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Research Reports |
V Dubost, MS, is a research engineer, Geriatrics Department, Saint-Etienne University Hospitals, Saint-Etienne, France, and is a doctoral student in the Physiology, Physiopathology of Exercise, and Handicap (PPEH) Laboratory, University J. Monnet Saint-Etienne, Saint-Etienne, France
O Beauchet, MD, MS, is a neurologist, Geriatrics Department, Saint-Etienne University Hospitals, and Department of Rehabilitation and Geriatrics, Geneva University Hospitals, Geneva, Switzerland. He is a doctoral student in the Physiology, Physiopathology of Exercise, and Handicap (PPEH) Laboratory, University J. Monnet Saint-Etienne. He also is a clinical lecturer and specialist in geriatric rehabilitation, Department of Rehabilitation and Geriatrics, Geneva University Hospitals, and School of Sport Science, University J. Monnet Saint-Etienne
P Manckoundia, MD, MS, is an internal medical doctor, Geriatrics Department, Dijon University Hospitals, Dijon, France, and is a doctoral student in the INSERM Laboratory (ERIT-M 0207) of Movement, Plasticity, and Performance, Burgundy University, Dijon, France
F Herrmann, MD, MPH, is a statistician, Department of Rehabilitation and Geriatrics, Geneva University Hospitals, and is a clinical lecturer, Statistics Department, Geneva University Hospitals
F Mourey, PT, PhD, is clinical leader in geriatric rehabilitation, Geriatrics Department, Dijon University Hospitals, and is a clinical lecturer in the INSERM Laboratory (ERIT-M 0207) of Movement, Plasticity, and Performance, Burgundy University
Ms Dubost, Dr Manckoundia, and Dr Mourey provided concept/idea/research design. Ms Dubost and Dr Mourey provided writing. Ms Dubost and Dr Manckoundia provided subjects and data collection, and Ms Dubost and Dr Herrmann provided data analysis. Dr Beauchet provided consultation (including review of manuscript before submission)
Address all correspondence to Ms Dubost at Service de Gérontologie Clinique, Hôpital de la Charité, CHU de Saint-Etienne, 42055 Saint Etienne Cedex 2, France (veronique-dubost{at}club-internet.fr)
Submitted March 9, 2004;
Accepted October 5, 2004
 | Abstract |
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Key Words: Aging • Kinematics • Movement • Postural transitions • Sitting down
| Introduction |
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Like standing up, sitting down is a postural transition that is performed many times during the course of a day. In contrast to the analysis of sit-to-stand transfers, only a few studies have been performed on stand-to-sit transfers.14–16 The aim of the study by Kralj et al14 was to provide normative data of both standing up and sitting down in young adults. Mourey et al15 compared the general kinematic features between young and older adults. Najafi et al16 described a new method of evaluating the characteristics of postural transitions and their correlation with the risk of falls. However, there is evidence from clinical observation that difficulty in performing sit-to-stand transfers is not observed in isolation, but rather in conjunction with an altered stand-to-sit movement pattern. For example, in frail elderly patients, sitting down from a standing position is characterized by difficulty in movement initiation followed by rapid descent to the seat, which is comparable to a backward fall. Although this movement seldom results in severe injuries, it may induce repeated misperception of voluntary movement17 and could lead to deterioration in balance function.
The lack of information concerning the stand-to-sit movement in older adults could be explained by the general feeling that the sit-to-stand transition has a greater functional impact than the stand-to-sit transition. Indeed, rising from a chair is an important prerequisite to the achievement of many functional and physiological goals. Moreover, although many older people with weakness, pain, or other disabilities are not able to stand up,18 they are still able to sit down.
Given the existing gaps in the literature concerning stand-to-sit transfers, it is very tempting to extrapolate the findings from the sit-to-stand transition to the stand-to-sit transition and to consider sit-to-stand and stand-to-sit transitions as symmetrical. However, this assumption is not correct for several reasons. These postural transitions are performed under different mechanical constraints: both standing up and sitting down involve the motion of the whole body in the vertical plane, but the sit-to-stand movement is performed against gravity (upward movement), whereas the stand-to-sit movement is performed with the assistance of gravity (downward movement). There also is no postural symmetry between these 2 movements because both the initial position and movement initiation are different. When a person is standing up, the first phase of the movement is characterized by the generation of upper-body momentum while the person remains seated; the whole body, therefore, is inherently stable.3 On the contrary, the forward trunk rotation into flexion required to sit down can be seen as a complex and particularly destabilizing postural task because it is superimposed on a standing position. Thus, for many older adults, performance of these routine transfers may be quite challenging, and, in view of postural and mechanical constraints, the risk of falling may be as great for the sit-to-stand transfer as it is for the stand-to-sit transfer.
The transfers from sitting to standing and back to sitting both require voluntary movement of the different segments that contribute to the change of posture and equilibrium control during the considerable displacement of the body's center of mass (CoM). Riley et al4 emphasized the role of the trunk in generating momentum to carry the body through the dynamic transition of standing up. Although researchers4,19 have found that the position of upper-body segments plays an important role in controlling the CoM in order to achieve the sit-to-stand maneuver, the displacements of these segments have not been analyzed during the stand-to-sit transition.
For these reasons, this study was conducted on both standing up and sitting down in order to investigate the angular displacements of the trunk and the additional segment of the shank. We were interested in testing the impact of aging on these 2 postural transitions because age-related angular changes may be of clinical interest in relation to the risk of falling. Due to different mechanical and postural conditions, we hypothesized that aging would affect sit-to-stand and stand-to-sit maneuvers in different ways.
| Method |
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Young adults ranged in age from 22 to 35 years (
=26.8, SD=4.7). There were 7 men and 2 women. Their mean height was 178.2 cm (SD=4.6), mean weight was 75.4 kg (SD=8.5), and mean body mass index was 23.7 (SD=2.2). The young adults reported no physical or mental disorders and were not on medication.
Older adults ranged in age from 71 to 80 years (=75.9, SD=3.2). There were 7 men and 3 women. Their mean height was 161.7 cm (SD=5.6), mean weight was 66.8 kg (SD=7.4), and mean body mass index was 25.6 (SD=3.2). They reported themselves to be in "good health." All older adults took part in a sporting activity once a week. They were enrolled in different exercise programs that focused on outdoor walking or balance training (about 90 minutes per week). They lived independently in the community, had no functional limitations, and reported not having fallen during the year before participation. Their mean number of chronic diseases was 0.8 (SD=0.9), but their diseases caused no major neurological or orthopedic problems. Three older adults reported having high blood pressure controlled with medication; one older adult had a history of thyroid deficiency, which was currently managed with medication; and one older adult had uncomplicated diabetes mellitus. Five older adults did not report having any disease.
Older adults were included after examination using standard geriatric assessment instruments. Cognition was evaluated based on the participants' score (maximum possible score of 30) on the Folstein Mini-Mental State Exam (MMSE), which assesses orientation, attention, calculation, immediate and short-term recall, language, and the ability to follow simple commands.20 Cognitive impairment was defined as having a score of less than 24.21 Basic mobility was assessed with the Timed "Up & Go" Test (TUG).22 Using the TUG, participants were timed from the instant they rose from an armchair, walked 3 m, turned around, and returned to a fully seated position in the chair. Abnormal mobility was defined as having a TUG score of 
20 seconds. Functional capacities were evaluated with common scales used to measure function: an activities of daily living (ADL) scale23 and an instrumental activities of daily living (IADL) scale.24 The ADL scale assesses basic activities such as bathing, dressing, transferring, continence, and feeding. The IADL scale augments this basic information with more complex tasks important for independent living in the community, such as the ability to use a telephone, to shop, to prepare food, and so forth. This scale has been demonstrated to yield reliable data for the screening of dementia in community-dwelling elderly people.25
Included older adults met the following inclusion criteria: (1) age over 70 years; (2) no acute medical illness in the past 3 months such as coronary heart disease, heart failure, or pulmonary infection; (3) MMSE score 24, (4) no orthopedic diagnoses involving the lower back, pelvis, or lower or upper extremities; (5) no neurological diseases (ie, stroke, Parkinson disease, cerebellar disease, myelopathy, peripheral neuropathy); (6) no muscular diseases; (7) TUG score 
20 seconds; and (8) ability to stand up from a chair without help.
Baseline testing of older adults also included noting the absence or presence of sensory or motor deficits involving the upper and lower extremities, the number of chronic diseases such as cardiovascular or pulmonary diseases, the practice of physical activity, and the incidence of falls during the past year.
None of the participants were familiar with the specific purpose of the study. The study was conducted in accordance with the ethical standards set forth in the Helsinki Declaration (1983).
Apparatus
Two cameras (sampling frequency of 100 Hz) were placed 3 m from each participant's sagittal axis and recorded movements of retro-reflective markers (15 mm in diameter) glued to 5 anatomical sites, using an optoelectronic measuring device (ELITE System*).26 The 5 markers were placed on the participant's right side at the following sites: acromion, greater trochanter, lateral knee joint space, lateral malleolus, and fifth metatarsophalangeal joint.
Kinematic variables based on these 5 markers were calculated from successive frames taken at 10-millisecond intervals. The accuracy was 1.5 degrees for angular positions for an observed field of view of 1.5 x 2 m. The relevant kinematic variables were low-pass filtered to eliminate high-frequency noise.
Procedure
The participants were seated on an armless adjustable chair, with the seat placed at knee height, and they kept their arms folded across their chest. A back support on the chair was used to set their trunk in the vertical position while their feet were placed flat, 10 cm apart at the heels, with the shanks positioned at a 10-degree angle relative to the vertical.
From this initial sitting posture, participants were asked to stand up from the chair and to maintain the upright standing position. After 10 seconds, they were asked to sit down and to remain seated for 10 seconds. This sequence was performed 5 times.
Participants were instructed not to use their arms or move their feet, but no other indications as to the strategy required to do the movements were given. Each participant thus executed a total of 10 movements: 5 sit-to-stand transfers and 5 stand-to-sit transfers, all at a self-selected speed. During an earlier practice period, participants were asked to execute the sequence twice.
Outcome Measures
Using Elite software*, the 5 markers were linked to construct a model with 4 segments: the trunk, the thigh, the shank, and the foot. Trunk and shank orientation angles were computed using the following segments: (1) trunk, the angle from the vertical axis to the trunk segment, and (2) shank, the angle from vertical axis to the shank segment.
The main dependent variables were defined as the values of the maximal trunk and shank orientation angles (ie, the maximal angular displacements of the trunk and shank with respect to the vertical) collected during the 5 trials. These variables were measured in 2 conditions: standing up and sitting down.
Data Analysis
The values of the maximal trunk and shank orientation angles were summarized using means and standard deviations. The normality of distribution of data was verified with skewness and kurtosis tests. Age effect was examined using a balanced (ie, 5 measurements for each movement for each participant) analysis of variance (ANOVA) model with a repeated-measures design for standing up and sitting down. A 2x5 two-way ANOVA was done to determine the effect of age group (young/old) across the 5 repeated trials on shank and trunk angle for each movement, resulting in 4 ANOVAs. Table 1 shows the 4 mean values for trunk and shank angle for each movement separated by age group. The P values in Table 1 are for the main effect of age group. The main effect for trials was not significant. All statistics were calculated using Stata statistical software (Release 8.2 program).
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| Results |
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The results obtained in the functional assessment indicated that the older adults in our study were able to live independently and safely, because they had maximal ADL scale scores of 6/6 (the range of the possible scores being 0–6) and had IADL scale scores between 6/8 and 8/8 (=6.9, SD=0.8) (the range of the possible scores being 0–8).
Thus, the assessment of cognition and functional capacities of older adults ensured that all of the older adults included in our study were not functionally impaired, were physically active, and maintained an active social life. Despite the presence of diseases typically encountered with increasing age, all of the older adults in our study reported being in "good health."
General Features of Sit-to-Stand and Stand-to-Sit Movements
All participants were able to complete the sequence without falling. Concerning the motion time course, the general pattern was comparable for young and older adults. To stand up, participants first flexed the hip while still in contact with the chair and then extended the hip and knee joints during the ascent part of the rise. The time of ankle joint reversal from flexion to extension occurred after the seat-off (initial loss of contact with the chair). To sit down, participants simultaneously flexed their hip and knee joints and then extended the hip after the seat-on (time of initial contact with the chair). The time of ankle joint reversal from flexion to extension occurred before the seat-on. Consequently, when the person is standing up, the maximal trunk orientation angle is at the time of seat-off and the maximal shank orientation angle is just after the seat-off. When the person is sitting down, the maximal trunk orientation angle is at the time of seat-on, while the maximal shank orientation angle is just before the seat-on.
The general characteristics of the sit-to-stand and stand-to-sit movements for one typical young subject and one typical older subject are shown in Figure 1. The stick-diagrams show that both young and older adults stood up and sat down with a large amount of trunk forward flexion, while the ranges of forward shank angular displacement were smaller.
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Typical examples of trunk orientation angle during the sit-to-stand and stand-to-sit movements are presented for one young subject and one older subject in Figure 2. Through the 5 cycles of each movement, the pattern is reproducible, and curves could be superimposed. However, it is clear that, with regard to the amplitude of trunk displacement during the stand-to-sit movement, there was a difference between young and older adults.
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| Discussion |
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TopAbstractIntroductionMethodResultsDiscussionConclusionsReferences |
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Health status in older adults can differ considerably because of the various cumulative effects of chronic diseases and of physiologic decline. These effects become even more pronounced and diverse with age and can lead to greater intersubject variability in older adults compared with young adults (for a recent review, see Martin and Hofer29). In our study, however, the sample of older adults was homogenous and without known impairments or functional limitations, which probably explained the low variability and lack of effect of repeated measures.
As depicted in Figure 1, standing up and sitting down are achieved with a great amount of trunk angular displacement. This feature, previously described in the literature, encouraged Kelley and colleagues30 to define 2 phases in the sit-to-stand transition in relation to trunk movement: forward flexion followed by extension. During each transfer, trunk displacement in a forward direction creates disequilibrium. At the beginning of the sit-to-stand movement, the forward trunk rotation generates the horizontal momentum of the CoM,31 whereas during the stand-to-sit movement, the forward trunk rotation contributes to stability control along the anteroposterior axis.15 Thus, it is important to note that trunk angular displacement has a different function in standing up and sitting down.
We did not observe a difference between young and older adults with regard to trunk and shank maximal orientation angles during rising from a chair. In contrast to our results, Gross et al32 observed that elderly women, while still seated, tended to flex their hips more compared with young women, and they attributed this change to the reduction in muscle force production. This feature also was found by Alexander et al33 in older adults with functional impairments when rising while using their hands for support. As stated by Moxley Scarborough et al34 and Schenkman et al,35 lower-extremity force production generally correlates directly with dynamic stability and is the stronger predictor of success in sit-to-stand transfers for older adults with functional impairments. Thus, it seems that age-related increases of trunk flexion may emerge only in older adults with force or functional limitations, but not with physiological aging alone.
In our sample of adults, the similar trunk motion observed across age groups may be interpreted as an invariant characteristic of the sit-to-stand maneuver in aiming to produce the horizontal momentum of the CoM to achieve a standing posture. This hypothesis is consistent with the results of Pai and colleagues,31,36 who studied the effects of speed of ascent, terminal constraint, and subject's age on the control of dynamic balance during the sit-to-stand movement. These authors demonstrated that the horizontal momentum of the CoM, which is generated by the trunk flexion, remained constant across different speeds and the 2 age groups. Thus, subjects had to limit horizontal momentum of the CoM (ie, the forward trunk flexion) in order to maintain equilibrium on completion of the task of standing up. The angular displacement of the trunk may be tightly controlled in sit-to-stand transfer: trunk motion must be sufficient to accelerate the whole body at movement initiation, but must be limited to avoid forward fall at the end of the transfer.
Pai and Lee31 studied the effects of speed and terminal constraint on control of balance during the sit-to-stand movement, but not the effect of age. Their results showed the importance of the control of the CoM, which is largely linked to the trunk displacement. The number of subjects in the study by Pai and Lee (N=9, aged 27–39 years) was the same as the number of younger adults in our study, and their data acquisition was similar to ours: 5 trials recorded, arms folded across the chest, the use of an optoelectronic motion analysis system. Their chair was not adjustable, but they selected 9 subjects with similar heights (=1.75 m, SD=0.05). Despite the difference in the range of ages of the subjects between our study and the study by Pai and Lee, we suppose that their finding concerning the horizontal momentum of the CoM may be applied in another sample of "healthy adults."
When sitting back down, our sample of older adults used a smaller trunk orientation angle than the younger adults, approximately 10 degrees less. According to Kaya et al,37 the ability to control the whole-body position during motor activities in which the CoM is displaced outside the base of support is defined as dynamic stability. Thus, when sitting down, our older participants achieved dynamic stability in a different way than the younger adults did: the trunk showed a smaller displacement, but it was not compensated for by a larger shank angular displacement. Taken together, these 2 angular features tend to minimize forward body displacement and, therefore, decrease the risk of anterior disequilibrium. Because this transfer is performed with the assistance of gravity, it was still possible despite limited forward trunk flexion. This strategy would appear to be less efficient during the sit-to-stand movement (against gravity), when the decreased horizontal momentum resulting from the decreased forward trunk flexion would have to be compensated for by too large muscular forces.
Thus, in our group of older adults who had no functional impairment, the movement control strategy adopted to sit down could reflect an adaptive mechanism to cope with the age-related, modified perception of stability limits.38 Because this feature has no functional impact, it could be considered as an early marker of aging on postural control.
We hope that these results will lead to practical applications for physical therapists, both in prevention programs for older adults and in rehabilitation of individuals who have an altered pattern of movement. We believe the clinical observation of the stand-to-sit movement, particularly of trunk mobility, should be included in routine functional assessment and in fall prevention programs. In a therapeutic setting, progressive trunk movements in a standing position could be introduced before learning a complete strategy used in transfer from a standing to a sitting position. These exercises create intrinsic disequilibrium, which may be useful in the first step of rehabilitation of frail older patients. If a relationship can be demonstrated between decreased trunk angular displacement in older adults without functional limitations and falls observed in frail elderly people, it may be useful to include such exercises in clinical practice.
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| Footnotes |
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This research was presented, in part, at the International Symposium of Posture and Gait Research; March 2003; Sydney, New South Wales, Australia.
* BTS Spa, Viale Forlanini, 36. I-20024 Garbagnate Milanese (MI), Italy. 
StataCorp LP, 4905 Lakeway Dr, College Station, TX 77845.
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