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Background: Recently, we determined that in a rigorously monitored environment an intensive diet-induced weight loss of 10% combined with exercise was significantly more effective at reducing pain in men and women with symptomatic knee osteoarthritis (OA) than either intervention alone. Compared to previous long-term weight loss and exercise trials of knee OA, our intensive diet-induced weight loss and exercise intervention was twice as effective at reducing pain intensity. Whether these results can be generalized to less intensively monitored cohorts is unknown. Thus, the policy relevant and clinically important question is: Can we adapt this successful solution to a pervasive public health problem in real-world clinical and community settings? This study aims to develop a systematic, practical, cost-effective diet-induced weight loss and exercise intervention implemented in community settings and to determine its effectiveness in reducing pain and improving other clinical outcomes in persons with knee OA. Methods/Design This is a Phase III, pragmatic, assessor-blinded, randomized controlled trial. Participants will include 820 ambulatory, community-dwelling, overweight and obese (BMI ≥ 27 kg/m2) men and women aged ≥ 50 years who meet the American College of Rheumatology clinical criteria for knee OA. The primary aim is to determine whether a community-based 18-month diet-induced weight loss and exercise intervention based on social cognitive theory and implemented in three North Carolina counties with diverse residential (from urban to rural) and socioeconomic composition significantly decreases knee pain in overweight and obese adults with knee OA relative to a nutrition and health attention control group. Secondary aims will determine whether this intervention improves self-reported function, health-related quality of life, mobility, and is cost-effective. Discussion Many physicians who treat people with knee OA have no practical means to implement weight loss and exercise treatments as recommended by numerous OA treatment guidelines. This study will establish the effectiveness of a community program that will serve as a blueprint and exemplar for clinicians and public health officials in urban and rural communities to implement a diet-induced weight loss and exercise program designed to reduce knee pain and improve other clinical outcomes in overweight and obese adults with knee OA. Trial registration clinicaltrials.gov Identifier: NCT02577549 October 12, 2015., Version of Record

We examined the hypothesis that metabolic surgery-induced massive weight loss causes mass-driven and behavioral adaptations in the kinematics and kinetics of obese gait. Gait analyses were performed at three time points over ~1 yr in initially morbidly obese (mass: 125.7 kg; body mass index: 43.2 kg/m²) but otherwise healthy adults. Ten obese adults lost 27.1% ± 5.1 (34.0 ± 9.4 kg) weight by the first follow-up at 7.0 mo (±0.7) and 6.5 ± 4.2% (8.2 ± 6.0 kg) more by the second follow-up at 12.8 mo (±0.9), with a total weight loss of 33.6 ± 8.1% (42.2 ± 14.1 kg; P = 0.001). Subjects walked at a self-selected and a standard 1.5 m/s speed at the three time points and were also compared with an age- and gender-matched comparison group at the second follow-up. Weight loss increased swing time, stride length, gait speed, hip range of motion, maximal knee flexion, and ankle plantarflexion. Weight loss of 27% led to 3.9% increase in gait speed. An additional 6.5% weight loss led to an additional 7.3% increase in gait speed. Sagittal plane normalized knee torque increased and absolute ankle and frontal plane knee torques decreased after weight loss. We conclude that large weight loss produced mechanical plasticity by modifying ankle and knee torques and gait behavior. There may be a weight loss threshold of 30 kg limiting changes in gait kinematics. Implications for exercise prescription are also discussed. [ABSTRACT FROM AUTHOR]

Abstract: This study tested the hypothesis that skeletal muscles generate more mechanical energy in gait tasks that raise the center of mass compared to the mechanical energy they dissipate in gait tasks that lower the center of mass despite equivalent changes in total mechanical energy. Thirteen adults ran on a 10° decline and incline surface at a constant average velocity. Three-dimensional (3D) joint powers were calculated from ground force and 3D kinematic data using inverse dynamics. Joint work was calculated from the power curves and assumed to be due to skeletal muscle–tendon actuators. External work was calculated from the kinematics of the pelvis through the gait cycle. Incline vs. decline running was characterized with smaller ground forces that operated over longer lever arms causing larger joint torques and work from these torques. Total lower extremity joint work was 28% greater in incline vs. decline running (1.32 vs. −1.03J/kgm, p<0.001). Total lower extremity joint work comprised 86% and 71% of the total external work in incline (1.53J/kgm) and decline running (−1.45J/kgm), which themselves were not significantly different (p<0.180). We conjectured that the larger ground forces in decline vs. incline running caused larger accelerations of all body tissues and initiated a greater energy-dissipating response in these tissues compared to their response in incline running. The runners actively lowered themselves less during decline stance and descended farther as projectiles than they lifted themselves during incline stance and ascended as projectiles. These data indicated that despite larger ground forces in decline running, the reduced displacement during downhill stance phases limited the work done by muscle contraction in decline compared to incline running. [Copyright &y& Elsevier]

A temporal analysis of electromyographic (EMG) activity has widely been used for non-invasive study of muscle activation patterns. Such an analysis requires robust methods to accurately detect EMG onset. We examined whether data conditioning, supplemented with Teager-Kaiser Energy Operator (TKEO), would improve accuracy of the EMG burst onset detection. EMG signals from vastus lateralis. collected during maximal voluntary contractions, performed by seventeen subjects (8 males, 9 females, mean age of 46 yrs), were analyzed. The error of onset detection using enhanced signal conditioning was significantly lower than that of onset detection performed on signals conditioned without the TKEO (40 ± 99 ms vs. 229 ± 356 ms, t-test, p = 0.023). The Pearson correlations revealed that neither accuracy after enhanced conditioning nor accuracy after standard conditioning was significantly related to signal-to-noise ratio (SNR) (r = -0.05, p = 0.8 and r = -0.19, p = 0.46, respectively). It is concluded that conditioning of the EMG signals with TKEO significantly improved the accuracy of the threshold-based onset detection methods, regardless of SNR magnitude. [ABSTRACT FROM AUTHOR]

The article discusses the evidence for spinal circuits interceding the change in motor behavior and muscle coactivation associated with age. It is said that age changes the control of voluntary movement of an individual. An oftentimes observed adaptation is the increased agonist and antagonist muscle coactivation. Disynaptic reciprocal inhibition is the main spinal coordinator of the agonist-antagonist muscle processes.

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. [ABSTRACT FROM AUTHOR]

Context: While 55 million Americans incorporate running into their exercise routines, up to 65% of runners sustain an overuse injury annually. It has been consistently shown that regular physical activity positively impacts quality of life (QOL), an essential public health indicator; however, the impact of running-related injuries on QOL is unknown. This study seeks to determine whether overuse injury severity impacts QOL in recreational runners, and if self-efficacy mediates this relationship. Design: Community-based prospective cohort study of 300 runners who had been running injury free for at least 5 miles/wk in the past 6 months. Methods: Self-efficacy for running and QOL measures (Short Form-12 Physical Component and Mental Component, Satisfaction with Life, Positive Affect and Negative Affect) were assessed at baseline, time of injury, and follow-up visits. Over 2 years of observation, overuse injuries were diagnosed by an orthopedic surgeon and injured runners were referred to a physical therapist. Results: Injury severity was significantly (P <.01) related with 2 indices of QOL, such that the effect of injury severity was −2.28 units on the Short Form-12 physical component and −0.73 units on positive affect. Self-efficacy accounted for 19% and 48% of the indirect effects on Short Form-12 physical component and positive affect, respectively. Conclusions: Since self-efficacy is a modifiable factor related to decreased QOL, these findings have important clinical implications for rehabilitation interventions. [ABSTRACT FROM AUTHOR]

Purpose: Hamstring strain injury is a frequent and serious injury in competitive and recreational sports. While Nordic hamstring (NH) eccentric strength training is an effective hamstring injury-prevention method, the protective mechanism of this exercise is not understood. Strength training increases muscle strength, but also alters muscle architecture and stiffness; all three factors may be associated with reducing muscle injuries. The purpose of this study was to examine the effects of NH eccentric strength training on hamstring muscle architecture, stiffness, and strength.Methods: Twenty healthy participants were randomly assigned to an eccentric training group or control group. Control participants performed static stretching, while experimental participants performed static stretching and NH training for 6 weeks. Pre- and post-intervention measurements included: hamstring muscle architecture and stiffness using ultrasound imaging and elastography, and maximal hamstring strength measured on a dynamometer.Results: The experimental group, but not the control group, increased volume (131.5 vs. 145.2 cm3, p < 0.001) and physiological cross-sectional area (16.1 vs. 18.1 cm2, p = 0.032). There were no significant changes to muscle fascicle length, stiffness, or eccentric hamstring strength.Conclusions: The NH intervention was an effective training method for muscle hypertrophy, but, contrary to common literature findings for other modes of eccentric training, did not increase fascicle length. The data suggest that the mechanism behind NH eccentric strength training mitigating hamstring injury risk could be increasing volume rather than increasing muscle length. Future research is, therefore, warranted to determine if muscle hypertrophy induced by NH training lowers future hamstring strain injury risk. [ABSTRACT FROM AUTHOR]

Background: Anterior cruciate ligament reconstruction is associated with early onset knee osteoarthritis. Running is a typical activity following this surgery, but elevated knee joint contact forces are thought to contribute to osteoarthritis degenerative processes. It is therefore clinically relevant to identify interventions to reduce contact forces during running among individuals after anterior cruciate ligament reconstruction. The primary purpose of this study was to evaluate the effect of reducing step length during running on patellofemoral and tibiofemoral joint contact forces among people with a history of anterior cruciate ligament reconstruction. Inter limb knee joint contact force differences during running were also examined. Methods: 18 individuals at an average of 54.8 months after unilateral anterior cruciate ligament reconstruction ran in 3 step length conditions (preferred, − 5%, − 10%). Bilateral patellofemoral, tibiofemoral, and medial tibiofemoral compartment peak force, loading rate, impulse, and impulse per kilometer were evaluated between step length conditions and limbs using separate 2 factor analyses of variance. Findings: Reducing step length 5% decreased patellofemoral, tibiofemoral, and medial tibiofemoral compartment peak force, impulse, and impulse per kilometer bilaterally. A 10% step length reduction further decreased peak forces and force impulses, but did not further reduce force impulses per kilometer. Tibiofemoral joint impulse, impulse per kilometer, and patellofemoral joint loading rate were lower in the previously injured limb compared to the contralateral limb. Interpretation: Running with a shorter step length is a feasible clinical intervention to reduce knee joint contact forces during running among people with a history of anterior cruciate ligament reconstruction. [ABSTRACT FROM AUTHOR]

Key Points: Question: Does a weight loss and exercise program in community settings lead to improvement in knee pain in patients with osteoarthritis and overweight or obesity? Findings: This randomized clinical trial included 823 patients with knee osteoarthritis and overweight or obesity treated with diet and exercise vs an attention control. After 18 months, the adjusted mean difference in Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain score (range, 0-20) was −0.6, a difference that met statistical significance. Meaning: In patients with knee osteoarthritis and overweight or obesity, an 18-month program of weight loss and exercise based in community settings, compared with an attention control group, led to a small difference in knee pain of uncertain clinical importance. Importance: Some weight loss and exercise programs that have been successful in academic center–based trials have not been evaluated in community settings. Objective: To determine whether adaptation of a diet and exercise intervention to community settings resulted in a statistically significant reduction in pain, compared with an attention control group, at 18-month follow-up. Design, Setting, and Participants: Assessor-blinded randomized clinical trial conducted in community settings in urban and rural counties in North Carolina. Patients were men and women aged 50 years or older with knee osteoarthritis and overweight or obesity (body mass index ≥27). Enrollment (N = 823) occurred between May 2016 and August 2019, with follow-up ending in April 2021. Interventions: Patients were randomly assigned to either a diet and exercise intervention (n = 414) or an attention control (n = 409) group for 18 months. Main Outcomes and Measures: The primary outcome was the between-group difference in the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) knee pain score (range, 0 [none] to 20 [severe]; minimum clinically important difference, 1.6) over 18 months, tested using a repeated-measures mixed linear model with adjustments for covariates. There were 7 secondary outcomes including body weight. Results: Among the 823 randomized patients (mean age, 64.6 years; 637 [77%] women), 658 (80%) completed the trial. At 18-month follow-up, the adjusted mean WOMAC pain score was 5.0 in the diet and exercise group (n = 329) compared with 5.5 in the attention control group (n = 316) (adjusted difference, −0.6; 95% CI, −1.0 to −0.1; P =.02). Of 7 secondary outcomes, 5 were significantly better in the intervention group compared with control. The mean change in unadjusted 18-month body weight for patients with available data was −7.7 kg (8%) in the diet and exercise group (n = 289) and −1.7 kg (2%) in the attention control group (n = 273) (mean difference, −6.0 kg; 95% CI, −7.3 kg to −4.7 kg). There were 169 serious adverse events; none were definitely related to the study. There were 729 adverse events; 32 (4%) were definitely related to the study, including 10 body injuries (9 in diet and exercise; 1 in attention control), 7 muscle strains (6 in diet and exercise; 1 in attention control), and 6 trip/fall events (all 6 in diet and exercise). Conclusions and Relevance: Among patients with knee osteoarthritis and overweight or obesity, diet and exercise compared with an attention control led to a statistically significant but small difference in knee pain over 18 months. The magnitude of the difference in pain between groups is of uncertain clinical importance. Trial Registration: ClinicalTrials.gov Identifier: NCT02577549 This randomized clinical trial assesses the effect of a diet and exercise intervention vs an attention control condition on knee pain at 18-month follow-up among individuals aged 50 years or older with knee osteoarthritis and overweight or obesity. [ABSTRACT FROM AUTHOR]

Abstract: Background: Although the squat exercise and its variations are commonly prescribed for anterior cruciate ligament rehabilitation, whether trunk position affects these ligament forces and strains during the squat is unclear. Our purpose was to evaluate the effects of trunk position on anterior cruciate ligament forces and strains during a single-leg squat. Methods: While instrumented for biomechanical analysis, twelve recreationally active subjects performed single-leg squats with minimal and moderate amounts of forward trunk lean. A combination of inverse dynamics, Hill-type muscle modeling, and mathematical computations estimated anterior cruciate ligament forces, strains and quadriceps, hamstrings, and gastrocnemius forces. Findings: The moderate forward trunk lean condition vs. minimal forward trunk lean condition had lower peak anterior cruciate ligament forces (↓24%), strains (↓16%), and average anterior cruciate ligament forces and strains during knee flexion ranges of motion of 25–55°(descent) and 35–55°(ascent). A moderate vs. minimal forward trunk lean also produced 35% higher hamstring forces throughout the majority of the squat, but lower quadriceps forces only at knee flexion angles greater than 65°. Interpretation: Single-leg squats performed with a moderate forward trunk lean (~40°) can minimize anterior cruciate ligament loads. Mechanistically, trunk lean reduced anterior cruciate ligament forces and strains through concomitant modulations in hip flexion angle and biarticular thigh muscle forces. These findings are clinically relevant for anterior cruciate ligament rehabilitation as a common goal is to minimize anterior cruciate ligament forces and strains through enhancing hamstring and quadriceps co-contractions. [Copyright &y& Elsevier]

Older compared with younger adults walk with different configurations of mechanical joint work and greater muscle activation but it is unclear if age, walking speed, and slope would each affect the relationship between muscle activation and net joint work. We hypothesized that a unit increase in positive but not negative net joint work requires greater muscle activation in older compared with younger adults. Healthy younger (age: 22.1 yrs, n = 19) and older adults (age: 69.8 yrs, n = 16) ascended and descended a 7° ramp at slow (~1.20 m/s) and moderate (~1.50 m/s) walking speeds while lower-extremity marker positions, electromyography, and ground reaction force data were collected. Compared to younger adults, older adults took 11% (incline) and 8% (decline) shorter strides, and performed 21% less positive ankle plantarflexor work (incline) and 19% less negative knee extensor work (decline) (all p <.05). However, age did not affect (all p >.05) the regression coefficients between the muscle activation integral and positive hip extensor or ankle plantarflexor work during ascent, nor between that and negative knee extensor or ankle dorsiflexor work during descent. With increased walking speed, muscle activation tended to increase in younger but changed little in older adults across ascent (10 ± 12% vs. −1.0 ± 10%) and descent (3.6 ± 10.2% vs. −2.6 ± 7.7%) (p =.006, r = 0.47). Age does not affect the relationship between muscle activation and net joint work during incline and decline walking at freely-chosen step lengths. The electromechanical cost of joint work production does not underlie the age-related reconfiguration of joint work during walking. [ABSTRACT FROM AUTHOR]

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. 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. 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. 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. • Obesity predicts pain in older adults with knee osteoarthritis. • Obesity predicts stair descent forces in older adults with knee osteoarthritis. • Obesity predicts stair descent ankle-joint load in people with knee osteoarthritis. [ABSTRACT FROM AUTHOR]

Supplemental digital content is available in the text. Introduction: Advanced age brings a distal-to-proximal redistribution of positive joint work during walking that is relevant to walking performance and economy. It is unclear whether negative joint work is similarly redistributed in old age. Negative work can affect positive work through elastic energy return in gait. We determined the effects of age, walking speed, and grade on positive and negative joint work in young and older adults. Methods: Bilateral ground reaction force and marker data were collected from healthy young (age = 22.5 yr, n = 18) and older (age = 76.0 yr, n = 22) adults walking on a split-belt instrumented treadmill at 1.1, 1.4, and 1.7 m·s−1 at each of three grades (0%, 10%, and −10%). Subjects also performed maximal voluntary eccentric, isometric, and concentric contractions for the knee extensors (120°·s−1, 90°·s−1, and 0°·s−1) and plantarflexors (90°·s−1, 30°·s−1, and 0°·s−1). Results: Compared with young adults, older adults exhibited a distal-to-proximal redistribution of positive leg joint work during level (P < 0.001) and uphill (P < 0.001) walking, with larger differences at faster walking speeds. However, the distribution of negative joint work was unaffected by age during level (P = 0.150) and downhill (P = 0.350) walking. Finally, the age-related loss of maximal voluntary knee extensor (P < 0.001) and plantarflexor (P = 0.001) strength was smaller during an eccentric contraction versus concentric contraction for the knee extensors (P < 0.001) but not for the plantarflexors (P = 0.320). Conclusion: The distal-to-proximal redistribution of positive joint work during level and uphill walking is absent for negative joint work during level and downhill walking. Exercise prescription should focus on improving ankle muscle function while preserving knee muscle function in older adults trying to maintain their independence. [ABSTRACT FROM AUTHOR]

Background: Pain is a cardinal symptom of knee osteoarthritis (OA) and although conservative treatments such as exercise and diet related interventions can reduce pain, effects are modest and can be improved. Frontal plane knee joint motion has been associated with knee pain, and is suggested as a patient-specific characteristic on which to tailor interventions.Research Question: Does the association between baseline frontal plane knee joint kinematics and pain-relief differ among overweight and obese people with knee OA who underwent an intervention from the Intensive Diet and Exercise for Arthritis (IDEA) clinical trial: diet-only, exercise-only, and combined diet and exercise intervention?Methods: 323 participants with knee OA were included in the analysis (77% females; 66 ± 6 years; 33.5 ± 3.7 kg/m2). At baseline, frontal plane knee joint kinematics during walking were measured using 3-dimensional gait analysis and characterised as peak varus-valgus knee angle, peak varus-valgus excursion, and peak varus angular velocity. Pain was assessed at baseline and 18-month follow-up using the Western Ontario and McMaster Universities Osteoarthritis Index pain subscale. Linear regressions were performed unadjusted and adjusted for covariates to determine if the associations between baseline frontal plane knee joint kinematics and 18-month change in pain differed according to intervention.Results: The interaction terms between the intervention and measures of frontal plane knee joint kinematics were not statistically significant (all P ≥ 0.05).Significance: We found no evidence to suggest that 18-months of either exercise, diet, or a combination of diet and exercise could be more effective than the other to improve pain based on frontal plane measures of knee kinematics. [ABSTRACT FROM AUTHOR]

Old compared to young adults exhibit increased hip and decreased ankle mechanical output during walking – a phenomenon known as biomechanical plasticity. Previous comparison studies suggest that low compared to high capacity old adults exhibit larger magnitudes of this plasticity, however the precise relationship between capacity and plasticity magnitude remains unclear. The purpose of this study was to quantify the relationships between physical capacity and biomechanical plasticity magnitude during level and incline walking. Data were collected for 32 old adults walking over level and inclined (+10°) surfaces at self-selected, comfortable speeds. Physical capacity was measured using the Short-Form Health Survey Physical Component (SF-36 PC) and biomechanical plasticity was quantified by ratios of hip extensor to ankle plantarfexor peak torques, angular impulses, peak positive powers, and positive work (larger ratios indicate larger magnitudes of plasticity). SF-36 PC scores correlated positively with all four biomechanical plasticity ratios during level walking and three of the four ratios during incline walking. Some of the biomechanical plasticity ratios correlated positively with comfortable walking speeds and stride frequencies, indicating better walking performance with larger magnitudes of plasticity. Additionally, all four biomechanical plasticity ratios were larger during incline compared to level walking, suggesting the need for larger magnitudes of plasticity during the more difficult task. These results indicate that larger magnitudes of biomechanical plasticity afford functional benefits such as increased level and incline walking performance for old adults. Increased walking performance has the potential to increase quality of life in the growing population of old adults. [ABSTRACT FROM AUTHOR]

The inherit injury risk associated with high-impact exercises calls for alternative ways to achieve the benefits of aerobic exercise while minimizing excessive stresses to body tissues. Skipping presents such an alternative, incorporating double support, flight, and single support phases. We used ground reaction forces (GRFs), lower extremity joint torques and powers to compare skipping and running in 20 healthy adults. The two consecutive skipping steps on each limb differed significantly from each other, and from running. Running had the longest step length, the highest peak vertical GRF, peak knee extensor torque, and peak knee negative and positive power and negative and positive work. Skipping had the greater cadence, peak horizontal GRF, peak hip and ankle extensor torques, peak ankle negative power and work, and peak ankle positive power. The second vs first skipping step had the shorter step length, higher cadence, peak horizontal GRF, peak ankle extensor torque, and peak ankle negative power, negative work, and positive power and positive work. The first skipping step utilized predominately net negative joint work (eccentric muscle action) while the second utilized predominately net positive joint work (concentric muscle action). The skipping data further highlight the persistence of net negative work performed at the knee and net positive work performed at the ankle across locomotion gaits. Evidence of step segregation was seen in distribution of the braking and propelling impulses and net work produced across the hip, knee, and ankle joints. Conclusions Skipping was substantially different than running and was temporally and spatially asymmetrical with successive foot falls partitioned into a dominant function, either braking or propelling whereas running had a single, repeated step in which both braking and propelling actions were performed equally. [ABSTRACT FROM AUTHOR]

Introduction/Purpose: Aging modifies neuromuscular activation of agonist and antagonist muscles during walking. Power training can evoke adaptations in neuromuscular activation that underlie gains in muscle strength and power but it is unknown if these adaptations transfer to dynamic tasks such as walking. We examined the effects of lower extremity power training on neuromuscular activation during level gait in old adults. Methods: Twelve community dwelling old adults (age ≥ 65 years) completed a 10-week lower extremity power-training program and thirteen old adults completed a 10-week control period. Before and after the interventions, we measured maximal isometric muscle strength and electromyographic (EMG) activation of the right knee flexor, knee extensor, and plantarflexor muscles on a dynamometer and we measured EMG amplitudes, activation onsets and offsets, and activation duration of the knee flexors, knee extensors, and plantarflexors during gait at habitual, fast, and standardized (1.25±0.6m·s-1) speeds. Results: Power training-induced increases in EMG amplitude (~41%; 0.47≤d≤1.47; P≤0.05) explained 33% (P=0.049) of increases in isometric muscle strength (~43%; 0.34≤d≤0.80; P≤0.05). Power training-induced gains in plantarflexor activation during push-off (+11%; d=0.38; p=0.045) explained 57% (P=0.004) of the gains in fast gait velocity (+4%; d=0.31; P=0.059). Furthermore, power training increased knee extensor activation (~18%; 0.26≤d≤0.29; P≤0.05) and knee extensor coactivation during the main knee flexor burst (~24%, 0.26≤d≤0.44; P≤0.05) at habitual and fast speed but these adaptations did not correlate with changes in gait velocity Conclusion: Power training increased neuromuscular activation during isometric contractions and level gait in old adults. The power training-induced neuromuscular adaptations were associated with increases in isometric muscle strength and partly with increases in fast gait velocity. [ABSTRACT FROM AUTHOR]

National Biomechanics Day (NBD) was initiated in 2016 as a nation-wide effort to introduce Biomechanics to high school students throughout the United States. After that initial year, many people around the world joined NBD to promote Biomechanics in their own countries. National Biomechanics Day became international. We describe NBD procedures and events in four of these countries with the intent of demonstrating mechanisms that may enable Biomechanists around the world to successfully join the NBD celebration. [ABSTRACT FROM AUTHOR]