Background

Rehabilitation of elderly patients with sit-to-stand (STS) dysfunction includes retraining coordinated movement among participating body segments. Although trunk position is considered important, spinal movement has not been measured.

Objective

The aim of this study was to describe the sagittal thoracolumbar kinematics and hip-lumbar interaction during the STS task in elderly people who were healthy in order to guide physical therapists in developing treatment strategies.

Design

This was an observational study.

Methods

Ten retroreflective markers were attached to the midline thoracolumbar spine, pelvis, and right lower limb of 41 elderly people who were healthy. A 2-dimensional video analysis system was used to measure sagittal thoracic, lumbar, hip, and knee joint angles during the STS task. Maximal available flexion-extension angles in these joints and regions also were determined.

Results

Prior to buttocks lift-off, forward trunk lean comprised concurrent hip and lumbar flexion and thoracic extension. Hip flexion dominated, with a hip/lumbar ratio of 4.7:1 and a thoracic/lumbar ratio of 1.7:1. The hip and lumbar spine contributed 90% and 23% of their maximal available flexion angle, respectively, and the thoracic spine contributed 86% of its maximal extension range of movement. After lift-off, the hips and lumbar spine extended (ratio of 5.2:1), and the thoracic spine flexed (thoracic/lumbar ratio of 0.4:1). At lift-off, the hips and knees were similarly flexed (96°) and then locked together in a linear pattern of extension. Following lift-off, there was a brief transition phase (5% of STS duration) in which, although the hips, knees, and lumbar spine were extending, the trunk continued to flex forward a few degrees.

Limitations

Results may differ in elderly people who are less active.

Conclusions

The revised model for image-based analysis demonstrated concurrent hip and thoracolumbar movement during the STS task. Close to full available hip flexion and thoracic extension were needed for optimal STS performance.

During activities of daily living, such as standing up from a sitting position and walking, the thoracolumbar spine (trunk) and lower limbs act as an interdependent kinematic chain of joints. The concept of a series of related joints providing coordinated movement during functional activities and of movement at one joint being affected by and affecting movement at adjacent joints is familiar to clinicians.

The activity of rising from a sitting position is an essential prerequisite for walking and, therefore, functional independence.15 It has been reported that people who have difficulty rising to a standing position have greater likelihood of falling during ambulation68 and to need help with daily activities.9,10 Inability to stand up has been linked to death in elderly people.11,12

The sit-to-stand (STS) task is a complex activity, involving movement of all body segments from head to foot. The task requires sufficient joint mobility, lower-limb strength (force-generating capacity), and balance to enable the center of mass to be transferred forward and upward from the stable seated position to erect standing on a small base of support, the feet.1214 For optimal performance, each joint or body part must move the correct amount in the right direction and at the appropriate time. Rehabilitation of patients with STS dysfunction includes retraining of this movement interaction.2,15,16 However, the ability of the therapist to facilitate the STS movement effectively depends on a background understanding of the interaction of all contributing joints and body segments in people who are healthy (ie, the movement pattern).

A consequence of the aging process is a decline in the attributes required for successfully completing the STS movement. Deficits include lower-limb muscle weakness9,14,1720 and decreased balance.2124 The kinematics of this important task have been well documented with respect to duration, velocity, and acceleration of body segments,2527 as well as the kinematics and kinetics of the lower-limb joints.2830 Although trunk angle has been measured with respect to an external reference (eg, horizontal or vertical plane) and with respect to the pelvis,17,18 the sagittal contribution of the thoracic and lumbar regions to trunk movement has been largely ignored. This failure to provide information regarding the thoracolumbar kinematics during the STS task is due to the model of measurement used in previous 2-dimensional (2D) image-based studies in which the spine was considered a “rigid unit” defined by skin reference markers located on proximal and distal ends of the trunk segment, such as markers on the spinous process of the first thoracic vertebra (T1) and first sacral spine (S1),31 the acromion and mid-iliac crest,25,32 the scapula spine and sacroiliac joints,33 and the lateral glenohumeral joint and greater trochanter.27,34,35 Even recent 3-dimensional (3D) studies13,36 failed to include the spine in their STS analysis, using the rigid trunk marker placement of earlier gait studies.37 As a result, it has been concluded that the pelvis and spine act together as a functional unit during the STS task, with minimal movement in the spine or between the spine and pelvis.16(p131)

Although recently the sagittal contribution of the lumbar spine38 and of the thoracic spine and lumbar spine39 during the STS task in young individuals has been described, the sagittal hip-spine movement pattern during the STS task in elderly people who are healthy appears not to have been investigated.

Previous image-based studies have reported the range of knee and ankle movement required for optimal STS performance; however, the measurement of hip angle has largely been inaccurate due to the model of reference marker placement. Markers on the shoulder, greater trochanter, and knee have been used to measure both trunk angle17,24,40 and hip angle.27,35,41 As a valid hip angle requires markers to be located on the body segments immediately adjacent to the hip joint (ie, pelvis and femur), inclusion of the joints of the thoracolumbar spine in the shoulder-greater trochanter-knee model has confounded the sagittal hip measurement. In addition, no study has determined the proportion of full available flexion-extension angles in the hip, lumbar spine, and thoracic spine used by elderly people during the STS task. Knowledge of the amount of movement required by the participating joints during STS performance enables the therapist to predict the effect of stiffness in interfering with or causing compensatory movements in other joints or regions and to include appropriate mobilizing exercises in the treatment plan.

Therefore, the aim of this study was to use a revised model of reference marker placement and a 2D video motion analysis system to describe the sagittal kinematics of the thoracic spine, lumbar spine, and hip and knee joints during the STS task in elderly people who were healthy.

Method

Participants

As in a previous study by this team,39 a sample of convenience of 41 community-dwelling elderly people (22 female and 19 male) were recruited through newspaper advertisement. The participants had a mean (SD) age of 69.9 (5.3) years, height of 1.67 (0.09) m, and body mass index of 26.0 (3.5) kg/m2. Informed consent was obtained from all participants, and the project had ethics approval from the Human Research Ethics Committee of the University of Melbourne. The participants were deemed to be healthy if they had no identifiable movement dysfunction; no history of significant spinal, hip, or knee pathology; and no presence of vertebrofemoral pain requiring treatment during the preceding 6 months. The Western Ontario and McMaster Universities Arthritis Index (WOMAC) Questionnaire (Likert scale)42 was used to determine the presence of any pain (5 items), stiffness (2 items), or functional difficulty (17 items) in this group.

Study Design/Instrumentation

A 2D Peak Motus video analysis system (PEAK)* was used to evaluate the STS transfer from a seat set at 100% of knee height (thigh horizontal). Based on a previous protocol,39 a single camera was positioned at a distance of 6.5 m, perpendicular to the sagittal plane. Six reflective spherical markers with black bases were attached over the midline thoracolumbar spine and pelvic landmarks, and 4 flat circular markers were placed over the right lateral aspect of the lower limb in an area that minimized skin movement on the lateral thigh (Fig. 1). Good test-retest reliability for skin marker placement was established in a standing position (intraclass correlation coefficient [1,1]=.80–.93).

Figure 1

(Left) Marker placement on body landmarks. (Right) Diagram illustrating method of calculation of thoracic, lumbar, hip, and knee flexion-extension angles (for definition of zero reference position, refer to text). PSIS=posterior superior iliac spine, ASIS=anterior superior iliac spine, 2/3Th=proximal thigh, SC=supracondylar, LTC=lateral tibial condyle, LM=10 cm above lateral malleolus.

Figure 1

(Left) Marker placement on body landmarks. (Right) Diagram illustrating method of calculation of thoracic, lumbar, hip, and knee flexion-extension angles (for definition of zero reference position, refer to text). PSIS=posterior superior iliac spine, ASIS=anterior superior iliac spine, 2/3Th=proximal thigh, SC=supracondylar, LTC=lateral tibial condyle, LM=10 cm above lateral malleolus.

Figure 1 illustrates angle definitions and calculation. Zero thoracic spine flexion or extension occurred when straight lines joining markers on the 1st and 3rd thoracic spinous processes (T1-T3) and markers on the 11th thoracic and 1st lumbar spinous processes (T11-L1) intersected at 0 degrees. Zero lumbar and hip angles were defined when a straight line joining the T11 and L1 markers or the proximal thigh (2/3Th) and supracondylar (SC) markers was perpendicular to the pelvic plane. The pelvic plane comprises a straight line joining posterior and anterior superior iliac spines (PSIS and ASIS). Zero knee flexion or extension occurred when straight lines joining the 2/3Th and SC markers and the LTC (lateral tibial condyle) and LM (10 cm above lateral malleolus) markers intersected at zero. Any spinal angle anterior to the zero position was called “x” degrees of flexion, whereas angles posterior to the zero reference represented “y” degrees of extension.

With arms folded, the participants performed 3 STS trials at a self-selected pace. Prior to videotaping, participants were encouraged to adopt their most comfortable anteroposterior (bare) foot position. They also performed tests for full available thoracic spine flexion (Fig. 2A), lumbar spine flexion (Fig. 2B), hip flexion (Fig. 2C), and thoracic spine extension (Fig. 2D).

Figure 2

Tests for maximal available (A) thoracic spine flexion, (B) lumbar spine flexion, (C) hip flexion, and (D) thoracic spine extension.

Figure 2

Tests for maximal available (A) thoracic spine flexion, (B) lumbar spine flexion, (C) hip flexion, and (D) thoracic spine extension.

Before performing 3 spinal flexibility trials, participants were given 3 practice trials to familiarize themselves with the specific movement. One (best) videotaped image of STS performance (judged from the videotape by the smoothness of the movement and the lack of out-of-plane motion) and the last of each of the spinal flexibility trials were automatically digitized for each participant using the 2D PEAK software program. The data then were converted to angles and smoothed using a fourth-order Butterworth (high cutoff) filter43 at an optimum cutoff frequency determined by the software.44 The accuracy and reliability of PEAK for uniplanar measurement of joint angles have been established previously.45 All STS angular data then were imported into the Microsoft Excel program and used in conjunction with Kaleidagraph version 3.8 to normalize the data to 100% movement duration.

In this study, 3 events were defined: (1) the start of the STS movement as the point of 10% increase in the horizontal (x) displacement of the T1 marker; (2) buttocks lift-off (LO) at the point of a 10% increase in the vertical (y) displacement of the proximal thigh (2/3Th) marker, as described by Mourey and colleagues29,32; and (3) the end of the STS movement at the point of no further hip extension. For the purpose of analysis, the STS movement then was divided into a pre-LO phase and a post-LO phase.

Data Analysis

Means and standard deviations for the excursions (end angle minus start angle), ranges used in the STS task (maximum angle minus minimum angle), angles at LO, and percentage of maximum joint and segment angles used during STS performance were calculated. The hip/lumbar ratio was calculated for each phase by dividing the range of hip movement by the lumbar spine range of movement. The thoracic/lumbar ratio was calculated in a similar manner.

Results

The results of the WOMAC Questionnaire confirmed that the participants had no pain (mean [SD] score=0 [0] out of 20), no significant stiffness (mean [SD] score=1 [1] out of 8), and no functional difficulty (mean [SD] score=2 [5] out of 68), suggesting that this group comprised elderly people who were healthy.

Movement Pattern

Figure 3 demonstrates the participants' angular movement pattern throughout the STS task. The figure shows that in the pre-LO phase, concurrent hip and lumbar flexion combined with thoracic extension comprised forward trunk lean. This interaction reversed in the post-LO phase, as the hips and knees and the lumbar spine extended while the thoracic spine flexed.

Figure 3

Mean sagittal thoracic and lumbar spine, hip and knee joints, and trunk slope angles plotted against normalized test duration throughout the sit-to-stand task from horizontal seat height in elderly adults who were healthy (N=41). A downward slope indicates extension, and an upward slope indicates flexion, except in the case of trunk slope. LO=buttocks lift-off, 2D=2-dimentional.

Figure 3

Mean sagittal thoracic and lumbar spine, hip and knee joints, and trunk slope angles plotted against normalized test duration throughout the sit-to-stand task from horizontal seat height in elderly adults who were healthy (N=41). A downward slope indicates extension, and an upward slope indicates flexion, except in the case of trunk slope. LO=buttocks lift-off, 2D=2-dimentional.

Lift-off occurred at 30.1% of STS duration and corresponded to an averaged 3.6° knee extension from a sitting flexion angle of 100.2 degrees. At LO, the hip and knee joints were similarly flexed (96.0° [8.2°] and 96.6° [8.1°], respectively), after which these joints were locked together in a linear pattern of extension to raise the body into the standing position. The sequence involved in change of movement direction around LO was as follows. The knee commenced extending at 20% of STS duration. The lumbar spine began to extend (23%) before the hip (27%), and the thoracic spine changed from extension to flexion at LO (30%). At LO, trunk forward lean was 50.8 degrees (9.4°) with respect to the horizontal plane. After LO, trunk forward lean was maintained, reaching a maximal angle of 49.8 degrees (9.1°) with respect to the horizontal (1° more flexion) at 35% of STS duration. Thus, there was a brief transition or balancing period occupying 5% of the total movement duration, where although the hips and knees were extending so that the buttocks were lifting from the chair, the trunk remained flexed forward.

Angular Changes

The excursion and range of movement of the sagittal thoracic spine and lumbar spine, hip and knee joints, and trunk slope (relative to the horizontal plane) during the STS task are shown in Table 1. The hip moved 19.4 degrees from the start position (77.1°) to its maximal flexion angle (96.5°) immediately prior to LO and was the dominant joint responsible for bringing the trunk forward. Although the lumbar spine moved through a range of 20.1 degrees from a sitting position to a standing position, it contributed only 4.1 degrees of flexion in the pre-LO phase, from a start angle of 2.7 degrees in the sitting position. Thus, the hip/lumbar ratio in the pre-LO phase was 4.7:1; that is, for every 4.7 degrees of hip flexion, there was 1 degree of lumbar flexion. The thoracic spine also extended through a relatively small range so that the thoracic flexion angle reduced from the initial 37.1 degrees in the sitting position to 30 degrees at LO. During the pre-LO phase, every 1 degree of lumbar flexion was accompanied by 1.7 degrees of thoracic extension. During the post-LO phase, there was significantly more range of movement for the lumbar spine (19.2°); however, there also was a greater increase in hip joint range of movement (98.8°), so that the hip/lumbar ratio was 5.2:1. The thoracic/lumbar ratio during the post-LO phase showed that for every 1 degree of lumbar extension, there was 0.4 degree of thoracic flexion (Tab. 2).

Table 1

Excursion and Range of Movement (in Degrees) of Participating Joints and Regions During the Sit-to-Stand (STS) Task in Elderly Adults Who Were Healthy (N=41)a

Region/Joint Start of STS Task At Buttocks Lift-off End of STS Task Maximum Minimum Range 
Mean (SD), 95% CI Mean (SD), 95% CI Mean (SD), 95% CI Mean (SD), 95% CI Mean (SD), 95% CI Mean (SD), 95% CI 
Thoracic spine 37.1 (10.3), 34.0 to 40.2 30.0 (10.6), 26.7 to 33.3 38.1 (9.8), 35.1 to 41.1 38.1 (9.9), 35.1 to 41.1 30.0 (11.1), 26.6 to 33.4 8.1 (2.8), 7.2 to 9.0 
Lumbar spine 2.7 (8.8), 0.0 to 5.4 5.9 (8.9), 3.2 to 8.6 −13.3 (7.0), −15.4 to −11.2 6.8 (10.0), 3.7 to 9.9 −13.3 (7.0), −15.4 to −11.2 20.1 (8.5), 17.5 to 22.7 
Hip joint 77.1 (8.2), 74.6 to 79.6 96.0 (8.2), 93.5 to 98.5 −2.8 (6.9), −4.9 to −0.7 96.5 (8.8), 93.8 to 99.2 −2.8 (6.9), −4.9 to −0.7 99.3 (9.2), 96.5 to 102.1 
Knee joint 100.2 (8.1), 97.7 to 102.7 96.6 (8.1), 94.1 to 99.1 1.2 (5.8), −0.6 to 3.0 100.2 (8.1), 97.7 to 102.7 1.2 (5.8), −0.6 to 3.0 99.0 (9.9), 96.0 to 102.0 
Trunk slope (to horizontal) 81.2 (4.5), 79.8 to 82.6 50.8 (9.4), 47.9 to 53.7 84.7 (3.3), 83.7 to 85.7 84.8 (3.3), 83.8 to 85.8 49.8 (9.1), 47.0 to 52.6 35.0 (8.6), 32.4 to 37.6 
Region/Joint Start of STS Task At Buttocks Lift-off End of STS Task Maximum Minimum Range 
Mean (SD), 95% CI Mean (SD), 95% CI Mean (SD), 95% CI Mean (SD), 95% CI Mean (SD), 95% CI Mean (SD), 95% CI 
Thoracic spine 37.1 (10.3), 34.0 to 40.2 30.0 (10.6), 26.7 to 33.3 38.1 (9.8), 35.1 to 41.1 38.1 (9.9), 35.1 to 41.1 30.0 (11.1), 26.6 to 33.4 8.1 (2.8), 7.2 to 9.0 
Lumbar spine 2.7 (8.8), 0.0 to 5.4 5.9 (8.9), 3.2 to 8.6 −13.3 (7.0), −15.4 to −11.2 6.8 (10.0), 3.7 to 9.9 −13.3 (7.0), −15.4 to −11.2 20.1 (8.5), 17.5 to 22.7 
Hip joint 77.1 (8.2), 74.6 to 79.6 96.0 (8.2), 93.5 to 98.5 −2.8 (6.9), −4.9 to −0.7 96.5 (8.8), 93.8 to 99.2 −2.8 (6.9), −4.9 to −0.7 99.3 (9.2), 96.5 to 102.1 
Knee joint 100.2 (8.1), 97.7 to 102.7 96.6 (8.1), 94.1 to 99.1 1.2 (5.8), −0.6 to 3.0 100.2 (8.1), 97.7 to 102.7 1.2 (5.8), −0.6 to 3.0 99.0 (9.9), 96.0 to 102.0 
Trunk slope (to horizontal) 81.2 (4.5), 79.8 to 82.6 50.8 (9.4), 47.9 to 53.7 84.7 (3.3), 83.7 to 85.7 84.8 (3.3), 83.8 to 85.8 49.8 (9.1), 47.0 to 52.6 35.0 (8.6), 32.4 to 37.6 
a

Positive values denote flexion movement; negative values denote extension movement. 95% CI =95% confidence interval.

Table 2

Hip/Lumbar and Thoracic/Lumbar Ratios and 95% Confidence Interval (CI) for Mean (SD) Values During the Sit-to-Stand Movement in Elderly Adults Who Were Healthy (N=41)

Phase Range (°) Hip/Lumbar Ratio Range (°) Thoracic/ Lumbar Ratio 
Hip Joint Lumbar Thoracic Lumbar 
Pre-LOa 19.4 (6.3) 4.1 (5.3) 4.7:1
95% CI=4.3–5.1 
7.1 (4.5) 4.1 (5.3) 1.7:1
95% CI=1.3–2.1 
Post-LO 98.8 (9.8) 19.2 (8.7) 5.2:1
95% CI=4.7–5.7 
8.1 (4.4) 19.2 (8.7) 0.4:1
95% CI=0.1–0.7 
Phase Range (°) Hip/Lumbar Ratio Range (°) Thoracic/ Lumbar Ratio 
Hip Joint Lumbar Thoracic Lumbar 
Pre-LOa 19.4 (6.3) 4.1 (5.3) 4.7:1
95% CI=4.3–5.1 
7.1 (4.5) 4.1 (5.3) 1.7:1
95% CI=1.3–2.1 
Post-LO 98.8 (9.8) 19.2 (8.7) 5.2:1
95% CI=4.7–5.7 
8.1 (4.4) 19.2 (8.7) 0.4:1
95% CI=0.1–0.7 
a

LO=buttocks lift-off.

Table 3 indicates the percentage of full available flexion-extension angle of the joints and regions used during the STS task. During the STS task, 90% of maximal available hip joint flexion was used during the pre-LO phase. However, the proportion of maximal lumbar flexion angle used was only 23%. Maximal available thoracic extension was 24.3 (11.3) degrees of flexion. Therefore, the maximum range of available thoracic extension is the arithmetic difference between maximal available thoracic flexion (66.4°) and extension (24.3°); that is, 42.1 (9.6) degrees. However, the maximum thoracic extension angle used during the STS task (equal to minimum STS thoracic flexion) was 30.0 (11.1) degrees of flexion, so that in this group there was only 5.7 degrees left for any further thoracic extension. Therefore, the maximum thoracic extension used during STS corresponded to 86.5% (9.8%) of available thoracic extension.

Table 3

Percentage of Maximal Available Mean Flexion and Extension Angles and 95% Confidence Interval (CI) for Thoracic Spine, Lumbar Spine, and Hip Joint Used During the Sit-to-Stand (STS) Task in Elderly Adults Who Were Healthy (N=41)

Region/Joint Maximal Angle (°) Available Maximal Angle (°) Used in STS Task % Maximal Angle Used in STS Task 95% CI P 
Mean (SD) Mean (SD) Mean (SD) 
Thoracic flexion 66.4 (7.9) 38.1 (9.9) 57.4 (11.2) 53.9–60.9 .03 
Lumbar flexion 29.6 (8.8) 6.8 (10.0) 23.0 (10.7) 17.7–28.3 .01 
Hip flexion 107.2 (10.6) 96.5 (8.8) 90.0 (6.4) 87.8–92.2 .01 
Region/Joint Maximal Angle (°) Available Maximal Angle (°) Used in STS Task % Maximal Angle Used in STS Task 95% CI P 
Mean (SD) Mean (SD) Mean (SD) 
Thoracic flexion 66.4 (7.9) 38.1 (9.9) 57.4 (11.2) 53.9–60.9 .03 
Lumbar flexion 29.6 (8.8) 6.8 (10.0) 23.0 (10.7) 17.7–28.3 .01 
Hip flexion 107.2 (10.6) 96.5 (8.8) 90.0 (6.4) 87.8–92.2 .01 

Duration

The mean (SD) time to stand up from a sitting position on a horizontal (thigh) seat, with arms folded across the chest and at a self-selected speed, was 2.0 (0.4) seconds.

Discussion

This study used a revised model of marker location to describe for the first time the coordinated sagittal movement pattern between the hips and knees and the lumbar spine and thoracic spine during the STS task in community-dwelling elderly people who were healthy. In addition, the proportion of full available flexion-extension angle used by the joints and regions during the STS task was determined. The use of a 2D method was supported by Baer and Ashburn33 and Shum et al,38 who concluded that out-of-sagittal-plane movements during the STS task were insignificant in individuals.

Hip-Spine Movement Interaction

The finding of concurrent hip and lumbar flexion during the pre-LO phase contradicts the statement in a clinical text that “flexion of the extended trunk at the hips”16(p143) is critical for effective STS performance and the belief that flexing the lumbar spine is a “trick” or compensatory movement.16 Although hip joint flexion remained the dominant factor in bringing the body mass forward, a small degree of lumbar flexion was nevertheless a component of trunk forward lean. These findings highlight errors in current beliefs regarding the spinal contribution to the STS movement that have resulted from use of a rigid trunk model in image-based studies with markers on proximal and distal ends of the trunk segment.25,27,31,32 These incorrect concepts regarding the movement pattern have the potential to adversely influence the assessment and retraining of patients with STS dysfunction.

The model used in this study also provided a more accurate measurement of the true hip or pelvic-femoral angle. Use of the shoulder-greater trochanter-knee marker placement has largely been responsible for the variation in sagittal hip joint angles reported in STS studies.19,20,27,46,47 Close to full available hip flexion (90%) was used by our participants during the pre-LO phase, indicating that hip limitation would pose a major problem in the kinematic chain. Possible compensation would include increased lumbar flexion or, in the case of very limited hip movement, thoracic flexion instead of extension to bring the trunk sufficiently forward and at an appropriate velocity. It is not clear why our elderly group used only 23% of their maximal available lumbar flexion angle during the pre-LO phase; however, sufficient range of movement remained to allow lumbar compensation for a stiff hip joint, if needed.

Our results also indicate that diminished mobility of the thoracic spine, which moves in the opposite direction to the lumbar spine and requires close to full (86.5%) extension in the pre-LO phase, may be a problem in some individuals. A key finding of the study by Ikeda et al17 was that the older participants did not extend their heads as the trunk was flexing forward, so that the older group was facing down at LO. In our group, the hips provided a large flexion angle (96.5°); however, the small flexion contribution (4.1°) from the lumbar spine may have put more demand on the adjacent thoracic spine to bring the center of the upper body mass forward over the feet. Thus, as the hips and lumbar spine flexed, the thoracic spine extended only 8.1 (2.8) degrees, despite some further (5.7°) thoracic extension being available. A review of the videotapes revealed that our participants did not appear to be looking down at LO. However, for people with larger thoracic curvatures (eg, elderly women with postmenopausal kyphosis), the lower cervical spine may not have the range of extension to fully compensate for a lack of thoracic extension. The role of vision in aiding postural control has been confirmed in previous studies.48,49 The ability to look directly forward at LO enables people to orient themselves with the vertical and horizontal features of the environment. This orientation provides visual feedback that is important in elderly people to help control the velocity of the center of mass and thus maintain control of the movement and balance during the STS task.29 It follows that elderly people with increased kyphosis or thoracic stiffness may require thoracic mobilizing exercises to enable optimal STS performance.

It is difficult to compare the timing of LO in the present study with that in previous studies, as researchers have used different definitions for the start and end of the STS movement and the LO event. However, the sequence of change in direction of the knee first and then the hip joints before LO is similar to that reported by other authors.4,27 In addition, our study demonstrated that the onset of knee extension at 20% of STS duration was closely followed by lumbar extension (23%) and then hip joint extension (27%). However, the thoracic spine did not change from extension to flexion until LO at 30% of STS duration.

Carr and Shepherd16 recommended that for optimum STS performance, the body mass should move forward and upward without a pause between the 2 movements. However, our participants demonstrated a brief transitional or balancing phase, where the trunk remained tipped forward following LO for 5% of STS duration. This phase appears to have been due to the knees extending approximately 3.5 degrees, whereas the lumbar spine and hips had only extended 1 to 2 degrees in this time. In addition, as the thoracic spine changed from extension to flexion at LO, this change may have added a small amount to trunk forward lean immediately post-LO. This brief balancing phase prior to the commencement of trunk extension appears not to have been reported previously, probably due to the use of different models for measurement of joint angles. It has been noted that trunk movement must be sufficient to propel the upper body mass forward50; however, this trunk movement must be limited to prevent the possibility of falling forward at LO.29 Furthermore, the importance of postural stability around LO by controlling the center of mass in relation to the foot support area has been emphasized.16 Thus, the priority of the elderly group in gaining stability before attempting to rise46 may explain this small delay in trunk extension.

There was a relatively large variation of spinal angular displacement during the STS task, as indicated by the standard deviations in the movement data. It is not unusual to see a large degree of variation in the erect thoracolumbar posture in people who are healthy. Stagnara et al51 suggested that the differences in spinal curvatures among participants in their study was so great that the average curve values were of little use as normative data. This variation may be exaggerated in elderly adults with interacting effects of age. It is possible that habitual postural differences may be associated with inter-subject variations in the thoracolumbar start posture in the sitting position and reflected in differences in the mobility of the spinal regions.

Compared with the young participants in our previous study,39 the elderly participants in the present study had a different start posture in the sitting position, with increased thoracic kyphosis (37.1° versus 32.2°) and a much straighter lumbar spine (2.7° versus 14.5° of flexion). The movement pattern was similar in both groups, with concurrent lumbar flexion and thoracic extension accompanying hip flexion during the pre-LO phase and a reversal of these movements in the post-LO phase. The sequence of change in movement direction of the joints and regions prior to LO also was similar in both groups. Although our young and old groups had a similar maximum hip flexion angle (98.9° versus 96°), the smaller contribution of lumbar flexion in the elderly group (4.1° versus 7.0°) resulted in a larger pre-LO hip-lumbar ratio (4.7:1 versus 3.1:1). The older participants also extended their thoracic spine less than the younger participants (8.1° versus 14.6° of flexion) in the pre-LO phase.

Using 3D motion analysis, Farquhar et al52 reported the lower-limb kinematics during the STS task in a control group of people of similar age (62 [6.3] years) who were healthy. Using a pelvic-femoral angle, their graph (Fig. 1)52(p570) indicated a similar occurrence of maximal hip flexion immediately before LO. However, in comparison with our group, the sitting hip flexion angle was only 60 degrees compared with 77 degrees, increasing to a maximum of 76 degrees versus 96.5 degrees in the pre-LO phase. The maximum knee flexion angles (79°–89°) versus 100 degrees in our group indicated that Farquhar and colleagues' participants were sitting on a higher chair, which possibly explains the different values obtained. These authors did not attempt to measure trunk slope or spinal movement.

Shum and colleagues38,53 appear to be the only other authors who have measured sagittal spinal angles during the STS task, although in a different age group (41.7 [8.2] years). Using an electromagnetic tracking device with sensors on the L1 spinous process, posterior sacrum, and lateral thigh, they demonstrated a similar hip-spine interaction in controls who were healthy that supported our results. Lumbar flexion led the hips during the pre-LO phase, and the hips extended more rapidly than the lumbar spine in the post-LO phase. Although agreeing with the pattern of joint interaction, Shum et al38 reported different values for hip and lumbar angles. Their sitting hip flexion angles were approximately 45 (9) degrees compared with 76.9 (7.3) degrees in our study, which again could be partially explained by the slightly higher seat height (110% versus 100%) in our study. The sitting lumbar angles of their middle-aged group were similar to those of our young group39 (14° versus 14.5°), with both groups showing considerably more lumbar flexion than the elderly participants in the present study (2.7°). Maximal hip flexion angles for the middle-aged group versus our young39 and old groups were 89 (11), 98.9 (6.5), and 96.5 degrees, respectively, which again may be explained by the higher seat, which required less trunk forward lean to rise. The major differences occurred in the maximal lumbar flexion angles used during the STS task, which were 41.8 (8) degrees in the middle-aged group38 versus 21.5 (9.2) degrees and 6.8 (10) degrees, respectively, for our young39 and old groups. These findings mean that during the pre-LO phase, our young group39 flexed the lumbar spine only 7 degrees as opposed to 27 degrees in Shum and colleagues'38 middle-aged group.

The explanation for the differences among studies is likely found in the use of different measurement tools. For example, it is not clear whether the electromagnetic device, which measures the tilt of the sacrum as opposed to the plane of the pelvis (PSIS-ASIS), would provide the same angle values. In their radiographic study of 109 people with low back pain (aged 21–83 years), Lord et al54 demonstrated that lumbar lordosis (from L1 to S1) averaged 49 degrees in a standing position and 34 degrees in a sitting position, which indicates that our surface-based studies have all underestimated the true bony lumbar posture. It also has been demonstrated that skin movement on the pelvis results in a small underestimation of maximal lumbar flexion angles (trunk toward thighs), more so in elderly people (average of 6.5°).55 Nevertheless, despite the value differences observed, the overall pattern of hip-lumbar spine movement interaction was similar in these STS studies.

Hip-Knee Interaction

Although not the focus of this investigation, the essential role of hip and knee extension in raising the body mass to a standing position must be acknowledged. Without effective hip and knee joint extension post-LO, people may be forced to sit back down in the chair.32,56 However, unexpected findings in this group of elderly participants rising from a thigh-horizontal seat height were the similar angle (96.0°) of hip and knee flexion at LO and the subsequent locking together of these joints in a linear pattern of extension. Presumably, this hip-knee movement interaction occurs to take the head upward in the shortest possible path, as indicated by the close to vertical displacement of the body's center of mass in the extension phase demonstrated by Roebroeck et al.26 Although lower-limb kinematics have been studied by many researchers,7,18,40,41 there are 2 major reasons why this close interaction between hip and knee joints appears not to have been reported: First, many researchers have placed the feet in a standardized position that may have prevented the natural kinematics of STS movement from being demonstrated. For example, Vander Linden et al7 and Schenkman et al18 used a dorsiflexion-forward leg angle of 18 degrees with respect to the vertical, which affects the knee angle at LO in people of different heights. In contrast, our participants practiced the STS task 2 to 3 times prior to videotaping and were encouraged to adopt their most comfortable anteroposterior foot position. Thus, we contend that the movement kinematics were close to natural for the STS task in our group. Second, use of the conventional model of marker placement by previous researchers (acromion, greater trochanter, and knee) resulted a hip flexion angle contaminated not only by the inclusion of spinal movement but also by possible protraction of the scapula and acromion (frequently observed as individuals attempt to rise), so that measurement error prevented the recording of true locking together of hip and knee joint extension.

In summary, although most previous authors ignored the spinal contribution to STS performance, the results of the present study demonstrate that in elderly people who are healthy, concurrent hip and lumbar flexion and thoracic extension position the upper body (trunk) segment in an appropriate forward lean posture during the pre-LO phase, and that this movement interaction reverses the post-LO phase. We acknowledge that, as with previous STS studies, this is a surface-based analysis that may not truly represent the movement of the underlying skeleton. In addition, our sample of elderly people appears to have been biased toward the top end of physical health, as indicated by the WOMAC results. Thus, the findings may not be generalizable to all elderly people, such as those with obesity or greater levels of stiffness.

Nevertheless, the results of this study provide knowledge of the sagittal kinematics of the hip-spine interaction during the STS task in elderly people who are healthy. This knowledge has practical implications for physical therapists providing both prophylactic and rehabilitation programs. Physical therapists are encouraged to use this knowledge to provide correct facilitation of this important daily activity. For example, encouraging patients to practice anterior pelvic tilting (lumbar extension) in a sitting position as a preparatory exercise for the STS task is based on incorrect assumptions. Attention to retraining of correct movement patterns of the spinal segments is important because of their potential to affect trunk movement during the STS task, as well as the movement of other segments in the kinematic chain such as hip or knee joints or cervical spine. It also seems advisable for elderly patients or those with pathology to practice spinal mobilizing exercises, in particular thoracic extension, to enable an optimal STS performance.

For future research, we recommend that a standardized pelvifemoral hip angle be used to provide more valid data and permit comparisons across kinematic studies. Further development of our 2D model to include the cervical spine and sagittal head tilt is in progress. This model will enable a detailed description of the hip-spine interaction during the STS task from different seat heights or during tasks such as sitting down from a standing position or standing to walk. The effect of limited sagittal movement in any of the component joints or of an intervention such as mobilizing exercises on the STS kinematics also should be investigated.

This research was carried out in partial fulfillment of Dr Fotoohabadi's PhD degree requirements at the University of Melbourne.
This project had ethics approval from the Human Research Ethics Committee of the University of Melbourne.
A platform presentation of this research was given at the Movement Analysis 2005: Building Bridges Conference; February 3–5, 2005; University of Auckland (Tamaki Campus), New Zealand.
*
Peak Performance Technologies Inc, 7388 S Revere Pkwy, Englewood, CO 80112.
Microsoft Corp, One Microsoft Way, Redmond, WA 98052-6399.
Synergy Software, 2457 Perkiomen Ave, Reading, PA 19606.

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Author notes

All authors provided concept/idea/research design, data analysis, project management, and consultation (including review of manuscript before submission). Dr Fotoohabadi and Dr Tully provided writing. Dr Fotoohabadi provided data collection. Dr Tully provided participants and facilities/ equipment.

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