The association between knee joint biomechanics and neuromuscular control and moderate knee osteoarthritis radiographic and pain severity.

OBJECTIVE: The objective of this study was to determine the association between biomechanical and neuromuscular factors of clinically diagnosed mild to moderate knee osteoarthritis (OA) with radiographic severity and pain severity separately. METHOD: Three-dimensional gait analysis and electromyography were performed on a group of 40 participants with clinically diagnosed mild to moderate medial knee OA. Associations between radiographic severity, defined using a visual analog radiographic score, and pain severity, defined with the pain subscale of the WOMAC osteoarthritis index, with knee joint kinematics and kinetics, electromyography patterns of periarticular knee muscles, BMI and gait speed were determined with correlation analyses. Multiple linear regression analyses of radiographic and pain severity were also explored. RESULTS: Statistically significant correlations between radiographic severity and the overall magnitude of the knee adduction moment during stance (r²=21.4%, P=0.003) and the magnitude of the knee flexion angle during the gait cycle (r²=11.4%, P=0.03) were found. Significant correlations between pain and gait speed (r²=28.2%, P<0.0001), the activation patterns of the lateral gastrocnemius (r²=16.6%, P=0.009) and the medial hamstring (r²=10.3%, P=0.04) during gait were found. The combination of the magnitude of the knee adduction moment during stance and BMI explained a significant portion of the variability in radiographic severity (R(2)=27.1%, P<0.0001). No multivariate model explained pain severity better than gait speed alone. CONCLUSIONS: This study suggests that some knee joint biomechanical variables are associated with structural knee OA severity measured from radiographs in clinically diagnosed mild to moderate levels of disease, but that pain severity is only reflected in gait speed and neuromuscular activation patterns. A combination of the knee adduction moment and BMI better explained structural knee OA severity than any individual factor alone.

The need for muscle co-contraction prior to a landing.

In landings from a flight phase the mass centre of an athlete experiences rapid decelerations. This study investigated the extent to which co-contraction is beneficial or necessary in drop landings, using both experimental data and computer simulations. High speed video and force recordings were made of an elite martial artist performing drop landings onto a force plate from heights of 1.2, 1.5 and 1.8m. Matching simulations of these landings were produced using a planar 8-segment torque-driven subject-specific computer simulation model. It was found that there was substantial co-activation of joint flexor and extensor torques at touchdown in all three landings. Optimisations were carried out to determine whether landings could be effected without any co-contraction at touchdown. The model was not capable of landing from higher than 1.05m with no initial flexor or extensor activations. Due to the force-velocity properties of muscle, co-contraction with net zero joint torque at touchdown leads to increased extensor torque and decreased flexor torque as joint flexion velocity increases. The same considerations apply in any activity where rapid changes in net joint torque are required, as for example in jumps from a running approach.

Effects of age on human muscle torque, velocity, and power in two muscle groups.

The purpose of this study was to test the hypotheses that, under isovelocity conditions, older compared with young humans would 1). be slower to reach target velocity and 2). exhibit a downward shift in the torque-velocity and power-velocity relationships in the ankle dorsiflexor and knee extensor muscles. We studied 12 young (26 +/- 5 yr, 6 men/6 women) and 12 older (72 +/- 6 yr, 6 men/6 women) healthy adults during maximal voluntary concentric contractions at preset target velocities (dorsiflexion: 0-240 degrees /s; knee extension: 0-400 degrees /s) using an isokinetic dynamometer. The time to target velocity was longer in older subjects in the dorsiflexors and knee extensors (both P

Muscular and metabolic costs of uphill backpacking: are hiking poles beneficial?

PURPOSE: The purpose of the present study was to compare pole and no-pole conditions during uphill backpacking, which was simulated on an inclined treadmill with a moderately heavy (22.4 kg, 30% body mass) backpack. METHODS: Physiological measurements of oxygen consumption, heart rate, and RPE were taken during 1 h of backpacking in each condition, along with joint kinematic and electromyographic comparisons from data collected during a third test session. RESULTS: The results showed that although imposing no metabolic consequence, pole use elicited a longer stride length (1.27 vs 1.19 m), kinematics that were more similar to those of unloaded walking, and reduced activity in several lower extremity muscles. Although pole use evoked a greater heart rate (113.5 vs 107 bpm), subjects were backpacking more comfortably as indicated by their ratings of perceived exertion (10.8 vs 11.6). The increased cardiovascular demand was likely to support the greater muscular activity in the upper extremity, as was observed in triceps brachii. CONCLUSION: By redistributing some of the backpack effort, pole use alleviated some stress from the lower extremities and allowed a partial reversal of typical load-bearing strategies.

An integrated biomechanical analysis of high speed incline and level treadmill running.

PURPOSE: Recent sprint training regimens have used high-speed incline treadmill running to provide enhanced loading of muscles responsible for increasing forward running speed. The goal of this study was to document the joint kinematics, EMG, and swing-phase kinetics of incline treadmill running at 4.5 m x s(-1) with a 30% grade, and compare these data to that of level running under similar conditions. METHODS: Sagittal plane video (200 Hz) and EMG from eight lower extremity muscles were recorded during each of three locomotion conditions: incline running at 4.5 m x s(-1) and 30% grade (INC), level running at 4.5 m x s(-1) (LSS), and level running at the same stride frequency as INC (LSSF). A rigid body model was used to estimate net muscle power and work values at the hip, knee, and ankle during swing. Timing and amplitude of EMG signals for each muscle relative to footstrike were compared between conditions. RESULTS: Stride frequency and percentage of stride spent in stance were significantly higher during INC (1.78 Hz; 32.8%) than in the LSS (1.39 Hz; 28.8%) condition. Stride frequency played an important role, as most measures were more similar between INC and LSSF. Extensor range of motion of all joints during push-off was higher for INC. During INC, average EMG amplitude of the gastrocnemius, soleus, rectus femoris, vastus lateralis, and gluteus maximus were higher during stance, whereas the hamstrings activity amplitudes were lower. Average power and energy generated during hip flexion and extension in the swing phase were greatest during INC. CONCLUSIONS: These data suggest that compared with LSSF and LSS, INC provides enhanced muscular loading of key mono- and bi-articular muscles during both swing and stance phases.

Influence of Q-angle on lower-extremity running kinematics.

STUDY DESIGN: Two-group posttest-only comparison. OBJECTIVE: To assess the influence of the Q-angle on the 3-dimensional lower-extremity kinematics during running. BACKGROUND: An excessive Q-angle has been implicated in the development of knee injuries by altering the lower-extremity locomotion kinematics. Previous investigations using 2-dimensional analyses during walking did not support this hypothesis. METHODS AND MEASURES: We hypothesized that individuals with Q-angles more than 15 degrees would display an increase in rearfoot eversion and tibial internal rotation during running. Thirty-two nonimpaired subjects (men: n = 16, mean age = 22 +/- 3 years; women: n = 16, mean age = 23 +/- 3 years) ran over ground, and 3-dimensional kinematic data were collected from the right lower extremity. Subjects with a Q-angle of 15 degrees or less comprised the low-Q-angle group, whereas those with Q-angles of more than 15 degrees comprised the high-Q-angle group. Segment and joint maximum angles and the times when the maxima occurred during stance were measured. RESULTS: The Q-angle magnitude did not increase the maximum segment or joint angles during running. The groups displayed similar maximum angles for rearfoot eversion (low Q-angle, -15.5 +/- 5.0 degrees; high Q-angle, -15.6 +/- 6.6 degrees) and tibial internal rotation (low Q-angle, -8.8 +/- 4.8 degrees; high Q-angle, -6.8 +/- 5.1 degrees). The high-Q-angle group (39.5 +/- 16.3%) achieved maximum tibial internal rotation later in the stance phase than the low-Q-angle group (28.8 +/- 10.7%). CONCLUSIONS: In support of the previous investigations involving Q-angle influences on kinematics, our study did not reveal any differences between groups in maximum joint or segment angles. The kinematic information did reveal that the high-Q-angle group displayed an increase in time to maximum tibial internal rotation. The impact of this single factor on producing knee injury is unknown.

How strongly is muscle activity associated with joint moments?

In this commentary we question whether the relationship between muscle activity and joint moments is the same for natural motor tasks as for controlled experimental situations. An important consideration in this regard is the identification of the correct electromechanical delay (EMD) for comparing EMG and joint moment data. Data from recent cycling studies are used to illustrate the importance of EMD, and how changing task constraints can alter the relation between muscle activity and joint moment balance for bi-articular antagonist pairs.

Coefficient of cross correlation and the time domain correspondence.

Time histories of neuromuscular and mechanical variables of human motion are often compared by using discrete timing events (onset, offset, time to peak, zero crossing, etc). The determination of these discrete timing points is often subjective and their interpretation can cause confusion when attempting to compare patterns. In this technical note, cross correlation and the 95% confidence interval of its maximum value are proposed as an objective means of pattern recognition and comparison. EMG patterns of cycling at different cadences were used as an example to demonstrate the effectiveness of this cross correlation method in identification of changes between conditions. Using a standard method of threshold identification, different onset and offset values can be found by using different thresholds, and the sequence of the offset timings between conditions can change. This is a clear indication of the inherent subjectivity with these discrete timing methods. In contrast, calculation of cross correlation for incremental phase shifts permits the identification of a maximal value that is an objective measure of the actual phase shifting between the two time series. Further, calculation of the 95% confidence interval allows one to determine whether the phase shifting is statistically significant. The application of this method is not limited to EMG pattern comparison, and can also be applied to other time histories such as kinematic and kinetic parameters of human motion.

Muscle coordination in cycling: effect of surface incline and posture.

The purpose of the present study was to examine the neuromuscular modifications of cyclists to changes in grade and posture. Eight subjects were tested on a computerized ergometer under three conditions with the same work rate (250 W): pedaling on the level while seated, 8% uphill while seated, and 8% uphill while standing (ST). High-speed video was taken in conjunction with surface electromyography (EMG) of six lower extremity muscles. Results showed that rectus femoris, gluteus maximus (GM), and tibialis anterior had greater EMG magnitude in the ST condition. GM, rectus femoris, and the vastus lateralis demonstrated activity over a greater portion of the crank cycle in the ST condition. The muscle activities of gastrocnemius and biceps femoris did not exhibit profound differences among conditions. Overall, the change of cycling grade alone from 0 to 8% did not induce a significant change in neuromuscular coordination. However, the postural change from seated to ST pedaling at 8% uphill grade was accompanied by increased and/or prolonged muscle activity of hip and knee extensors. The observed EMG activity patterns were discussed with respect to lower extremity joint moments. Monoarticular extensor muscles (GM, vastus lateralis) demonstrated greater modifications in activity patterns with the change in posture compared with their biarticular counterparts. Furthermore, muscle coordination among antagonist pairs of mono- and biarticular muscles was altered in the ST condition; this finding provides support for the notion that muscles within these antagonist pairs have different functions.

Energy absorption of impacts during running at various stride lengths.

PURPOSE: The foot-ground impact experienced during running produces a shock wave that is transmitted through the human skeletal system. This shock wave is attenuated by deformation of the ground/shoe as well as deformation of biological tissues in the body. The goal of this study was to investigate the locus of energy absorption during the impact phase of the running cycle. METHODS: Running speed (3.83 m x s[-1]) was kept constant across five stride length conditions: preferred stride length (PSL), +10% of PSL, -10% of PSL, +20% of PSL, and -20% of PSL. Transfer functions were generated from accelerometers attached to the leg and head of ten male runners. A rigid body model was used to estimate the net energy absorbed at the hip, knee, and ankle joints. RESULTS: There was an increasing degree of shock attenuation as stride length increased. The energy absorbed during the impact portion of the running cycle also increased with stride length. Muscles that cross the knee joint showed the greatest adjustment in response to increased shock. CONCLUSION: It was postulated that the increased perpendicular distance from the line of action of the resultant ground reaction force to the knee joint center played a role in this increased energy absorption.

Impact shock and attenuation during in-line skating.

Although impact and shock attenuation associated with foot contact during running has been studied extensively, much less is known about these phenomena during in-line skating (ILS). The purpose of this study was to describe these impact characteristics for ILS and to test the hypothesis that there is lower impact shock during ILS than in running at preferred velocities. Subjects ran and skated on a treadmill at preferred velocity, with low-mass accelerometers attached to both the distal tibia and head. Tibia and head acceleration data during stance were used to calculate peak acceleration (PA), peak frequency (PF), and median frequency (MedF). Impact attenuation (IA) between the tibia and head was quantified by comparison of PA values and by calculating a transfer function between the head and tibia frequency spectra. PA, PF, and MedF values were significantly lower in ILS than in running for both tibial and head data, whereas ILS was similar between the two movements. The ILS condition exhibited almost no power in the frequency range between 10 and 20 Hz, which has been associated with the foot impacting the ground. It is concluded that in-line skating results in less impact shock to the body with each foot contact, and may be a useful exercise modality for those wishing to reduce impact shock during aerobic training.

From cognition to biomechanics and back: the end-state comfort effect and the middle-is-faster effect.

Consistent preferences for particular types of movement suggest criteria for movement selection. These can be important when, as is usually the case, infinitely many movements allow a task to be achieved. The experiments reported here were designed to identify the source of a strong preference observed in earlier object-manipulation studies. In those earlier studies, subjects usually grabbed objects to be moved from one location to another in a way that afforded a comfortable final posture rather than a comfortable initial posture (the end-state comfort effect). The comfortable final state usually allowed the forearm to be at or near the middle of its range of motion on the pronation-supination dimension. The hypothesis tested here was that the end-state comfort effect stemmed from an expectation that movements can be made more quickly in the middle of the pronation-supination range than at either extreme. To test this hypothesis, we asked subjects, in the first experiment, to perform a handle rotation task that demanded little or no precision and so no need to make rapid to-and-fro homing-in movements near the end of the rotation. Half the subjects did not show the end-state comfort effect, in contrast to all previous studies, where all subjects showed the effect. An incidental finding of the first experiment was that handle rotations that ended at or near the end of the range of motion took longer than handle rotations that ended at or near the middle of the range of motion. To test the latter result more carefully, we asked subjects, in Experiments 2 and 3, to oscillate the forearm as quickly as possible, either in the supination part of the forearm rotation range, in the middle part of the range, or in the pronation part of the range. As predicted, oscillation frequencies were highest in midrange, and this was true for both hands. The results as a whole have implications for the relation between cognitive psychology and biomechanics, and for human factors.

A simulation study of vertical jumping from different starting postures.

This paper addresses the question of whether maximal vertical jump height depends on initial jumping posture. A direct dynamics computer simulation approach was used to avoid subject preference and practice effects. The human body was modeled as four rigid segments connected by ideal hinge joints, with movement constrained to the sagittal plane and driven by three single-joint torque actuators. Maximal height jumps were found for each of 125 different initial postures. For each initial posture, the optimal pattern of joint torque actuator onset times was found using a multidimensional simplex algorithm searching for maximal jump height. The model results revealed that maximal jump height is relatively insensitive to initial posture, but that the pattern of joint torque onset times necessary to effect these optimal heights varies considerably. Model kinematics indicate that the variability in onset times is necessary to allow the body to re-orient itself in different ways during the downward countermovement phase. This variable re-orientation strategy is followed by a more stereotyped upward thrust phase that is similar despite the differences in starting postures. Model center of mass, joint and segmental kinematics show many features found in experimental studies of jumping, despite the exclusive use of single torque actuators. However, a proximal-to-distal sequence of joint coordination was not found, possibly because of the omission of antagonist and bi-articular muscles. The results suggest that similar vertical jump heights should be obtained using a wide range of initial starting positions.

Physiology and interpretation of the electromyogram.

The purpose of this review is to consider some issues in the interpretation of the electromyogram (EMG) and to discuss current areas of controversy regarding use of the EMG. We consider the underlying physiology and origin of the EMG signal and offer an abbreviated discussion of measurement issues and selected factors that affect the characteristics of the EMG signal. We discuss many of the problems affecting interpretation, including normalization, crosstalk, and issues specific to contraction. In the final section, we consider topics of current interest in electromyography, such as muscle fatigue, task specificity, multichannel representations, and muscle fiber conduction velocity. We present, in addition, alternative analysis techniques. This review should interest researchers and clinicians who seek to obtain the valuable information inherent in the EMG while respecting the potential sources of variance and misinterpretation.

Improved agreement of foot segmental power and rate of energy change during gait: inclusion of distal power terms and use of three-dimensional models.

Traditional models used to calculate foot segmental power have yielded poor agreement between foot power and the rate of energy change during the stance phase of gait and limited the applicability of foot segmental power analyses to swing phase only. The purpose of this study was to improve the agreement of foot segmental power and rate of energy change by using more inclusive models to calculate foot segmental power and energy. The gait of 15 adult subjects was studied and models were used to calculate foot segmental power that included either the proximal terms only (Model P, the most common method in the literature) or both proximal and distal terms (Model PD, a mathematically complete model). Power and energy terms were computed in two ways, from sagittal plane vector components only (two-dimensional condition) and from complete three-dimensional components (three-dimensional condition). Results revealed that the more inclusive the model, the higher the agreement of foot power and rate of energy change. During stance phase, Model P produced poor agreement (r(c) = 0.108) for both two-dimensional and three-dimensional conditions, Model PD-2D yielded higher agreement (r(c) = 0.645), and Model PD-3D exhibited nearly perfect agreement (r(c) = 0.956). The advantages of a segmental power analysis include the ability to identify the mechanisms of energy transfer into and out of the foot during movement. The results of this study suggest that foot power analyses are valid when using Model PD-3D to describe foot function during locomotion.

An Energetic Comparison of Symmetrical and Asymmetrical Human Gait.

This article contrasts the mechanical energy profiles of asymmetrical galloping with those of symmetrical running in adult humans. Seven female subjects were filmed while performing overground running and galloping at their preferred velocities. A previous study (Whitall & Caldwell, 1992) showed that kinematic differences between these gait modes included higher preferred velocity for running than galloping, with distinct differences in interlimb coordination but surprisingly similar intralimb patterns. Energetically, in the present study the whole body center of mass during galloping was found to behave much as it does in walking; kinetic and potential energy profiles were out of phase, as compared with running, which exhibited in-phase fluctuations of kinetic and potential energies. The primary reason for these center of mass differences was found in the energetics of the back leg of galloping, which demonstrated alterations in timing of its energy fluctuations and less energy generation than the front leg. Analysis of the power sources underlying the segmental energies during swing phase showed that the back leg's energy changes were accomplished mainly through reduced use of the hip muscles and less interlimb energy transfer. The back leg's energetics during swing also displayed a shift toward greater reliance on nonmuscular energy sources. A pattern of energy inflow during early swing and energy outflow during late swing was common to both running and galloping, although the galloping legs both demonstrated more abrupt transitions between these phases. The possibility is raised that the 67/33 interlimb phasing ratio used in galloping is selected to reduce mechanical energy variations of the total body center of mass. These data suggest that models of asymmetric gait in humans must account for more than merely phase alteration.

Dual degree of freedom tasks: Flexion effect on supination/pronation response.

This study investigated the influence of an elbow flexion task, graded from 0-100% maximum voluntary contraction (MVC), on torque production and muscle activity in isometric supination and pronation MVC tasks. Torque in both degrees-of-freedom (df) and surface electromyographic (EMG) records from several sites on muscles crossing the elbow were collected as subjects performed isometric elbow supination or pronation MVCs while ostensibly maintaining a flexion torque target. Task effects were statistically tested using analysis of covariance (ANCOVA) and modelled with polynomial regression techniques. Muscular synergism was examined using a multivariate analysis of covariance (MANCOVA) model to test interactions between EMG site responses and flexion torque changes. The results demonstrate that the flexion torque level modulates the supination MVC torque level and the EMG amplitude of all monitored muscles. Further, the synergistic pattern of muscle activity was significantly influenced by the flexion df task. These results suggest that both uni- and multifunctional muscles may be influenced by dual df tasks. Comparison of these results with the dual df task literature suggests that investigating these behaviours across a full range of torque levels is critical because the present findings lead to conclusions that differ somewhat from studies investigating tasks performed only at low or high torque levels.

The influence of task and angle on torque production and muscle activity at the elbow.

This study investigated the effect of changing internal mechanical variables and task demands on muscle activity and torque production during high effort isometric contractions of the elbow flexors. The effect of adding a 50% maximal voluntary contraction (MVC) of supination to an MVC of elbow flexion was studied over a range of angles from 30° to 110° of elbow flexion. Surface EMGs were recorded from the biceps brachii (BIC), brachioradialis (BRAD) and triceps brachii (TRI) of 10 healthy subjects. BIC was the only muscle to show a consistent trend of increasing root mean square (rms) EMG with increasing elbow flexion angle. BIC activity also remained constant or increased with the addition of the supination task at all angles. In contrast, BRAD showed decreased activity when supination was added at several angular positions. Maximal flexion torque was reduced when the second task of submaximal supination was added. This torque reduction was statistically significant at all angles except 70° and appeared related to the decreased contribution from BRAD. In a small subset of subjects, however, BRAD activity did not decrease when the second degrees of freedom (df) task was added. These subjects exhibited higher flexion torques averaged over task than the majority, at all angles except 30°. These data support the view that internal mechanical considerations influence the manner in which the central nervous system (CNS) distributes activity to muscular synergists in response to altered task demands. Further, subject-specific patterns exist which must be recognized if these findings are to be incorporated in training or rehabilitation programmes.

Muscle synergies and isometric torque production: influence of supination and pronation level on elbow flexion.

1. Twenty normal subjects performed a series of isometric elbow flexion (F) maximum voluntary contractions (MVC) while simultaneously maintaining one of seven targeted torque levels in the supination/pronation (S/P) degree of freedom (df). Experimental measures were torque in both df s and surface electromyograms (EMG) from brachioradialis (BRAD), triceps brachii (TB), biceps brachii (BB) short head (BBSH), and a medial and lateral site on biceps brachii long head (MED BB and LAT BB). Task effects were tested for significance using analysis of covariance models for the torque and EMG variables. Polynomial multiple regression models were developed for significant effects. The synergism among muscles was examined by statistically testing the EMG data for differing responses to the S/P torque changes across the five electrode sites. 2. The magnitude of the S/P target torque had a statistically significant effect on flexion MVC (F MVC) torque. Changes in S/P torque markedly influenced the F MVC torque magnitude, with as much as a 25% F torque decrement relative to an F MVC with an S/P torque target of 0. This suggests that the second df task affects some aspect of joint function that causes the CNS to reduce F torque capacity. 3. The S/P torque had a significant effect on EMG amplitude at all electrode sites other than TB. The EMG amplitude at the BB sites responded strongly to both F and S/P torque changes. The F+S tasks tended to facilitate BB EMG, whereas the F+P tasks tended to diminish it. The BRAD EMG, although primarily related to F torque amplitude, also was influenced by the S/P torque changes. The trends for BRAD EMG were opposite those for the BB in that BRAD EMG tended to be enhanced by the F+P tasks and reduced by the F+S tasks. 4. The synergistic pattern of stimulation (i.e., the relationship among the 5 EMG amplitude measures) was also significantly influenced by the S/P df task. Significant differences in the EMG behavior between BBSH and LAT BB were detected; however, no statistically significant differences were found between LAT BB and MED BB. The EMG behaviors at the BRAD and TB electrode sites were significantly different from those at the BB sites. 5. These inversely related responses from the BB and BRAD stress the importance of understanding the relationship between muscular activity and the function of muscles in more than one df. This finding further suggests that the synergistic relationships between muscles are dynamically related to task in all applicable dfs. It is suggested that this dynamic synergism is a natural consequence of the redundant musculoskeletal system.(ABSTRACT TRUNCATED AT 400 WORDS)

Torque/velocity properties of human knee muscles: peak and angle-specific estimates.

Angle-specific (AS) torque/velocity data have been used to avoid angle related variation in peak torque capacity. However, series elastic structures cause the contractile velocity of active force-producing tissue to differ from external joint velocity except at peak torque. Alternatively, angle related variation may be removed by normalizing peak torque to the isometric maximum at that angular position. The AS, peak (P), and normalized peak (NP) methods were compared in isovelocity knee flexion and extension at velocities between 50 and 250 degrees s-1 for 8 male subjects. The P and NP methods gave more similar torque/velocity relations than the AS method. Further, very little variation in peak torque was attributed to differences in joint angle. Both the P and AS methods illustrate that relative quadriceps/hamstrings torque capability (flexor/extensor ratio) increases slightly with velocity. It is proposed that antagonist muscle torque capabilities should be compared at different angular positions to assess muscular imbalance.