J Rehabil Health Sci 2015; 13: 1-5Ⓒ 2015 Osaka Prefecture University

Journal of Rehabilitation and Health Sciences
Online ISSN 2185-8004

Original Article

Coordination between Trunk and Ankle during Sit-to-stand Task
in Healthy Young Subjects
Abbas Abdolrahmani† and Ryo Yonetsu
Graduate School of Comprehensive Rehabilitation, Osaka Prefecture University, 3-7-30 Habikino, Habikino-city, Osaka 583-8555, Japan
Received 8 October 2014; accepted 17 August 2015

Sit-to-stand (STS) requires inter-segmental coordination between the upper body and lower limbs to shift
the bodyʼs center of mass forward and upward, while also maintaining balance over the small base of support. Specifically, coordination between the trunk and ankle might be important to perform STS more efficiently. The present study aimed to determine the interaction between the trunk and ankle during an STS
task. Fifteen healthy young subjects participated in this study. To assess the STS task, we used a motion analysis system with 4 cameras that were synchronized to a force plate. Five trials were recorded for each subject, who performed the task at slow speed to mimic the STS of persons with disabilities. The mean and standard deviation values were calculated for the total STS task duration and the percentage of total task time atwhich the kinematic events occurred, including initiation of ankle dorsiflexion (DF) and plantar flexion (PF),maximum angular movement of trunk forward inclination (FI) and ankle DF, maximum angular velocity oftrunk FI and trunk backward inclination (BI), and lift off (LO). The total duration of the STS task was 3.30 ±0.30 seconds. The initiation of ankle DF (29.5 ± 8.4%) and maximum angular velocity of trunk FI (29.9 ±
7.2%) occurred simultaneously before LO. In addition, the maximum angular velocity of trunk BI (64.7 ±
7.9%) occurred at the same time as the initiation of ankle PF (64.7 ± 6.6%). A significant positive correlation
was found between the maximum angular velocity of trunk FI and initiation of ankle DF (r ＝ 0.89, p < 0.01),
and between the maximum angular velocity of trunk BI and initiation of ankle PF (r ＝ 0.49, p < 0.01). Thesefindings indicate that inter-segmental interaction between trunk and ankle motions might help healthy young
subjects perform STS with more effective LO and achieve sufficient balance after LO.
Key words : sit-to-stand task; inter-segmental interaction; trunk motions; ankle motions

1 Introduction
Sit-to-stand (STS) task is a common skill of dailyliving and an important measure of physical function. Inability to effectively perform STS task can lead to dependence in daily activities among disabled persons 1. Thismechanically demanding task requires inter-segmental coordination between the upper body and lower limbs tocontrol the bodyʼs center of mass (CoM) while maintaining balance over the small base of support2-5.
According to basic kinematics, STS is initiated withtrunk forward inclination (FI) that brings the CoM forward, within the area supported by the feet6, 7. During thetrunk FI, ankle dorsiflexion (DF) stabilizes the feet on thefloor and also indirectly contributes to the angular acceleration of trunk FI8. In this manner, acceleration of trunk FI†

Corresponding author, Email: abas_rahmani@ymail.com

in the presence of feet stability generates the horizontal
momentum in the CoM prior to lift off (LO)9. As demonstrated by Yu et al.ʼs study, the CoM cannot achieve adequate horizontal momentum without ankle DF, which curtails the effective LO 10 . After LO, trunk backward
inclination (BI) coordinates the horizontal momentum of
the CoM to achieve quiet standing10. During trunk BI, ankle plantar flexion (PF) acts to stabilize the feet and assist
the trunk BI to decelerate the horizontal momentum8, 9, 11.
Inability to control the horizontal momentum of the CoM
results in forward falling when ankle PF is absence or insufficient9.
In terms of coordination, trunk motions (FI and BI)
might be complemented by ankle motions (DF and PF) togenerate the horizontal momentum of the CoM before LO
and to control this momentum after LO. Therefore, coordination between the trunk and ankle motions is an im-

2portant factor in the STS task to produce effective LO andachieve sufficient standing balance after LO. However,
the initiation of ankle motions and its relation with trunk
motions has not been fully clarified. Therefore, this present study aimed to determine the kinematic relationshipbetween trunk and ankle motions during STS task inhealthy young subjects. The findings of this study can beused in rehabilitation to improve the efficiency of STS
task in persons with functional disabilities.
2 Methods
2.1 Subjects
A convenience sample of 15 healthy students (9males, 6 females) with no history of neuromuscular disorders, and who were 20-22 years old, was selected for thepresent study. The average height and body mass index ofthese subjects were 166.8±5.8 cm, and 21.8±1.7 kg/m2,
respectively. This research study was conducted under theapproval of the ethics committee of the Osaka Prefecture
University (2012-PT11). The purpose of this study was
explained to each subject, and their written consent was
obtained.
2.2 Motion procedures
The subjects sat on a hard surface stool, which was
set to the height of the subjectʼs knee joint in the sitting
position. The size of the support surface of this stool was
30 cm wide×25 cm long.
Each subject performed the STS task barefoot andtheir arms were folded across the chest to minimize differences due to movement of the upper limbs. Both feet were
kept shoulder width apart. The task began with the subjectʼs trunk upright and in the vertical shank position. Subjects were asked to look forward and start the task withoutchanging the position of their feet. The task ended withthe subject standing motionless. The subjects performed
the slow task, as faster STS creates a shorter flexion phaseand less trunk flexion12-14. Moreover, the STS task in mostdisabilities is characterized by slow speed15, 16. Before datacollection, subjects practiced slow STS for approximately
5 minutes until they could smoothly perform the task. A
metronome was set at 40 beats per minute to maintain an
appropriate speed, needing to rise in 3 seconds.
2.3 Data analysis
To assess the STS task, we used a motion analysis
system (Kinema Tracer, Kissei Comtec) with 4 cameras(30 Hz) that were synchronized by 1 force plate (100 Hz)(TF-3040-A, Tec Gihan). Two cameras were placed on eachside of the subject, one perpendicular and one oblique tothe sagittal plane of the subjectʼs body. The force plate
was placed beneath the stool to measure the time at which
the subjects lost contact with the seat (Fig. 1). Ten reflec-

Fig. 1

Schematic view of the subjectʼs position relative to thecameras and force plate.

tive markers were placed bilaterally at the acromion process, greater trochanter, lateral tibial condyle, lateral malleolus and the lateral aspect of 5th metatarsal. All markers
had a 5 cm black base to maximize the contrast between
the marker and the subjectʼs skin. Five trials were recorded for each subject while rising at the practiced speed
without using metronome. Three trials with a total task
time closest to the mean total time were selected for eachsubject for analysis.
The sagittal angular movement and angular velocity
were calculated. All these data were normalized from the
beginning of the STS task (0%) to the endpoint of the STS
task (100%). The beginning of the STS task was represented by the time at which the magnitude of the horizontal velocity at the midpoint between the acromion markers
was more than 5% of its peak value8. The time at which
the magnitude of the hip extensionʼs angular velocity firstreached 0 m/s was considered to be the endpoint of the
STS task2. Accordingly, angular movement of the hip was
defined as between the line from the midpoint of acromion process to that of greater trochanter and the line fromthe greater trochanter to that of lateral femoral condyle.
The time at which the magnitude of the vertical force on
the force plate first reached its lowest point was defined as
LO. The task was divided into the before LO and after LOphases.
Regarding angular movement, angles that included
the trunk and ankle were collected. Several previous studies17-19 have demonstrated that healthy subjects exhibit
significantly different asymmetry during STS task. To
control the bias of bilateral asymmetric movement, anoriginal model was used to define each angular movement

3(Fig. 2). First, the midpoints between the bilateral reflective markers, which included the acromion process, greater trochanter, lateral tibial condyle, lateral malleolus andthe lateral aspect of 5th metatarsal, were set and each angular movement were calculated. Angular movement of
the trunk was defined as the angle between lines from the
midpoint of the acromion process to that of the greater
trochanter, and the vertical line through the midpoint of
the greater trochanter. In a similar way, angular movementof the ankle was defined as movement between the linefrom the midpoint of the lateral malleolus and that of lateral tibial condyle, and the line from the midpoint of thelateral malleolus to that of the lateral aspect of the fifth
metatarsal head. We then calculated the mean and standard deviation values for the total STS task duration andthe percentage of total task time at which the kinematic
events occurred, including the initiation of ankle motions,maximum angular movement of trunk FI and ankle DF,
maximum angular velocity of trunk motions and LO. In
this study, the initiation of DF and PF were especially difficult to identify accurately using the plot of the ankle angular displacement. We therefore used the angular velocity of ankle motion to define the initiation of ankle DF. The
time at which the magnitude of angular velocity of ankle
DF fell outside the mean ± 2 SD of 1 second of angularvelocity during the static initial posture was regarded as
initiation of ankle DF. Similarly, the initiation of ankle PF
was regarded as the time at which the magnitude of angu-

Fig. 2

The angular movement definition for each joint.

∠ A: Trunk, ∠ B: Ankle. Gray points represent the reflective
markers, and black points represent the midpoints between
markers on the bilateral acromion process, greater trochanter,
lateral tibial condyle, lateral malleolus and the lateral aspect offifth metatarsal.

lar velocity of ankle PF fell outside the mean±2 SD of 1
second of angular velocity during the static initial posture.
To determine the relation between trunk and ankle
motions, the movement pattern of each motion and timingof kinematic events were evaluated. Descriptive statistics
were obtained using SPSS version 23. A Pearsonʼs correlation coefficient was computed to assess the correlation between the percentages of total task time for the maximum
angular velocity of trunk motions and the initiation of ankle motions. A difference was considered statistically significant when the P-value was < 0.05.
3 Results
3.1 STS duration
The mean total time of the STS task was 3.30±0.30
seconds. The duration of the before and after LO phases
was 1.31±0.29 seconds and 1.98±0.25 seconds, respectively.
3.2 Kinematic events
Figure 3 illustrates the order of the kinematic events
during the STS cycle. The initiation of ankle DF (29.5±8.4%) and maximum angular velocity of trunk FI (29.9±
7.2%) occurred simultaneously before LO. In addition, themaximum angular velocity of trunk BI occurred at thesame time (64.7±7.9%) as the initiation of ankle PF (64.7±6.6%). Furthermore, trunk FI and ankle DF reached the
maximum angle after LO (39.6 ± 7.0%) at 42.9 ± 6.9%
and 54.3±6.9%, respectively.
There was a significant positive correlation between
the percentages of the total task time for the maximum angular velocity of trunk FI and the initiation of ankle DF

Fig. 3The order of kinematic events during the STS task.

Values are expressed as the mean percentage of the total task duration. PF; Plantar Flexion, Max; Maximum, V; Angular Velocity, BI; Backward Inclination, DF; Dorsiflexion, FI; Forward Inclination.

4

Fig. 4The correlation between trunk and ankle motions.

A) The correlation between the percentages (%) of the total task time for maximum angularvelocity of trunk forward inclination and the initiation of ankle dorsiflexion, B) The correlation between the percentages (%) of the total task time for maximum angular velocity of trunk
backward inclination and the initiation of ankle plantar flexion. DF; Dorsiflexion, Max; Maximum, V; Angular Velocity, FI; Forward Inclination, PF; Plantar Flexion, BI; Backward Inclination.

(r ＝ 0.89, p < 0.01) (Fig. 4A), and also between the percentages of the total task time for the maximum angularvelocity of trunk BI and the initiation of ankle PF (r ＝0.49, p < 0.01) (Fig. 4B).
4 Discussion
The purpose of this study was to determine the kinematic relation between trunk and ankle motions during
STS task in healthy young subjects. The subjects performed slow STS, which is typically observed in persons
with disabilities, such as cerebral palsy and stroke15, 16. In
this study, the mean total STS time for healthy young subjects was 3.30±0.30 seconds, which was slower than thatin other studies6, 13. However, the LO occurred at 39.6 ±
7.0%, which is similar to the results of pervious STS studies that used force plate to determine this event6, 20, 21.
Therefore, to determine the relation between trunk andankle motions, the STS task was performed in the same
STS pattern as in other studies.
The major findings of this study indicate that STS
task in healthy young subjects was performed using two
kinematic strategies of trunk and ankle interaction. The
first kinematic strategy was the similar timing for the initiation of ankle DF and the maximum angular velocity oftrunk FI, which was confirmed by a significant positive
correlation. As previously reported, trunk FI and ankle DF
produce horizontal CoM momentum during STS task, andthe ankle joints provide stability during the trunkʼs acceleration8, 9, 11. In Khelmani et al.ʼs study, the tibialis anteriorstabilized the feet and indirectly contributed to the angularacceleration of trunk FI8. In the present study, once trunk
FI reached its maximum angular velocity, the ankleʼs function changed from stability to mobility. Thus, the ankle
joints initiate DF to assist trunk FI in producing sufficient
CoM momentum, and this strategy might allow healthy
young subjects to LO from the seat more efficiently.
The second kinematic strategy was that the initiationof ankle PF occurred when the angular velocity of trunk
BI reached its maximum value, which was confirmed by asignificant positive correlation. The magnitude of the actual CoM momentum is generally greater than the required CoM momentum22, and this extra momentum mustbe limited to achieve adequate balance after LO23. In thismanner, interaction between trunk BI and ankle PF has
been reported as an important factor to control the CoM in
relation to the area supported by the feet. In this study, theankle reached maximum DF and remained unchanged forapproximately 10% of the STS task to provide stability
for trunk BI acceleration. Similar to the first strategy, theankleʼs function changed from stability to mobility once
trunk BI reached its maximum angular velocity. Therefore, using this strategy can help healthy subjects achievesufficient balance after LO. This interaction between trunk
BI and ankle PI has been supported by previous studies, inwhich backward movement of the shank decelerated thehorizontal momentum of the CoM after LO8, 10. In addition, similar to Schenkman et al.ʼs study, we observed thatthe maximum trunk FI angle and ankle DF angle occurred

5

after LO.
In this study, the kinematic strategies of the trunk andankle interaction were only observed during slow speed
STS and may not accurately reflect the interaction during
normal STS. Therefore, further STS studies using bothnormal and slow speeds are suggested to confirm our findings.
In conclusion, the inter-segmental interaction between the trunk and ankle motions might help young
healthy subjects produce sufficient horizontal momentum
in the CoM, and thereby achieve LO more effectively
during STS. Moreover, this interaction might be necessary
to control the CoMʼs momentum after LO, and thereby
achieve sufficient balance in the standing position.
References
1 Levitt S (2010) “Treatment of Cerebral Palsy andMotor Delay,” Wiley-Blackwell, New Jersey, pp.125259.
2 Schenkman M, Berger RA, Riley PO, et al (1990)
Whole-body movements during rising to standing
from sitting. Phys Ther, 70: 638-648.
3 Roebroeck ME, Doorenbosch CA, Harlaar J, et al(1994) Biomechanics and muscular activity during
sit-to-stand transfer. Clin Biomech, 9: 235-244.
4 Schultz AB, Alexander NB, Ashton-Miller JA (1992)
Biomechanical analyses of rising from a chair. J Biomech, 25: 1383-1391.
5 Riley PO, Schneckman ML, Mann RW, et al (1991)
Mechanics of a constrained chair-rise. J Biomech,
24: 77-85.
6 Pai YC, Rogers MW (1991) Speed variation and resultant joint torques during sit-to-stand. Arch Phys
Med Rehabil, 72: 881-885.
7 Shepherd RB, Gentile AM (1994) Sit-to-stand: functional relationship between upper body and lower
limb segments. Hum Mov Sci, 13: 817-840.
8 Khemlani MM, Carr JH, Crosbie WJ (1999) Muscle
synergies and joint linkages in sit-to-stand under two
initial foot positions. Clin Biomech, 14: 236-246.
9 Doorenbosch C, Harlaar J, Roebroeck M, et al (1994)
Two strategies of transferring from sit-to-stand: theactivation of monoarticular and bi-articular muscles.
J Biomech, 27: 1299-1307.
10 Yu B, Holly-Crichlow N, Brichta P, et al (2000) The
effects of the lower extremity joint motions on the
total body motion in sit-to-stand movement. Clin
Biomech, 15: 449-455.

11 Goulart FR, Valls-Solé J (1999) Patterned electromyographic activity in the sit-to-stand movement. J
Clin Neurophysiol, 110: 1634-1640.
12 Gross MM, Stevenson PJ, Charette SL, et al (1998)
Effect of muscle strength and movement speed on thebiomechanics of rising from a chair in healthy elderly and young women. Gait Posture, 8: 175-185.
13 Hanke TA, Pai YC, Rogers MW (1995) Reliability ofmeasurements of body center-of-mass momentum
during sit-to-stand in healthy adults. Phys Ther, 75:
105-113.
14 Vander Linden DW, Brunt D, McCulloch MU (1994)
Variant and invariant characteristics of the sit-tostand task in healthy elderly adults. Arch Phys Med
Rehabil, 75: 653-660.
15 Park ES, Park CI, Lee HJ, et al (2003) The characteristics of sit-to-stand transfer in young children withspastic cerebral palsy based on kinematic and kinetic
data. Gait Posture, 17: 43-49.
16 Faria CDCM, Saliba VA, Teixeira-Salmela LF (2010)
Musculoskeletal biomechanics in sit-to-stand andstand-to-sit activities with stroke subjects: a systematic review. Fisioter Mov, 23: 35-52.
17 Schofield JS, Parent EC, Lewicke J, et al (2013)
Characterizing asymmetry across the whole sit to
stand movement in healthy participants. J Biomech,
18: 2730-2735.
18 Gilleard W, Crosbie J, Smith R (2008) Rising tostand from a chair: symmetry, and frontal and transverse plane kinematics and kinetics. Gait Posture, 27:
8-15.
19 Lundin TM, Grabiner MD, Jahnigen DW (1995) On
the assumption of bilateral lower extremity joint moment symmetry during the sit-to-stand task. J Biomech, 28: 109-112.
20 Pai YC, Rogers MW (1990) Control of body masstransfer as a function of speed of ascent in sit-tostand. Med Sci Sports Exerc, 22: 378-384.
21 Etnyre B, Thomas DQ (2007) Event standardizationof sit-to-stand movements. Phys Ther, 87: 16511666.
22 Crosbie J, Herbert RD, Bridson JT (1997) Inter-segmental dynamics of standing from sitting. Clin Biomech, 12: 227-235.
23 Mourey F, Grishin A, dʼAthis P, et al (2000) Standing
up from a chair as a dynamic equilibrium task: acomparison between young and elderly subjects. J
Gerontol A Biol Sci Med Sci, 55: B425-431.