Occupational physical activity assessment for chronic disease prevention and management: A review of methods for both occupational health practitioners and researchers.

Occupational physical activity (OPA) is an occupational exposure that impacts worker health. OPA is amenable to measurement and modification through the hierarchy of controls. Occupational exposure scientists have roles in addressing inadequate physical activity, as well as excessive or harmful physical activity. Occupational health researchers can contribute to the development of novel OPA exposure assessment techniques and to epidemiologic studies examining the health impacts of physical activity at work. Occupational health practitioners stand to benefit from understanding the strengths and limitations of physical activity measurement approaches, such as accelerometers in smartphones, which are already ubiquitous in many workplaces and in some worksite health programs. This comprehensive review of the literature provides an overview of physical activity monitoring for occupational exposure scientists. This article summarizes data on the public health implications of physical activity at work, highlighting complex relationships with common chronic diseases. This article includes descriptions of several techniques that have been used to measure physical activity at work and elsewhere, focusing in detail on pedometers, accelerometers, and Global Positioning System technology. Additional subjective and objective measurement strategies are described as well.

Self-selected speeds and metabolic cost of longboard skateboarding.

PURPOSE: The purpose of this study was to determine self-selected speeds, metabolic rate, and gross metabolic cost during longboard skateboarding. METHODS: We measured overground speed and metabolic rate while 15 experienced longboarders traveled at their self-selected slow, typical and fast speeds. RESULTS: Mean longboarding speeds were 3.7, 4.5 and 5.1 m s(-1), during slow, typical and fast trials, respectively. Mean rates of oxygen consumption were 24.1, 29.1 and 37.2 ml kg(-1) min(-1) and mean rates of energy expenditure were 33.5, 41.8 and 52.7 kJ min(-1) at the slow, typical and fast speeds, respectively. At typical speeds, average intensity was ~8.5 METs. There was a significant positive relationship between oxygen consumption and energy expenditure versus speed (R(2) = 0.69 (P < 0.001), and R(2) = 0.78 (P < 0.001), respectively). The gross metabolic cost was ~2.2 J kg(-1) m(-1) at the typical speed, greater than that reported for cycling and ~50% smaller than that of walking. CONCLUSION: These results suggest that longboarding is a novel form of physical activity that elicits vigorous intensity, yet is economical compared to walking.

An in vivo ovine model of bone tissue alterations in simulated microgravity conditions.

Microgravity and its inherent reduction in body-weight associated mechanical loading encountered during spaceflight have been shown to produce deleterious effects on important human physiological processes. Rodent hindlimb unloading is the most widely-used ground-based microgravity model. Unfortunately, results from these studies are difficult to translate to the human condition due to major anatomic and physiologic differences between the two species such as bone microarchitecture and healing rates. The use of translatable ovine models to investigate orthopedic-related conditions has become increasingly popular due to similarities in size and skeletal architecture of the two species. Thus, a new translational model of simulated microgravity was developed using common external fixation techniques to shield the metatarsal bone of the ovine hindlimb during normal daily activity over an 8 week period. Bone mineral density, quantified via dual-energy X-ray absorptiometry, decreased 29.0% (p < 0.001) in the treated metatarsi. Post-sacrifice biomechanical evaluation revealed reduced bending modulus (-25.8%, p < 0.05) and failure load (-27.8%, p < 0.001) following the microgravity treatment. Microcomputed tomography and histology revealed reduced bone volume (-35.9%, p < 0.01), trabecular thickness (-30.9%, p < 0.01), trabecular number (-22.5%, p < 0.05), bone formation rate (-57.7%, p < 0.01), and osteoblast number (-52.5%, p < 0.001), as well as increased osteoclast number (269.1%, p < 0.001) in the treated metatarsi of the microgravity group. No significant alterations occurred for any outcome parameter in the Sham Surgery Group. These data indicate that the external fixation technique utilized in this model was able to effectively unload the metatarsus and induce significant radiographic, biomechanical, and histomorphometric alterations that are known to be induced by spaceflight. Further, these findings demonstrate that the physiologic mechanisms driving bone remodeling in sheep and humans during prolonged periods of unloading (specifically increased osteoclast activity) are more similar than previously utilized models, allowing more comprehensive investigations of microgravity-related bone remodeling as it relates to human spaceflight.

Biomechanical contributions of the trunk and upper extremity in discrete versus cyclic reaching in survivors of stroke.

BACKGROUND: Stroke rehabilitation interventions and assessments incorporate discrete and/or cyclic reaching tasks, yet no biomechanical comparison exists between these 2 movements in survivors of stroke. OBJECTIVE: To characterize the differences between discrete (movements bounded by stationary periods) and cyclic (continuous repetitive movements) reaching in survivors of stroke. METHODS: Seventeen survivors of stroke underwent kinematic motion analysis of discrete and cyclic reaching movements. Outcomes collected for each side included shoulder, elbow, and trunk range of motion (ROM); peak velocity; movement time; and spatial variability at target contact. RESULTS: Participants used significantly less shoulder and elbow ROM and significantly more trunk flexion ROM when reaching with the stroke-affected side compared with the less-affected side (P < .001). Participants used significantly more trunk rotation during cyclic reaching than discrete reaching with the stroke-affected side (P = .01). No post hoc differences were observed between tasks within the stroke-affected side for elbow, shoulder, and trunk flexion ROM. Peak velocity, movement time, and spatial variability were not different between discrete and cyclic reaching in the stroke-affected side. CONCLUSIONS: Survivors of stroke reached with altered kinematics when the stroke-affected side was compared with the less-affected side, yet there were few differences between discrete and cyclic reaching within the stroke-affected side. The greater trunk rotation during cyclic reaching represents a unique segmental strategy when using the stroke-affected side without consequences to end-point kinematics. These findings suggest that clinicians should consider the type of reaching required in therapeutic activities because of the continuous movement demands required with cyclic reaching.

What Matters When Children Play: Influence of Social Cognitive Theory and Perceived Environment on Levels of Physical Activity Among Elementary-Aged Youth.

OBJECTIVES: Social Cognitive Theory (SCT) has often been used as a guide to predict and modify physical activity (PA) behavior. We assessed the ability of commonly investigated SCT variables and perceived school environment variables to predict PA among elementary students. We also examined differences in influences between Hispanic and non-Hispanic students. DESIGN: This analysis used baseline data collected from eight schools who participated in a four-year study of a combined school-day curriculum and environmental intervention. METHODS: Data were collected from 393 students. A 3-step linear regression was used to measure associations between PA level, SCT variables (self-efficacy, social support, enjoyment), and perceived environment variables (schoolyard structures, condition, equipment/supervision). Logistic regression assessed associations between variables and whether students met PA recommendations. RESULTS: School and sex explained 6% of the moderate-to-vigorous PA models' variation. SCT variables explained an additional 15% of the models' variation, with much of the model's predictive ability coming from self-efficacy and social support. Sex was more strongly associated with PA level among Hispanic students, while self-efficacy was more strongly associated among non-Hispanic students. Perceived environment variables contributed little to the models. CONCLUSIONS: Our findings add to the literature on the influences of PA among elementary-aged students. The differences seen in the influence of sex and self-efficacy among non-Hispanic and Hispanic students suggests these are areas where PA interventions could be tailored to improve efficacy. Additional research is needed to understand if different measures of perceived environment or perceptions at different ages may better predict PA.

The effects of walking speed on tibiofemoral loading estimated via musculoskeletal modeling.

Net muscle moments (NMMs) have been used as proxy measures of joint loading, but musculoskeletal models can estimate contact forces within joints. The purpose of this study was to use a musculoskeletal model to estimate tibiofemoral forces and to examine the relationship between NMMs and tibiofemoral forces across walking speeds. We collected kinematic, kinetic, and electromyographic data as ten adult participants walked on a dual-belt force-measuring treadmill at 0.75, 1.25, and 1.50 m/s. We scaled a musculoskeletal model to each participant and used OpenSim to calculate the NMMs and muscle forces through inverse dynamics and weighted static optimization, respectively. We determined tibiofemoral forces from the vector sum of intersegmental and muscle forces crossing the knee. Estimated tibiofemoral forces increased with walking speed. Peak early-stance compressive tibiofemoral forces increased 52% as walking speed increased from 0.75 to 1.50 m/s, whereas peak knee extension NMMs increased by 168%. During late stance, peak compressive tibiofemoral forces increased by 18% as speed increased. Although compressive loads at the knee did not increase in direct proportion to NMMs, faster walking resulted in greater compressive forces during weight acceptance and increased compressive and anterior/posterior tibiofemoral loading rates in addition to a greater abduction NMM.

Accuracy of self-reported height and weight in children aged 6 to 11 years.

The purpose of this study was to determine the ability of first-, third-, and fifth-graders to accurately self-report height and weight. Self-reported and measured values for height and weight were recorded for 487 students. The ability to self-report a reasonable value for height and weight improved with grade level, but children in all 3 grade levels significantly underreported their height and weight. Only fifth-graders accurately self-reported their weight; therefore, using self-reported height and weight to determine the prevalence of overweight and obesity for elementary school-aged children is not recommended.

Biomechanics of walking with snowshoes.

Snowshoeing is a popular form of winter recreation due to the development of lightweight snowshoes that provide flotation, traction, and stability. The purpose of this study was to determine the effects of snowshoes on lower extremity kinematics during level walking. Twelve adults (6 males, 6 females, body mass = 67.5 +/- 10.7kg) completed six 3-minute level walking trials. Subjects walked overground without snowshoes and on packed snow using conventional and flexible tail snowshoes. We placed lightweight inertial/gyroscopic sensors on the sacrum, thigh, shank, and foot. We recorded sensor orientation and calculated hip, knee, and ankle joint angles and angular velocities. Compared to level overground walking, subjects had greater hip and knee flexion during stance and greater hip flexion during swing while snowshoeing. Ankle plantarflexion began during late swing when snowshoeing vs. heel strike during overground walking. Lower extremity kinematics were similar across snowshoe frame designs during level walking. Our results show that snowshoeing on packed snow results in a more flexed leg compared to overground walking and may reflect a strategy to limit the effects of walking with an extended heel.

The effects of pediatric obesity on patellofemoral joint contact force during walking.

BACKGROUND: Obesity increases a child's risk of developing knee pain across the lifespan, potentially through elevated patellofemoral joint loads that occur during habitual weight-bearing activities. RESEARCH QUESTION: Do obese children have greater absolute and patellar-area-normalized patellofemoral joint forces compared to healthy weight children during walking? METHODS: We utilized a cross-sectional design to address the aims of this study. Experimental biomechanics data were collected during treadmill walking in 10 healthy-weight and 10 obese 8-12 year-olds. We used radiographic images to develop subject-specific musculoskeletal models, generated walking simulations from the experimental data, and predicted patellofemoral joint contact force using established techniques. RESULTS: We found that the obese children had 1.98 times greater absolute (p = 0.002) and 1.81 times greater patellar-area-normalized (p = 0.008) patellofemoral joint contact forces compared to the healthy-weight children. We observed a stronger relationship between absolute patellofemoral joint contact force and BMI (r2=0.58) than between patellofemoral joint contact force and body fat percentage (r2=0.38). SIGNIFICANCE: Our results indicate that obese children walk with increased patellofemoral loads in absolute terms and also relative to the area of the articulating surfaces, which likely contributes to the increased risk of knee pain in this pediatric population. This information, which provides a baseline comparison for future longitudinal studies, also informs the type and frequency of physical activity prescription aimed at reducing the risk of knee injury and improving long-term outcomes.

Recess environment and curriculum intervention on children's physical activity: IPLAY.

Understanding the impacts of the built environment on physical activity (PA) is essential to promoting children's PA. The purpose of this study was to investigate the effects of schoolyard renovations and a PA recess curriculum alone and in combination on children's PA. This was a 2 (learning landscape [LL] vs. non-LL) × 2 (curriculum intervention vs. no curriculum intervention) factorial design with random assignment to the curriculum intervention, and six elementary schools per condition. PA outcomes were assessed preprogram, mid-program, immediate postprogram, and one year postprogram. No meaningful intervention effects were found. Lack of an effect may be due to the brief dose of recess, the curriculum not being integrated within the schoolyard, the LL implementation occurring prior to the study, or the already high levels of PA. Potential avenues to promote PA include making recess longer, integrating recess into the school curricula, and developing recess PA curricula integrating schoolyards.

Effects of obesity on the biomechanics of walking at different speeds.

PURPOSE: Walking is a recommended form of exercise for the treatment of obesity, but walking may be a critical source of biomechanical loads that link obesity and musculoskeletal pathology, particularly knee osteoarthritis. We hypothesized that compared with normal-weight adults 1) obese adults would have greater absolute ground-reaction forces (GRF) during walking, but their GRF would be reduced at slower walking speeds; and 2) obese adults would have greater sagittal-plane absolute leg-joint moments at a given walking speed, but these moments would be reduced at slower walking speeds. METHODS: We measured GRF and recorded sagittal-plane kinematics of 20 adults (10 obese and 10 normal weight) as they walked on a level, force-measuring treadmill at six speeds (0.5-1.75 m.s(-1)). We calculated sagittal-plane net muscle moments at the hip, knee, and ankle. RESULTS: Compared with their normal-weight peers, obese adults had much greater absolute GRF (N), stance-phase sagittal-plane net muscle moments (N.m) and step width (m). CONCLUSIONS: Greater sagittal-plane knee moments in the obese subjects suggest that they walked with greater knee-joint loads than normal-weight adults. Walking slower reduced GRF and net muscle moments and may be a risk-lowering strategy for obese adults who wish to walk for exercise. When obese subjects walked at 1.0 versus 1.5 m.s(-1), peak sagittal-plane knee moments were 45% less. Obese subjects walking at approximately 1.1 m.s(-1) would have the same absolute peak sagittal-plane knee net muscle moment as normal-weight subjects when they walk at their typical preferred speed of 1.4 m.s(-1).

The effects of adding mass to the legs on the energetics and biomechanics of walking.

PURPOSE: The metabolic cost of walking increases when mass is added to the legs, but the effects of load magnitude and location on the energetics and biomechanics of walking are unclear. We hypothesized that with leg loading 1) net metabolic rate would be related to the moment of inertia of the leg (I(leg)), 2) kinematics would be conserved, except for heavy foot loads, and 3) swing-phase sagittal-plane net muscle moments and swing-phase leg-muscle electromyography (EMG) would increase. METHODS: Five adult males walked on a force-measuring treadmill at 1.25 m.s(-1) with no load and with loads of 2 and 4 kg per foot and shank, 4 and 8 kg per thigh, and 4, 8, and 16 kg on the waist. We recorded metabolic rate and sagittal-plane kinematics and net muscle moments about the hip, knee, and ankle during the single-stance and swing phases, and EMG of key leg muscles. RESULTS: Net metabolic rate during walking increased with load mass and more distal location and was correlated with I(leg) (r2 = 0.43). Thigh loading was relatively inexpensive, helping to explain why the metabolic rate during walking is not strongly affected by body mass distribution. Kinematics, single-stance and swing-phase muscle moments, and EMG were similar while walking with no load or with waist, thigh, or shank loads. The increase in net metabolic rate with foot loading was associated with greater EMG of muscles that initiate leg swing and greater swing-phase muscle moments. CONCLUSIONS: Distal leg loads increase the metabolic rate required for swinging the leg. The increase in metabolic rate with more proximal loads may be attributable to a combination of supporting (via hip abduction muscles) and propagating the swing leg.

Effects of obesity and sex on the energetic cost and preferred speed of walking.

The metabolic energy cost of walking is determined, to a large degree, by body mass, but it is not clear how body composition and mass distribution influence this cost. We tested the hypothesis that walking would be most expensive for obese women compared with obese men and normal-weight women and men. Furthermore, we hypothesized that for all groups, preferred walking speed would correspond to the speed that minimized the gross energy cost per distance. We measured body composition, maximal oxygen consumption, and preferred walking speed of 39 (19 class II obese, 20 normal weight) women and men. We also measured oxygen consumption and carbon dioxide production while the subjects walked on a level treadmill at six speeds (0.50-1.75 m/s). Both obesity and sex affected the net metabolic rate (W/kg) of walking. Net metabolic rates of obese subjects were only approximately 10% greater (per kg) than for normal-weight subjects, and net metabolic rates for women were approximately 10% greater than for men. The increase in net metabolic rate at faster walking speeds was greatest in obese women compared with the other groups. Preferred walking speed was not different across groups (1.42 m/s) and was near the speed that minimized gross energy cost per distance. Surprisingly, mass distribution (thigh mass/body mass) was not related to net metabolic rate, but body composition (% fat) was (r2= 0.43). Detailed biomechanical studies of walking are needed to investigate whether obese individuals adopt novel energy saving mechanisms during walking.

Compressive and shear hip joint contact forces are affected by pediatric obesity during walking.

Obese children exhibit altered gait mechanics compared to healthy-weight children and have an increased prevalence of hip pain and pathology. This study sought to determine the relationships between body mass and compressive and shear hip joint contact forces during walking. Kinematic and kinetic data were collected during treadmill walking at 1ms(-1) in 10 obese and 10 healthy-weight 8-12 year-olds. We estimated body composition, segment masses, lower-extremity alignment, and femoral neck angle via radiographic images, created personalized musculoskeletal models in OpenSim, and computed muscle forces and hip joint contact forces. Hip extension at mid-stance was 9° less, on average, in the obese children (p<0.001). Hip abduction, knee flexion, and body-weight normalized peak hip moments were similar between groups. Normalized to body-weight, peak contact forces were similar at the first peak and slightly lower at the second peak between the obese and healthy-weight participants. Total body mass explained a greater proportion of contact force variance compared to lean body mass in the compressive (r(2)=0.89) and vertical shear (perpendicular to the physis acting superior-to-inferior) (r(2)=0.84) directions; lean body mass explained a greater proportion in the posterior shear direction (r(2)=0.54). Stance-average contact forces in the compressive and vertical shear directions increased by 41N and 48N, respectively, for every kilogram of body mass. Age explained less than 27% of the hip loading variance. No effect of sex was found. The proportionality between hip loads and body-weight may be implicated in an obese child׳s increased risk of hip pain and pathology.

Pediatric obesity and walking duration increase medial tibiofemoral compartment contact forces.

With the high prevalence of pediatric obesity there is a need for structured physical activity during childhood. However, altered tibiofemoral loading during physical activity in obese children likely contribute to their increased risk of orthopedic disorders of the knee. The goal of this study was to determine the effects of pediatric obesity and walking duration on medial and lateral tibiofemoral contact forces. We collected experimental biomechanics data during treadmill walking at 1 m•s(-1) for 20 min in 10 obese and 10 healthy-weight 8-12 year-olds. We created subject-specific musculoskeletal models using radiographic measures of tibiofemoral alignment and centers-of-pressure, and predicted medial and lateral tibiofemoral contact forces at the beginning and end of each trial. Obesity and walking duration affected tibiofemoral loading. At the beginning of the trail, the average percent of the total load passing through the medial compartment during stance was 85% in the obese children and 63% in the healthy-weight children; at the end of the trial, the medial distribution was 90% in the obese children and 72% in the healthy-weight children. Medial compartment loading rates were 1.78 times greater in the obese participants. The medial compartment loading rate increased 17% in both groups at the end compared to the beginning of the trial (p = 0.001). We found a strong linear relationship between body-fat percentage and the medial-lateral load distribution (r(2) = 0.79). Altered tibiofemoral loading during walking in obese children may contribute to their increased risk of knee pain and pathology.

Computational characterization of fracture healing under reduced gravity loading conditions.

The literature is deficient with regard to how the localized mechanical environment of skeletal tissue is altered during reduced gravitational loading and how these alterations affect fracture healing. Thus, a finite element model of the ovine hindlimb was created to characterize the local mechanical environment responsible for the inhibited fracture healing observed under experimental simulated hypogravity conditions. Following convergence and verification studies, hydrostatic pressure and strain within a diaphyseal fracture of the metatarsus were evaluated for models under both 1 and 0.25 g loading environments and compared to results of a related in vivo study. Results of the study suggest that reductions in hydrostatic pressure and strain of the healing fracture for animals exposed to reduced gravitational loading conditions contributed to an inhibited healing process, with animals exposed to the simulated hypogravity environment subsequently initiating an intramembranous bone formation process rather than the typical endochondral ossification healing process experienced by animals healing in a 1 g gravitational environment. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1206-1215, 2016.

Soft Tissue Deformations Contribute to the Mechanics of Walking in Obese Adults.

UNLABELLED: Obesity not only adds to the mass that must be carried during walking but also changes body composition. Although extra mass causes roughly proportional increases in musculoskeletal loading, less well understood is the effect of relatively soft and mechanically compliant adipose tissue. PURPOSE: This purpose of this study was to estimate the work performed by soft tissue deformations during walking. The soft tissue would be expected to experience damped oscillations, particularly from high force transients after heel strike, and could potentially change the mechanical work demands for walking. METHODS: We analyzed treadmill walking data at 1.25 m·s for 11 obese (BMI >30 kg·m) and nine nonobese (BMI <30 kg·m) adults. The soft tissue work was quantified with a method that compares the work performed by lower extremity joints as derived using assumptions of rigid body segments, with that estimated without rigid body assumptions. RESULTS: Relative to body mass, obese and nonobese individuals perform similar amounts of mechanical work. However, negative work performed by soft tissues was significantly greater in obese individuals (P = 0.0102), equivalent to approximately 0.36 J·kg vs 0.27 J·kg in nonobese individuals. The negative (dissipative) work by soft tissues occurred mainly after heel strike and, for obese individuals, was comparable in magnitude to the total negative work from all of the joints combined (0.34 J·kg vs 0.33 J·kg for obese and nonobese adults, respectively). Although the joints performed a relatively similar amount of work overall, obese individuals performed less negative work actively at the knee. CONCLUSIONS: The greater proportion of soft tissues in obese individuals results in substantial changes in the amount, location, and timing of work and may also affect metabolic energy expenditure during walking.

Posture and activity recognition and energy expenditure estimation in a wearable platform.

The use of wearable sensors coupled with the processing power of mobile phones may be an attractive way to provide real-time feedback about physical activity and energy expenditure (EE). Here, we describe the use of a shoe-based wearable sensor system (SmartShoe) with a mobile phone for real-time recognition of various postures/physical activities and the resulting EE. To deal with processing power and memory limitations of the phone, we compare the use of support vector machines (SVM), multinomial logistic discrimination (MLD), and multilayer perceptrons (MLP) for posture and activity classification followed by activity-branched EE estimation. The algorithms were validated using data from 15 subjects who performed up to 15 different activities of daily living during a 4-h stay in a room calorimeter. MLD and MLP demonstrated activity classification accuracy virtually identical to SVM (∼ 95%) while reducing the running time and the memory requirements by a factor of >10 3. Comparison of per-minute EE estimation using activity-branched models resulted in accurate EE prediction (RMSE = 0.78 kcal/min for SVM and MLD activity classification, 0.77 kcal/min for MLP versus RMSE of 0.75 kcal/min for manual annotation). These results suggest that low-power computational algorithms can be successfully used for real-time physical activity monitoring and EE estimation on a wearable platform.

How tibiofemoral alignment and contact locations affect predictions of medial and lateral tibiofemoral contact forces.

Understanding degeneration of biological and prosthetic knee joints requires knowledge of the in-vivo loading environment during activities of daily living. Musculoskeletal models can estimate medial/lateral tibiofemoral compartment contact forces, yet anthropometric differences between individuals make accurate predictions challenging. We developed a full-body OpenSim musculoskeletal model with a knee joint that incorporates subject-specific tibiofemoral alignment (i.e. knee varus-valgus) and geometry (i.e. contact locations). We tested the accuracy of our model and determined the importance of these subject-specific parameters by comparing estimated to measured medial and lateral contact forces during walking in an individual with an instrumented knee replacement and post-operative genu valgum (6°). The errors in the predictions of the first peak medial and lateral contact force were 12.4% and 11.9%, respectively, for a model with subject-specific tibiofemoral alignment and contact locations determined through radiographic analysis, vs. 63.1% and 42.0%, respectively, for a model with generic parameters. We found that each degree of tibiofemoral alignment deviation altered the first peak medial compartment contact force by 51N (r(2)=0.99), while each millimeter of medial-lateral translation of the compartment contact point locations altered the first peak medial compartment contact force by 41N (r(2)=0.99). The model, available at www.simtk.org/home/med-lat-knee/, enables the specification of subject-specific joint alignment and compartment contact locations to more accurately estimate medial and lateral tibiofemoral contact forces in individuals with non-neutral alignment.

Modulating tibiofemoral contact force in the sheep hind limb via treadmill walking: Predictions from an opensim musculoskeletal model.

Sheep are a predominant animal model used to study a variety of orthopedic conditions. Understanding and controlling the in-vivo loading environment in the sheep hind limb is often necessary for investigations relating to bone and joint mechanics. The purpose of this study was to develop a musculoskeletal model of an adult sheep hind limb and investigate the effects of treadmill walking speed on muscle and joint contact forces. We constructed the skeletal geometry of the model from computed topography images. Dual-energy x-ray absorptiometry was utilized to establish the inertial properties of each model segment. Detailed dissection and tendon excursion experiments established the requisite muscle lines of actions. We used OpenSim and experimentally-collected marker trajectories and ground reaction forces to quantify muscle and joint contact forces during treadmill walking at 0.25 m• s(-1) and 0.75 m• s(-1) . Peak compressive and anterior-posterior tibiofemoral contact forces were 20% (0.38 BW, p = 0.008) and 37% (0.17 BW, p = 0.040) larger, respectively, at the moderate gait speed relative to the slower speed. Medial-lateral tibiofemoral contact forces were not significantly different. Adjusting treadmill speed appears to be a viable method to modulate compressive and anterior-posterior tibiofemoral contact forces in the sheep hind limb. The musculoskeletal model is freely-available at www.SimTK.org.