Representation and realization of operational differential equations with time-varying coefficients

An algebraic treatment of operational differential equations with time-varying coefficients is presented in terms of skew rings of differential polynomials defined over a Noetherian ring. Included in this framework are delay differential equations with time- varying coefficients. The operator equations are characterized by transfer matrices which are utilized to construct realizations given by first-order vector differential equations with operator coefficients. It is shown that the realization of matrix equations can be reduced to the realization of scalar equations. Finally, a simple procedure is derived for realizing scalar equations.     

Fractionated Reaction Time Responses to Auditory and Electrocutaneous Stimuli

Abstract

It is well documented that simple reaction time (RT) varies inversely with stimulus intensity, but there is disagreement as to which stimulus modality produces the fastest simple RT. An investigation was conducted to equate two stimulus modalities, auditory (A) and electrocutaneous (EC), using varying stimulus intensities in a simple RT protocol. A second investigation was then conducted to examine neuromotor characteristics of stimulus-evoked responses using previously equated A and EC stimuli of varying intensity from the first investigation. Results showed that RT, premotor time (PMT), and motor time (MT) were all inversely related to stimulus intensity, while maximum displacement (MAXD) was directly related to stimulus intensity, and movement time was not affected by stimulus intensity. We conclude that: (a) both central and peripheral components of RT are altered by varying stimulus intensities, and (b) rapid movements are enhanced by increasing stimulus intensity.     

Book Reviews

Abstract

Carter, J. E. Lindsay, and Heath, Barbara Honeyman. Somatotyping: Development and Applications. (Cambridge Studies in Biological Anthropology, 5). Cambridge: Cambridge Univenity Press, 1990. pp. xiv, 503. Reviewed by Gaston Beunen, Study Centre for Physical Development Research, Institute of Physical Education, Katholieke Universiteit Leuven

Clark, Jane E., &; Humphrey, J. H. (Eds.). Advances in Motor Development Research (Vol. 3). New York: AMS Press, 1990. pp. xi, 259. Index, references. Reviewed by Mary Ann Roberton, Bowling Green State University

Kyle, Donald G., and Stark, Gary D. (Ed.), Essays on sport History and sport Mythology. College Station, TX: Texas A&;M University Press, for the University of Texas at Arlington. pp. vi, 154. Reviewed by Synthia S. Slowikowski, University of Illinois at Urbana–Champaign

MacDougall, J. D., Wenger, H. A., &; Green, H. J. (Eds.). Physiologiml Testing ofthe High Peifonnance Athlete. Champaign, IL: Human Kinetics, 1991. Pp, vii, 424. Tables, figures, photos, references. Reviewed by Paul Vaccaro, University of Maryland

Malina, Robert M., and Bouchard, C. Growth, Maturation, and Physical Activity. Champaign, IL: Human Kinetia, 1991, pp. 501. Index. Reviewed by Kathleen Haywood, University of Missouri–St. Louis

Metzler, M. Instructional Supervision for Physical Education. Champaign, IL: Human Kinetics, 1990. pp. vii, 248. References, index. Reviewed by Paul Paese, Southwest Texas State University

Parkhouse, Bonnie L, (Ed.). The Management of Sport: Its Foundation and Application. St. Louis: Mosby–Year Book, 1991, Pp. xviii, 404. Reviewed by Kathleen Davis, Northeastern University

Thomas, Jerry R., and Nelson, Jack K. Researda Methods in Physical Activity (2nd ed.), Champaign, Il.: Human Kinetics. 1990. 568 pp. Appendixes. Reviewed by Susan J. Hall, California State University, Northridge

Wells, Christine L. Women, sport, and Performance: A Physiological Perspective (2nd ed.) Champaign, IL: Human Kinetics. 1991, 367 pp. Reviewed by Ann Ward, University of Massachusetts Medical Center     

Stimulus intensity and experimental design effects on motor response processing

Experimental design effects and range effects may have influenced previous studies on motor response processing (Grice & Hunter, 1964; Grice, Nullmeyer, & Schnizlein, 1979; Poulton, 1973). This investigation was conducted concurrently with two experiments. First, Erlebacher's (1977) more powerful analysis of variance (ANOVA) model, which allows for the testing of the independent variable (stimulus intensity effect), the experimental design effect (between-subjects [BS] vs. within-subjects [WS]), and the important interaction between independent variable and experimental design was utilized to clarify if the nature of the experimental design (BS, WS) biases motor response processing. Second, Erlebacher's (1977) ANOVA model was used to determine if motor response processing was affected by stimulus intensity and experimental design when different ranges of auditory stimuli were compared. Results indicate motor response processing was inversely affected by increasing stimulus intensity. Experimental design effects and range effects did not appear to bias motor response processing. We conclude stimulus intensity effects on motor response processing appear to be the result of true neuromotor functioning and not artifacts of experimental design or of range effects.     

Neuromotor issues in human performance: introduction

Two current approaches frequently implemented to understand mechanisms involved in motor control are presented in a series of papers. One approach aims at understanding what specific neural mechanisms are responsible for motor behavior Such neural mechanisms might be operative at any of several sites in the nervous system, including spinal sites capable of complex reflex organization, as well as supraspinal sites involved in integrating multiple sensory and motor processes. Alternative approaches involve the assessment of kinematic and other variables used to describe the behavior using dynamical systems theory. Such an approach allows the researcher to explore relationships among groups of variables in, for example, multijoint control. In the series of papers that follow, the value of both of these approaches is discussed using examples from tasks that involve both rhythmic activities (running and cycling) and discrete movement (weight lifting and golf).     

Characteristics of the Achilles Tendon Reflex Following Isometric and Isotonic Exercise

Abstract

An investigation was conducted to determine the effects of fatiguing exercise upon the Achilles tendon reflex. Eleven subjects performed one of four exercise tasks on each of four separate days. The exercise conditions involved low-intensity isometric, high-intensity isometric, low-intensity isotonic or high-intensity isotonic exercise. The low-intensity tasks required a 25% MVC load, while the high-intensity conditions required a 50% MVC load. Results showed that low-intensity isometric exercise reduced reflex force, as well as the time needed to reach peak force, while high-intensity exercise produced an enhancement of reflex force. Half-relaxation time was faster after subjects executed low-intensity isometric exercise, but generally somewhat prolonged following high-intensity isometric exercise. Thus, the Achilles tendon reflex may be either enhanced or depressed depending upon the type and intensity of exercise performed.     

Differences in Sensorimotor Processing of Visual and Proprioceptive Stimuli

Abstract

The present study sought to determine whether individuals could be trained to attenuate the visual dominance effect by selecting a proprioceptive stimulus for attention. Using a reaction time (RT) task, subjects received either: (a) visual (V), (b) proprioceptive (P), or (c) combined V and P (VP) stimuli during the first four days. Each subject was then tested under all three stimuli conditions. Results showed that reaction time to the P cue was always faster than that to V or combined VP stimuli. The order in which subjects were tested under each stimulus modality significantly affected the results such that those subjects who received initial exposure to the V stimulus produced the slowest premotor time scores but the fastest motor time scores. These results suggest that the nature of the stimulus which initiates the volitional task can affect both the central processing requirements to initiate the response, and the qualitative manner in which the motor command is executed.     

Neural Issues in the Control of Muscular Strength

Abstract

During the earliest stages of resistance exercise training, initial muscular strength gains occur too rapidly to be explained solely by muscle-based mechanisms. However, increases in surface-based EMG amplitude as well as motor unit discharge rate provide some insight to the existence of neural mechanisms in the earliest phases of resistance exercise training. Moreover, other phenomena such as the cross transfer of strength following unilateral exercise and neural changes following limb immobilization also support a role for neural control in muscular strength. While studies to date have focused on the phenomenon of neural change, future studies will need to focus on the many motoneuron influences as well as intrinsic motoneuronal properties that may be responsible for these neural adaptations.     

A Comparison of Statistical Models for Calculating Reliability of the Hoffmann Reflex

The Hoffmann reflex is obtained through surface electromyographic recordings, and it is one of the most common neurophysiological techniques in exercise science. Measurement and evaluation of the peak-to-peak amplitude of the Hoffmann reflex has been guided by the observation that it is a variable response that requires multiple trials to obtain a stable mean. As a result, reliability assessment of the Hoffmann reflex has thus far been limited to trial-to-trial variability or the mean of multiple trials across test days to evaluate day-to-day variability, without considering how the two dimensions of measurement interact to affect test–retest reliability. This article compares two analysis of variance models for reliability assessment of the peak-to-peak amplitude of the Hoffmann reflex: one model incorporated both days and trials, and the other used the mean of multiple trials on each test day. The intraclass correlation coefficient calculated from an analysis of variance model that incorporated both trial-to-trial and day-to-day error variances was R = .93. Using the mean of the trials for each test day as a single score resulted in a decrease in the intraclass correlation coefficient (R _2,1 = .76). This study demonstrated that an analysis of variance model that accounts for both trial-to-trial and day-to-day error variances provided a higher estimate of reliability. Further, reliability estimation based on the interaction between both trials and days revealed that a schedule with additional test days had a disproportionate impact upon securing a reliable measure of Hoffmann reflex amplitude.     

Neural issues in the control of muscular strength

During the earliest stages of resistance exercise training, initial muscular strength gains occur too rapidly to be explained solely by muscle-based mechanisms. However; increases in surface-based EMG amplitude as well as motor unit discharge rate provide some insight to the existence of neural mechanisms in the earliest phases of resistance exercise training. Moreover, other phenomena such as the cross transfer of strength following unilateral exercise and neural changes following limb immobilization also support a role for neural control in muscular strength. While studies to date have focused on the phenomenon of neural change, future studies will need to focus on the many motoneuron influences as well as intrinsic motoneuronal properties that may be responsible for these neural adaptations.