Asymmetric Loading Patterns Research Articles

Asymmetrical Loading Patterns in Military Personnel With a History of Self-Reported Low Back Pain.

Servicemembers are required to operate at high levels despite experiencing common injuries such as chronic low back pain. Continuing high levels of activity while compensating for pain may increase the risk of musculoskeletal injuries. As such, the purpose of this project was to determine if servicemembers with chronic low back pain have reduced lower extremity performance, and if they use alternate strategies to complete a functional performance task as compared to healthy servicemembers. Of a total of 46 male United States Marine Corps Forces Special Operations Command (MARSOC) personnel, 23 individuals who suffered from chronic low back pain (age = 28.6 ± 4.4 years, weight = 84.2 ± 6.8 kg) and 23 healthy controls (age = 27.9 ± 3.8 years, weight = 83.8 ± 7.7 kg) completed a stop jump task. In this task, three-dimensional biomechanics were measured, and lower extremity and trunk strength were assessed. The low back pain group exhibited higher vertical ground reaction force impulse on the dominant limb (0.26% body weight [BW]/s), compared to the nondominant limb (0.25% BW/s, p = .036). The control group demonstrated relationships between jump height and strength in both limbs (dominant: r = 0.436, p = .043; nondominant: r = 0.571, p = .006), whereas the low back pain group demonstrated relationships between jump height and dominant limb knee work (r = 0.470, p = .027) and ankle work (r = 0.447, p = .037). This study demonstrates that active-duty MARSOC personnel with a history of low back pain reach similar levels of jump height during a counter movement jump, as compared to those without a history of low back pain. However, the asymmetries displayed by the low back pain group suggest an alternate strategy to reaching similar jump heights as compared to healthy individuals.

A Finite Element Model for Estimation of Contact Dynamics During a Jumping Movement on a Trampoline

In order to fully understand contact dynamics on a trampoline, a simulation approach using a musculoskeletal model coupled with a dynamic model of the trampoline is essential. The purpose of the study was to examine dynamics and selected lower extremity muscle forces in a landing and jumping movement on a trampoline, using a combination of finite element modeling and musculoskeletal modeling. The rigid frame of the trampoline was modeled in ADAMS and coupled with a finite element model of the elastic trampoline net surface in ANSYS. A musculoskeletal model of an elite trampoline athlete was further developed in LifeMod and combined with the finite element model of the trampoline. The results showed that the peak trampoline reaction forces (TRF) were 3400 N (6.6 BW) and 2900 N (5.6 BW) for the left and right limb, respectively. The right hip, knee and ankle joint reaction forces reached the maximum between 3000-4000 N (5.8 – 7.7 BW). The gluteus maximum and quadriceps reached the maximum muscle force of 380 N (0.7 BW) and 780 N (1.5 BW), respectively. Asymmetric loading patterns between left and right TRFs and lower extremities joint reaction forces were observed due to the need to generate the rotational movement during the takeoff. The observed rigid and erect body posture suggested that the hip and knee extensors played important roles in minimizing energy absorption and maximizing energy generation during the trampoline takeoff.

Prediction of in vivo lower cervical spinal loading using musculoskeletal multi-body dynamics model during the head flexion/extension, lateral bending and axial rotation.

Cervical spine diseases lead to a heavy economic burden to the individuals and societies. Moreover, frequent post-operative complications mean a higher risk of neck pain and revision. At present, controversy still exists for the etiology of spinal diseases and their associated complications. Knowledge of in vivo cervical spinal loading pattern is proposed to be the key to answer these questions. However, direct acquisition of in vivo cervical spinal loading remains challenging. In this study, a previously developed cervical spine musculoskeletal multi-body dynamics model was utilized for spinal loading prediction. The in vivo dynamic segmental contributions to head motion and the out-of-plane coupled motion were both taken into account. First, model validation and sensitivity analysis of different segmental contributions to head motion were performed. For model validation, the predicted intervertebral disk compressive forces were converted into the intradiskal pressures and compared with the published experimental measurements. Significant correlations were found between the predicted values and the experimental results. Thus, the reliability and capability of the cervical spine model was ensured. Meanwhile, the sensitivity analysis indicated that cervical spinal loading is sensitive to different segmental contributions to head motion. Second, the compressive, shear and facet joint forces at C3-C6 disk levels were predicted, during the head flexion/extension, lateral bending and axial rotation. Under the head flexion/extension movement, asymmetric loading patterns of the intervertebral disk were obtained. In comparison, symmetrical typed loading patterns were found for the head lateral bending and axial rotation movements. However, the shear forces were dramatically increased during the head excessive extension and lateral bending. Besides, a nonlinear correlation was seen between the facet joint force and the angular displacement. In conclusion, dynamic cervical spinal loading was both intervertebral disk angle-dependent and level-dependent. Cervical spine musculoskeletal multi-body dynamics model provides an attempt to comprehend the in vivo biomechanical surrounding of the human head-neck system.

Biomechanical compensations of the trunk and lower extremities during stepping tasks after unilateral transtibial amputation

BackgroundLower extremity movement compensations following transtibial amputation are well-documented and are likely influenced by trunk posture and movement. However, the biomechanical compensations of the trunk and lower extremities, especially during high-demand tasks such as step ascent and descent, remain unclear. MethodsKinematic and kinetic data were collected during step ascent and descent tasks for three groups of individuals: diabetic/transtibial amputation, diabetic, and healthy. An ANCOVA was used to compare peak trunk, hip and knee joint angles and moments in the sagittal and frontal planes between groups. Paired t-tests were used to compare peak joint angles and moments between amputated and intact limbs of the diabetic/transtibial amputation group. FindingsDuring step ascent and descent, the transtibial amputation group exhibited greater trunk forward flexion and lateral flexion compared to the other two groups (P<0.016), which resulted in greater low back moments and asymmetric loading patterns in the lower extremity joints. The diabetic group exhibited similar knee joint loading patterns compared to the amputation group (P<0.016), during step descent. InterpretationThis study highlights the biomechanical compensations of the trunk and lower extremities in individuals with dysvascular transtibial amputation, by identifying low back, hip, and knee joint moment patterns unique to transtibial amputation during stepping tasks. In addition, the results suggest that some movement compensations may be confounded by the presence of diabetes and precede limb amputation. The increased and asymmetrical loading patterns identified may predispose individuals with transtibial amputation to the development of secondary pain conditions, such as low back pain or osteoarthritis.

Experimental and Analytical Investigation of Deformations and Stress Distribution in Steel Bands of a Two-Span Stress-Ribbon Pedestrian Bridge

The article is dedicated to the analysis of problems related to design of pedestrian bridges with flexible ribbon bands made of steel. The study is based on test results of a bridge model that has two spans (each with a length of five meters). A simplified analytical technique has been proposed for predicting vertical deformations of the bridge structure subjected to symmetrical or asymmetrical loading patterns. The technique also allows assessing the tension forces in the ribbons, which are very important for design of such structures. The analysis reveals the importance of the flexural rigidity of the ribbons that might cause significant redistribution of stresses within the steel bands.

Musculoskeletal Asymmetry in Football Athletes: A Product of Limb Function over Time.

Asymmetrical loading patterns are commonplace in football sports. Our aim was to examine the influence of training age and limb function on lower-body musculoskeletal morphology. Fifty-five elite football athletes were stratified into less experienced (≤3 yr; n = 27) and more experienced (>3 yr; n = 28) groups by training age. All athletes underwent whole-body dual-energy x-ray absorptiometry scans and lower-body peripheral quantitative computed tomography tibial scans on the kicking and support limbs. Significant interactions between training age and limb function were evident across all skeletal parameters (F16, 91 = 0.182, P = 0.031, Wilks Λ = 0.969). Asymmetries between limbs were significantly larger in the more experienced players than the less experienced players for tibial mass (P ≤ 0.044, d ≥ 0.50), total cross-sectional area (P ≤ 0.039, d ≥ 0.53), and stress-strain indices (P ≤ 0.050, d ≥ 0.42). No significant asymmetry was evident for total volumetric density. More experienced players also exhibited greater lower-body tibial mass (P ≤ 0.001, d ≥ 1.22), volumetric density (P ≤ 0.009, d ≥ 0.79), cross-sectional area (P ≤ 0.387, d ≥ 0.21), stress-strain indices (P ≤ 0.012, d ≥ 0.69), fracture loads (P ≤ 0.018, d ≥ 0.57), and muscle mass and cross-sectional area (P ≤ 0.016, d ≥ 0.68) than less experienced players. Asymmetries were evident in athletes as a product of limb function over time. Chronic exposure to routine high-impact gravitational loads afforded to the support limb preferentially improved bone mass and structure (cross-sectional area and cortex thickness) as potent contributors to bone strength relative to the high-magnitude muscular loads predominantly afforded to the kicking limb.

D-67 Clinical Case Slide - Lower Extremity Issues II

Wolff’s law states that tissue adapts in response to mechanical loads placed upon it. While clinicians typically evaluate athletes for symmetry, some sports require bilaterally asymmetric movement, which may result in bilateral differences in tissue adaptations. There is limited sports-specific data regarding bone mineral density (BMD) and therefore it is believed that asymmetric athletes might have a significantly different BMD in their asymmetrically loaded leg. PURPOSE: To determine if there are bilateral differences in hip BMD in track and field athletes competing in events which require asymmetric loading patterns. METHODS: Men’s and women’s NCAA Division I track and field, soccer, and lacrosse teams underwent hip DEXA scans. Bone mineral density of Ward’s triangle (BMDW) and of the femoral neck (BMDFN) were measured bilaterally. Track and field athletes competing in events where asymmetric lower extremity loading patterns are required (ASYM) were identified (e.g., those utilizing a “plant” leg, lead / trail leg, or running high speeds on a curve). These events were defined as jumping events, javelin, hurdles, pole vault, and the 200m. The asymmetric athletes were matched with non-asymmetric athletes (NON) based on similar age, height, and body mass. The absolute value of the difference in BMD measurements between the left and right hips was computed for each individual for both regions. Paired t-tests were used to compare bilateral differences for BMDW and BMDFN between asymmetric athletes and matched controls. RESULTS: 15 males and 19 females were included for each group. There were no significant differences in BMDFN between ASYM and NON for males (p = 0.794), females (p = 0.485), or combined (p = 0.473). There were no significant differences between groups in BMDW for males (p = 0.779), females (p = 0.446), or combined (p = 0.508). CONCLUSIONS: Lack of bilateral differences in BMD at two regions of the hip in ASYM compared to NON suggests that event-specific asymmetric movement is not sufficient stimulus to cause major adaptation in bone relative to general athletic participation. It remains possible that older athletes with greater event-specific experience may exhibit bilateral asymmetries. Clinicians do not need to consider event-specific movement when interpreting hip BMD in collegiate athletes.