Moment Arm Ratio Research Articles

Sexual dimorphisms in three-dimensional masticatory muscle attachment morphometry regulates temporomandibular joint mechanics

Temporomandibular joint (TMJ) disorders disproportionally affect females, with female to male prevalence varying from 3:1 to 8:1. Sexual dimorphisms in masticatory muscle attachment morphometry and association with craniofacial size, critical for understanding sex-differences in TMJ function, have not been reported. The objective of this study was to determine sex-specific differences in three-dimensional (3D) TMJ muscle attachment morphometry and craniofacial sizes and their impact on TMJ mechanics. Human cadaveric TMJ muscle attachment morphometry and craniofacial anthropometry (10Males; 11Females) were determined by previously developed 3D digitization and imaging-based methods. Sex-differences in muscle attachment morphometry and craniofacial anthropometry, and their correlation were determined, respectively using multivariate general linear and linear regression statistical models. Subject-specific musculoskeletal models of the mandible were developed to determine effects of sexual dimorphisms in mandibular size and TMJ muscle attachment morphometry on joint loading during static biting. There were significant sex-differences in craniofacial size (p = 0.024) and TMJ muscle attachment morphometry (p < 0.001). TMJ muscle attachment morphometry was significantly correlated with craniofacial size. TMJ contact forces estimated from biomechanical models were significantly, 23% on average (p < 0.001), greater for females compared to those for males when generating the same bite forces. There were significant linear correlations between TMJ contact force and both 3D mandibular length (R2 = 0.48, p < 0.001) and muscle force moment arm ratio (R2 = 0.68, p < 0.001). Sexual dimorphisms in masticatory muscle morphology and craniofacial sizes play critical roles in subject-specific TMJ biomechanics. Sex-specific differences in the TMJ mechanical environment should be further investigated concerning mechanical fatigue of TMJ discs associated with TMJ disorders.

筋束長－モーメントアーム比と等速性関節トルクとの関係:―ヒトのヒラメ筋および足関節底屈動作を対象として―

筋束長－モーメントアーム比と等速性関節トルクとの関係:―ヒトのヒラメ筋および足関節底屈動作を対象として―

Evaluation of Intrinsic Biomechanical Risk Factors in Patellar Tendinopathy: A Retrospective Radiographic Case-Control Series.

Background:Patellar tendinopathy is an overuse condition often affecting athletes. It has been postulated that patellar tendinopathy is associated with patella alta; however, this and any other anatomic risk factors have not been identified.Purpose:To explore whether lever arm differences from radiographic measurements exist between patients with and without tendinopathy. This may provide surgeons with a simple radiographic means to identify patients at risk.Study Design:Cross-sectional study; Level of evidence, 3.Methods:Magnetic resonance imaging scans of the knee from a sports imaging facility were screened and reviewed to identify 2 groups of patients: those with and those without imaging signs of patellar tendinopathy. The lateral radiographs were reviewed and measurements made to determine (1) lever arm ratio, (2) moment arm ratio, (3) angle between the moment and line of pull of the patellar tendon, (4) patellar tendon pivot point angle, and (5) patellar height (alta). Measurements were obtained directly from radiographs. The images and measurements were reviewed by 2 experienced orthopaedic clinicians.Results:A total of 105 patients were included in this study: 52 with patellar tendinopathy and 53 without patellar tendinopathy (controls). The mean age was similar between groups (23 years); females accounted for 8 of 52 patients with patellar tendinopathy and 24 of 53 patients without. The lever arm ratio in the group with patellar tendinopathy versus controls was 1.71 versus 1.01 (P = .01), with a moment arm difference of 1.00 versus 0.80 (P < .01), respectively. There was no difference detected between groups for patellar tendon angle, patellar tendon pivot point angle, knee flexion angle, or incidence of patella alta. No correlation was found with our measurements and the Insall-Salvati ratio. Statistical analysis was also performed according to sex, and a statistically significant difference between groups was found for differences in lever arm ratio and moment arm.Conclusion:The lever arm ratio and moment arm ratio from lateral radiographs were significantly different between patients with and without patellar tendinopathy. Further study is needed on the biomechanical implications of the pivot point and how altering it can affect stress within the patellar tendon, patellofemoral joint, and associated clinical outcomes.

Achilles tendon strain energy in distance running: consider the muscle energy cost.

The return of tendon strain energy is thought to contribute to reducing the energy cost of running (Erun). However, this may not be consistent with the notion that increased Achilles tendon (AT) stiffness is associated with a lower Erun. Therefore, the purpose of this study was to quantify the potential for AT strain energy return relative to Erun for male and female runners of different abilities. A total of 46 long distance runners [18 elite male (EM), 12 trained male (TM), and 16 trained female (TF)] participated in this study. Erun was determined by indirect calorimetry at 75, 85, and 95% of the speed at lactate threshold (sLT), and energy cost per stride at each speed was estimated from previously reported stride length (SL)-speed relationships. AT force during running was estimated from reported vertical ground reaction force (Fz)-speed relationships, assuming an AT:ground reaction force moment arm ratio of 1.5. AT elongation was quantified during a maximal voluntary isometric contraction using ultrasound. Muscle energy cost was conservatively estimated on the basis of AT force and estimated cross-bridge mechanics and energetics. Significant group differences existed in sLT (EM > TM > TF; P < 0.001). A significant group × speed interaction was found in the energy storage/release per stride (TM > TF > EM; P < 0.001), the latter ranging from 10 to 70 J/stride. At all speeds and in all groups, estimated muscle energy cost exceeded energy return (P < 0.001). These results show that during distance running the muscle energy cost is substantially higher than the strain energy release from the AT.

Empirical evaluation of gastrocnemius and soleus function during walking

Distinguishing gastrocnemius and soleus muscle function is relevant for treating gait disorders in which abnormal plantarflexor activity may contribute to pathological movement patterns. Our objective was to use experimental and computational analysis to determine the influence of gastrocnemius and soleus activity on lower limb movement, and determine if anatomical variability of the gastrocnemius affected its function. Our hypothesis was that these muscles exhibit distinct functions, with the gastrocnemius inducing limb flexion and the soleus inducing limb extension. To test this hypothesis, the gastrocnemius or soleus of 20 healthy participants was electrically stimulated for brief periods (90ms) during mid- or terminal stance of a random gait cycle. Muscle function was characterized by the induced change in sagittal pelvis, hip, knee, and ankle angles occurring during the 200ms after stimulation onset. Results were corroborated with computational forward dynamic gait models, by perturbing gastrocnemius or soleus activity during similar portions of the gait cycle. Mid- and terminal stance gastrocnemius stimulation induced posterior pelvic tilt, hip flexion and knee flexion. Mid-stance gastrocnemius stimulation also induced ankle dorsiflexion. In contrast mid-stance soleus stimulation induced anterior pelvic tilt, knee extension and plantarflexion, while late-stance soleus stimulation induced relatively little change in motion. Model predictions of induced hip, knee, and ankle motion were generally in the same direction as those of the experiments, though the gastrocnemius׳ results were shown to be quite sensitive to its knee-to-ankle moment arm ratio.

A comparison of the moment arms of pelvic limb muscles in horses bred for acceleration (Quarter Horse) and endurance (Arab)

Selective breeding for performance has resulted in distinct breeds of horse, such as the Quarter Horse (bred for acceleration) and the Arab (bred for endurance). Rapid acceleration, seen during Quarter Horse racing, requires fast powerful muscular contraction and the generation of large joint torques, particularly by the hind limb muscles. This study compared hind limb moment arm lengths in the Quarter Horse and Arab. We hypothesized that Quarter Horse hind limb extensor muscles would have longer moment arms when compared to the Arab, conferring a greater potential for torque generation at the hip, stifle and tarsus during limb extension. Six Quarter Horse and six Arab hind limbs were dissected to determine muscle moment arm lengths for the following muscles: gluteus medius, biceps femoris, semitendinosus, vastus lateralis, gastrocnemius (medialis and lateralis) and tibialis cranialis. The moment arms of biceps femoris (acting at the hip) and gastrocnemius lateralis (acting at the stifle) were significantly longer in the Quarter Horse, although the length of the remaining muscle moment arms were similar in both breeds of horse. All the Quarter Horse muscles were capable of generating greater muscle moments owing to their greater physiological cross-sectional area (PCSA) and therefore greater isometric force potential, which suggests that PCSA is a better determinant of muscle torque than moment arm length in these two breeds of horse. With the exception of gastrocnemius and tibialis cranialis, the observed muscle fascicle length to moment arm ratio (MFL : MA ratio) was greater for the Arab horse muscles. It appears that the Arab muscles have the potential to operate at slower velocities of contraction and hence generate greater force outputs when compared to the Quarter Horse muscles working over a similar range of joint motion; this would indicate that Arab hind limb muscles are optimized to function at maximum economy rather than maximum power output.

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Distinguishing gastrocnemius and soleus muscle function is relevant for treating gait disorders in which abnormal plantarflexor activity may contribute to pathological movement patterns. Our objective was to use experimental and computational analysis to determine the influence of gastrocnemius and soleus activity on lower limb movement, and determine if anatomical variability of the gastrocnemius affected its function. Our hypothesis was that these muscles exhibit distinct functions, with the gastrocnemius inducing limb flexion and the soleus inducing limb extension. To test this hypothesis, the gastrocnemius or soleus of 20 healthy participants was electrically stimulated for brief periods (90 ms) during mid- or terminal stance of a random gait cycle. Muscle function was characterized by the induced change in sagittal pelvis, hip, knee, and ankle angles occurring during the 200 ms after stimulation onset. Results were corroborated with computational forward dynamic gait models, by perturbing gastrocnemius or soleus activity during similar portions of the gait cycle. Mid- and terminal stance gastrocnemius stimulation induced posterior pelvic tilt, hip flexion and knee flexion. Mid-stance gastrocnemius stimulation also induced ankle dorsiflexion. In contrast mid-stance soleus stimulation induced anterior pelvic tilt, knee extension and plantarflexion, while late-stance soleus stimulation induced relatively little change in motion. Model predictions of induced hip, knee, and ankle motion were generally in the same direction as those of the experiments, though the gastrocnemius׳ results were shown to be quite sensitive to its knee-to-ankle moment arm ratio.

Muscle synergism during isometric plantarflexion in achilles tendon rupture patients and in normal subjects revealed by velocity-encoded cine phase-contrast MRI

The triceps surae muscle is often considered to be the sole contributor to the plantarflexion torque although the deeper plantarflexor muscles may also be activated in the plantarflexion task. We measured coordinative strategies and muscle synergism during isometric plantarflexion task from 11 volunteers. Velocities from the distal end of the medial gastrocnemius, soleus, and flexor hallucis longus muscles were encoded in the superior-inferior direction using cine phase-contrast magnetic resonance imaging. Eight of the subjects were healthy and served as controls for subject to subject variability. Three of the subjects had experienced an Achilles tendon rupture followed by surgical repair and they were measured up to 8 weeks of rehabilitation. There were marked individual differences in the use of the different muscles during plantarflexion task in control subjects. Soleus to flexor hallucis longus displacement ratio during contraction varied from 0.4 to 9.6 while the moment arm ratio between Achilles tendon and flexor hallucis longus tendons was 1.9 (standard deviation 0.2). In Achilles tendon rupture patients the relative contribution of flexor hallucis longus was very high both in their injured and uninjured leg. This coordinative strategy remained throughout rehabilitation. The findings suggest that early recovery of plantarflexion torque after Achilles tendon rupture may be due to compensation by flexor hallucis longus as well as to normalization of the triceps surae muscle function. Also, this study suggests that the individual differences in coordinative strategies in addition to moment arms and muscle-tendon properties can influence the calculation of forces produced by individual muscles.

ヒト肩関節を規範としたロボットアーム関節機構の開発

The purpose of this study was to develop a new joint system based on the human shoulder mechanism. The human shoulder joint is constrained by multiple muscles and ligaments which surround the ball joint, and is driven by the balance of those forces. It is thought that the construction of the human shoulder mechanism could provide motion with three degrees of freedom and with compact size and light weight in comparison with an industrial robot arm composed of the usual pin joints. Therefore, the authors thought that the new joint mechanism for a robot arm with three degrees of freedom should be a ball joint mechanism driven by wires.In the development of the new joint mechanism, we tried to construct two types of joints. These were a five-wire model and a six-wire model. An anatomical skeletal structure has been introduced to the mechanism, especially on the muscle arrangements of the human shoulder.The movability of the new joint mechanism was evaluated by the ratio of moment arm to ball radius produced from the wires that surround the ball joint. The method of estimating moment arm was to find the slope of the wire excursion against the joint angle. Thus, to compensate some deficiency of moment arm, occurring in a specific area of flexion-extension or rotation motion, the wire position corresponding to the lack of moment arm was adjusted to an adequate position using evaluation of the moment arm. As a result of improvement processes, the effective movability was ascertained in the specified movable area for the six-wire model. Sufficient movability was not acquired in the five-wire model, however, because the movable area was considerably reduced.When the joint is driven as a robot arm, an inverse kinematics must be solved. In the present study, the problem was solved by utilizing an artificial neural network (NN), which learns data sets for arm posture and wire displacement. The additional differential outputs installed in the learned NN and consideration of a theory of virtual work balance were applied to a control system to drive the joint by a feedback control system in the range of three degrees of freedom. It was properly and precisely driven by the control system on the six-wire model. Thus, the movability and capability of the new joint system of a robot arm based on the human shoulder mechanism, as described in this paper, was demonstrated to be satisfactory.

Static Turning Analysis of Vehicles Subject to Externally Applied Forces - A Moment Arm Ratio Formulation

SUMMARY A formulation for representing the static turning response of a two-axle vehicle due to applied external or control forces is expressed in terms of a simple ratio of two distances along the vehicle longitudinal axis. The two distancescoincide with points on the vehicle at which externally applied/ control forces and their reactive inertial forces act with respect to the vehicle neutral steer point. The resulting formulation is equivalent to the rotational equilibrium equation written with respect to the neutral steer point. The method allows a simple “visual analysis” of the steady turning process by showing how key forces and associated moment arms can change with respect to one another due to vehicle modifications or different operatingconditions, thereby affecting the static turning response of the vehicle.

Geometry of Adult Rectus Abdominis and Erector Spinae Muscles

Mathematical modeling of human joints requires accurate information concerning anthropometric parameters such as muscle cross-sectional areas and muscle moment arms. The purpose of this study was to calculate the average crosssectional area, average volume, and length of the muscle moment arms about the spinal column for the rectus abdominis (RA) and the erector spinae (ES) for those portions of the muscles that are involved in spinal flexion and extension. Materials for this study came from archival computed tomography scans of 28 living subjects. The muscle outlines were digitized and the moment arms calculated as a percentage of anteroposterior trunk depth. The average cross-sectional area of the RA was 10.5 cm2, and 31.75 cm2 for the ES. The average volumes for the RA and ES were 356.16 cm3 and 843.46 cm3, respectively. The muscle moment arm ratio was 0.29 for the ES, while the males and females had ratios of 0.50 and 0.40, respectively, for the RA. Computed tomography scanning is a method that allows the accurate calculation of internal anthropometric parameters that will be of use in mathematical modeling. J Orthop Sports Phys Ther 1985;6(5):278-280.

Earthquake design considerations in reinforced concrete columns

AbstractDamages resulting from the Tokachi‐Oki earthquake of 1968 demonstrated that many code‐designed reinforced concrete columns do not have adequate earthquake resistance. A review of Japanese research revealed that the axial force ratio, the moment arm ratio, and the type and ratio of transverse reinforcement control the resistance and ductility of concrete columns. A recent experimental study at the Kajima Institute of Construction Technology evaluated the resistance of columns with three types of transverse reinforcement and three reinforcement ratios subjected to repeated alternating loads. Tied and spiral columns proved to be superior to hooped columns.