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Evaluation of the age-related changes in movement smoothness in the lower extremity joints during lifting
Abstract
The purpose of this study was to analyze age-related movement smoothness changes in the lower extremity joints during load lifting. A total of 10 young and 13 elderly subjects participated in the study. Infrared reflective markers were attached to body landmarks in each subject. While the subjects stood on force plates and lifted a box, the marker displacements and ground reaction forces were measured using a 3D motion analysis system. The jerk square mean value (JSM) was defined as the lower extremity joint movement smoothness index during lifting. JSM represented the average of the square of the joint angle third derivative value, according to the jerk third derivative of the position data. Each subject's JSM values were calculated for the hip, knee and ankle joints. Movement smoothness appeared to decrease as JSM increased. Multiple regression analyses were performed for dependent variables (hip, knee and ankle joint JSM values) and independent variables (age, hand grip strength, sex difference and lifting duration). The level of significance was set at p<0.05. For the hip joint JSM, the regression coefficient for age was significantly positive and that for lifting duration was significantly negative. For the knee joint JSM, the regression coefficient for lifting duration was significantly negative. For the ankle joint JSM, the regression coefficients for age and hand grip strength were significantly positive and that for lifting duration was significantly negative. These results suggest that movement smoothness in the hip and ankle joints during lifting decreases with advancing age.
... where J i is the instantaneous value of the jerk, and n is the total number of data points (101). The JSM is an index of smoothness of movement: the lower the Jerk is, the smoother the movements are [36]. ...
... The flexion-extension angles of trunk, elbow and knee were evaluated using the kinematic data. The angular jerk, that is the third derivative over time of the angle displacement [degrees/s 3 ]) [36], was calculated for the trunk (Jtrunk), elbow (Jelbow) and knee (Jknee) angles ([degrees/s 3 ]). ...
... where is the instantaneous value of the jerk, and n is the total number of data points (101). The JSM is an index of smoothness of movement: the lower the Jerk is, the smoother the movements are [36]. ...
Work-related low-back disorders (WLBDs) can be caused by manual lifting tasks. Wearable devices used to monitor these tasks can be one possible way to assess the main risk factors for WLBDs. This study aims at analyzing the sensitivity of kinematic data to the risk level changes, and to define an instrument-based tool for risk classification by using kinematic data and artificial neural networks (ANNs). Twenty workers performed lifting tasks, designed by following the rules of the revised NIOSH lifting equation, with an increasing lifting index (LI). From the acquired kinematic data, we computed smoothness parameters together with kinetic, potential and mechanical energy. We used ANNs for mapping different set of features on LI levels to obtain an automatic risk estimation during these tasks. The results show that most of the calculated kinematic indexes are significantly affected by changes in LI and that all the lifting condition pairs can be correctly distinguished. Furthermore, using specific set of features, different topologies of ANNs can lead to a reliable classification of the biomechanical risk related to lifting tasks. In particular, the training sets and numbers of neurons in each hidden layer influence the ANNs performance, which is instead independent from the numbers of hidden layers. Reliable biomechanical risk estimation can be obtained by using training sets combining body and load kinematic features.
... In addition, by analyzing jerk, Yan et al. found that the arm movement involved in overarm throwing becomes smoother as one becomes an adult [14]. More recently, Sakata et al. studied the effect of age-related changes in the smoothness of lower body joints during lifting, and demonstrated high jerk values in the ankle and hip joints of older subjects, pointing to less smooth movements in this group [15]. ...
... High jerk values can be interpreted in 2 ways: strong muscles or decreased smoothness [15]. Puniello et al. proposed that the jerk for the vertical trajectory of box lifting is significantly and positively correlated with hip extensor strength [24]. ...
... Puniello et al. proposed that the jerk for the vertical trajectory of box lifting is significantly and positively correlated with hip extensor strength [24]. Sakata et al. proposed that the jerk values of the ankle and hip joints increased because the smoothness of lower body joints was lower in the aged group [15]. In general, professional athletes are much stronger than amateurs, and according to previous studies, professional athletes have better muscle balance in the lower body, better weight shifts during movements, and more coordinated sequential muscle activation than amateurs [5,25]. ...
When the human body is introduced to a new motion or movement, it learns the placement of different body parts, sequential muscle control, and coordination between muscles to achieve necessary positions, and it hones this new skill over time and repetition. Previous studies have demonstrated definite differences in the smoothness of body movements with different levels of training, i.e., amateurs compared with professionals. Therefore, we tested the hypothesis that skilled golfers swing a driver with a smoother motion than do unskilled golfers. In addition, the relationship between the smoothness of body joints and that of the clubhead was evaluated to provide further insight into the mechanism of smooth golf swing.
Two subject groups (skilled and unskilled) participated in the experiment. The skilled group comprised 20 male professional golfers registered with the Korea Professional Golf Association, and the unskilled group comprised 19 amateur golfers who enjoy golf as a hobby. Six infrared cameras (VICON460 system) were used to record the 3D trajectories of markers attached to the clubhead and body segments, and the resulting data was evaluated with kinematic analysis. A physical quantity called jerk was calculated to investigate differences in smoothness during downswing between the two study groups.
The hypothesis that skilled golfers swing a driver with a smoother motion than do unskilled golfers was supported. The normalized jerk of the clubhead of skilled golfers was lower than that of unskilled golfers in the anterior/posterior, medial/lateral, and proximal/distal directions. Most human joints, especially in the lower body, had statistically significant lower normalized jerk values in the skilled group. In addition, the normalized jerk of the skilled group's lower body joints had a distinct positive correlation with the normalized jerk of the clubhead with r = 0.657 (p < 0.01).
The result of this study showed that skilled golfers have smoother swings than unskilled golfers during the downswing and revealed that the smoothness of a clubhead trajectory is related more to the smoothness of the lower body joints than that of the upper body joints. These findings can be used to understand the mechanisms behind smooth golf swings and, eventually, to improve golf performance.
... On the other hand, although a correct execution of the lifting by the lower limbs can allow the trunk to stoop less reducing net moments, muscle forces, and internal spinal load [23], lower limbs have received little consideration to date and few studies are available in the literature [24][25][26][27][28]. Furthermore, lower limb work-related musculoskeletal diseases 2 of 12 are still present and widespread [29], (e.g., it is possible to see the incidence and prevalence of work-related musculoskeletal diseases in Italy at the link https://bancadaticsa.inail.it, ...
The central nervous system uses muscle co-activation for body coordination, effector movement control, and joint stabilization. However, co-activation increases compression and shear stresses on the joints. Lifting activity is one of the leading causes of work-related musculoskeletal problems worldwide, and it has been shown that when the risk level rises, lifting enhances trunk muscle co-activation at the L5/S1 level. This study aims to investigate the co-activation of lower limb muscles during liftings at various risk levels and lifting types (one-person and vs. two-person team lifting), to understand how the central nervous system governs lower limb rigidity during these tasks. The surface electromyographic signal of thirteen healthy volunteers (seven males and six females, age range: 29–48 years) was obtained over the trunk and right lower limb muscles while lifting in the sagittal plane. Then co-activation was computed according to different approaches: global, full leg, flexor, extensor, and rostro-caudal. The statistical analysis revealed a significant increase in the risk level and a decrease in the two-person on the mean and/or maximum of the co-activation in almost all the approaches. Overall, our findings imply that the central nervous system streamlines the motor regulation of lifting by increasing or reducing whole-limb rigidity within a distinct global, extensor, and rostro-caudal co-activation scheme, depending on the risk level/lifting type.
... Hlucny and Novack [18] used movements, absolute velocities, and accelerations of specified body joints measured by 17 Inertial measurement units (IMUs) to classify the lifting load (3/10 kg) with a 64.3% accuracy. Jerk, a popular indicator of smoothness of motion [19] calculated by taking the derivative of acceleration, has been used as a feature to estimate the lifting load [20]. Furthermore, Lee [21] illustrated that people tend to shorten the acceleration period and keep the object closer to their bodies when lifting heavier objects. ...
Safety practitioners widely use the lifting index (LI) to determine workers’ lifting risk but are hampered by the difficulties of estimating the lifting load without intervention or intrusive sensors. This study proposes a computer vision method for estimating the LI across varying lifting loads. The proposed method can also predict the Brog rating of perceived exertion (RPE), a measure associated with the lifting load. A controlled lifting experiment was conducted to demonstrate the approach. Thirty participants performed 2176 lifting tasks at three LI levels. These levels were controlled by varying the lifting load and fixing other task variables (e.g., the lifting distance). The proposed method combined the pose estimation (OpenPose) and the optical flow estimation (SelFlow) techniques for extracting the participants’ body motion and posture features; a facial expression recognition algorithm (OpenFace) built upon the facial action unit coding system (FACS) was used to extract the participants’ facial features. The extracted features were combined and used to develop prediction models. The best-performing model was an integration of the 1-D convolutional neural network and the long short-term memory network. It achieved an area under curve of 0.890 in classifying the LI and a root mean square of 2.264 in predicting the participants’ RPE. Critical indicators were identified by investigating the contribution of the features through interpretable machine learning techniques. In summary, this study demonstrates a nonintrusive method for lifting risk assessment and discovers behavioral indicators that predict changes in the LI and RPE due to varying loads.
... Since the ability to make the coordinated motions of the two joints is required in the design of any upper limb prosthesis [29], the dynamic appearance is a desirable quality in the prosthetic field. The movement smoothness (often quantified in terms of 'jerk' [45]) is usually used in the literature to evaluate the altered or coordinated joint movements [46][47][48][49][50], where the smoothest movement is less altered and, thus, more coordinated or more natural. Unlike a jerky movement, a coordinated movement exhibits a dynamic appearance more similar to a natural movement. ...
Upper limb prostheses can greatly improve the condition of amputees. However, prosthetic mechanisms have different topologies and there is no consensus on the choice of an appropriate mechanism. This paper evaluates the impact of prosthetic mechanism topology on the prosthesis’ performance during daily tasks. The proposed multibody model is compared to four open-loop and one closed-loop existing mechanisms according to: (1) consumed energy, (2) global and local movement reconstruction errors during inverse kinematics, (3) movement smoothness, which reflects the dynamic appearance of the prosthesis, also called ‘dynamic cosmesis’. Flexion–extension (FE) and pronation–supination (PS) tasks were studied in 15 healthy subjects. All parameters identified at least one group difference (p < 0.0001) in both tasks. Most closed-loop mechanisms (50% in FE and 100 % in PS) including the proposed model were among the most energy-efficient mechanisms. Out of all models, the proposed model was the most energy efficient in FE (2.07 ± 0.69 KJ) and in PS (0.25 ± 0.16 KJ). This model also reproduced the studied movements with the lowest errors (1.39 ± 0.2 mm in FE and 1.38 ± 0.25 mm in PS), especially at the forearm level. The results show that the wrist plays a major role in motion smoothness and that two series mechanisms have exhibited a poor dynamic cosmesis because of their higher jerk cost ((1.73 ± 0.30) × 10¹⁰) in FE and (9.29 ± 17) × 10¹³ in PS tasks)). Finally, the mechanism topology affects the performance of upper limb prostheses and represents a novel aspect in the prostheses design which can be applied to exoskeleton design.
... This effect is such that even simple measures of smoothness-evaluated in sit-tostand tests, for example-can distinguish between older adults at risk of falls, older adults who are not a falls risk and younger adults [23,24]. Similarly, smoothness during lifting movements-assessed at hip and ankle-declines with advancing age [25], and many disease states, such as Parkinson's and Huntington's, are accompanied by deteriorating smoothness [26]. Furthermore, in children, developmental disorders such as autism and Asperger's are typified by a lack of movement smoothness [27], and smoothness measures accurately detect delayed motor skill acquisition [8]. ...
Over the expanse of evolutionary history, humans, and predecessor Homo species, ran to survive. This legacy is reflected in many deeply and irrevocably embedded neurological and biological design features, features which shape how we run, yet were themselves shaped by running.
Smoothness is a widely recognised feature of healthy, proficient movement. Nevertheless, although the term ‘smoothness’ is commonly used to describe skilled athletic movement within practical sporting contexts, it is rarely specifically defined, is rarely quantified and remains barely explored experimentally. Elsewhere, however, within various health-related and neuro-physiological domains, many manifestations of movement smoothness have been extensively investigated. Within this literature, smoothness is considered a reflection of a healthy central nervous system (CNS) and is implicitly associated with practiced coordinated proficiency; ‘non-smooth’ movement, in contrast, is considered a consequence of pathological, un-practiced or otherwise inhibited motor control.
Despite the ubiquity of running across human cultures, however, and the apparent importance of smoothness as a fundamental feature of healthy movement control, to date, no theoretical framework linking the phenomenon of movement smoothness to running proficiency has been proposed. Such a framework could, however, provide a novel lens through which to contextualise the deep underlying nature of coordinated running control. Here, we consider the relevant evidence and suggest how running smoothness may integrate with other related concepts such as complexity, entropy and variability. Finally, we suggest that these insights may provide new means of coherently conceptualising running coordination, may guide future research directions, and may productively inform practical coaching philosophies.
... 7 Smoothness in movement, such as during walking and running, is assumed to be attained by adulthood; however, disruptions in gait pattern due to injury or performance enhancement can alter the smoothness of the movement, and this is often quantified in terms of "jerk". 8,9 Jerk is defined as a change in the acceleration rate of a movement, and is the third derivative of displacement, with the smoothest movement having the lowest jerk. Several previous reports have sought to use the smoothness of joint movement to explain, coordinate, or alter joint movement. ...
Background
Patients with knee osteoarthritis can significantly affect the function of the knee joint in terms of joint range and mobility and have a stereotypical pattern of knee stiffness during gait, caused by an increased resistance in the muscles and soft tissues during the stance phase of knee joint movement. Smoothness in movement, such as during walking and running, is assumed to be attained by adulthood; however, disruptions in gait pattern due to injury or performance enhancement can alter the smoothness of the movement, and this is often quantified in terms of “jerk”. A higher jerk value is linked with a decrease in smoothness. However few have reported to evaluate the smoothness of the knee joint movement during walking in patients with knee osteoarthritis. The purpose of the present study was to quantify the smoothness of the knee joint movement during walking in people with knee osteoarthritis.
Methods
Patients were classified as having early or severe knee osteoarthritis. There were eight patients in each group (16 knees; three males, five females). The normalized angular jerk was calculated as an indicator of the walking knee joint smoothness in each of the four periods of the stance phase. Two-way ANOVA was performed to compare the smoothness of knee joint movement between groups and between each period of the stance phase.
Results
The angular change in the sagittal plane of those with severe knee osteoarthritis was smaller than that of those with early knee osteoarthritis in all periods of the stance phase. Normalized angular jerk did not significantly differ between groups in all periods. In both groups, the normalized angular jerk in the sagittal plane was significantly larger in the mid-stance and terminal stance periods than in the early stance and pre-swing periods. Only in patients with severe knee osteoarthritis, there was a significantly larger jerk in the frontal plane in the mid-stance period.
Conclusion
The present results revealed that the smoothness of joint movement decreases during the single leg supporting phase of the stance phase in the frontal plane with severe knee osteoarthritis, although there is no difference in smoothness of joint movement according to the severity of knee osteoarthritis The instability during single leg support due to increase of the knee joint load and destruction cause the impaired smoothness of the knee joint movement.
... Also, in their study, time, path length, depth perception, and motion smoothness were positively correlated. Sakata et al. 23 used the jerk square mean value as the average of the square of the joint angle third derivative value to study age-related changes in smoothness of lower extremity joint movement during load lifting. These results verified that smoothness in the hip and ankle joints during lifting decreases with advancing age. ...
Objectives:
This article presents a quantitative technique to assess motion quality and smoothness during the performance of micromanipulation tasks common to surgical maneuvers. The objective is to investigate the effectiveness of the jerk index, a derivative of acceleration with respect to time, as a kinetostatic measure for assessment of surgical performance.
Design:
A surgical forceps was instrumented with a position tracker and accelerometer that allowed measurement of position and acceleration relative to tool motion. Participants were asked to perform peg-in-hole tasks on a modified O'Connor Dexterity board and a Tweezer Dexterity pegboard (placed inside a skull). Normalized jerk index was calculated for each individual task to compare smoothness of each group.
Setting:
This study was conducted at Project neuroArm, Cumming School of Medicine, the University of Calgary.
Participants:
Four groups of participants (surgeons, surgery residents, engineers, and gamers) participated in the tests.
Results:
Results showed that the surgeons exhibited better jerk index performance in all tasks. Moreover, the residents experienced motions closer to the surgeons compared to the engineers and gamers. One-way analysis of variance test indicated a significant difference between the mean values of normalized jerk indices among 4 groups during the performance of all tasks. Moreover, the mean value of the normalized jerk index significantly varied for each group from one task to another.
Conclusions:
Normalized jerk index as an independent parameter with respect to time and amplitude is an indicator of motion smoothness and can be used to assess hand motion dexterity of surgeons. Furthermore, the method provides a quantifiable metrics for trainee assessment and proficiency, particularly relevant as surgical training shifts toward a competency-based paradigm.
... Since the jerk cost, which is a measurement of smoothness, represents the rate of change of acceleration in the movement, the smoothest movement is one with constant acceleration. Therefore, a lack of movement smoothness is observed with severe irregular changes in acceleration [5]. ...
... Effectiveness of measuring joint instability in terms of acceleration and jerk-based movement irregularities has been known as reliable indicators of ageing (9), adaptation to arthroplasty (10) and motor disorders (11). Measurement of dynamic change in the intraarticular space is necessary to infer mechanical effects of the condylar movement on the joint disc and connective tissue. ...
Influence of mandibular asymmetry and cross-bite on temporomandibular joint (TMJ) articulation remained unknown. This study aimed to investigate whether/how the working-side condylar movement irregularity and articular spaces during chewing differ between patients with mandibular asymmetry/cross-bite and control subjects. The cross-bite group and the control group consisted of 10 adult female patients and 10 adult female subjects, respectively. They performed unilateral gum-chewing. The mandibular movements were recorded using a video-based opto-electronic system. The 3D articular surface of the TMJ for each individual was reconstructed using CT/MRI data. For local condylar points, the normalised jerk cost (NJC) towards normal direction to the condylar surface, the angle between tangential velocity vector and condylar long axis and intra-articular space were measured. Three rotatory angles at centre of the condyle were also measured. During closing and intercuspation, (i) movements of posterior portion of the deviated side condyle showed significantly less smoothness as compared with those for the non-deviated side and control subjects, (ii) the rotations of the condyle on the deviated side induced greater intra-articular space at posterior and lateral portions. These findings suggest that chewing on the side of mandibular deviation/cross-bite may cause irregular movement and enlarged intra-articular space at posterior portion of the deviated side condyle.
... It has been shown that smoothness of incisor point movement quantifies acute adaptive responses after insertion of the OI (13). In need for clinical diagnosis of dysfunction of human knee and hip joints, effectiveness of measuring joint instability in terms of acceleration and jerk-based parameters have been demonstrated as reliable indicators of ageing (14), adaptation to arthroplasty (12) and motor disorders (15). For these reasons, it can be postulated that progress or limitation of TMJ adaptation to the OI may be clearly understood by measuring the smoothness of condylar movement and intra-articular space after insertion of the OI. ...
Response of temporomandibular joint (TMJ) articulation adapting to occlusal alteration has been sparsely known. For 10 healthy adults with acceptably good occlusion, an artificial occlusal interference (OI) was introduced to the lower molar on the balancing side of unilateral chewing. Subjects were asked to chew a gum on their preferred side. The chewing jaw movements with/without the OI were recorded using a video-based optoelectronic system. The mandibular movements were generated in each individual's TMJ model reconstructed by magnetic resonance images. The smoothness of local condylar point movements towards the normal direction of the condylar surface and interarticular space on the working side was measured. Overall, the smoothness of condylar point movements in the closing phase was impaired immediately after introduction of the OI. In the intercuspal phase, the OI increased the joint space. After about 60 chewing cycles, the movement smoothness and joint space began to recover. These findings suggest that OI on the balancing side induced irregular stress field translation on the working-side condylar surface followed by acute recovery process.
Knee osteoarthritis (OA) gait is characterized by simultaneous flexor and extensor use, or co-contraction. Co-contraction can stabilize and redirect joint forces. However, co-contraction can push and pull on the femur and tibia that exacerbate OA symptoms and make walking difficult. Such movements are quantifiable by limb dynamics (i.e., linear acceleration and jerk); thus, this study examines limb dynamics and its relationship with co-contraction and OA related walking difficulty.
Three groups of age-and-sex-matched subjects with and without OA and walking difficulty (N = 13 per group) walked with electromyography (EMG) on the knee extensors and flexors and inertial measurement units (IMUs) at the femur and tibia. We calculated co-contraction from antagonistic EMG signals and linear acceleration and its derivative jerk from IMUs. We determined group differences using one-way ANOVAs, nonparametric equivalence, and effect sizes, and main and interaction effects of walking difficulty with regression modeling.
Medium effect sizes and differences for femoral acceleration (d = 0.64; P = .02) and jerk (d = 0.51; P = .01) were observed between with and without knee OA. Medium to large effect sizes (r = 0.33 to 0.51 and d = 0.81 to 0.97) and differences (P = .01 to 0.05) for tibial acceleration and jerk were obsevered between with and without walking difficulty. Walking difficulty moderated the relationship between tibial jerk and co-contraction (p < .05).
Tibial jerk differences were observed based on walking difficulty. The significant interaction effect suggested that walking difficulty explained the relationship between limb dynamics and co-contraction. Perhaps co-contraction levels used by those with knee OA and no walking difficulty are optimal as compared to those with walking difficulty.
Golf requires proper dynamic balance to accurately control the club head through a harmonious coordination of each human segment and joint. In this study, we evaluated the ability for dynamic balance during a golf swing by using the centre of mass (COM)-centre of pressure (COP) inclination variables. Twelve professional, 13 amateur and 10 novice golfers participated in this study. Six infrared cameras, two force platforms and SB-Clinic software were used to measure the net COM and COP trajectories. In order to evaluate dynamic balance ability, the COM-COP inclination angle, COM-COP inclination angular velocity and normalised COM-COP inclination angular jerk were used. Professional golfer group revealed a smaller COM-COP inclination angle and angular velocity than novice golfer group in the lead/trail direction (P < 0.01). In the normalised COM-COP inclination angular jerk, the professional golfer group showed a lower value than the other two groups in all directions. Professional golfers tend to exhibit improved dynamic balance, and this can be attributed to the neuromusculoskeletal system that maintains balance with proper postural control. This study has the potential to allow for an evaluation of the dynamic balance mechanism and will provide useful basic information for swing training and prevention of golf injuries.
The purposes of this study were to clarify which period of the stance phase shows the greatest decrease in the smoothness of the knee joint movement and to analyze the relationships between kinetic variables and the smoothness of the knee joint movement during the stance phase using the angular jerk cost (AJC). The study subjects were 11 healthy adults. To clarify the relationships between the kinetic variables and the AJC, Pearson's product correlation coefficients were calculated for the AJC and three kinetic variables. The AJC in the early stance phase was significantly larger than those in the other three phases, and it was confirmed that the early stance phase showed the greatest decrease in smoothness of the knee joint movement. Furthermore, there was a positive correlation between the AJC and the vertical component of the ground reaction force in the early stance phase. Correlations between the AJC and the kinetic variables were also found in the other three phases. Regarding evaluation of the smoothness of the knee joint movement using the AJC based on the present results, the AJC may be an important index for understanding the dynamics of the knee joint in the early stance phase.
The angular jerk cost (AJC) was proposed to objectively represent the smoothness of joint movement by calculating the time-dependent changes in acceleration during motion. There are currently no reports focusing on smoothness using AJC measurements of the knee joint movement during the stance phase of gait. The purpose of this study was to verify whether a reduced walking speed affects the smoothness of the knee joint movement during the stance phase of gait. The gaits of 12 healthy adults were assessed. A slower walker showed a significant reduction in the AJC value in the period between the initial contact and the loading response, as compared with someone walking at a comfortable speed.
The maximum ground reaction force of the stance phase at a comfortable walking speed was significantly larger than that at a slower walking speed. Thus, although the smoothness of the knee joint was impaired by a rapid load in the early stance phase, a slower walking speed reduced the ground reaction force and angular acceleration of the knee joint and created a smoother movement. The AJC can be an important index for understanding the smoothness of the knee joint in the early stance phase.
This study was undertaken to investigate the effect of low-level loading on digit tracking and the associated physiological tremors in the moving and the stationary digits. Sixteen healthy adults conducted positional tracking with the middle finger under the loaded and unloaded conditions; meanwhile, trajectory of the middle finger, electromyographic activities of the extensor digitorum (ED)/flexor digitorum superficialis, and physiological tremors of the index, middle, ring, and little fingers were recorded. The results showed that load imposition (<70 g) on the middle finger improved tracking congruency, in association with reduction of inter-digit tremor coupling and enhancement of tiny movement jerks. Principal component analysis suggested that inertial load suppressed the 8-12 Hz central rhythm but potentiated the 25-40 Hz coherence spectra of major principal components and electromyographic signals of the ED. It was concluded that low-level inertial load could facilitate corrective movement adjustments and selective digit control during manual tracking, relevant implicitly to decreased common central drive and enhanced heteronymous reflex loops.
This study addressed the dimensionality and construct validity of physical functional capacity within the context of performance-based measures. Sixty-two individuals (M= 70yrs), classified as "healthy" based on several screening procedures, completed a battery of standard neuromuscular and physical performance tests. Scores were submitted to a principal components factor analysis to examine and describe potential dimensions of physical functional capacity. Orthogonal and oblique rotations of axes were performed. Six interpretable and meaningful factors were extracted from the orthogonal rotation and identified as strength, unimanual dexterity, mobility/agility, static balance, general upper-extremity control, and movement planning speed. The results indicated that physical functioning in older persons is a multidimensional construct. Moreover, assessment techniques involving performance-based measures should be designed to diagnose physical functional status in separate motor dimensions and plan intervention approaches accordingly.
We propose a novel indicator for smoothness of movement, i.e., the power spectrum entropy of the acceleration time-series, and compare it with conventional indices of smoothness. For this purpose, nineteen healthy adults (21.3+/-2.5 years old) performed the task of raising and lowering a beaker between the level of the umbilicus and eye level under the two following conditions: one with the beaker containing water and the other with the beaker containing a weight of the same mass as the water. Moving the beaker up and down when it contained water required extra control to prevent the water from being spilled. This means that movement was not as smooth as when the beaker contained a weight. Under these two conditions, entropy was measured along with a traditional indicator of smoothness of movement, the jerk index. The entropy could distinguish just as well as the jerk index (p<0.01) between when water was used and when the weight was used. The entropy correlated highly with the jerk index, with Spearman's rho at 0.88 (p<0.01). These results showed that the entropy derived from the spectrum of the acceleration time-series during movement is useful as an indicator of the smoothness of that movement.
Isometric handgrip force, isokinetic knee flexion and extension torque, and anthropometric data were obtained on 67 older men and women (ranging in age from 45 to 75 years, mean 59.7 years). Hydrostatic and skinfold estimates of lean body mass were quite closely correlated with each other in this sample (r = 0.93). Handgrip force, isokinetic knee flexion and extension torque, and lean mass all decreased by 6-8% per decade over the age span examined, although in the men the loss was most marked in terms of handgrip and lean mass, whereas in the women the loss of torque in the knee muscles was dominant. Because of these differences, the handgrip data were only weakly correlated with the isokinetic strength measurements (r = 0.22), and the isokinetic data were more strongly related to lean body mass and body mass. The optimum equation for a field prediction of isokinetic strength in this age group (a combination of age, sex, age-sex interaction and lean body mass) has an error approaching 25%, with a multiple r2 of 0.37, and a standard error of the estimate (s.e.e.) of 24.5%. It is concluded that handgrip data and slow isokinetic torque measurements evaluate relatively independent aspects of the ageing of muscular function.
This paper reviews 92 papers related to the biomechanics of low-back pain and potential risk factors associated with age and heavy manual work. The functional anatomy of the lumbar region is reviewed with special emphasis on tissue changes caused by normal aging. A brief explanation of the biomechanics associated with load lifting, twisting, and bending tasks common to manual work in industry is given. It is argued that certain work conditions may present a special risk to an older individual's low back. The need for further research to test hypothesized risk factors believed to be associated with the older worker is indicated.
The concept of a generalized aging effect on a generalized balance mechanism is discussed, and an alternative, multicomponent approach to understanding the heterogeneity of postural dyscontrol in the elderly is presented. Neural sensorimotor components of normal postural control mechanisms are identified and discussed. The effects of Parkinson's disease, hemiplegia, cerebellar degeneration, peripheral vestibular loss, and other disorders on the components of postural control are summarized. Quantitative posturography is advocated to detect preclinical manifestation of multiple musculoskeletal and neuromuscular pathologies and reduced compensatory abilities in posturally unstable elderly adults.
This paper presents studies of the coordination of voluntary human arm movements. A mathematical model is formulated which is shown to predict both the qualitative features and the quantitative details observed experimentally in planar, multijoint arm movements. Coordination is modeled mathematically by defining an objective function, a measure of performance for any possible movement. The unique trajectory which yields the best performance is determined using dynamic optimization theory. In the work presented here, the objective function is the square of the magnitude of jerk (rate of change of acceleration) of the hand integrated over the entire movement. This is equivalent to assuming that a major goal of motor coordination is the production of the smoothest possible movement of the hand. Experimental observations of human subjects performing voluntary unconstrained movements in a horizontal plane are presented. They confirm the following predictions of the mathematical model: unconstrained point-to-point motions are approximately straight with bell-shaped tangential velocity profiles; curved motions (through an intermediate point or around an obstacle) have portions of low curvature joined by portions of high curvature; at points of high curvature, the tangential velocity is reduced; the durations of the low-curvature portions are approximately equal. The theoretical analysis is based solely on the kinematics of movement independent of the dynamics of the musculoskeletal system and is successful only when formulated in terms of the motion of the hand in extracorporal space. The implications with respect to movement organization are discussed.
A review of the biomechanics of weight lifting as it relates to low-back stresses is presented first. This serves as the basis for the development of a Lifting Strength Rating (LSR) methodology. Then a study is reported wherein the LSR methodology is used to evaluate 103 jobs having various amounts of required two-handed load lifting. The 411 people populating these jobs were also evaluated. For a period of one year following their evaluation, any low-back pain problems in the group were noted. The primary result of the field study is that the incidence rate of low-back pain is correlated with higher lifting strength requirements as determined by assessment of both the location and magnitude of the load lifted. It is, therefore, recommended that load lifting be considered potentially hazardous, and that the LSR methodology be used to guide corrective actions.
This paper presents a mathematical model which predicts both the major qualitative features and, within experimental error, the quantitative details of a class of perturbed and unperturbed large-amplitude, voluntary movements performed at intermediate speed by primates. A feature of the mathematical model is that a concise description of the behavioral organization of the movement has been formulated which is separate and distinct from the description of the dynamics of movement execution. Based on observations of voluntary movements in primates, the organization has been described as though the goal were to make the smoothest movement possible under the circumstances, i.e., to minimize the accelerative transients. This has been formalized by using dynamic optimization theory to determine the movement which minimizes the rate of change of acceleration (jerk) of the limb. Based on observations of muscle mechanics, the concept of a "virtual position" determined by the active states of the muscles is rigorously defined as one of the mechanical consequences of the neural commands to the muscles. This provides insight into the mechanics of perturbed and unperturbed movements and is a useful aid in the separation of the descriptions of movement organization and movement execution.
One hypothesis for the generation of spatially oriented arm movements by the central nervous system is that a desired joint position is determined by the ratio of the tensions of agonist and antagonist muscles. According to this hypothesis, the transition between equilibrium states should be solely a function of the contraction time of the motor units and the mechanical properties of the arm. We tested this hypothesis in intact and deafferented rhesus monkeys by holding the forearm and measuring the accelerative transient after release of the forearm and by directly measuring the time course of the increase in torque during the movement. Both methods indicated an average time of 400 msec for attaining peak torque in a movement with a duration of 700 msec. In addition, by displacing the arm from its normal trajectory during the movement, we observed that the arm returned neither to the initial nor to the final equilibrium positions, but to points intermediate between them. We conclude that the processes underlying trajectory formation must be more complex than a simple switch between one equilibrium position and another.
Objective:
To compare the ability of three modelling approaches to resolve the muscle and joint forces in a lumbar spine model during dynamic sagittal plane lifting.
Design:
Trunk muscle forces, spine compression, and coactivity predicted through double linear optimization, EMG-assisted, and EMG assisted by optimization approaches were compared.Background. The advantages of EMG-based approaches are known from static task analyses. Limited assessment has been made for dynamic lifting.
Methods:
Eleven male subjects performed sagittal plane lifting-lowering at fixed cadence from 0 degrees to 45 degrees of trunk flexion with and without an external load of 12 kg. Three-dimensional kinematics and dynamics as well as surface EMG provided inputs to a 12 muscle lumbar spine model.
Results:
Trunk muscle coactivity was different between the modelling approaches but spine compression was not. Both EMG-based approaches were sensitive to trunk muscle coactivity and imbalance in left-right muscle forces during sagittal plane lifting. Overall, the best correlations between predicted forces and EMG as well as between forces predicted by different modelling approaches were obtained with the EMG-based models. Only the EMG assisted by optimization approach simultaneously satisfied mechanical and physiological validity.
Conclusions:
Both EMG-based approaches demonstrated their potential to detect individual trunk muscle strategies. A more detailed trunk anatomy representation would improve the EMG-assisted approach and reduce the adjustment to muscle force gain through EMG assisted by optimization.
Relevance:
Injury to the lumbar spine could command alternative strategies of motion to attenuate pain and damage. To understand these strategies, the ideal lumbar spine model should predict individual muscle force patterns and satisfy mechanical equilibrium.
Even simple movements require the coordination of a bewildering number of muscles. How does the brain cope with this task? How can we begin to understand this extraordinarily complex behavior? One effective way is to formulate a quantitative, mathematical theory of movement control. A theory simplifies matters because complex, detailed and experimentally testable predictions can be derived from basic concepts. This article will briefly review some attempts to develop a quantitative theory of motor coordination.
Maximum values for isometric strength, dynamic strength, and speed of movement (MEV) in the quadriceps muscle were measured in 114 male subjects who were between 11 and 70 yr. Biopsy samples were taken from the quadriceps muscle in 51 of the subjects (22-65 yr. old). Isometric and dynamic strength increased up to the third decade, remained almost constant to the fifth decade, and then decreased with increasing age. However, no measurable external atrophy of the quadriceps muscle, explaining the decline in strength, could be seen in old age. Histochemical changes in the muscle tissue such as decreased proportion of type II fibers and a selective atrophy of type II fibers, were seen with increasing age. The strength decline in old age was also observed to correlate significantly with the type II fiber area. Multiple regression analyses indicated, however, that mechanisms other than the type II fiber atrophy might be responsible for the decline in strength performance during aging. The implications of these findings are discussed.
Net joint moments are often used to quantify the loading of structures (e.g. the intervertebral disc at L5S1) during lifting. This quantification method is also used to evaluate the loading of the knee, for instance, to determine the effect of backlifting as opposed to leglifting. However, the true loading of the joint as derived from net joint moments can be obscured by a possible co-contraction of antagonists. To unravel the mechanisms that determine the net joint moments in the knee, the leglift was compared to the backlift. Although a completely different net knee moment curve was found when comparing the two lifting techniques, it appeared to be closely related to the ground reaction force vector and its orientation with respect to the joint centre of rotation (R > 0.995). This close relation was established by co-contraction of both flexors and extensors of the knee. Furthermore, a close relation appeared to exist between the joint moment difference between hip and knee and the activity difference between rectus femoris muscle and hamstring (R = 0.72 and 0.83 in leglift and backlift, respectively). The knee-ankle joint moment difference and the activity of the gastrocnemius showed a close relation as well (R = -0.89 and 0.96 in leglift and backlift, respectively). These relations can be interpreted as a mechanism to distribute net moments across joints. It is concluded that during lifting tasks the intermuscular coordination is aimed at coupling of joint moments, such that the ground reaction force points in a direction that provides balance during the movement. The use of net joint moments as direct indicators for joint loading (e.g. knee) seems, therefore, questionable.
The effects of aging on maximal voluntary strength and on the isometric twitch were determined in the ankle dorsiflexor and plantarflexor muscles of 111 healthy men and women aged 20-100 yr. Men were found to be stronger than women at all ages. In both sexes, the average values for maximum voluntary strength of the dorsiflexors and plantarflexors began to decline in the 6th decade. Although the absolute loss of strength was greater for the plantarflexor muscles, the relative losses were similar in the two muscle groups. During maximum voluntary effort, stimulation of motor nerves produced no additional torque in the majority of elderly men and women, indicating that these subjects remained able to utilize their descending motor pathways for optimal muscle activation. Comparisons of muscle compound action potentials, twitch torques, and muscle cross-sectional areas suggested that a decrease in excitable muscle mass was entirely responsible for the lower strength of the elderly. An additional effect of aging was the gradual prolongation of twitch contraction and half-relaxation times throughout the adult life-span.
The purpose of this study was to investigate the lifting characteristics of elders with functional limitations using burden lifting smoothness, trunk angular momentum, and back and hip torque, and to correlate these characteristics with strength and functional measures.
Thirty elders (65-89 years old) consented to biomechanical analysis of lifting, gait, and chair rise, and to maximum isometric strength testing of the hip and knee extensors and shoulder flexors. Jerk, the rate of change of acceleration, is a measure of smoothness of motion. We calculated peak vertical jerk of the box at the beginning part of the lift. Momentum is the product of mass and velocity. HAT (head, arms, trunk) angular momentum was calculated during chair rise.
Hip extensor strength correlated positively with box jerk, as did box jerk and peak trunk angular momentum between subjects. There was an inverse correlation between peak upper body angular momentum when lifting a box from floor to knee height, and gait speed normalized to body weight. There was a positive correlation between trunk angular momentum during lifting and trunk angular momentum during chair rise.
Stronger subjects used more peak vertical box jerk and more trunk peak angular momentum to lift a box from floor to knee height. Stronger subjects who used more HAT angular momentum during free speed chair rise also used more trunk peak angular momentum during the first phase of the lift, but lifting characteristics were independent of gait velocity. Weaker subjects used less peak momentum and peak jerk, choosing instead a more conservative, and apparently more stable, lifting strategy. Before counseling elderly patients on proper body mechanics for lifting, clinicians should assess strength and functional status. Weak elders should be taught a lifting strategy that allows them to maintain optimal balance, and to lift without jerking the load.
Few reports address lifting in disabled elders. Resistance training may facilitate function by improving coordination and muscular recruitment in common lifting tasks. Subjects were considered "functionally limited" if they reported a limitation in at least 1 of 9 possible functional areas listed on the Short-Form Health Survey physical function scale (SF-36), excluding the vigorous activity item. Eighty-nine functionally limited elders (60.3 to 89.8 years old) consented to participate in an intervention trial consisting of a 6-month in-home video-facilitated resistance exercise program using elastic bands. Biomechanical variables (leg extensor power, work, squared jerk), temporal outcomes (lift time and time to peak leg powers), and leg extensor strength were analyzed with the use of analysis of variance (ANOVA) between the (1) experimental group versus control group and the (2) subgroup of the weakest third of subjects (pretest leg extensor strength as percent of body weight [BW]). The experimental group had significant improvements in strength in knee extension (16.7%) and hip extension (20.5%). Resistance-trained weak subjects significantly increased hip extension strength compared to controls. A trend toward improved performance in lifting--decreased total lift time--was noted in the resistance-trained subjects. Significant correlations were found between total leg extension power, total leg extension strength, total work, and lift time. Resistance-trained disabled elders demonstrated strength benefits and several trends consistent with improved coordination and more efficient lifting. Leg-muscle power was related to better functional performance in lifting.
To test the hypothesis that older age significantly affects hip abduction and adduction joint torque-time generating capability in women.
Cross-sectional study, wherein subjects were tested in a supported standing position.
University human performance laboratory.
Seventy-six healthy, adult women (38 young; 38 old).
Not applicable.
The dependent variables were peak isometric torque and its corresponding torque rate and average peak isokinetic torque. Age group differences were assessed by analysis of variance.
Isometric peak torques were significantly lower in older women (P</=.001) for hip abduction (34%) and adduction (24%). Decreases with age were also significant for isometric rates of torque for both muscle groups (P</=.001). Average isokinetic peak torque of hip abduction and adduction showed even greater declines in older women versus the young (P</=.001) with losses of 44% and 56%, respectively.
The hip abductor and adductor torques showed relatively marked age-related changes. To enhance balance assessment and treatment, and to reduce the risk of falls and related injuries in older women, greater focus should be placed on understanding the role of joint torque-time changes on frontal plane balance control.
Motion differences in a repetitive lifting task have been described previously using differences in the timing of body angle changes during the lift. These timing changes relied on small differences of motion and are difficult to measure. The purpose of this study was to evaluate shoulder jerk (rate of change of acceleration) in a repetitive lifting task as an alternative parameter to detect differences of motion between controls and chronic lower back pain (CLBP) patients and to measure the impact of a rehabilitation program on jerk. The jerk calculation was a noisy measure, since jerk is the third derivative of position; consequently a simulation was performed to evaluate smoothing methods. Woltring's generalized cross-validation spline produced the best estimates of the third derivative and was fit to subject data. The root mean square (rms) amplitude of jerk was used for comparison. Significant group differences were found. CLBP patients performed lifts with lower jerk values than controls and, as the task progressed, both groups increased jerk. After completion of a rehabilitation program, CLBP patients performed lifts with greater rms jerk. In general, patients performed lifts with lower jerk values than controls, suggesting that pain impacts lifting style.