Exploring how metronome pacing at varying movement speeds influences local dynamic stability and coordination variability of lumbar spine motion during repetitive lifting

Auditory metronomes have been used to preserve movement consistency when examining local dynamic stability (LDS) and coordination variability (CV) of lumbar spine motion during repetitive movements. However, the potential influence of the metronome itself on these outcome measures has rarely been considered. Therefore, this study investigated the influence of different metronome paces (i.e., lifting speeds) on measures of lumbar spine LDS and thorax-pelvis CV during a repetitive lifting/lowering task in comparison to self-paced movements. Ten participants completed 5 repetitive lift/lower trials, where participants completed 35 consecutive repetitions (analysis on last 30 repetitions) at a self-selected pace for the first and last trial, and were paced by a 10 lift/min, 15 lift/min, and 20 lift/min metronome, in randomized order, for the remaining three trials. The average self-paced lift/lower speed before and after experiencing the three different metronome paced speeds was 16.2 (±1.02) and 17.2 (±0.73) lifts/min, respectively, and the most-preferred metronome pace trial was 15 lifts/min. Thorax-pelvis CV during the self-paced trials were similar (p > 0.05) to the 15 lift/min metronome paced trials, while greater thorax-pelvis CV was observed for the 10 lift/min compared to the 15 lift/min and 20 lift/min and second self-paced trial (all p < 0.026). This movement speed effect was not observed for lumbar spine LDS; however, more-dynamically stable movements were observed during all metronome paced trials in comparison to the self-paced trials. This study highlights that careful consideration is required when employing a metronome to control/manipulate movement characteristics while examining neuromuscular control using non-linear dynamical systems measures.

The relationship between the local dynamic stability of gait to cognitive and physical performance in older adults: A scoping review

BACKGROUND

Local dynamic stability (LDS) has become accepted as a gait stability indicator. The deterioration of gait stability is magnified in older adults.

RESEARCH QUESTION

What is the current state in the field regarding rthe relationship between LDS and cognitive and/or physical function in older adults?

METHODS

A scoping review design was used to search for peer-reviewed literature or conference proceedings published through May 2023 for an association between LDS and cognitive (e.g., Montreal Cognitive Assessment) or physical performance (e.g., Timed Up & Go Test) in older adults. Only studies investigating gait stability via LDS during controlled walking, when dealing with a subject group consisting of healthy older adults, and quantifying LDS relationship to cognitive and/or physical measure were included. We analysed data from the studies in a descriptive manner.

RESULTS

In total, 814 potentially relevant articles were selected, of which 15 met the inclusion criteria. We identified 37 LDS quantifiers employed in LDS-cognition and/or LDS-physical performance relationship assessment. Nine measures of cognitive and 20 measures of physical performance were analysed. Most studies estimated LDS quantities using triaxial acceleration data. However, there was a variance in sensor placement and signal direction. Out of the 56 studied relationships of LDS to physical performance measures, sixteen were found to be relevant. Out of 22 studied relationships between LDS and cognitive measures, only two were worthwhile.

SIGNIFICANCE

Considering the heterogeneity of the utilized LDS (caused by different sensors locations, signals, and signal directions as well as variety of computational approaches to estimate LDS) and cognitive/physical measures, the results of this scoping review does not indicate a current need for a systematic review with meta-analysis. To assess the overall utility of LDS to reveal a relationship between LDS to cognitive and physical performance measures, an analysis of other subject groups would be appropriate.

Ankle strategy assistance to improve gait stability using controllers based on in-shoe center of pressure in 2 degree-of-freedom powered ankle-foot orthoses: a clinical study

Background

Although the ankle strategy is important for achieving frontal plane stability during one-leg stance, previously developed powered ankle–foot orthoses (PAFOs) did not involve ankle strategies because of hardware limitations. Weakness of movement in frontal plane is a factor that deteriorates gait stability and increases fall risk so it should not be overlooked in rehabilitation. Therefore, we used PAFO with subtalar joint for frontal plane movement and tried to confirm that the existence of it is important in balancing through clinical experiments.

Methods

We developed a proportional CoP controller to assist ankle strategy or stabilizing moment and enhance eversion to compensate for the tilting moment with 2 dof PAFO. It was true experimental study, and we recruited seven healthy subjects (30 ± 4 years) who did not experience any gait abnormality participated in walking experiments for evaluating the immediate effect of subtalar joint of PAFO on their gait stability. They walked on the treadmill with several cases of controllers for data acquisitions. Indices of gait stability and electromyography for muscle activity were measured and Wilcoxon signed-rank tests were used to identify meaningful changes.

Results

We found that subjects were most stable during walking (in terms of largest Lyapunov exponents, p < 0.008) with the assistance of the PAFO when their electromyographic activity was the most reduced (p < 0.008), although postural sway increased when a proportional CoP controller was used to assist the ankle strategy (p < 0.008). Other indices of gait stability, kinematic variability, showed no difference between the powered and unpowered conditions (p > 0.008). The results of the correlation analysis indicate that the actuator of the PAFO enhanced eversion and preserved the location of the CoP in the medial direction so that gait stability was not negatively affected or improved.

Conclusions

We verified that the developed 2 dof PAFO assists the ankle strategy by compensating for the tilting moment with proportional CoP controller and that wearer can walk in a stable state when the orthosis provides power for reducing muscle activity. This result is meaningful because an ankle strategy should be considered in the development of PAFOs for enhancing or even rehabilitating proprioception.

Trial registration 7001988-202003-HR-833-03

Effects of barefoot vs. shod walking during indoor and outdoor conditions in younger and older adults

BACKGROUND

Gait stability and variability measures in barefoot and shod locomotion are frequently investigated in younger but rarely in older adults. Moreover, most studies examine gait measures in laboratory settings instead of real-life settings.

RESEARCH QUESTIONS

How are gait stability and variability parameters affected by footwear compared to barefoot walking in younger and older adults as well as under indoor vs. outdoor conditions?

METHODS

Healthy younger (<35 years) and older adults (>65 years) participated in the randomised within-subject study design. Participants conducted consecutive 25 m walking trials barefoot and with standardised footwear inside and outside. Inertial measurement units were mounted on the participant's foot and used to calculate local dynamic stability (LDS), velocity and minimal toe clearance (MTC), stride length and stride time, including variabilities for these parameters. Linear mixed models were calculated.

RESULTS

Data of 32 younger (17 female, 15 male, age: 30 ± 4 years) and 42 older participants (24 female, 18 male, age: 71 ± 4 years) were analysed. MTC variability was higher in shod conditions compared to barefoot (p = 0.048) and in outdoor conditions (p < 0.001). LDS was different between age groups (p < 0.001). Gait velocity and MTC were higher in shod and outdoor conditions (both p < 0.001). Stride length and time were higher in shod conditions (both p < 0.001) and different between outdoor vs. indoor (longer stride length and shorter stride time outdoor, both (p < 0.001) as well as age groups (shorter stride length (p < 0.021) and stride time in older adults (p < 0.001).

SIGNIFICANCE

Results suggest that gait stability and variability in older and younger adults are acutely affected by footwear vs. barefoot and indoor vs. outdoor walking conditions, indicating a high adaptiveness of these parameters to different experimental conditions. Consequently, future studies should be careful with generalising results obtained under certain conditions. Findings stress the clinical potential of barefoot walking.

Associations of low-back pain and pain-related cognitions with lumbar movement patterns during repetitive seated reaching

BACKGROUND

Development of more effective interventions for nonspecific chronic low back pain (LBP), requires a robust theoretical framework regarding mechanisms underlying the persistence of LBP. Altered movement patterns, possibly driven by pain-related cognitions, are assumed to drive pain persistence, but cogent evidence is missing.

AIM

To assess variability and stability of lumbar movement patterns, during repetitive seated reaching, in people with and without LBP, and to investigate whether these movement characteristics are associated with pain-related cognitions.

METHODS

60 participants were recruited, matched by age and sex (30 back-healthy and 30 with LBP). Mean age was 32.1 years (SD13.4). Mean Oswestry Disability Index-score in LBP-group was 15.7 (SD12.7). Pain-related cognitions were assessed by the 'Pain Catastrophizing Scale' (PCS), 'Pain Anxiety Symptoms Scale' (PASS) and the task-specific 'Expected Back Strain' scale(EBS). Participants performed a seated repetitive reaching movement (45 times), at self-selected speed. Lumbar movement patterns were assessed by an optical motion capture system recording positions of cluster markers, located on the spinous processes of S1 and T8. Movement patterns were characterized by the spatial variability (meanSD) of the lumbar Euler angles: flexion-extension, lateral-bending, axial-rotation, temporal variability (CyclSD) and local dynamic stability (LDE). Differences in movement patterns, between people with and without LBP and with high and low levels of pain-related cognitions, were assessed with factorial MANOVA.

RESULTS

We found no main effect of LBP on variability and stability, but there was a significant interaction effect of group and EBS. In the LBP-group, participants with high levels of EBS, showed increased MeanSD_{lateral-bending} (p = 0.004, η² = 0.14), indicating a large effect. MeanSD_{axial-rotation} approached significance (p = 0.06).

SIGNIFICANCE

In people with LBP, spatial variability was predicted by the task-specific EBS, but not by the general measures of pain-related cognitions. These results suggest that a high level of EBS is a driver of increased spatial variability, in participants with LBP.

Accuracy of image data stream of a markerless motion capture system in determining the local dynamic stability and joint kinematics of human gait

Assessment of gait parameters is commonly performed through the high-end motion tracking systems, which limits the measurement to sophisticated laboratory settings due to its excessive cost. Recently, Microsoft Kinect (v2) sensor has become popular in clinical gait analysis due to its low-cost. But, determining the accuracy of its RGB-D image data stream in measuring the joint kinematics and local dynamic stability remains an unsolved problem. This study examined the suitability of Kinect(v2) RGB-D image data stream in assessing those gait parameters. Fifteen healthy participants walked on a treadmill during which lower body kinematics were measured by a Kinect(v2) sensor and a optophotogrametric tracking system, simultaneously. Extended Kalman filter was used to extract the lower extremity joint angles from Kinect, while inverse kinematics was used for the gold standard system. For both systems, local dynamic stability was assessed using maximal Lyapunov exponent. Sprague's validation metrics, root mean square error (RMSE) and normalized RMSE were computed to confirm the difference between the joint angles time series of the two systems while relative agreement between them was investigated through Pearson's correlation coefficient (p_r). Fisher's Exact Test was performed on maximal Lyapunov exponent to investigate the data independence while reliability was assessed using intraclass correlation coefficients. This study concludes that the RGB-D data stream of Kinect sensor is efficient in estimating joint kinematics, but not suitable for measuring the local dynamic stability.

Local dynamic stability during long-fatiguing walks in people with multiple sclerosis

BACKGROUND

Altered balance/stability during walking is common in people with multiple sclerosis (PwMS). While dynamic gait stability has been related to falling and localized muscle fatigue, it has rarely been studied in MS. Specifically, the effects of walking-related fatigue on dynamic stability are unclear in PwMS.

RESEARCH QUESTIONS

1) Are temporal changes in dynamic stability during long-walks different among PwMS and healthy controls (HC)? 2) Is there a relationship between stability and walking performance changes in PwMS?

METHODS

Twenty-five PwMS and ten HC participated in the six-minute walk test (6MWT) wearing six-wireless inertial sensors. Local dynamic stability (LDS) during gait was quantified by maximum-finite-time Lyapunov exponents (λS), where larger λS indicates less stable dynamics. Linear mixed models were fit to compare changes in LDS and walking performance over time among two groups. Additionally, the percent changes in λS and distance from minute 1 to 6 were recorded as Dynamic Stability Index (DSI6-1) and Distance-Walked Index (DWI6-1) respectively. Finally, Pearson correlation compared the association between DSI6-1 and DWI6-1.

RESULTS

A significant group*time interaction was found for LDS. PwMS did not have different LDS than HC until minute-4 of walking, and differences persisted at minute-6. Further, PwMS walked significantly shorter distances and demonstrated a greater decline in walking performance (DWI6-1) during the 6MWT. Finally, DSI6-1 and DWI6-1 were significantly correlated in PwMS. Significance The dynamic stability differences among PwMS and HC were only apparent after 3-minutes of walking and ∼60% of PwMS became less stable over time, supporting the use of long walks in MS to capture stability changes during the motor task performance. A significant relationship between the decline in stability and poor walking performance over time during the 6MWT suggested a possible role of walking-related fatigue in the worsening of balance during long walks in PwMS.

Concurrent validity of a wearable IMU for objective assessments of functional movement quality and control of the lumbar spine

Inertial measurement units (IMUs) are being recognized in clinical and rehabilitation settings for their ability to assess movement-related disorders of the spine for better guidance of treatment-planning and tracking of recovery. This study evaluated the Mbientlab MetaMotionR IMUs, relative to Vicon motion capture equipment in measuring local dynamic stability of the spine (quantified using maximum finite-time Lyapunov exponent; λ_max), lumbopelvic coordination (quantified using mean absolute relative phase; MARP), and intersegmental motor variability (quantified using deviation phase; DP) of lumbopelvic segments in 10 participants during 35 cycles of repetitive spine flexion-extension (FE). Intraclass correlations were strong between systems when using both the FE angle time-series and the sum of squares (SS) time-series to measure local dynamic stability (0.807 ≤ICC_2,1^λmax,FE ≤ 0.919; 0.738 ≤ ICC_2,1^λmax,SS ≤ 0.868), sagittal-plane lumbopelvic coordination (0.961 ≤ICC_2,1^MARP ≤ 0.963), and sagittal-plane lumbopelvic variability (0.961 ≤ICC_2,1^DP ≤ 0.963). It was concluded that the MetaMotionR IMUs can be reliably used for measuring features associated with spine movement quality and motor control during a repetitive FE task. Future work will assess the reliability of sensor placement, performance during multi-directional movements, and ability to discern clinical and healthy populations based on assessment of movement quality and control.

Impaired local dynamic stability during treadmill walking predicts future falls in patients with multiple sclerosis: A prospective cohort study

BACKGROUND

Falling is a significant problem in patients with multiple sclerosis (MS) and the majority of falls occur during dynamic activities. Recently, there have been evidences focusing on falls and local stability of walking based on dynamic system theory in the elderly as well as patients with cerebral concussion. However, in patient with MS, this relationship has not been fully investigated. The aim of this study was to investigate local stability of walking as a risk factor for falling in patients with MS.

METHODS

Seventy patients were assessed while walking at their preferred speed on a treadmill under single and dual task conditions. A cognitive task (backward counting) was used to assess the importance of dual tasking to fall risk. Trunk kinematics were collected using a cluster marker over the level of T₇ and a 7-camera motion capture system. To quantify local stability of walking, maximal finite-time Lyapunov exponent was calculated from a 12-dimensional state space reconstruction based on 3-dimensional trunk linear and angular velocity time series. Participants were classified as fallers (≥1) and non-fallers based on their prospective fall occurrence.

FINDINGS

30 (43%) participants recorded ≥1 falls and were classified as fallers. The results of multiple logistic regression analysis revealed that short-term local dynamic stability in the single task condition (P<0.05, odds ratio=2.214 (1.037-4.726)) was the significant fall predictor.

INTERPRETATION

The results may indicate that the assessment of local stability of walking can identify patients who would benefit from gait retraining and fall prevention programs.

Nonlinear approach to study the acute effects of static and dynamic stretching on local dynamic stability in lower extremity joint kinematics and muscular activity during pedalling

Researchers have reported contradictory results on the effect of static and dynamic stretching on subsequent performance. Due to the importance of performance through static and dynamic stretching, the aim of this study is to investigate the acute effects of static and dynamic stretching protocols on local dynamic stability in lower extremity joint kinematics and muscular activities during pedalling using a nonlinear dynamics approach. Using a randomised crossover trial design, fifteen active males participated voluntarily in this research (mass: 69.02 ± 10.52 kg, height: 174.00 ± 6.74 cm, and age: 21.20 ± 1.47 years) and completed a pedalling trial in situations of without stretching (WS), after static (SS), and dynamic stretching (DS) of lower extremity. The lower extremity joint angles in the sagittal plane and the electrical activity of soleus, gastrocnemius medialis, tibialis anterior, vastus medialis, biceps femoris, and rectus femoris muscles were collected during 30 pedalling cycles at 70 rates per minute. The results of the repeated measure ANOVA indicated that the knee and ankle angle largest LyE was significantly lower in DS compared to WS and SS. The largest LyE in muscle activity is also significantly lower for all the muscles after DS compared to WS and SS (P ≤ 0.05). Regarding the positive effects of DS on the joints and the muscle activity local dynamic stability, it is suggested to use DS than SS in the warm-up program before repetitive activities like pedalling.

The effects of protective footwear on spine control and lifting mechanics

Manual materials handling is often performed in hazardous environments where protective footwear must be worn; however, workers can wear different types of footwear depending on the hazards present. Therefore, the goal of this study was to investigate how three-dimensional lifting mechanics and trunk local dynamic stability are affected by different types of protective footwear (i.e. steel-toed shoes (unlaced boot), steel-toed boots (work boot), and steel-toed boots with a metatarsal guard (MET)). Twelve males and twelve females performed a repetitive lifting task at 10% of their maximum lifting effort, under three randomized footwear conditions. Footwear type influenced ankle range of motion (ROM). The work boot condition reduced ankle sagittal ROM (p = 0.007) and the MET condition reduced ankle ROM in the sagittal (p = 0.004), frontal (p = 0.001) and transverse (p = 0.003) planes. Despite these differences at the ankle, no other changes in participant lifting mechanics were observed.

Kinematic variability and local dynamic stability of gait in individuals with hip pain and a history of developmental dysplasia

BACKGROUND

Individuals with developmental dysplasia of the hip (DDH) often report hip pain and exhibit gait adaptations. Previous studies in this patient population have focused on average kinematic and acceleration measures during gait, but have not examined variability.

RESEARCH QUESTION

Do individuals with hip pain and DDH have altered kinematic variability or local dynamic stability (LDS) compared to individuals without hip pain?

METHODS

Twelve individuals with hip pain and DDH and 12 matched controls walked for two minutes on a treadmill at three speeds: preferred, fast (25% faster than preferred), and prescribed (1.25 m/s). Kinematic variability of spatiotemporal measures, joint and segment angles, and LDS of the trunk were calculated for each speed.

RESULTS

At the prescribed speed, individuals with hip pain and DDH had more kinematic variability than controls at the hip, pelvis, and trunk as well as greater variability in spatiotemporal measures. LDS was not different between groups. Kinematic variability of the joints decreased and LDS of the trunk increased (i.e., increased gait stability) with increased speed.

SIGNIFICANCE

Individuals with hip pain and DDH had greater kinematic variability compared to individuals without hip pain when walking at the same prescribed speed, indicating either an adaptation to pain or reduced neuromuscular control. LDS of the trunk was not different between groups, suggesting that hip pain does not affect overall gait stability. Kinematic variability and LDS were affected by walking speed, but in different ways, emphasizing that these measures quantify different aspects of walking behavior.

Local dynamic stability of the lower extremity in novice and trained runners while running intraditional and minimal footwear

BACKGROUND

Understanding how footwear cushioning influences movement stability may be helpful in reducing injuries related to repetitive loading.

RESEARCH QUESTION

The purpose of this study was to identify the relationship between running experience and midsole cushioning on local dynamic stability of the ankle, knee and hip.

METHODS

Twenty-four trained and novice runners were recruited to run on a treadmill for five minutes at the same relative intensity. Midsole thickness (thick/thin) and stiffness (soft / hard) were manipulated yielding four unique conditions. Lyapunov exponents were estimated using the Wolf algorithm from sagittal ankle, knee and hip kinematics.

RESULTS

Trained runners had increased movement stability in all shoe conditions compared to their novice counterparts. Midsole thickness and stiffness, overall, did not affect movement stability within each of the running groups. Novice runners displayed decreased movement stability at the hip while running in the thick/soft running shoes. It was found that running experience has a greater influence on movement stability in the lower limbs compared to the midsole characteristics that were manipulated in this experiment. The hip was most stable followed by the knee and the ankle highlighting decreased stability in distal joints.

CONCLUSIONS

It appears that midsole design within current design ranges do not have the ability to influence movement stability.

Differential effects of muscle fatigue on dynamic spine stability: Implications for injury risk

This study was designed to assess the utility of using a measure of dynamic spine stability in an unfatigued, rested state as a predictor of dynamic spine stability in a challenged, fatigued state. Participants completed three trials (Day 1: Rested, Fatigued; Day 2: Recovery) during which the dynamic stability of the spine was assessed over 30 repeated flexion/extension motions using maximum finite-cycle Lyapunov exponents. Multiple sets of dynamic trunk extensions were performed to fatigue the trunk extensor muscles. Across the sample population, an increase in dynamic spine stability when fatigued was observed, as well as a moderate correlation between the level of dynamic stability when rested and a stabilizing response when fatigued. Further analysis of the data on a person-by-person basis revealed three distinct responses in which participants either stabilized, destabilized or had no change in dynamic spine stability when fatigued. Therefore, the mean response of the sample population did not adequately represent the true, meaningful response of individuals within the population. These results illustrate the importance of considering individualized responses when examining dynamic stability measures, and provide preliminary evidence that suggests that individual injury risk cannot be completely captured by measures taken in an unchallenged, rested state.

Analysis of running stability during 5000 m running. Eur J Sport Sci 2018;19:413-421. [PMID: 30257130 DOI: 10.1080/17461391.2018.1519040]

In the analysis of human walking, the assessment of local dynamic stability (LDS) has been widely used to determine gait stability. To extend the concepts of LDS to the analysis of running biomechanics, this study aimed to compare LDS during exhaustive running between competitive and recreational runners. Fifteen recreational and fifteen competitive runners performed an exhaustive 5000 m run. Inertial measurement units at foot, pelvis, and thorax were used to determine local dynamic running stability as quantified by the largest Lyapunov exponent. In addition, we measured running velocity, lactate levels, perceived exertion, and foot strike patterns. LDS at the start, mid, and end of a 5000 m run was compared between the two groups by a two-way repeated-measures analysis of variance (ANOVA). Local dynamic stability increased during the run (thorax, pelvis) in both recreational and competitive runners (P_Thorax = 0.006; P_Pelvis = 0.001). During the whole run, competitive runners showed a significantly higher LDS (P = 0.029) compared to recreational runners at the foot kinematics. In conclusion, exhaustive running can lead to improvements in LDS, indicating a higher local dynamic stability of the running technique with increasing exhaustion. Furthermore, LDS of the foot differs between the two groups at all measurement points. The results of this study show the value of determining LDS in athletes as it can give a better understanding into the biomechanics of running.

Local dynamic stability during treadmill walking can detect children with developmental coordination disorder

OBJECTIVE

Developmental coordination disorder (DCD) is an innate impairment of motor coordination that affects basic locomotion and balance. This study investigated local dynamic stability of trunk accelerations during treadmill walking as an objective evaluation of gait stability and the sensitivity and specificity of this measure to discriminate children with DCD from typically developing children.

METHOD

Eight children with DCD and ten age- and gender-matched typically developing children (TD) walked four minutes on a treadmill. Trunk accelerations in vertical, medio-lateral and anterior-posterior directions were recorded with a sternum mounted accelerometer at 256Hz. Short term local dynamic stability (λs), root mean square (RMS) and relative root mean square (RMSR) were calculated from measures of orthogonal trunk accelerations. Receiver operating characteristic curve (ROC) analysis was performed to discriminate between groups based on short term local dynamic stability.

RESULTS

λs was significantly greater in children with DCD in the main movement direction (AP) (DCD: 1.69±0.17 λs; TD:1.41±0.17 λs; p=0.005), indicating reduced local dynamic stability. RMS and RMSR accelerations showed no difference between children with DCD and TD children in any direction. The ROC analysis of λs in separate directions and in two dimensions showed an excellent accuracy of discriminating between children with DCD and TD children. Anterior-posterior direction in combination with medio-lateral or vertical showed best performance with an area under the curve (AUC) of 0.91.

CONCLUSION

We have shown that children with developmental coordination disorder have general reduced local dynamic stability and that the short term Lyapunov exponent has good power of discrimination between DCD and TD.

Local dynamic stability and gait variability during attentional tasks in young adults

Cell phone use while walking may be a cognitive distraction and reduce visual and motor attention. Thus, the aim of this study was to verify the effects of attentional dual-tasks while using a cell phone in different conditions. Stability, regularity, and linear variability of trunk kinematics, and gait spatiotemporal parameters in young adults were measured. Twenty young subjects of both genders were asked to walk on a treadmill for 4min under the following conditions: (a) looking forward at a fixed target 2.5m away (walking); (b) talking on a cell phone with unilateral handling (talking); (c) texting messages on a cell phone with unilateral handling (texting); and (d) looking forward at the aforementioned target while listening to music without handling the phone (listening). Local dynamic stability measured in terms of the largest Lyapunov exponent decreased while handling a cell phone (talking and texting). Gait variability and regularity increased when talking on a cell phone, but no variable changed in the listening condition. Under all dual-task conditions, there were significant increases in stride width and its variability. We conclude that young adults who use a cell phone when walking adapt their gait pattern conservatively, which can be because of increased attentional demand during cell phone use.

The effect of physical exhaustion on gait stability in young and older individuals

Fatigue directly affects key features of the sensorimotor system which disorganizes voluntary control of movement accuracy. Local dynamic stability of walking is considered a sensitive measure for neuromuscular performance. To gain greater insight in the role of fatigue in motor behaviour in older and young adults during walking, the current experiment analyses gait patterns of healthy young but maximal fatigued individuals and gait patterns in submaximal fatigued older adults. Ten young and 18 older subjects performed a bicycle incremental exercise test on a cycle ergometer. In young subjects, the incremental test was performed until total physical exhaustion. In older subjects, the test was performed until submaximal fatigue. Prior to and after the test, the participants walked for 2.5min on a treadmill. Based on linear acceleration data of the trunk, local dynamic stability was assessed. Student's t-test was used to check if differences are statistically significant. In young individuals, we found a significant decrease in the finite-time maximal Lyapunov exponents between unfatigued walking and maximal fatigued walking. In older participants, significant increases in the finite-time maximal Lyapunov between unfatigued walking and submaximal fatigued walking were observed. The results indicate that (1) young and sporty subjects become more stable after having passed a maximum cardiopulmonary exercise test on a cycle ergometer while (2) older individuals walk less locally stable in a submaximal fatigued condition. Older cohorts might show a higher fall risk when they are physically fatigued.

Measurement strategy and statistical power in studies assessing gait stability and variability in older adults

Background

Gait variability and stability measures might be useful to assess gait quality changes after fall prevention programs. However, reliability of these measures appears limited.

Aims

The objective of the present study was to assess the effects of measurement strategy in terms of numbers of subjects, measurement days and measurements per day on the power to detect relevant changes in gait variability and stability between conditions among healthy elderly.

Methods

Sixteen healthy older participants [65.6 (SD 5.9) years], performed two walking trials on each of 2 days. Required numbers of subjects to obtain sufficient statistical power for comparisons between conditions within subjects (paired, repeated-measures designs) were calculated (with confidence intervals) for several gait measures and for different numbers of trials per day and for different numbers of measurement days.

Results

The numbers of subjects required to obtain sufficient statistical power in studies collecting data from one trial on 1 day in each of the two compared conditions ranged from 7 to 13 for large differences but highly correlated data between conditions, up to 78–192 for data with a small effect and low correlation.

Discussion

Low correlations between gait parameters in different conditions can be assumed and relatively small effects appear clinically meaningful. This implies that large numbers of subjects are generally needed.

Conclusion

This study provides the analysis tools and underlying data for power analyses in studies using gait parameters as an outcome of interventions aiming to reduce fall risk.

Low back skin sensitivity has minimal impact on active lumbar spine proprioception and stability in healthy adults

The purpose of the current work was to (1) determine whether low back cutaneous sensitivity could be reduced through the use of a topical lidocaine-prilocaine anesthetic (EMLA(®)) to mirror reductions reported in chronic lower back pain (CLBP) patients, as well as to (2) identify whether reductions in cutaneous sensitivity resulted in decreased lumbar spine proprioception, neuromuscular control and dynamic stability. Twenty-eight healthy participants were divided equally into matched EMLA and PLACEBO treatment groups. Groups completed cutaneous minimum monofilament and two-point discrimination (TPD) threshold tests, as well as tests of sagittal and axial lumbar spine active repositioning error, seated balance and repeated lifting dynamic stability. These tests were administered both before and after the application of an EMLA or PLACEBO treatment. Results show that low back minimum monofilament and TPD thresholds were significantly increased within the EMLA group. Skin sensitivity remained unchanged in the PLACEBO group. In the EMLA group, decreases in low back cutaneous sensitivity had minimal effect on low back proprioception (active sagittal and axial repositioning) and dynamic stability (seated balance and repeated lifting). These findings demonstrate that treating the skin of the low back with an EMLA anesthetic can effectively decrease the cutaneous sensitivity of low back region. Further, these decreases in peripheral cutaneous sensitivity are similar in magnitude to those reported in CLBP patients. Within this healthy population, decreased cutaneous sensitivity of the low back region has minimal influence on active lumbar spine proprioception, neuromuscular control and dynamic stability.

A comparison study of local dynamic stability measures of daily life walking in older adult community-dwelling fallers and non-fallers

In the present study we compared the performance of three different estimations of local dynamic stability λ to distinguish between the dynamics of the daily-life walking of elderly fallers and non-fallers. The study re-analyses inertial sensor data of 3-days daily-life activity originally described by Weiss et al. (2013). The data set contains inertial sensor data from 39 older persons who reported less than 2 falls and 31 older persons who reported two or more falls the previous year. 3D-acceleration and 3D-velocity signals from walking epochs of 50s were used to reconstruct a state space using three different methods. Local dynamic stability was estimated with the algorithms proposed by Rosenstein et al. (1993), Kantz (1994), and Ihlen et al. (2012a). Median λs assessed by Ihlen׳s and Kantz׳ algorithms discriminated better between elderly fallers and non-fallers (highest AUC=0.75 and 0.73) than Rosenstein׳s algorithm (highest AUC=0.59). The present results suggest that the ability of λ to distinguish between fallers and non-fallers is dependent on the parameter setting of the chosen algorithm. Further replication in larger samples of community-dwelling older persons and different patient groups is necessary before including the suggested parameter settings in fall risk assessment and prediction models.

Does visual augmented feedback reduce local dynamic stability while walking?

Augmented feedback is frequently used in gait training to efficiently correct specific gait patterns in patients with different disorders. The patients use this external augmented feedback to align actual movements in a way that predefined gait characteristics can be achieved. Voluntary changes of gait characteristics are reported to reduce local dynamic stability (LDS) which in turn is associated with increased risk of falling. The aim of this study was to evaluate the instantaneous effect of visual feedback, provided to help patients to correct frontal plane pelvis and trunk movements, on the LDS of pelvis and trunk. Kinematic gait data was captured in ten women with gait disorders. The effect of visual feedback on LDS, quantified with the largest Lyapunov exponent, of walking was examined. We found a significant decreased LDS (e.g. pelvis: p=.009) in our subjects when they were using visual augmented feedback. Our data suggest that the use of visual augmented feedback causes less stable gait patterns indicating a reduced ability to respond to small perturbations which might increase risk of falling. Therefore, researchers or clinicians who aim to correct gait patterns through real time based external augmented feedback should consider the potential negative effect on gait stability. It should be evaluated if the possible increased fall risk provoked by visual feedback exceeds possible increases in fall risk induced by conventional gait-retraining interventions. The external validity of the study is limited because of the low sample size and inhomogeneous group characteristics. Thus, further studies including homogeneous cohorts are required.

Associations between measures of gait stability, leg strength and fear of falling

Fear of falling (FoF) in elderly frequently leads to decreased quality of life. FoF is suggested to be associated with changes in gait quality and muscle strength with aging. The aim of this study was to determine whether gait quality and maximal voluntary torque (MVT) of knee extensor muscles are associated with FoF. We hypothesized that high between-stride variability and local divergence exponent (LDE) of trunk kinematics in gait are associated with higher FoF in non-fallers, but not in fallers. Moreover, we hypothesized that knee extensor muscle strength is associated with a high variability and LDE of trunk kinematics during gait. 134 four adults, aged 62.4 (SD 6.2) years agreed to participate. FoF was assessed on a 10-point numerical rating scale. Subjects with at least one fall in the past 12 months were considered as fallers. LDE and variability were calculated from data of a trunk-mounted inertial-sensor collected during several minutes of treadmill walking. Maximal voluntary knee extension torque (MVT) was assessed isometrically. Fall history was an effect modifier in the association between LDE and FoF only, i.e. only subjects without fall history and a high LDE had a five times higher chance of reporting FoF. Gait variability was not associated with FoF. Low MVT was associated with FoF. Multivariate analysis demonstrated that LDE was more strongly associated with FoF than MVT. Decreased stability of gait as reflected in a high LDE and low muscle strength are associated with and a potential cause of FoF in subjects without fall history.

Effect of age on the variability and stability of gait: a cross-sectional treadmill study in healthy individuals between 20 and 69 years of age

Falls during walking are a major health issue in the elderly population. Older individuals are usually more cautious, walk more slowly, take shorter steps, and exhibit increased step-to-step variability. They often have impaired dynamic balance, which explains their increased falling risk. Those locomotor characteristics might be the result of the neurological/musculoskeletal degenerative processes typical of advanced age or of a decline that began earlier in life. In order to help determine between the two possibilities, we analyzed the relationship between age and gait features among 100 individuals aged 20-69. Trunk acceleration was measured during a 5-min treadmill session using a 3D accelerometer. The following dependent variables were assessed: preferred walking speed, walk ratio (step length normalized by step frequency), gait instability (local dynamic stability, Lyapunov exponent method), and acceleration variability (root mean square [RMS]). Using age as a predictor, linear regressions were performed for each dependent variable. The results indicated that walking speed, walk ratio and trunk acceleration variability were not dependent on age (R(2)<2%). However, there was a significant quadratic association between age and gait instability in the mediolateral direction (R(2)=15%). We concluded that most of the typical gait features of older age do not result from a slow evolution over the life course. On the other hand, gait instability likely begins to increase at an accelerated rate as early as age 40-50. This finding supports the premise that local dynamic stability is likely a relevant early indicator of falling risk.

Effects of unilateral leg muscle fatigue on balance control in perturbed and unperturbed gait in healthy elderly

This study assessed effects of unilateral leg muscle fatigue (ULMF) on balance control in gait during the stance and swing phases of the fatigued leg in healthy elderly, to test the assumption that leg muscle strength limits balance control during the stance-phase. Ten subjects (aged 63.4, SD 5.5 years) walked on a treadmill in 4 conditions: unperturbed unfatigued, unperturbed fatigued, perturbed unfatigued, and perturbed fatigued. The perturbations were lateral trunk pulls just before contralateral heel contact. ULMF was evoked by unilateral squat exercise until task failure. Isometric knee extension strength was measured to verify the presence of muscle fatigue. Between-stride standard deviations and Lyapunov exponents of trunk kinematics were used as indicators of balance control. Required perturbation force and the deviation of trunk kinematics from unperturbed gait were used to assess perturbation responses. Knee extension strength decreased considerably (17.3% SD 8.6%) as a result ULMF. ULMF did not affect steady-state gait balance. Less force was required to perturb subjects when the fatigued leg was in the stance-phase compared to the swing-phase. Subjects showed a faster return to the unperturbed gait pattern in the fatigued than in the unfatigued condition, after perturbations in swing and stance of the fatigued leg. The results of this study are not in line with the hypothesized effects of leg muscle fatigue on balance in gait. The healthy elderly subjects were able to cope with substantial ULMF during steady-state gait and demonstrated faster balance recovery after laterally directed mechanical perturbations in the fatigued than in the unfatigued condition.

Local dynamic stability associated with load carrying

Objectives

Load carrying tasks are recognized as one of the primary occupational factors leading to slip and fall injuries. Nevertheless, the mechanisms associated with load carrying and walking stability remain illusive. The objective of the current study was to apply local dynamic stability measure in walking while carrying a load, and to investigate the possible adaptive gait stability changes.

Methods

Current study involved 25 young adults in a biomechanics research laboratory. One tri-axial accelerometer was used to measure three-dimensional low back acceleration during continuous treadmill walking. Local dynamic stability was quantified by the maximum Lyapunov exponent (maxLE) from a nonlinear dynamics approach.

Results

Long term maxLE was found to be significant higher under load condition than no-load condition in all three reference axes, indicating the declined local dynamic stability associated with load carrying.

Conclusion

Current study confirmed the sensitivity of local dynamic stability measure in load carrying situation. It was concluded that load carrying tasks were associated with declined local dynamic stability, which may result in increased risk of fall accident. This finding has implications in preventing fall accidents associated with occupational load carrying.

Fall risk assessments based on postural and dynamic stability using inertial measurement unit

Objectives

Slip and fall accidents in the workplace are one of the top causes of work related fatalities and injuries. Previous studies have indicated that fall risk was related to postural and dynamic stability. However, the usage of this theoretical relationship was limited by laboratory based measuring instruments. The current study proposed a new method for stability assessment by use of inertial measurement units (IMUs).

Methods

Accelerations at different body parts were recorded by the IMUs. Postural and local dynamic stability was assessed from these measures and compared with that computed from the traditional method.

Results

The results demonstrated: 1) significant differences between fall prone and healthy groups in IMU assessed dynamic stability; and 2) better power of discrimination with multi stability index assessed by IMUs.

Conclusion

The findings can be utilized in the design of a portable screening or monitoring tool for fall risk assessment in various industrial settings.