The association between obesity, knee pain, and gait during stair descent in older adults with knee osteoarthritis.

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.

Collegiate Dancers With Chronic Ankle Instability Possess Altered Strength and saut de chat Leap Landing Mechanics.

INTRODUCTION: Ankle sprains are among the most common injuries in dancers. Following one or more severe sprains, some individuals will experience residual mechanical and functional deficits, otherwise known as chronic ankle instability (CAI). Dancers who suffer from CAI may have weaker musculature surrounding the ankle and altered landing mechanics. The purpose of this study was to compare ankle strength and saut de chat landing mechanics between dancers with and without CAI. METHODS: Dancers with and without CAI, defined by the Identification of Functional Ankle Instability (IdFAI), participated in the study (CAI n = 8; IdFAI = 18.75 ± 5.50 points; age = 20 ± 1.5 years; training = 15.5 ± 3.5 years) (Control n = 8; IdFAI = 7.13 ± 3.40 points; age = 19 ± 0.6 years; training = 15.9 ± 2.5 years). Strength and leap landing mechanics were measured on the affected ankle for the CAI group and on the preferred landing leg of a leap for the control group. Concentric and eccentric ankle plantar flexion, and subtalar inversion and eversion strength were determined with dynamometry set at an angular velocity of 60°â€¢s-1. Force plates and motion capture cameras were used to calculate lower extremity kinematic and kinetic data as participants performed 3 saut de chat leaps. Independent t-tests were calculated to determine differences between groups. RESULTS: Compared to dancers without CAI, dancers with CAI had lower eccentric plantar flexor strength, landed with higher vertical ground reaction forces, and absorbed greater power at the knee-joint during landing. CONCLUSION: Whether dancers who are weaker are more prone to injury or ankle-joint injury leads to muscular weakness is unknown. Dancers with CAI appear to lack control during leap landing while concomitantly shifting loads proximally away from the ankle-joint. We encourage dancers with and without CAI to engage in additional training that enhances ankle strength.

The osteoarthritis prevention study (TOPS) - A randomized controlled trial of diet and exercise to prevent Knee Osteoarthritis: Design and rationale.

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) â€‹≥ â€‹30 â€‹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, health-related 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. Discussion: This study will assess the efficacy and cost effectiveness of a dietary weight loss, exercise, and weight-loss maintenance program designed to reduce incident knee OA. Trial registration: ClinicalTrials.gov Identifier: NCT05946044.

Titin force in muscle cells alters lattice order, thick and thin filament protein formation.

Skeletal muscle force production is increased at longer compared to shorter muscle lengths because of length-dependent priming of thick filament proteins in the contractile unit before contraction. Using small-angle X-ray diffraction in combination with a mouse model that specifically cleaves the stretch-sensitive titin protein, we found that titin cleavage diminished the length-dependent priming of the thick filament. Strikingly, a titin-sensitive, length-dependent priming was also present in thin filaments, which seems only possible via bridge proteins between thick and thin filaments in resting muscle, potentially myosin-binding protein C. We further show that these bridges can be forcibly ruptured via high-speed stretches. Our results advance a paradigm shift to the fundamental regulation of length-dependent priming, with titin as the key driver.

Micro-biopsies: a less invasive technique for investigating human muscle fiber mechanics.

The purpose of this investigation was to demonstrate that muscle fiber mechanics can be assessed on micro-biopsies obtained from human medial gastrocnemii. Three micro-biopsy samples were collected from female dancers (n=15). Single fibers and fiber bundles were isolated and passively stretched from 2.4 to 3.0 µm at 0.015 and 0.04 µm s-1 (n=50 fibers total) and in five increments at 0.12 µm s-1 (n=42 fibers total). Muscle fibers were then activated isometrically at 2.4 µm (n=4 fibers total) and 3.0 µm (n=3 fibers total). Peak stress and steady-state stress were significantly greater (P<0.0001) after stretching at 0.04 µm s-1 than at 0.015 µm s-1. Furthermore, peak stresses and steady-state stresses increased non-linearly with fiber length (P<0.0001). We conclude that active and passive muscle fiber mechanics can be investigated using tissue from micro-biopsies.

Isolated Joint Block Progression Training Improves Leaping Performance in Dancers.

The purpose of this study was to investigate the effect of a 12-week ankle-specific block progression training program on saut de chat leaping performance [leap height, peak power (PP), joint kinetics and kinematics], maximal voluntary isometric plantar flexion (MVIP) strength, and Achilles tendon (AT) stiffness. Dancers (training group n = 7, control group n = 7) performed MVIP at plantarflexed (10◦) and neutral ankle positions (0◦) followed by ramping isometric contractions equipped with ultrasound to assess strength and AT stiffness, respectively. Dancers also performed saut de chat leaps surrounded by 3-D motion capture atop force platforms to determine center of mass and joint kinematics and kinetics. The training group then followed a 12-week ankle-focused program including isometric, dynamic constant external resistance, accentuated eccentric loading, and plyometric training modalities, while the control group continued dancing normally. We found that the training group's saut de chat ankle PP (59.8%), braking ankle stiffness (69.6%), center of mass PP (11.4%), and leap height (12.1%) significantly increased following training. We further found that the training group's MVIP significantly increased at 10◦ (17.0%) and 0◦ (12.2%) along with AT stiffness (29.6%), while aesthetic leaping measures were unchanged (peak split angle, mean trunk angle, trunk angle range). Ankle-specific block progression training appears to benefit saut de chat leaping performance, PP output, ankle-joint kinetics, maximal strength, and AT stiffness, while not affecting kinematic aesthetic measures. We speculate that the combined training blocks elicited physiological changes and enhanced neuromuscular synchronization for increased saut de chat leaping performance in this cohort of dancers.

Stretch-Shortening Cycle Performance and Muscle-Tendon Properties in Dancers and Runners.

The purpose of this investigation was to elucidate whether ankle joint stretch-shortening cycle performance, isometric and isokinetic plantarflexion strength, and maximal Achilles tendon force and elongation differ between dancers, endurance runners, and untrained controls. To differentiate between dancers, endurance runners, and controls, the authors measured maximal Achilles tendon force and elongation during isometric ramp contractions with ultrasonic imaging, maximal isometric and isokinetic plantarflexion strength with dynamometry, and stretch-shortening cycle function during countermovement hopping and 30-cm drop hopping with a custom-designed sled. The Achilles tendon of dancers elongated significantly (P ≤ .05) more than runners and controls. Dancers were significantly stronger than controls during isometric contractions at different ankle angles. Concentric and eccentric strength during isokinetic contractions at 60°·s-1 and 120°·s-1 was significantly higher in dancers and runners than controls. Dancers hopped significantly higher than runners and controls during hopping tasks. Dancers also possessed significantly greater countermovement hop relative peak power, drop hop relative impulse, and drop hop relative peak power than controls. Finally, dancers reached significantly greater velocities during countermovement hops than runners and controls. Our findings suggest dancing and running require or likely enhance plantarflexion strength. Furthermore, dancing appears to require and enhance ankle joint stretch-shortening cycle performance and tendon elongation.

Strength and power capabilities predict weighted parameter ranking of saut de chat leaping performance in dancers.

Limited research exists on the relationship between aesthetic saut de chat performance and muscle-tendon unit (MTU) characteristics of dancers. We developed a weighted parameter ranking (WPR) tool to incorporate aesthetic leaping aspects (i.e., height, peak split angle, average trunk angle and trunk angle range) for correlation with MTU properties. The purpose was to identify the relationship of saut de chat WPR and leap height with maximal plantarflexion strength, medial gastrocnemius (MG) stiffness, Achilles tendon (AT) stiffness and relative peak power (PP). Dancers (n = 18) performed maximal plantarflexion, short-range stretches and isometric ramping contractions on a dynamometer equipped with ultrasound to determine strength, MG stiffness and AT stiffness, respectively. Subjects then performed saut de chat leaps atop force platforms surrounded by motion capture cameras. A principal component analysis (PCA) was performed to compare WPR variable weightings with PCA results and rankings. Moderate-strong relationships were identified among WPR, maximal plantarflexion strength, MG stiffness and PP. Strong-very strong relationships were also identified between leap height and maximal plantarflexion strength, MG stiffness, AT stiffness, peak split angle and PP. A very strong correlation existed between PCA rankings and WPRs. Practitioners may consider developing strength and power capabilities in dancers to improve leaping.

When Task Constraints Delimit Movement Strategy: Implications for Isolated Joint Training in Dancers.

Athletic performance is determined by numerous variables that cannot always be controlled or modified. Due to aesthetic requirements during sports such as dance, body alignment constrains possible movement solutions. Increased power transference around the ankle-joint, coupled with lower hip-joint power, has become a preferential strategy in dancers during leaps and may be considered a dance-specific stretch-shortening cycle (SSC) demand. Newell's theoretical model of interacting constraints includes organismic (or individual), environmental, and task constraints describing the different endogenous and exogenous constraints individuals must overcome for movement and athletic performance. The unique task constraints imposed during dance will be used as a model to justify an isolated joint, single-targeted block progression training to improve physical capacity within the context of motor behavior to enhance dance-specific SSC performance. The suggested ankle-specific block progression consists of isometrics, dynamic constant external resistance, accentuated eccentrics, and plyometrics. Such programming tactics intend to collectively induce tendon remodeling, muscle hypertrophy, greater maximal strength, improved rate of force development, increased motor unit firing rates, and enhanced dynamic movement performance. The current perspective provides a dualistic approach and justification (physiological and motor behavioral) for specific strength and conditioning programming strategies. We propose implementation of a single-targeted block progression program, inspired by Newell's theoretical model of interacting constraints, may elicit positive training adaptations in a directed manner in this population. The application of Newell's theoretical model in the context of a strength and conditioning supports development of musculoskeletal properties and control and is conceptually applicable to a range of athletes.

Bone health, muscle properties and stretch-shortening cycle function of young and elderly males.

The aim of this study was to examine bone, muscle, strength and stretch-shortening cycle (SSC) performance in young and elderly individuals with an ankle model to elucidate potential effects of ageing that have been suggested to influence fall risk. Moderately active young (n=10; age=22.3±1.3 yrs) and elderly (n=8; age=67.5±3.3 yrs) males completed a peripheral quantitative computed tomography scan on the dominant lower leg, maximal voluntary isometric plantarflexions (MVIP) and SSC tasks: a countermovement hop and drop hops from three different heights. Bone stress-strain index at 14% of the lower leg and muscle density, muscle cross-sectional area and muscle+bone cross-sectional area at 66% of the lower leg were all significantly greater (p≤0.05) in younger males than elderly males. Younger males also had significantly greater rate of force development and peak force during the MVIP when compared to the elderly. Younger males achieved significantly higher forces, velocities and hop heights during all SSC tasks than elderly males. Such information provides support for greater specificity in exercise interventions that prevent lower leg morphological and functional decrements in the ageing population.

Comparison of Quadriceps and Hamstring Muscle Activity during an Isometric Squat between Strength-Matched Men and Women.

The primary purpose of this investigation was to determine whether strength-matched men and women exhibit a different magnitude and ratio of leg muscle activity during a maximal voluntary isometric squat. The secondary purpose was to assess the effect of normalization method on differences in strength between men and women. Thirty-two men (n = 16) and women (n = 16) were successfully strength-matched (≤10% difference) by maximal force produced during an isometric squat (IS) when normalized to body weight. Subjects first performed a maximal isometric knee extension (IKE) and knee flexion (IKF) followed by the IS and muscle activity (EMGmax) was recorded for the vastus medialis (VMO), vastus lateralis (VL), semitendinosus (ST) and biceps femoris (BF). Muscle activity during the IS was expressed relative to the maximums observed during the IKE and IKF (%EMGmax). The results indicate that VMO, VL, ST and BF %EMGmax were not significantly different (p > 0.05) between men and women during the IS (Men VMO = 136.7 ± 24.9%, Women VMO = 157.1 ± 59.8%, Men VL = 126.2 ± 38.2%, Women VL = 128.1 ± 35.5%, Men ST = 25.5 ± 13.6%, Women ST = 25.2 ± 21.8%, Men BF = 46.1 ± 26.0%, Women BF = 42.2 ± 24.8%). Furthermore, the VMO:VL and hamstring to quadriceps (H:Q) %EMGmax ratio were not significantly different between groups in the IS (Men VMO:VL = 1.15 ± 0.28, Women VMO:VL = 1.22 ± 0.26, Men H:Q = 0.28 ± 0.14, Women H:Q = 0.24 ± 0.20). This investigation indicates that the magnitude of muscle activity and the ratios examined are not significantly different between men and women in a maximal voluntary isometric squat when matched for normalized strength. Future investigations should consider subject strength and normalization procedures in the experimental design to elucidate possible sex differences in neuromuscular performance capabilities.

Influence of Mirror Feedback and Ankle Joint Laxity on Dynamic Balance in Trained Ballet Dancers.

Enhanced understanding of dynamic postural stability (DPS) has the potential to curtail lower extremity injuries with important implications for athletic and scientific populations. The ability to stabilize following dynamic tasks such as jumping is dependent on several intrinsic factors, including ligamentous laxity, proprioception, and neuromuscular control. Ballet dancers are a unique group of aesthetic performers who frequently must perform unipedal balance during dynamic tasks. The purpose of this study was to evaluate the effects of mirror feedback and ankle laxity on dynamic balance and muscle activation in 15 trained ballet dancers during a hop-to-stabilization task with and without mirror feedback. Anteroposterior and inversion-eversion ankle laxity was measured with an arthrometer. Surface electromyography was then applied to the tibialis anterior, peroneus longus, and lateral gastrocnemius muscles to record activity during the task in question. The main finding was that time-to-stabilization during the task was unaffected by mirror feedback (F = 0.105, p = 0.900; mirror = 3.31 ± 0.10 s; no-mirror = 3.37 ± 0.12 s). Greater antero-posterior laxity, however, negatively affected DPS with (r = 0.655, p = 0.008) and without the mirror (r = 0.858, p < 0.001). These results suggest that visual feedback does not affect performance during a DPS task; however, increased ankle laxity may influence balancing ability in ballet dancers.

Physiological and Biomechanical Responses to an Acute Bout of High Kicking in Dancers.

Rice, PE, Gurchiek, RD, and McBride, JM. Physiological and biomechanical responses to an acute bout of high kicking in dancers. J Strength Cond Res 32(10): 2954-2961, 2018-High-kick precision competitive dance involves the integration of kicking inline, jumping, and turning during a 3-minute routine and causes a disturbance to both aerobic and anaerobic systems. However, no known study has quantified the effect of a hick-kick-specific protocol on blood lactate (BL), heart rate (HR), and countermovement jump (CMJ) performance. A group of adolescent high-kick dancers (n = 20; age = 15.0 ± 1.8 years; height = 161.5 ± 8.2 cm; body mass = 56.3 ± 11.0 kg; and dance team/weight lifting experience = 2.1 ± 0.9 years) participated in this investigation. Participants' BL was collected, and 3 CMJ trials were performed before (PRE) and after (POST) completing the high-kick protocol. The high-kick protocol consisted of intermittent running and kicking in place for a total of 1:45 at a tempo of 160 b·min, while average and peak HR (HRavg; HRpeak) were recorded. Jump height (JH), maximal trunk flexion (MTF), take-off angle (TOA), and relative peak power (PP) were determined from PRE and POST CMJ trials. During kicking, HRavg and HRpeak (n = 13) were 172.4 ± 15.7 b·min and 207.0 ± 23.0 b·min, respectively. Dancers' (n = 20) BL significantly (p ≤ 0.05) increased from 1.5 ± 0.5 to 8.6 ± 1.5 mmol·L, and JH and PP significantly decreased from 0.42 ± 0.08 to 0.36 ± 0.04 m and 41.3 ± 5.5 to 38.5 ± 4.0 W·kg, respectively, from PRE to POST. No significant changes occurred in MTF and TOA measurements from PRE to POST. The demands introduced during a high-kick-specific protocol can therefore be recognized as a metabolic and mechanical stimulus for fatigue; however, esthetics seem to be unaffected. Such findings may indicate that this modality of dance necessitates supplemental strength and conditioning training similar to other sports to sustain the loads of high-kick dance.

Lower Leg Morphology and Stretch-Shortening Cycle Performance of Dancers.

Greater levels of bone ultimate fracture load, bone stress-strain index, muscle cross-sectional area, and maximal voluntary isometric plantarflexion (MVIP) strength of the lower leg may be adaptations from chronic exposure to stretch-shortening cycle (SSC) actions. Dancers, a population that habitually performs SSC movements primarily about the ankle joint, may serve as a novel population to gain broader understanding of SSC function. A total of 10 female collegiate dancers and 10 untrained controls underwent peripheral quantitative computed tomography scans of both lower legs and performed MVIPs, countermovement hops, and drop hops at 20, 30, and 40 cm on a custom-made inclined sled. Dancers had greater right and left ultimate fracture load values and significantly (P ≤ .05) greater left leg stress-strain index than controls. Dancers had significantly larger right and left muscle cross-sectional area and MVIP values and hopped significantly higher during all hopping conditions in comparison with controls. Average force-time and power-time curves revealed significantly greater relative force and power measurements during the concentric phase for all hopping conditions in dancers when compared with controls. This investigation provides evidence that dance may be a stimulus for positive muscle and bone adaptations, strength levels, and enhanced SSC capabilities.

Gastrocnemius fascicle and achilles tendon length at the end of the eccentric phase in a single and multiple countermovement hop.

The purpose of this investigation was to compare fascicle and tendon length of the gastrocnemius at the end of the eccentric phase during a hop utilizing a single countermovement (sCM) versus multiple countermovement (mCM1, mCM2, mCM3) strategy. Seventeen healthy males performed nine hopping trials of sCM and nine trials of mCM. Ankle and knee joint angle and lower leg length from videography and muscle ultrasound were used to calculate muscle-tendon unit (MTU), fascicle and tendon length. Sacral marker data was used to determine hopping height. Force- and displacement-time curves were utilized to calculate work. Muscle activity of the lateral and medial gastrocnemius was also measured. Fascicle length was significantly shorter (mCM3: 6.2 ±â€¯1.5 cm, sCM: 7.3 ±â€¯2.0 cm) and tendon length was significantly longer (mCM3: 36.5 ±â€¯3.6 cm, sCM: 35.5 ±â€¯3.8 cm) at the end of the eccentric phase in mCM3 in comparison to sCM. Maximal hopping height (mCM: 14.6 ±â€¯3.1 cm, sCM: 13.1 ±â€¯2.5 cm), eccentric phase gastrocnemius muscle activity (mCM medial gastrocnemius: 0.10 ±â€¯0.03 mV, mCM lateral gastrocnemius: 0.08 ±â€¯0.04 mV, sCM medial gastrocnemius: 0.07 ±â€¯0.03 mV, sCM lateral gastrocnemius: 0.05 ±â€¯0.04 mV), and both eccentric (mCM3: 46.6 ±â€¯19.4 J, sCM: 38.5 ±â€¯15.9 J) and concentric work (mCM3: 87.6 ±â€¯26.5 J, sCM: 80.9 ±â€¯27.6 J) were significantly higher for mCM3 compared to sCM. The results indicate that a multiple countermovement hop strategy results in shorter fascicle length and longer tendon length at the end of the eccentric phase. In addition, greater eccentric phase muscle activity during the third countermovement (mCM3) in comparison to a single countermovement hop (sCM) was observed. A multiple countermovement strategy appears to result in higher hopping height and greater work done in both the eccentric and concentric phase indicating possible contribution of stored-elastic energy from the tendon.

A Comparison of Musculo-Articular Stiffness and Maximal Isometric Plantar Flexion and Knee Extension Force in Dancers and Untrained Individuals.

Dance involves a high volume of aesthetic, stretch-shortening cycle (SSC) actions, which may cause unique adaptations to performance. The strength dancers possess to withstand such frequency of SSCs remains elusive. The extensive training that dancers experience from a young age, however, yields anatomical and strength development that may contrast with that of untrained individuals. Therefore, the purpose of this study was to investigate differences in musculo-articular stiffness and maximal isometric plantar flexion and knee extension force between dancers and untrained individuals. A total of 16 females volunteered to participate in the study (N = 8 dancers; N = 8 untrained individuals). Dancers had a minimum of 10 years of dance experience and were currently training at the collegiate dance level three or more times per week. Untrained individuals had no dance background, nor were they currently involved in any form of regularized physical activity. All subjects completed a series of lower leg measurements and strength tests. This included a musculo-articular stiffness measurement using a free-oscillation technique, along with maximal isometric plantar flexion (MIP) and maximal isometric knee extension (MIKE) testing. The data indicate that dancers had a significantly greater rate of force development and peak force during MIP and rate of force development during MIKE in comparison to untrained individuals. Dancers also possessed significantly greater musculo-articular stiffness. Hence, the data provide some evidence that involvement in dance can result in greater muscle force generating capacity and musculo-articular stiffness due to the SSC mechanisms involved in dance movements.

Force- and power-time curve comparison during jumping between strength-matched male and female basketball players.

The purpose of this study was to compare force- and power-time curve variables during jumping between Division I strength-matched male and female basketball athletes. Males (n = 8) and females (n = 8) were strength matched by testing a one-repetition maximum (1RM) back squat. 1RM back squat values were normalised to body mass in order to demonstrate that strength differences were a function of body mass alone. Subjects performed three countermovement jumps (CMJ) at maximal effort. Absolute and relative force- and power-time curve variables from the CMJs were analysed between males and females. Average force- and power-time curves were generated for all subjects. Jump height was significantly greater (p ≤ .05) in males than females. Absolute force was higher in males during the concentric phase, but not significantly different (p ≥ .05) when normalised to body mass. Significance was found in absolute concentric impulse between sexes, but not when analysed relative to body mass. Rate of force development, rate of power development, relative peak force, and work were not significantly different between sexes. Males had significantly greater impulse during the eccentric phase as well as peak power (PP) during the concentric phase of the CMJ than did females in both absolute and relative terms. It is concluded that sex differences are not a determining factor in measured force during a CMJ when normalised to body mass between strength-matched subjects. However, eccentric phase impulse and concentric phase PP appear to be influenced by sex differences independent of matching strength levels.