A BIOMECHANICAL ANALYSIS OF THE TAKE-OFF PHASE IN BELOW-KNEE AMPUTEE HIGH JUMP

An analysis of below-knee amputee take-off technique was performed on two athletes competing in the high jump finals of the 2004 Paralympic Games. Two digital video cameras were used to film the event with the data later digitised and reconstructed using standard 3-0 OLT procedures. Some similarities with non-amputee high jump technique were noted in that centre of mass height was low at touch-down (TO), there was a similar reported magnitude of negative vertical velocity at TO, and most of the vertical velocity generated occurred in the first half of the take-off phase. However, both below-knee amputee athletes exhibited a slower horizontal approach velocity, a lower positive vertical take-off velocity, a more upright leg position at touch-down and a greater range of motion of the hip throughout the take-off phase compared to what is known about non-amputee high jump technique. These differences may be associated with taking off from the prosthetic limb on the last stride of approach. Understanding why these differences occur has implications for coaching and improving technique

Tai Chi for osteopenic women: design and rationale of a pragmatic randomized controlled trial

<p>Abstract</p> <p>Background</p> <p>Post-menopausal osteopenic women are at increased risk for skeletal fractures. Current osteopenia treatment guidelines include exercise, however, optimal exercise regimens for attenuating bone mineral density (BMD) loss, or for addressing other fracture-related risk factors (e.g. poor balance, decreased muscle strength) are not well-defined. Tai Chi is an increasingly popular weight bearing mind-body exercise that has been reported to positively impact BMD dynamics and improve postural control, however, current evidence is inconclusive. This study will determine the effectiveness of Tai Chi in reducing rates of bone turnover in post-menopausal osteopenic women, compared with standard care, and will preliminarily explore biomechanical processes that might inform how Tai Chi impacts BMD and associated fracture risks.</p> <p>Methods/Design</p> <p>A total of 86 post-menopausal women, aged 45-70y, T-score of the hip and/or spine -1.0 and -2.5, have been recruited from primary care clinics of a large healthcare system based in Boston. They have been randomized to a group-based 9-month Tai Chi program plus standard care or to standard care only. A unique aspect of this trial is its pragmatic design, which allows participants randomized to Tai Chi to choose from a pre-screened list of community-based Tai Chi programs. Interviewers masked to participants' treatment group assess outcomes at baseline and 3 and 9 months after randomization. Primary outcomes are serum markers of bone resorption (C-terminal cross linking telopeptide of type I collagen), bone formation (osteocalcin), and BMD of the lumbar spine and proximal femur (dual-energy X-ray absorptiometry). Secondary outcomes include health-related quality-of-life, exercise behavior, and psychological well-being. In addition, kinetic and kinematic characterization of gait, standing, and rising from a chair are assessed in subset of participants (n = 16) to explore the feasibility of modeling skeletal mechanical loads and postural control as mediators of fracture risk.</p> <p>Discussion</p> <p>Results of this study will provide preliminary evidence regarding the value of Tai Chi as an intervention for decreasing fracture risk in osteopenic women. They will also inform the feasibility, value and potential limitations related to the use of pragmatic designs for the study of Tai Chi and related mind-body exercise. If the results are positive, this will help focus future, more in-depth, research on the most promising potential mechanisms of action identified by this study.</p> <p>Trial registration</p> <p>This trial is registered in Clinical Trials.gov, with the ID number of NCT01039012.</p

A. Stacoff) 68 REFERENCES De Clercq

INTRODUCTION Perception of the severity of repeated lower limb impacts is important in adapting to loading conditions and minimising overloading of the musculo-skeletal system. The ability to discriminate the severity of typical impact loads experienced during locomotion was evaluated using an established psychophysical protocol. Lower limb impacts were administered under controlled initial conditions across a range of impact severities manipulated using a range of soft and hard EVA materials. REVIEW AND THEORY There is evidence for distinct differences in absolute sensitivity of the footsole in a normal population as characterised by sensory thresholds of tactile and vibration stimuli (Nurse et al., 1998). Transients of lower limb impact loads are highly related to perceived impact severity, while transients of initial contact are also important in the ability to discriminate object softness in tactile tasks PROCEDURES A group of 20 male subjects (mean mass = 75.2 kg) free of lower extremity injury experienced controlled impacts of 1.05 m s -1 to the bare right heel using a human pendulum apparatus. Impact severity was manipulated using a range of sixteen 24mm mats of EVA materials of increasing hardness (shore A20-A68) comprising both homogenous and composite materials. A range of 9 sheets was selected from both the low severity (shore A20-A40) and high severity (shore A35-A68) end of the range. Mechanical impact severity was quantified by the external impact force recorded by a wall mounted Kistler (9218B) force platform, and shock to the shank recorded by a surface mounted Entran uni-axial accelerometer (EGAX-25). Signals were sampled at 2000 Hz and peaks and transient rates of the signals characterised the severity of impacts. The method of constant stimuli was used to determine the discrimination threshold (DL) of impact severity for the low and high impact ranges. A two alternative forced choice paradigm was used by subjects to rate the perceived severity of the 9 experimental conditions, in terms of greater or lesser severity, relative to a central standard condition. All subjects were exposed to 20 impacts per condition. The order of the conditions was counterbalanced about the standard and presented in a randomised order. Probit analysis (Finney, 1971) was used to fit normal distribution curves to the psychometric functions of each subject for the low and high ranges. Group and subject DL&apos;s for each mechanical input was calculated as half the difference between the 25 th and 75 th percentiles ( RESULTS AND DISCUSSION Across the low and high ranges of impact severity subjects experienced mean peak impact forces of 2.14 -2.36 BW and 2.20 -2.84 BW, and peak shank shocks of 6.68 -9.55 g and 8.65 -16.83 g, respectively. This range represents loads typically experienced during jogging and running. A highly significant difference between low and high DL&apos;s was present for the group (F [8, 12] = 64.53, P &lt; 0.0005) as illustrated i

A Preliminary assessment of a novel pneumatic unloading knee brace on the gait mechanics of patients with knee osteoarthritis

Objectives: To determine whether a knee brace incorporating inflatable air bladders can alter the net peak external knee adduction moment in persons with medial compartment knee osteoarthritis. Design: Prospective cohort study. Setting: Motion analysis laboratory. Participants: Subjects (n = 18) diagnosed with knee osteoarthritis as defined by the Diagnostic and Therapeutic Criteria Committee of the American Rheumatism Association. Methods: Instrumented gait analysis was performed while subjects walked with and without the knee brace. When subjects wore the knee brace, the air bladders were either uninflated or inflated to 7 psi. The net external knee adduction moment was obtained by subtracting the abduction moment produced by the knee brace (estimated using a finite element analysis model) from the external knee adduction moment (estimated using a camera-based motion analysis system). Main Outcome Measurements: The net external knee adduction moment was compared across all testing conditions. Results: A 7.6% decrease in net peak external knee adduction moment was observed when subjects wore the knee brace uninflated compared with when they did not wear the brace. Inflation of the bladders to 7 psi led to a 26.0% decrease in net peak external knee adduction moment. Conclusions: The results of the study suggest that the effects of an unloading knee brace may be enhanced by incorporating inflatable air bladders into the design of the brace, thus leading to an improved correction of the excessive peak external knee adduction moment observed in patients with medial compartment knee osteoarthritis.</br