Trunk kinematics and muscle activation patterns during stand-to-sit movement and the relationship with postural stability in aging

The central nervous system adjusts muscle synergy structure and tightly controls rollator-supported transitions between sitting and standing

BACKGROUND

Older individuals are at risk of falling. Assistive devices like rollators help to reduce that risk, especially by compensating for decreased leg muscle strength and balance problems. Paradoxically, rollators have been found to be a fall risk as well as being difficult to use. To investigate the causes, this study examines how different levels of rollator support (no assistance, light touch, and full support) and balance demands (standard lab floor, balance pads) affect movement coordination during standing up and sitting down movements.

METHODS

Twenty young participants stood up and sat down while full-body kinematics and muscle activity (30 channels) were recorded. Participants stood up and sat down using different movement strategies (e.g., forward leaning, hybrid, and vertical rise standing up movement strategies). For each movement strategy, spatial and temporal muscle synergies were extracted from the muscle activity patterns. Temporal muscle synergies provided a more compact, low-dimensional representation than spatial muscle synergies, so they were subsequently clustered with k-means++. The activation duration of the temporal muscle synergies was assessed with full-width at half-maximum at the main peak. Multivariate linear mixed models were used to investigate if the muscle weightings associated with the temporal muscle synergies differed across the support conditions.

RESULTS

The timings of the temporal muscle synergy activations, but not the shape, differed across the movement strategies for both types of movement. Across all tasks, temporal muscle synergies showed a narrower width of activation around the time of seat-off and seat-on than at the movement start and end. No support-specific temporal muscle synergies were found, but lower limb muscle weightings decreased while upper-limb muscle weightings increased with increased support.

CONCLUSION

The narrow shape of the temporal synergy activation profiles suggests that the central nervous system controls the movements tightly, especially around seat-off and seat-on and in challenging conditions with increased balance demands. Furthermore, rollator support increases the weightings of upper body and decreases the weightings of lower limb muscles, especially around seat-off and seat-on. Future studies may further investigate how the loss of tight movement control may cause falls in older individuals.

Vision-based postural balance assessment of sit-to-stand transitions performed by younger and older adults

BACKGROUND

The use of inertial measurement units (IMUs) in assessing fall risk is often limited by subject discomfort and challenges in data interpretation. Additionally, there is a scarcity of research on attitude estimation features. To address these issues, we explored novel features and representation methods in the context of sit-to-stand transitions. This study recorded sit-to-stand transition test data from three groups: community-dwelling elderly, elderly in day care centers (DCC), and college students, captured using mobile phone cameras.

METHOD

We employed pose estimation technology to extract key point kinematic features from the video data and used 10-fold cross-validation to train a random forest classifier, mitigating the impact of individual differences. We trained classifiers with the top 5, 10, and 15 features, calculating the average area under the receiver operating characteristic curve (AUC) for each model to compare feature importance.

RESULTS

Our results indicated that elbow key point features, such as (KP08) mean Y, (KP08)RMS Y, (KP09) mean Y, and (KP09) RMS Y, are crucial for distinguishing between subject groups. Statistical tests further validated the significance of these features. The application of human pose estimation and key point signals shows promise for clinical postural balance screening. The identified features can be utilized to develop non-invasive tools for assessing postural instability risk, contributing to fall prevention efforts.

CONCLUSION

This study lays the groundwork for integrating additional measurement modalities into sit-to-stand transition analysis to enhance clinical strategies.

Effects of initial foot position on neuromuscular and biomechanical control during the stand-to-sit movement: Implications for rehabilitation strategies

BACKGROUND

Initial foot position (IFP) is one of the important movement strategies that influence neuromuscular and biomechanical control during sit-to-stand (STS) movements. Similarly, stand-to-sit (StandTS) is vital in rehabilitation settings for evaluating strength and balance control during descending movements. Understanding how IFP impacts changes in biomechanical and neuromuscular movement control factors during StandTS can provide valuable insights for designing effective rehabilitation programs.

METHODS

Twelve healthy young adults participated in this study, examining three symmetric IFPs: (1) REF (reference); (2) wide: each foot was shifted outwards by 30% from REF; (3) TO (toes-out): symmetric toes-out angle of 30° from REF. Kinematic and kinetic differences among the three IFPs during StandTS were analyzed, along with the characteristics of muscle activation patterns using muscle synergy analysis.

RESULTS

In the wide IFP, trunk flexion angle was reduced, and valgus angle was greater than in the other IFPs. The TO IFP resulted in greater dorsiflexion and knee flexion angles compared to the REF and wide IFPs. Compared to the REF IFP, both wide and TO IFPs showed greater eccentric work at the hip joint in the anterior-posterior (power absorption) and the vertical direction (gravitational force control) and demonstrated reduced postural sway in medio-lateral and vertical directions. Muscle synergy analysis of EMG activity revealed increased activation of back and plantar flexor muscle in the wide IFP, and increased contribution of hip joint muscles in the TO IFP.

CONCLUSION

The wide IFP increased the valgus angle, leading to reduced trunk flexion with increased back muscle activation. The TO IFP enabled greater angular displacement at the ankle and knee joints, enhancing hip joint muscle involvement in StandTS movement control. Both the wide and TO IFPs facilitated hip joint work, improving postural sway control during the descent phase of StandTS. These findings provide valuable insights for designing rehabilitation strategies tailored to specific patient needs.

Activity-Dependent Compensation at the Hip and Ankle at 8 Years After the Reconstruction of Isolated and Combined Posterior Cruciate Ligament Injuries

BACKGROUND

After posterior cruciate ligament reconstruction (PCLR), functional deficits at the knee can persist. It remains unclear if neighboring joints compensate for the knee during demanding activities of daily living.

PURPOSE

To assess long-term alterations in lower limb mechanics in patients after PCLR.

STUDY DESIGN

Descriptive laboratory study.

METHODS

A total of 28 patients who had undergone single-bundle unilateral isolated or combined PCLR performed stair navigation, squat, sit-to-stand, and stand-to-sit tasks at 8.2 ± 2.2 years after surgery. Motion capture and force plates were used to collect kinematic and kinetic data. Then, 3-dimensional hip, knee, and ankle kinematic data of the reconstructed limb were compared with those of the contralateral limb using statistical parametric mapping.

RESULTS

Side-to-side differences at the knee were primarily found during upward-driven movements at 8 years after surgery. The reconstructed knee exhibited lower internal rotation during the initial loading phase of stair ascent versus the contralateral knee (P = .005). During the sit-to-stand task, higher flexion angles during the midcycle (P = .017) and lower external rotation angles (P = .049) were found in the reconstructed knee; sagittal knee (P = .001) and hip (P = .016) moments were lower in the reconstructed limb than the contralateral limb. In downward-driven movements, side-to-side differences were minimal at the knee but prominent at the ankle and hip: during stair descent, the reconstructed ankle exhibited lower dorsiflexion and lower external rotation during the midcycle versus the contralateral ankle (P = .006 and P = .040, respectively). Frontal hip moments in the reconstructed limb were higher than those in the contralateral limb during the stand-to-sit task (P = .010); during squats, sagittal hip angles in the reconstructed limb were higher than those in the contralateral limb (P < .001).

CONCLUSION

Patients after PCLR exhibited compensations at the hip and ankle during downward-driven movements, such as stair descent, squats, and stand-to-sit. Conversely, residual long-term side-to-side differences at the knee were detected during upward-driven movements such as stair ascent and sit-to-stand.

CLINICAL RELEVANCE

After PCLR, side-to-side differences in biomechanical function were activity-dependent and occurred either at the knee or neighboring joints. When referring to the contralateral limb to assess knee function in the reconstructed limb, concentric, upward-driven movements should be prioritized. Compensations at the hip and ankle during downward-driven movements lead to biases in long-term functional assessments.

The influence of smoothness and speed of stand-to-sit movement on joint kinematics, kinetics, and muscle activation patterns

Background

Stand-to-sit (StandTS) is an important daily activity widely used in rehabilitation settings to improve strength, postural stability, and mobility. Modifications in movement smoothness and speed significantly influence the kinematics, kinetics, and muscle activation patterns of the movement. Understanding the impact of StandTS speed and smoothness on movement control can provide valuable insights for designing effective and personalized rehabilitation training programs.

Research question

How do the smoothness and speed of StandTS movement affect joint kinematics, kinetics, muscle activation patterns, and postural stability during StandTS?

Methods

Twelve healthy younger adults participated in this study. There were two StandTS conditions. In the reference condition, participants stood in an upright position with their feet positioned shoulder-width apart on the force plate. Upon receiving a visual cue, participants performed StandTS at their preferred speed. In the smooth condition, participants were instructed to perform StandTS as smoothly as possible, aiming to minimize contact pressure on the seat. Lower leg kinetics, kinematics, and coordination patterns of muscle activation during StandTS were measured: (1) angular displacement of the trunk, knee, and hip flexion; (2) knee and hip extensor eccentric work; (3) muscle synergy pattern derived from electromyography (EMG) activity of the leg muscles; and (4) postural sway in the anterior-posterior (A-P), medio-lateral (M-L), and vertical directions.

Results

Compared to the reference condition, the smooth condition demonstrated greater eccentric knee extensor flexion and increased joint work in both the knee and hip joints. Analysis of specific muscle synergy from EMG activity revealed a significant increase in the relative contribution of hip joint muscles during the smooth condition. Additionally, a negative correlation was observed between knee extensor and vertical postural sway, as well as hip extensor work and M-L postural sway.

Conclusion

Smooth StandTS facilitates enhanced knee eccentric control and increased joint work at both the hip and knee joints, along with increased involvement of hip joint muscles to effectively manage falling momentum during StandTS. Furthermore, the increased contributions of knee and hip joint work reduced postural sway in the vertical and M-L directions, respectively. These findings provide valuable insights for the development of targeted StandTS rehabilitation training.

Online Monitoring for Human Sit-to-Stand Movement Based on Karush-Kuhn-Tucker Optimized Zonotope Set-Membership Filter

As the global aging population continues to grow, there has been a significant increase in the number of fall-related injuries among the elderly, primarily due to reduced muscle strength and balance control, especially during sit-to-stand (STS) movements. Intelligent wearable robots have the potential to provide fall prevention assistance to individuals at risk, but an accurate and timely assessment of human movement stability is essential. This article presents a fall prediction algorithm for STS movements based on the Karush-Kuhn-Tucker (KKT) optimized zonotope set-membership filter (KKT-ZSMF), enabling real-time assessment of human stability. To quantify the feasible stability region of human STS movement, a mathematical model is proposed based on dynamic stability theory. Additionally, an online fall-prediction approach is developed, utilizing the zonotope set-membership filter to iteratively update the set that represents the instantaneous stability region. The approach incorporates a KKT optimization algorithm to compute the optimal convex hull, thereby enhancing the accuracy and efficiency of the set-membership filter. Experimental validation is conducted with the participation of 13 subjects including 5 elderly subjects, comparing the performance of the proposed KKT-ZSMF algorithm with other relevant methods. The results confirm the accuracy and real-time performance of the KKT-ZSMF algorithm for predicting human STS movement stability, achieving an overall prediction accuracy of 93.49% and a runtime of no more than 7.91 ms. These findings demonstrate the suitability of the algorithm for fall prevention assistance in daily activities.

Turning and sitting movements during timed up and go tests predict deterioration of physical function in middle-aged adults

BACKGROUND

Deterioration of physical function in middle-aged adults is a significant challenge that can lead to increased risk of future falls. However, a screening method for the functional decline in middle-aged adults has not been established.

RESEARCH QUESTION

To evaluate the relationship between biomechanical parameters assessed by the timed up and go test (TUG) and locomotive syndrome (LS) in middle-aged adults.

METHODS

The inclusion criterion was: under 65 years of age. A total of 97 volunteers (mean age 51.1 years) participated in this study. An LS test was performed, including a 2-step test, a stand-up test, and a 25-question Geriatric Locomotive Function Scale. The TUG was measured using inertial measurement units (IMUs) at comfortable and fast speeds. We then determined the minimum values for anterior-posterior acceleration and angular velocity around the medial-lateral axis, as well as the maximum values of angular velocity around the vertical axis for the upper trunk and sacrum in a TUG phase.

RESULTS

Angular velocity around the vertical axis for upper trunk and sacrum were significantly smaller in LS than non-LS in the turn phase of both speed conditions. For the fast speed condition, the minimum anterior-posterior acceleration for sacrum was greater in LS than in the non-LS condition for the stand-to-sit phase. Angular velocity around the vertical axis for turning and anterior-posterior acceleration from sitting were associated with detection of LS.

SIGNIFICANCE

Turning and sitting movements during TUG should be observed using IMU to screen for physical function decline in middle aged adults.

The Effect on Muscle Activity of Reaching Beyond Arm's Length on a Mobile Seat: A Pilot Study for Trunk Control Training for People After Stroke

Objective

This pilot study compared muscle activity during lateral reaching tasks between mobile and stable sitting using a novel therapy chair in people after stroke and healthy controls.

Design

Observational pilot study.

Setting

This study was conducted in a rehabilitation center for people after stroke and at the university's movement laboratory for healthy participants.

Participants

A total of eleven people after stroke and fifteen healthy people (N=26) took part.

Interventions

Lateral reaching exercises to the ipsilateral and contralateral sides were performed on a mobile and a stable seat.

Main Outcome Measure

Muscular activity of the multifidus, erector spinae and external oblique was measured bilaterally. A within-subject linear mixed model was applied to analyze the effects of seat condition, task, muscle side, and group.

Results

A seat condition effect was found for the multifidus and external oblique that was dependent on the muscle side and task. During ipsilateral reaching, the activity of the multifidi decreased for people after stroke on the mobile seat, while increasing for healthy participants. The erector spinae showed no condition effect. Decreased activity of the external oblique was found for both groups on the mobile seat.

Conclusions

Mobile sitting influences muscular activity. However, these preliminary results should be further investigated in order to generate recommendations for rehabilitation.

Rollator usage lets young individuals switch movement strategies in sit-to-stand and stand-to-sit tasks

The transitions between sitting and standing have a high physical and coordination demand, frequently causing falls in older individuals. Rollators, or four-wheeled walkers, are often prescribed to reduce lower-limb load and to improve balance but have been found a fall risk. This study investigated how rollator support affects sit-to-stand and stand-to-sit movements. Twenty young participants stood up and sat down under three handle support conditions (unassisted, light touch, and full support). As increasing task demands may affect coordination, a challenging floor condition (balance pads) was included. Full-body kinematics and ground reaction forces were recorded, reduced in dimensionality by principal component analyses, and clustered by k-means into movement strategies. Rollator support caused the participants to switch strategies, especially when their balance was challenged, but did not lead to support-specific strategies, i.e., clusters that only comprise light touch or full support trials. Three strategies for sit-to-stand were found: forward leaning, hybrid, and vertical rise; two in the challenging condition (exaggerated forward and forward leaning). For stand-to-sit, three strategies were found: backward lowering, hybrid, and vertical lowering; two in the challenging condition (exaggerated forward and forward leaning). Hence, young individuals adjust their strategy selection to different conditions. Future studies may apply this methodology to older individuals to recommend safe strategies and ultimately reduce falls.

Sensor-Based Assessment of Variability in Daily Physical Activity and Frailty

INTRODUCTION

Frailty is a common geriatric syndrome associated with decline in physiological reserve. While several digital biomarkers of daily physical activity (DPA) have been used in frailty assessment, the association between DPA variability and frailty is still not clear. The goal of this study was to determine the association between frailty and DPA variability.

METHODS

This is an observational cross-sectional study conducted between September 2012 and November 2013. Older adults (≥65 years), without any severe mobility disorder, and the ability to walk 10 m (with or without an assistive device) were eligible for the study. DPA including sitting, standing, walking, lying, and postural transition were recorded for 48 h continuously. DPA variability was analyzed from two perspectives: (i) DPA duration variability in terms of coefficient of variation (CoV) of sitting, standing, walking, and lying down durations; and (ii) DPA performance variability in terms of CoV of sit-to-stand (SiSt) and stand-to-sit (StSi) durations and stride time (i.e., slope of power spectral density - PSD).

RESULTS

Data was analyzed from 126 participants (44 non-frail, 60 pre-frail, and 22 frail). For DPA duration variability, CoV of lying and walking duration was significantly larger among non-frail compared to pre-frail and frail groups (p < 0.03, d = 0.89 ± 0.40). For DPA performance variability, StSi CoV and PSD slope were significantly smaller for non-frail compared to pre-frail and frail groups (p < 0.05, d = 0.78 ± 0.19).

CONCLUSION

Lower DPA duration variability in pre-frail and frail groups may be attributed to the set daily routines frail older adults tend to follow, compared to variable physical activity routines of non-frail older adults. Higher DPA performance variability in the frail group may be attributed to reduced physiological capabilities toward walking for longer durations and the reduced muscle strength in the lower extremities, leading to incosistency in performing postural transitions.

Effects of Visual Input Absence on Balance Recovery Responses to Lateral Standing Surface Perturbations in Older and Younger Adults

Although the ability to recover balance in the lateral direction has important implications with regard to fall risk in older adults, the effect of visual input on balance recovery in response to lateral perturbation and the effect of age are not well studied. We investigated the effect of visual input on balance recovery response to unpredictable lateral surface perturbations and its age-related changes. Ten younger and 10 older healthy adults were compared during balance recovery trials performed with the eyes open and eyes closed (EC). Compared with younger adults, older adults showed increased electromyography (EMG) peak amplitude of the soleus and gluteus medius, reduced EMG burst duration of the gluteus maximus and medius, and increased body sway (SD of the body's center of mass acceleration) in EC. In addition, older adults exhibited a smaller % increase (EC-eyes open) of the ankle eversion angle, hip abduction torque, EMG burst duration of the fibularis longus, and a greater % increase of body sway. All kinematics, kinetics, and EMG variables were greater in EC compared with eyes open in both groups. In conclusion, the absence of visual input negatively affects the balance recovery mechanism more in older adults compared with younger adults.

Age affects the relationships between kinematics and postural stability during gait

BACKGROUND

Past work has identified relationships between postural stability and joint kinematics during balance and sit-to-stand tasks. However, this work has not been extended to a thorough examination of these relationships during gait, and how these relationships change with age. An improved understanding of age-related changes in these relationships during gait is necessary to identify early predictors of gait impairments and implement targeted interventions to prevent functional decline in older adulthood.

RESEARCH QUESTION

How does age affect relationships between time-varying signals representing joint/segment kinematics and postural stability during gait?

METHODS

Three-dimensional, whole-body motion capture data from 48 participants (19 younger, 29 older) performing overground gait were used in this secondary analysis. Lower extremity joint angles, trunk segment angles, and margins of stability in the antero-posterior and mediolateral directions were subsequently derived. Pairings of angle and margin of stability signals were cross-correlated across the gait cycle. Metrics representing the strength of relationships were extracted from the cross-correlation functions and compared between groups.

RESULTS

At the ankle, significant age-related differences were only identified in the mediolateral direction, with older adults' coefficients being of greater magnitude and more tightly clustered, relative to younger adults. Differences were observed in both directions at the hip, with an overall trend of greater-magnitude and more tightly clustered coefficients among younger adults. For the trunk, the groups exhibited coefficients of opposite signs in the antero-posterior direction.

SIGNIFICANCE

While overall gait performance was similar between groups, age-related differences were identified in relationships between postural stability and kinematics, with stronger relationships at the hip and ankle for younger and older adults, respectively. Relationships between postural stability and kinematics may have potential as a marker for the early identification of gait impairment and/or dysfunction in older adulthood, and for quantifying the effectiveness of interventions to reduce gait impairment.

Between-day reliability of trunk orientation measured with smartphone sensors during sit-to-stand in asymptomatic individuals

BACKGROUND

Trunk kinematics during sit-to-stand is often impaired in individuals with musculoskeletal disorders. Trunk kinematics is commonly assessed in laboratories using motion capture; however, this equipment is often not available outside research centers. Smartphones are widely available and may be a suitable alternative to assess trunk orientation during sit-to-stand remotely.

OBJECTIVES

We investigated whether trunk orientation in the sagittal plane during sit-to-stand can be measured reliably between days when collected remotely using smartphones.

DESIGN

Cross-sectional study.

METHOD

Forty-three asymptomatic participants performed 15 sit-to-stand movements in two separate sessions remotely over videoconferencing. Trunk orientation was measured using each participant's smartphone. Absolute peak trunk orientation in the sagittal plane was extracted during standing, sitting, stand up and sit down. Relative trunk orientation was calculated as the difference between sitting and stand up, or sitting and sit down. Reliability was assessed using Intraclass Correlation Coefficient (ICC_2,k), Standard Error of Measurement (SEM) and Minimal Detectable change (MDC). Between day bias and between-gender differences were assessed using T tests.

RESULTS

All measures showed good reliability (ICC_2,k > 0.80; SEM < 5.6°; MDC < 13.6°) and no between-day bias (p > 0.31). Relative measures were more consistent (ICC_2,k > 0.88; SEM < 3.6°; MDC < 9.9°). No between-gender differences were observed for relative orientation (p > 0.75).

CONCLUSIONS

Sagittal trunk orientation during sitting, standing, and sit-to-stand can be measured reliably when asymptomatic individuals use their own smartphones supervised over videoconferencing. These findings support the use of smartphone sensors for assessing how trunk orientation changes over time, which may assist physiotherapists assess movement patterns of individuals with musculoskeletal disorders remotely.

Development of a screening formula for sarcopenia using ground reaction force during sit-to-stand motion

BACKGROUND

Ground reaction force during sit-to-stand motion is related to lower extremity strength, and such measurements indicating weak muscle strength, may be linked to sarcopenia. We aimed to examine and describe the relationship between sarcopenia and ground reaction force during sit-to-stand motion to develop a diagnostic tool.

RESEARCH QUESTION

Can ground reaction force during sit-to-stand motion help detect sarcopenia?

METHODS

This study included 627 community-dwelling older adults who were divided into non-sarcopenia and sarcopenia groups to compare ground reaction force parameters. A sit-to-stand force analyzer was used to measure the ground reaction force, power, and time between the minimum and maximum ground reaction force. We assessed the association between sarcopenia and each ground reaction force parameter. Receiver operating characteristic curve analysis was performed with sarcopenia as the dependent variable and ground reaction force-related measurements as independent variables. The probability of predicting sarcopenia was calculated using multiple logistic regression analysis, with sex and age as independent variables, and another receiver operating characteristic analysis was performed using the probability value.

RESULTS

Ground reaction force parameters related to strength and power were lower in the sarcopenia group than in the non-sarcopenia group. Furthermore, we were able to develop a formula to detect sarcopenia using the maximum ground reaction force (area under the curve; 0.906 [95% CI 0.858-0.954] for men and 0.858 [0.808-0.908] for women). The sensitivity and specificity of sarcopenia detection using this formula were 89.7% and 80.5%, respectively, for men and 95.0% and 60.9%, respectively, for women.

SIGNIFICANCE

Ground reaction force during sit-to-stand motion may reflect low skeletal muscle strength associated with sarcopenia. We were able to develop a method for sarcopenia detection by analyzing the sit-to-stand force required in only one or two sit-to-stand motions, even though it does not measure the skeletal muscle mass directly.

Comparison of the lower extremity kinematics and center of mass variations in sit-to-stand and stand-to-sit movements of non-faller and faller elderly

Objective

To compare the differences in sit-to-stand and stand-to-sit movements of older nonfalling males and older male fallers (also referred to herein as fallers) to contribute to the development of posture transfer–assisting devices or interventional therapies to prevent falls.

Design

Controlled study.

Setting

University research laboratory.

Participants

Ten older men (mean age, 75.9±5.4 years) who had fallen or been unstable at least once in the past year and 10 nonfalling older men (mean age, 70.0±5.0 years) participated in this study.

Interventions

Not applicable.

Main Outcome Measures

Movement duration; sagittal trunk, hip, knee, and ankle joint range of motion (ROM); anteroposterior and mediolateral (ML) center of mass (COM) total trajectory.

Results

During the sit-to-stand transition, fallers exhibited greater trunk joint ROM in the flexion and extension phase and smaller hip joint ROM in the extension phase as well as greater ML COM total trajectory. During stand-to-sit, older fallers exhibited greater trunk joint ROM in the flexion phase and smaller hip and knee joint ROM in the flexion phase as well as greater ML COM total trajectory. Older fallers took more time to perform the stand-to-sit and had greater ML COM total trajectory during the movement; additionally, they exhibited different proportional distributions of ROM for each joint compared with nonfaller.

Conclusion

Older fallers had more difficulty performing stand-to-sit than sit-to-stand; they exhibited more body sway in COM motion and, in particular, were unable to control ML motion y. Older fallers were more likely to adopt trunk, hip, and knee joint flexion strategies to maintain balance during sit-to-stand and stand-to-sit than nonfaller participants were.

Postural Balance in Individuals With Knee Osteoarthritis During Stand-to-Sit Task

Objective: Stand-to-sit task is an important daily function, but there is a lack of research evidence on whether knee osteoarthritis (knee OA) affects the postural balance during the task. This study aimed to compare individuals with knee OA and asymptomatic controls in postural balance and identify kinematic and lower extremity muscle activity characteristics in individuals with knee OA during the stand-to-sit task. Methods: In total, 30 individuals with knee OA and 30 age-matched asymptomatic controls performed the 30-s Chair Stand Test (30sCST) at self-selected speeds. Motion analysis data and surface electromyography (sEMG) were collected while participants performed the 30sCST. To quantify postural balance, the displacement of the center of mass (CoM) and the peak instantaneous velocity of the CoM were calculated. The kinematic data included forward lean angles of the trunk and pelvic, range of motion (RoM) of the hip, knee, and ankle joints in the sagittal plane. The averaged activation levels of gluteus maximus, vastus lateralis, vastus medialis, rectus femoris, biceps femoris (BF), tibialis anterior (TA), and medial head of gastrocnemius muscles were indicated by the normalized root mean square amplitudes. Results: Compared with the asymptomatic control group, the knee OA group prolonged the duration of the stand-to-sit task, demonstrated significantly larger CoM displacement and peak instantaneous CoM velocity in the anterior-posterior direction, reduced ankle dorsiflexion RoM, greater anterior pelvic tilt RoM, and lower quadriceps femoris and muscles activation level coupled with higher BF muscle activation level during the stand-to-sit task. Conclusion: This study indicates that individuals with knee OA adopt greater pelvic forward lean RoM and higher BF muscle activation level during the stand-to-sit task. However, these individuals exist greater CoM excursion in the anterior-posterior direction and take more time to complete the task. This daily functional activity should be added to the rehabilitation goals for individuals with knee OA. The knee OA group performs reduced ankle dorsiflexion RoM, quadriceps femoris, and TA activation deficit. In the future, the rehabilitation programs targeting these impairments could be beneficial for restoring the functional transfer in individuals with knee OA.

Influence of Anterior-Posterior External Surface Perturbation on Trunk Stability During Abdominal Stabilization Strategies While Sitting

Background

Spinal and pelvic injuries during an unexpected perturbation are closely related to spinal stability, which is known to be controlled by abdominal stabilization maneuvers. This study aimed to evaluate the effects of unexpected perturbations on trunk stability and abdominal stabilization strategies in 42 sedentary adults while sitting.

Material/Methods

Abdominal stabilization strategies consisted of bracing and hollowing maneuvers. Abdominal bracing maneuvers (ABM) were focused on the abdominal wall muscles [inferior oblique (IO), exterior oblique (EO)], and abdominal hollowing maneuvers (AHM) were focused on deep muscle (TrA) activation. The subjects were instructed in abdominal stabilization maneuvers. Afterward, subjects were seated in a chair that could be moved forward or backward suddenly with the support surface.

Results

Angular displacements of the upper thorax, lower thorax, and lumbopelvic during unexpected perturbation, with different abdominal stabilization maneuvers, were measured. During forward perturbation (d=0.71, F=10.324, P=0.001) and backward perturbation in high speed (d=0.62, F=9.265, P=0.011), there were significant differences in angular displacements of the upper thorax between hollowing and bracing maneuvers. Additionally, significant differences were found in the lumbopelvic angular displacement between the hollowing and bracing maneuvers (d=0.62, F=4.071, P=0.044).

Conclusions

Our findings indicate that the ABM is a better stabilizing technique for the upper thorax, and the AHM is a better stabilizing technique for the lumbopelvic region during unexpected perturbations at high speed in the seated position.

Effects of initial foot position on postural responses to lateral standing surface perturbations in younger and older adults

BACKGROUND

An age-related decline in standing balance control in the medio-lateral direction is associated with increased risk of falls. A potential approach to improve postural stability is to change initial foot position (IFP).

RESEARCH QUESTIONS

In response to a lateral surface perturbation, how are lower extremity muscle activation levels different and what are the effects of different IFPs on muscle activation patterns and postural stability in younger versus older adults?

METHODS

Ten younger and ten older healthy adults participated in this study. Three IFPs were tested [Reference (REF): feet were placed parallel, shoulder-width apart; Toes-out with heels together (TOHT): heels together with toes pointing outward; Modified Semi-Tandem (M-ST): the heel of the anterior foot was placed by the big toe of the posterior foot]. Unexpected lateral translations of the standing surface were applied. Electromyographic (EMG) activity of the lower extremity muscles, standard deviation (SD) of the body's CoM acceleration (SD of CoMAccel), and center of pressure (CoP) sway area were compared across IFPs and age.

RESULTS

Activation levels of the muscles serving the ankle and gluteus medius were greater than for the knee joint muscles and gluteus maximus in the loaded leg across all IFPs in both groups. TOHT showed greater EMG peak amplitude of the soleus and fibularis longus compared to REF, and had smaller SD of CoMAccel and CoP sway area than M-ST. Compared to younger adults, older adults demonstrated lower EMG peak amplitude and delayed peak timing of the fibularis longus and greater SD of CoMAccel and CoP sway area in all IFPs during balance recovery.

SIGNIFICANCE

During standing balance recovery, ankle muscles and gluteus medius are important active responders to unexpected lateral surface perturbations and a toes-out IFP could be a viable option to enhance ankle muscle activation that diminishes with age to improve postural stability.