THE EFFECT OF PENNATION ANGLE CHANGES DURING CONTRACTION ON THE ESTIMATED TRICEPS SURAE MOMENT

INTRODUCTION: Forward dynamics simulations are important tools in biomechanics research but the accuracy of the muscle model parameters (such as pennation angle, optimal fiber length, force-velocity relationship, etc.) is critical for realistic force and joint moment estimations. The pennation angle in particular determines the efficiency of force transmission to the tendon. The purpose of this study was to investigate changes in the modeled triceps surae complex and its predicted maximum moment using a computer based musculoskeletal model when incorporating in vivo measured pennation angle values. METHODS: The Software for Interactive Musculoskeletal Modeling (SIMM) (Delp et al., 1990) was used to obtain the triceps surae maximum isometric moment at ankle angles of -15o (dorsiflexion), 0o (neutral ankle position), +150 and +300 (plantarflexion). Moments were estimated using pennation angle values a) based on literature pennation angle data used normally in the SIMM model and b) from in vivo pennation angle measurements. Pennation angle measurements were taken using ultrasonography (Esaote Biomedica, Italy) from gastrocnemius medialis, gastrocnemius lateralis and soleus in six males during maximum isometric plantarflexions using an electromechanical dynamometer (Lido Active, Loredan Biomedical, USA) at ankle angles of -15o, 0o, +15o and +30o. RESULTS: The estimated triceps surae moment using cadaveric pennation angle data were approximately 122 Nm, 85 Nm, 17 Nm and 0 Nm at ankle angles of - 15o, 0o, +15o and +30o respectively. The corresponding estimated moments taken incorporating the experimentally observed pennation angles in the model were approximately 106 Nm, 72, Nm, 17 Nm and 0 Nm. Substantially overestimated moment values at ankle angles of -15o (15%) and 0o (18%) were obtained when using cadaveric pennation angle data from the literature compared with the model moment predictions taken incorporating in vivo pennation angle data. CONCLUSIONS: The findings of this study suggest that a realistic model estimation of the moment generating capacity around a joint requires the incorporation of changes in the muscle pennation angle occurring during contraction. REFERENCES: Delp, S., Bleck, E., Zajac, F., Bollini, G. (1990). An Interactive, Graphics-Based Model of the Lower Extremity to Study Orthopaedic Surgical Procedures. IEEE Transactions on Biomedical Engineering 37, 757-767

Automated Method for Tracking Human Muscle Architecture on Ultrasound Scans during Dynamic Tasks

Existing approaches for automated tracking of fascicle length (FL) and pennation angle (PA) rely on the presence of a single, user-defined fascicle (feature tracking) or on the presence of a specific intensity pattern (feature detection) across all the recorded ultrasound images. These prerequisites are seldom met during large dynamic muscle movements or for deeper muscles that are difficult to image. Deep-learning approaches are not affected by these issues, but their applicability is restricted by their need for large, manually analyzed training data sets. To address these limitations, the present study proposes a novel approach that tracks changes in FL and PA based on the distortion pattern within the fascicle band. The results indicated a satisfactory level of agreement between manual and automated measurements made with the proposed method. When compared against feature tracking and feature detection methods, the proposed method achieved the lowest average root mean squared error for FL and the second lowest for PA. The strength of the proposed approach is that the quantification process does not require a training data set and it can take place even when it is not possible to track a single fascicle or observe a specific intensity pattern on the ultrasound recording.UK-India Education and Research Initiative (UKIERI)Department of Science and Technology (DST), New DelhiPeer Reviewe

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

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

In vivo human tendon mechanical properties: effect of resistance training in old age

Recent advances in ultrasound scanning have made it possible to obtain the mechanical properties of human tendons in vivo. Application of the in vivo method in elderly individuals showed that their patellar tendons stiffened in response to a 14- week resistance training program by ~65% both structurally and materially. The rate of muscle torque development increased by ~27%, indicating faster contractile force transmission to the skeleton. The present findings suggest that strength training in old age can at least partly reverse the deteriorating effect of ageing on tendon properties and function

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

Automated Method for Tracking Human Muscle Architecture on Ultrasound Scans during Dynamic Tasks

Existing approaches for automated tracking of fascicle length (FL) and pennation angle (PA) rely on the presence of a single, user-defined fascicle (feature tracking) or on the presence of a specific intensity pattern (feature detection) across all the recorded ultrasound images. These prerequisites are seldom met during large dynamic muscle movements or for deeper muscles that are difficult to image. Deep-learning approaches are not affected by these issues, but their applicability is restricted by their need for large, manually analyzed training data sets. To address these limitations, the present study proposes a novel approach that tracks changes in FL and PA based on the distortion pattern within the fascicle band. The results indicated a satisfactory level of agreement between manual and automated measurements made with the proposed method. When compared against feature tracking and feature detection methods, the proposed method achieved the lowest average root mean squared error for FL and the second lowest for PA. The strength of the proposed approach is that the quantification process does not require a training data set and it can take place even when it is not possible to track a single fascicle or observe a specific intensity pattern on the ultrasound recording

Muscular adaptations to resistance exercise in the elderly

Neuropathic, metabolic, hormonal, nutritional and immunologic factors contribute to the development of sarcopenia. This loss of muscle mass associated with ageing, is a main cause of muscle weakness, but the loss of muscle strength typically exceeds that of muscle size, with a resulting decrease in force per unit of muscle cross-sectional area. Recent evidence suggests that, in addition to a reduction in neural drive and in fibre specific tension, changes in muscle architecture contribute significantly to the loss of muscle force through alterations in muscle mechanical properties. Older muscle, however, maintains a high degree of plasticity in response to increased loading since considerable hypertrophy and a reversal of the alterations in muscle architecture associated with ageing are observed with resistive training

Bone adaptation to altered loading after spinal cord injury: a study of bone and muscle strength

Bone loss from the paralysed limbs after spinal cord injury (SCI) is well documented. Under physiological conditions, bones are adapted to forces which mainly emerge from muscle pull. After spinal cord injury (SCI), muscles can no longer contract voluntarily and are merely activated during spasms. Based on the Ashworth scale, previous research has suggested that these spasms may mitigate bone losses. We therefore wished to assess muscle forces after SCI with a more direct measure and compare it to measures of bone strength. We hypothesized that the bones in SCI patients would be in relation to the loss of muscle forces. Six male patients with SCI 6.4 (SD 4.3) years earlier and 6 age-matched, able-bodied control subjects were investigated. Bone scans from the right knee were obtained by pQCT. The knee extensor muscles were electrically stimulated via the femoral nerve, isometric knee extension torque was measured and patellar tendon force was estimated. Tendon force upon electrical stimulation in the SCI group was 75% lower than in the control subjects (p<0.01). Volumetric bone mineral density of the patella and of the proximal tibia epiphysis were 50% lower in the SCI group than in the control subjects (p<0.01). Cortical area was lower by 43% in the SCI patients at the proximal tibia metaphysis, and by 33% at the distal femur metaphysis. No group differences were found in volumetric cortical density. Close curvilinear relationships were found between stress and volumetric density for the tibia epiphysis (r(2)=0.90) and for the patella (r(2)=0.91). A weaker correlation with the tendon force was found for the cortical area of the proximal tibia metaphysis (r(2)=0.63), and none for the distal femur metaphysis. These data suggest that, under steady state conditions after SCI, epiphyseal bones are well adapted to the muscular forces. For the metaphysis of the long bones, such an adaptation appears to be less evident. The reason for this remains unclear

Supersonic shear wave elastography of human tendons is associated with in vivo tendon stiffness over small strains

Supersonic shear wave (SW) elastography has emerged as a useful imaging modality offering researchers and clinicians a fast, non-invasive, quantitative assessment of tendon biomechanics. However, the exact relationship between SW speed and in vivo tendon stiffness is not intuitively obvious and needs to be verified. This study aimed to explore the validity of supersonic SW elastography against a gold standard method to measure the Achilles tendon’s in vivo tensile stiffness by combining conventional ultrasound imaging with dynamometry. Twelve healthy participants performed maximal voluntary isometric plantarflexion contractions (MVC) on a dynamometer with simultaneous ultrasonographic recording of the medial gastrocnemius musculotendinous junction for dynamometry-based measurement of stiffness. The tendon’s force-elongation relationship and stress-strain behaviour were assessed. Tendon stiffness at different levels of tension was calculated as the slope of the stress-strain graph. SW speed was measured at the midportion of the free tendon and tendon Young’s modulus was estimated. A correlation analysis between the two techniques revealed a statistically significant correlation for small strains (r(10)=0.604, p=.038). SW-based assessments of in vivo tendon stiffness were not correlated to the gold standard method for strains in the tendon greater than 10% of the maximum strain during MVC. The absolute values of SW-based Young’s modulus estimations were approximately three orders of magnitude lower than dynamometry-based measurements. Supersonic SW elastography should be only used to assess SW speed for the detection and study of differences between tissue regions, differences between people or groups of people or changes over time in tendon initial stiffness (i.e., stiffness for small strains)