Effectiveness of and preference for a picture-based home office ergonomics assessment compared to a traditional in-person office ergonomics assessment: A case study from a Canadian University during the COVID-19 pandemic

During the COVID-19 pandemic, telework best practices decreased in importance compared to the need for social distancing. It is important that ergonomics assessments for home office workstations are equally as effective as assessment for traditional offices to maintain teleworker wellbeing. The purpose of this case study is to compare a remote, picture-based, home office assessment to a traditional, in-person, office assessment for employees of one Canadian University. Intraclass Correlation Coefficients (ICCs) and Bland-Altman Analyses (BAAs) revealed that the two methods provide repeatable results, with good agreement. Feedback from the participants suggested that picture-based assessments were as effective as in-person assessments; but that picture-based assessments could be improved with video conferencing to discuss findings and ask follow-up questions. Participants found value in remote assessments and, while they preferred in-person assessments, picture-based assessments are suitable when needed as they allow for many assessments to be completed without violating social distancing restrictions.

The effect of training and workstation adjustability on teleworker discomfort during the COVID-19 pandemic

Technological advancements have increased occupational flexibility for employees and employers alike. However, while effective telework requires planning, the COVID-19 pandemic required many employees to quickly shift to working from home without ensuring that the requirements for telework were in place. This study evaluated the transition to telework on university faculty and staff and investigated the effect of one's telework setup and ergonomics training on work-related discomfort in the at-home environment. Fifty-one percent of respondents reported increases in their existing discomfort while 24% reported new discomfort since working from home. These results suggest a need for ergonomic interventions including ergonomic training and individual ergonomic assessments for those who work from home.

Using an accelerometer and the step-up-and-over test to evaluate the knee function of patients with anterior cruciate ligament reconstruction

BACKGROUND

Evaluating the dynamic knee function of patients after anterior cruciate ligament reconstruction is a challenge. A variety of objective tests have been developed but for various reasons few are regularly used in the clinic. It may be practical to perform the step-up-and-over test with an accelerometer.

METHODS

A control group (N=26) and an experimental group with a reconstructed anterior cruciate ligament (N=25) completed questionnaires quantifying subjective knee function and fear of re-injury and then completed the step-up-and-over test.

FINDINGS

Results showed that the experimental group performed differently than the control group for the step-up-and-over test's Lift Symmetry and Impact Symmetry (P<0.05) and performance on these measures was related to the participant's subjective knee function (ρ=-0.46, P<0.01; ρ=-0.33, P<0.05, respectively). Supplemental results for individual leg performance and the patient's fear of re-injury are also reported and discussed.

INTERPRETATION

Performance on the step-up-and-over test is different for participants with anterior cruciate ligament reconstruction than for those with intact anterior cruciate ligaments, and that performance is related to one's opinion of their knee's function.

Subjective and objective analysis of three water pump systems carried by forest firefighters

BACKGROUND

The Mark 3 (M3) water power pump is an integral piece of wildfire fighting equipment. However, it is provided to fire stations without a carrying harness. The currently-used carrying harness is very uncomfortable, especially when carrying the pumps considerable distance in a forest to reach a water source.

OBJECTIVE

The purpose of this study was to advise the Ontario Ministry of Natural Resources on the selection of a new M3 load carriage system.

PARTICIPANTS

Twenty Fire Rangers wore the three systems (Original, Prototype, and Modified) through a circuit of tasks representative of their working environment.

METHODS

Subjective and objective approaches were combined to assess and rank the M3 carriage systems. Subjective visual analogue scale ratings were obtained for ease of loading/unloading, comfort, system stability, and overall performance. Tri-axial accelerometers were mounted on each pump and at the sternum of each participant to determine relative pump-carrier accelerations.

RESULTS

Overall, the Prototype was ranked as the best system; it resulted in the lowest relative pump-carrier accelerations on 10 out of 15 objective measures, and also received a first place ranking on all subjective measures.

CONCLUSION

It was recommended that the Prototype be implemented as the M3 carriage system for fire suppression teams.

Shouldering the load: A review of Joan Stevenson's work on occupational lifting and design evaluation of load carriage equipment

OBJECTIVE

In this paper, Dr. Joan Stevenson's work on assessment of the effects of lifting, supporting and transporting loads is reviewed. A defining attribute of this work is the use of objective, biomechanical measures as the basis from which a fuller understanding of all factors affecting worker performance can be obtained, and how such performance should be measured and evaluated.

METHODS

The central objectives and conclusions of Dr. Stevenson's research programs spanning the years from 1985 through 2012 are summarized and discussed in terms of an overall research trajectory.

CONCLUSIONS

The guiding principle of Dr. Stevenson's work is to reduce the potential harm to which workers are exposed through the development of bona fide occupational standards, a better understanding of risk factors leading to low back pain, and the establishment of an enhanced objective design process for functional load-bearing clothing and equipment.

Local dynamic stability of the lifting kinematic chain

While a stable trunk and centre of mass (CoM) trajectory are required during lifting, it is unclear how stability is controlled. Thirty healthy participants (15M, 15F) performed repetitive, symmetric lifting at 10 cycles per minute for 3 min with a load-in-hands equivalent to 10% of their maximum back strength. Short- and long-term maximum finite-time Lyapunov exponents (λ(max-s) and λ(max-l)), describing responses to small (local) perturbations, estimated the local dynamic stability of the foot, shank, thigh, pelvis, lower back, and upper back segments. Instability (λ(max-s)) significantly increased when moving up the kinematic chain (p<0.001). Therefore, to maintain trunk equilibrium and accurately regulate CoM trajectory during lifting, stability of the distal (fixed) lower limb segments is prioritized. This is contrary to previous results observed during gait, indicating that trunk control via kinematic chain stability is accomplished differently for walking and lifting.

The free moment in walking and its change with foot rotation angle

BACKGROUND

This investigation characterized the time-history pattern of the free moment (FM) during walking and, additionally, assessed whether walking with either an internally or externally rotated foot position altered the FM's time-history.

METHODS

Force plate and foot kinematic data were acquired simultaneously for 11 healthy subjects (6 males, 5 females) while walking at their self-selected comfortable speed in 3 foot rotation conditions (normal, internal and external). The FM was calculated and normalized by the product of each participant's body weight and height prior to extraction of peak FM, occurrence of peak FM in stance and net relative impulse. Differences in these values across foot rotation conditions were assessed using separate one-way, repeated measures analysis of variance and subsequent pair-wise comparisons.

RESULTS

The average FM pattern during normal walking exhibits a biphasic shape: resisting inward rotation during approximately the first half of stance and outward rotation during the latter part of stance. While no differences in peak FM or net relative impulse were observed between the internal foot rotation condition and normal walking, the external foot rotation condition resulted in significantly greater peak FM and relative net impulse in comparison to normal walking.

CONCLUSION

The differences in selected FM variables between normal walking and the external foot rotation condition are attributable to individual subject response to walking with an externally rotated foot. In this condition, some subjects displayed a FM pattern that was similar to that recorded during normal walking, while others displayed markedly larger FM patterns that are comparable in magnitude to those reported for running. The larger FM values in these latter subjects are speculated to be a result of excessive transverse plane body movements. Whilst further investigation is warranted regarding the FM time-history characteristics during walking, our results indicate that the FM may provide useful information in assessment of gait.

The effect of internal and external foot rotation on the adduction moment and lateral–medial shear force at the knee during gait

It has been hypothesised that those with medial compartment knee osteoarthritis tend to externally rotate their foot during gait in order to unload the diseased compartment. This has been found to decrease the adduction moment at the knee during late stance, although the effects of foot rotation on shear forces at the knee have not yet been determined. Also, the effects of internal foot rotation on the knee during gait are not clear. This study performed a gait analysis on 11 healthy participants (M: 6; mean age 22.9+/-1.8 years) in three conditions: (1) natural foot rotation position; (2) internal foot rotation and (3) external foot rotation. Three-dimensional gait analysis calculated the knee adduction moment and lateral-medial shear force for all three foot rotation conditions. Internal rotation of the foot increased the knee adduction moment and lateral-medial shear force magnitude during late stance, while external rotation of the foot decreased the magnitude of both these measures. This implies that walking with an externally and internally rotated foot may unload the diseased compartment for those with medial and lateral compartment knee OA, respectively. Also, the relationship of foot rotation angle to the adduction moment and lateral-medial shear force was strengthened when data were corrected for the subject's normal walking condition. Knee OA subject data revealed that they were able to reduce the knee adduction moment more than normal subjects during late stance, indicating that other factors besides the rotation of the foot need to be investigated.

Mechanical factors relate to pain in knee osteoarthritis

BACKGROUND

Pain experienced by people with knee osteoarthritis is related to psychosocial factors and damage to articular tissues and/or the pain pathway itself. Mechanical factors have been speculated to trigger this pain experience; yet mechanics have not been identified as a source of pain in this population. The purpose of this study was to identify whether mechanics could explain variance in pain intensity in people with knee osteoarthritis.

METHODS

Data from 53 participants with physician-diagnosed knee osteoarthritis (mean age=68.5 years; standard deviation=8.6 years) were analyzed. Pain intensity was reported on the Western Ontario and McMaster Universities Osteoarthritis Index. Mechanical measures included weight-bearing varus-valgus alignment, body mass index and isokinetic quadriceps torque. Gait analysis captured the range of adduction-abduction angle, range of flexion-extension angle and external knee adduction moment during level walking.

FINDINGS

Pain intensity was significantly related to the dynamic range of flexion-extension during gait and body mass index. A total of 29% of the variance in pain intensity was explained by mechanical variables. The range of flexion-extension explained 18% of variance in pain intensity. Body mass index added 11% to the model. The knee adduction moment was unrelated to pain intensity.

INTERPRETATION

The findings support that mechanical factors are related to knee osteoarthritis pain. Because limitations in flexion-extension range of motion and body size are modifiable factors, future research could examine whether interventions targeting these mechanics would facilitate pain management.

Effect of foot rotation on knee kinetics and hamstring activation in older adults with and without signs of knee osteoarthritis

BACKGROUND

To determine the effects of changing the natural foot progression angle during gait (internal and external foot rotation) on the knee's adduction moment, lateral-medial shear force, and the ratio of medial-lateral hamstring muscle activation in those with signs of knee osteoarthritis and a matched healthy control group.

METHODS

Twelve subjects with signs of knee osteoarthritis and 12 matched healthy control subjects were evaluated. A 3D gait analysis system calculated forces and moments at the knee while the subjects walked in three conditions: (1) normal foot position, (2) external foot rotation, (3) internal foot rotation. Medial and lateral hamstring EMG data was also collected simultaneously and used to calculate the medial-lateral hamstring activation ratio during the stance phase of the gait cycle. Repeated measures ANOVAs were used to compare foot rotation conditions within each group; while between group comparisons were performed in the normal rotation condition only using t-tests.

FINDINGS

Those with knee osteoarthritis (OA) had an increased late stance knee adduction moment and a decreased medial-lateral hamstring activation ratio as compared to the healthy control group. Also, external foot rotation decreased the late stance knee adduction moment, lateral-medial shear force, and hamstring activation ratio. However, internal foot rotation did not increase these measures.

INTERPRETATION

Changes in foot position during gait have the ability to alter both the external loading of the knee joint and hamstring muscle activation patterns during gait. This may have implication in helping to unload the knee's articular cartilage.

The influence of gait pattern on signs of knee osteoarthritis in older adults over a 5-11 year follow-up period: a case study analysis

There is evidence that joint load is a factor in the development of osteoarthritis (OA) and, while altered gait profiles have been linked with OA, it is unknown if abnormal gait is a cause or effect of the disease. While the knee's adduction moment has been implicated in the development and progression of knee OA, it is also known that shearing forces are detrimental to the health of cartilage. The purpose of this pilot study was to examine the adduction moment and gait shear forces to determine if they may lead to signs of knee OA in older adults as they age. Knee gait kinetics, standardized radiographs and a questionnaire were collected on 28 older adults (M:13) during an initial visit, and 5 to 11 years later. Radiographic score increased (knees became more osteoarthritic in 15 of 28 subjects) over time. However, gait time-distance measures remained constant in disease free participants. Two returning participants developed symptoms and radiographic evidence of knee OA. The subject with the largest adduction moment developed signs of medial OA while the subject with the smallest adduction moment developed signs of lateral OA. In addition, there was a strong correlation between the magnitudes of the adduction moment and lateral-medial shear force that needs to be investigated further. Results suggest that gait can remain stable over time in older adults. Also, the medial and lateral OA case study findings suggest that the extreme gait profiles seen in these two participants may be important in explaining cartilage breakdown and the development of OA. This longitudinal study would suggest that perhaps it is the abnormal gait pattern that leads to the development of OA, although a much larger study would be needed to confirm this finding.

Role of knee kinematics and kinetics on performance and disability in people with medial compartment knee osteoarthritis

BACKGROUND

Although gait characteristics have been well documented in people with knee osteoarthritis, little is known about the relationships between gait characteristics and performance or disability. Our purpose was to examine the role of knee kinematics and kinetics on walking performance and disability in people with knee osteoarthritis. We also examined whether pain mediated the relationship between the knee adduction moment and performance or disability.

METHODS

Three-dimensional gait analysis was conducted on 54 people with medial compartment knee osteoarthritis. Performance was quantified with the Six Minute Walk test and disability was self-reported on the Short Form-36. The pain subscale of the Western Ontario McMaster Universities Osteoarthritis Index and the functional self-efficacy subscale of the Arthritis Self-Efficacy scale were completed.

FINDINGS

A step-wise linear regression demonstrated that the variance in Six Minute Walk test scores was explained by functional self-efficacy (50%) and the range of knee motion (8%). The variance in Short Form-36 was explained by pain (36%), the peak extension angle (19%) and the range of knee motion (4%). Pain was unrelated to the knee adduction moment so analyses of pain as a mediator of the adduction moment on either performance or disability were halted.

INTERPRETATION

Kinematic output from the motor control system is useful in understanding some variance in current performance and disability in people with knee osteoarthritis. The knee adduction moment was unrelated to these variables and pain did not mediate between the knee adduction moment and performance or disability. Therefore this moment does not explain current clinical status in people with knee osteoarthritis based on the measures of performance and disability used in this study.

Determinants of Self-Report Outcome Measures in People With Knee Osteoarthritis

OBJECTIVES

To identify the determinants of self-report mobility measures in people with knee osteoarthritis (OA) and to compare self-report measures with physical performance.

DESIGN

Cross-sectional, prospective.

SETTING

Motor performance laboratory and human mobility research center.

PARTICIPANTS

A convenient sample of 54 participants with medial compartment knee OA (32 women, 22 men; age 68.3+/-8.7y; range, 50-87y). Three participants were excluded because of the presence of lateral knee OA on radiographs.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Self-reports were recorded by using the Western Ontario McMaster Universities Osteoarthritis Index (WOMAC) and the Medical Outcomes Study 36-Item Short-Form Health Survey (SF-36). Performance measures included the six-minute walk test (6MWT), Timed Up & Go (TUG) test, and a standardized stair-climbing task (STR).

RESULTS

Stepwise linear regression analysis identified models that included pain, quadriceps and hamstrings strength, and depression to explain 62% to 73% of the variance in scores on the physical functioning subscale of the WOMAC and the SF-36. These self-report measures had a moderate relation (r range, .46-.64) with performance measures (6MWT, TUG, STR).

CONCLUSIONS

Self-report measures were strongly related to pain; physical performance measures were strongly related to self-efficacy. Regression models showed that self-report scores reflect pain, knee strength, and depression. The relation between self-report and performance measures was moderate, suggesting that these examine different aspects of mobility.

Determinants of self efficacy for physical tasks in people with knee osteoarthritis

OBJECTIVE

Self efficacy, the confidence an individual has to perform a task, is an important determinant of physical performance in individuals with knee osteoarthritis (OA). The purpose of this study was to determine what personal, pathophysiologic, and impairment factors relate to self efficacy for physical tasks in community-dwelling adults with knee OA.

METHODS

Fifty-four persons with radiographically confirmed knee OA (mean +/- SD age 68.3 +/- 8.7 years, range 50-87 years) participated. The Functional Self-Efficacy subscale of the Arthritis Self-Efficacy Scale was the dependent measure. Independent measures included age, education, scores from the Center for Epidemiologic Studies Depression and State-Trait Anxiety Inventory questionnaires, medial joint space and varus/valgus tibiofemoral angle from radiographs, body mass index, and isokinetic quadriceps and hamstrings strength. Knee pain and stiffness, assessed using the Western Ontario and McMaster Universities Osteoarthritis Index, were independent measures.

RESULTS

Fifty-one percent of the variance of Functional Self Efficacy was explained by knee stiffness, hamstrings strength, age, and depression scores. Pain, education, anxiety, radiographic joint space, and body weight did not significantly contribute to the variance in Functional Self-Efficacy scores. Substituting quadriceps strength for hamstrings strength resulted in a regression model that included only stiffness, age, and depression, which explained nearly as much variance as the original model.

CONCLUSION

Self efficacy for physical tasks is related to the sensation of stiffness, hamstrings strength, age, and level of depressive symptoms in persons with knee OA. Clinicians and researchers could consider these variables when assessing the level of self efficacy for physical tasks in persons with knee OA.

Contribution of psychosocial and mechanical variables to physical performance measures in knee osteoarthritis

BACKGROUND AND PURPOSE

This cross-sectional study evaluated the relative contributions of psychosocial and mechanical variables to physical performance measures in people with knee osteoarthritis (OA).

SUBJECTS

Fifty-four subjects (age, in years: mean=68.3, SD=8.7, range=50-87) with radiographically confirmed knee OA were included in this study.

METHODS

Physical performance measures included the Six-Minute Walk Test (SMW), the Timed "Up & Go" Test (TUG), and a stair-climbing task (STR). Responses to psychosocial questionnaires that reflect depression, anxiety, and self-efficacy (a person's confidence in his or her ability to complete a task) were collected. Mechanical variables measured included body mass index and knee strength (force-generating capacity of muscle). Stepwise linear regressions were performed with the SMW, TUG, and STR as separate dependent variables.

RESULTS

Functional self-efficacy explained the greatest amount of variance in all performance measures, contributing 45% or more. Knee strength and body weight also explained some variance in performance measures. Anxiety and depression did not explain any variance in performance.

DISCUSSION AND CONCLUSION

Physical therapists evaluating the significance of the SMW, TUG, and STR scores in subjects with knee OA should note that a large part of each score reflects self-efficacy, or confidence, for physical tasks, with some contributions from knee strength and body weight.

Reliability and validity of ankle proprioceptive measures

OBJECTIVE

To determine the reliability and validity of ankle proprioceptive measures.

DESIGN

Reliability was assessed between test occasions. Construct validity was addressed by the ability of measures to differentiate among groups.

SETTING

Laboratory of an educational institution.

PARTICIPANTS

Eight healthy adults were recruited into each of 3 groups: (1) young (20-39y), (2) middle-aged (40-59y), and (3) older adults (>or=60y). Four subjects from each group (n=12) participated in retesting.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Threshold for perception of passive movement, error in active reproduction of position, error in reproduction of velocity, and error in reproduction of torque.

RESULTS

Intersession reliability was excellent (intraclass correlation coefficient [ICC] range, .79 - .95) for threshold for perception of movement, error in active reproduction, error in velocity reproduction, and error in dorsiflexion torque reproduction; intersession reliability was good for error in reproduction of plantarflexion torque (ICC=.72). Threshold for perception of movement differed between groups 1 and 3 and between groups 2 and 3 (P<.05). Error in reproduction of position was greater in group 2 than in group 1 (P<.05).

CONCLUSION

Differences in proprioception between the older and the 2 younger groups were best detected by using threshold for perception of passive movement.

Static and dynamic biomechanics of foot orthoses in people with medial compartment knee osteoarthritis

OBJECTIVE

Gait biomechanics (knee adduction moment, center of pressure) and static alignment were investigated to determine the mechanical effect of foot orthoses in people with medial compartment knee osteoarthritis.

DESIGN

Repeated measures design in which subjects were exposed to three conditions (normal footwear, heel wedge and orthosis) in random order.

BACKGROUND

The knee adduction moment is an indirect measure of medial compartment loading. It was hypothesized that the use of a 5 degrees valgus wedge and 5 degrees valgus modified orthosis would shift the center of pressure laterally during walking, thereby decreasing the adduction moment arm and the adduction moment.

METHODS

Peak knee adduction moment and center of pressure excursion were obtained in nine subjects with medial compartment knee OA during level walking using an optoelectric system and force plate. Static radiographs were taken in 12 subjects using precision radiographs.

RESULTS

There was no difference between conditions in static alignment, the peak adduction moment or excursion of the center of pressure in the medial-lateral direction. No relationship was found between the adduction moment and center of pressure excursion in the medial-lateral plane. The displacement of the center of pressure in the anterior-posterior direction, measured relative to the laboratory coordinate system, was decreased with the orthosis compared to the control condition (P=0.036) and this measure was correlated with the adduction moment (r=0.45, P=0.019).

CONCLUSIONS

The proposed mechanism was not supported by the findings. The reduction in the center of pressure excursion in the anterior-posterior direction suggests that foot positioning was altered, possibly to a toe-out position, while subjects wore the orthoses. Based on the current findings, we hypothesize that toe-out positioning may reduce medial joint load.

RELEVANCE

Knee Osteoarthritis is the most common cause of chronic disability amongst seniors. Developing inexpensive, non-invasive treatment strategies for this large population has potential to impact health care costs, quality of life and clinical outcomes.

Knee and hip kinetics during normal stair climbing

Understanding joint kinetics during activities of daily living furthers our understanding of the factors involved in joint pathology and the effects of treatment. In this study, we examined hip and knee joint kinetics during stair climbing in 35 young healthy subjects using a subject-specific knee model to estimate bone-on-bone tibiofemoral and patello-femoral joint contact forces. The net knee forces were below one body weight while the peak posterior-anterior contact force was close to one body weight. The peak distal-proximal contact force was on average 3 times body weight and could be as high as 6 times body weight. These contact forces occurred at a high degree of knee flexion where there is a smaller joint contact area resulting in high contact stresses. The peak knee adduction moment was 0.42 (0.15) Nm/kg while the flexion moment was 1.16 (0.24) Nm/kg. Similar peak moment values, but different curve profiles, were found for the hip. The hip and knee posterior-anterior shear forces and the knee flexion moment were higher during stair climbing than during level walking. The most striking difference between stair ascent and level walking was that the peak patello-femoral contact force was 8 times higher during stair ascent. These data can be used as baseline measures in pathology studies, as input to theoretical joint models, and as input to mechanical joint simulators.

The effect of segment parameter error on gait analysis results

The extent to which errors in predicting body segment parameters (SP) influence biomechanical analysis of human motion is unclear. Therefore, the current study quantitatively evaluated the differences in SP estimates using literature predictive functions and computed the effect of SP variation on the kinetic output of walking. For a group of 15 young males, significant differences (P<0. 05) were observed between SP estimates for the leg and thigh using the literature predictive functions, with mass and moment of inertial values differing by more than 40%. Using kinematic and ground reaction force data collected for each subject while walking, inverse dynamic analysis was performed iteratively to compute hip forces and moments while simultaneously varying SP values over nine intervals within +/-40% of a baseline value. SP variations were found to significantly affect (P<0.05) most of the kinetic estimates produced, particularly those taken during the swing phase. However, the magnitude of these effects was generally less than 1% of body weight. The data from the current study allows researchers to estimate the errors in kinetic measures due to SP variation. The results also indicate that the accuracy of SP prediction should be of concern in biomechanical research particularly for open chain and high acceleration activities. Further study is necessary to identify the importance of SP variation on other motion skills.

Elbow kinematics during sit-to-stand and stand-to-sit movements

The sit-to-stand and stand-to-sit movements of 10 healthy women (mean age 52.4 years) were subjected to a descriptive analysis that yielded a definition of phases, determination of the peak angles reached, maximum angular velocity during each movement, and the sequencing of key events. While subjects showed little intrasubject variability, intersubject variability was evident. Subjects differed in the joint angles and angular velocity recorded, but the sequence of flexion/extension and rotation events were unchanged. Changes in direction of flexion/extension and rotation tended to occur very close in time, if not at the same time.

An integrated procedure to assess knee-joint kinematics and kinetics during gait using an optoelectric system and standardized X-rays

This paper describes a 3-D gait analysis system, which combines optoelectric motion tracking and a standardized X-ray procedure, to calculate the net knee-joint forces and moments of a normal subject group during walking. The optoelectric system collects kinematic data from infra-red LED markers placed at selected skin surface locations and projecting probes attached to the lower limb. A standardized X-ray procedure is used to move surface markers into their designated bony landmarks based on individual bone structure, which reduces the error caused by uncertainty of skin-surface marker locations. Based on moved-in marker information, different joint coordinate systems are proposed for kinematic and kinetic analysis of the knee joint. Normalized data of knee angles, net reaction forces and net moments from 35 young, normal subjects are presented.

A procedure to validate three-dimensional motion assessment systems

The automation provided by computer-assisted motion-tracking systems allows for three-dimensional motion and force analysis. These systems combined with mathematical modelling are able to analyse quickly the intricate dynamics of human movement. Understanding the limitations of human motion analysis as performed by the present measurement techniques is essential for proper application of the results. It is necessary to validate the analysis system prior to subject testing. This paper provides a validation of an optoelectric motion-tracking system used in a dynamic knee assessment study. While the validation is shown with one particular system only, it is suggested that all systems used in two- or three-dimensional motion analysis should be tested similarly in the actual configuration used. Three simple mechanical representations of the human knee have been used in this validation. The first model provided an understanding of the source and behaviour of the error introduced to the accuracy of defining a vector between the recorded coordinates of two markers. The other two models investigated the effect of processing methods specific to the knee analysis project. Separating the markers by at least 180 mm is recommended to produce stable vectors. Relative joint angles could be calculated in all three planes of rotation. The error in calculating flexion and longitudinal rotation was less than 2.0 degrees, while calculating adduction introduced errors of 4.0 degrees. Force calculations were found to be within 8%. The system behaviour was found to be consistent within the calibrated volume about the force platform. Simple mechanical models combined with straightforward procedures can provide validation in terms of clinically relevant parameters.

Semiautomatic three-dimensional knee motion assessment system

A semiautomatic three-dimensional knee motion assessment system has been developed based on an optoelectric motion tracking system connected to an IBM-compatible computer. Critical decisions made in implementing the software component of the system include the modelling of the thigh and lower leg segments, calculating the knee angles, reaction forces, and moments; the file structure used and the format of the programs used to process the data are outlined. Once the subject-specific data have been collected, the system of programs requires no other user-intervention during processing. Also, selected curve parameters are automatically extracted from the output and combined with the subject-specific data that include precision X-ray and anthropometric data, which are all added to a knee motion assessment database. The automated portion of the system frees the experimenter from data processing and allows concentration on data analysis.

Trunk muscle balance and muscular force

An investigation of the absolute strength of the human muscle was carried out on the in vivo erector spinae muscle using magnetic resonance tomography coupled with dynamic muscular testing. The absolute strength of the erector spinae was calculated to be 48 N/cm2. The area of the rectus abdominis was 15.1 cm2, and the area of the erector spinae was 54.5 cm2. The internal moment arm for the rectus abdominis and erector spinae muscles was 7.04 and 5.64 cm, respectively. The static force measures showed the trunk extensor moment to be only 30% greater than the flexor moment. The difference is discussed in terms of the absolute strength of muscle, and other anatomic factors.

Mechanical energy patterns in gait of cerebral palsied children with hemiplegia

The mechanical energy costs of walking were studied in 10 cerebral palsied children with hemiplegia to determine whether their values were substantially different from normal and, if so, to discover the movements that were responsible. A two-dimensional, sagittal-plane cinematographic analysis of the subjects' normal walking was undertaken. This technique provided continuous information about the mechanical energy costs of the whole body and each of its parts, the energy types involved, and the amounts of energy conserved. In most cases, the energy costs were above normal and were attributable to poor patterns of exchange between the potential and kinetic energy types of the head, arms, and trunk segment; to very low levels of kinetic energy that precluded exchange; or to both. We concluded that attention should be directed to restoring the sinusoidal pattern of motion and to the fluctuating speeds during each gait cycle when energy costs are a therapeutic consideration.

Prediction of trunk muscle areas and moment arms by use of anthropometric measures

The prediction of five internal muscle variables extracted from computed tomography scans was attempted using 27 anthropometric variables. Stable regression equations are presented for the prediction of the cross-sectional area of the rectus abdominis, psoas, and erector spinae, as well as for the moment arm of the erector spinae. No stable regression equation was found for the prediction of the moment arm of the rectus abdominis, and the results indicated that the method was group dependent. These findings have implications for human modeling studies that use estimated parameters for the internal muscle variables.

Mechanical energy of walking of stroke patients

The mechanical energy costs of walking have been studied in ten stroke patients with hemiplegia. A two-dimensional sagittal plane cinematographic analysis of two strides of the subjects' normal walking was undertaken, yielding continuous information about the mechanical energy costs of the whole body and each of its parts, about the energy types involved, and the amounts of energy conservation. The large head, arms, and trunk (HAT) were found to dominate the total pattern. Three major disturbances were seen. In contrast to normal subjects who show energy-conserving negatively correlated potential and kinetic energy curves for the HAT, the subjects who demonstrated the first disturbance showed gross irregularity of the curves, with almost no opportunity for exchange between energy types. In a second disturbance the curves of the HAT showed some energy-conserving portions, but levels of kinetic energy curves were low, resulting in little energy exchange. In the third disturbance, some exchange was evident, but the pattern was dominated by potential energy changes in the form of a single large rise and fall, coinciding with swing phase of the affected leg. Each of these disturbances would require a different approach to treatment. Although mechanical energy analyses do not reflect certain energy costs, such as the effort required to hold the body up against the pull of gravity and that used in contracting antagonist muscles, they could be of considerable assistance in pinpointing costly variations in energy patterns during walking and in determining appropriate treatment procedures.