Why We Walk the Way We Do

By using inverse dynamics and forceplate recordings, this study established the principle of oscillating systems and the influence of gravity and body parameters on the programming of the gait parameters, step frequency and length. Calculation of the ratio of the amplitude of the center of mass (CM) and the center of foot pressure (CP) oscillations yielded an equation and established a biomechanical constant, the natural body frequency (NBF). NBF appears to be an absolute invariant parameter, specific to human standing posture and gait in terrestrial gravity, which influences the relative positions of CM and CP and whose value separates the frequency bands of standing posture from those for gait. This equation was tested by using the experimental paradigm of stepping in place and then used in calculating the magnitude of CM oscillations during gait. The biomechanical analysis of the experimental observations allows one to establish the relationships between body parameters and gravity and the central programming of locomotor parameters.     

Influence of Destabilization on the Temporal Characteristics of “Volitional” Stepping

Previous work suggests that there may be fundamental differences between compensatory stepping responses evoked by postural perturbation and visually cued “volitional” stepping (e.g., gait initiation). In contrast to visual cueing, postural destabilization evokes an array of sensory inputs that are intrinsically linked to the mobilization of rapid compensatory responses. The hypothesis examined in this study was that this fundamental difference would lead to distinct changes in the temporal characteristics of the stepping response. Six healthy young adults were instructed to step quickly in response to either visual cueing or anterioposterior platform motion. Both forward and backward stepping responses were characterized, using measures of vertical ground reaction force. A stereotypical temporal patterning of the stepping response occurred in both stimulus conditions and both directions of stepping, and anticipatory postural adjustments were evident in all trials. However, postural destabilization led to a more rapid initiation and execution of the temporal pattern, in comparison with visually cued responses. The most pronounced effect was seen in the duration of the response, which was reduced by a factor of two, with approximately proportional foreshortening of both the preparatory and swing phases. The results suggest that sensory information conveying a state of instability has a distinct influence on the characteristics of a subsequent stepping reaction. The persistence of the anticipatory postural adjustments suggests that the failure to see this element of the response in previous studies may reflect fundamental differences between volitional and unplanned compensatory stepping.     

Timing Precision in Circle Drawing Does Not Depend on Spatial Precision of the Timing Target

The authors manipulated the width of a timing target in continuous circle drawing to determine whether a more stringent spatial-timing criterion would produce an increase in participants' (N = 30) temporal variability. They also examined the effect of the computational method of determining cycle duration. There was no effect of spatial precision on temporal variability in circle drawing, and tapping and circle drawing were found to use the same criterion. Those findings lend strong support to the earlier view of R. B. Ivry, R. M. Spencer, H. N. Zelaznik, and J. Diedrichsen (2002), who argued that continuous tasks such as circle drawing are timed differently from discrete-like tasks such as tapping. Therefore, the results of the present study provide support for the event and emergent timing frameworks.     

Multivariate Relationships Between Motor and Personality Measures in Culturally Deprived High School Pupils

The relationship between personality, as measured by the IPAT-HSPQ, and certain motor performance variables was studied by utilizing the multivariate technique of canonical correlation. Ss for the study were 91 culturally deprived high school students who were achieving well below their expected capacity. A significant canonical relationship was not found between the domains of personality and motor performance. Also, no significant relationships between motor sub-domains and personality were found. It was thus concluded that for the population under study, the domains of motor performance and personality were independent Some discussion of the multivariate technique of canonical correlation was offered and compared with univariate procedures.     

The Effect of Fatigue on Learning and Performance of a Gross Motor Task

40 college males were sequentially assigned to 1 of 2 groups to examine the effects of induced physical fatigue upon the performance and learning of a gross motor task, the stabilometer. All Ss were given 32 practice trials over 3 practice sessions, with 48 hr. rest interpolated between sessions. Trials 1 and 2 were performed under control conditions (no fatigue) for both groups. The Experimental Group was then required to perform under conditions of physical fatigue during Trials 3-26. Trials 27-32 (Session 3) were performed under control conditions. The condition of fatigue was achieved on Trials 3-26 by having Ss pedal a bicycle ergometer until a heart rate of 180 beats/min was attained prior to each trial. The Control Group cancelled vowels. The results indicated that physical fatigue was detrimental to the performance and learning of the Experimental Group.     

Adaptation to a Nonlinear Visuomotor Amplitude Transformation With Continuous and Terminal Visual Feedback

The control of a cursor on a computer monitor offers a simple means of exploring the limits of the plasticity of human visuomotor coordination. The authors explored the boundary conditions for adaptation to nonlinear visuomotor amplitude transformations. The authors hypothesized that only with terminal visual feedback during practice, but not with continuous visual feedback, humans might develop an internal model of the nonlinear visuomotor amplitude transformation. Thus, 2 groups were engaged in a sensorimotor adaptation task receiving either continuous or terminal visual feedback during the practice phase. In contrast to expectations, adaptive shifts and aftereffects observed in visual open-loop tests were linearly related to target amplitudes for both groups. Although the 2 feedback groups did not differ with respect to adaptive shifts and aftereffects, terminal visual feedback resulted in stable visual open-loop performance for an extended period, whereas movement errors increased after continuous visual feedback during practice. The benefit of continuous visual feedback, on the other hand, was faster closed-loop performance, indicating an optimization of visual closed-loop control.     

Immediate and Latent Interlimb Transfer of Gait Stability Adaptation Following Repeated Exposure to Slips

The authors trained 21 participants by using blocked-and-mixed exposure to right-side slips and then caused them to slip unexpectedly on the untrained left side. Authors retested participants with a right slip and a left slip at 1 week, 2 weeks, 1 month, and 4 months. The authors found that preslip stability on the first untrained left slip improved and was significantly greater than that on the first right slip, which probably contributed to the reduction in incidence of falls from ~30% to ~10%. Postslip stability and base of support (BOS) slip velocity were similar to those on the first right slip and much lower than those on the last right slip. Increases in pre- and postslip stabilities and BOS slip velocity during the left slip led to reductions in backward balance loss (BLOB) from ~95% on initial left slip to ~60% and to ~25% on the 1st and 3rd retest sessions, respectively. In contrast, BLOB remained at a constant ~40% level on the right slip of the same retest sessions. The results indicate a partial immediate transfer and a possible latent transfer.     

Index for Volume 23

In this study, changes in movement coordination caused by fatigue that developed during repetitive lifting were examined. Five men performed 6 times a 5-min bout of lifting an 8-kg barbell at 15 lifts/min, using two lifting techniques; one minimized trunk rotation (squat lift), and the other minimized rotation in the knee joint (stoop lift). Kinematics and dynamics were studied by means of movement analysis and inverse dynamics, using a two-dimensional linked segment model. Within-subject variation over repetitive lifts of the time course of joint angles was smaller than between-subjects variation on the first analyzed lift. Relative timing between joint rotations did not change significantly across repetitive lifts, except between knee and hip in the squat lift. No change of the lumbosacral torque over repetitive lifts was found. The adaptability of the neural control appeared to be sufficient to accommodate the strong changes of the input-output characteristics of the muscles caused by fatigue so that an essentially constant performance of the movement act was maintained.     

EMG Activity as a Function of the Performer's Focus of Attention

In previous studies of attentional focus effects, investigators have measured performance outcome. Here, however, the authors used electromyography (EMG) to determine whether differences between external and internal foci would also be manifested at the neuromuscular level. In 2 experiments, participants (N = 11, Experiment 1; N = 12, Experiment 2) performed biceps curls while focusing on the movements of the curl bar (external focus) or on their arms (internal focus). In Experiment 1, movements were performed faster under external than under internal focus conditions. Also, integrated EMG (iEMG) activity was reduced when performers adopted an external focus. In Experiment 2, movement time was controlled through the use of a metronome, and iEMG activity was again reduced under external focus conditions. Those findings are in line with the constrained action hypothesis (G. Wulf, N. McNevin, & C. H. Shea, 2001), according to which an external focus promotes the use of more automatic control processes.     

The Effect of Interpolated Motor Activity on the Short-Term Retention of Movement Distance and End-Location

The effect of an interpolated movement on the recall of a blind, lever-positioning movement was assessed separately for the reproduction cues of distance and end-location. Both cues showed the context effect of assimilation, that is, the end-location of the interpolated movement caused directional biasing of the algebraic or constant error (CE) for location reproduction while the length of the interpolated movement caused similar directional biasing for distance reproduction. Variability about algebraic error (VE) was used to assess forgetting. There was no change in VE for location reproduction, and an increase in VE for distance reproduction was limited to the relatively large movements. Thus, an interpolated movement that does not have to be remembered does not cause interference with the retention of location information, but does cause some interference with the retention of distance information. The findings are discussed in relation to a model of motor short-term memory which incorporates both CE and VE.