Influence of the relative difference in chair seat height according to different lower thigh length on floor reaction force and lower-limb strength during sit-to-stand movement

Lower extremity muscle strength equation of older adults assessed by Five Time Sit to Stand Test (FTSST)

Background

The decline in lower limb muscle strength, one of the risk factors for falling in the older adults, puts older persons at an increased risk of falling. The assessment of the lower limb muscle strength is very important.

Objective

The purpose of this study was to construct the equation for predicting knee extensor muscle strength based on demographic data and the results of the Five-Time Sit-to-Stand Test (FTSST).

Methods

A total of 121 healthy elders (mean age 68 . 00 ± 7 . 26 ) were asked to complete the FTSST and submit the demographic information. By using a stationary push-pull dynamometer, the knee extensor strength of each participant was assessed. The multiple regression analysis was used to explore knee extensor strength prediction equation.

Results

The findings demonstrated that the knee extensor strength equation was developed using variables obtained from gender, weight, and time to complete the FTSST. The equation was found to have a high correlation (r = 0 . 838 ) and 70.1% estimation power. Its formula was as follows: Knee extensor strength = 32 . 735 + 3 . 688 (gender; female = 0 or male = 1 ) + 0.189 (weight) - 2.617 (time to complete the FTSST). However, there was an estimating error in this equation of 4.72 kg.

Conclusion

The determining factors influencing knee extensor strength, which can be utilized to estimate the strength in elderly individuals, are demographic variables including gender, weight, and the time taken to complete the FTSST.

Overweight in elderly increases postural instability during sit-to-stand test: a Kinect-based assessment

BACKGROUND

Being overweight increases the risk of falls and subsequent injuries. However, conventional functional balance tests may not be appropriate for this population as body weight can affect test performance. Thus, it is crucial to develop reliable methods for assessing balance ability in overweight individuals.

AIM

The purpose of this study was to utilize a portable gaming device (Kinect Xbox 360) to measure the center of mass (CoM) of elderly individuals and compare the results between normal weight and overweight elderly women.

METHODS

The study included 64 female elderly individuals who were divided into two groups: 32 normal weight and 32 overweight subjects, matched for age (matched pairs design). The study collected the body's CoM during the five-time sit-to-stand test (FTSST) using Kinect camera. Additionally, the participants underwent the time up and go test (TUGT) and one-leg standing balance (OLSB) tests. The Kinect Xbox 360 demonstrated high test-retest reliability for measuring body's center of mass sway, with ICC3,1 value of 0.982 in the vertical direction, 0.983 in the mediolateral (ML) direction, and 0.997 in the anteroposterior (AP) direction. Additionally, the technical error of measurement (TEM) was very low at 0.006, 0.002, and 0.004, respectively. The % coefficient of variation ranged from 1.31% to 5.68%, indicating good measurement consistency.

RESULTS

Overweight individuals took longer to complete FTSST and TUGT compared to normal weight individuals, but no significant difference was observed in OLSB tests. Moreover, overweight elderly individuals had greater sway length in the ML and AP directions compared to normal weight elderly individuals.

DISCUSSION AND CONCLUSION

Overweight elderly individuals had poorer balance than their normal weight counterparts when using Kinect camera. The researchers suggest that Kinect device can be a cost-effective alternative to measure balance performance among overweight elderly in the community-based setting.

Effects of Visual-Motor Illusion via Image Videos Showing Increased Exercise Intensity on the Tibial Anterior during Sit-to-Stand Movement: A Study of Healthy Participants

Visual-motor illusion (VMI) elicits kinesthetic sensation from visual stimulation. We have previously performed ankle motion VMI with resistance applied to the ankle joint on the paralyzed side (power-VMI (P-VMI)) and ankle motion VMI without resistance (standard-VMI (S-VMI)) to activate the tibialis anterior (TA) muscle in stroke-paralyzed patients and compared sit-to-stand (STS) durations, but these studies did not measure TA activity during the STS movement. The purpose of this study was to evaluate the effects of different intensities of visual stimuli presented during VMI on TA and STS movement. Healthy right-footed adults (n = 18) observed two different VMI videos of ankle dorsiflexion, including S-VMI and P-VMI, with an observation time of 2 min each. STS movement was evaluated before and after watching each video. Each participant performed both S-VMI and P-VMI interventions on the same day. Only P-VMI enhanced the integrated electromyogram of the TA, increased the angular velocities of the trunk forward inclination and the ankle dorsiflexion, and shortened the STS duration. Our results indicate that P-VMI facilitates the activation of TA during STS, and we believe that we have clarified the intervention mechanism of VMI.

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.

Concurrent Validity Between Potential Screening Tests for Early Mobility Decline in Independent Community Dwellers

BACKGROUND AND PURPOSE

Standardized screening tests that detect early mobility decline, regardless of etiology, are needed for healthy aging. The locomotive syndrome (LS) tests are designed to identify stages of mobility decline and inform appropriate levels of intervention. The long-term goal of this research is to develop standardized mobility screening tests that can be used across health care settings and throughout a patient's lifespan to guide appropriate medical care. As the first step in this process, this study examines the concurrent validity between the reference and the LS tests.

METHODS

This cross-sectional study examined correlations between the LS functional tests and a set of reference tests and the ability to differentiate the 3 stages of mobility decline. The reference tests included the stair-climbing test, the 30-second chair rise test, the 6-minute walk test, the Global Physical Health (GPH) portion of the PROMIS, and the Lower Extremity Functional Scale (LEFS). The LS tests included the Stand-Up Test, the 2-Step Test, and the 25-question Geriatric Locomotive Function Scale (25-GLFS). A total of 115 community dwellers of 61.2 years old on average (±10.0 years), with n = 71 (61%) older than 60 years, voluntary participated in this prospective study. Nonparametric analyses of variance and correlations were used to examine the concurrent validity.

RESULTS AND DISCUSSION

Performance-based tests were significantly correlated (| r | = 0.38-0.61, P < .001) with LS tests. The LEFS was correlated with all LS tests, but the GPH was only correlated with the 25-GLFS. Also, significant differences were found in reference test scores between the 3 LS stages ( P < .05).

CONCLUSIONS

The LS tests and reference tests demonstrated significant correlations, and participants performed significantly worse on reference tests as LS severity increased. Given these results, it is possible that the LS standardized tests may play an important role in mobility screening. Future research should investigate feasibility, sensitivity, and specificity of these tests.

Sit to stand muscle power reference values and their association with adverse events in Colombian older adults

Recently, a valid method to assess lower-body muscle power based on a sit-to-stand field test (STS) has been published. Our study aimed to describe lower-body muscle power in older individuals aged ≥ 60 years and examine the relationship of muscle weakness with adverse events according to gender- and age-specific muscle weakness cut-off points. A total of 3689 Colombian older adults (57.6% women, age 69.1 ± 6.9 years) from the 2015 Survey on Health, Well-Being, and Aging in Latin America and the Caribbean (SABE) participated in this study. Lower-body muscle power normalized to body mass was estimated by the five-repetitions STS test. Anthropometric, physical performance and clinical characteristics were collected. Age-specific percentiles using the LMS method, cut-off points and association with adverse events were calculated. Lower-body muscle power was greater in men than among women (2.2 ± 0.7 vs. 1.6 ± 0.5 W·kg⁻¹, respectively; p < 0.001) at all ages. Muscle power ranked in the 50th percentile between 2.38 and 1.30 W·kg⁻¹ in men, whereas women ranked between 1.79 and 1.21 W·kg⁻¹. According to the cut-off points, lower-limb muscle power < 1 standard deviation  in men was associated with having dynapenia, poor gait speed, cognitive impairment and mental, visual, hearing and memory problems. While, women were associated with having sarcopenia, dynapenia, poor gait speed, cognitive impairment, mental, hearing and memory problems, dementia and hospitalizations of > 24 h in the last year. Overall, participants with poor lower-limb muscle power had a significantly higher risk of adverse events [in men: odds ratio (OR) = 1.51, 95% confidence interval (CI) = 1.19–1.91, p < 0.001; in women: OR = 1.52, 95% CI = 1.27–1.87, p = 0.001] than their stronger counterparts. This study is the first to describe lower-limb muscle power values and cut-off points among a nationally representative sample of Colombian older adults. In men, 7 of the 14 adverse events studied were associated with lower muscle strength, whereas in women, it was 9 of the 14 adverse events.

The impact of seat height on 1-min sit-to-stand test performance in COPD: a randomised crossover trial

Study question

Is there a difference in the number of repetitions in the 1-minute sit-to-stand (1MSTS) test using an individually adapted seat height to 90° knee flexion (1MSTS_IND), compared with the commonly used standard chair seat height of 46 cm (1MSTS_STD), in people with COPD?

Methods

We conducted a single-centre, single-blinded, randomised crossover trial in people with COPD between August 2020 and March 2021 at a specialised rehabilitation clinic in Switzerland. After a learning 1MSTS test, all participants performed two 1MSTS tests in random order on consecutive days. Participants were blinded, as they did not receive detailed information on the testing protocols.

Results

49 individuals with COPD (47% female) participated. In a regression model adjusted for sequence period and subject, 1MSTS test performance was lower on 1MSTS_IND compared to 1MSTS_STD (−0.78 repetitions, 95% CI −1.47 to −0.11). In a second regression model additionally including the knee angle and an interaction term (1MSTS_IND×knee angle), the interaction term was significant: 0.18 (95% CI 0.05 to 0.30). The limits of agreement were between −5.5 and 4 repetitions.

Conclusion

Although we observed a statistically significant difference between 1MSTS_IND and 1MSTS_STD on a population level, the difference is negligible. Further studies may be needed to determine whether individual adaptation of seat height is needed for very tall or short people to ensure a valid assessment of 1MSTS test performance in COPD.

Performing the 1MSTS test on an individually adjusted chair versus a standard chair results in fewer repetitions (mean difference −0.78, 95% CI −1.47 to −0.11). However, the difference in repetitions is clinically negligible.https://bit.ly/3Oc8Rvp

Effect of different seat heights on lumbar spine flexion during stand-to-sit motion

[Purpose] This study aimed to investigate the movement of the thorax, lumbar spine, and pelvis when healthy participants sit on a chair, and to identify the kinematic characteristics due to changes in the height of the seat. [Participants and Methods] Twenty healthy participants (14 males, 6 females; mean age, 29 ± 5 years) were recruited for this study. They performed stand-to-sit motion using one seat with a height of 100% that of the lower leg length (standard) and another with a height of 60% that of the lower leg length (lower). A three-dimensional motion analysis system and four force plates were used to analyze each joint angle. [Results] The mean lumbar spine flexion angle was significantly increased in the lower versus the standard seat. As a kinematic characteristic, the pelvis tilted posteriorly while the thorax tilted anteriorly, which increased the lumbar spine flexion angle. The pelvis was tilted posteriorly when the hip joint flexed about 60° regardless of the seat height. [Conclusion] The lumbar spine flexion angle increased in the lower seat stand-to-sit motion, which suggested an increase in the load on the lumbar spine. The lumbar spine flexion angle was influenced by the characteristic movements of the thorax and pelvis.

Effects of seat height on whole-body movement and lower limb muscle power during sit-to-stand movements in young and older individuals

Sit-to-stand (STS) movements from low seat height are not easily executed by older individuals. Although young individuals increase their lower limb muscle power (LLMP) based on the product of the ground reaction force (GRF) and center of mass velocity (CoMv) during STS movement from a low seat height, it remains unclear whether seat height has an effect on LLMP during STS movement in older individuals. The present study aimed to investigate differences in the LLMP during STS movements when seat height is lowered between young and older individuals. Twelve older and twelve height-matched young individuals were instructed to perform STS movements from low (20 cm), middle (40 cm), and high (60 cm) seat heights. STS movement and GRF were obtained by a motion analysis system and force plates. In the low-seat-height condition, the forward and upward LLMPs and the upward CoMv were significantly lower in older individuals than those in young individuals, but the forward CoMv was not. The completion time of STS movement from a low seat height was significantly longer in older individuals than in young individuals. Our findings suggest that the slower upward CoMv due to the lower upward LLMP extends the completion time of STS movement from a low seat height in older individuals. Furthermore, in the low-seat-height condition, older individuals may move their center of mass (CoM) forward in a different way when compared with young individuals, and they may not use forward LLMP for moving CoM forward.

Impact of home-based squat training with two-depths on lower limb muscle parameters and physical functional tests in older adults

This study investigated the effect of home-based shallow and deep squat trainings on knee extension peak torque, muscle thickness, one-repetition maximum (1RM) leg press, and physical function in older individuals. Sixteen participants were randomly assigned to the shallow squat group (SS group; age, 71.0  ±  4.0 years) or deep squat group (DS group, age; 68.6  ± 3.6 years). Chairs of 40-cm height and chairs with a cushion of 20-cm height (60-cm in total) were used as the depth targets for squats, with participants instructed to sink until their hip touched the chair and cushion. Participants performed four sets of squats per day (35 repetitions per set), three days per week, for 12 weeks at their home. Knee extension peak torque, muscle thickness of quadriceps femoris (e.g., vastus lateralis, rectus femoris, and vastus intermedius), and physical function were measured at weeks 0 (baseline), 4, 8, and 12. Maximal isometric knee extension peak torque, muscle thickness, and walking speed did not change significantly over the 12-week training period in either group (P > 0.05). However, compared with the baseline, there was significant improvement in the results of 30-s sit-to-stand repetition tests after weeks 8 and 12 in both groups (P < 0.05). Additionally, 1RM leg press results were significantly improved after weeks 4 and 12 in the DS group, and weeks 4, 8, and 12 in the SS group (P < 0.05). Results indicate that home-based weight-bearing squat training improves lower limb function in older adults, as well as performance in physical functional tests related to activities of daily living. Moreover, such training benefits older adults regardless of whether squats are shallow or deep.

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.

The features of muscle activity during chair standing and sitting motion in submerged condition

This study aimed to measure muscle activity and motion kinematics during chair-based exercises under submerged and non-submerged conditions. Twelve healthy men performed chair-based standing and sitting movements. Surface electrodes were attached at the tibialis anterior, gastrocnemius, rectus femoris, biceps femoris, rectus abdominis, and erector spinae. The ankle, knee, and hip joint angles and forward inclination angle of the trunk segment in the sagittal plane were calculated. The mean muscle activities during both movements in the submerged condition for the entire motion were lower than those in the non-submerged condition except in the tibialis anterior and biceps femoris during the sitting movement (in the standing exercise, rectus femoris: 14.1% and 5.2%; and erector spinae: 18.3% and 13.6% in non-submerged and submerged conditions, respectively; and in the sitting exercise, rectus femoris: 12.1% and 4.5% and erector spinae: 12.9% and 9.9% in the non-submerged and submerged conditions, respectively). However, the integrated muscle activity in submerged conditions was similar or higher to that in non-submerged conditions during both movements, except for the rectus femoris. This was mainly due to the increased duration of motion (44.3% and 39.9% longer for standing and sitting exercises in submerged conditions, respectively, compared with non-submerged conditions). The hip joint flexion at the beginning and end of movement and forward inclination angles of the trunk segment at the beginning of the movement in the submerged condition were larger than those in the non-submerged condition during both movements (hip: 126.1° and 111.5° at the beginning, 182.3° and 178.4° at the end and trunk: 2.7° and 17.4° at the beginning in non-submerged and submerged conditions for the standing exercise, respectively; hip: 182.4° and 178.0° at the beginning, 125.9° and 111.1° at the end and trunk: 2.2° and 16.9° at the end in non-submerged and submerged conditions for the sitting exercise, respectively). Reduced or similar muscle activity but similar or higher muscular effort was observed in the submerged condition for all the muscles except the rectus femoris, with the upper body inclined forward. These findings could have beneficial implications for the prescription of exercise and rehabilitation regimens.

Measurement of the total body center of gravity during sit-to-stand motion using a markerless motion capture system

PURPOSE

In order to evaluate the movement strategy in sit-to-stand (STS) motion, it is necessary to measure the center of gravity (COG). However, there is no established method for enabling this using convenience device in the clinical setting. The purpose of this study was to validate the measurement of the COG during the STS motion using an inexpensive, portable and markerless motion capture system (MLS).

METHOD

Eighteen healthy adults participated in our study. The coordinates of the joint centers during the STS motion were collected using the Microsoft Kinect system (as a MLS) and the Vicon system (as a marker-based motion capture system [MBS]). The center of mass of each segment-which was calculated based on the segmental mass and length-were synthesized to calculate the COG. The displacement, velocity, acceleration of the COG during the STS motion were calculated from the data obtained using each system and compared between systems.

RESULTS

The two systems showed significant difference in their measurements of displacement in both the vertical and anteroposterior directions. However, in the anteroposterior direction, there was no significant difference in the measurements of either velocity or acceleration.

CONCLUSION

Our results suggested the validity of the COG in the anteroposterior direction during the STS motion measured using the MLS. The method developed in the present study enables the evaluation of a patient's movement strategy.

Instruction in Reliability and Magnitude of Evaluation Parameters at Each Phase of a Sit-to-Stand Movement

The sit-to-stand movement strategy of each subject is different depending on whether the subjects perform voluntary movements or have concrete instructions (i.e., stand quickly), which is strongly reflected in the performance of each sit-to-stand movement phase. Thirty young-adult male subjects participated in this study ( M age = 20.7 yr; SD = 2.6). Subjects performed the two movements from a chair height adjusted to the subject's lower thigh length. In the self-administered (SA) condition, subjects voluntarily stood up from the chair without instruction, and in the assigned-ordered (AO) condition subjects stood up from the chair as fast as possible. Vertical floor reaction force and electromyograms of the rectus femoris and tibialis anterior muscles were measured, and 15 parameters were selected. The parameters in the phase between the peak value of the floor reaction force and completion of the movement was highly reliable regardless of instruction. However, other parameters had different reliabilities between the instruction conditions. In particular, the parameters in the phase between starting the movement and the peak value of the floor reaction force under the assigned-order were higher than those of the self-administered condition. Moreover, the sit-to-stand movement was conducted faster in the assigned-order condition during the phase between starting the movement and buttocks-syneresis, and the peak value of the floor reaction force and completion of the movement. From the above, in the assigned-order condition “as fast as possible,” the anteflexion bending movement and extension of knee and trunk joints were faster, and anteflexion movement was repeated more similarly under a concrete instruction such as moving as fast as possible.

Height of Chair Seat and Movement Characteristics in Sit-to-Stand by Young and Elderly Adults

The height of a chair seat affects the burden on the lower limbs during the sit-to-stand (STS). To develop an objective test to evaluate muscle function of the lower limbs using floor reaction force during a STS, the relationship between chair-seat height and the burden on the lower legs must be assessed. To examine the influence of the chair-seat height, floor reaction forces during a STS performed with 5 chair heights adjusted to each subject's lower leg length were compared. The force production and quickness of movement tended to decrease in the phases of trunk flexion and knee and hip joint extension when performing a STS from a lower chair, when the chair height differed by 20% (6.2 cm) from the lower leg length, and was marked when the difference between chair height and lower leg length became larger. In 52 elderly and 50 young adults, floor reaction forces during a STS performed from a chair of the same height as subjects' lower leg lengths were compared. Elderly persons were inferior in force production (strength) and quickness of movement, which decreased as elderly stood up from a chair of a lower height.

Repetitive sit-to-stand training with the step-foot position on the non-paretic side, and its effects on the balance and foot pressure of chronic stroke subjects

[Purpose] This study aimed to improve the asymmetrical weight-bearing ratio by applying repetitive sit-to-stand training methods that feature a step-foot position to the paretic-side foot of hemiplegic patients; it sought also to provide the information needed to apply weight-bearing and balance training to hemiplegic patients. [Subjects and Methods] The subjects were divided into two groups: a spontaneous group and a step group. They all performed repetitive sit-to-stand training five times per week for a total of six weeks. The Biodex Balance System, TUG, and 5XSST were used to measure the static and dynamic standing balance of each patient. A foot mat system was used to measure foot pressure. [Results] In the balance measurements, differences in the Overall index, Ant-post index, Med-lat index, Fall risk index, TUG, and 5XSST after training was significantly different between the two study groups. In evaluating foot pressure measurements, we found that the COP (Ant-post), Peak pressure: hind foot, and Contact area: hind foot measurements significantly differed between the groups after the training. [Conclusion] Repetitive sit-to-stand training that involves positioning the non-paretic leg upward can be considered a significant form of training that improves the symmetric posture adjustment and balance of hemiplegic patients following a stroke.

The Effect of Different Standing up Frequencies in Sit-to-stand Exercise on Oxygen Uptake

[Purpose] The aim of this study was to investigate the steady state of oxygen uptake (VO₂) at several standing up frequencies to clarify whether workload in the sit-to-stand exercise (STSE) is greater than the anaerobic threshold (AT). [Subjects] Ten healthy young subjects performed the STSE. [Methods] In the STSE, subjects stood up and sat down without using their arms to push-off from the chair at standing up frequencies of 6, 12, 18, 24, 30, and 36 times per minutes. Subjects exercised for 5 minutes at each frequency with 5 minutes of rest between each consecutive frequency trial. The steady state of VO₂ was evaluated by the difference in the VO₂ between the 3rd and 5th min at each frequency. The correlation between the VO₂ of the STSE and the standing up frequency was analyzed. [Results] At standing up frequencies greater than 24 times/min, the steady state of VO₂ could not be confirmed. The relationship between the standing up frequency (at less than 24 times/min) and VO₂ was strong (r=0.94). [Conclusion] The STSE may be a potentially useful test for determining AT and predicting the physical capacity of patients.

The Relationship Between Different Body Mass Index Categories and Chair Rise Performance in Adult Women

An important prerequisite to carry out daily activities is the sit-to-stand movement. However, in obese people, this movement is characterized by altered biomechanics, which might lead to daily life activity impairments. The aim of this study was to investigate whether there are differences in kinetic and kinematic variables between three different BMI categories when performing a specific sit-to-stand test. Thirty-six adult women (BMI = 17–45 kg/m2) performed the sit-to stand test five times consecutively and as quickly as possible. Analyses of variance were used to determine differences between three BMI groups (normal or overweight: BMI < 30 kg/m2; obese: 30 ≤ BMI < 35; severely obese: BMI ≥ 35). Peak and mean vertical sacrum velocity indicated a decrease in severely obese subjects. Obese and severely obese individuals did not show higher fatigue over the five consecutive movements. Peak force and rate of force development decreased in normal or overweight subjects. The ability to successfully complete the test decreased with a higher BMI, probably due to a reduced ability to rapidly generate a high force.

The influence of chair seat height on the performance of community-dwelling older adults' 30-second chair stand test

BACKGROUND AND AIMS

Although chair seat height affects the performance of sit-to-stand movement, no previous study has examined the influence of chair seat height on the 30-second chair stand test (CST).

METHODS

Fifty-five community-dwelling older adults (age 70.0 ± 6.3 years) performed the test from the standard height of 43 cm and then from five randomly ordered seat heights from 80 to 120 % of each participant's lower leg length.

RESULTS

Chair seat height significantly influences the performance of community-dwelling older adults' 30-s CST (F = 57.50, p < 0.001). The mean score for standard conditions was significantly lower from those at 120, 110, and 100 % conditions (p < 0.05). No significant difference was observed between the standard and 80 % conditions (p > 0.95) and between the standard and 90 % conditions (p = 0.353). When comparing the scores between the randomly ordered chair seat heights, all comparisons were significantly different (p < 0.001) except for the difference between the 120 and 110 % conditions (p = 0.104).

CONCLUSION

Chair seat height's relation to the lower leg length should be considered when interpreting 30-s CST scores. Additionally, it is necessary to optimize the chair seat height when using the 30-s CST as an outcome measure for exercise intervention or to screen for people with weaker lower extremities.

Sit-to-stand alterations in advanced knee osteoarthritis

This study investigated the full-body strategies utilized during a sit-to-stand (STS) task in patients with knee osteoarthritis (OA) and the association between STS alterations and clinical measurements. Twenty-five patients with advanced knee OA and twenty healthy elderly adults were recruited to participate in this study. Patients were asked to stand up from a chair four times without using their arms. A 3D motion analysis system was used to capture the full-body kinematics during the task. Two force plates were used to capture the forces under each leg. The following parameters were investigated in the knee OA group and compared with the control group: the time to realize STS, the force ratio between both limbs, the knee and hip kinetics and the trunk kinematics. The pain and functional capacity were obtained from the WOMAC. The results showed that patients with knee OA put 10% additional weight on the contralateral side when compared with the symmetrical strategy of the control group. Patients with knee OA showed a significantly lower knee flexion moment (0.51 Nm/kg vs. 0.72 Nm/kg), a higher maximal trunk flexion (46.4° vs. 37.5°), and a higher lateral trunk lean on the contralateral side (2.4° vs. 0.9°) when compared with the control group. The main correlations were found between pain and the averaged time to complete the STS task (r=0.55). With the quantification of the full-body mechanisms utilized during the STS task, which includes both distal and proximal compensations, our study brings new insights, leading to a better understanding of the functional alterations in patients with advanced knee OA.

Biomechanical analysis of gait and sit-to-stand patterns using a specially made knee supporter in healthy young and elderly individuals

This study examined the ergonomic effects of a specially made knee supporter containing spiral bone springs aimed at reducing physical stress on the leg muscles during sit-to-stand (STS) and walking. Twelve young females and fifteen elderly subjects performed STS and treadmill walking with and without a specially made supporter, which may be a simple device for aiding STS and/or walking. During STS, electromyography (EMG) was observed from the vastus lateralis of the right leg. The root mean square (RMS) and mean power frequency (MPF) were calculated from the observed EMG. The changing rate of maximal leg acceleration, the third time derivative of the leg position, was also assessed during treadmill walking at a freely chosen stride frequency and speed. A significant decrease in the RMS was observed during STS when wearing the supporter in both groups. A significant increase in the changing rate of maximal leg acceleration was found during walking with the supporter in both groups. MPF significantly increased when wearing the supporter only in the young group. These results showed that the supporter with spiral bone springs reduced physical stress placed on the quadriceps muscles during STS and walking. This ergonomic contrivance will reduce the possible "risk" of stumbling and/or falling in elderly individuals. The reduced physical burden on the quadriceps muscles will also reduce or delay muscle fatigue, which will further result in an increase in the amount of daily physical activities exhibited in physically poor populations.

The ergonomic relevance of anthropometrical proportions. Part I: body length measures

Anthropometrical findings about proportions of the human body have a long tradition; most of them, however, are rather theoretical. To improve this situation a pragmatic and applicable definition of proportions, normal as well as deviating, is needed. The purpose of this paper is to set up three proportion types for body length measures: leggy-normal-stocky, and their rate in the population of adults in an industrial society (Germany). Based on queries of an actual anthropometrical database metrical limits for these three types are suggested regarding their influence on the most important body length measures in standing and sitting positions. The number of cases with normal proportions is about 60%, leggy and stocky types both reaching up to 20%. The metrical limits are proposed in order to account for differences between those proportion types which are relevant for ergonomics. When solving complex multidimensional design tasks (e.g. workplaces, vehicle interior design, personal equipment) users of anthropometrical data who do not have the opportunity to work with multivariate databases need supplementary information about the proportions of the human body. For this reason such supplementary information concerning proportions is being given here by physiological anthropologists. The application of the findings presented is exemplified in scenarios of ergonomic relevance.

The relationship of age and leg strength in the step test with stipulated tempo in the elderly

This study aimed to examine age differences in the step test with stipulated tempo, a test of dynamic balance ability in the elderly. One hundred eighty-nine healthy elderly people (96 men and 93 women) executed the step test for 20 s twice, with adjustments of the metronome (40 bpm, 60 bpm and 120 bpm). The knee extension strength of both legs was each measured twice. Evaluation parameters included the time difference between metronome sound and the time when each foot hit the ground, two-leg support time, and one-leg support time. The time difference and two-leg support time were significantly longer in the order of 40 bpm, 60 bpm, and 120 bpm tempos, and one-leg support time was shorter in the 40 bpm tempo than the 60 bpm and 120 bpm tempos. A significant age difference was found in the 40 bpm or 60 bpm tempo, and the former two parameters were longer in the older groups and the one-leg support time was shorter. Three evaluation parameters showed significant relationships with knee extension strength. In conclusion, because the step test with a slow tempo (40 bpm or 60 bpm) requires longer one-leg support time, it is effective for the evaluation of dynamic balance ability and leg strength of the elderly.

The relation between the changes of postural achievement, lower limb muscle activities, and balance stability in three different deep-squatting postures

Deep squatting places a burden on the lower limb muscles and influences postural balance. We attempted to determine the effects of postural changes on the rectus femoris, tibialis anterior, gastrocnemius, soleus, and extensor digitorum brevis muscles during squatting in 8 healthy male subjects. Three squatting conditions were involved: full squatting (FS), tiptoe squatting (TT), and tiptoe squatting on a 15 degrees slope (TTS), performed randomly and recorded in a period of 4 min for each task. The influence of the squatting condition on electromyography and vertical ground reaction force parameters was examined in order to observe the effect of postural alteration on muscle activity and balance control. The results showed that the change of squatting posture from FS to TT decreased the activity of the rectus femoris and tibialis anterior muscles. FS has been suspected as a main cause of musculoskeletal complaint during prolonged squatting. In contrast, as the heel was lifted, the extensor digitorum brevis muscle increased to 39% of maximum activation. On the other hand, sway analysis at TT showed balance instability regarding the large area occupation of the center of pressure displacement. The presence of a 15 degrees slope significantly reduced the muscular load. This simple study suggests that the inclusion of a sloping surface in daily activities that requires a squatting posture would be an effective means to reduce muscular load.