Proceedings of the 2020 IEEE/SICE
International Symposium on System Integration
Honolulu, Hawaii, USA, January 12-15, 2020

Lower-limb moments during sit-to-stand movement with different
handrail grip position and trunk tilt angle
Chongyang QIU1 , Shogo OKAMOTO1 , Yasuhiro AKIYAMA1 , and Yoji YAMADA1

Abstract— Reducing the burden on the lower-limb joint can
improve the quality of life for individuals who encounter difﬁculties in sit-to-stand movement due to weak lower limbs. This
research compared several conditions in which the handrail
grip position and the trunk-tilt angle differed in terms ofthe moments of the lower-limb joint. It was determined thatthe maximum reduction of hip moment occurred when theparticipants stood up from an erect sitting posture with the grip
position above the great trochanter. The maximum reductionof knee moment was observed when the participants stoodup at a tilt angle of 30◦ with the grip position above thegreat trochanter. In contrast, the participants preferred anothercondition whereby the upper body was tilted 30◦ and thehandrail grip position was located beneath the chest. Moreover,
two types of strategies for handrail use were observed among
the participants. In one strategy, the handrail is primarily used
when the gluteal region separates from the chair’s surface. In
another strategy, the handrail is used during the entire STS
movement. These results aid in the determination of the optimal
conditions required for handrail use.

I. INTRODUCTION
Sit-to-stand (STS) movements are an important daily activity in addition to walking and stair-climbing. In recent
years, with the aging of the general population, there has
been an increase in the number of individuals who encounter
difﬁculties in performing STS movement due to hypokinesia
or knee diseases. There is a deterioration in the quality oflife if these movements cannot be easily performed or if
pain is experienced during motion. Hence, the investigationof the burden on lower-limb joints during STS movement
can potentially contribute to the development of a supportive
environment for affected individuals.
To date, numerous studies have been conducted to investigate the moments of lower-limb joints during STS
movements [1]. Rodosky et al. and Burdett et al. investigatedthe moments of lower-limb joints during STS movement
for chairs of different heights [2], [3]. They determinedthat a higher chair could result in lower joint moments.
Fleckenstein et al. investigated the relationship between theinitial angle of the knee joint to the moment of the hip
joint. It was determined that the maximum hip joint moment
was larger when the initial knee ﬂexion angle was 75◦ ,compared to the initial knee angle of 105◦ [4]. Gilletteet al. investigated how the position of the feet inﬂuenced
the moments of the lower-limb joints [5]. Ankle and knee
moments signiﬁcantly increased when a foot was positioned*This study was in part supported by MEXT Kakenhi (19K21584).
1 Department of Mechanical Systems Engineering, Nagoya University,Japan

978-1-7281-6667-4/20/$31.00 ©2020 IEEE

Fig. 1. Grip position, center of gravity (COG) of body and base of support

in the posterior position compared to the anterior position.
Schenkman et al. discovered that the momentum generated
by the forward ﬂexion of the upper body prior to seat-off
was transmitted to the lower limbs in the next phase [6].
Those suffering from knee OA do not take advantage of such
upper body momentum [7]. Doorenbosch et al. performed anexperiment whereby participants in an erect sitting positioned
ﬂexed their upper body forward as far as possible and thenstood up. This resulted in a smaller knee moment whencompared to the normal STS movement [8]. Shepherd etal. concentrated on the initial tilt angle of the upper bodyand they determined that with the increase of the initial tilt
angle of the upper body, the duration of maximum support
moment increased [9]. Based on the aforementioned results,
standing up from higher chairs, increasing the initial knee
ﬂexion angle, placing the feet at an appropriate position andexploiting the ﬂexion of the trunk are all able to reducethe burden of lower-limb joints during the STS movement.
These studies investigated STS movement without handrails
or other assistive tools.
Handrails are widely used to reduce the burden on thelower limbs. For example, Kinoshita et al. investigated the
optimum height, shape, and position of handrails [10], [11].
They determined that the use of low handrails led to anincrease in the maximum ﬂexion angle of the hip joint, knee
joint, as well as the trunk, and a combination of low andhigh handrails resulted in the largest decrease of the lowerlimb joint moments. Takeda et al. compared four types ofhandrails in a study that included pregnant women [12].
In the case of bilateral handrails, the participants tended
to apply additional weight and symmetric lower-limb joint
moments were observed during the experiments. Moreover,305

a discussion on the determination of the better side to seta handrail assuming a patient suffers from unilateral knee
osteoarthritis was presented [13], [14]. It was determined thata larger decrease of the maximum knee moment and greater
stability with a handrail set at the impaired side. O’Mearaet al. investigated the effects of a unilateral handrail during
STS movement and a larger knee moment was observed at
the side with the handrail, while the knee moment of theother side became smaller [15]. These studies focused on
the height, shape and lateral position of handrails. Someof the earlier reports are in disagreement with each other,resulting in continuing debates and discussions. Katsuhira etal. investigated the effects of different grip positions on ahandrail during natural STS movement and found that theposition above the great trochanter resulted in the smallest
knee and hip moments [16]. According to these studies, it
is evident that handrails can reduce the burden on lowerlimb joints during STS movement. However, there are many
associated parameters that should be considered. To date,there is no general consensus on the effective utilization ofhandrails.
Based on previous studies on STS movement with orwithout handrails, it has been determined that grip positionon the handrail and the trunk-tilt angle both signiﬁcantly
inﬂuence the lower-limb joint moments. However, there
are few studies in which the grip position and trunk tilt
angle are simultaneously controlled. This research compares
several conditions whereby the grip position on the handrail
and trunk tilt-angle differ. The objective is to specify STS
movements that minimize the burden on the lower limbs.
From a mechanical perspective, as shown in Fig. 1, thetotal moment of the lower-limb joints decreases if the centerof gravity (COG) of the body and the grip position are
horizontally close to the base of support. In comparison,
the hip joint moment decreases if the COG and the grip
position are close to the hip joint. Moreover, healthy andyoung individuals can rapidly tilt their trunks forward andexploit the reactive moment around their hips to stand up
using smaller muscular contractions of their lower bodies [6];however, the present report does not address such dynamic
STS movement.
II. METHODS
A. Participants
Five healthy male (25 ± 6.2-year old, 174.6 ± 1.7 cm,
59.2 ± 2.2 kg) participated in the experiment. None ofthe participants had a history of diseases that affected STS
movement and they were informed of the signiﬁcance andobjective of the investigation prior to the experiment.
B. Settings
As shown in Fig. 2, a height-adjustable chair was usedin this experiment and its height was adjusted to be thesame height as that of each participant’s knee. One handrail
was set at each side of the chair with a separation distanceof 0.7 m. They were adjusted to the height of the greater
trochanter when the participants were in a standing posture.

Height adjustable handrail

Force sensor

Goniometer
Force plate
Fig. 2.

A
Fig. 3.

Settings of STS experiment

B

C

D

Schematic showing the four conditions used in the experiment

The force applied to the handrails was measured using
internal force sensors (PFS055YA251G6, Leptrino, Japan),while the ground reaction force was measured using a force
plate positioned under each foot. This plate consisted of four
load cells (FX1901, TE Connectivity, USA). The angles of
the ankle and knee joints of each lower limb were measured
using two goniometers (SG series, Biometrics Ltd., UK). A
pressure sensor (FSR-406, Interlink Electronics, USA) was
positioned under the chair to determine the instance of seatoff. Prior to standing up, the participants were instructed toadjust their knee joints at a ﬂexion of 90◦ and the distance
between their feet was set as the same distance as thatbetween their acromion. In addition, they were not allowed
to move their feet during the trials. Moreover, to control the
posture of their head, a mark was set at a height of 1.7 m
and at a distance of 3 m in front of the chair. Participants
were instructed to look at the mark all the time during the
STS movement.
C. Tasks
Every participant performed STS movement under four
conditions. As shown in Fig. 3, in condition A, the grip
position was above the greater trochanter and participants
stood up from an erect sitting position. Under this condition,
the grip position and the COG of the upper body were
extremely close to the hip joint. Condition B also required
participants to grip the position above the greater trochanter,but with a trunk-tilt angle of 30◦ . Under this condition, thegrip position was near the hip joint while the COG of the
body was within the base of support. For condition C, thegrip position was above the ankle joint and the trunk-tilt

306

Normalized ankle moment(Nm/kg/m)

angle was 30◦ . The grip position and the COG of the body
were both within the base of support under this condition. For
the control group, condition D required the participants tostand up from the initial tilt angle of 30◦ , similar to condition
B and C. However, their arms were folded across their chestin this case. Under all the conditions, the participants were
instructed to not ﬂex their trunk any further until they left
their seats. The trunk-tilt angle was aligned with referencemarks on the wall beside the participant. Also, the initial
trunk-tilt angle was monitiored by an experimenter for eachtrial. The speed of the movement and the force applied tothe handrails were determined by the participants provided
that they could perform these tasks naturally. Moreover,the four conditions were implemented in random orderand the STS movement was repeated eight times for eachcondition. Hence, a total of 32 trials were performed by eachparticipant. At the end of the experiment, all the participants
were questioned to determine the most comfortable condition
among the aforementioned four.

Condition A
Condition B
Condition C
Condition D

0.3

0.2

0.1

0

20

40

60

80

100

80

100

80

100

% of cycle

Normalized knee moment(Nm/kg/m)

1
0.8
0.6
0.4
0.2

0

20

D. Data Analysis

40

60% of cycle

Fr
g

(1)

Mj
Wef f × H

(2)

Wef f = W −Mjnorm =where Wef f represents the effective weight, W represents
the actual weight, Fr is the handrail reaction force, Mjnorm
is the normalized joint moment, Mj represents the actual internal joint moment, H represents the height of participants,
and g is the acceleration due to gravity.
III. RESULTS
The internal joint moments of one participant are shownin Fig. 4 as a representative result. Under all conditions, themaximum of the lower-limb joint moments was observed
immediately after leaving the seat. For the knee moment,
condition B was the smallest for nearly all the cycle. Regarding the hip moment, condition A was the smallest, while
condition B was the largest. These results were calculated as
the mean of all the trials for one participant.
The mean values of the maximum lower-limb joint moments of all participants are shown in Fig. 5, as well as
the standard errors among the participants. Using two-way

0.8

Normalized hip moment(Nm/kg/m)

The experimental data were obtained at a sampling rateof 50 Hz. The data during the period of the seat-off to theinstance when the knee joint was at a ﬂexion of 10◦ werenormalized to 100% of the task and analyzed. The static joint
moments of ankle, knee and hip during the movement were
calculated in this study provided that the effects of inertia
were relatively small. The force applied to the handrails differed for each individual, and thus it was difﬁcult to compare
the results for all the participants. Therefore, the effective
weight was determined by subtracting the component of theweight supported by the handrails from the actual weight ofthe participants. Thus, the joint moments were normalized by
the height and effective weight of each participant as follow:

0.6

0.4

0.2
0

20

40

60

% of cycle
Fig. 4. Representative ankle joint moment, knee joint moment, and hip
joint moment

ANOVA in which the factors were the participants and theconditions of the STS movement, signiﬁcant differences wereobserved among the conditions for all the joints. Therefore,
as a post hoc analysis, we compared the joint moments for
two of the three conditions using two-way ANOVA for eachjoint.
The conditions of the STS movement signiﬁcantly inﬂuenced the maximum knee moment among the three conditions (F (2, 105) = 29.9, p < 0.001; interaction p <0.001). The maximum knee moment for condition B was thesmallest among the three conditions (B vs. A: F (1, 70) =43.2, p < 0.001; B vs. C: F (1, 70) = 44.1, p < 0.001).
However, there was no statistically signiﬁcant difference
between conditions A and C (F (1, 70) = 0.05, p = 0.83).
Moreover, considering the interaction effects, no statisticallysigniﬁcant difference was observed between conditions B
and C for two participants, and among three conditions foranother participant.
The effects on the maximum hip moment were also determined to be statistically signiﬁcant (F (2, 105) = 28.6, p <0.001; interaction p < 0.001). The largest reduction wasobserved for the maximum hip moment under condition

307

Joint moment (Nm/kg/m)

1.2

1

0.8

0.6

0.4

0.2

0

Ankle

Knee

Hip

Handrail reaction force normalizedby body weightFig. 5. Maximum joint moments under the four different conditions. The
mean and standard errors among the participants. Two-way ANOVA wasused to test for the effects of conditions and participants. Asterisks ***indicate a signiﬁcance level of 0.001.

0.5
A
B
C

0.4

0.3

0.2

0.1

0

Maximum

Mean

Fig. 6.
The maximum and mean handrail reaction force under threedifferent conditions. The mean and standard errors among the participants.
Two-way ANOVA was used to test for the effects of conditions andparticipants. Asterisks ** and *** indicate the signiﬁcance level of 0.01
and 0.001, respectively.

A (A vs. B: F (1, 70) = 54.2, p < 0.001; A vs. C:
F (1, 70) = 32.4, p < 0.001). However, the effects did notseem to be statistically signiﬁcant for conditions B and C(F (1, 70) = 1.9, p = 0.17). For the interaction effects, nosigniﬁcant difference was observed between conditions A
and C for one participant, and among all three conditions
for another participant.
The conditions signiﬁcantly inﬂuenced the maximum of
the ankle moment as well (F (2, 105) = 11.5, p < 0.001;
interaction p < 0.05). The maximum for condition A wasthe smallest (A vs. B: F (1, 70) = 15.2, p < 0.001; A
vs. C: F (1, 70) = 22.8, p < 0.001) and there was no
statistically signiﬁcant difference between condition B and C(F (1, 70) = 0.9, p = 0.36). However, regarding the resultsfor each participant, for two individuals, the maximum ankle
moment was the largest under condition A. Hence, a deﬁnite
conclusion cannot be made with regards to the effects of theconditions on the ankle moments.
On average, condition B yielded the smallest knee mo-ments, followed by condition A and C. Condition A resulted
in the smallest hip moments, followed by condition B andC.
During the entire STS movement, the direction of thehandrail reaction force was almost upward and the horizontal
component was extremely small. The maximum and meanvalues of the handrail reaction forces under the three conditions during the STS movement are shown in Fig. 6. In
this case, the handrail reaction force was the sum of two
handrails. The participants tended to apply larger forces tothe handrails under condition A in terms of the maximum(A vs. B: F (1, 70) = 29.9, p < 0.001; A vs. C: F (1, 70) =121.2, p < 0.001) and mean (A vs. B: F (1, 70) = 12.0, p <0.001; A vs. C: F (1, 70) = 9.9, p < 0.01). No statisticallysigniﬁcant difference was observed between condition B andcondition C.
The handrail reaction force of the ﬁve participants can belargely divided into two patterns as shown in Fig. 7. For type
1 (2 individuals), during almost the entire cycle the force
applied to the handrails was the largest under condition A,
while the smallest under condition C. Moreover, considering
condition A and B, the value at 0% of the cycle was relatively
small compared to type 2. It decreased by approximately 1/5
at 50% of the cycle but did not decrease to zero at 100% of
the cycle. In contrast, the feature of type 2 (3 individuals) wasthat a large force was applied to the handrails at the instanceof seat-off and the handrail reaction force under condition C
was the largest after 30% of the cycle. Regarding condition
A and B, it decreased to less than half at 50% of the cycle
and was nearly zero at 100%.
Furthermore, the COP trajectories in the anterior-posterior
direction under condition A of these two patterns are shownin Fig. 8. The COP position of type 1 was close to the heel,and moved slowly during the entire cycle. In the case oftype 2, it was relatively far behind the heel at the beginning,then quickly moved across the heel and almost reached theposition of the ankle at the end of the cycle.
All ﬁve participants acknowledged that performing the
STS movement under condition C was the easiest. In contrast, four participants selected condition A was the hardest
while one participant selected condition B.
IV. DISCUSSION
For every condition, the maximum of the joint moment
was observed almost immediately after leaving the seat.
Hence, the posture right after seat-off is discussed. Thebalance of the single joint moments can be expressed by
the formula (3) as follows:
Mj + Mg + Mr − I θ̈ = 0(3)

where, Mj represents the internal moment of the joint,
Mg represents the moment generated by the regions of the
body over the joint in question, Mr represents the moment
generated by the handrail reaction force, and I θ̈ is therotation moment of the regions of the body over the joint
in question, respectively. In this experiment, the rotation
moment is relatively small and not taken into consideration.

308

Handrail normal reaction force
normalized by body weight

Condition A
Condition B
Condition C
Condition D

0.4
0.3
0.2
0.1
0
-0.1
0

20

40

60

80

A

100

Handrail normal reaction force
normalized by body weightC

Fig. 9. Forces and joint moments for three conditions (Fr : handrail reaction
force, G: gravity force of the trunk, Mh : hip joint moment, Mk : knee joint
moment)% of cycle(a) Type 1
0.5
0.4
0.3
0.2
0.1
0
-0.1
0

20

40

60

80

100

% of cycle(b) Type 2
Fig. 7.

Position of COP to the heel (cm)B

Example of two types of handrail reaction forces
Condition A of type 1
Condition A of type 2

10

6

2
Heel
-2

-6

-10

0

20

40

60

80

100

% of cycle
Fig. 8. Example of two types of COP offset under condition A. A positive
value indicate that the COP is in front of the heel, while a negative value
indicates that it is behind the heel.

Firstly, we discuss the differences in the maximum hip
moments among the conditions. As shown in Fig. 9, for conditions B and C, the COG of the upper body is horizontallynear the ankle joint because of the 30◦ forward ﬂexion. Given
that the COG of the body is far away from the hip joint, alarge magnitude of the moment is generated. In the case of
condition A, the moment generated by gravity is very small
when considering the short distance between this force andthe hip joint. The experimental results are consistent with
our expectation and the hip moment was the smallest forcondition A. Furthermore, the grip position is far away fromthe hip joint under condition C, which generates a relatively
large moment when compared with condition B, and results
in a great compensation for the moment generated by gravity.
Therefore, the hip moment in the case of condition C was

expected to be smaller than that for condition B. However,no signiﬁcant difference was observed between these two
conditions in the experiment.
Secondly, the maximum knee moments are discussed. The
moment generated by gravity is the largest for condition A
due to the long distance between the COG of the upper
body and the knee joint. Comparing conditions B and C,
the point of the handrail reaction force for condition B isfurther away from the knee joint, thus resulting in a larger
reaction moment. Therefore, the maximum knee moment forcondition B is the smallest among the three conditions, whichis consistent with the results of the experiment.
Moreover, the use of the handrail differed among participants during the STS movement. According to the two typesof the reaction force curve and COP trajectory shown in
Fig. 7 and Fig. 8, two strategies for use in the STS movement
under condition A and condition B are proposed. Strategy 1
is described as supporting the body with handrails as longas possible. This strategy is effective for reducing the joint
moments of the lower limbs during the entire period of the
STS movement. Furthermore, this also results in a small andslow movement of the COP as represented by the solid curvein Fig. 8. However, the participants who used strategy 2tended to apply a strong force to the handrails when their hipleft the seat and the COP quickly moved from the posterior
position to the anterior position. As such, the handrails wereused to reduce the maximum hip moment needed during seatoff and to make it easier to leave the seat.
For most participants, the smallest hip moment occurredunder condition A, while the smallest knee moment wasobserved for condition B. However, according to the answers
from the participants, condition C was subjectively regarded
as the easiest. These results suggest that subjectively easy
STS movement is not realized by minimizing the momentof single joints, which is similar to the conclusion given
by Chihara et al. [17]. In condition C, the grip position
was above the ankle joint, and the trunk was tilted 30◦
forward. Therefore, the grip position and the COG of the
body were always within the base of support during the STS
movement. As a result, the participants were freely able tocontrol the force applied to the handrails until the end of the
STS movement with great stability. This is likely one of thereasons that condition C was perceived to be the easiest for309

the performance of the STS movement.
V. CONCLUSIONSIn this study, the effects of grip position on handrails andthe trunk-tilt angle were investigated during STS movement
for the use of bilateral handrails. While the importanceof these parameters were known in the earlier studies,
their combinations have not been thoroughly studied undercontrolled settings. Throughout the experiment, lower-limb
joint moments were compared among three conditions fordifferent grip positions and trunk-tilt angles. The condition
where the grip position was above the greater trochanter andparticipants stood up from an erect sitting position resulted
in the smallest hip joint moment, while the condition where
the grip position was above the greater trochanter but witha trunk-tilt angle of 30◦ resulted in the smallest knee joint
moment. The subjectively easiest movement occurred under
the condition where the grip position was above the ankle
joint and the trunk-tilt angle was 30◦ . The results facilitate
the determination of the optimum conditions such that theburden on the lower limbs is minimized.

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