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Shihui Chen, Ernest Lange, Paul Miko, Jiabei Zhang and Daniel Joseph

The purpose of this study was to investigate the effectiveness of the progressive time delay (PTD) procedure on teaching gross motor skills to adult males with severe mental retardation. A multiple probe design across three skills and replicated across 4 participants was utilized. Results indicated that a PTD procedure with a 0 to 5 s delay was effective in teaching 4 participants three gross motor skills (tee-ball batting, softball pitching, croquet striking) over a period of 13 weeks. Data on effectiveness were analyzed in terms of the number of instructional sessions (M = 9.58), the number of trials (M = 105.41), the number of min (M = 84.66), and the number of performing errors to criterion (M = 4.08%). A maintenance level (M = 96.87%) was also determined across 4 participants and three skills on the 1st, 4th, 14th, and 24th sessions after terminating the PTD instruction.

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Joan E. Deffeyes, Regina T. Harbourne, Wayne A. Stuberg and Nicholas Stergiou

Sitting is one of the first developmental milestones that an infant achieves. Thus measurements of sitting posture present an opportunity to assess sensorimotor development at a young age. Sitting postural sway data were collected using a force plate, and the data were used to train a neural network controller of a model of sitting posture. The trained networks were then probed for sensitivity to position, velocity, and acceleration information at various time delays. Infants with typical development developed a higher reliance on velocity information in control in the anterior-posterior axis, and used more types of information in control in the medial-lateral axis. Infants with delayed development, where the developmental delay was due to cerebral palsy for most of the infants in the study, did not develop this reliance on velocity information, and had less reliance on short latency control mechanisms compared with infants with typical development.

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Jiabei Zhang, Michael Horvat and David L. Gast

It is imperative that teachers utilize effective and efficient instructional strategies to teach task-analyzed gross motor skills in physical education activities to individuals with severe disabilities. The purpose of this paper is to describe the constant time delay procedure, which has been shown to be effective in teaching task-analyzed fine motor skills in daily living and safety activities. In this article, guidelines are presented for teaching task-analyzed gross motor skills to individuals with severe intellectual disabilities. These guidelines are based on a review of the constant time delay procedure reported in the special education literature and current research being conducted by the authors.

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Oliver Faude, Tim Meyer and Wilfried Kindermann

Purpose:

The work rate (WR) corresponding to ventilatory threshold (VT) is an appropriate intensity for regenerative and low-intensity training sessions. During incremental ramp exercise, VO2 increase lags behind WR increase. Traditionally, a VO2 time delay (t d) of 45 seconds is used to calculate the WR at VT from such tests. Considerable inaccuracies were observed when using this constant t d. Therefore, this study aimed at reinvestigating the temporal relationship between VO2 and WR at VT.

Methods:

20 subjects (VO2peak 49.9 to 72.6 mL · min–1 · kg–1) performed a ramp test in order to determine VT and a subsequent steady-state test during which WR was adjusted to elicit the VO2 corresponding to VT. The difference in WR and heart rate at VT was calculated between the ramp and the steady-state test (WRdiff, HRdiff) as well as the time delay corresponding to WRdiff during ramp exercise.

Results:

Mean values were t d = 85 ± 26 seconds (range 38 to 144), WRdiff = 45 ± 12 W (range 23 to 67), HRdiff = 1 ± 9 beats/min (range –21 to +15). The limits of agreement for the difference between WR at VT during ramp and steady-state exercise were ± 24 W. No signifi cant influence on t d, WRdiff, or HRdiff from differences in endurance capacity (VO2peak and VT; P > .10 for all correlations) or ramp increment (P = .26, .49, and .85, respectively) were observed.

Conclusion:

The wide ranges of t d, WRdiff, and HRdiff prevent the derivation of exact training guidelines from single-ramp tests. It is advisable to perform a steady-state test to exactly determine the WR corresponding to VT.

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Sarah J. Willis, Jules Gellaerts, Benoît Mariani, Patrick Basset, Fabio Borrani and Grégoire P. Millet

constant, and the time delay of the primary phase of oxygen kinetics. Oxygen cost was calculated as the difference between the average V ˙ O 2 of the last 2 minutes of each stage and the baseline prior the stage ( V ˙ O 2 net ) divided by speed (in km·h −1 ) and multiplied by 60. Energy cost was

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Maurice R. Yeadon and Grant Trewartha

The goal of this study was to investigate the control strategy employed by gymnasts in maintaining a hand balance. It was hypothesized that a “wrist strategy” was used in which perturbations in the sagittal plane were corrected using variations in wrist flexor torque with synergistic shoulder and hip torques acting to preserve a fixed body configuration. A theoretical model of wrist strategy indicated that control could be effected using wrist torque that was a linear function of mass center displacement and velocity. Four male gymnasts executed hand balances and 2-dimensional inverse dynamics was used to determine net joint torque time histories at the wrist, shoulder, and hip joints in the sagittal plane. Wrist torque was regressed against mass center position and velocity values at progressively earlier times. It was found that all gymnasts used the wrist strategy, with time delays ranging from 160 to 240 ms. The net joint torques at the shoulder and hip joints were regressed against the torques required to maintain a fixed configuration. This fixed configuration strategy accounted for 86% of the variance in the shoulder torque and 86% of the variance in the hip torque although the actual torques exceeded the predicted torques by 7% and 30%, respectively. The estimated time delays are consistent with the use of long latency reflexes, whereas the role of vestibular and visual information in maintaining a hand balance is less certain.

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Walter E. Davis, William A. Sparrow and Terry Ward

A fractionation technique was employed to determine the locus of reaction time delay in Down syndrome (DS) and other adult subjects with mental retardation (MH). Twenty-three subjects (8 nondisabled, 8 MH, and 7 DS) responded to a light, sound, and combination light/sound signal. Dependent measures of premotor time, motor time, total reaction time, and movement time were obtained during a 20° elbow extension movement and were analyzed separately. As expected, both MH and DS subjects were slower and more variable in their responses than the subjects without disabilities. In turn, DS subjects were significantly slower but not more variable than the MH subjects. There were no significant differences between the DS and MH subjects on movement times. Evidence for both a specific (premotor) and a generalized (both premotor and motor) locus of delay was found. Some difference in signal effect was also found for the DS subjects.

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Cyril Burdet and Patrice Rougier

To question the relation between uni- and bipedal postural skills, 21 subjects were required to stand on a force platform through uni- and bipedal conditions. These two protocols are commonly used paradigms to assess the balance capacities of healthy and disabled patients. The recorded displacements of the center of pressure (CP) were decomposed along mediolateral and anteroposterior axes and assessed through variance positions and parameters obtained from fractional Brownian motion (fBm) modeling to determine the nature and the spatiotemporal organization of the successive controlling mechanisms. The variances underline the relative independence of the two tasks. Nevertheless, as highlighted by the fBm framework, postural correction is initiated for the unipedal stance after shorter time delays and longer covered distances. When compared to bipedal standing, one of the main characteristics of unipedal standing is to induce better-controlled CP trajectories, as deduced from the scaling regimes computed from the fBm modeling. Lastly, the control of the CP trajectories during the shortest time intervals along the anteroposterior axis appears identical for both uni- and bipedal conditions. Unipedal and bipedal standing controls should thus be viewed as two complementary tasks, each providing specific and complementary insights into the postural control organization.

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Vladimir M. Zatsiorsky and Marcos Duarte

A method of decomposing stabilograms into two components, termed rambling and trembling, was developed. The rambling component reveals the motion of a moving reference point with respect to which the body's equilibrium is instantantly maintained. The trembling component reflects body oscillation around the reference point trajectory. The concepts of instant equilibrium point (IEP) and discrete IEP trajectory are introduced. The rambling trajectory was computed by interpolating the discrete IEP trajectory with cubic spline functions. The trembling trajectory is found as a difference between the approximated rambling trajectory and the COP trajectory. Instant values of the trembling trajectory are negatively correlated with the values of the horizontal ground reaction force at a zero time lag. It suggests that trembling is strongly influenced by a restoring force proportional to the magnitude of COP deviation from the rambling trajectory and acts without a time delay. An increment in relative COP position per unit of the restoring force, in mm/N, was on average 1.4 ± 0.4. The contribution of rambling and trembling components in the stabilogram was ascertained. The rambling variability is approximately three times larger than the trembling variability.

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James R. Tresilian

The λ version of the equilibrium point (EP) hypothesis for motor control is examined in light of recent criticisms of its various instantiations. Four important assumptions that have formed the basis for recent criticism are analyzed: First, the assumption that intact muscles possess invariant force-length characteristics (ICs). Second, that these ICs are of the same form in agonist-antagonist pairs. Third, that muscle control is monoparametric and that the control parameter, λ, can be given a neurophysiological interpretation. Fourth, that reflex loop time delays and the known, asymmetric, nonlinear mechanical properties of muscles can be ignored. Mechanical and neurophysiological investigations of the neuromuscular system suggests that none of these assumptions is likely to be correct. This has been taken to mean that the EP hypothesis is oversimplified and a new approach is needed. It is argued that such an approach can be provided without rejecting the EP hypothesis, rather to regard it as an input-output description of muscle and associated segmental circuits. The operation of the segmental circuitry can be interpreted as having the function, at least in part, of compensating for a variety of nonlinearities and asymmetries such that the overall system implements the λ-EP model equations.