Biomechanical and metabolic differences between skipping and running suggest the nervous system may require an alternative motor control strategy to execute skipping. Motor control strategies can be compared across gaits by muscle modules based on which muscles are coactivated (module composition) and whether the same module compositions are used across gaits (module generalization). The purposes of this study were to identify and compare the module composition of skipping and running and determine the module generalization present across these two gaits. Six healthy young adults performed 10 s skipping and running trials on a treadmill at 2.5 m/s while electromyography (EMG) was collected from 8 muscles. A non-negative matrix factorization extracted motor modules from the EMG data. Generalization of modules, both at the group and individual level, was determined with correlations of module weights. Participants required 3.7 ± 0.5 (range: 3-4) modules to control skipping and 3.8 ± 0.4 (range: 3-4) modules to control running. Three generalized modules were found across gaits at the group level, and at the individual level each participant had at least one generalized module. The generalized modules contributed to similar biomechanical subtasks across gaits, highlighting similar gross motor task demands. The unique biomechanical demands of the skipping hop resulted in gait-specific control of the tibialis anterior and gluteus medius. Future work is needed to identify the factors that influence the amount of generalization an individual uses across locomotor tasks and whether the degree of generalization impacts the performance of each gait.

The purpose of this study was to investigate whether individuals carrying vest-borne loads of 0%, 15%, and 30% body weight can decrease peak vertical ground reaction force (vGRF) when given peak vGRF feedback and examine if the gait adaptations induced by vGRF feedback decrease peak tibiofemoral joint (TFJ) contact force and impulse. Twenty-four participants walked without and with vGRF feedback at 1.4 m·s-1 with 0%, 15%, and 30% load added. They received feedback on the average peak vGRF for each leg in two-second epochs during each of the six conditions. Participants significantly decreased the second peak vGRF and vGRF impulse with feedback, but not the first peak vGRF. Due to an adopted crouched pattern, participants increased both first and second peak TFJ contact forces. vGRF and TFJ contact forces increased directly with increased load in both feedback conditions. vGRF force feedback represents an intuitive tool for modifying walking mechanics, but when employed to decrease ground reaction forces during load carriage in this study, it did not lead to decreased TFJ contact forces. Participants adopted a crouched gait that involved increased knee flexion and subsequent quadriceps demand, ultimately elevating TFJ loading. Future strategies aimed at decreasing joint load should consider targeting primary contributors of joint load, such as knee extensor moments, quadriceps force, or joint contact forces directly.

OBJECTIVE:We examined whether 18 months of strength training in individuals with knee varus alignment and medial tibiofemoral osteoarthritis (OA) reduced knee joint loads during walking compared to an attention control group. METHODS:This study was a secondary analysis of a randomized clinical trial that compared the effects of strength training to a control group in adults with knee OA. For this analysis, control participants had knee varus malalignment (≥2° varus; N = 49); participants in the strength training group met the varus malalignment criterion and increased their hip abductor strength by ≥20% from baseline to 18-month follow-up (N = 39). Linear regressions were used to compare means between groups at 18 months. RESULTS:The strength training group had greater increases in strength in the quadriceps (45%), hamstrings (68%), and hip abductors (42%) than the control group (16%, 11%, 4%, respectively; P < 0.05). There were no significant differences in the mean peak internal knee abduction moment or mean peak knee compressive force between groups at 18-month follow-up. The adjusted means at 18-month follow-up for the internal knee extension moment were significantly less (27%) in the strength training group (Padjusted = 0.03). CONCLUSION:Among older adults with knee OA and varus alignment, long-term lower extremity strength training results in significant increases in strength but does not significantly alter most measures of knee joint loading during walking relative to an attention control group. The results cast doubt on whether clinically meaningful improvement in lower extremity muscle strength translates to clinically important attenuation in knee joint loading.

It is unknown whether interlimb differences in gait mechanics affect the magnitude or distribution of tibiofemoral joint contact forces or whether load carriage increases potential effects of limb dominance. Thus, this study aimed to compare the effects of load carriage on total, medial, and lateral tibiofemoral joint contact force between the dominant and nondominant limbs. Twenty-four adults (12 women, 21 right-leg dominant) walked at 1.4 m·s-1 during 3 load carriage conditions (0%, 15%, and 30% body weight). Medial and lateral tibiofemoral joint contact forces were calculated during 5 stance phases for each limb in each condition. A 3 × 2 repeated-measures analysis of variance was used to compare the dominant and nondominant limbs across the 3 loading conditions. Peak tibiofemoral joint forces increased directly with load carriage (P < .001). The nondominant limb peak medial tibiofemoral joint contact force was greater than that of the dominant limb (P = .026), whereas dominant limb peak lateral tibiofemoral joint contact force was greater than that of the nondominant (P < .001) limb. Although the results were close to the minimal detectable difference, we concluded that the distribution of tibiofemoral joint contact force during load carriage may be influenced by limb dominance. These findings underscore the relevance of limb dominance as a consideration in research design and data interpretation.

Skipping represents a training alternative to running due to its lower knee contact forces and higher whole-body metabolic cost. The increased metabolic cost of skipping is associated with a higher vertical center-of-mass (COM) displacement during the support and flight phases of the skipping hop compared to running. However, skipping has lower muscle force impulses than running. Therefore, the study purpose was to compare the flow of mechanical power between body segments during skipping and running to determine the mechanisms enabling higher vertical displacement in skipping despite the lower vertical impulse. Running and skipping cycles were simulated in OpenSim for 5 adults (22.4 ± 2.2 y) using motion capture data collected at 2.5 m/s on an instrumented dual-belt treadmill. A segmental power analysis quantified muscle contributions to vertical body segment mechanical power, which were integrated over the stance phase of running (Run) and the hop (Skip 1) and step (Skip 2) of skipping to calculate mechanical work. Higher vertical work was done by the gluteus maximus, vasti, and soleus in Skip 1, primarily through power generation to the trunk, compared to power absorption in Run and Skip 2. Thus, despite lower muscle force impulses in Skip 1, muscles generate power through concentric contractions, leading to greater metabolic cost than in running. These muscle force impulses contribute to propelling the COM upward in Skip 1 (rather than decelerating downward COM motion in Run and Skip 2), which raises the COM and contributes to the greater COM displacement in skipping compared to running.

Objective The purpose of this study was to determine whether clinical, health‐related quality of life (HRQL), and gait characteristics in adults with knee osteoarthritis (OA) differed by obesity category. Methods This cross‐sectional analysis of 823 older adults (mean age 64.6 years, SD 7.8 years) with knee OA and overweight or obesity compared clinical, HRQL, and gait outcomes among obesity classifications (overweight or class I, body mass index [BMI] 27.0–34.9; class II, BMI 35.0–39.9; class III BMI ≥40.0). Results Patients with class III obesity had worse Western Ontario McMasters Universities Arthritis Index knee pain (0–20) than the overweight or class I (mean 8.6 vs 7.0; difference 1.5; 95% confidence interval [CI] 1.0–2.1; P < 0.0001) and class II (mean 8.6 vs 7.4; difference 1.1; 95% CI 0.6–1.7; P = 0.0002) obesity groups. The Short Form 36 physical HRQL measure was lower in the class III obesity group compared to the overweight or class I (mean 31.0 vs 37.3; difference −6.2; 95% CI −7.8 to −4.7; P < 0.0001) and class II (mean 31.0 vs 35.0; difference −3.9; 95% CI −5.6 to −2.2; P < 0.0001) obesity groups. The class III obesity group had a base of support (cm) during gait that was wider than that for the overweight or class I (mean 14.0 vs 11.6; difference 3.3; 95% CI 2.6–4.0; P < 0.0001) and class II (mean 14.0 vs 11.6; difference 2.4; 95% CI 1.6–3.2; P < 0.0001) obesity groups. Conclusion Among adults with knee OA, those with class III obesity had significantly higher pain levels and worse physical HRQL and gait characteristics compared to adults with overweight or class I or class II obesity. image

OBJECTIVE:Obesity exacerbates pain and functional limitation in persons with knee osteoarthritis (OA). In the Weight Loss and Exercise for Communities with Arthritis in North Carolina (WE-CAN) study, a community-based diet and exercise (D + E) intervention led to an additional 6 kg weight loss and 20% greater pain relief in persons with knee OA and body mass index (BMI) >27 kg/m2 relative to a group-based health education (HE) intervention. We sought to determine the incremental cost-effectiveness of the usual care (UC), UC + HE, and UC + (D + E) programs, comparing each strategy with the "next-best" strategy ranked by increasing lifetime cost. METHODS:We used the Osteoarthritis Policy Model to project long-term clinical and economic benefits of the WE-CAN interventions. We considered three strategies: UC, UC + HE, and UC + (D + E). We derived cohort characteristics, weight, and pain reduction from the WE-CAN trial. Our outcomes included quality-adjusted life years (QALYs), cost, and incremental cost-effectiveness ratios (ICERs). RESULTS:In a cohort with mean age 65 years, BMI 37 kg/m2, and Western Ontario and McMaster Universities Osteoarthritis Index pain score 38 (scale 0-100, 100 = worst), UC leads to 9.36 QALYs/person, compared with 9.44 QALYs for UC + HE and 9.49 QALYS for UC + (D + E). The corresponding lifetime costs are $147,102, $148,139, and $151,478. From the societal perspective, UC + HE leads to an ICER of $12,700/QALY; adding D + E to UC leads to an ICER of $61,700/QALY. CONCLUSION:The community-based D + E program for persons with knee OA and BMI >27kg/m2 could be cost-effective for willingness-to-pay thresholds greater than $62,000/QALY. These findings suggest that incorporation of community-based D + E programs into OA care may be beneficial for public health.

BACKGROUND:Obesity and knee osteoarthritis adversely affect activities of daily living in older adults. Together, the complexities of their interaction on mobility, including stair negotiation, are unresolved. The purpose of this study was to determine the relationship between obesity, pain, and stair negotiation in older adults with knee osteoarthritis. METHODS:Older adults with symptomatic knee osteoarthritis and overweight or obesity participated in the study (n = 28; age range = 57.0-78.0 yrs.; body mass index range = 26.6-42.8 kg•m-2). The Western Ontario and McMaster Universities Osteoarthritis Index pain subscale was used to measure knee pain. Measurements included a three-dimensional biomechanical analysis during descent on a set of force plate-instrumented stairs and a timed stair descent test. Pearson's r was used to determine associations between body mass index and pain, stair descent weight-acceptance phase vertical ground reaction force (vGRF) variables and lower extremity joint kinematics and kinetics, and timed stair descent performance. FINDINGS:Significant correlations existed between body mass index and pain (r = 0.41; p = 0.03), peak vGRF (r = 0.39; p = 0.04), vertical impulse (r = 0.49; p = 0.008), and peak ankle plantar flexor moments (r = 0.50; p = 0.007) in older adults with knee osteoarthritis. INTERPRETATION:Greater obesity in older adults with knee osteoarthritis was associated with greater knee pain and higher ankle joint loads during stair descent. These results support the recommendations of osteoarthritis treatment guidelines for weight-loss as a first-line of treatment for older adults with obesity and knee osteoarthritis.

The increased running participation in women and men over 40 years has contributed to scientific interest on the age-related and gender differences in running performance and biomechanics over the last decade. Gender differences in running biomechanics have been studied extensively in young runners, with inconsistent results. Understanding how gender influences the age-related differences in running mechanics could help develop population-specific training interventions or footwear to address any potential different mechanical demands. The purpose of this study was to assess gender and age effects on lower limb joint mechanics while running. Middle-aged men (57 +/- 5 years) and women (57 +/- 8 years) and young men (28 +/- 6 years) and women (30 +/- 6 years) completed five overground running trials at a set speed of 2.7 m/s while lower limb kinematics and ground reaction forces were collected. Lower limb joint kinetics were computed, normalized to body mass and compared between age and gender groups using two-factor analyses of variance. Women reported slower average running paces than men and middle-aged runners reported slower running paces than young runners. We confirmed that young runners run with more ankle, but less hip positive work and peak positive power compared to middle-aged runners (i.e., age-related distal-to-proximal shift in joint kinetics). We also present a novel finding that women run with more ankle, but less hip peak positive power compared to men suggesting an ankle dominant strategy in women at a preferred and comfortable running pace. However, the age-related distal-to-proximal shift in joint kinetics was not different between genders.

OBJECTIVE:The study objective was to determine whether the clinical response of older adults with knee osteoarthritis and overweight or obesity to 18 months of diet and exercise (D + E) or attention control (C) interventions differed between participants from rural versus urban communities. METHODS:Participants were 823 older adults (mean age, 64.6 years; 77% women) with knee osteoarthritis and overweight or obesity who resided in rural (n = 410) and urban (n = 413) counties in North Carolina. All were enrolled in the Weight Loss and Exercise for Communities with Arthritis in North Carolina clinical trial that randomly assigned participants to either 18 months of D + E or C interventions. General linear models were used to examine differences in clinical outcomes between rural and urban groups after adjusting for covariates. RESULTS:The rural group had significant differences (P < 0.05) at baseline in clinical outcomes, education, comorbidities, medication use, and income compared with the urban dwellers. After adjusting for baseline differences, the group (rural or urban) by treatment (D + E or C) interactions for Western Ontario McMasters Universities Osteoarthritis Index (WOMAC) pain (rural: D + E - C = -0.63, 95% confidence interval [CI] -1.31 to 0.06; urban: D + E - C= -0.29, 95% CI -0.99 to 0.41; P = 0.50) and WOMAC function (rural: D + E - C = -4.60, 95% CI -6.89 to -2.31; urban: D + E - C = -1.38, 95% CI -3.73 to 0.94; P = 0.054) indicated that the groups responded similarly to the interventions. CONCLUSION:Among participants with knee osteoarthritis and overweight or obesity, D + E compared to C led to similar pain outcomes in rural and urban dwellers that favored D + E. The possibility that there may be greater differential efficacy in functional outcomes among rural participants needs further study.

Background: Osteoarthritis (OA), the leading cause of disability among adults, has no cure and is associated with significant comorbidities. The premise of this randomized clinical trial is that, in a population at risk, a 48-month program of dietary weight loss and exercise will result in less incident structural knee OA compared to control. Methods/design: The Osteoarthritis Prevention Study (TOPS) is a Phase III, assessor-blinded, 48-month, parallel 2 arm, multicenter randomized clinical trial designed to reduce the incidence of structural knee OA. The study objective is to assess the effects of a dietary weight loss, exercise, and weight-loss maintenance program in preventing the development of structural knee OA in females at risk for the disease. TOPS will recruit 1230 ambulatory, community dwelling females with obesity (Body Mass Index (BMI) >= 30 kg/m2) and aged >= 50 years with no radiographic (Kellgren-Lawrence grade <= 1) and no magnetic resonance imaging (MRI) evidence of OA in the eligible knee, with no or infrequent knee pain. Incident structural knee OA (defined as tibiofemoral and/or patellofemoral OA on MRI) assessed at 48-months from intervention initiation using the MRI Osteoarthritis Knee Score (MOAKS) is the primary outcome. Secondary outcomes include knee pain, 6-min walk distance, healthrelated quality of life, knee joint loading during gait, inflammatory biomarkers, and self-efficacy. Cost effectiveness and budgetary impact analyses will determine the value and affordability of this intervention.

Chronic exposure to high tibiofemoral joint (TFJ) contact forces can be detrimental to knee joint health. Load carriage increases TFJ contact forces, but it is unclear whether medial and lateral tibiofemoral compartments respond similarly to incremental load carriage. The purpose of our study was to compare TFJ contact forces when walking with 15% and 30% added body weight. Young healthy adults (n = 24) walked for 5 minutes with no load, 15% load, and 30% load on an instrumented treadmill. Total, medial, and lateral TFJ contact peak forces and impulses were calculated via an inverse dynamics informed musculoskeletal model. Results of 1-way repeated measures analyses of variance (α = .05) demonstrated total, medial, and lateral TFJ first peak contact forces and impulses increased significantly with increasing load. Orthogonal polynomial trends demonstrated that the 30% loading condition led to a curvilinear increase in total and lateral TFJ impulses, whereas medial first peak TFJ contact forces and impulses responded linearly to increasing load. The total and lateral compartment impulse increased disproportionally with load carriage, while the medial did not. The medial and lateral compartments responded differently to increasing load during walking, warranting further investigation because it may relate to risk of osteoarthritis.

Purpose: Knee osteoarthritis (OA) is a prevalent, debilitating, and costly condition that is exacerbated by excess body weight. The Weight Loss and Exercise for Communities with Arthritis in North Carolina (WE-CAN) trial tested both community-based Health Education (HE) and Diet and Exercise (D+E) interventions. HE consisted of periodic group meetings focused on nutrition and other health literacy topics. D+E consisted of a calorie-restricted dietary plan and group exercise sessions delivered in community settings by trained exercise interventionists.