted upward, the four fingers still maintain the holding
position, and the muscles of the thumb will not move to the four‐
finger muscle. Moreover, the contour gauge is used to lean lightly
against the surface of the hand without compressing the soft tissue;
therefore, it will affect the original contour readout as little as
possible.
Figure 3shows all of the dimensional locations of the handle.
The average dimensions of large, medium, and small hands were
used to construct 3D handle models. The curved dimensions mea-
sured the distance from the centerline to the tangent of the arc. The
handle slope was determined by the angle between the gripping
TABLE 1 The results of the hand dimensions for large, medium, and small hands (unit: mm)
Item
Large hand (75th–95th
percentile)
Medium hand
(30th–75th percentile)
Small hand (5th–30th
percentile) All hand
Mean SD Mean SD Mean SD Mean SD
A 183.6 14.2 178.4 13.3 171.7 9.8 177.9 12.4
B 81.9 7.7 79.6 7.2 76.6 5.8 79.4 6.9
C 39.7 9.2 38.4 7.5 37.3 7.1 38.5 7.9
D 32.6 8.0 31.7 6.7 30.8 6.4 31.7 7
E E1 38.3 8.3 34.8 7.9 33.2 7.5 35.4 7.9
E2 21.9 7.5 21.3 6.6 20.5 4.7 21.3 6.3
E3 13.0 4.2 12.6 4.5 11.7 4.1 12.3 4.3
F F1 19.9 7.0 18.7 5.5 17.9 4.8 18.9 5.8
F2 43.7 9.8 42.1 8.2 40.4 9.0 42.0 9
F3 69.1 12.7 67.3 13.2 64.5 11.8 67.0 12.6
F4 13.7 5.3 13.4 4.9 12.5 4.7 13.3 5
F5 16.4 6.1 15.8 4.2 14.9 4.9 15.7 5.1
F6 12.5 5.2 12.3 6.8 11.6 4.6 12.3 5.5
F7 11.7 4.1 11.2 4.8 9.9 3.9 10.9 4.3
G G1 17.4 4.8 16.9 5.1 14.6 6.1 16.3 5.3
G2 39.2 8.3 37.9 9.3 36.2 6.9 37.7 8.2
G3 67.0 14.2 65.2 12.9 62.7 13.9 64.9 13.7
G4 13.1 5.7 12.6 4.8 12.1 2.3 12.5 4.3
G5 14.5 4.1 14.0 4.7 13.6 3.8 14.1 4.2
G6 12.2 4.2 11.1 3.7 10.5 5.1 11.4 4.3
G7 19.2 4.2 18.7 6.5 17.2 4.9 18.4 5.2
Note:
(A) Hand length: distance from top of the medium finger to the distal crease of the wrist.
(B) Hand breadth (four fingers): maximum hand breath where the fingers join the palm.
(C) Grip breadth inside major diameter: inside hand elliptical diameter with the length of major axis measured at grip breadth.
(D) Grip breadth inside minor diameter: inside hand elliptical diameter with the length of minor axis measured at grip breadth.
(E) The curve of the medium phalanges: the curve of medium phalanges from forefinger to little finger.
(F) The curve of metacarpals: the curve from the second metacarpal to the fifth metacarpal.
(G) The curve of the palm: the curve from the proximal crease of thumb to the bottom left hand side of the palm.
TABLE 2 The comparison of hand length and hand breadth of this
study with Wang et al. (2002) (unit: mm)
Item
This study Wang et al. (2002)
Male Female All Male Female All
A hand length 187.9 167.9 177.9 183 167 175
B hand breadth
(four fingers)
83.6 75.2 79.4 86 75 80.5
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WANG AND CAI
central line and the forearm shaft at 110° (Kroemer, Kroemer, &
Kroemer‐Elbert, 1994).
2.4 |3D construction and manufacturing of the
handle
All of the handles were constructed as 3D models using the solid
modeling software Creo Parametric 2.0, as shown in Figure 4. The
software was created by Parametric Technology Corporation (PTC)
in America. To compare the newly designed handles, this study added
cylindrical and elliptical handles that were manufactured based on
traditional methods with recommendations, such as the handle
length (Konz, 1983), handle slope (Kroemer et al., 1994), and handle
diameter (Ayoub & Lo Presti, 1971; Rigby, 1973). The design speci-
fications for cylindrical and elliptical handles contained: (a) handle
length: small (5th–30th percentile), medium (30th–75th percentile),
and large (75th–95th percentile) handle lengths were 100, 102.9, and
105.9 mm, respectively (Konz, 1983); (b) handle slope: 110°
(Kroemer et al., 1994); (c) diameter of cylindrical handle: 38 mm
(Ayoub & Lo Presti, 1971; Rigby, 1973); and (d) diameter of elliptical
handle: the ratio of width to height is 1:1.25 (Cochran & Riley, 1986).
Based on suggestions by Kong and Lowe (2005) for hand length,
each type of handle corresponded to one of the following three sizes
for the design with the best fit for different populations: small
(5th–30th percentile), medium (30th–75th percentile), and large
(75th–95th percentile) hand lengths. The nine handles, consisting of
three shapes of three handle sizes (small‐cylindrical, medium‐
cylindrical, large‐cylindrical, small‐elliptical, medium‐elliptical, large‐
elliptical, small‐curved, medium‐curved, and large‐curved), were
manufactured by a CNC machine, as shown in Figure 5.
Table 3shows the results of ratios of width to length for the
cross‐section of small, medium, and large handles. The curved handle
had three different ratios of cross‐sectional areas. The largest of all
FIGURE 2 Two‐dimensional hand data acquisition
FIGURE 3 Stimuli for the three types of handles for the small, medium, and large population (unit: mm) (large‐cylindrical, medium‐cylindrical,
small‐cylindrical, large‐elliptical, medium‐elliptical, small‐elliptical, large‐curved, medium‐curved, and small‐curved handles)
WANG AND CAI
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the cross‐sectional areas was the below‐curved handle (mean =
1:1.41). The ratio of cross‐section of above‐curved handle (mean =
1:1.21) was close to that of the elliptical handle (mean = 1:1.25).
Moreover, the cylindrical and medium‐curved handles have similar
ratios of cross‐sectional areas (mean = 1:1 and 1:1.12, respectively).
2.5 |User testing
The experiment evaluates the user's push force when operating each
handle. Each corresponding handle was given to 30 undergraduate
students (15 males; 15 females; mean age = 25.7 years; SD =3.9years).
Each participant underwent anthropometric measurements of hand
length to be assigned into one of the three hand size groups (Table 1).
The participants were all right‐handed and healthy, with no upper limb
injury or musculoskeletal disorders.
Before the experiment, the participants were asked to sit on a
chair (45‐cm seat height) with a seat back and without armrests, as
shown in Figure 6. To control the upper‐body posture of each par-
ticipant, the participants were asked to keep their body straight
without leaning on the seat back and while grasping one of the three
types of handles (cylindrical, elliptical, and contoured) randomly,
while keeping upper arm vertical and elbow at a 90° angle, as sug-
gested in ISO 10819 (1996). There was a specially designed stand in
front of the participants, in which a digital force gauge with load cell
(MITSU MASA LAD‐1000 from Mitsumasa Enterprises Co., Ltd.;
measurable range of weight: 0–2,942 N) could measure to record the
push force data. This stand was constructed with angle brackets, and
screw bolts were used to adjust the force gauge so that the stand and
the participant's forearm were at the same height. The push force
direction was labeled with an adhesive marker based on the handle
reference z‐axis, which was aligned with the direction of the z‐axis.
At the start of the experiment, all participants were given a start
instruction and then performed the maximal volitional contraction (MVC)
ofpushforcefor15s.Thebaseofthepalmofthehandwasapplyingthe
push (Rossi et al., 2012). All participants tested all nine handles in a
random order. Each handle was continuously tested three times. After
each push, there was a 5‐min break. MVC was measured using the mean
of three peak values (Kwon, Bahn, Hee Ahn, Lee, & Yun, 2016). The 15‐s
setting was based on a previous study (Semmler, Tucker, Allen, &
Proske, 2007) that suggested after 15 s, muscle contractions produce
muscle fatigue, which decreases the contractile capacity of the muscles
(de Haan, Lodder, & Sargeant, 1989; van Dieen, Boke, Oosterhuis, &
Toussaint, 1996); therefore, MVC was measured for each handle.
2.6 |Localized perceived discomfort scale ratings of
the hand
After each handle test, the participants were given a subjective com-
fort rating questionnaire based on a LPD scale in order to understand
which parts of the handle affected discomfort of the hand. This LPD
scale was based on and modified the scale of Vink and van Eijk (2007).
The participants were asked to evaluate the discomfort in zones A, B,
C, D, and E (Figure 7) shown on a diagram of the hand, using a scale
ranging from 1 (not comfortable) to 5 (highly comfortable).
2.7 |Data analysis
Repeated measures analysis of variance (ANOVA) were used to
analyze the push force and the comfort rating.
Multivariate analysis of variance (MANOVA) of push force for
independent variables was “handle shape”(cylindrical, elliptical, and
curved handle) and “handle size”(large, medium, and small handle).
MANOVA of the comfort rating for independent variables was
“region”(A, B, C, D, and E regions of the hand), “handle shape”
(cylindrical, elliptical, and curved handle), and “handle size”(large,
medium, and small handle). Both the push force and comfort rating
for the dependent variables was “gender”(male and female) and
“hand length”(large, medium, and small hand).
Secondary MANOVAs for pairwise comparisons were conducted
to check for any significant effects of the condition factor. The
Greenhouse–Geisser correction for nonsphericity was applied as
appropriate. Posthoc comparisons employed a Bonferroni correction,
which is commonly used and significantly reduces the risk of carrying
out the complex analysis (McHugh, 2011).
2.8 |Results
2.8.1 |Push forces
Table 4shows the results of the push force measurements across the
nine handles. Push strength for males was higher than for females.
FIGURE 4 Three‐dimensional modeling handles were
constructed using the Pro‐Engineering CAD software
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WANG AND CAI
Participants with large hands produced the highest push perfor-
mances, followed by the medium hands and small hands. Participants
using curved handles had the greatest push strength, followed by the
elliptical handles and cylindrical handles. The participants using large
handles produced the highest push forces, followed by medium
handles and small handles.
Figure 8shows the results of the push forces for the nine han-
dles. The global MANOVA for push force showed that both gender
and hand length were significant (F[1,24] = 55.72; p< .001 and
F[2,24] = 75.83; p< .001, respectively). Males had significantly
greater push force than females (F[1,28] = 8.83; p< .01, Figure 8a).
The participants with larger hands had greater push force than those
with medium and small hands, and small hands produced the lowest
forces (all p< .001, Figure 8b).
Handle shape had the main effect (F[2,48] = 11.76; p< .001,
ε= .77), but its interactions with gender and hand length were not
FIGURE 5 The nine tool handles consisting of three shapes and three handle sizes (large‐cylindrical, medium‐cylindrical, small‐cylindrical,
large‐elliptical, medium‐elliptical, small‐elliptical, large‐curved, medium‐curved, and small‐curved handles) were manufactured by a CNC
machine
WANG AND CAI
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significant (p=.44 and p= .91, respectively). The pairwise com-
parison indicated that the participants using the curved handles
had significantly greater push force than those using the cylind-
rical handles (F[1,28] = 26.72; p= .001). The elliptical handles
produced greater push force than the cylindrical handles
(F[1,28] = 12.47; p= .001, Figure 8c). However, there was no sig-
nificant difference between the curved and elliptical han-
dles (p=.06).
Additionally, handle size had no main effect (p=.30), but its
interaction with hand length was significant (F[4,48] = 4.62;
p<.01).However,therewasnointeraction between the handle
size and gender (p= .53). The pairwise comparison showed that the
participants with large hands using the large handles produced
greater push force than those using the small handles
(F[1,9] = 9.66; p<.05). The participants with medium‐sized hands
had greater push force than those with the small handles when
using the medium handles (F[1,9] = 5.72; p<.05). Follow‐up ana-
lyses for the participants with small hands revealed greater push
force using the small handles than when using the large handles
(F[1,9] = 6.9; p<.05, Figure 8d).
TABLE 3 The ratio of width to length for the cross‐section of small, medium, and large handles
Handle shape
Cross‐section
position
Large hand (75th–95th
percentile)
Medium hand (30th–75th
percentile)
Small hand (5th–30th
percentile) All hand
Cylindrical handle Middle 1:1 1:1 1:1 1:1
Elliptical handle Middle 1:1.25 1:1.25 1:1.25 1:1.25
Curved handle Above 1:1.22 1:1.21 1:1.21 1:1.21
Medium 1:1.11 1:1.12 1:1.14 1:1.12
Below 1:1.38 1:1.40 1:1.46 1:1.41
FIGURE 6 Experiment 1: Push force. Each handle was used to
perform a push force task for 15 s. The marker on the hand was to
ensure a consistent hand grip orientation for each handle
FIGURE 7 Localized perceived discomfort (LPD) scale of regions
A–E (A = distal proximal phalanges of all four fingers; B = media and
proximal phalanges of all four fingers; C = metacarpals; D = palm; E =
the thenar area of the thumb). Participants gave a rating from 1 to 5
(1 = not comfortable; 2 = very little comfortable; 3 = moderately
comfortable; 4 = highly comfortable; 5 = very highly comfortable) for
each region in the hand
TABLE 4 The overall means and standard deviations of push
forces (unit: N)
Item nMean SD
Gender Male 15 75.13 12.77
Female 15 60.07 14.92
Hand length Large hand 10 83.10 10.72
Medium hand 10 66.70 5.70
Small hand 10 53.00 11.70
Handle a Cylindrical shape Large hand 61.19 24.17
Handle b Medium hand 61.48 19.76
Handle c Small hand 60.53 23.72
Handle d Elliptic shape Large hand 68.18 25.11
Handle e Medium hand 70.77 23.05
Handle f Small hand 64.50 18.96
Handle g Curved shape Large hand 74.16 26.60
Handle h Medium hand 76.28 24.21
Handle i Small hand 71.03 20.00
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WANG AND CAI
2.8.2 |Comfort ratings
Table 5displays the results of the comfort ratings for the nine
handles. The overall rating means for males (score = 3.73) were
higher than for females (score = 2.33). Participants rated the curved
handle (score = 3.56) highest, followed by the elliptical handles
(score = 3.26) and cylindrical handles (score = 3). There were
slightly different scores among the large, medium, and small hands
(score = 3.25, 3.32, and 3.25, respectively). Both the larger handles
(score = 3.58) and medium (score = 3.31) handles were
rated moderately comfortable, but the small handle was not
(score = 2.92).
Figure 9shows the results of the comfort ratings for the nine
handles. The global MANOVA for comfort ratings showed that both
the gender and hand length were significant (F[1,24] = 509,769.99;
p< .001 and F[2,24] = 1,243.48; p< .001, respectively). For hand
evaluations, males were rated more comfortable than females
(F[1,28] = 5,598.82; p< .001, Figure 9a). However, there were no
different ratings for the participants with larger, medium, and small
hands (p= .94, Figure 9b).
There were significant, main effects for the region, handle shape,
and handle size (F[4,96] = 35,505.42; p< .001, ε= .72;
F[2,48] = 41,857.08, p< .001; ε= .97 and F[2,48] = 89,867.30; p< .001,
ε= .98, respectively), and their interactions with hand length were
FIGURE 8 The results of the push forces for the nine handles. The multivariate analysis of variance (MANOVA) results for the push forces
show that (a) males had greater push force compared to females, (b) the participants with larger hands had greater push force than those with
medium and small hands, and small hands produced the lowest forces, (c) the participants using the curved handles had greater push force than
those using the cylindrical handles. The elliptical handles produced greater push force than the cylindrical handles, and (d) the participants with
large hands using the large handles produced greater push force than those using the small handles. The participants with medium‐sized hands
had greater push force than those with the small handles when using the medium handles. Moreover, the participants with small hands revealed
greater push force using the small handles than when using the large handles
WANG AND CAI
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significant (all p< .001), but the difference with these interactions
between genders was not significant (all p> .05). The pairwise com-
parisons for these five regions of the hand showed significant dif-
ferences for all of the participants with large, medium, and small
hands (all p< .001, Figure 9c). The participants perceived significantly
greater comfort when using the curved handles than when using the
cylindrical and elliptical handles (p< .001 for all hands), and the el-
liptical handles were rated more comfortable than the cylindrical
handles (p< .001 for large and small hands and p< .05 for medium
hands, Figure 9d). The most comfortable handles for the different
hand push forces were large hands using large handles, medium
hands using medium handles, and small hands using small handles
(Figure 9e).
3|EXPERIMENT 2: GRIP FORCE
According to Experiment 1, the results of comfort ratings, the un-
comfortable regions C, D, and E were selected to measure hand
TABLE 5 The overall means and standard deviations of comfort
ratings by using a scale ranging from 1 (not comfortable) to 5 (highly
comfortable)
Items nMean SD
Gender Males 15 3.73 0.71
Females 15 2.33 0.22
Hand lengths Large 10 3.25 0.49
Medium 10 3.32 0.56
Small 10 3.25 0.23
Handle a Cylindrical handle Large 3.32 0.61
Handle b Medium 3.16 0.58
Handle c Small 2.52 0.70
Handle d Elliptic handle Large 3.71 0.54
Handle e Medium 3.17 0.63
Handle f Small 2.89 0.74
Handle g Curved handle Large 3.73 0.59
Handle h Medium 3.61 0.54
Handle i Small 3.34 0.65
FIGURE 9 The results of the LPD using a scale ranging from 1 (not comfortable) to 5 (highly comfortable) for the nine handles. The MANOVA
results for the comfort ratings show that: (a) males were rated as more comfortable than were females, (b) there were no different ratings for
participants with larger, medium, and small hands, (c) these five regions of the hand showed significant differences for the participants with large,
medium, and small hands, (d) the curved handles were rated more comfortable than the cylindrical and elliptical handle, and the elliptical handles
were rated more comfortable than the cylindrical handles and (e) the most comfortable handles were large hands using large handles, medium
hands using medium handles, and small hands using small handles. LPD, localized perceived discomfort; MANOVA, multivariate analysis of variance
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WANG AND CAI
pressure; therefore, A and B regions were neglected and grip tasks
were not performed.
Application of grip force verifies the contact pressure distribution in
handles of different shapes. Because holding different shaped handles
may affect the distribution of hand contact area, this study suggests
that contact areas that do not fit the shape of the hand will compress
the muscles, which may exert higher pressure in this area, and vice
versa. When the grip fits the shape of the hand, the pressure of the grip
is evenly distributed on the hand, and the pressure is relatively small.
Experiment 1 has confirmed that different hand lengths must be
matched with handles of different sizes. Therefore, we deleted the
“handle size”and “hand length”variables in Experiment 2 to shorten the
experiment time, and focus on verifying the influence factors of the
“handle shape”variable on the hand pressure. Three sets of medium‐sized
handles were selected to measure the cylindrical, elliptical, and curved
handles, and the pressure sensors were pasted on the hand to measure
the hand pressure of the grip force. Three sets of medium‐sized handles
were selected to measure the cylindrical, elliptical, and curved handles to
measure the hand pressure of the grip force using the force sensor.
3.1 |Participants
Twelve participants with medium‐sized hands (six males and six fe-
males; mean age = 25.4 years; SD = 1.6 years) were selected for the
grip force task. The average hand length was 177.13 mm
(SD = 10.35).
3.2 |Equipment
Contact pressure was recorded using the NeXus‐10 device (product
number: NX10‐A; label: MindMedia, Figure 10a). The NeXus‐10 is a
versatile and integrated system for biofeedback, neurofeedback, or
psychophysiological research. It is suitable for measuring a wide
range of physiological signals simultaneously, including the channels
of electroencephalogram, EMG, electrocardiogram, and electro‐
oculograph signals. The force sensor (product number: NX‐FORCE‐
NXX, model: LBS‐100, cap: 100 lbf, Figure 10b) was attached to the
participant's hand for measuring the contact pressure. The mea-
surement range was 0–100 blf.
3.3 |Procedure
Figure 11 shows the actual experimental scenario. The force sensor
was attached to the palm of the hand (regions C, D, and E) using
paper tape (Figure 11a). In each region, the pressure values were
recorded the pressure values. The gripping position of the handle was
the same as that in Experiment 1. Before the experiment, the
FIGURE 10 Device for recording contact pressure: (a) The NeXus‐10 device for biofeedback, neurofeedback or psychophysiological
research and (b) the force sensor with measuring contact pressure of a load cell connecting to the Nexus‐10 device
FIGURE 11 Experiment 2: Grip force: (a) Each handle was used to perform a grip force task for 15 s. Pressure sensors were pasted on the
hand surface of the C, D, and E regions to measure hand pressure; (b) after the regions C, D and E were completed, the pressure data were
output via the BioTrace software
WANG AND CAI
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participant was asked to randomly pick the handle. The maximum
grip force was performed in the standing position for 15 s and the
maximum pressure value was recorded. A 5‐min rest was taken at
intervals and the pressure at the next site was measured. After the
pressure was computed in regions C, D, and E via the BioTrace
software (Figure 11b) the pressure at the D region (2.20 psi) was the
smallest, followed by the E (2.53 psi) and C (2.73 psi) regions.
3.4 |Data analysis
A repeated measure ANOVA with two within‐subjects factors as the
independent variables, namely, “handle shape”(cylindrical, elliptical,
and curved handle) and “region”(C, D, and E regions of the hand) and
one between‐subjects factors, namely, “gender”(male and female), as
the dependent variable, was used to compare the differential grip
forces of the handles.
3.5 |Results
3.5.1 |The contact pressure of the hand
Table 6shows the results of the grip forces for the three handles. The
overall grip force mean for males (2.93 psi) was higher than for fe-
males (2.05 psi). Holding the curved handle (1.99 psi) produced the
smallest hand pressure, followed by the elliptical handle (2.51 psi)
and the cylindrical handle (2.96 psi). The pressure at the D region
(2.20 psi) was the smallest, followed by the E (2.53 psi) and C
(2.73 psi) regions.
Figure 12 shows the results of the pressure of the hand for the
nine handles. The global MANOVA for grip forces showed that both
the handle shape and region had the main effects (F[2,20] = 20.31;
p< .001, ε= .96 and F[2,20] = 12.53; p< .001, ε= 1, respectively), but
there was no interaction between them (p= .46). The pairwise com-
parison indicated that males had significantly greater hand pressure
than females (p< .001, Figure 12a). The participants using the curved
handles had significantly lower hand pressure than those using the
cylindrical and elliptical handles (p< .001 and p< .01, respectively,
Figure 12b). However, there was no difference in hand pressure
between those using the cylindrical and elliptical handles (p= .12). In
addition, the hand pressure in the D region was less than in the C and
E regions (both p< .01, Figure 12c). Nevertheless, there was no dif-
ference in hand pressure between the C and E regions (p= .37).
4|DISCUSSION
4.1 |Handle design for fitting to the human hand
This study attempted to find a new measurement approach to con-
struct a tool handle with a curved shape based on a contour gauge and
test handle performance and comfort ratings. The shape of the curved
handle was a better fit for the human hand than the cylindrical and
elliptical shapes of the handles that have been developed by
previous studies (Cochran & Riley, 1986; Lemerle et al., 2008;
Putz‐Anderson, 1988; Rossi et al., 2012; Seo & Armstrong, 2008,2011;
Welcome et al., 2004). The curved handle increased the user comfort
rating. The handle design for fitting to the human hand can provide
stability when holding the handle and prevent finger sliding and rota-
tion of the handle in operation.
The experiment found that there were many areas of handles
that did not fit the human hand when holding the cylindrical and
elliptical handles. We estimated that these handles without mapping
hand shapes squeeze the fingers or palm when operating. In the
shape of the newly designed handles (see Figure 3), the right side of
the handle (G curved line) has a convex shape to fill the vacancy of
the thenar area when the thumb flexes to grip the handle. The large
arc (E curved line) was designed for the four flexed fingers. In addi-
tion, the handle shape on both sides (F curved line) has a slight
convex shape that can support the push pressure on the center of the
palm. Because the palm was the main contributor to handle force
(Rossi et al., 2012), the participants used the palm to push; the area
near the thenar region of the thumb might exert higher extrusion and
pressure in push force tasks. Therefore, the convex shape of the
design handle could provide a force‐supporting area, especially the
palm, and reduce pressure.
The overall appearance of the curved handle in this study is a
symmetrical shape to allow for use with both hands. To compare with
the anatomical shape of handles in previously developed methods
(Harih & Čretnik, 2013; Harih & Dolšak, 2013,2014), this
TABLE 6 The overall means of grip forces for cylindrical, elliptic,
and curved handles on the C, D, and E regions of the hand (unit: psi)
Items nMean SD
Gender Males 6 2.93 0.21
Females 6 2.05 0.13
Cylindrical handle 2.96 0.89
Elliptic handle 2.51 0.65
Curved handle 1.99 0.50
C region 2.73 0.69
D region 2.20 0.61
E region 2.53 0.74
Cylindrical handle C region 3.15 0.86
D region 2.57 0.82
E region 3.16 0.99
Elliptic handle C region 2.74 0.70
D region 2.24 0.58
E region 2.56 0.67
Curved handle C region 2.30 0.52
D region 1.80 0.43
E region 1.88 0.55
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WANG AND CAI
symmetrical handle was more generalized and can be used by a wider
target population for a wider range of tasks. This symmetrical con-
sideration was consistent with the suggestions of Harih (2014). Our
symmetrical handle only lost the shape of the thumb groove, which
had no effect on the participant's push force and comfort. To achieve
the smooth surface of the handle in this study, a profile gauge was
used to measure the complex surface topography of the hand. This
method of measurement can retain the importance of the outline of
the hand and reach a more generalized shape without depressions
and small topological details.
4.2 |Relationship of hand length and comfort/
discomfort
Users should grasp a handle that fits their hand to provide better
muscle length to perform push force tasks. The handle size to max-
imize subjective comfort is defined by the user's hand length (Kong &
Lowe, 2005). In this study, participants with small hands benefit from
using a smaller handle, and participants with large hands benefit from
using a larger one. The result of the push forces showed a decreasing
tendency when smaller hands were extended to grasp larger handles;
conversely, larger hands were more flexed as the handle size de-
creased. For smaller hands, when pushing large handles, their fingers
were more extended to produce relative muscle length, which may
easily cause uncomfortable reactions. Because their fingers lack the
mechanical advantages of a lever, it is hard to exert more force. For
large hands, when pushing small handles, the finger flexion results in
skin folding and reduced contact with the handle. These results are
consistent with previous research (Blackwell, Kornatz, & Heath, 1999).
Males have larger hand length than females in the anthropo-
metric measurements. Gender has previously been described as an
important independent predictor of hand strength (Angst et al., 2010;
Janssen, Heymsfield, Wang, & Ross, 2000; Liao, 2016; McGee
et al., 2019). There is a positive correlation between hand length and
push force. Participants with large hands had the greatest push for-
ces, followed by medium hands and small hands. Participants with
small hands were more likely to be females who had a lower force
capability, which may be the main reason that the capacity of push
force is produced by the agonist muscles of the hand that complete
the action of the muscles. Habes and Grant (1997) concluded that the
relationship between the force output of an exertion and muscle
activity is not constant—the relationship can be affected by muscle
length. We inferred that there is a positive relationship between the
hand length and muscle length because there is evidence that the
mass of skeletal muscle is significantly greater in men than in women,
and the difference in upper limbs is greater. Janssen et al. (2000)
stated that skeletal muscles in men account for nearly 40% of their
body weight and in women, only 30%. The large hands with greater
muscle cross‐sectional areas resulted in larger muscular strength
than the others. Therefore, the muscles for large hands are more
developed, and the relatively higher power consumption produces
better push force.
In addition, participants rated the handles fitting their hand
lengths as the most comfortable for push force exertions. This result
was not consistent with the results of Kong and Lowe (2005), where
the mid‐sized handles were the best for pushing force tasks. A tool
handle should be designed for different size hand lengths to max-
imize force capability for each hand. Participants with large, medium,
and small hands should select a tool corresponding to one of the
large, medium, and small sizes to obtain maximum force with the
highest benefits. The overall result indicated that the curved handle
design could improve the operator's work performance and hand
comfort.
FIGURE 12 The results of the pressure of hand for the nine handles. The MANOVA results for the pressure of hand show that: (a) males had
significantly greater hand pressure than females did, (b) the participants using the curved handles had lower hand pressure than those using the
cylindrical and elliptical handles and (c) the hand pressure in the D region was less than in the C and E regions. MANOVA, multivariate analysis
of variance
WANG AND CAI
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4.3 |Relationship between push force and comfort/
discomfort
Maintaining the maximum push force for 15 s may cause fatigue and
decrease strength over time. In observing the change in force, the max-
imum push force can be reached immediately at the beginning (about
5–10 s). After that (approximately 11–15 s), strength did not increase and
may cause muscle fatigue. Therefore, each trial provided enough rest
time to reduce muscle fatigue; the participants were asked whether they
had recovered or continued to rest before proceeding to the next trial.
The palm is the main contributor to push force; fingers are the
auxiliary power and support the handle stability. In this study, the LPD
scale was based on and modified after Vink and van Eijk (2007). In
their study, the participants were asked to fasten screws, followed by
rating the discomfort in one of the regions. In addition, Groenesteijn
et al. (2004) and Kuijt‐Evers et al. (2007) measured the discomfort
with pliers and handsaws, respectively, using the LPD method. All of
them assessed the discomfort of the palm and fingers. Compared to
push force, twisting and shearing are finer moves using screwdriver
and pliers, respectively. Therefore, the LPD scale was divided into
many regions for finger evaluation. Although, these manual tools had
different uses and directions of force, pressure, feelings of pain,
tiredness and numbness cause hand discomfort (Groenesteijn
et al., 2004). Any discomfort during push force would affect the per-
formance of the push force and the evaluation of the handle.
Application of high push force responds to comfort. Handle
shape, specifically the curved handle, affects working performance.
The push force was highest for curved handles, which were rated as
the most comfortable, followed by the elliptical handles and cylind-
rical handles. The push force was the lowest for cylindrical handles
that were subjectively assessed as less comfortable. These results are
similar to previous studies (Das et al., 2005; Eikhout et al., 2001;
Kuijt‐Evers et al., 2007), which found a positive relationship between
push force and comfort. Moreover, during the experiment, the par-
ticipants had better impressions of the curved handles, which also
had high push force, showing that the performance of push force
depended on the handle shape. Therefore, push force was achieved
with curved handle that had higher comfort; in contrast, a handle
that caused discomfort resulted in lower push force.
4.4 |Relationship between hand forces and contact
pressure distributions
The curved‐shape handle can increase the contact area between the
hand and the handle. Previous studies have shown that the magni-
tudes of peak pressure of the contact area depend upon the handle
size, grip, and push forces (Aldien et al., 2005). The shape of the
handle is also a factor that affects hand pressure. The palm for
pushing is the major contributor to the handle, and the grip force
concentrates the pressure at the thenar area of the thumb (Aldien
et al., 2005). Pushing the cylindrical and elliptical handles, the palm
(zone C, D, and E) caused a more uncomfortable reaction than other
areas. The result was consistent with the findings of previous studies
(Das et al., 2005; Dong, Wu, Welcome, & McDowell, 2008; Eikhout
et al., 2001; Kuijt‐Evers et al., 2007; Rossi et al., 2012). Because the
palm contains important blood vessels, including the ulnar artery,
other arteries, and nerves, it is particularly sensitive to pressure
(Sanders & McCormick, 1993). The palm plays an important role in
hand force, contact pressure, working performance, and comfort.
Different shapes of handles affect the contact force distribution of
grip force. Better contact area depends on the consistency between
the hand curvature and handle shape. Curved handles could reduce
hand pressure more than cylindrical and elliptical handles. The con-
tribution of the thenar area (zone E) to the total contact force was
highest after the metacarpals (zone C). This is similar to the findings of
Aldien et al. (2005). The curved handle with a bulged shape corre-
sponds to the palm position to disperse the contact pressure of the
hand and increase the contact area. The cylindrical and elliptical
handles without the curved shape might concentrate the localized
pressure on the palm and result in uncomfortable responses and ATD
(e.g., vibration diseases, overuse injuries, and pressure ulcers).
5|CONCLUSIONS
This study presented a novel approach to tool handle design and
development based on measurements of hand shape using a contour
gauge. It was possible to develop and manufacture a best shaped tool
handle for users. The newly developed handles in the grip force tasks
have the highest push performance and the best comfort ratings
compared to traditional cylindrical and elliptical handles. Regarding
the definition of the term “performance,”we believe that perfor-
mance in this study is based on two main measures: (a) Push/grip
performance of the handle and (b) comfort level. Several factors in-
fluence the comfort ratings of handles: (a) Shape of the tool handle
that fits the hand, (b) a correctly shaped handle increases comfort
perceptions when pushed, (c) a higher comfort rating provides higher
push force, (d) increasing the contact area can reduce hand pressure,
and (e) other advantages: such as improving the user's visual eva-
luation of the handle, having a market segmentation differing from
other handles, and so on. All of these positive relationships are im-
portant for developing a comfortable tool handle.
ACKNOWLEDGMENT
This research was supported by a grant from the National Science
Council, Taiwan, to Ching‐Yi Wang (106‐2813‐C‐036‐011‐E).
ORCID
Ching‐Yi Wang http://orcid.org/0000-0001-8142-5796
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How to cite this article: Wang C‐Y, Cai D‐C. Hand tool handle
size and shape determination based on hand measurements
using a contour gauge. Hum Factors Man. 2020;1–16.
https://doi.org/10.1002/hfm.20846
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