Philip K. Schot

Effect of an abdominal binder during wheelchair exercise.

The purpose of this study was to determine whether use of an abdominal binder would affect oxygen uptake, trunk range of motion, and duration of the stroke phase during wheelchair propulsion. The subjects were six paraplegic wheelchair athletes with T1-T6 injuries and no abdominal muscle function. Each subject performed two trials, one while wearing the binder and one without the binder. Each trial consisted of submaximal and maximal exercise tests conducted on wheelchair rollers. Oxygen uptake was determined by open circuit spirometry while heart rate was determined by telemetry. Max VO2 values averaged 2.51 l.min-1 while average maximum heart rate values were 190 b.min-1. A 3-D video-based motion analysis system was used to obtain kinematic parameters of wheelchair propulsion. In general, 30% of the cycle time was comprised of the stroke phase, while 70% was comprised of the recovery phase across speeds. There were no statistically significant effects of the abdominal binder on any of the cardiovascular or kinematic variables at submaximal or maximal levels of exercise. Under the conditions of this laboratory investigation, it appears that an abdominal binder does not alter physiological or selected biomechanical measures in highly trained athletes.

Bilateral performance symmetry during drop landing: a kinetic analysis.

The assumption that lower extremity function is bilaterally symmetrical is prevalent throughout the biomechanics literature. The unilateral development of many overuse and acute injuries may suggest that this assumption is inaccurate. Analyses of bilateral function report conflicting results and may be partially attributable to the types of movement activities utilized and to research methodology. The purpose of this study was to evaluate the concurrent bilateral performance of the lower extremities during an apparently symmetrical movement task. Concurrent left/right side vertical ground reaction forces (VGRF) and lower extremity joint moments (JM) were obtained for 10 subjects performing 25 voluntary hanging drop landings (60 cm) on each of 3 consecutive days. Bilateral variability (BV) and systematic bilateral asymmetry (BA) were calculated for each trial. Bilateral variability was less for VGRF variables (12.8%) than JM variables (25.3%). Bilateral asymmetry was identified more often among VGRF variables (52.5%) than JM variables (16.7%). The magnitude of identified BA was greater than either the group BV (25%) or BA (110%) and indicates that bilateral differences are biomechanically meaningful.

Sit-to-Stand Performance of Older Adults following Strength Training

Abstract A group of healthy older adults completed an 8-week resistance-training program. For 38 participants (14 men, 24 women; ages 60–90 years; M mass = 73.2 kg, SD = 12.3; M height = 1.65 m, SD = 0.08), pre- and postprogram sit-to-stand performance was analyzed (60 Hz video) focusing on center of mass kinematics surrounding transition. Significant changes were attributed to improved strength. Peak forward, downward, and upward velocities increased (16, 59, and 26%, respectively), and relative transition time was delayed 27%. These behaviors were more similar to those of healthy younger adults. Results also indicated strategy changes. Participants exploited their improved strength, forming a distinctive movement pattern emphasizing stability followed by a brisk rise. These adaptations represent meaningfully improved function in an important daily living activity.

The force driven harmonic oscillator model accurately predicts the preferred stride frequency for backward walking

Abstract It has been established that when gait speed is freely selected, there is a strong natural tendency for a stride rate and length combination to be utilized that results in minimized metabolic cost. A possible mechanism for this self-optimizing behavior is that a biomechanically optimal movement pattern is adopted, which should reduce or minimize metabolic cost. When the legs are modeled as pendular force driven harmonic oscillators (FDHO) the stride frequency during freely selected gait is predictable as the pendulums resonant frequency — the state in which force inputs to maintain oscillations are minimal. Thus, resonance has been proposed as a mechanism responsible for gait optimization. To further examine the durability of this mechanism, the FDHO model was applied to predict stride rates during both free forward and backward walking for two separate test sessions. Stride measures were stable across sessions. Forward walking resulted in 25% greater stride lengths than backward, however, stride rates were statistically equal. Also, the FDHO model successfully predicted the preferred stride rate for both backward and forward walking. The resulting invariance of the stride frequency and adjustment of stride length were interpreted as offering additional support for the resonance mechanism.

A biomechanical analysis of two functional knee braces.

The influence of knee bracing was evaluated during the activity of running by examining ground reaction forces and knee joint movement parameters assessed electrogoniometrically. Twenty-one subjects were assigned to 1 of 3 groups based on medical records provided by a physician: normal or non-injury group; anterior cruciate ligament lesion/laxity group; and anterior cruciate ligament repair group. Four test conditions were investigated: healthy or control limb; injured or experimental limb; Generation II knee brace; and Marquette Knee Stabilizer knee brace. Ten running trials were performed for each condition at a photoelectrically controlled running pace (3.33 +/- 0.11 m X s-1). There were no significant differences as a result of group membership for both electrogoniometer and force platform analyses (P less than 0.05). There was a significant difference across the four test conditions. Both knee brace applications were shown to significantly reduce knee flexion during swing and support, total rotation, and total varus/valgus movement parameters of the experimental knee joint. Both brace applications were also shown to alter the experimental limb by increasing the relative time to the achievement of the initial collision force, creating a greater collision force and thereby creating larger impulses in both the vertical and foreaft directions during the initial contact phase.

Grip responses to object load perturbations are stimulus and phase sensitive

Responses to load changes of a held object that challenge grasp stability are known to be adept and fast, but the responses to changes in load where grasp stability is not challenged are not well understood. In order to compare responses to these functionally opposite perturbations, the grasp response to increases and decreases in the load of a held object was examined. A pulling force used to create object load was abruptly altered so that it felt lighter (decreased load) or felt heavier (increased load). The perturbation occurred either during movement of the object (lift) or when the object was held steady (hold). Grip force modulation was earlier, larger, had a faster maximum rate and a smaller change in relative safety margin when load increased. Also, the grip force modulation was earlier, larger, had a faster maximum grip force rate and a smaller change in relative safety margin when the perturbation occurred during active lift. In the decreased loading condition, participants were not required to make a grip force adjustment to maintain grip. Interestingly, participants chose to make the adjustment (decreasing grasp force), albeit more slowly. During the lift phase, the nature of the task is more dynamic and the resulting additional mechanical stimulation may have lead to a facilitated response. The results point to the greater functional significance of increasing load for grip force modulation and the potential for greater sensory or motor facilitation during dynamic lifting.

Within-participant variation in landing kinetics: movement behavior trait or transient?

Variation across repeat performances ofa particular movement task by an individual is an inherent feature ofhuman motor behavior (Bates, DeVita,&Kinoshita, 1983; Newell and Corcos, 1993). This phenomenon is referred to as intraparticipant or within-participant variability (WPV) and is observed at multiple levels in movement processes (evidenced in muscular, kinetic, and kinematic measures) as well as in various behavioral outcome measures (e.g., speed and accuracy scores). Using a single score or the mean score from repeated tests to characterize some phenomenon is a common approach in science. However, WPV measures have been used in several domains to characterize and evaluate system functioning. Evaluating motor skill and motor skill learning has long incorporated such measures with the basic notion that less variation indicates better skill (Higgins, 1977; Latash, 1993; Lees & Bouracier, 1994). Heart rate variation is viewed as a symptom of healthy cardiac regulation and function that has been shown to respond positively (increases) with exercise (Seals & Chase, 1989). Also, variation in the temporal characteristics ofvarious cyclic behaviors (Ivry& Corcos, 1993) has been linked to specific neurological pathologies. Different explanations for the causes or sources of WPV have been given. For the human movement sci-