Gyan C. Agarwal

Oscillation of the human ankle joint in response to applied sinusoidal torque on the foot

1. Low‐frequency (3‐30 Hz) oscillatory rotation of the ankle joint in plantarflexion—dorsiflexion was generated with a torque motor. Torque, rotation about the ankle and electromyograms (e.m.g.s) for the gastrocnemius—soleus and the anterior tibial muscles were recorded.

Principles Underlying Single-Joint Movement Strategies

Humans make “rational” decisions in different ways. One is according to a plan that optimizes some consequence of the decision. Such a decision-making strategy is normative, leading to a behavior appropriate for achieving some desired goal. Another way is to use a heuristic or rule based approach that guides behavior on the basis of simpler criteria than those characterized by an “optimal” result. For example, optimal strategies for obtaining wealth from the stock market or the race track are sufficiently subtle that few have found them. On the other hand, “rules of thumb” are many, and perhaps almost as much money is made from the sale of such rules as from their application. In fact, people often apply such rules in the face of objective evidence that they are in fact not optimal.

Predictor Operator in Pursuit and Compensatory Tracking

The predictor operator is a well established property of a human controller in manual control systems with a pursuit display. For periodic inputs, the human controller has been shown to use what is called a synchronous tracking mode to improve system performance considerably. The performance change is most evident in the phase portion of the systems Bode plot. The present study investigated the predictor operator in a manual control system with a compensatory display and compared it to a pursuit display. Four types of input signal were used: (1) single sinusoids, (2) narrow-band summed sinusoids, (3) variable-band summed sinusoids, and (4) wide-band summed sinusoids. The frequency range was from 0.04 to 1.5 Hz. The data from pursuit tracking were similar to data obtained in several previous studies. In this study the predictor operator in compensatory tracking was found to be similar to the predictor operator in pursuit tracking. This indicates the ability of the predictor operator to function in the absence of much important visual information found in the pursuit display and which the compensatory display lacks.

Organizing Principles Underlying Motor Skill Acquisition

A review of the literature on motor behavior suggests that there have been few attempts to understand motor learning and motor control from a common theoretical perspective. Both fields of study have a long history of research but with little overlap. This is unfortunate since the development of knowledge in each field must ultimately depend on the development of knowledge in the other. For example, many experimental results in the motor control literature are potentially confounded by the prior history of experimental subjects and the degree of learning that took place before and during data collection. Experimental paradigms requiring subjects “not to intervene” (Asatryan and Feldman, 1965; Gottlieb and Agarwal, 1988) usually require considerable subject practice and are seldom possible in untrained subjects.

Time series modeling of neuromuscular system

The dynamic response of the human ankle joint to a bandlimited random torque perturbation superimposed on a constant bias torque is observed in normal human subjects. The applied torque input, the joint angular rotation output, and the electromyographic activity using surface electrodes from the extensor and the flexor muscles of the ankle joint were recorded. Transfer function models using time series techniques were developed for the torque — angular rotation input-output pair and for the angular rotation — electromyographic activity input-output pair. A parameter constraining technique was applied to develop more reliable models. It is shown that the asymptotic behavior of the system must be taken into account during parameter optimization to develop better predictive models.

Reflex response to sinusoidal forces at the ankle joint

The dynamic properties of muscle contraction and its neurological control mechanisms have been extensively studied by the application of sinusoidal length changes. Sinusoidal oscillations are easy to generate and the methods of analysis are well understood. Most studies have been in animals which have the advantage of allowing subsystem analysis and recording from points within the system (such as the alpha motoneurons), but these studies do not provide information concerning normal working processes, nor are they in humans. Joyce, Rack & Ross ( 1 9 7 4 ) studied the forced oscillation of the human elbow joint. Many of their results are confirmed by those to be reported here. Walsh (1973) applied sinusoidally varying forces to the wrist and observed a resonance and jump phenomenon. In this paper we will consider the effects of low frequency (3 to 30 Hz) forced sinusoidal oscillation of the ankle joint in normal human subjects.