Search

In order to fully understand contact dynamics on a trampoline, a simulation approach using a musculoskeletal model coupled with a dynamic model of the trampoline is essential. The purpose of the study was to examine dynamics and selected lower extremity muscle forces in a landing and jumping movement on a trampoline, using a combination of finite element modeling and musculoskeletal modeling. The rigid frame of the trampoline was modeled in ADAMS and coupled with a finite element model of the elastic trampoline net surface in ANSYS. A musculoskeletal model of an elite trampoline athlete was further developed in LifeMod and combined with the finite element model of the trampoline. The results showed that the peak trampoline reaction forces (TRF) were 3400 N (6.6 BW) and 2900 N (5.6 BW) for the left and right limb, respectively. The right hip, knee and ankle joint reaction forces reached the maximum between 3000-4000 N (5.8 – 7.7 BW). The gluteus maximum and quadriceps reached the maximum muscle force of 380 N (0.7 BW) and 780 N (1.5 BW), respectively. Asymmetric loading patterns between left and right TRFs and lower extremities joint reaction forces were observed due to the need to generate the rotational movement during the takeoff. The observed rigid and erect body posture suggested that the hip and knee extensors played important roles in minimizing energy absorption and maximizing energy generation during the trampoline takeoff.

Highlights • Greater Q-Factor (QF) increased peak knee abduction moment in ergometer cycling. • For a given QF, peak knee abduction moment increased with increased workrate. • Increased QF did not affect peak knee extension moment. • Modulating frontal-plane joint loading via QF changes may have clinical applications., Background Q-Factor (QF), or the inter-pedal width, in cycling is similar to step-width in gait. Although increased step-width has been shown to reduce peak knee abduction moment (KAbM), no studies have examined the biomechanical effects of increased QF in cycling at different workrates in healthy participants. Methods A total of 16 healthy participants (8 males, 8 females, age: 22.4 ± 2.6 years, body mass index: 22.78 ± 1.43 kg/m2, mean ± SD) participated. A motion capture system and customized instrumented pedals were used to collect 3-dimensional kinematic (240 Hz) and pedal reaction force (PRF) (1200 Hz) data in 12 testing conditions: 4 QF conditions—Q1 (15.0 cm), Q2 (19.2 cm), Q3 (23.4 cm), and Q4 (27.6 cm)—under 3 workrate conditions—80 watts (W), 120 W, and 160 W. A 3 × 4 (QF × workrate) repeated measures of analysis of variance were performed to analyze differences among conditions (p < 0.05). Results Increased QF increased peak KAbM by 47%, 56%, and 56% from Q1 to Q4 at each respective workrate. Mediolateral PRF increased from Q1 to Q4 at each respective workrate. Frontal-plane knee angle and range of motion decreased with increased QF. No changes were observed for peak vertical PRF, knee extension moment, sagittal plane peak knee joint angles, or range of motion. Conclusion Increased QF increased peak KAbM, suggesting increased medial compartment loading of the knee. QF modulation may influence frontal-plane joint loading when using stationary cycling for exercise or rehabilitation purposes., Graphical abstract Image, graphical abstract

Changes in the workrate and seat position have been linked to changes in internal knee extension moment. However, there is limited research on effects of those changes on knee kinetics in recumbent bike. The purpose of this study was to examine the effects of different seat positions and workrates on KAbM, knee extension moment and perceived effort during stationary recumbent cycling. Fifteen cyclists cycled on a recumbent ergometer in 6 test conditions of pedalling in far, medium and close seat positions in each of the two workrates of 60 and 100 W at the cadence of 80 RPM. A three-dimensional motion analysis system and a pair of instrumented pedals collected kinematic and kinetic data. A 3 ×2 repeated measures ANOVA was used to examine the effect of seat positions and workrates on selected variables of interest. Different seat positions did not change either peak KAbM (p = 0.592) or knee extension moment (p = 0.132). Increased workrates significantly increased peak KAbM (p

The aim of this study was to examine ground reaction force (GRF) and knee biomechanical characteristics of certain knee-unfriendly Tai Chi movement elements, comparing them with slow walking, and e...

Background The purpose of this study was to compare knee biomechanics of the replaced limb to the non-replaced limb of total knee replacement (TKR) patients and healthy controls during walking on level ground and on decline surfaces of 5°, 10°, and 15°. Methods Twenty-five TKR patients and 10 healthy controls performed 5 walking trials on different decline slopes on a force platform and an instrumented ramp system. Two analyses of variance, 2 × 2 (limb × group) and 2 × 4 (limb × decline slope), were used to examine selected biomechanics variables. Results The replaced limb of TKR patients had lower peak loading-response and push-off knee extension moment than the non-replaced and the matched limb of healthy controls. No differences were found in loading-response and push-off knee internal abduction moments among replaced, non-replaced, and matched limb of healthy controls. The knee flexion range of motion, peak loading-response vertical ground reaction force, and peak knee extension moment increased across all slope comparisons between 0° and 15° in both the replaced and non-replaced limb of TKR patients. Conclusion Downhill walking may not be appropriate to include in early stage rehabilitation exercise protocols for TKR patients.

Adding a shock pad as an underlayment to synthetic turf aims to improve attenuation of impact forces. The purpose of this research was to investigate effects of an infilled synthetic turf with three different shock pads on impact attenuation related biomechanics of lower extremity during the drop landing. Twelve active and healthy recreational male athletes performed 60 cm drop landing with a controlled landing technique on five surface conditions: a baseline surface (force platform), an infilled synthetic turf surface, turf plus foam shock pad, turf plus a low-density shock pad, and turf plus a high-density shock pad. Furthermore, a mechanical impact test was conducted (ASTM F355). Turf plus foam shock pad, turf plus low-density shock pad, and turf plus high-density shock pad all resulted in significantly lower 1st vertical peak ground reaction force (13.3%, 13.3%, and 12.7% reductions, respectively) and loading rate (20.4%, 25.4%, and 21.1% reductions, respectively) compared to baseline surface. Significantly greater trunk extension moment was found on turf plus low-density shock pad compared to turf surface (21.2%) and turf plus foam shock pad (12.0%). These results suggest that synthetic turf plus shock pad surfaces provide improved impact attenuation compared to baseline surface in the early landing phase.

AB Although effects of workload and cadence on sagittal plane knee biomechanics in cycling have been widely studied, few studies have examined their impact on the frontal plane. Purpose: The purpose of this study was to investigate the effects of different workloads and cadences on knee sagittal and frontal plane biomechanics. Methods: Eighteen healthy participants (age, 55.7 +/- 11.0 yr) volunteered for this study. A motion analysis system and a custom instrumented pedal were used to collect five cycles of three-dimensional kinematics (240 Hz) and pedal reaction force (PRF, 1200 Hz) during 2 min of cycling in each of eight testing conditions, including five workload conditions of 0.5, 1, 1.5, 2, and 2.5 kg at 60 rpm, and three cadence conditions of 70, 80, and 90 rpm with 1-kg workload. Two one-way repeated measures analyses of variance were used to examine the influence of cadence and workload on selected variables (P < 0.05). Results: Increased workloads with constant rpm caused an increased peak knee abduction moment from 5.82 to 14.36 N[middle dot]m and peak knee extension moment from 11.61 to 37.16 N[middle dot]m. Increased workloads also significantly increased peak medial and vertical PRF. Increased cadences at the constant workload had no effects on peak knee abduction moment but caused increased peak anterior and vertical PRF and peak knee flexion moment. Conclusions: The findings of this study indicate that increasing workload at constant cadence significantly increased peak knee abduction moment. Further study may be needed to demonstrate the efficacy of appropriate levels of workload and cadence in knee osteoarthritis and other populations with knee problems

Purpose The purpose of this study was to examine the effects of landing on a combined inversion and plantarflexion surface on the ankle kinematics and electromyographic (EMG) activities of medial gastrocnemius (MG), peroneus longus (PL), and tibialis anterior (TA) muscles. Methods Twelve recreational athletes performed five drop landings from an overhead bar of 30 cm height on to three surfaces: a flat surface, a 25° inversion surface, and a combined surface of 25° inversion and 25° plantarflexion. The kinematic variables and integrated EMG (IEMG) of the three muscles were assessed using a one-way repeated measures ANOVA and a 3 × 3 (surface × muscle) ANOVA, respectively ( p Results The IEMG results showed a significant muscle by surface interaction. The flat surface induced higher TA activity than the two tilted surfaces. The inverted surface produced significantly higher inversion peak angle and velocity than the flat surface, but similar PL activity across the surfaces. The MG IEMG, ankle plantarflexion angle, and inversion range of motion were significantly higher for the combined surface compared to the inverted surface. Conclusion These findings suggest that compared to the inversion surface, the combined plantarflexion and inversion surface seems to provide a more unstable surface condition for lateral ankle sprains during landing.

Purpose: Toe-in (TI) and toe-in with wider step width (TIW) gait modifications have successfully reduced the internal peak knee adduction moment (KAM) during level walking and stair ascent tasks, respectively, for healthy and knee osteoarthritis populations. However, the concurrent effects of these modifications have not previously been combined to reduce both the first and the second peak KAM during stair ascent or tested among the different knee alignment groups. Therefore, the purpose of this study was to examine effects of TI and TIW gait modifications on knee biomechanics during stair ascent in individuals with varus, neutral, and valgus knee alignments. Methods: Thirty-eight healthy individuals (age 18–30 yr) with varus, neutral, and valgus knee alignments confirmed using radiographs, performed stair ascent in normal, TI, and TIW gait conditions. A 3 × 3 (group × condition) mixed model repeated-measures ANOVA compared alignment groups across the stair ascent gait conditions (P < 0.05). Results: The TI and the TIW reduced the first peak KAM and KAM impulses compared with normal stair ascent. The TIW also reduced the second peak KAM compared with normal gait and reduced KAM impulses compared with TI. The varus group had increased first peak KAM compared with neutral and valgus groups. The TI and the TIW also reduced peak knee flexion moments compared with normal gait. The TIW also reduced peak external rotation moments compared with normal gait. Conclusions: The TIW gait modification seems to be successful in reducing knee joint loading in all three planes during stair ascent, regardless of knee alignment. The success of TIW in varus knee alignments may have important implications for people with medial knee osteoarthritis, or those susceptible to knee osteoarthritis.

The purpose of the study was to establish a dynamics model and a three-dimensional (3D) finite element model to analyze loading characteristics of femoral neck during walking, squat, single-leg standing, and forward and lateral lunges. One male volunteer performed three trials of the five movements. The 3D kinematic data were captured and imported into the LifeMOD to establish a musculoskeletal dynamics model to obtain joint reaction and muscle forces of iliacus, gluteus medius, gluteus maximus, psoas major and adductor magnus. The loading data LfeMOD were imported and transformed into a hip finite-element model. The results of the finite element femur model showed that stress was localized along the compression arc and the tension arc. In addition, the trabecular bone and tension lines of the Ward's triangle also demonstrated high stress. The compact bone received the greatest peak stress in the forward lunge and the least stress in the squat. However, the spongy bone in the femoral neck region had the greatest stress during the walk and the least stress in the squat. The results from this study indicate that the forward lunge may be an effective method to prevent femoral neck fractures. Walking is another effective and simple method that may improve bone mass of the Ward's triangle and prevent osteoporosis and femoral neck fracture.

BackgroundNo studies have compared effectiveness of resistance training and Tai Ji exercise on relieving symptoms of knee osteoarthritis (OA). The purpose of the study was to evaluate effects of a 10-week Tai Ji and resistance training intervention on improving OA symptoms and mobility in seniors with knee OA.MethodsThirty-one seniors (60–85 years) were randomly assigned to a Tai Ji program (n = 12), a resistance training program (n = 13), and a control group (n = 6). All participants completed the Western Ontario and McMaster (WOMAC) Osteoarthritis Index and performed three physical performance tests (6-min walk, timed-up-and-go, and timed stair climb and descent) before and after the 10-week intervention.ResultsThe participants in the resistance training group significantly improved on the timed-up-and-go test (p = 0.001), the WOMAC pain sub-score (p = 0.006), WOMAC stiffness sub-score (p < 0.001), and WOMAC physical function sub-score (p = 0.011). The Tai Ji group significantly improved on the timed-up-and-go test (p < 0.001), but not on the WOMAC scores.ConclusionResistance training was effective for improving mobility and improving the symptoms of knee OA. Tai Ji was also effective for improving mobility, but did not improve knee OA symptoms.

Barefoot or minimal footwear running is currently a highly debated topic among runners and researchers. Several footwear companies have developed minimal running footwear to simulate barefoot running but few studies have compared minimal footwear to barefoot and shoes during running. The primary goal of this study was to compare acute changes in three-dimensional (3D) ground reaction forces (GRFs) and lower limb kinematics and kinetics of habitually shod rearfoot strike (RFS) and forefoot strike (FFS) runners between minimal shoes (MSH), barefoot and neutral cushion running shoes (SH). Lower extremity joint biomechanical variables of RFS and FFS runners were analysed using a 3D motion capture system and a force platform during overground running in barefoot, MSH and running shoes. Barefoot and MSH showed a more anterior foot strike than shoes. The loading rate of the impact peak GRF was greater in barefoot and MSH than in shoes. MSH showed greater ankle plantarflexor moment and negative power in early sta...

Although landing in a plantarflexion and inversion position is a well-known characteristic of lateral ankle sprains, the associated kinematics of the knee and hip is largely unknown. Therefore, the purpose of this study was to examine the changes in knee and hip kinematics during landings on an altered landing surface of combined plantarflexion and inversion. Participants performed five drop landings from 30 cm onto a trapdoor platform in three different conditions: flat landing surface, 25° inversion, or a combined 25° plantarflexion and 25° inversion. Kinematic data were collected using a seven camera motion capture system. A 2 × 3 (leg × surface) repeated measures ANOVA was used for statistical analysis. The combined surface showed decreased knee and hip flexion range of motion (ROM) and increased knee abduction ROM (p

Biomechanical data for gait in unstable rocker bottom shoes reported in the literature is not comprehensive across available shoe types. Purpose: The objective of this study was to comprehensively evaluate centre of pressure (COP), ground reaction force (GRF), joint kinematics and kinetics, and electromyography (EMG) of selected muscles while walking in an unstable shoe compared to a control shoe. Methods: Fifteen subjects performed five walking trials at 1.3 m/s and 1.8 m/s in control and unstable shoes. Kinematic, GRF and EMG data were simultaneously collected. Results: The unstable shoe caused an increased mediolateral COP displacement. Greater loading rate of initial peak vertical GRF, reduced ankle plantarflexion range of motion (ROM) and greater total sagittal-plane ankle ROM were also observed for the unstable shoe compared to the control shoe. Peak dorsiflexion and plantarflexion moments, peak knee flexion moment as well as EMG activation of tibialis anterior and rectus femoris were reduced in the...

Background Short-leg walking boots are a common intervention for acute and chronic lower extremity injury. Few studies have examined the neuromuscular adaptations associated with short-leg walking boots and no previous study has investigated timing characteristics of muscle activation during gait. The purpose of the current study was to examine the timing and amplitudes of muscle activation of the extrinsic ankle musculature during walking in two types of short-leg walking boots. Methods Eleven healthy young adults performed five level walking trials at a self-selected pace in each of three conditions: normal walking, Gait Walker and Equalizer short-leg walking boots. Ground reaction forces were collected from a force platform while surface electromyography (EMG) was collected from the tibialis anterior, peroneus longus and medial gastrocnemius. EMG signals were rectified and smoothed using the root mean squared with a 20-ms smoothing window and were normalized to the largest mean of the normal walking trials. A repeated measures analysis of variance was used to assess the effect of short-leg walking boots on the onset, duration and amplitude of muscle activation. Results Short-leg walking boots were generally associated with earlier onsets of muscle activation and longer durations of muscle activation. However, there was no reduction in EMG amplitude. Conclusion The findings of this study show that the induced alterations in muscle activation patterns may limit the short-leg walking boots.

OBJECTIVE: To investigate biomechanical (kinematic) differences between 2 ankle brace testing protocols: landing on an inverted surface (IS) and inversion drop on an inversion platform. DESIGN: Five trials in each of 4 dynamic movement conditions were performed: inversion drop and drop landing from 0.45 m onto an IS without and with an ankle brace. A 7-camera motion analysis system was used to obtain the 3-dimensional kinematics. A 2 × 2 (brace × movement) repeated measures analysis of variance was used to evaluate selected variables for inversion drop and IS landing. SETTING: Research laboratory. PATIENTS: Eleven healthy subjects participated in the study. INTERVENTIONS: None. MAIN OUTCOME MEASURES: Maximum ankle frontal plane and sagittal plane joint angles, range of motion, and maximum angular velocity. RESULTS: The IS landing resulted in significantly earlier maximum inversion, inversion velocities, dorsiflexion range of motion (ROM), contact dorsiflexion velocity, and maximum dorsiflexion velocity compared with the inversion drop. The ankle brace application during the IS landing reduced the contact plantarflexion angle, dorsiflexion ROM and maximum dorsiflexion velocity, and maximum inversion. CONCLUSIONS: The results from this study showed that the IS landing protocol produced significantly earlier maximum inversion angle and velocity and inversion velocities compared with the inversion drop protocol. These results showed that the IS landing is more demanding and should be considered in future investigations of ankle braces and lateral ankle performance/injury mechanisms.

A Comparison of a Multi-body Model and 3D Kinematics and EMG of Double-leg Circle on Pommel Horse The purpose of this study was to establish a multi-segment dynamic model in the LifeMOD to examine kinematics of the center of mass and foot, and muscle forces of selected upper extremity muslces during a double-leg circle (DLC) movement on pommel horse in gymnastics and compared with three-dimensional kinematics of the movement and surface electromyographic (sEMG) activity of the muscles. The DLC movement of one elite male gymnast was collected. The three-dimensional (3D) data was imported in the Lifemod to create a full-body human model. A 16-Channel surface electromyography system was used to collect sEMG signals of middle deltoid, biceps brachii, triceps brachii, latissimusdorsi, and pectoralis major. The 3D center of mass and foot displacement showed a good match with the computer simulated results. The muscle force estimations from the model during the four DLC phases were also generally supported by the integrated sEMG results, suggesting that the model was valid. A potential application of this model is to help identify shortcomings of athletes and help establish appropriate training plans errors in the DLC technique during training.

Controlled laboratory study.To examine effectiveness of an ankle brace with a subtalar locking system in restricting ankle inversion during passive and dynamic movements.Semirigid ankle braces are considered more effective in restricting ankle inversion than other types of brace, but a semirigid brace with a subtalar locking system may be even more effective.Nineteen healthy subjects with no history of major lower extremity injuries were included in the study. Participants performed 5 trials of an ankle inversion drop test and a lateral-cutting movement without wearing a brace and while wearing either the Element (with the subtalar locking system), a Functional ankle brace, or an ASO ankle brace. A 2-way repeated-measures analysis of variance (ANOVA) was used to assess brace differences (P?.05).All 3 braces significantly reduced total passive ankle frontal plane range of motion (ROM), with the Element ankle brace being the most effective. For the inversion drop the results showed significant reductions in peak ankle inversion angle and inversion ROM for all 3 braces compared to the no brace condition; and the peak inversion velocity was also reduced for the Element brace and the Functional brace. In the lateral-cutting movement, a small but significant reduction of the peak inversion angle in early foot contact and the peak eversion velocity at push-off were seen when wearing the Element and the Functional ankle braces compared to the no brace condition. Peak vertical ground reaction force was reduced for the Element brace compared to the ASO brace and the no brace conditions.These results suggest that the tested ankle braces, especially the Element brace, provided effective restriction of ankle inversion during both passive and dynamic movements.

[Purpose] The purpose of the study was to design and implement a multichannel dynamic functional electrical stimulation system and investigate acute effects of functional electrical stimulation of the tibialis anterior and rectus femoris on ankle and knee sagittal-plane kinematics and related muscle forces of hemiplegic gait. [Subjects and Methods] A multichannel dynamic electrical stimulation system was developed with 8-channel low frequency current generators. Eight male hemiplegic patients were trained for 4 weeks with electric stimulation of the tibia anterior and rectus femoris muscles during walking, which was coupled with active contraction. Kinematic data were collected, and muscle forces of the tibialis anterior and rectus femoris of the affected limbs were analyzed using a musculoskelatal modeling approach before and after training. A paired sample t-test was used to detect the differences between before and after training. [Results] The step length of the affected limb significantly increased after the stimulation was applied. The maximum dorsiflexion angle and maximum knee flexion angle of the affected limb were both increased significantly during stimulation. The maximum muscle forces of both the tibia anterior and rectus femoris increased significantly during stimulation compared with before functional electrical stimulation was applied. [Conclusion] This study established a functional electrical stimulation strategy based on hemiplegic gait analysis and musculoskeletal modeling. The multichannel functional electrical stimulation system successfully corrected foot drop and altered circumduction hemiplegic gait pattern.

Multiple playing surfaces and footwear used in American football warrant a better understanding of relationship between different combinations of turf and footwear. The purpose of this study was to examine effects of shoe and stud types on ground reaction force (GRF) and ankle and knee kinematics of a 180° cut and a single-leg 90° land-cut on synthetic turf. Fourteen recreational football players performed five trials of the 180° cut and 90° land-cut in three shoe conditions: non-studded running shoe, and football shoe with natural and synthetic turf studs. Variables were analyzed with a 3 × 2 (shoe × movement) repeated measures analysis of variance (p < 0.05). Peak vertical GRF (p < 0.001) and loading rate (p < 0.001) were greater during 90° land-cut than 180° cut. For 180° cut, natural turf studs produced smaller peak medial GRFs compared to synthetic turf studs and non-studded shoe (p = 0.012). For land-cut, peak eversion velocity was reduced in running shoes compared to natural (p = 0.016) and synthetic (p = 0.002) turf studs. The 90° land-cut movement resulted in greater peak vertical GRF and loading rate compared to the 180° cut. Overall, increased GRFs in the 90° land-cut movement may increase the chance of injury.

Randomized controlled trial.To determine the effects of instruction to improve frontal plane knee biomechanics during a jump-landing task.Technique training is a common component of knee injury-prevention programs. In developing programs that minimize time commitment and increase the likelihood of adoption by target groups, there is a need to evaluate individual program components.A total of 26 female recreational athletes (average age, 21.2 years), who presented with medial knee displacement during a jump-landing task, completed the study protocol. Participants were randomly placed into 1 of 2 groups, an experimental or control group. The experimental group received instructions aimed at improving knee abduction during jump landings. The control group received a sham training. Prior to training, baseline kinematics and kinetics (peak knee abduction angle, peak internal knee adductor moment, knee flexion excursion, peak internal knee extensor moment, and peak vertical ground reaction force) were obtained from participants while performing a basketball rebound task. Immediate (5 minutes postinstruction) and delayed (15-20 minutes postinstruction) retention tests were performed within the instructional session. Two additional retention tests were performed following home-based training (1 and 2 weeks following the initial training).The initial instructional session resulted in greater knee flexion excursion (9°) and a 20% reduction in the peak internal knee adductor moment in the experimental group. Following home-based training, the experimental group continued to exhibit increased knee flexion excursion, along with decreased peak vertical ground reaction forces. No biomechanical changes were observed in the control group for any of the retention tests when compared to baseline.The jump-training instructions employed in the current study resulted in kinematic and kinetic changes in the sagittal plane as opposed to the frontal plane.Prevention, level 2b-.

The purpose of this study was to explore the footwear effects on impact forces and soft-tissue vibrations during landing. 12 male basketball players were instructed to perform drop jumps and unanticipated drop landings from 30 cm, 45 cm, and 60 cm heights in basketball shoes (BS) and control shoes (CS). 3D kinematics, ground reaction force (GRF), and soft-tissue vibrations of the leg, and acceleration of the shoe heel counter were measured simultaneously. The results showed no significant shoe effect on the characteristics of the impact force nor on the resonance frequency and peak transmissibility of soft-tissue vibrations during the impact phase of the drop jump. For the unanticipated drop landings, however, the magnitude of both peak GRF and peak loading rate were significantly lower with BS compared to CS across all 3 heights ( p 0.05); meanwhile BS showed a significant decrease in GRF frequency compared to CS at 45 cm ( p 0.05) and 60 cm ( p 0.01) heights. Furthermore, the peak transmissibility in BS was significantly lower than that in CS for both the quadriceps and hamstrings during the 60 cm unanticipated drop landing ( p 0.05). These findings provide p reliminary evidence suggesting that if the neuromuscular system fails to prepare properly for an impact during landing, a shoe intervention may be an effective method for minimizing impact force and reducing soft tissue resonance.

Shock reduction has been well studied in moderate activities such as walking and running. However, there is a clear lack of research concerning shock wave transmission and reduction in more strenuous landing activities. In this study, we examined the impact of shock transmission and reduction in landing activities with varied mechanical demands. Ten active males were recruited for the study. They performed five successful step-off landing trials from each of five heights: 30, 45, 60, 75, and 90 cm. Right sagittal kinematics, ground reaction forces, and acceleration were recorded simultaneously. Impact frequencies were analysed using a discrete Fast Fourier Transform and power spectral density was computed. Increased range of motion for the ankle, knee, and hip joints was observed at higher landing heights. The peaks of the vertical ground reaction force, forehead and tibial accelerations, and eccentric muscle work by lower extremity joints were increased with increased landing heights. The peak head power spectral density was severely attenuated at higher frequencies but the peak tibia power spectral density did not demonstrate this trend. Shock reduction showed increased reduction at higher frequencies, but minimal changes across five landing heights. Unlike the responses observed for walking and running, the shock reduction did not show significant improvement with elevated mechanical demands.

Osteoarthritis (OA) is the most common form of arthritis. The knee and hip joints are the most common sites for OA, and knee OA is more prevalent than hip OA. Knee OA patients often suffer pain, functional disability, articular cartilage wear and related joint space narrowing. Among U.S. adults, 46.4 million have physician-diagnosed arthritis representing 21.6% of the U.S. population, and 8.3% (17.4 million) had activity limitations attributable to arthritis. It is estimated that by 2030, the number of physician-diagnosed arthritis cases will reach 67 million, and 25 million will have arthritisattributable activity limitations. Although 7.9% of U.S. adults aged 18e44 years have arthritis, this percentage increases to 29.3% and 50.0% for adults between 45 and 64 years and older than 65 years, respectively. Currently, there is no cure for this degenerative disease. The economic and functional impacts of this disease have become an increased burden for society and individuals. The treatment strategies for knee OA often are aimed at reducing pain, improving physical function, decreasing disability, and limiting OA progression. Over the two decades, several national and international medical organizations including the American College of Rheumatology (ACR), European League Against Rheumatology (EULAR), Osteoarthritis Research Society International (OARSI), and National Institute of Health (NIH) have published evidence-based guidelines for the management of knee OA. These guidelines are mostly evidence-based with expert consensus. The treatment recommendations from these guidelines include non-pharmacological and pharmacological therapies, intraarticular injections, and surgical procedures including arthroscopy, osteotomy and total/unicompartmental knee replacement. A combination of pharmacological and non-pharmacological treatments is commonly recommended in clinical practice and is universally recommended in existing guidelines for the management of knee OA. The non-pharmacological therapies commonly include patient education, selfmanagement programs, personalized social support through telephone contact, weight loss (if overweight), aerobic exercise programs, physical therapy, range-of-motion exercises, muscle strengthening, transcutaneous electrical nerve stimulation (TENS), electromagnetic field therapy (EFT), acupuncture, ultrasound, laser, spa, assistive devices for ambulation, patellar taping, the appropriate footwear, lateral-wedged insoles (for genu varum), bracing, occupational therapy, joint protection and energy conservation, and assistive devices for activities of daily living. In earlier guidelines, acupuncture, TENS, EFT, ultrasound, laser, bracing/taping, and footwear and orthotics were not usually recommended as non-pharmacological treatments. Among the non-pharmacological recommendations, patient education, muscle strengthening, aerobic and range of motion exercises and walking aids received the highest support. Chinese acupuncture as a knee OA treatment alternative first appeared in the knee OA guidelines in 2000 and since then, has been included inmore recent recommendations. In an earlier systematic review of OA, it was found that seven of the studies included reported positive results for acupuncture treatment, and six reported non-significant results. The NIH OA working group made the evidence-based conclusion that “the research to date on the efficacy of acupuncture in osteoarthritis is inconclusive but promising”. In a recentmeta-analysis of acupuncture for knee OA, patients receiving acupuncture showed short-term improvements in pain (effect size (ES) 1⁄4 0.96) and function (ES 1⁄4 0.93) as compared to patients in a waitlist control group. However, when compared to a sham control group, acupuncture showed diminished short-term effects on pain (ES1⁄4 0.35) and function (ES1⁄4 0.35). The ES for pain relief was further reduced at 6 months after treatment. In a more recent review of 16 qualified randomized control trials (RCT) for knee OA, it was shown that the external validity was inadequate in the E-mail address: szhang@utk.edu. Peer review under responsibility of Shanghai University of Sport

In the most recent report of injury data on 15 sports from the U.S. National Collegiate Athletic Association (NCAA) Injury Surveillance System over a span of 16 years (1988e2004), ankle ligament sprains were the most common injury. Residual symptoms such as recurrent sprains, pain, instability, and giving way are common after an initial, acute ligament sprain. Chronic ankle instability (CAI) is one of these common problems, and has enjoyed increased interest in the recent literature. However, CAI remains a poorly-defined and understood condition. CAI has been commonly associated with two types of instability, namely mechanical and functional instability. Hertel in 2002 proposed a CAI model that has been very popular (Fig. 1). In this model, CAI is attributed to both mechanical instability and functional instability. Functional instability may be caused by deficits in proprioception, neuromuscular control, postural control, and/or muscular strength. Mechanical instability may be caused by altered mechanics in one or more joints within the ankle complex. Rather than treating these two types of instability independently, this model considers that they are both part of an instability continuum. When both types of instability are present, recurrent ankle sprain occurs. In a recent paper, Hiller et al. proposed a new and updated CAI model that was evolved from Hertel’s original model. In this new model, CAI has a total of seven sub-groups (Fig. 2). In the new model, the triad consists of mechanical instability, perceived instability (instead of functional instability in

The purpose of the study was to investigate changes in lower extremity joint energy absorption for different landing heights and landing techniques.Nine healthy, active male subjects volunteered to perform step-off landings from three different heights (0.32 m, 2.5 m(-s); 0.62 m, 3.5 m(-s); and 1.03 m, 4.5 m(-s)) using three different landing techniques (soft, SFL; normal, NML; and stiff landing, STL). Each subject initially performed five NML trials at 0.62 m to serve as a baseline condition and subsequently executed five trials in each of the nine test conditions (3 heights x 3 techniques).The results demonstrated general increases in peak ground reaction forces, peak joint moments, and powers with increases in landing height and stiffness. The mean eccentric work was 0.52, 0.74, and 0.87 J x kg(-1) by the ankle muscles, and 0.94, 1.31, and 2.15 J x kg(-1) by the hip extensors, at 0.32, 0.62, and 1.03 m, respectively. The average eccentric work performed by the knee extensors was 1.21, 1.63, and 2.26 J x kg(-1) for the same three heights.The knee joint extensors were consistent contributors to energy dissipation. The ankle plantarflexors contributed more in the STL landings, whereas the hip extensors were greater contributors during the SFL landings. Also a shift from ankle to hip strategy was observed as landing height increased.

The purpose of the study was to investigate the effects of variability as a function of sample size on the Pearson product-moment correlation coefficient (PCC) under the assumption of a perfect relationship between two variables. The effects of sample size (subjects/trials) and variability on the PCC were demonstrated using a computer model. The model was also used to evaluate selected examples taken from the literature. The results indicated that variability in excess of 10% of the range for each variable resulted in a mean reduction of the shared variance by 50% or greater. Although sample size did not affect the mean PCC, it did have a dramatic effect on extreme percentile values producing unreliable results. These results indicate that a small PCC value can be an artifact of variability. It is suggested, therefore, that one should be cautious when stating conclusions regarding the relationship between two variables without having knowledge of the associated variabilities.