Curb descent testing of suspension manual wheelchairs.
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Manual wheelchair users are subjected to whole-body vibrations (WBV) on a regular basis as they traverse obstacles and uneven surfaces. One way users could protect themselves from secondary injuries related to WBV is by using a suspension manual wheelchair. This study investigated the ability of suspension manual wheelchairs to reduce seat accelerations during curb descents of various heights (5, 10, and 15 cm). Sixteen manual wheelchairs (four suspension, four folding, four rigid, and four rigid titanium) were tested. Suspension wheelchairs transmitted significantly lower peak seat accelerations than folding wheelchairs during the 5 cm curb descents (p = 0.048) and significantly lower frequency-weighted peak seat accelerations during the 5 and 10 cm curb descents (p = 0.03 for both heights). However, when the suspension wheelchair Quickie XTR (Sunrise Medical; Carlsbad, California) was removed from the analysis, the suspension wheelchairs were not significantly different from the nonsuspension wheelchairs. When weight was considered, the suspension wheelchairs had significantly lower peak seat accelerations than the lighter rigid wheelchairs during 5 cm curb descents (p = 0.047). While suspension manual wheelchairs offer some reduction in WBV during curb descents, their limitations should be considered when a wheelchair is selected for everyday use. (+info)
Effects of backrest positioning and gear ratio on nondisabled subjects' handcycling sprinting performance and kinematics.
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Backrest position is a significant parameter in handcycling that one must consider when seeking to optimize the user-to-chair interface. We studied the effects of backrest position on handcycle propulsion kinematics. Ten nondisabled partici pants with no handcycle propulsion experience repeated an 8 s sprint with three backrest positions (backrest angle between 45 degrees and 50 degrees to the horizontal, backrest angle between 65 degrees and 70 degrees to the horizontal, and without backrest) and three gear ratios (GRs) (GR22/21 = low, GR32/21 = medium, and GR44/21 = high). We used three-dimensional movement analysis to calculate the average maximal velocity, cycle frequency, and angle parameters for the arms and trunk. Our results showed statistically higher trunk flexion/extension (p < 0.001) and maximal velocity (p < 0.001) when a backrest was not used. Moreover, these differences were accentuated as the GR increased (GR44/21). Our results suggest that handcycle users with unimpaired upper-body and trunk function can improve handcycling performance by removing the backrest. Nevertheless, future studies on specific groups of subjects with spinal cord injury should be conducted. (+info)
Reliability and validity of two frequently used self-administered physical activity questionnaires in adolescents.
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Direct measurement of the performance of the Drosophila jump muscle in whole flies.
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We have developed a novel apparatus, an ergometer, to simultaneously measure the horizontal and vertical components of the work done during takeoff by the fruitfly, Drosophila. We confirm the anatomical prediction that all the work comes from the middle (mesothoracic) legs. With all six legs on the ergometer platform, displacement is directed roughly 45 degrees forwards or backwards. Both directions are equally likely. This provides for a random, rapid horizontal component to the escape behaviour for flies. When the thoracic stiffness is reduced (due to a mutation in which the indirect flight muscles (IFM) do not form myofibrils), jump output is increased. We conclude that the jump muscle, the tergal depressor of trochanter (TDT), which lacks direct muscle antagonists, performs work during the jump against thoracic stiffness. Both cuticle and IFM contribute to the thoracic stiffness as the TDT still produces repeated contractions in the absence of the IFM. Degeneration of the TDT due to mutants in three sarcomeric proteins results in reduction of the jump output. In one of these, the myosin heavy chain mutant, Mhc5, we show that degeneration occurs with age. The anatomical characteristics of Drosophila mean that we are recording, for the first time in the intact fly, the output of a single muscle that has high homology to vertebrate skeletal muscle. Developing an ergometer for Drosophila offers novel opportunities to assess the functional consequences of mutations in muscle proteins, synaptic physiology, neuromuscular development and aging. (+info)