Our goal was to understand the bases for selection of alternate foot placement during locomotion when the normal landing area is undesirable. In this study, a light spot of different shapes and sizes simulated an undesirable landing area. Participants were required to avoid stepping on this spot under different time constraints. Alternate chosen foot placements were categorised into one of eight choices. Results showed that selection of alternate foot placement is systematic. There is a single dominant choice for each combination of light spot and normal landing spot. The dominant choice minimises the displacement of the foot from its normal landing spot (less than half a foot length). If several response choices satisfy this criterion, three selection strategies are used to guide foot placement: placing the foot in the plane of progression, choosing to take a longer step over a shorter step and selecting a medial rather than lateral foot placement. All these alternate foot-placement choices require minimal changes to the ongoing locomotor muscle activity, pose minimal threat to dynamic stability, allow for quick initiation of change in ongoing movement and ensure that the locomotor task runs without interruption. Thus, alternate foot-placement choices are dependent not only on visual input about the location, size and shape of the undesirable surface, but also on the relationship between the characteristics of the undesirable surface and the normal landing area.

The issues explored in this article are the role of exproprioceptive input and the nature of exteroceptive input provided by the visual system in the control of limb elevation as obstacles are stepped over during locomotion. In the first experiment, the differences in limb trajectory of movements over solid and fragile obstacles of similar dimensions were examined. Subjects increased their toe clearance, vertical position of the hip, and the hip vertical velocity when going over a fragile obstacle with the leading limb. This suggests that in addition to visually observable properties of obstacles such as height or width, other properties, such as rigidity or fragility, which may be classified as visually inferred, also influence the limb trajectory. Part of the first and the second experiment was focused on understanding differences in leading limb and trailing limb trajectory over obstacles. The toe clearance of the trailing limb was lower for smaller obstacles. There was no consistent correlation between the toe clearance values of the leading and trailing limbs. The variability in toe clearance was higher for the trailing limb, which is attributable to lack of visual exproprioceptive input about trailing limb movements and to the shorter time available following toe-off to fine-tune the trailing limb trajectory. Because the body center of mass is moving toward the supporting foot when the trailing limb goes over obstacles and the trailing limb foot is moving up, the chances of a trip are minimized and recovery from an unexpected trip are more likely. These results highlight the role of exproprioceptive input provided by the visual system and possible cognitive influences on the limb trajectory as one travels over uneven terrains.

Functional performance testing is often used in lower extremity rehabilitation to help determine a patient's readiness to return to sports participation. 2,11,25,28 Hopping or jumping tasks are most commonly used, 3,18,25,28 but other types of tasks also exist. 2,15Functional performance tests impart high forces to an injured joint or body segment that may more closely replicate the forces experienced in sport. Consequently, these tests can reveal impairments in muscle force generation or proprioception and neuromuscular control that might not be obvious with other clinical measures. 7,19Several studies have found that lower extremity functional performance test results predict future functional outcome, 1,8,12,21,22 indicating their usefulness in lower extremity rehabilitation.Functional performance testing is not standard in upper extremity rehabilitation and is absent from most upper extremity rehabilitation protocols. 5,23,27 The lack of functional performance testing occurs in spite of several functional performance tests described for the upper extremity. 4,6,17,24 A dearth of research to guide the selection and implementation of upper extremity functional performance tests may be a barrier to more widespread clinical use.The unilateral seated shot put test is an upper extremity functional performance test with many appealing aspects for clinical use. The test requires pushing a weighted ball forward in a shot put motion. 16 The test requires little equipment and would therefore be easy to administer in most clinical settings. Distance thrown on the unilateral seated shot put test has shown positive correlation with distance on a softball throw, providing external validity. 17 Moreover, in a sample T T STUDY DESIGN: Cross-sectional study. T T OBJECTIVES:To examine the effect of different normalization methods on unilateral seated shot put test results. T T BACKGROUND:The unilateral seated shot put test could assist clinical decision making in upper extremity rehabilitation, but test results must be normalized to compare across patients. The effect of normalization methods based on body size and upper-limb dominance is unknown. T T METHODS:One hundred twenty-five collegiate athletes (63 males) performed the unilateral seated shot put test with each upper extremity. Anthropometric measures (height, body mass, arm length) and distance thrown were recorded. Normalization based on body size included ratio scaling and allometric scaling. Ratio scaling was performed with the anthropometric measure having the highest correlation to distance thrown (distance/anthropometric measure). Allometric scaling was performed with body mass raised to the theoretical exponent 0.67 (distance/body mass 0.67 ) and a derived exponent. Correlations of nonnormalized and normalized values with body mass were then determined. The limb symmetry index [(dominant-side distance/nondominantside distance) × 100] was used for normalization based on limb dominance. Sex differences were examined. T T RESULTS:Body mass was selected for ratio...

The characteristics of visual sampling required for successful locomotion over various terrains is the focus of this work. In the first experiment we directly address the role of continuous visual monitoring of the environment in guiding locomotion by allowing the subjects to choose when and where to take a visual sample of the terrain and examine the effects of different terrains on characteristics of visual sampling. Young subjects walked over travel paths of varying difficulties while wearing opaque liquid crystal eyeglasses and pressed a hand-held switch to make the glasses transparent when they needed to sample the environment. Travel time and visual sampling characteristics were recorded. Results show that intermittent sampling (less than 50%) of the environment is adequate for safe locomotion, even over a novel travel path. The frequency, duration and timing of visual samples are dependent on terrain characteristics. Visual sampling of the environment is unaffected by preview restriction of the travel path and is increased when specific foot placement is required and there is a potential hazard in the travel path. In the second experiment we dissociated steering control and obstacle avoidance from specific foot placement and examined visual sampling demands prior to the initiation of the swing phase and during the swing phase. The results show that steering control and obstacle avoidance do influence the visual sampling time, which is scaled to the magnitude of change. Vision was used in a feedforward control mode to plan for and initiate appropriate changes in the swing limb trajectory: its use during the swing phase to provide on-line control was minimal.

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