Increased Auditory Dual Task Cost During Gait Initiation in Adult Patients With Persistent Concussion Symptoms.

OBJECTIVE: To compare dual task cost (DTC) during gait initiation (GI) between a population of patients with persistent concussion symptoms (PCS) and age-matched healthy participants. DESIGN: Cohort study. SETTING: University research center. PARTICIPANTS: A cohort sample including 15 participants with PCS (43.9±11.7y, 73.3% female) and 23 age-matched healthy participants (42.1±10.3y, 65.2% female) as controls. INTERVENTIONS: Participants were tested on a single occasion where they performed 5 trials of single task and 5 trials of dual task GI with 12-camera motion capture and 3 force plates. MAIN OUTCOME MEASURES: The dependent variables of interest were the DTC for the center of pressure (COP) displacement and velocity during the anticipatory postural adjustment (APA) phase, the COP-center of mass (COP-COM) separation, and the response accuracy during the auditory cognitive tasks. RESULTS: There were significant group differences with worse DTC for the PCS participants in anterior (A)/posterior (P) displacement (PCS, -37.5±22.1%; Control, -9.7±39.2%; P=.016, d=0.874), APA medial (M)/lateral (L) velocity (PCS, -34.8±28.8%; Control, -17.0±40.21%; P=.041, d=0.866), and the peak COP-COM separation (PCS, -7.3±6.7%; Control, 0.6±6.5%; P=.023, d=1.200). There were no significant group differences in the APA A/P velocity (PCS, -38.8±33.1%; Control, -19.8±43.9%; P=.094), APA M/L displacement (PCS, -34.8±21.8%; Control, -10.6±25.3%; P=.313), or cognitive task performance (PCS, -2.7±10.8%; Control, -0.2±4.3%; P=.321). CONCLUSIONS: PCS participants had greater (worse) DTC during both the planning and execution of the task, with large effect sizes (d>0.80). PCS participants also used a posture-second strategy whereby attentional resources were inappropriately allocated to the cognitive task. These deficits may challenge a patient's ability to complete activities of daily living and limit their functional independence.

Gait kinematics differ by bout duration and setting.

BACKGROUND: Gait kinematics differ between settings and among young and older adults with and without knee osteoarthritis. Out-of-lab data has a variety of walking bout characteristics compared to controlled in-lab settings. The effect of walking bout duration on gait analysis results is unclear, and there is no standardized procedure for segmenting or selecting out-of-lab data for analysis. RESEARCH QUESTION: Do gait kinematics differ by bout duration or setting in young and older adults with and without knee osteoarthritis? METHODS: Ten young (28.1±3.5 yrs), ten older adults (60.8±3.3 yrs), and ten older adults with knee osteoarthritis (64.1±3.6 yrs) performed a standard in-lab gait analysis followed by a prescribed walking route outside the lab at a comfortable speed with four IMUs. Walking speed, stride length, and sagittal hip, knee, and ankle angular excursion (ROM) were calculated for each identified stride. Out-of-lab strides included straight-line, level walking divided into strides that occurred during long (>60 s) or short (≤60 s) bouts. Gait kinematics were compared between in-lab and both out-of-lab bout durations among groups. RESULTS: Significant main effects of setting or duration were found for walking speed and stride length, but there were no significant differences in hip, knee, or ankle joint ROM. Walking speed and stride length were greater in-lab followed by long and short bout out-of-lab. No significant interaction was observed between group and setting or bout duration for any spatiotemporal variables or joint ROMs. SIGNIFICANCE: Out-of-lab gait data can be beneficial in identifying gait characteristics that individuals may not encounter in the traditional lab setting. Setting has an impact on walking kinematics, so comparisons of in-lab and free-living gait may be impacted by the duration of walking bouts. A standardized approach for to analyzing out-of-lab gait data is important for comparing studies and populations.

Challenges and advances in the use of wearable sensors for lower extremity biomechanics.

The use of wearable sensors for the collection of lower extremity biomechanical data is increasing in popularity, in part due to the ease of collecting data and the ability to capture movement outside of traditional biomechanics laboratories. Consequently, an increasing number of researchers are facing the challenges that come with utilizing the data captured by wearable sensors. These challenges include identifying/calculating meaningful measures from unfamiliar data types (measures of acceleration and angular velocity instead of positions and joint angles), defining sensor-to-segment alignments for calculating traditional biomechanics metrics, using reduced sensor sets and machine learning to predict unmeasured signals, making decisions about when and how to make algorithms freely available, and developing or replicating methods to perform basic processing tasks such as recognizing activities of interest or identifying gait events. In this perspective article, we present our own approaches to common challenges in lower extremity biomechanics research using wearable sensors and share our perspectives on approaching several of these challenges. We present these perspectives with examples that come mostly from gait research, but many of the concepts also apply to other contexts where researchers may use wearable sensors. Our goal is to introduce common challenges to new users of wearable sensors, and to promote dialogue amongst experienced users towards best practices.

Lower Extremity Inverse Kinematics Results Differ Between Inertial Measurement Unit- and Marker-Derived Gait Data.

In-lab, marker-based gait analyses may not represent real-world gait. Real-world gait analyses may be feasible using inertial measurement units (IMUs) in combination with open-source data processing pipelines (OpenSense). Before using OpenSense to study real-world gait, we must determine whether these methods estimate joint kinematics similarly to traditional marker-based motion capture (MoCap) and differentiate groups with clinically different gait mechanics. Healthy young and older adults and older adults with knee osteoarthritis completed this study. We captured MoCap and IMU data during overground walking at 2 speeds. MoCap and IMU kinematics were computed with OpenSim workflows. We tested whether sagittal kinematics differed between MoCap and IMU, whether tools detected between-group differences similarly, and whether kinematics differed between tools by speed. MoCap showed more anterior pelvic tilt (0%-100% stride) and joint flexion than IMU (hip: 0%-38% and 61%-100% stride; knee: 0%-38%, 58%-89%, and 95%-99% stride; and ankle: 6%-99% stride). There were no significant tool-by-group interactions. We found significant tool-by-speed interactions for all angles. While MoCap- and IMU-derived kinematics differed, the lack of tool-by-group interactions suggests consistent tracking across clinical cohorts. Results of the current study suggest that IMU-derived kinematics with OpenSense may enable reliable evaluation of gait in real-world settings.

A novel method to quantify individual limb contributions to standing postural control.

BACKGROUND: Understanding individual limb contributions to standing postural control is valuable when evaluating populations with asymmetric function (e.g., stroke, amputations). We propose a method of quantifying three contributions to controlling the net anteroposterior center of pressure (CoP) during quiet standing: CoP moving under left and right limbs and weight shifting between the two limbs. RESEARCH QUESTION: Can these contributions to standing postural control be quantified from CoP trajectories in neurotypical adults? METHODS: Instantaneous contributions can be negative or larger than one, and integrated contributions sum to equal one. Proof-of-concept demonstrations validated these calculated contributions by restricting CoP motion under one or both feet. We evaluated these contributions in 30 neurotypical young adults who completed two (eyes opened; eyes closed) 30-s trials of bipedal standing. We evaluated the relationships between limb contributions, self-reported limb dominance, and between-limb weight distributions. RESULTS: All participants self-reported as right-limb dominant; however, a range of mean limb contributions were observed with eyes opened (Left: mean [range] = 0.52 [0.37-0.63]; Right: 0.48 [0.31-0.63]) and with eyes closed (Left: 0.51 [0.39-0.63]; Right: 0.49 [0.37-0.61]). Weight-shift contributions were small with eyes opened (0.00 [-0.01 to 0.01]) and eyes closed (0.00 [-0.01 to 0.02]). We did not identify any between-limb differences in contributions when grouped by self-reported limb dominance (p > 0.10, d < 0.31). Contributions did not significantly correlate with Waterloo Footedness scores (-0.22 < r < 0.21, p > 0.25) or between-limb weight distributions (0 < r < 0.24, p > 0.20). SIGNIFICANCE: Across neurotypical participants, we observed a notable range of limb contributions not related to self-reported limb dominance or between-limb weight distributions. With this tool, we can characterize differences in the amount of CoP motion and the underlying control strategies. Changes in limb contribution can be measured longitudinally (i.e., across rehabilitation programs, disease progression, aging) representative of limb function, which may be particularly useful in populations with asymmetric function.

Effects of contact/collision sport history on gait in early- to mid-adulthood.

BACKGROUND: To determine the effect of contact/collision sport participation on measures of single-task (ST) and dual-task (DT) gait among early- to middle-aged adults. METHODS: The study recruited 113 adults (34.88 ± 11.80 years, (mean ± SD); 53.0% female) representing 4 groups. Groups included (a) former non-contact/collision athletes and non-athletes who are not physically active (n = 28); (b) former non-contact/collision athletes who are physically active (n = 29); (c) former contact/collision sport athletes who participated in high-risk sports and are physically active (n = 29); and (d) former rugby players with prolonged repetitive head impact exposure history who are physically active (n = 27). Gait parameters were collected using inertial measurement units during ST and DT gait. DT cost was calculated for all gait parameters (double support, gait speed, and stride length). Groups were compared first using one-way analysis of covariance. Then a multiple regression was performed for participants in the high-risk sport athletes and repetitive head impact exposure athletes groups only to predict gait outcomes from contact/collision sport career duration. RESULTS: There were no significant differences between groups on any ST, DT, or DT cost outcomes (p > 0.05). Contact/collision sport duration did not predict any ST, DT, or DT cost gait outcomes. CONCLUSION: Years and history of contact/collision sport participation does not appear to negatively affect or predict neurobehavioral function in early- to mid-adulthood among physically active individuals.

Adults with knee osteoarthritis use different coordinative strategies to transition from swing to stance compared to young asymptomatic adults.

BACKGROUND: Neuromuscular changes that occur with aging or joint pathology likely alter the coordinative strategies that adults use to walk and to recover from perturbations during gait. Differences in coordination patterns or in how coordination changes in response to a challenge may provide insight into neuromuscular targets for falls prevention interventions. RESEARCH QUESTION: Do young asymptomatic adults, older asymptomatic adults, and older adults with knee OA alter their lower extremity segment coordination differently in response to an increase in walking speed?. METHODS: We captured lower extremity kinematics using inertial measurement units as 29 participants (10 young, 10 older, 9 older with knee osteoarthritis) walked on a treadmill at self-selected preferred and faster speeds. We calculated lower extremity segment coordination and coordination variability using vector coding. We compared coordination and its variability among groups and speeds. RESULTS: There were no significant interactions between group and speed. Overall group or speed differences in coordination or variability occurred mostly during terminal swing or early stance. Coordination patterns differed between young adults and adults with knee osteoarthritis in all segment couples during terminal swing and at the foot vs. shank during early stance. During these same gait cycle phases for the foot vs. shank and shank vs. thigh segment couples, coordination patterns shifted towards those of young adults when participants walked faster. Where coordination variability differed by group or speed, it was lower in the young adults than in the older adults with or without knee osteoarthritis and at faster walking speed. SIGNIFICANCE: Our results identified that older adults with knee osteoarthritis have a different strategy for transitioning from swing to stance compared to young adults, especially at distal limb segments. These results may help target fall prevention interventions to specific gait cycle phases or strategies.

Interactions Between Different Age-Related Factors Affecting Balance Control in Walking.

Maintaining balance during walking is a continuous sensorimotor control problem. Throughout the movement, the central nervous system has to collect sensory data about the current state of the body in space, use this information to detect possible threats to balance and adapt the movement pattern to ensure stability. Failure of this sensorimotor loop can lead to dire consequences in the form of falls, injury and death. Such failures tend to become more prevalent as people get older. While research has established a number of factors associated with higher risk of falls, we know relatively little about age-related changes of the underlying sensorimotor control loop and how such changes are related to empirically established risk factors. This paper approaches the problem of age-related fall risk from a neural control perspective. We begin by summarizing recent empirical findings about the neural control laws mapping sensory input to motor output for balance control during walking. These findings were established in young, neurotypical study populations and establish a baseline of sensorimotor control of balance. We then review correlates for deteriorating balance control in older adults, of muscle weakness, slow walking, cognitive decline, and increased visual dependency. While empirical associations between these factors and fall risk have been established reasonably well, we know relatively little about the underlying causal relationships. Establishing such causal relationships is hard, because the different factors all co-vary with age and are difficult to isolate empirically. One option to analyze the role of an individual factor for balance control is to use computational models of walking comprising all levels of the sensorimotor control loop. We introduce one such model that generates walking movement patterns from a short list of spinal reflex modules with limited supraspinal modulation for balance. We show how this model can be used to simulate empirical studies, and how comparison between the model and empirical results can indicate gaps in our current understanding of balance control. We also show how different aspects of aging can be added to this model to study their effect on balance control in isolation.

Propulsive joint powers track with sensor-derived angular velocity: A potential tool for lab-less gait retraining.

Lower propulsive joint powers, particularly at the ankle, are often observed in older compared to young adults. Interventions to increase joint powers often require labs with motion capture and force treadmill technology. Translating these interventions out of the lab requires identifying portable measures that track (i.e., strongly correlate with) changes in joint powers. The purpose of this study was to determine if kinematics collected using inertial measurement units (IMUs) correlate with propulsive joint powers calculated using inverse dynamics. We collected data simultaneously with motion capture, force plates, and IMU sensors as young and older adults walked at varying speeds overground in a laboratory. Hip, knee, and ankle joint powers were calculated using inverse dynamics and positive peaks in the second half of stance were identified as the propulsive powers of interest. Raw IMU gyroscope data were oriented to a functional medial-lateral axis and peaks in the second half of stance were identified for segment (thigh, shank, foot) and joint (hip, knee, ankle) angular velocities. Pearson correlation coefficients were calculated between peak joint powers and peak angular velocities. We identified significant (all p < 0.001) correlations between hip joint power and hip and thigh angular velocities (r = 0.80-0.83) and between ankle joint power and ankle, shank, and foot angular velocities (r = 0.77-0.89). Correlation strength was similar between young and older adults and between segment and joint angular velocities. These results suggest that changes in joint powers longitudinally or over the course of an intervention could be tracked using a minimal set of wearable sensors.

Comparisons of Knee Extensor Functional Demand During Gait by Age, Physical Activity Level, and the Impact of Acute Exercise and Walking Speed.

The link between age-related changes in muscle strength and gait is unclear. We tested if knee extensor functional demand differs by age and physical activity status and if functional demand increases with walking speed or after exercise. Gait and knee extensor muscle torque were collected from young adults and highly and less active older adults before and after treadmill walking. Functional demand was the ratio of knee moments during gait to knee extensor muscle torques estimated from participant-specific torque-velocity curves. Functional demand at the peak knee flexion moment was greater in less active older adults than young adults (29.3% [14.3%] vs 24.6% [12.1%]) and increased with walking speed (32.0% [13.9%] vs 22.8% [10.4%]). Functional demand at both knee extension moments increased ∼2% to 3% after exercise. The low functional demand found in this study suggests that healthy adults maintain a reserve of knee extensor strength.

Comparison of measurement protocols to estimate preferred walking speed between sites.

BACKGROUND: Walking speed influences a variety of typical outcome measures in gait analysis. Many researchers use a participant's preferred walking speed (PWS) during gait analysis with a goal of trying to capture how a participant would typically walk. However, the best practices for estimating PWS and the impact of laboratory size and walk distance are still unclear. RESEARCH QUESTION: Is measured PWS consistent across different distances and between two laboratory sites? METHODS: Participants walked overground at a "comfortable speed" for six different conditions with either dynamic (4, 6, 10, and 400 m) or static (4 and 10 m) starts and stops at two different data collection sites. Repeated measures ANOVA with Bonferroni corrections were used to test for differences between conditions and sites. RESULTS: Participants walked significantly faster in the 4, 6, and 10 m dynamic conditions than in the 400 m condition. On average, participants walked slower in the static trials than the dynamic trials of the same distance. There was a significant interaction of lab and condition and so results were examined within each lab. Across both labs, we found that the 4 and 10 m dynamic conditions were not different than the 6 m dynamic condition at both sites, while other tests did not provide consistent results at both sites. SIGNIFICANCE: We recommend researchers use a 6 m distance with acceleration and deceleration zones to reliably test for PWS across different laboratories. Given some of the differences found between conditions that varied by site, we also emphasize the need to report the test environment and methods used to estimate PWS in all future studies so that the methods can be replicated between studies.

Measuring markers of aging and knee osteoarthritis gait using inertial measurement units.

Differences in gait with age or knee osteoarthritis have been demonstrated in laboratory studies using optical motion capture (MoCap). While MoCap is accurate and reliable, it is impractical for assessment outside the laboratory. Inertial measurement units (IMUs) may be useful in these situations. Before IMUs are used as a surrogate for MoCap, methods that are reliable, repeatable, and that calculate metrics at similar accuracy to MoCap must be demonstrated. The purpose of this study was to compare spatiotemporal gait parameters and knee range of motion calculated via MoCap to IMU-derived variables and to compare the ability of these tools to discriminate between groups. MoCap and IMU data were collected from young, older, and adults with knee osteoarthritis during overground walking at three self-selected speeds. Walking velocity, stride length, cadence, percent of gait cycle in stance, and sagittal knee range of motion were calculated and compared between tools (MoCap and IMU), between participant groups, and across speed. There were no significant differences between MoCap and IMU outcomes, and root mean square error between tools was ≤0.05 m/s for walking velocity, ≤0.07 m for stride length, ≤0.5 strides/min for cadence, ≤5% for percent of gait cycle in stance, and ≤1.5° for knee range of motion. No interactions were present, suggesting that MoCap and IMU calculated metrics similarly across groups and speeds. These results demonstrate IMUs can accurately calculate spatiotemporal variables and knee range of motion during gait in young and older, asymptomatic and knee osteoarthritis cohorts.

The Roles of Sex and Physical Activity in Gait and Knee Extensor Function With Age.

Older females experience higher rates of disability than males, potentially due to sex-specific differences in gait and muscle function. The authors evaluated the effects of age and physical activity (PA) on gait mechanics and knee extensor muscle function in males and females. Three groups of 20 individuals (each 10 females) participated: young (21-35 y) and highly and less active older (55-70 y) adults. Knee extensor strength and joint mechanics during preferred speed gait were collected before and after 30 minutes of walking. Age by sex and PA by sex interactions indicated older and less active older females had lower concentric knee extensor muscle power and larger hip extension moments than males. After 30 minutes of walking, older less active adults had larger decreases in knee extensor power than their highly active older counterparts, and older adults of both sexes had decreases in ankle dorsiflexion moments while young adults did not. These results suggest that older, particularly less active, adults are susceptible to knee extensor muscle fatigue from moderate activity. For older adults, high levels of PA may be necessary to preserve gait mechanics in response to a bout of exercise. This new information may be important for targeting interventions in at-risk older adults.

Ultrasound elastographic assessment of plantar fascia in runners using rearfoot strike and forefoot strike.

Forefoot strike is increasingly being adopted by runners because it can better attenuate impact than rearfoot strike. However, forefoot strike may overload the plantar fascia and alter the plantar fascia elasticity. This study aimed to use ultrasound elastography to investigate and compare shear wave elasticity of the plantar fascia between rearfoot strikers and forefoot strikers. A total of 35 participants (21 rearfoot strikers and 14 forefoot strikers), who were free of lower limb injuries and diseases, were recruited from a local running club. Individual foot strike patterns were identified through the measured plantar pressure during treadmill running. The B-Mode ultrasound images and shear wave elastographic images of the plantar fascia were collected from each runner. Two independent investigators reviewed the images and examined the plantar fascia qualitatively and quantitatively. The results demonstrated an overall good agreement between the investigators in the image review outcomes (ICC:0.96-0.98, κ: 0.89). There were no significant differences in the fascial thickness (p = 0.50) and hypoechogenicity on the gray-scale images (p = 0.54) between the two groups. Shear wave elastography showed that forefoot strikers exhibited reduced plantar fascia elasticity compared to rearfoot strikers (p = 0.01, Cohen's d = 0.91). A less elastic fascial tissue was more easily strained under loading. Tissue overstrain is frequently related to the incidence of plantar fasciitis. While further study is needed for firm conclusions, runners using forefoot strike were encouraged to enhance their foot strength for better protection of the plantar fascia.

Gait mechanics contribute to exercise induced pain flares in knee osteoarthritis.

BACKGROUND: Exercise-induced pain flares represent a significant barrier for individuals with knee osteoarthritis to meet physical activity recommendations. There is a need to understand factors that contribute to pain flares and the potential for the motor system to adapt and reduce joint loading should a flare occur. The study aim was to examine the impact of a bout of exercise on self-reported pain, walking mechanics and muscle co-contraction for participants with knee osteoarthritis. METHODS: Thirty-six adults (17 healthy older and 19 knee osteoarthritis) participated in this study. Self-reported pain, joint mechanics and muscle co-activation during gait at two self-selected speeds were collected before and after a 20-min preferred pace treadmill walk (20MTW). RESULTS: Eight of nineteen osteoarthritis participants had a clinically significant pain flare response to the 20MTW. At baseline the participants that did not experience a pain flare had smaller knee flexion and total reaction moments compared to both the participants with pain flares (p = 0.02; p = 0.05) and controls (p < 0.001; p < 0.001). In addition, the 2nd peak knee adduction (p = 0.01) and internal rotation (p = 0.001) moments were smaller in the no flares as compared to controls. The pain flare participants differed from controls with smaller knee internal rotation moments (p = 0.03), but greater relative hamstrings (vs. quadriceps) and medial (vs. lateral) muscle activation (p = 0.04, p = 0.04) compared to both controls and no flare participants (p = 0.04, p = 0.007). Following the 20MTW there were greater decreases in the 1st and 2nd peak knee adduction (p = 0.03; p = 0.02), and internal rotation (p = 0.002) moments for the pain flare as compared to the no flare group. In addition, for the pain flare as compared to controls, greater decreases in the knee flexion (p = 0.03) and internal rotation (p = 0.005) moments were found. CONCLUSIONS: Individuals who adapt their gait to reduce knee joint loads may be less susceptible to exercise-induced pain flares. This highlights a potential role of gait biomechanics in short-term osteoarthritis pain fluctuations. The results also suggest that despite the chronic nature of osteoarthritis pain, the motor system's ability to respond to nociceptive stimuli remains intact.

Physical activity and age-related biomechanical risk factors for knee osteoarthritis.

BACKGROUND: Knee osteoarthritis (OA) is a highly prevalent disease leading to mobility disability in the aged that could, in part, be initiated by age-related alterations in knee mechanics. However, if and how knee mechanics change with age remains unclear. RESEARCH QUESTION: What are the impacts of age and physical activity (PA) on biomechanical characteristics that can affect the loading environment in the knee during gait? METHODS: Three groups (n = 20 each, 10 male and 10 female) of healthy adults were recruited: young (Y, 21-35 years), mid-life highly active (MHi, 55-70 years, runners), and mid-life less active (MLo, 55-70 years, low PA). Outcome measures included knee kinematics and kinetics and co-activation during gait, and knee extensor muscle torque and power collected at baseline and after a 30-minute treadmill trial to determine the impact of prolonged walking on knee function. RESULTS: At baseline, high-velocity concentric knee extensor power was lower for MLo and MHi compared with Y, and MLo displayed greater early (6.0 ± 5.8 mm) and peak during stance (11.3 ± 7.8 mm) femoral anterior displacement relative to the tibia compared with Y (0.2 ± 5.6 and 4.4 ± 6.8 mm). Also at baseline, MLo showed equal quadriceps:hamstrings activation, while Y showed greater relative hamstrings activation during midstance. The walking bout induced substantial knee extensor fatigue (decrease in maximal torque and power) in Y and MLo, while MHi were fatigue-resistant. SIGNIFICANCE: These results indicate that maintenance of PA in mid-life may impart small but measurable effects on knee function and biomechanics that may translate to a more stable loading environment in the knee through mid-life and thus could reduce knee OA risk long-term.

Segment Coordination Variability Differs by Years of Running Experience.

Running is a popular activity that results in high rates of overuse injury, with less-experienced runners becoming injured at higher rates than their more-experienced peers. Although measures of joint kinematics and kinetics and ground reaction forces have been associated with overuse running injuries, similar differences across levels of running experience have not been found. Because running is a motor skill that may develop with experience, an analysis of segment coordination and its variability could provide additional insight into why injury incidence decreases with increasing experience. PURPOSE: The purpose of this study was to determine if less-experienced runners have different segment coordination and lower segment coordination variability compared with their more-experienced peers. METHODS: This retrospective analysis included 20 more-experienced (≥10 yr running) and 21 less-experienced (≤2 yr running) runners. Sagittal thigh versus shank and shank versus foot segment coordination and coordination variability were calculated using a modified vector coding approach as individuals ran on a treadmill at preferred pace. Coordination and its variability were compared between groups during terminal swing and early, mid, and late stance for both segment couples. RESULTS: Segment coordination was similar between less- and more-experienced runners. Less-experienced runners had lower segment coordination variability compared with more-experienced runners for both the thigh versus shank and shank versus foot couples. This lower variability occurred during early and mid stance. CONCLUSIONS: Runners appeared to attain stable segment coordination patterns within 2 yr of consistent running, but had lower coordination variability compared with individuals who had been running for 10 or more years. These results suggest that assessment of movement patterns and their flexibility may help inform injury prevention or treatment strategies for less-experienced runners.

Age related differences in segment coordination and its variability during gait.

BACKGROUND: Aging is associated with a loss of mobility and altered gait mechanics. Loss of function and mobility may be due to or exacerbated by low levels of physical activity in the aged. The mechanisms linking age-related changes in physiology, altered mobility and gait may be elucidated by examining movement coordination and coordination variability. RESEARCH QUESTION: The purpose of this study was to examine the impacts of age and habitual physical activity level on segment coordination and coordination variability during gait. METHODS: A modified vector coding technique was used to calculate segment coordination and coordination variability during treadmill gait for three groups of healthy adults: young (21-35 years), older highly active (55-70 years), and older less active (55-70 years). Segment couples of interest included those whose coordination could contribute to typical age-related changes in gait mechanics at the hip, knee, and ankle. RESULTS: Differences in coordination and its variability occurred mainly during terminal swing and midstance and in couples across the hip and ankle. Across the hip, coordination differed between older highly active adults and the other cohorts, while variability was higher in young compared to all older adults. Across the ankle, young adults displayed different coordination and greater variability than all older adults except for the sagittal couple in midstance, where older highly active adults had greater coordination variability than the other cohorts. SIGNIFICANCE: These results suggest that older adults, independent of habitual physical activity, may use a different strategy to control hip and ankle motion during periods of single-limb stance.

Exertion and pain do not alter coordination variability in runners with iliotibial band syndrome.

BACKGROUND: Iliotibial band syndrome is a common overuse running injury which results in altered mechanics. While injuries alter discrete mechanics, they may also cause a change in coordination variability, the stride-to-stride organization of runners' movement patterns. Uninjured and injured runners may experience a change in coordination variability during a run to exertion due to fatigue, pain, or a combination of these factors. The aim of the current study was to determine if runners with iliotibial band syndrome and uninjured runners display different segment coordination variability across the course of a run to exertion. METHODS: 3D kinematics were collected as 13 uninjured runners and 12 runners with iliotibial band syndrome ran on a treadmill. A modified vector coding technique was used to calculate coordination variability during stance for segment couples of interest. Coordination variability was compared between uninjured and injured runners at the beginning and end of the run. The influence of pain on coordination variability was also examined. FINDINGS: There were no differences in coordination variability at the beginning or end of the run between uninjured runners and those with iliotibial band syndrome. The change in coordination variability due to the run was not different between uninjured runners, injured runners who experienced no change in pain, and injured runners who did experience a change in pain. INTERPRETATION: Runners do not constrain the patterns of segment motion they use in response to exertion nor does it appear that occurrence of pain during running results in a differential change in coordination variability.

Systematic review and meta-analysis of gait mechanics in young and older adults.

BACKGROUND: Age-related gait changes may play a critical role in functional limitations of older adults. Despite sizable interest in determining how age alters walking mechanics, small sample sizes and varied outcome measures have precluded a comprehensive understanding of the impact of age on lower extremity joint kinematics and kinetics. OBJECTIVE: The aim of this study was to perform a systematic review and meta-analysis of the aging gait mechanics literature. METHODS: The overall standardized effect of age on walking mechanics was computed for 29 studies (200 standardized effects). To account for variation in reported outcome variables, analyses were carried out for comparisons between young and older adult results using all discrete kinematic or kinetic variables reported for the ankle, knee, or hip. Different variables reported for a given joint were then analyzed as separate categorical moderators. RESULTS: The overall standardized effect of age was large for ground reaction forces, moderate for ankle and small for knee and hip kinematics and ankle and hip kinetics. When the analysis was restricted to studies with similar or matched walking speed, the standardized effects of age remained similar except for hip power generation and knee kinematic variables. CONCLUSIONS: The results of this meta-analysis provide evidence to support moderate standardized effects, with and without consideration of walking speeds, for changes in lower extremity kinematics, joint moments and powers at the ankle, and ground reaction forces. The standardized effects of age for knee mechanics are less conclusive and would benefit from further research.