Biomechanical analysis of effects of foot placement with varying chair height on the motion of standing up

Electromyographic Analysis of Thigh Muscle Activity in Arthritic Knees During Sit-to-Stand and Stand-to-Sit Movements: Effects of Seat Height and Foot Position

Background: Knee osteoarthritis (OA) impairs functional mobility, including sit-to-stand and stand-to-sit movements. Thigh muscles stabilize the knee during these transitions, and variations in seat height and foot positioning may affect muscle activation. Assessing thigh muscle activity during these tasks may provide strategies to enhance function and guide targeted rehabilitation for individuals with knee OA. Objective: The aim of this study was to examine the EMG activity of the vastus medialis oblique (VMO), rectus femoris (RF), and biceps femoris (BF) muscles of arthritic knees during sit-to-stand and stand-to-sit movements when using varying seat heights and feet positions. Methods: The EMG activity was recorded from the three thigh muscles in the arthritic side during sit-to-stand and stand-to-sit movements under six different seating conditions from eight patients (three females; mean age: 64.6 ± 11.0 years). A three-way ANOVA was used to examine the effects of seat height, foot positioning, and movement type on muscle activation. Results: The results demonstrated significant interactions between muscle activation, movement type, and seating conditions (p = 0.022). The EMG activity of VMO and RF increased significantly during sit-to-stand movements from lower seat heights compared to knee-height seats (p < 0.05). RF activation was also significantly elevated during stand-to-sit transitions at low seat heights (p = 0.023). Additionally, sit-to-stand transitions with symmetrical foot placement elicited significantly greater VMO activation compared to BF activation (p < 0.05). While BF activation remained relatively low across most conditions, it was highest when the arthritic knee was positioned behind the sound foot during both movements. Conclusions: Seat height and foot positioning significantly impact thigh muscle activation in individuals with knee OA during sit-to-stand and stand-to-sit transitions. Lower seat heights require greater VMO and RF activation, indicating increased mechanical demands. Additionally, placing the arthritic knee behind the sound foot enhances BF activation, suggesting a potential strategy for targeted hamstring engagement. These findings provide directions for quadriceps and hamstring strengthening, alongside strategic seating adjustments to optimize functional mobility and reduce joint stress in individuals with knee OA.

Age and initial position affect movement biomechanics in sit to walk transitions: Lower limb muscle activity and joint moments

Facilitating forward movement while maintaining dynamic stability during transitions like sit-to-walk (STW) requires coordination from many muscles. Age-related muscle, sensory, and neural decline can introduce compensatory biomechanics when completing STW, such as adjusting initial foot position or rising with arm support. Many previous STW studies restrict arm movement and prescribe symmetric foot positions, therefore the purpose of this study was to quantify lower limb muscle excitations and joint moments in STW transitions from four initial foot positions [symmetric, posterior offset, wide, narrow] and two arm placements [hands on knees, arms folded] in 15 younger and 15 older adults. Peak knee and ankle joint extension moments, as well as peak electromyography of five bilateral lower-limb muscles were analyzed. In all conditions, older adults had larger knee extension moments, whereas younger adults had larger ankle plantarflexion moments. Older adults generated larger peak excitation from the knee extensor muscles during rising compared to younger adults, consistent with the higher knee extension moments. Older adults had greater peak dorsiflexor and plantarflexor muscle excitation while rising compared to younger adults. Posterior offset and wide foot positions required the largest peak ankle plantarflexion and knee extension moments and plantarflexor muscle excitation. Arm-supported rising decreased peak knee extensor muscle excitation. In addition, there were interaction effects between age and initial foot position/arm placement for multiple quantities, indicating that the effects of foot and arm placement vary with age. These results inform assessments of movement performance and guidelines for rising given individual lower limb capability.

Age and initial position affect movement biomechanics in sit to walk transitions: Whole body balance and trunk control

Maintaining dynamic balance during transitional movements like sit-to-walk (STW) can be challenging for older adults. Age-related neuromuscular decline can alter movement in STW, such as rising with greater trunk flexion, narrowing the feet, or using arms to push off. Initial foot and arm position can affect subsequent movement biomechanics, with different ground reaction forces (GRFs) that stabilize and advance the body center of mass (COM). The purpose of this study was to quantify whole-body biomechanics and trunk control of STW transitions. Fifteen younger adults (18-35 years) and fifteen older adults (50-79 years) performed STW from four initial foot positions and two arm positions. Three-dimensional (3D) GRFs, 3D body COM displacement, and integrated electromyography values from the lumbar paraspinals and gluteus medius were evaluated. Younger adults generated greater mediolateral GRF ranges while rising, whereas older adults generated greater mediolateral GRF ranges when stepping forward suggesting different strategies to laterally control the body COM. Initial foot position affected the STW movement, with narrow foot positions having smaller body COM displacement than wide foot positions, associated with smaller medial GRFs to move the body COM toward the stance limb. Rising with arm support required less lumbar paraspinal excitation, which was further reduced when with a posteriorly offset foot. Gluteus medius activity was greater for older adults compared to younger adults in STW. Completing STW with arm support can reduce the muscle activity required to stabilize the torso when rising, which likely has implications for balance control and low back loading.

Brain (EEG) and muscle (EMG) activity related to 3D sit-to-stand kinematics in healthy adults and in central neurological pathology - A systematic review

BACKGROUND

The sit-to-stand transfer is a fundamental functional movement during normal activities of daily living. Central nervous system disorders can negatively impact the execution of sit-to-stand transfers, often impeding successful completion. Despite its importance, the neurophysiological basis at muscle (electromyography (EMG)) and brain (electroencephalography (EEG)) level as related to the kinematic movement is not well understood.

OBJECTIVES

This review synthesises the published literature addressing central and peripheral neural activity during 3D kinematic capture of sit-to-stand transfers.

METHODS

A pre-registered systematic review was conducted. Electronic databases (PubMed, CINAHL Plus, Web of Science, Scopus and EMBASE) were searched from inception using search operators that included sit-to-stand, kinematics and EMG and/or EEG. The search was not limited by study type but was limited to populations comprising of healthy individuals or individuals with a central neurological pathology.

RESULTS

From a total of 28,770 identified papers, 59 were eligible for inclusion. Ten of these 59 studies received a moderate quality rating; with the remainder rated as weak using the Effective Public Health Practice Project tool. Fifty-eight studies captured kinematic data of sit-to-stand with associated EMG activity only and one study captured kinematics with co-registered EMG and EEG data. Fifty-six studies examined sit-to-stand transfer in healthy individuals, reporting four dynamic movement phases and three muscle synergies commonly used by most individuals to stand-up. Pre-movement EEG activity was reported in one study with an absence of data during execution. Eight studies examined participants following stroke and two examined participants with Parkinson's disease, both reporting no statistically significant differences between their kinematics and muscle activity and those of healthy controls.

SIGNIFICANCE

Little is known about the neural basis of the sit-to-stand transfer at brain level with limited focus in central neurological pathology. This poses a barrier to targeted mechanistic-based rehabilitation of the sit-to-stand movement in neurological populations.

Optimal procedure and characteristics in using five times sit to stand test among older adults: A systematic review

BACKGROUND

Falls are a major concern for people of all ages, especially older adults with declining physical functions and deteriorating muscle strength. The Five Times Sit to Stand Test is used for the assessment of lower limb strength along with balance and postural control. Therefore, the systematic review at hand aimed to determine the optimal procedure and characteristics among older adults.

METHODS

The following databases served as the primary sources through which the target studies were searched for and obtained for review. They included Google Scholar, Pedro, BIOMED Central, Cochrane Library, MEDLINE, PUBMED and Science DIRECT. With the aim of fulfilling the eligibility criteria, 16 full-text studies were included and the quality assessment was performed. using the Thomas Tool.

RESULTS

The total number of the subjects who participated in the included studies was 15,130 and the ages of the aforementioned participants ranged from 60 to 80 years. In 15 of the studies, a stopwatch was used as the scoring method where the mean chair height of 42 cm was reported. Two studies reported that no significant influence of the arm position (P = .096) on the time allocated for test completion was identified. However, posterior foot placement (P < .001) led to shorter times of completion. Individuals who are unable to complete the test are more susceptible to activities of daily living related disabilities (P < .01) when compared to fall risk (P = .09).

CONCLUSION

The Five Times Sit-to-Stand Test is a safe test, providing added value to apply risk for falls in people at moderate risk and in healthy populations using standardized chair heights and stopwatches.

Increased hip adductor activation during sit-to-stand improves muscle activation timing and rising-up mechanics in individuals with hemiparesis

Long sit-to-stand (STS) time has been identified as a feature of impaired functional mobility. The changes in biomechanics of STS performance with simultaneous hip adductor contraction have not been studied, which may limit indications for use of hip adductor activation during STS training. Ten individuals with hemiplegia (mean age 61.8 years, injury time 29.8 ± 15.2 months) performed the STS with and without squeezing a ball between two legs. The joint moments, ground reaction force (GRF), chair reaction force and movement durations and temporal index of electromyography were calculated from the control condition for comparison with those from the ball squeezing condition. Under the squeeze condition, reduced peak vertical GRF during the ascension phase with increased loading rate was observed in the nonparetic limb, and the peak knee extensor moment occurred earlier in the paretic. Earlier activation of tibialis anterior and gluteus maximus, and gluteus medius were found in squeeze STS. Squeezing a ball between limbs during STS increased the contraction timing of tibialis anterior, gluteus maximus, gluteus medius, and soleus as well as a more symmetric rising mechanics encourage the use of squeezing a ball between limbs during STS for individuals with hemiparesis.

The effects of standardised versus individualised seat height on 1-minute sit-to-stand test performance in healthy individuals: a randomised crossover trial

PURPOSE

We aimed to (i) investigate differences in 1-minute sit-to-stand test (1MSTST) performance (i.e., the number of repetitions) between a standardised modality (i.e., starting from a conventional chair with 46 cm seat height) and an individualised modality (i.e., starting with a knee joint flexion angle of 90°), and to (ii) quantify the influence of tibia and femur length on 1MSTST performance.

METHODS

Healthy participants were recruited for this randomised crossover study, performing each 1MSTST modality twice in a randomised order. The primary outcome was the number of repetitions in the 1MSTST. Secondary endpoints were the acute responses in peripheral oxygen saturation, heart rate, and leg fatigue and dyspnoea. Additionally, we investigated correlations of performance with knee extensor strength in both modalities.

RESULTS

Thirty participants were recruited and completed the study. They achieved significantly less repetitions in the standardised 1MSTST compared to the individualised 1MSTST (B = - 12.1, 95% confidence interval [95% CI] =  - 14.8/- 9.4, p < 0.001). We found a significant effect of femur length on 1MSTST performance (B = - 1.6, 95% CI = - 2.6/- 0.7, p = 0.01), tibia length showed significant interaction with the 1MSTST modality (B = 1.2, 95% CI = 0.2/2.2, p = 0.03).

CONCLUSION

An individualisation of the 1MSTST starting position to 90° knee flexion angle leads to more repetitions compared to the traditional starting position. The higher repetition count is explained by controlling for differences in tibia length. We recommend individualisation of the 1MSTST, enabling more valid comparisons across populations and study samples.

TRIAL REGISTRATION NUMBER

http://www.

CLINICALTRIALS

gov , NCT04772417.

TRIAL REGISTRATION DATE

February 26, 2021.

Effect of initial foot angle (IFA) on kinematics and dynamics of body during sit-to-stand transfer

Sit-to-stand (STS) is considered the most common functional activities in daily life and the basis for other activities. The elderly and patients with lower limb disorders could not complete the STS motion very well due to limb pain and muscle weakness. Physiotherapist find that specific STS transfer strategies can make patients more easily to complete this task. However, few researchers pay attention to the effect of initial foot angle (IFA) on STS motion. Twenty-six healthy subjects were randomly selected to perform STS transfer experiment. The motion characteristic parameters of subjects under 4 different IFAs (nature, 0°, 15°, and 30°) were obtained, including the percentage of duration in each phase, the velocity of joints, rotation angle and angular velocity of joints (shoulder, hip and knee), center of gravity (COG) trajectory. the change of plantar pressure parameters, and dynamic margin of stability. By comparing the motion characteristic parameters obtained under different IFAs and carrying out statistical analysis, the influence of different IFAs on body kinematics and dynamics during STS task was further explored. The kinematic parameters obtained under different IFAs are significantly different. The percentage of duration in each phase of the STS transfer was different with different IFA, the main differences were in phase I and phase II. The phase I of U15 took 24.5% T, while phase I of N, U0 and U30 took about 20% T, and the maximum difference was (U15-U0) 5.4%. The phase II of U15 took the least time, about 30.8% T. When the IFA is nature (N) and 15°(U15), the trajectories of COG are basically in coincidence; when the IFA is 0°(U0) and 30°(U30), the displacement of COG in anterior-posterior direction is larger. The larger the IFA, the smaller the plantar pressure parameter. When the IFA is 15°, the COG is close to the center of limits of stability, which can provide a better stability. This paper summarizes the influence under 4 different experimental conditions of IFAs on STS transfer, so as to provide a starting point and bases for clinicians to develop rehabilitation training protocols and STS motion strategies for patient.

Perceived Usability of Seating in an Outpatient Waiting Area: A Combined Approach Utilizing Virtual Reality and Actual Seating Prototypes

OBJECTIVE

This study proposed a combined methodology to evaluate the perceived usability of healthcare seats that were first selected in a virtual waiting room which provided the context of use for the seats.

BACKGROUND

There has been an increased interest in using virtual reality (VR) for evaluation of seating in interior environments. Although VR offers a less expensive approach compared to evaluating seats in situ, using VR has limitations as users cannot experience the actual seat prototypes.

METHOD

Participants (N = 92) experienced a virtual waiting room with various seat groupings and were prompted with four task-based scenarios through which they selected a seat. After the VR phase, they experienced their selected seats in a lab and used an online questionnaire to evaluate the seating. Semi-structured interviews were conducted to garner similarities and differences in participants' experience of virtual and real seats.

RESULTS

Three categories including comfort, support, and flexibility were extracted from the questionnaire. While support and comfort categories were highly ranked by participants, the category rankings varied depending on participants' age, gender, tasks, and seat types. Interviews revealed that there were differences in experience of the seating materials in VR versus reality, and therefore experiencing the real seats was useful in seating evaluation.

CONCLUSIONS

The findings suggest that the combined methodology using VR and real seating in a lab is a reliable tool for designers and furniture manufacturers to obtain users' perceived usability evaluation of seating during the design process while the actual context is absent.

Effect of Seat Backrest Inclination on the Muscular Pattern and Biomechanical Parameters of the Sit-to-Stand

Objectives: The sit-to-stand (STS) transfer mobilizes an extended part of the kinematic chain throughout a postural phase characterized by a flexion of the trunk and a focal phase consisting of a whole-body extension. The aim of this study was to analyze the variations of the global muscular pattern and the biomechanical parameters in both phases, in relation with seat backrest inclination.

Methods: Fifteen participants were asked to stand up from a seat with 5 backrest inclination settings and at 2 execution speeds. The ground reaction forces and the activity levels of fifteen muscles of the trunk and lower limbs were investigated.

Results: Backrest-induced modifications were mainly observed in the postural phase: inclining the backrest backward increased the phase duration and the activity level of the sternocleidomastoideus and the rectus abdominis, while it reduced the activity of the tibialis anterior. It also allowed for an increased maximal anteroposterior velocity of the body center of mass. Higher execution speed led to increased and earlier muscular activities of many trunk and lower limbs muscles, predominantly in the postural phase.

Discussion: Taken together, these results suggest that a greater backrest inclination increases the demand in the postural phase due to the increase of the upper body gravity torque about the ischial tuberosities, and requires an adaptation of muscular activity levels and timing, but with the same overall pattern. The kinetic energy gained during the longer excursion of the trunk may also require less activation of the lower limbs muscles involved in the generation of propulsive forces of the body.

Compensation due to age-related decline in sit-to-stand and sit-to-walk

Capacity is the physiological ability of the neuromusculoskeletal systems; this declines with age. This decline in capacity may result in the inability to stand up (sit-to-stand, sit-to-walk), which is an important movement for independent living. Compensation, as a result of functional redundancy, is key in understanding how much age-related decline can be tolerated before movement limitations arise. Yet, this topic has been underexposed in the biomechanics literature. The purpose of this systematic review was to approach the literature on sit-to-stand and sit-to-walk studies from the perspective of compensation and create an overview of our current understanding of compensation in standing up, identifying the limitations and providing future recommendations. A literature search was performed, using the keywords and their synonyms: strateg*(approach, technique, way)AND, sit-to-walk OR sit-to-stand OR rise (raise, arise, stand, stand-up) AND chair (seat). Inclusion criteria: full articles on biomechanics or motor control on sit-to-stand or sit-to-walk in healthy adults (<60y), healthy or frail elderly adults (>60y), and adults with osteoarthritis. The results show that the experimental set-ups and musculoskeletal models in STS and STW studies generally exclude compensation by using restricted protocols and simplifications. Moreover, factors are mostly analysed in isolation, excluding confounding causes within capacity and/or movement objectives which limits the generalization of the results. Future studies in the standing up task should consider to (1) determine the effect of varying arm push-off strategies, (2) focus on sit-to-walk, (3) determine the biomechanical implications of asymmetry, and (4)incorporate assessments of physical capacity as well as changes in psychological priorities.

Fast Motion Speed Alters the Sit-to-Walk Spatial and Temporal Pattern in Healthy Young Men

Sit-to-Walk (STW) is a critical task for daily independence, yet its two inherent destabilizing events (seat-off, walking initiation) may diminish postural stability under fast motion speed (FS). This study aimed at the FS effect on the STW spatial and temporal patterns, with a specific interest in the relative STW temporal pattern. The STW kinetics and kinematics were recorded (n=18 men, 20.7±2.0 years) at preferred and FS. Statistics included One-Way repeated measures ANOVA (SPSS 25.0, p≤0.05). The FS spatial pattern reveals a discontinuous mode of the forward ground reaction force, indicating a balance rather than a propulsive strategy during the Rising phase. The FS relative temporal pattern reveals the prolongation of the Leaning phase (most possibly due to the feet repositioning), the shortening of the Rising and the Walking phases, and a relative delay in the spatial variables (p≤0.05). Overall, the results do not allow the STW consideration at FS as a "magnified" with respect to force, or a "shrinked-in" with respect to time, copy of the preferred motion speed. As more generic and versatile than the absolute one, the relative temporal pattern may be used as a reference for a variety of populations.

Effects of shelf bar assistance on kinetic control during sit-to-stand in healthy young and elderly subjects

This study aimed to determine the kinetic effects of using unilateral shelf bar, vertical grab bar (GB), and horizontal GB during sit-to-stand (STS) in young and elderly subjects. Twenty young adults aged 20-40 years and eighteen healthy elderly people aged ≥ 65 years old were recruited. The subjects performed STS with and without using the three types of bars. Bar reaction force (BRF) and maximum power (MP) defined as the maximal product calculated by multiplying the GRF and the velocity of the center of mass in each direction were measured using three-dimensional motion analysis, two load sensors of GB, and four force plates. The use of the shelf bar generated a significantly larger BRF in the vertical direction than the other bars (p < 0.05) and lower MP in the vertical direction than the horizontal bar (p < 0.05) and no bar (p < 0.05). In the younger subjects, only the use of the vertical bar generated a significantly larger BRF (p < 0.05) and negative MP (p < 0.05) in the forward direction than those in elderly subjects. The use of the shelf bar may assist the decreased MP in the vertical direction during STS in elderly people, resulting in decrease of failed STS in daily living. In contrast, the use of the vertical bar in the elderly may not generate sufficient BRF in the forward direction because of lack of eccentric control in the whole body in the forward direction during STS.

Distinguishing Two Types of Variability in a Sit-to-Stand Task

Variability is commonly observed in complex behavior, such as the maintenance of upright posture. The current study examines the value added by using nonlinear measures of variability to identify dynamic stability instead of linear measures that reflect average fluctuations about a mean state. The largest Lyapunov exponent (λ1) and SD were calculated on mediolateral movement as participants performed a sit-to-stand task on a stable and unstable platform. Both measures identified changes in movement across postures, but results diverged when participants stood on the unstable platform. Large SD indicated an increase in movement variability, but small λ1 identified those movements as stable and controlled. The results suggest that a combination of linear and nonlinear analyses is useful in identifying the proportion of observed variability that may be attributed to structured, controlled sources. Nonlinear measures of variability, like λ1, can further be used to make predictions about transitions between stable postures and to identify a system’s resistance to disruption from external perturbations. Those features make nonlinear analyses highly applicable to both human movement research and clinical practice.

Individual joint contributions to the total support moment during the sit-to-stand task differentiate mild and moderate knee osteoarthritis

BACKGROUND

Knee osteoarthritis tends to modify the kinematics and kinetics of the sit-to-stand task. However, it is not clear whether the different degrees of knee osteoarthritis differentiate regarding these aspects. The objective was to identify if the trunk flexion, lower limb kinetics, total support moment, and individual joint contributions to the total support moment during the sit-to-stand task are different between patients with mild and moderate knee osteoarthritis.

METHODS

Sixty-two participants were grouped as follows: moderate knee osteoarthritis (n = 16), mild knee osteoarthritis (n = 25), and controls (n = 21). The participants performed a sit-to-stand task, which was analyzed using a 3D-motion system and a force plate.

FINDINGS

The three phases of the sit-to-stand task were analyzed. During Phase₁, the moderate osteoarthritis group decreased the total support moment (P = 0.012). During Phase₂, the moderate osteoarthritis group showed higher trunk flexion (P = 0.023) and lower internal hip and knee extension moments (P ≤ 0.001 and P ≤ 0.040, respectively) when compared to controls. Also in Phase₂, both the mild and moderate groups used lower total support moment (P = 0.019, and P ≤ 0.001, respectively). When compared to the controls and mild osteoarthritis group_, those with moderate osteoarthritis presented higher hip joint contribution to the total support moment (P ≤ 0.001 and P = 0.006, respectively) as well as lower knee joint contribution (P ≤ 0.003 and P = 0,013, respectively).

INTERPRETATION

Those with moderate osteoarthritis showed modified sit-to-stand movement pattern. While in Phase₃ a higher contribution of the hip joint to the total support moment was observed, during previous phases the individuals were able to decrease the load on the knee without influencing the lower limb load distribution.

The Automatic Assessment of Strength and Mobility in Older Adults: A Test-Retest Reliability Study

Background: Simple field tests such as the Timed Up and Go test (TUG) and 30 s Chair Stand test are commonly used to evaluate physical function in the elderly, providing crude outcome measures. Using an automatic chronometer, it is possible to obtain additional kinematic parameters that may lead to obtaining extra information and drawing further conclusions. However, there is a lack of studies that evaluate the test-retest reliability of these parameters, which may help to judge and interpret changes caused by an intervention or differences between populations. Thus, the aim of this study was to evaluate the test-retest reliability of the Timed Up and Go test (TUG) and 30 s Chair Stand test in healthy older adults. Methods: A total of 99 healthy older adults participated in this cross-sectional study. The TUG and the 30 s Chair Stand test were performed five times and twice, respectively, using an automatic chronometer. The sit-to-stand-to-sit cycle from the 30 s Chair Stand test was divided into two phases. Results: Overall, reliability for the 30 s Chair Stand test was good for almost each variable (intraclass correlation coefficient (ICC) >0.70). Furthermore, the use of an automatic chronometer improved the reliability for the TUG (ICC >0.86 for a manual chronometer and ICC >0.88 for an automatic chronometer). Conclusions: The TUG and the 30 s Chair Stand test are reliable in older adults. The use of an automatic chronometer in the TUG is strongly recommended as it increased the reliability of the test. This device enables researchers to obtain relevant and reliable data from the 30 s Chair Stand test, such as the duration of the sit-to-stand-to-sit cycles and phases.

Muscle activity and balance control during sit-to-stand across symmetric and asymmetric initial foot positions in healthy adults

BACKGROUND

Rising from a sit to a stand has biomechanical factors that are dependent on initial foot position. Little is known about the effect of initial foot position on leg muscle activation patterns during a sit-to-stand and balance maintenance of stance after a sit-to-stand.

RESEARCH QUESTION

What are the effects of different symmetric and asymmetric initial foot positions on leg muscle activation patterns and balance during and after a sit-to-stand?

METHODS

Three symmetric (neutral; both ankles positioned under the knees at a 90° flexion; one-third; and two-thirds foot length posterior to neutral) and three asymmetric (neutral non-dominant leg with one-third back dominant leg, neutral non-dominant with two-thirds back dominant leg, and one-third back non-dominant leg with two-thirds back dominant leg) initial foot positions were tested. EMG of the lower extremity muscles and sagittal plane kinematic data were measured along with balance assessments in the anterior-posterior and medial-lateral axes.

RESULTS

In the symmetric initial foot positions, a faster forward velocity of the body's center of mass was required for more anterior initial foot positions. Even though the hip extensors activated earlier to decelerate the forward velocity of the body's center of mass before rising, the greater forward velocity caused postural sway following completion of upright stance. In the asymmetric initial foot positions, the posterior leg supported more weight during the sit-to-stand, resulting in balance perturbations in the posterior leg. In the one-third back non-dominant leg with two-thirds back dominant leg asymmetric initial foot position, however, the weight-bearing symmetry was not different from the symmetric initial foot positions during the sit-to-stand. Postural stability after completion of uprising was also improved in this asymmetric initial foot position, showing greater but delayed onset of the tibialis anterior in the anterior leg during the momentum transfer phase.

SIGNIFICANCE

With a neutral symmetric initial foot position, earlier onset of the hip extensors during eccentric lengthening contributed to decelerating the forward velocity of the body's center of mass for balance control during a sit-to-stand. With asymmetric initial foot positions, the weight distribution during a sit-to-stand can be increased by positioning both feet posterior to neutral foot position. Performing a sit-to-stand with this asymmetric initial foot position can improve postural stability after uprising. Thus, this foot position could be used in designing rehabilitation interventions for clinical populations and the frail elderly.

Knee extensor torque and BMI differently relate to sit-to-stand strategies in obesity

BACKGROUND

Obesity alters whole body kinematics during activities of daily living such as sit-to-stand (STS), but the relative contributions of excess body mass and decreased relative strength are unknown.

METHODS

Three-dimensional motion analysis data was collected on 18 obese subjects performing sit-to-stand (chair height: 52 cm). Isometric knee extensor strength was measured at 90⁰ knee flexion. Forward stepwise linear regression was used to determine the association between the independent variables BMI and the knee extensor torque with the dependent variables: foot position and trunk kinematics.

FINDINGS

BMI, but not knee extensor torque, was inversely related to shank angle and positively related to stance width. Relative knee extensor torque, but not BMI, was inversely associated with initial trunk angle, peak trunk flexion angle, and peak trunk extension velocity (r² = 0.470-0.495). BMI was positively associated with peak trunk flexion velocity, but no other parameters of trunk kinematics. In the final regression model, BMI was the primary predictor (r² = 0.423) and relative knee extensor strength served as a secondary predictor (r² = 0.118) of peak trunk flexion velocity.

INTERPRETATION

BMI and knee extensor strength differently contribute to sit-to-stand performance strategies in obese subjects. Muscle strength may be an important determinant of whole-body kinematics during activities of daily living such as STS.

Asymmetrical loading during sit-to-stand movement in patients 1 year after total hip arthroplasty

BACKGROUND

Asymmetrical loading during functional performance can occur after total hip arthroplasty. We hypothesized that during sit-to-stand movements, the loading of the limbs of patients who undergo total hip arthroplasty is more asymmetrical than that of those who do not. The objective of the present study was to compare asymmetrical loading during the sit-to-stand movements of patients at 1 year after undergoing total hip arthroplasty, and that of healthy adults.

METHODS

Twenty-eight patients at 1 year after undergoing total hip arthroplasty and 16 healthy adults were included. We measured the vertical ground reaction force during the sit-to-stand movement for each leg and calculated the ratio of the peak vertical ground reaction force, and the ratio at the time of peak magnitude of the non-operated limb (control, right limb).

FINDINGS

The mean peak vertical ground reaction force ratio of the patients was 0.77 (0.2), and it was significantly lower than that of healthy adults. The vertical ground reaction force ratio for these patients at the time of peak magnitude of the non-operated limb was 0.72 (0.2), and was significantly lower than that of healthy adults.

INTERPRETATION

Loading on the operated leg during the sit-to-stand movement was lower than that on the non-operated leg in patients at 1 year after undergoing total hip arthroplasty. Furthermore, loading during sit-to-stand movement of patients 1 year after undergoing total hip arthroplasty was more asymmetrical than that of healthy adults. Even at 1 year after undergoing total hip arthroplasty, these patients performed the sit-to-stand movement asymmetrically.

Electromyographic activity of quadriceps muscle during sit-to-stand in patients with unilateral knee osteoarthritis

Objective

The sit-to-stand (STS) is a simple test to evaluate the functional performance of the quadriceps muscle in patients with knee osteoarthritis (OA). The aim was to evaluate the electromyographic (EMG) activity of the ipsilateral quadriceps during STS task at different seat heights and feet positions in patients with severe unilateral OA. The EMG activity was recorded in a group of eight participants with unilateral OA during the performance of STS task in four conditions: (1) knee-height seat with feet together, (2) knee-height seat with feet askew (feet side by side and heel-to-toe), (3) low-height seat (25% lower than knee-height seat) with feet together, and (4) low-height seat with feet askew.

Results

There was a statistically significant difference among the four conditions in the EMG activity (p =0.004). Particularly, the EMG activity of the quadriceps was significantly higher when participants rose from the low height with their feet askew than when they rose from the knee height with their feet placed together (p =0.004) or askew (p =0.002). These results recommend considering initial feet position and seat height when evaluating the functional activity of the quadriceps in patients with unilateral OA using STS test.

Nondestructive Estimation of Muscle Contributions to STS Training with Different Loadings Based on Wearable Sensor System

Partial body weight support or loading sit-to-stand (STS) rehabilitation can be useful for persons with lower limb dysfunction to achieve movement again based on the internal residual muscle force and external assistance. To explicate how the muscles contribute to the kinetics and kinematics of STS performance by non-invasive in vitro detection and to nondestructively estimate the muscle contributions to STS training with different loadings, a wearable sensor system was developed with ground reaction force (GRF) platforms, motion capture inertial sensors and electromyography (EMG) sensors. To estimate the internal moments of hip, knee and ankle joints and quantify the contributions of individual muscle and gravity to STS movement, the inverse dynamics analysis on a simplified STS biomechanical model with external loading is proposed. The functional roles of the lower limb individual muscles (rectus femoris (RF), gluteus maximus (GM), vastus lateralis (VL), tibialis anterior (TA) and gastrocnemius (GAST)) during STS motion and the mechanism of the muscles' synergies to perform STS-specific subtasks were analyzed. The muscle contributions to the biomechanical STS subtasks of vertical propulsion, anteroposterior (AP) braking and propulsion for body balance in the sagittal plane were quantified by experimental studies with EMG, kinematic and kinetic data.

Noninvasive Estimation of Joint Moments with Inertial Sensor System for Analysis of STS Rehabilitation Training

An original approach for noninvasive estimation of lower limb joint moments for analysis of STS rehabilitation training with only inertial measurement units was presented based on a piecewise three-segment STS biomechanical model and a double-sensor difference based algorithm. Joint kinematic and kinetic analysis using a customized wearable sensor system composed of accelerometers and gyroscopes were presented and evaluated compared with a referenced camera system by five healthy subjects and five patients in rehabilitation. Since there is no integration of angular acceleration or angular velocity, the result is not distorted without offset and drift. Besides, since there are no physical sensors implanted in the lower limb joints based on the algorithm, it is feasible to noninvasively analyze STS kinematics and kinetics with less numbers and types of inertial sensors than those mentioned in other methods. Compared with the results from the reference system, the developed wearable sensor system is available to do spatiotemporal analysis of STS task with fewer sensors and high degree of accuracy, to apply guidance and reference for rehabilitation training or desired feedback for the control of powered exoskeleton system.

Immediate effects of quick trunk movement exercise on sit-to-stand movement in children with spastic cerebral palsy: a pilot study

[Purpose] This pilot study examined the immediate effects of quick-seated trunk exercise on sit-to-stand movement in children with cerebral palsy. [Subjects and Methods] Five children with spastic cerebral palsy (hemiplegia, 3; diplegia, 2; age 6–17 years) performed five sessions of natural-seated trunk exercise at a self-selected speed (control). Following a 50-min rest period, five sessions of the quick-seated trunk exercise were conducted (experimental intervention) for each child. Each seated trunk exercise included 10 repetitions in the anterior-posterior and lateral directions. Sit-to-stand was assessed before and after each intervention using a motion analysis system. The total sit-to-stand task duration and sagittal, angular movements of the trunk, hip, knee, and ankle were calculated. [Results] There was a significant difference in the total duration of the sit-to-stand movement before and after natural-seated trunk exercise (2.40 ± 0.67 s vs. 2.24 ± 0.44 s) as well as quick seated trunk exercise (2.41 ± 0.54 s vs. 2.06 ± 0.45 s). However, the sit-to-stand duration increased after natural-seated trunk exercise in one participant while that after quick-seated trunk exercise decreased in all participants. [Conclusion] Performing a trunk exercise in a seated position resulted in immediate improvement of the temporal sit-to-stand parameters in children with spastic cerebral palsy.

Study of the Relationship Between Sit-to-Stand Activity and Seat Orientation

Sit-to-stand (STS) activity from a chair is an important motion in daily life. Some commercial products assist with STS activity in toilet use. These products control seat orientation by changing three parameters, i.e., seat height, tilt, and shift in a forward-backward direction. The reason for selection of these three parameters for seat orientation control has not been reported. Moreover, there are no reports on the best combination of these parameters. Therefore, in this study, we investigated the relationship between ease of STS activity and seat orientation during STS activity. We found that seat tilting provided good support for STS activity when the seat was in a high position (0.55 m), and shifting the seat forward provided good support for STS activity when the seat was higher than 0.45–0.55 m.

Impact of Fibromyalgia in the Sit-to-Stand-to-Sit Performance Compared With Healthy Controls

BACKGROUND

Fibromyalgia is associated with a reduction in the ability to perform activities of daily living. Sit-to-stand-to-sit performance is one of the most common activities of daily living and often is evaluated by counting the number of repetitions of the 30-second chair-stand test. No study, however, has examined the performance over the 30 seconds of this test of female patients with fibromyalgia on a phase-by-phase basis.

OBJECTIVE

To evaluate the impact of fibromyalgia on performance of the 30-second chair-stand test and to analyze how the kinematic performance changed over the 30-second test period.

DESIGN

A cross-sectional study.

SETTING

Local association of fibromyalgia.

PARTICIPANTS

Fifteen females with fibromyalgia and nine healthy female controls.

INTERVENTION

Participants performed the 30-second chair-stand test while wearing a motion capture device.

MAIN OUTCOME MEASURE

Duration of each sit-to-stand-to-sit phase within the 30-second time limit was compared between groups using repeated measures analysis of variance. The association between duration of phases and scores from the revised version of the Fibromyalgia Impact Questionnaire was tested using bivariate correlations.

RESULTS

The duration of impulse and sit-to-stand phases were gradually increased over the 30 seconds of the chair-stand test for women with fibromyalgia compared with healthy controls (P = .04 and P = .02, respectively). The mean duration of these 2 phases was associated with symptom duration and the function domain of the revised version of the Fibromyalgia Impact Questionnaire (P < .05). Also, stiffness was directly associated with the duration of the stand-up phase (P = .04).

CONCLUSION

Kinematic performance during the 30-second chair-stand test differed between women with fibromyalgia and healthy controls. Since sit-to-stand from a chair is a common daily activity, women with fibromyalgia may require specific exercises to improve performance of this task.

LEVEL OF EVIDENCE

Not applicable.

Searching for strategies to reduce the mechanical demands of the sit-to-stand task with a muscle-actuated optimal control model

BACKGROUND

The sit-to-stand task, which involves rising unassisted from sitting on a chair to standing, is important in daily life. Many people with muscle weakness, reduced range of motion or loading-related pain in a particular joint have difficulty performing the task. How should a person suffering from such impairment best perform the sit-to-stand task and, in the case of pain in a particular joint, with reduced loading of that joint?

METHODS

We developed a musculoskeletal model with reference parameter values based on properties of healthy strong subjects. The model's muscle stimulation-time input was optimized using direct collocation to find strategies that yielded successful sit-to-stand task performance with minimum 'control effort' for the reference set and modified sets of parameter values, and with constraints on tibiofemoral compression force.

FINDINGS

The sit-to-stand task could be performed successfully and realistically by the reference model, by a model with isometric knee extensor forces reduced to 40% of reference, by a model with isometric forces of all muscles reduced to 45% of reference, and by the reference model with the tibiofemoral compression force constrained during optimization to 65% of the peak value in the reference condition.

INTERPRETATION

The strategies found by the model in conditions other than reference could be interpreted well on the basis of cost function and task biomechanics. The question remains whether it is feasible to teach patients with musculoskeletal impairments or joint pain to perform the sit-to-stand task according to strategies that are optimal according to the simulation model.

A novel protocol to test age-related decreases in sit-to-stand movement abilities in healthy subjects

BACKGROUND

The development of simple approaches to quantitatively estimate functional motor performance in a wide range of ages is crucial for early detection of locomotive syndrome (LS). Sit-to-stand (STS) movements from a chair are important in activities of daily living (ADL), although such tasks are the most mechanically demanding among all ADL. Here, we propose a novel test to score STS abilities to estimate individual functional motor status and investigated age-related changes in STS scores as a method to evaluate reduction in performance.

METHODS

A total of 606 healthy subjects (average age, 48.4 years; age range, 20-87 years) without neuromusculoskeletal disorders participated in the study. We designed a test to score STS abilities, based on STS determinant variables, including seat height, foot positioning, and both-leg- or one-leg-standing tasks. STS scores ranged from 0 to 14 points, depending on the difficulty or mechanical demands of the STS task. We evaluated the STS score of the subjects divided into seven 10-year age groups.

RESULTS

A significant and negative correlation was observed between STS scores and subject age (men: r = -0.65, P < 0.001; women: r = -0.62, P < 0.001). The proportion of subjects able to stand on one leg from a chair seat height of 100% of knee height decreased with age from 100% for both men and women aged 20-29 years to 0.0% and 7.1% for men and women aged 80-87 years, respectively. A large variation in STS scores was observed for subjects aged >60 years. There was a negative linear correlation between mean STS score per age group and mean age (men: R(2) = 0.93, slope = -0.10, intercept = 16.63 points; women: R(2) = 0.92, slope = -0.08, intercept = 14.76 points).

CONCLUSIONS

The ability to perform STS was negatively correlated with age among healthy subjects aged 20-87 years. For subjects aged >60 years, STS abilities decreased, but within-group variability increased. This test was useful to identify the deterioration of functional motor performance and prevent early LS.

Comparison of center-of-pressure displacement during sit-to-stand according to chair height in children with cerebral palsy

[Purpose] In patients with cerebral palsy (CP), performance of the sit-to-stand (STS) task is influenced by an asymmetrical motor pattern. The purpose of this study was to analyze the effects of an elevated chair on STS performance in patients with CP. [Subjects and Methods] Nine CP patients performed STS from a height-adjustable instrumented chair at their natural speed, with the ankle at a 90° angle to the floor. The center-of-pressure (COP) displacement was recorded under the feet. Each foot position was tested at two chair heights corresponding to 100% and 120% of the leg length. The extent and speed of COP were calculated. [Results] The anteroposterior speed and extent of COP were greater with the standard chair than with the elevated chair. The other parameters such as mediolateral speed, extent, and vertical speed of the COP were not different between the two chairs. [Conclusion] These findings suggest that the sway with STS performed from the elevated chair was lesser than that with STS performed from the standard chair. This information will be relevant to clinicians involved in the rehabilitation of CP patients and will help identify factors that influence STS performance.

Effect of arm position and foot placement on the five times sit-to-stand test completion times of female adults older than 50 years of age

The five times-sit-to stand test (FTSTS) is a clinical test which is commonly used to assessed the functional muscle strength of the lower limbs of older adults. The aim of this study was to examine the effect of different arm positions and foot placements on the FTSTS completion times of older female adults. [Subjects and Methods] Twenty-nine healthy female subjects, aged 63.1±5.3 years participated in this cross-sectional study. The times required to complete the FTSTS with 3 different arm positions (hands on thighs, arms crossed over chest, and an augmented arm position with the arms extended forward) and 2 foot placements (neutral and posterior) were recorded. The interaction effect and main effect of arm positions and foot placements were examined using a 3 (arm position) × 2 (foot placement) two-way repeated measures analysis of variance (ANOVA). [Results] There was no interaction effect among the 3 arm positions in the 2 foot placements. A significant main effect was identified for foot placement, but not arm position. Posterior foot placement led to a shorter FTSTS time compared to that of normal foot placement. [Conclusion] With the same arm position, FTSTS completion times with posterior foot placement tended to be shorter. Therefore, the standard foot placement should be used for FTSTS administration.

The effect of total hip and hip resurfacing arthroplasty on vertical ground reaction force and impulse symmetry during a sit-to-stand task

BACKGROUND

The aim of this study was to determine the influence of total hip arthroplasty and hip resurfacing arthroplasty on limb loading symmetry before, and after, hip reconstruction surgery during a sit-to-stand task.

METHODS

Fourteen patients were recruited that were about to receive either a total hip prosthesis (n=7) or a hip resurfacing prosthesis (n=7), as well as matched controls. Patients performed a sit-to-stand movement before, 3 months after, and 12 months after surgery. Peak vertical ground reaction force and impulse were measured for each leg, from which ground reaction force and impulse symmetry ratios were calculated.

FINDINGS

Before surgery, hip resurfacing patients showed a small asymmetry which was not different to normal for ground reaction force (0.88(0.28) vs. 1.00(0.11); p=0.311) or impulse (0.87(0.29) vs. 0.99(0.09); p=0.324) symmetry ratios. Total hip patients offloaded their affected hip by 30% in terms of impulse symmetry ratio (0.71(0.36) vs. 0.99(0.23); p=0.018). At 3 months following surgery asymmetries were seen that were different to normal in both hip resurfacing patients for ground reaction force (0.77(0.16); p=0.007), and total hip patients for ground reaction force (0.70(0.15); p=0.018) and impulse (0.72(0.16); p=0.011) symmetry ratios. By 12 months after surgery total hip patients regained a symmetrical loading pattern for both ground reaction force (0.95(0.06); p=0.676) and impulse (1.00(0.06); p=0.702) symmetry ratios. Hip resurfacing patients, however, performed the task by overloading their operated hip, with impulse symmetry ratio being larger than normal (1.16(0.16); p=0.035).

INTERPRETATION

Physiotherapists should appreciate the need for early recovery of limb loading symmetry as well as subsequent differences in the responses observed with different prostheses.

The effects of seat height and foot placement on lumbar spine load during sit-to-stand tasks

The purpose of this study was to determine the influence of seat height and foot position in the sagittal plane on L5-S1 joint load. Fourteen healthy male adults stood up from a chair with three different seat heights and positions of the feet in the sagittal plane. L5-S1 net joint torque, mechanical work, range of motion and electromyographic activity of the erector spinae muscle were measured. L5-S1 net joint work increased by about 50% from high to low seat position. The mean and peak L5-S1 net joint torques increased about 30% from foot-back to foot-neutral position. These results were reinforced by a greater integrated electromyography signal from the erector spinae from high to low seat position and from foot-back to foot-neutral position. A high chair and placement of the feet behind the knees may be advisable to lessen lumbar load during sit-to-stand movements.

Foot placement and arm position affect the five times sit-to-stand test time of individuals with chronic stroke

Objectives. To investigate the effect of two foot placements (normal or posterior placement) and three arm positions (hands on the thighs, arms crossed over chest, and augmented arm position with elbow extended) on the five times sit-to-stand (FTSTS) test times of individuals with chronic stroke. Design. Cross-sectional study. Setting. University-based rehabilitation clinic. Participants. A convenience sample of community-dwelling individuals with chronic stroke (N = 45). Methods. The times in completing the FTSTS with two foot placements and the three arm positions were recorded by stopwatch. Results. Posterior foot placement led to significantly shorter FTSTS times when compared with normal foot placement in all the 3 arm positions (P ≤ 0.001). In addition, hands on thigh position led to significantly longer FTSTS times than the augmented arm position (P = 0.014). Conclusion. Our results showed that foot placement and arm position could influence the FTSTS times of individuals with chronic stroke. Standardizing the foot placement and arm position in the test procedure is essential, if FTSTS test is intended to be used repeatedly on the same subject.

Muscle Synergy Analysis Between Young and Elderly People in Standing-Up Motion

Standing up is fundamental to daily activities of the elderly. It is necessary both to enhance muscle strength and to strengthen muscle coordination for improvement of their motor function. In this paper, we extract important data related to muscle coordination, called synergy, to perform standing motion by young and elderly participants. The contribution of muscle synergy to body kinematics is calculated through neural networks that estimate joint torque and body kinematics. To explain deficient motor function in elderly persons, extracted synergy is classified into 4 clusters based on how synergy contribute to body kinematics. Cluster analysis explains that elderly participants have weaker synergy than young persons in bending their backs to generate momentum. Compared to younger persons, older persons require additional muscle coordination to stabilize posture after standing-up in order to avoid falling.

Sagittal plane center of mass movement strategy and joint kinetics during sit-to-walk in elderly fallers

BACKGROUND

Biomechanical studies have shown that the horizontal center of mass momentum at seat-off during sit-to-walk is reduced among elderly adults. However, the underlying mechanism of this phenomenon is still lacking. The purpose of this study was to examine differences in center of mass movement strategies and lower extremity joint kinetics in the elderly during sit-to-walk.

METHODS

Fifteen healthy young adults, fifteen healthy elderly adults (70 years or older) and fifteen elderly fallers performed Timed Up and Go test. Biomechanical data collected from sit-to-walk phase of Timed Up and Go test were analyzed. Outcome measures included center of mass-ankle inclination angles, hip, knee and ankle joint moments, and ground reaction forces of the stance limb.

FINDINGS

Results reported here are from 10 participants in each group due to missing force place data. Elderly fallers adopted a movement strategy that included a posterior foot placement at seat-off, a longer duration, and a shorter initial step length. When compared to healthy individuals, elderly fallers demonstrated a greater ankle plantarflexor moment at seat-off.

INTERPRETATION

Increased ankle plantarflexor moment in elderly fallers could be a movement strategy to improve stability during sit-to-walk and may be related to the reduced ankle dorsiflexor strength commonly reported in elderly fallers. Results of this study enhance our understanding on the underlying mechanisms of the altered sit-to-walk movement and could aid in developing effective screening and rehabilitation programs to prevent falling in the elderly.

Association between chair stand strategy and mobility limitations in older adults with symptomatic knee osteoarthritis

OBJECTIVE

To determine which lower limb strength and joint kinetic and kinematic parameters distinguish sit-to-stand (STS) performance of older adults with symptomatic knee osteoarthritis (OA) with higher and lower chair stand time.

DESIGN

Cross-sectional.

SETTING

Motion analysis laboratory.

PARTICIPANTS

Individuals (N=49; 26 men, 23 women) aged 50 to 79 years (mean ± SD age, 64.7±8.1y) with radiographic knee OA and daily symptoms, stratified by chair stand times.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Lower limb strength and STS strategy.

RESULTS

The chair stand times (mean ± SD) in the high-, moderate-, and low-functioning groups in men were 6.5±0.7, 8.6±0.7, and 11.5±1.3 seconds, respectively, and in women were 7.6±1.2, 10.0±0.5, and 12.8±1.8 seconds, respectively. Chair stand time (P=.0391) and all measures of lower limb strength (all P<.0001) differed by sex. In men, no strength measure differed between groups, whereas in women hip abductor strength on the more affected side differed between groups. In men, sagittal hip range of motion (ROM) (P=.0122) differed between groups, and there was a trend toward a difference in sagittal knee power (P=.0501) during STS, while in women only sagittal knee ROM (P=.0392) differed between groups.

CONCLUSIONS

Higher- and lower-functioning adults with symptomatic knee OA appear to use different strategies when standing from a chair. Higher-functioning men flexed more at the hip and produced greater knee power than lower-functioning men. Higher-functioning women used less knee flexion than lower-functioning women. Since STS is an important mobility task, these parameters may serve as foci for rehabilitation aimed at reducing mobility limitations.

The effects of symmetric and asymmetric foot placements on sit-to-stand joint moments

The purpose of this study was to determine the effects of symmetric and asymmetric foot placements on joint moments during sit-to-stand movements. Three symmetric (foot-neutral, foot-back, and foot-intermediate) and three asymmetric foot placements (preferred stagger, nonpreferred stagger, and intermediate stagger) were tested. Standard (46 cm) and low (41 cm) seat heights were chosen to represent an average public seat height and a 10% lower seat height. Using inverse dynamics, maximum ankle plantarflexion, knee extension, hip extension, and hip abduction moments were calculated. Hip extension moments were significantly increased when using foot-neutral as compared to foot-back. Ankle plantarflexion and knee extension moments were significantly increased when a foot was placed in the posterior position as compared to the anterior position for preferred and nonpreferred stagger. Knee extension moments were significantly increased at the low seat height as compared to the standard seat height. When shifting the feet anterior or posterior for symmetric placements during sit-to-stand, the most dramatic effect was an increase in hip extension moments when the feet are shifted anteriorly. Utilizing asymmetric foot placements during sit-to-stand produced increases in ankle plantarflexion and knee extension moments for the posteriorly placed limb, with reductions in the anteriorly placed limb.

Sit-to-stand movement in children with cerebral palsy: a critical review

Sit-to-stand (STS) movement is widely performed in daily life and an important pre requisite for acquisition of functional abilities. However, STS is a biomechanical demanding task which requires high levels of neuromuscular coordination, muscle strength and postural control. As children with cerebral palsy (CP) exhibit a series of impairments in body structures and functions, STS movement performance could be impaired in this population. Thus, this article aimed to review studies that had described how STS movement is performed by children with CP, the factors that influence it and the methodological procedures adopted in it analyses. A search was performed by one reviewer in relevant databases. In all, 12 articles were identified and 9 were selected for the present review. It was detected a large variation in sample characteristics and methodological issues among studies. In fact, standardization of the method applied to STS movement analysis is not fully established. With regard to STS performance, children with CP exhibited variations among them and also when compared with their typical peers. Moreover extrinsic factors appear to influence STS movement performance in these children and its manipulation could be incorporated into rehabilitation protocols. Moreover, the relationship between STS movement and functionality in reviewed articles was not reported. Therefore the review allowed to observe that STS movement has been under-explored in children with CP, with a lack of standardized methodologies and a not well established relationship between this movement and functionality. Thus, further studies about STS movement in CP are necessary.

Prolonged weight-shift and altered spinal coordination during sit-to-stand in practitioners of the Alexander Technique

The Alexander Technique (AT) is used to improve postural and movement coordination and has been reported to be clinically beneficial, however its effect on movement coordination is not well-characterized. In this study we examined the sit-to-stand (STS) movement by comparing coordination (phasing, weight-shift and spinal movement) between AT teachers (n=15) and matched control subjects (n=14). We found AT teachers had a longer weight-shift (p<0.001) and shorter momentum transfer phase (p=0.01), than control subjects. AT teachers also increased vertical foot force monotonically, rather than unweighting the feet prior to seat-off, suggesting they generate less forward momentum with hip flexors. The prolonged weight-shift of AT teachers occurred over a greater range of trunk inclination, such that their weight shifted continuously onto the feet while bringing the body mass forward. Finally, AT teachers had greatly reduced spinal bending during STS (cervical, p<0.001; thoracic, p<0.001; lumbar, p<0.05). We hypothesize that the low hip joint stiffness and adaptive axial postural tone previously reported in AT teachers underlies this novel "continuous" STS strategy by facilitating eccentric contractions during weight-shift.

Challenging horizontal movement of the body during sit-to-stand: impact on stability in the young and elderly

There are 3 significant challenges to sit-to-stand: (a) bringing the center of mass forward, (b) vertically raising the center of mass from the sitting to standing position, and (c) transition from a relatively large and stable base of support in sitting to a considerably smaller base of support when standing. The authors explored the challenges to stability control following sit-to-stand when the requirement for horizontal movement of the center of mass was influenced by foot position and their potential effect on the preceding phases of sit-to-stand. Eleven healthy young and 11 healthy elderly individuals performed the sit-to-stand with their feet further away and closer to the chair. Kinetic and kinematic data were recorded. Regardless of foot position, challenges in stability were greater in elderly participants than young participants despite their similar movement time and shear forces. The greater instability in elderly participants, despite their comparable movement characteristics, emphasizes the importance of stability control following sit-to-stand performance. For both young and elderly participants, the sit-to-stand duration and the shear forces were greater in the far condition. However, foot position did not affect the stability measures (i.e., duration of the stabilization phase and the total center of pressure path during the 1st second of the stabilization phase).

An in situ study of the habits of users that affect office chair design and testing

OBJECTIVE

The purpose of this study was to perform an in situ assessment of office seating habits that influence chair testing and design.

BACKGROUND

Many chair testing parameters were derived decades ago when the average weight of people within the United States was dramatically lower and the office work tasks less computer based.

METHOD

For the study, 51 participants were randomly selected from Brazos Valley, Texas, businesses to participate in 8-hr assessments of office seating habits. Overall results were compared with current chair testing and design assumptions. Data were collected through written survey and through data logging of seat and back contact pressure and duration with the use of the X-SENSOR pressure mapping device and software. Additionally, I day per participant of caster roll distance was recorded with the use of a caster mounted digital encoder. Participants were grouped by body mass index (BMI) and weight (BMI <35 and weight < 102 kg or BMI >35 and weight >102 kg).

RESULTS

It was determined that a significant difference did exist between the groups in mean seat time per shift (p < .001), back cycles per shift (p < .002), seat cycles per shift (p < .01), and caster distance rolled per shift (p < .001).

CONCLUSION

Several key parameters and assumptions of current chair test methods and design specifications may no longer be valid for the upper quartile of weight range of the current U.S. population.

APPLICATION

The data collected in this study will enable engineers to determine whether revision of design standards for testing office seating for both normal weight and extremely obese workers is indicated.

Non-paretic lower limb constraint with a step decreases the asymmetry of vertical forces during sit-to-stand at two seat heights in subjects with hemiparesis

This study investigated the effects of non-paretic leg constraint by a step, combined with two different seat heights, on weight-bearing on the paretic leg and reduction of asymmetry during STS. Thirteen adult subjects (60.4 ± 5.7 years) were selected, with chronic hemiparesis (43.7 ± 50 months) due to stroke. Two force plates were used to analyze the vertical force (Fz) in the standing position and during STS. Individuals were instructed to rise from an instrumented bench at two seat heights, 100% (normal) and 130% (elevated) of knee height with four foot positions: (1) spontaneous (SPO); (2) symmetrical (SYM); (3) asymmetrical (ASY; non-paretic limb in front of paretic); and (4) step (STP; non-paretic limb supported on a step and paretic at ground level). A reduction of asymmetry occurred during STS movement when the non-paretic leg was constrained by a step compared with positions SPO (p<0.001), SYM (p<0.001) and ASY (p=0.02) at the normal seat level. Raising seat height to 130% increased asymmetry in the SPO condition (p=0.01); however, this effect was reversed in the ASY and STP conditions. Constraint of the non-paretic leg by a step is presented as a potential therapeutic route to a less asymmetrical STS. Together with a higher seat level this can benefit the training of individuals with hemiparesis unable to keep the paretic foot backward during STS from a standard seat height.

Musculoskeletal biomechanics in sit-to-stand and stand-to-sit activities with stroke subjects: a systematic review

INTRODUCTION: Sit-to-stand and stand-to-sit are two of the most mechanically demanding activities undertaken in daily life and which are usually impaired in stroke subjects. OBJECTIVES: To determine the distinguishing characteristics in musculoskeletal biomechanical outcomes of the sit-to-stand and stand-to-sit activities with stroke subjects, with an emphasis on the clinical management of stroke disabilities, in a systematic review. MATERIAL AND METHODS: An extensive literature search was performed with the MEDLINE, CINAHL, EMBASE, PEDro, LILACS, and SciELO databases, followed by a manual search, to select studies on musculoskeletal biomechanical outcomes in both activities with stroke subjects, without language restrictions, and published until December/2007. RESULTS: Out of the 432 studies, only 11 reported biomechanical outcomes of both activities and none reached the total score on the selected quality parameters. The majority of the experimental studies which compared groups did not achieve acceptable scores on their methodological quality (PEDRo). The investigated conditions and interventions were also restricted. Only one study compared biomechanical outcomes between the activities, but only evaluated the time spent to perform them. Few musculoskeletal biomechanical outcomes have been investigated, being weight bearing on the lower limbs and duration of the activities the most investigated. CONCLUSION: There is little information regarding musculoskeletal biomechanical outcomes during these activities with stroke subjects and no definite conclusions can be drawn regarding the particularities of these outcomes on their performance with stroke survivors.

Influence of moving visual environment on sit-to-stand kinematics in children and adults

The effect of visual field motion on the sit-to-stand kinematics of adults and children was investigated. Children (8 to12 years of age) and adults (21 to 49 years of age) were seated in a virtual environment that rotated in the pitch and roll directions. Participants stood up either (1) concurrent with onset of visual motion or (2) after an immersion period in the moving visual environment, and (3) without visual input. Angular velocities of the head with respect to the trunk, and trunk with respect to the environment, w ere calculated as was head andtrunk center of mass. Both adults and children reduced head and trunk angular velocity after immersion in the moving visual environment. Unlike adults, children demonstrated significant differences in displacement of the head center of mass during the immersion and concurrent trials when compared to trials without visual input. Results suggest a time-dependent effect of vision on sit-to-stand kinematics in adults, whereas children are influenced by the immediate presence or absence of vision.

Total knees designed for normal kinematics evaluated in an up-and-down crouching machine

We constructed a crouching machine to study the motion of the knee joint, in which a motor was used to wind the quadriceps tendon so as to move the knee from high flexion to extension and back into flexion, while springs simulated hamstrings forces. Seven human cadaveric knees were tested intact and then after anterior cruciate ligament (ACL) resection. Motions of the femur, tibia, and patella were recorded by an optical tracking system. We then inserted plastic models representing commonly used total condylar and posterior stabilized knee replacement designs. Femoral motion was described by successive positions of the transverse axis of the femur projected onto the tibial surface. In the knee replacements, motions were similar to that of an ACL-deficient knee. We then tested two new designs with features intended to prevent anterior paradoxical sliding and to promote a medial pivot motion with femoral rollback primarily on the lateral side. The motion path more closely followed that of the normal intact knee. We concluded that motion guiding features in a total knee replacement could reproduce a normal neutral path that might result in functional improvements for the patient.

Sit-to-stand 3 months after unilateral total knee arthroplasty: comparison of self-selected and constrained conditions

After unilateral total knee arthroplasty (TKA), rehabilitation specialists often constrain knee angles or foot positions during sit-to-stand, to encourage increased weight bearing through the operated limb. Biomechanical studies often constrain limb position during sit-to-stand in an effort to reduce variability. Differences between self-selecting or constraining position are unknown in persons after TKA. Twenty-six subjects with unilateral TKA participated in motion analysis. Subjects performed the sit-to-stand using a self-selected position (ssSTS); next, trials were collected in a constrained condition (ccSTS), where both knees were positioned with the tibia vertical, perpendicular to the floor. Repeated measures ANOVA (limb x condition) assessed differences between limbs and between conditions. Subjects used greater hip flexion bilaterally during ccSTS (91 degrees) compared to ssSTS (87 degrees; p=0.001) and knee flexion on the non-operated limb was greater during ssSTS (84 degrees) compared to ccSTS (82 degrees; p=0.018). The ccSTS resulted in larger extensor moments on the non-operated limb at the hip (ssSTS -0.473, ccSTS -0.521; p=0.021) and knee (ssSTS -0.431, ccSTS -0.457; p=0.001) compared to the operated limb. The ccSTS exacerbated the asymmetries at the hip and knee compared to ssSTS, and did not improve use of the operated limb. Reliance on the non-operated limb may put them at risk for progression of osteoarthritis in other joints of the lower extremities.