Most running studies have considered level running (LR), yet the regulation of locomotor behaviour during uphill (UR) and downhill (DR) running is fundamental to increase our understanding of human ...locomotion. The purpose of this article was to review the existing literature regarding biomechanical, neuromuscular and physiological adaptations during graded running. Relative to LR, UR is characterized by a higher step frequency, increased internal mechanical work, shorter swing/aerial phase duration, and greater duty factor, while DR is characterized by increased aerial time, reduced step frequency and decreased duty factor. Grade also modifies foot strike patterns, with a progressive adoption of a mid- to fore-foot strike pattern during UR, and rear-foot strike patterns during DR. In UR, lower limb muscles perform a higher net mechanical work compared to LR and DR to increase the body's potential energy. In DR, energy dissipation is generally prevalent compared to energy generation. The increased demands for work as running incline increases are met by an increase in power output at all joints, particularly the hip. This implies that UR requires greater muscular activity compared to LR and DR. Energy cost of running (C
) linearly increases with positive slope but C
of DR decreases until a minimum slope is reached at -20 %, after which C
increases again. The effects of slope on biomechanics, muscle contraction patterns and physiological responses have important implications for injury prevention and success of athletes engaged in graded running competitions.
Changes in gallop stride parameters prior to injury have been documented previously in Thoroughbred racehorses. Validating solutions for quantification of fundamental stride parameters is important ...for large scale studies investigating injury related factors. This study describes a fast Fourier transformation-based method for extracting stride frequency (SF) values from speed fluctuations recorded with a standalone GPS-logger suitable for galloping horses. Limits of agreement with SF values derived from inertial measurement unit (IMU) pitch data are presented. Twelve Thoroughbred horses were instrumented with a GPS-logger (Vbox sport, Racelogic, 10 Hz samplerate) and a IMU-logger (Xsens DOT, Xsens, 120 Hz samplerate), both attached to the saddlecloth in the midline caudal to the saddle and time synchronized by minimizing root mean square error between differentiated GPS and IMU heading. Each horse performed three gallop trials with a target speed of 36miles per hour (16.1 ms−1) on a dirt racetrack. Average speed was 16.48 ms−1 ranging from 16.1 to 17.4 ms−1 between horses. Limits of agreement between GPS- and IMU-derived SF had a bias of 0.0032 Hz and a sample-by-sample precision of +/−0.027 Hz calculated over N = 2196 values. The stride length uncertainty related to the trial-by-trial SF precision of 0.0091 Hz achieved across 100 m gallop sections is smaller than the 10 cm decrease in stride length that has been associated with an increased risk of musculoskeletal injury. This suggests that the described method is suitable for calculating fundamental stride parameters in the context of injury prevention in galloping horses.
Abstract The purpose of this research was to utilize a series of models to estimate the stress in a cross section of the tibia, located 62% from the proximal end, during walking. Twenty-eight male, ...active duty soldiers walked on an instrumented treadmill while external force data and kinematics were recorded. A rigid body model was used to estimate joint moments and reaction forces. A musculoskeletal model was used to gather muscle length, muscle velocity, moment arm and orientation information. Optimization procedures were used to estimate muscle forces and finally internal bone forces and moments were applied to an inhomogeneous, subject specific bone model obtained from CT scans to estimate stress in the bone cross section. Validity was assessed by comparison to stresses calculated from strain gage data in the literature and sensitivity was investigated using two simplified versions of the bone model-a homogeneous model and an ellipse approximation. Peak compressive stress occurred on the posterior aspect of the cross section (−47.5±14.9 MPa). Peak tensile stress occurred on the anterior aspect (27.0±11.7 MPa) while the location of peak shear was variable between subjects (7.2±2.4 MPa). Peak compressive, tensile and shear stresses were within 0.52 MPa, 0.36 MPa and 3.02 MPa respectively of those calculated from the converted strain gage data. Peak values from a inhomogeneous model of the bone correlated well with homogeneous model (normal: 0.99; shear: 0.94) as did the normal ellipse model ( r =0.89–0.96). However, the relationship between shear stress in the inhomogeneous model and ellipse model was less accurate ( r =0.64). The procedures detailed in this paper provide a non-invasive and relatively quick method of estimating cross sectional stress that holds promise for assessing injury and osteogenic stimulus in bone during normal physical activity.
Atypical femoral fractures (AFF) are characterized as low-energy fractures of the femoral shaft or subtrochanteric region. Femoral geometry is known to play a role in AFF risk; it is hypothesized ...that high-risk geometries are associated with elevated femoral shaft strain. However, it is not well known which geometric parameters have the greatest effect on strain, or whether interaction between parameters is significant. The purpose of this study was to thoroughly quantify the relationship between femoral geometry and diaphyseal strain, using patient specific finite element (FE) modelling in concert with parametric mesh morphing.
Ten FE models were generated from computed tomography (CT) images of cadaveric femora. Heterogeneous material properties were assigned based on average CT intensities at element locations and models were subject to loads and boundary conditions representing the stance phase of gait. Mesh morphing was used to manipulate 8 geometric parameters: neck shaft angle (NSA), neck version angle (NV), neck length (NL), femoral length (FL), lateral bowing angle (L.Bow), anterior bowing angle (A.Bow), shaft diameter (S.Dia), and cortical bone thickness (C·Th). A 2-Level full factorial analysis was used to explore the effect of different combinations of physiologically realistic minimum and maximum values for each parameter. Statistical analysis (Generalized Estimating Equations) was used to assess main effects and first order interactions of each parameter.
Six independent parameters and seven interaction terms had statistically significant (p<0.05) effects on peak strain and strained volume. For both measures, the greatest changes were caused by S.Dia, L.Bow, and A.Bow, and/or first order interactions involving two of these variables.
As hypothesized, a large number of geometric measures (six) and first order interactions (seven) are associated with changes in femoral shaft strain. These measures can be evaluated radiographically, which may have important implications for future studies investigating AFF risk in clinical populations.
•Femoral geometry influences diaphyseal strain, and may contribute to risk of atypical femoral fracture (AFF)•Shaft diameter, lateral bowing, and anterior bowing angles have the greatest effects on peak strain and strained volume.•Greater bowing angles may also predispose patients to suffer AFF at the midshaft rather than the intertrochanteric region.
A fatigue-failure process is hypothesized to govern the development of tibial stress fractures, where bone damage is highly dependent on the peak strain magnitude. To date, much of the work examining ...tibial strain during running has ignored uphill and downhill running despite the prevalence of this terrain. This study examined the sensitivity of tibial strain to changes in running grade and speed using a combined musculoskeletal-finite element modelling routine. Seventeen participants ran on a treadmill at ±10, ±5 and 0 deg; at each grade, participants ran at 3.33 m s-1 and at a grade-adjusted speed of 2.50 and 4.17 m s-1 for uphill and downhill grades, respectively. Force and motion data were recorded in each grade and speed combination. Muscle and joint contact forces were estimated using inverse-dynamics-based static optimization. These forces were applied to a participant-adjusted finite element model of the tibia. None of the strain variables (50th and 95th percentile strain and strained volume ≥4000 με) differed as a function of running grade; however, all strain variables were sensitive to running speed (F1≥9.59, P≤0.03). In particular, a 1 m s-1 increase in speed resulted in a 9% (∼260 με) and 155% (∼600 mm3) increase in peak strain and strained volume, respectively. Overall, these findings suggest that faster running speeds, but not changes in running grade, may be more deleterious to the tibia.
Females are up to four times more likely to sustain a stress fracture than males. Our previous work, using statistical appearance modeling in combination with the finite element method, suggested ...that sex-related differences in tibial geometry may increase bone strain in females. The purpose of this study was to cross-validate these findings, by quantifying sex-related differences in tibia-fibula bone geometry, density, and finite element-predicted bone strain in a new cohort of young physically active adults. CT scans of the lower leg were collected for fifteen males (23.3 ± 4.3 years, 1.77 ± 0.09 m, 75.6 ± 10.0 kg) and fifteen females (22.9 ± 3.0 years, 1.67 ± 0.07 m, 60.9 ± 6.7 kg). A statistical appearance model was fit to each participant's tibia and fibula. The average female and male tibia-fibula complex, controlled for isotropic scaling, were then calculated. Bone geometry, density, and finite element-predicted bone strains in running were compared between the average female and male. The new cohort illustrated the same patterns as the cohort from the previous study: the tibial diaphysis of the average female was narrower and had greater cortical bone density. Peak strain and the volume of bone experiencing ≥4000 με were 10 % and 80 % greater, respectively, in the average female when compared to the average male, which was driven by a narrower diaphysis. The sex-related disparities in tibial geometry, density, and bone strain described by our previous model were also observed in this entirely new cohort. Disparities in tibial diaphysis geometry likely contribute to the elevated stress fracture risk observed in females.
•Sex disparities in geometry, density, and strain were confirmed in a new cohort.•Controlled for size the average female illustrated higher tibial strain.•Elevated strain in the average female was driven by a narrower tibia.•Sexual dimorphism likely contributes to the greater stress fracture risk in females.
We examined the sensitivity of internal tibial forces and moments during running to different subtalar/ankle moment constraints in a static optimization routine. Seventeen participants ran at 2.20, ...3.33, and 4.17 ms-1 while force and motion data were collected. Ankle joint contact force was estimated using inverse-dynamics-based static optimization. Three sets of joint moment constraints were tested. All sets included the flexion-extension and abduction-adduction moments at the hip and the flexion-extension moment at the knee but differed in the constraints used at the subtalar/ankle: (1) flexion-extension at the ankle (Sag), (2) flexion-extension and inversion-eversion at ankle (Sag + Front), and (3) flexion-extension at the ankle and supination-pronation at the subtalar (Sag + SubT). Internal tibial forces and moments were quantified at the distal one-third of the tibia, by ensuring static equilibrium with applied forces and moments. No interaction was observed between running speed and constraint for internal tibial forces or moments. Sag + SubT resulted in larger internal mediolateral force (+41%), frontal (+79%), and transverse (+29%) plane moments, compared to Sag and Sag + Front. Internal axial force was greatest in Sag + Front, compared to Sag and Sag + SubT (+37%). Faster running speeds resulted in greater internal tibial forces and moments in all directions (≥+6%). Internal tibial forces and moments at the distal one-third of the tibia were sensitive to the subtalar and ankle joint moment constraints used in the static optimization routine, independent of running speed.
State-of-the-art participant-specific finite element models require advanced medical imaging to quantify bone geometry and density distribution; access to and cost of imaging is prohibitive to the ...use of this approach. Statistical appearance models may enable estimation of participants' geometry and density in the absence of medical imaging. The purpose of this study was to: (1) quantify errors associated with predicting tibia-fibula geometry and density distribution from skin-mounted landmarks using a statistical appearance model and (2) quantify how those errors propagate to finite element-calculated bone strain. Participant-informed models of the tibia and fibula were generated for thirty participants from height and sex and from twelve skin-mounted landmarks using a statistical appearance model. Participant-specific running loads, calculated using gait data and a musculoskeletal model, were applied to participant-informed and CT-based models to predict bone strain using the finite element method. Participant-informed meshes illustrated median geometry and density distribution errors of 4.39-5.17 mm and 0.116-0.142 g/cm3, respectively, resulting in large errors in strain distribution (median RMSE = 476-492 με), peak strain (limits of agreement =±27-34%), and strained volume (limits of agreement =±104-202%). These findings indicate that neither skin-mounted landmark nor height and sex-based predictions could adequately approximate CT-derived participant-specific geometry, density distribution, or finite element-predicted bone strain and therefore should not be used for analyses comparing between groups or individuals.
Characterizing the biomechanical properties of articular cartilage is crucial to understanding processes of tissue homeostasis vs. degeneration. In mouse models, however, limitations are imposed by ...their small joint size and thin cartilage surfaces. Here we present a three-dimensional (3D) automated surface mapping system and methodology that allows for mechanical characterization of mouse cartilage with high spatial resolution. We performed repeated indentation mappings, followed by cartilage thickness measurement via needle probing, at 31 predefined positions distributed over the medial and lateral femoral condyles of healthy mice. High-resolution 3D x-ray microscopy (XRM) imaging was used to validate tissue thickness measurements. The automated indentation mapping was reproducible, and needle probing yielded cartilage thicknesses comparable to XRM imaging. When comparing healthy vs. degenerated cartilage, topographical variations in biomechanics were identified, with altered thickness and stiffness (instantaneous modulus) across condyles and within anteroposterior sub-regions. This quantitative technique comprehensively characterized cartilage function in mice femoral condyle cartilage. Hence, it has the potential to improve our understanding of tissue structure-function interplay in mouse models of repair and disease.
Bone strains in the lower extremity may be influenced by neuromuscular fatigue. In this study, we examined potential changes in finite element (FE) predicted tibial strains over the course of a ...fatiguing downhill-running protocol. Twelve physically active males ran for 30 min on an instrumented treadmill at a speed of 2.8 m s-1 and a grade of -11.3 deg. Motion capture and inverse-dynamic-based static optimization were used to estimate lower-extremity joint contact and muscle forces at the beginning, middle, and end stages of the downhill run. Finite element models of the tibia-fibula complex, from database-matched computed tomography images, were then used to estimate resulting 90th percentile strain (peak strain) and strained volume (volume of elements above 3000 με). In the fatigued state, peak ankle joint contact forces decreased an average of 8.1% (p < 0.002) in the axial direction, but increased an average of 7.7% (p < 0.042) in the anterior-posterior direction; consequently, finite element estimations of peak strain and strained volume were unaffected (p > 0.190). Although neuromuscular fatigue may influence ankle joint contact forces, it may not necessarily influence tibial strains due to the complex, and sometimes nonintuitive, relationship between applied load and resulting bone strain.
