MODELLING DYNAMIC MUSCULOSKELETAL FUNCTION AND IMPLICATIONS FOR COMPUTER SIMULATION AND INVERSE DYNAMICS APPLICATIONS IN SPORT

Musculoskeletal modelling is widely used in sports biomechanics for the estimation of joint and muscle loading in inverse dynamics applications or the simulation and optimisation of human performance in forward dynamics simulations. The relative motion of the segments is normally modelled using three different approaches: a) as a simple pin joint allowing only rotation around a fixed axis, b) a parametric description of relative motion describing the linear displacement of one segment relative to another as a function of the rotation angle and c) as the motion of a full biomechanical model of the joint that includes mechanical models of muscles, tendons, ligaments and other restraining structures and is based on the response of the model to the applied internal and external forces. In the first two approaches that are the most common, the relative movement of the segments due to the contraction of muscles and the resulting internal forces is ignored and this can have significant implications for the output of the model, especially in more complex models of the musculoskeletal system. In forward dynamics applications with the above models, joint rotation is generated using either torque generators or Hill-type muscle models. Torque generators are functions of torque based on the joint angular position and velocity. These functions are typically calculated by measuring the joint moment at different joint positions and angular velocities using isokinetic dynamometry. In general, it is assumed that the moment measured using dynamometry is equivalent to the actual joint moment. However, it has been documented that this is not the case due to a) gravitational forces, b) inertial forces (e.g. Herzog, 1988) and c) misalignment of the joint and dynamometer axes of rotation resulting from the non rigidity of the dynamometer arm-lower leg system (Herzog, 1988; Kaufman et al., 1995; Arampatzis et al., 2004). Implementations of appropriate methods for the correction of the gravitational and inertial forces have been reported. The movement of the segment relative to the dynamometer is the main factor for the differences between measured and actual joint moments. Hence, the main purpose of this study was to use X-ray image analysis to examine the effects of the non-rigidity of the dynamometer chair, arm and lower leg system on the knee joint kimematics and the resulting joint forces calculations using inverse dynamics and the measurement of active knee extension moment-angular position relationship that is the basis for toque generator functions in forward dynamics applications

BIOMECHANICS TOOLBOX: A SOFTWARE FOR BIOMECHANICAL DATA PROCESSING AND MODELLING

INTRODUCTION: One of the main problems in biomechanics and especially in teaching is that software modules implementing the different data processing and modelling methods are usually part of integrated data collection systems such as optoelectronic, force plate and electromyography systems. The cost and the specific function of these systems does not allow easy access to the different data processing methods for practice especially when teaching large classes of students. To overcome these problems we have developed a user-friendly, stand alone, Windows based software that implements the main data processing and modelling techniques in biomechanics. METHODS: The Biomechanics Toolbox (Infomedia Ltd) was developed for the Microsoft Windows operating system in order to provide a familiar, user friendly and consistent environment. The biomechanical signal processing methods include filtering factor determination, various filtering methods (such as recursive and non-recursive digital filters and cubic and quintic splines), frequency spectrum analysis using different Fourier transformation methods and numerical differentiation and integration methods. There are also other time domain processing tools such as signal rectification, normalisation, extension and windowing. These methods accept standard text files as input so that data exported from different instrumentation systems (e.g. kinematic, force plate or electromyography signals) can be processed in the time or frequency domain, making the system independent of any particular data collection system. The output of these methods can be presented graphically or saved in text files for further processing. The software also includes inverse dynamics tools using the actual or the resultant force and moment methods. Indeterminate systems can be solved using different linear or non-linear optimisation procedures. There is also a simple, interactive, single segment forward dynamics simulation where the user can adjust the various parameters of the muscle model and the inertial properties and explore their effects on the resultng movement of the segment. These tools allow extensive interactive practice using standard biomechanical modelling methods. CONCLUSIONS: Implementation of this software in a large class of students indicated that it is a very effective teaching and learning tool. Installation of the software on a computer network together with example text files exported from laboratory data collection systems allows teaching, access and practice of a large number of students. This enables independent practice and effective learning of the main biomechanical data processing and modelling methods without the need to use laboratory equipment for data analysis by large groups

Muscle activation capacity: effects of method, stimuli number and joint angle

To assess the sensitivity of existing measurement methods for muscle activation capacity to potential errors introduced by a) evoking inadequate force by stimulation and b) neglecting differences in series elasticity between conditions, the effect of different number of stimuli and joint angle on the interpolation twitch interpolation technique [ITT = (1- superimposed stimulus torque / resting stimulus torque) x 100] and central activation ratio (CAR = maximal voluntary contraction torque / maximal voluntary contraction torque + superimposed stimulus torque) was examined. Ten subjects performed knee extension maximal voluntary contractions at 30 and 90o knee flexion angles (0o is full knee extension). Singlets, doublets, quadruplets and octuplets of supramaximal intensity were applied via percutaneous quadriceps muscle stimulation at rest and during the plateau phase of the contraction. A mixed-design 2 x 2 x 4 repeated factorial ANOVA was used to examine for differences in activation capacity between methods, knee joint angles and stimuli number, and simple effects tests were used for post hoc analysis where appropriate. Joint angle had a significant effect (P 0.05). It is, therefore, suggested that in the quantification of voluntary drive during contraction with the ITT and CAR methods, consideration be given not only to the number of stimuli applied but also to the effect of series elasticity due to joint angle differences, since these factors may affect differently the outcome of the calculation, depending on the approach followed

COORDINATION VARIABILITY DURING OVERGROUND, TREADMILL AND TREADMILL-ON-DEMAND RUNNING

The purpose of this study was to investigate differences in lower extremity coordination variability between overground, treadmill and treadmill-on-demand running. A modified normalised root mean square difference technique was used to quantify the variability in lower extremity coordination calculated from the kinematic data collected during ten strides of overground, treadmill and treadmill-on-demand running at 3.5 m.s". Although no significant differences were observed between the two types of treadmill, significantly reduced (p < 0.02) coordination variability was seen in the treadmill and treadmill-ondemand conditions compared to overground locomotion. Therefore, a constant belt speed during treadmill locomotion does not account for the differences seen between overground and treadmill running and further work is required to determine factors that cause the difference

Differences in human antagonistic ankle dorsiflexor coactivation between legs; can they explain the moment deficit in the weaker plantarflexor leg?

The present study examined the hypothesis that the antagonistic ankle dorsiflexor coactivation level during maximum isometric voluntary plantarflexion (MVC) is a function of ankle angle. Six male subjects generated plantarflexion and dorsiflexion MVC trials at ankle angles of −15 deg (dorsiflexed direction), 0 deg (neutral position), +15 deg (plantarflexed direction) and +30 deg having the knee flexed at an angle of 90 deg. In all contractions surface EMG measurements were taken from tibialis anterior and soleus which were considered representative muscles of all dorsiflexors and plantarflexors, respectively. Antagonistic dorsiflexor coactivation was expressed as normalized EMG and moment. Calculations of the antagonistic dorsiflexor moment were based on the tibialis anterior EMG—dorsiflexor moment relationship from contractions at 50, 40, 30, 20 and 10% of the dorsiflexion MVC moment. In both legs dorsiflexor coactivation level followed an open U-shaped pattern as a function of ankle angle. Differences of 9 and 14% (P < 0·05) were found in the measured net plantarflexion MVC moment between legs at ankle angles of −15 and +30 deg, respectively. No difference (P > 0·05) was found in the calf circumference between legs. Differences were found in the antagonistic dorsiflexor coactivation between legs at ankle angles of −15 and +30 deg. In the weaker leg the antagonistic EMG measurements were higher by 100 and 45% (P < 0·01) and the estimated antagonistic moments were higher by 70 and 43% (P < 0·01) compared with the weaker leg at −15 and +30 deg, respectively. This finding was associated with a decreased range of motion (ROM) in the weaker leg (14%, P < 0·01), such that no difference (P > 0·05) was found in dorsiflexor antagonistic coactivation between legs at end-range ankle angles. The findings of the study (i) have to be taken into consideration when estimating musculoskeletal loads in the lower extremity, (ii) imply that stretching training can result in a stronger plantarflexion at end-range ankle angles through inhibition of the dorsiflexors, and (iii) imply a neural drive inadequacy during a plantarflexion MVC at end-range angles

An investigation of movement dynamics and muscle activity during traditional and accentuated-eccentric squatting.

Accentuated-eccentric loading (AEL) takes advantage of the high force producing potential of eccentric muscle contractions, potentially maximising mechanical tension within the muscle. However, evidence is lacking on how AEL squatting may load the involved musculature, limiting scientifically justified programming recommendations. The purpose of this study was to investigate the effects of concentric and eccentric loads on joint loading and muscle activity of the lower limbs. Resistance trained males performed traditional squatting (20–100% of concentric one-repetition maximum [1RM]) and AEL squatting with eccentric loads (110–150% of 1RM) provided by a novel motorised isotonic resistance machine (Kineo). Kinetics and kinematics of the hip, knee, and ankle joints were collected, with electromyography from the gluteus maximus, vastus lateralis, biceps femoris, and gastrocnemius medialis. A secondary cohort underwent a kinematic and electromyography analysis of squatting technique to compare Kineo and back and front barbell squatting. Knee joint peak eccentric moments occurred at 120% 1RM (P = 0.045), with no further increase thereafter. As eccentric load increased, the time course of moment development occurred earlier in the eccentric phase. This resulted in a 37% increase in eccentric knee extensor work from the 80% 1RM trial to the 120% 1RM trial (P<0.001). Neither hip nor ankle joints displayed further change in kinetics as eccentric load increased above 100% 1RM. Electromyographic activity during traditional squatting was ~15–30% lower in all eccentric trials than in concentric trials for all muscles. EMG plateaued between a load of 80–100% 1RM during the eccentric trials and did not increase with AEL. No significant differences in kinematics were found between Kineo and barbell squatting. The knee extensors appear to be preferentially loaded during AEL squatting. The greater work performed during the eccentric phase of the squat as eccentric load increased suggests greater total mechanical tension could be the cause of adaptations from AEL. Our data suggest that AEL should be programmed with a load of 120% of 1RM. Further studies are needed to confirm the longer-term training effects of AEL

KINETICS, KINEMATICS AND MUSCLE ACTIVATION DURING ECCENTRIC SQUATTING

The purpose of this study was to examine the kinetics, kinematics and muscle activation of the knee and hip extensors during the eccentric (ECC) phase of the squat exercise. Resistance trained males (n=9) performed isotonic loaded ECC squats at loads from 20-150% of squat 1-rep max. Inverse dynamic calculations were used to identify knee and hip joint moment, and iEMG was used to quantify muscle activation of the vastus lateralis and gluteus maximus. In contrast to previous literature examining the concentric phase of the squat, this study found the knee extensors experienced the greatest loading, plateauing when exposed to a load of \u3e120% of 1RM, with no changes in joint kinematics. Vastus lateralis iEMG plateaued after 80% of 1RM, suggesting activation-independent factors for this increase in joint moment. If maximising knee extensor loading to promote adaptation is a training object, this data recommends an ECC load of 120%

In vivo measurements of muscle specific tension in adults and children

This article is available open access through the publisher’s website at the link below. Copyright @ 2009 The Authors.To better understand the effects of pubertal maturation on the contractile properties of skeletal muscle in vivo, the present study investigated whether there are any differences in the specific tension of the quadriceps muscle in 20 adults and 20 prepubertal children of both sexes. Specific tension was calculated as the ratio between the quadriceps tendon force and the sum of the physiological cross-sectional area (PCSA) multiplied by the cosine of the angle of pennation of each head within the quadriceps muscle. The maximal quadriceps tendon force was calculated from the knee extension maximal voluntary contraction (MVC) by accounting for EMG-based estimates of antagonist co-activation, incomplete quadriceps activation using the interpolation twitch technique and magnetic resonance imaging (MRI)-based measurements of the patellar tendon moment arm. The PCSA was calculated as the muscle volume, measured from MRI scans, divided by optimal fascicle length, measured from ultrasound images during MVC at the estimated angle of peak quadriceps muscle force. It was found that the quadriceps tendon force and PCSA of men (11.4 kN, 214 cm2) were significantly greater than those of the women (8.7 kN, 152 cm2; P 0.05) between groups: men, 55 ± 11 N cm−2; women, 57.3 ± 13 N cm−2; boys, 54 ± 14 N cm−2; and girls, 59.8 ± 15 N cm−2. These findings indicate that the increased muscle strength with maturation is not due to an increase in the specific tension of muscle; instead, it can be attributed to increases in muscle size, moment arm length and voluntary activation level

Stair Gait in Older Adults Worsens With Smaller Step Treads and When Transitioning Between Level and Stair Walking.

Older people have an increased risk of falling during locomotion, with falls on stairs being particularly common and dangerous. Step going (i.e., the horizontal distance between two consecutive step edges) defines the base of support available for foot placement on stairs, as with smaller going, the user's ability to balance on the steps may become problematic. Here we quantified how stair negotiation in older participants changes between four goings (175, 225, 275, and 325 mm) and compared stair negotiation with and without a walking approach. Twenty-one younger (29 ± 6 years) and 20 older (74 ± 4 years) participants negotiated a 7-step experimental stair. Motion capture and step-embedded force platform data were collected. Handrail use was also monitored. From the motion capture data, body velocity, trunk orientation, foot clearance and foot overhang were quantified. For all participants, as stair going decreased, gait velocity (ascent pA = 0.033, descent pD = 0.003) and horizontal step clearance decreased (pA = 0.001), while trunk rotation (pD = 0.002) and foot overhang increased (pA,D A D = 0.001) and their foot clearance tended to be smaller. With a walking approach, the older group (Group x Start interaction) showed a larger trunk rotation (pA = 0.011, pD = 0.015), and smaller lead foot horizontal (pA = 0.046) and vertical clearances (pD = 0.039) compared to the younger group. A regression analysis to determine the predictors of foot clearance and amount of overhang showed that physical activity was a common predictor for both age groups. In addition, for the older group, medications and fear of falling were found to predict stair performance for most goings, while sway during single-legged standing was the most common predictor for the younger group. Older participants adapted to smaller goings by using the handrails and reducing gait velocity. The predictors of performance suggest that motor and fall risk assessment is complex and multifactorial. The results shown here are consistent with the recommendation that larger going and pausing before negotiating stairs may improve stair safety, especially for older users