Kozey, Cheryl

Permanent URI for this collectionhttps://hdl.handle.net/10222/45655

Cheryl Kozey

Professor

Email: cheryl.kozey@dal.ca

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Open Access
The Effect of Total Knee Arthroplasty on Knee Joint Kinematics and Kinetics During Gait
(Elsevier, 2011-02) Hatfield, G; Hubley-Kozey, C; Astephen Wilson, J
This study determined how total knee arthroplasty (TKA) altered knee motion and loading during gait. Three-dimensional kinematic and kinetic gait patterns of 42 patients with severe knee osteoarthritis were collected 1 week prior and 1-year post-TKA. Principal component analysis extracted major patterns of variability in the gait waveforms. Overall and midstance knee adduction moment magnitude decreased. Overall knee flexion angle magnitude increased due to an increase during swing. Increases in the early stance knee flexion moment and late stance knee extension moment were found, indicating improved impact attenuation and function. A decrease in the early stance knee external rotation moment indicated alteration in the typical rotation mechanism. Most changes moved toward an asymptomatic pattern and would be considered improvements in motion, function, and loading.
Open Access
Temporal coactivation of abdominal muscles during dynamic stability exercises
(Wolters Kluwer, 2010-05) Hubley-Kozey, C; Hatfield, G; Davidson, K
The purpose of this study was to determine abdominal muscle temporal responses to a leg-loading exercise protocol and if differences exist between those able and unable to minimize lumbar-pelvic motion during this protocol. The focus was a supine bilateral leg-loading task that incorporated a slide (level 4) or no slide (level 5). Thirty-three healthy subjects (mean age 24 years) completed the task while surface electromyograms (EMG) from 5 abdominal muscle sites were recorded. Subjects were assigned to stable or unstable groups based on their ability to minimize lumbar-pelvic motion. After time and amplitude normalization, electromyography waveforms were entered into a pattern recognition procedure and scores for each principal pattern were calculated. Four principal patterns explained 90% of variance in the waveform data, with these principal patterns capturing the mean pattern, the relative amplitude change during the leg-extension phase, and subtle changes in shape throughout the exercise. Significant interactions (p < 0.05) were found for principal patterns; 1, 2, and 4 scores; and significant main (p < 0.05) effects for principal pattern 3 scores. These results illustrate temporal synchrony among the abdominal wall muscle activation during the bilateral leg-loading tasks; however, there was less variability in the activation patterns during the leg-lift and leg extension-phases for those who were able to minimize lumbar-pelvic motion compared to those who were unable to perform the task correctly. These results illustrate the need to focus on coordinated recruiting of the abdominal wall muscles in an organized manner and not simply increasing the intensity of activation for stabilization training.
Open Access
Characterisation of trunk muscle activation amplitude patterns during a simulated checkstand operation with continuously changing flexor and lateral moment demands
(Taylor & Francis, 2010-04) Butler, H; Hubley-Kozey, C; Kozey, J
While the typical physical exposure to modern-day workers has changed from heavy to low level repetitive demands, there is limited research that examines light occupations. This study examined trunk muscle recruitment strategies in response to a simulated checkout operation. Surface electromyography and kinematic variables were recorded from 29 healthy subjects. Four principal patterns accounted for 95.3% of the variation. Significant differences in scores captured different strategies in response to reach conditions and external moment directions. Synergistic co-activation of ipsilateral back sites and differential activation among external oblique and erector spinae sites suggests that the central nervous system may control different regions of the trunk musculature to optimally account for asymmetrical demands. The strategy between the internal oblique and back extensor sites suggests that a specific co-activation strategy may be needed during lighter work. During low-load occupational tasks, several recruitment strategies were required to maintain spinal stability and account for changing external moments.
Open Access
The interpretation of abdominal wall muscle recruitment strategies change when the electrocardiogram (ECG) is removed from the electromyogram (EMG)
(Elsevier, 2009-04) Butler, Heather L; Newell, Robyn; Hubley-Kozey, Cheryl L; Kozey, John W
The purpose of this study was to determine the effect of the ECG artifact on low-level trunk muscle activation amplitudes and assess the effectiveness of two methods used to remove the ECG. Simulations were performed and percent error in root mean square (RMS) amplitudes were calculated from uncontaminated and contaminated EMG signals at various ECG to EMG ratios. Two methods were used to remove the ECG: (1) filtering by adaptive sampling (FAS) and (2) Butterworth high pass filter at 30 Hz (BW-30 Hz HPF). The percent error was also calculated between the ECG removed and the uncontaminated EMG RMS amplitudes. Next, the BW-30 Hz HPF method was used to remove the ECG from 3-bilateral external oblique (EO) muscle sites collected from 30 healthy subjects performing a one handed lift and replace task. Two separate ANOVA models assessed the effects of ECG on the statistical interpretation of EO recruitment strategies. One model included EMG data that contained the ECG and the other model included EMG data after the ECG was removed. Large percent errors were observed when the ECG was not removed. These errors increased with larger ECG to EMG ratios. Both removal methods reduced the errors to below 10%, but the BW-30 Hz HPF method was more time efficient in removing the ECG artifact. Different statistical findings were observed among the muscle sites for the ECG contaminated model compared to the ECG removed model, which resulted in different conclusions concerning neuromuscular control.
Open Access
Activation amplitude patterns do not change for back muscles but are altered for abdominal muscles between dominant and non-dominant hands during one-handed lifts
(SpringerLink, 2009-05) Butler, Heather L; Hubley-Kozey, Cheryl L; Kozey, John W
It is assumed when lifting with the dominant hand that the relationship between contralateral and ipsilateral trunk muscle responses are similar to when lifting with the non-dominant hand. The purpose of this study was to quantify trunk muscle activation amplitude patterns during right- and left-handed lifts. Surface electromyography (EMG) and kinematic variables were recorded from 29 healthy subjects. Minimal trunk and pelvis motion was observed. Three principal patterns accounted for 95% of the variation in the EMG data indicating minimal variation in the pattern. Significant differences in scores captured different recruitment strategies for reach and hand. Selective and differential recruitment of back sites characterized lifts at greater distances from the body, whereas co-activation between internal oblique and back sites characterized lifts closer to the body. While the results showed no handedness effect for back muscles, the external oblique responded differently between right- and left-handed lifts. Specific recruitment strategies were used to account for subtle changes in reach and asymmetrical demands.
Open Access
Electromyographic assessment of trunk muscle activation amplitudes during a simulated lifting task using pattern recognition techniques
(Elsevier, 2009-12) Butler, Heather L; Hubley-Kozey, Cheryl L; Kozey, John W
This study sought to determine the patterns of neuromuscular response from 24-trunk muscle sites during a symmetrical lift and replace task. Surface electromyograms (EMG) and kinematic variables were recorded from 29 healthy subjects. Pattern recognition techniques were used to examine how activation amplitude patterns changed with the different physical demands of the task (reach, phase of movement). The results indicated that there was very little trunk and pelvis motion during the task. Three principal patterns accounted for 95% of the total variation suggesting that the measured data had a simple underlying structure of variance. ANOVA results revealed significant differences in principal pattern scores. These differences captured subtle changes in muscle recruitment strategies that most likely reflect different stability and biomechanical demands. More balanced activations (bracing) between the abdominal and back sites were observed during the lighter demands, whereas differential recruitment among the back extensor sites was more predominant in the more demanding conditions. A pattern recognition technique offers a novel method to examine the relationships among a large number of muscles and test how different work characteristics change the relationships among the muscle sites.
Open Access
Differences in Abdominal Muscle Activation Patterns of Younger and Older Adults Performing an Asymmetric Leg-Loading Task
(Elsevier, 2009-11) Hubley-Kozey, Cheryl L; Hanada, Edwin Y; Gordon, Sarah; Kozey, John W; McKeon, Melissa
Objectives: To determine whether differences exist between younger (20-50 years) and older adults ( 65 years) in abdominal muscle amplitudes, temporal patterns, and threedimensional (3D) pelvic motion, while performing an asymmetric leg-loading task. Design: Cross-sectional. Setting: Neuromuscular function laboratory. Participants: Ten healthy younger (33.3 7.7 years) and 10 healthy gender- and body mass index–matched older adults (69.0 6.6 years). Intervention: Surface electromyograms from 6 abdominal muscle sites bilaterally and pelvic motions were simultaneously recorded. Main Outcome Measure(s): Root mean square (RMS) amplitude during the leg extension phase was calculated for each muscle. Ensemble average waveforms for the total exercise were analyzed using principal component (PC) analysis. Total angular displacement of the pelvis was calculated. Student t tests were performed on demographic and angular displacement data. Three-factor mixed model analysis of variances (group, muscle, side) tested main effects and interactions (P .05) for the RMS amplitude and PC scores from the temporal waveforms. Bonferroni post-hoc analyses tested pair-wise differences. Results: There were no between-group differences for the pelvic motions. Three PC patterns captured 85% of the variance in the waveforms. The external oblique (EO) RMS amplitudes were significantly (P .05) higher than those of the other 3 muscle sites, similar for the PC1 scores which captured overall amplitude. The PC2 score for the internal oblique (IO) was significantly higher (P .05) than that of all other muscles, illustrating a higher initial amplitude compared with later in the movement. There was a significant group by muscle interaction for PC3 scores, demonstrating group differences in temporal patterns. Conclusions: Both groups were able to minimize lumbopelvic motion and recruited their abdominal muscles to similar overall amplitudes, with the IO muscle activated to higher amplitudes early in the movement task. The older adult group demonstrated a distinctive drop in abdominal activity during the leg-lowering phase of the exercise and less symmetry among muscle sites.
Open Access
Asymptomatic and symptomatic individuals with the same radiographic evidence of knee osteoarthritis walk with different knee moments and muscle activity
(Wiley, 2016-11-01) Astephen Wilson, Janie L; Stanish, William D; Hubley-Kozey, Cheryl L
There is an established discordance between the structural joint damage and clinical symptoms of knee osteoarthritis; however, there has been little investigation into the differences in joint level biomechanics and muscle activation patterns during gait between symptomatic and asymptomatic individuals with the same radiographic evidence of osteoarthritis. The objective of this study was to examine three-dimensional knee joint biomechanics and muscle activation differences during gait between asymptomatic and symptomatic individuals with radiographic knee osteoarthritis. A total of 54 asymptomatic and 59 symptomatic individuals with a Kellgren–Lawrence osteoarthritis radiographic grade of 2 underwent a comprehensive gait analysis to examine differences in the magnitude and patterns of the knee flexion angle, three-dimensional net resultant moments, and electromyography of the quadriceps, hamstrings, and gastrocnemii during over ground walking between the two groups. The symptomatic group walked with significantly higher overall magnitudes and less mid-stance unloading of the net resultant knee adduction moment, lower peak flexion moments, and higher lateral hamstrings and quadriceps activity during stance than the Asymptomatic group (p < 0.05, sex-adjusted analysis), with a trend (p = 0.07) toward greater transverse plane range of moment over stance. The differences found suggest a “stiffer” frontal and sagittal plane pattern with symptomatic individuals, but with more muscle activity and a trend toward more torsional loading in the transverse plane, which may have implications for shear loading of the joint. This is the first evidence of differences in three-dimensional knee joint biomechanics and muscle activation between asymptomatic and symptomatic individuals with the same radiographic grade.
Open Access
Obesity is associated with prolonged activity of the quadriceps and gastrocnemii during gait
(Elsevier, 2015-12) Amiri, P; Hubley-Kozey, CL; Landry, SL; Stanish, WD; Astephen Wilson, JL
Purpose: To examine the effect of obesity and its potential interaction with knee OA presence on the electromyography patterns of the major knee joint periarticular muscles during walking. Scope: One hundred and eighteen asymptomatic adults and 177 adults with moderate knee osteoarthritis were subdivided into categories of healthy weight (n = 77; 20 kg/m2 < BMI < 25 kg/m2), overweight (n = 117; 25 kg/m2 ⩽ BMI < 30 kg/m2), and obese (n = 101; BMI ⩾ 30 kg/m2 based on their body mass index (BMI). All individuals underwent a three-dimensional gait analysis. Surface electromyograms from the lateral and medial gastrocnemii, lateral and medial hamstrings, vastus lateralis, vastus medialis, and rectus femoris were recorded during self-selected speed walking. Principal component analysis was used to extract major features of amplitude and temporal pattern variability from the electromyograms of each muscle group (gastrocnemii, quadriceps, hamstrings separately). Analysis of variance models tested for main BMI category effects and interaction effects for these features (α = 0.05). Statistically significant BMI category (i.e. obesity) effects were found for features that described more prolonged activations of the gastrocnemii and quadriceps muscles during the stance phase of gait with obesity (P < 0.05). Conclusions: Obesity was associated with prolonged activation of quadriceps and gastrocnemii, which can result in prolonged knee joint contact loading, and thereby may contribute to the predisposition of knee OA development and progression in obese individuals.
Open Access
Obesity is associated with higher absolute tibiofemoral contact and muscle forces during gait with and without knee osteoarthritis
(Elsevier, 2016-01) Harding, Graeme T; Dunbar, Michael J; Hubley-Kozey, Cheryl L; Stanish, William D; Astephen Wilson, Janie L
Background Obesity is an important risk factor for knee osteoarthritis initiation and progression. However, it is unclear how obesity may directly affect the mechanical loading environment of the knee joint, initiating or progressing joint degeneration. The objective of this study was to investigate the interacting role of obesity and moderate knee osteoarthritis presence on tibiofemoral contact forces and muscle forces within the knee joint during walking gait. Methods Three-dimensional gait analysis was performed on 80 asymptomatic participants and 115 individuals diagnosed with moderate knee osteoarthritis. Each group was divided into three body mass index categories: healthy weight (body mass index < 25), overweight (25 ≤ body mass index ≤ 30), and obese (body mass index > 30). Tibiofemoral anterior–posterior shear and compressive forces, as well as quadriceps, hamstrings and gastrocnemius muscle forces, were estimated based on a sagittal plane contact force model. Peak contact and muscle forces during gait were compared between groups, as well as the interaction between disease presence and body mass index category, using a two-factor analysis of variance. Findings There were significant osteoarthritis effects in peak shear, gastrocnemius and quadriceps forces only when they were normalized to body mass, and there were significant BMI effects in peak shear, compression, gastrocnemius and hamstrings forces only in absolute, non-normalized forces. There was a significant interaction effect in peak quadriceps muscle forces, with higher forces in overweight and obese groups compared to asymptomatic healthy weight participants. Interpretation Body mass index was associated with higher absolute tibiofemoral compression and shear forces as well as posterior muscle forces during gait, regardless of moderate osteoarthritis presence or absence. The differences found may contribute to accelerated joint damage with obesity, but with the osteoarthritic knees less able to accommodate the high loads.
Open Access
Effect of a high intensity quadriceps fatigue protocol on knee joint mechanics and muscle activation during gait in young adults.
(SpringerLink, 2012-02) Murdock, GH; Hubley-Kozey, CL
The purpose of this study was to determine the effect of impaired quadriceps function on knee joint biomechanics and neuromuscular function during gait. Surface electromyograms, three-dimensional motion and ground reaction forces were collected during gait before and after 20 healthy adults completed a high intensity quadriceps fatigue protocol. Pattern recognition techniques were utilized to examine changes in amplitude and temporal characteristics of all gait variables. The fatigue protocol resulted in decreased knee extensor torque generation and quadriceps median power frequencies for 18 of 20 participants (p < 0.05). The gait data from these 18 participants was analyzed. The knee external rotation angle increased (p < 0.05), the net external flexion and external rotation moments decreased (p < 0.05), and the net external adduction moment increased (p < 0.05). Post-fatigue changes in periarticular muscle activation patterns were consistent with the biomechanical changes, but were not significantly altered. Even for this low demand task of walking the knee motion and loading characteristics were altered following a high intensity fatigue protocol in a manner that may place the knee joint at greater risk for joint pathology and injury.
Open Access
Activation amplitude and temporal synchrony among back extensor and abdominal muscles during a controlled transfer task: comparison of men and women
(Elsevier, 2012-08) Hubley-Kozey, CL; Butler, HL; Kozey, JW
Muscle synergies are important for spinal stability, but few studies examine temporal responses of spinal muscles to dynamic perturbations. This study examined activation amplitudes and temporal synergies among compartments of the back extensor and among abdominal wall muscles in response to dynamic bidirectional moments of force. We further examined whether responses were different between men and women. 19 women and 18 men performed a controlled transfer task. Surface electromyograms from bilateral sites over 6 back extensor compartments and 6 abdominal wall muscle sites were analyzed using principal component analysis. Key features were extracted from the measured electromyographic waveforms capturing amplitude and temporal variations among muscle sites. Three features explained 97% of the variance. Scores for each feature were computed for each measured waveform and analysis of variance found significant (p < .05) muscle main effects and a sex by muscle interaction. For the back extensors, post hoc analysis revealed that upper and more medial sites were recruited to higher amplitudes, medial sites responded to flexion moments, and the more lateral sites responded to lateral flexion moments. Women had more differences among muscle sites than men for the lateral flexion moment feature. For the abdominal wall muscles the oblique muscles responded with synergies related to fiber orientation, with women having higher amplitudes and more responsiveness to the lateral flexion moment than men. Synergies between the abdominal and back extensor sites as the moment demands change are discussed. These findings illustrate differential activation among erector spinae compartments and abdominal wall muscle sites supporting a highly organized pattern of response to bidirectional external moments with asynchronies more apparent in women.
Open Access
Pre-operative muscle activation patterns during walking are associated with TKA tibial implant migration.
(Elsevier, 2012-11) Wilson, DA; Hubley-Kozey, CL; Astephen Wilson, JL; Dunbar, MJ
Background Gait biomechanical variables have been associated with total knee arthroplasty tibial implant migration measured with Radiostereometric Analysis (RSA), but no studies have examined the role of the periarticular musculature, which is responsible for a high proportion of the forces on the joint. The purpose of this study was to measure the pre-operative electromyography (EMG) patterns of the periarticular knee muscles during gait and determine the association of these patterns with the post-operative tibial implant migration measured with RSA. We hypothesized that pre-operative muscle activation patterns (specifically the activation patterns of the vastus and gastrocnemius muscle groups) measured with EMG are associated with migration at 6 months. Methods Electromyographic data were collected from 6 periarticular knee joint muscles on 37 patients pre-operatively during gait. Radiostereometric exams were performed immediately and at 6 months post-operatively. Relationships between the pre-operative patterns of muscle activation and micromotion of the implant were examined using Pearson correlation and regression models. Findings Statistically significant correlations were found between the pattern of the quadriceps and gastrocnemius muscle activations during gait and implant translation in the posterior direction. Regression analysis illustrated that a substantial proportion of the variance in the post-operative tibial component posterior translation (R2 = 0.49) was explained by a prolonged activation of the vastus medialis muscle and higher activation of the lateral gastrocnemius muscle during early stance. Interpretation The variability in migration explained by the muscle activation patterns supports the hypothesis that pre-operative functional characteristics can contribute to predicting implant migration following total knee arthroplasty surgery.
Open Access
Changes in electromyographic activity of trunk muscles within the sub-acute phase for individuals deemed recovered from a low back injury
(Elsevier, 2013-04) Butler, Heather L; Hubley-Kozey, Cheryl; Kozey, John W
Evidence indicates that previous low back injury (LBI) is a strong predictor for re-injury. The purpose of this study was to examine whether neuromuscular patterns remain altered in a LBI group who were deemed recovered. Surface electromyograms from 12-abdominal and 12-back extensors sites and motion variables were recorded from 33 LBI individuals (sub-acute phase) and 54 asymptomatic controls. Pain-related variables were recorded and a clinical assessment performed for LBI participants. Subjects performed a symmetrical lift and replace task in two reaches. Pattern recognition techniques were applied to normalized activation amplitude patterns to extract key recruitment strategies. Mixed model ANOVAs tested for effects (p < 0.05). Despite similar task performance, significantly (p < 0.05) different recruitment strategies were observed for the LBI group. There were higher activation amplitudes for LBI subjects in all muscles (except posterior external oblique) and greater co-activation between abdominal and back extensor sites compared to controls. Local abdominal and back extensor sites showed altered responses to increased physical demands in the LBI group. Despite outcomes indicating recovery, the LBI group had altered neuromuscular patterns compared to asymptomatic controls supporting that residual alterations remain following recovery.
Open Access
Trunk neuromuscular pattern alterations during a controlled functional task in a low back injured group deemed ready to resume regular activities.
(IOS Press, 2014) Hubley-Kozey, C; Moreside, JM; Quirk, DA
BACKGROUND: Trunk neuromuscular alterations have been found in those with chronic low back pain, but less well studied are whether responses are altered in those deemed recovered following an injury. Furthermore, coordinated trunk muscle responses are deemed important for normal spinal function, but there are no studies of temporal patterns early after a low back injury. Determining whether altered trunk muscle patterns exist early after injury could improve our understanding of recovery by providing an objective assessment of functional recovery and risk of re-injury. OBJECTIVE: To determine if amplitude and temporal characteristics of trunk neuromuscular patterns differ during a dynamic functional task in a group of participants with recent (within 12 weeks) low back injury (LBI), but deemed ready to resume normal activities, when compared to those with no similar history of injury (ASYM). PARTICIPANTS: 35 participants in each group (17 females) were matched for age and body mass index (BMI); (ASYM 36 yrs, BMI 26, LBI 39 yrs, BMI 27). METHODS: Participants performed a controlled lifting task (2.9 kg) in a standing maximum reach position, which altered frontal and sagittal plane moments of force. Electromyographic activity of 24 trunk muscle sites, as well as thoracic and pelvis position via an electromagnetic sensor was collected. Principal component analyses extracted the temporal and amplitude waveform patterns. Mixed model ANOVAs tested for effects (p< 0.05) in the main patterns. Preliminary data regarding re-injury status after 1 year was included. RESULTS: Three principal patterns explained 97% of the variance, with the LBI group demonstrating increased amplitude and a more constant level of activity compared to the ASYM group. The LBI group also demonstrated more thoracic motion in all 3 axes during this highly constrained task. The no re-injury group had lower activation than the re-injury group, but similar temporal patterns. CONCLUSIONS: Despite the perception of readiness to return to work and low pain scores, the temporal and amplitude muscle activation patterns were altered in this LBI group indicating that differences exist compared to a non-low back injured group. The differences are not just relative amplitude differences among muscles but include differences in the temporal response to the flexion moment.
Open Access
Knee joint biomechanics and neuromuscular control during gait before and after total knee arthroplasty are sex-specific.
(Elsevier, 2015-01-30) Astephen Wilson, JL; Dunbar, MJ; Hubley-Kozey, CL
The future of total knee arthroplasty (TKA) surgery will involve planning that incorporates more patient-specific characteristics. Despite known biological, morphological, and functional differences between men and women, there has been little investigation into knee joint biomechanical and neuromuscular differences between men and women with osteoarthritis, and none that have examined sex-specific biomechanical and neuromuscular responses to TKA surgery. The objective of this study was to examine sex-associated differences in knee kinematics, kinetics and neuromuscular patterns during gait before and after TKA. Fifty-two patients with end-stage knee OA (28 women, 24 men) underwent gait and neuromuscular analysis within the week prior to and one year after surgery. A number of sex-specific differences were identified which suggest a different manifestation of end-stage knee OA between the sexes.
Open Access
Relationship between knee adduction moment patterns extracted using principal component analysis and discrete measures with different amplitude normalizations: Implications for knee osteoarthritis progression studies.
(Elsevier, 2015-12-30) Hatfield, GL; Stanish, WD; Hubley-Kozey, CL
BACKGROUND: Knee adduction moment discrete features (peaks and impulses) are commonly reported in knee osteoarthritis gait studies, but they do not necessarily capture loading patterns. Principal component analysis extracts dynamic patterns, but can be difficult to interpret. This methodological study determined relationships between external knee adduction moment discrete measures and principal component analysis features, and examined whether amplitude-normalization methods influenced differences in those with knee osteoarthritis who progressed to surgery versus those that did not. METHODS: 54 knee osteoarthritis patients had three-dimensional biomechanical measures assessed during walking. Knee adduction moments were calculated and non-normalized and amplitude-normalized waveforms using two common methods were calculated. Patterns were extracted using principal component analysis. Knee adduction moment peak and impulse were calculated. Correlation coefficients were determined between two knee adduction moment patterns extracted and peak and impulse. T-tests evaluated between-group differences. FINDINGS: An overall magnitude pattern was correlated with peak (r=0.88-0.90, p<0.05) and impulse (r=0.93, p<0.05). A pattern capturing a difference between early and mid/late -stance knee adduction moment was significantly correlated with peak (r=0.27-0.40, p<0.05), but explained minimal variance. Between-group peak differences were only affected by amplitude-normalization method. INTERPRETATION: Findings suggest that the overall magnitude knee adduction moment principal pattern does not provide unique information from peak and impulse measures. However, low correlations and minimal variance explained between the pattern capturing ability to unload the joint during mid-stance and the two discrete measures, suggests that this pattern captured a unique waveform feature.
Open Access
Temporal Patterns of the Trunk Muscles Remain Altered in a Low Back–Injured Population Despite Subjective Reports of Recovery
(Elsevier, 2014) Moreside, Janice; Quirk, D. Adam; Hubley-Kozey, Cheryl
Objective To compare temporal activation patterns from 24 abdominal and lumbar muscles between healthy subjects and those who reported recovery from recent low back injury (LBI). Design Cross-sectional comparative study. Setting University neuromuscular function laboratory. Participants Healthy adult volunteers (N=81; 30 LBI, 51 asymptomatic subjects). Interventions Trunk muscle electromyographic activity was collected during 2 difficulty levels of a supine trunk stability test aimed at challenging lumbopelvic control. Main Outcome Measures Principal component (PC) analysis was applied to determine differences in temporal and/or amplitude electromyographic patterns between groups. Mixed-model analyses of variance were performed on PC scores that explained more than 89% of the variance (α=.05). Results Four PCs explained 89% and 96% of the variance for the abdominal and back muscles, respectively, with both muscle groups having similar shapes in the first 3 PCs. Significant interactions or group main effects were found for all PC scores except PC4 for the back extensors. Overall activation amplitudes for both the abdominal and back muscles (PC1 scores) were significantly (P<.05) higher for the LBI group, with both abdominal and back muscles of the LBI group demonstrating an increased response to the leg-loading phase (PC2 scores) compared with the asymptomatic group. Differences were also found between groups in their preparatory activity (PC3 scores), with the LBI group having a higher early relative amplitude of abdominal and back extensor activity. Conclusions Despite perceived readiness to return to work and low pain scores, muscle activation patterns remained altered in this LBI group, including reduced synergistic coactivation and increased overall amplitudes as well as greater relative amplitude differences during specific phases of the movement. Electromyographic measures provide objective information to help guide therapy and may assist with determining the level of healing and return-to-work readiness after an LBI.
Open Access
Hip abductor function in individuals with medial knee osteoarthritis: Implications for medial compartment loading during gait
(Elsevier, 2014) Rutherford, Derek; Hubley-Kozey, Cheryl; Stanish, William
Background Hip abductor muscles generate moments of force that control lower extremity frontal plane motion. Strengthening these muscles has been a recent trend in therapeutic intervention studies for knee osteoarthritis. The current study investigated the relationship between hip abductor muscle function (strength and activation) and the net external knee adduction moment during gait in those with medial compartment knee osteoarthritis. Methods 54 individuals with moderate knee osteoarthritis walked at their self-selected velocity while gluteus medius electromyograms, segment motions and ground reaction forces were recorded. Net external knee adduction moment (KAM) and linear enveloped electromyographic profiles were calculated. Peak KAM was determined and then principal component analyses (PCA) were applied to KAM and electromyographic profiles. Isometric hip abductor strength, anthropometrics and gait velocity were measured. Multiple regression models evaluated the relationship between walking velocity, hip abductor strength, electromyographic variables recorded during gait and KAM waveform characteristics. Findings Minimal peak KAM variance was explained by abductor strength (R2 = 9%, P = 0.027). PCA-based KAM waveform characteristics were not explained by abductor strength. Overall gluteus medius amplitude (PP1-scores) was related to a reduction in the bi-modal KAM (PP3-scores) pattern (R2 = 16%, P = 0.003). Interpretation There was no clear relationship between hip abductor muscle strength and specific amplitude and temporal KAM characteristics. Higher overall gluteus medius activation amplitude was related to a sustained KAM during mid-stance. 84 to 90% of the variance in KAM waveform characteristics was not explained by hip abductor muscle function showing hip abductor muscle function has minimal association to KAM characteristics.
Open Access
Age-related changes in trunk neuromuscular activation patterns during a controlled functional transfer task include amplitude and temporal synergies
(Elsevier, 2014) Quirk, D. Adam; Hubley-Kozey, Cheryl
While healthy aging is associated with physiological changes that can impair control of trunk motion, few studies examine how spinal muscle responses change with increasing age. This study examined whether older (over 65 years) compared to younger (20–45 years) adults had higher overall amplitude and altered temporal recruitment patterns of trunk musculature when performing a functional transfer task. Surface electromyograms from twelve bilateral trunk muscle (24) sites were analyzed using principal component analysis, extracting amplitude and temporal features (PCs) from electromyographic waveforms. Two PCs explained 96% of the waveform variance. Three factor ANOVA models tested main effects (group, muscle and reach) and interactions for PC scores. Significant (p < .0125) group interactions were found for all PC scores. Post hoc analysis revealed that relative to younger adults, older adults recruited higher agonist and antagonistic activity, demonstrated continuous activation levels in specific muscle sites despite changing external moments, and had altered temporal synergies within abdominal and back musculature. In summary both older and younger adults recruit highly organized activation patterns in response to changing external moments. Differences in temporal trunk musculature recruitment patterns suggest that older adults experience different dynamic spinal stiffness and loading compared to younger adults during a functional lifting task.