The response of the peroneal muscles to sudden inversion of the ankle during standing was investigated. The variation of the inversion angle with time was measured by means of a potentiometer attached to a specially designed test apparatus. During the tests, volunteers were subjected to sudden and unexpected inversion of their ankle, during which the surface EMG of the peroneal muscles was also recorded. Two groups were tested, one of normal subjects and one consisting of subjects with recurrent ankle sprains. There were 8 females and 3 males in each group. The subjects in the second group, who suffered from recurrent ankle sprains, had been asymptomatic during the last 2 months prior to the tests. For each subject in the two groups, both ankles were tested. The results indicated a latency time ranging from 60 to 80 ms for both groups. It was concluded that the reflex contraction of the peroneal muscles due to a sudden stretch inversion motion has no role in protecting the ankle joint during sprain and that this protection is mainly provided by the passive tissues.
Objective-To evaluate uninjured and recurrent sprained ankles during single leg standing, both with and without visual input, and the contribution ofrelated proprioceptive feedback in this event.Methods-A force measuring system was used for monitoring reaction forces in the anteroposterior and mediolateral directions during single leg standing. Differences between selected variables obtained in the uninjured and sprained ankles were analysed using two way analysis ofvariance. Results-Foot-ground Two different theories have been suggested to explain recurrent ankle sprains.'01 The first is the functional instability theory, which assumes that the afferent nerve fibres in the capsule, ligaments, and muscles subserve reflexes that help to stabilise the ankle. The second is the mechanical instability theory, which assumes that instability is due to a loss of integrity in the supporting ligaments of the ankle complex. The result is a pathological anterior drawer sign.' However, no consistent relation has been found between functional and mechanical instability. Assuming that ankle stability depends on intact peripheral afferent proprioceptive input,812 the reaction time of the peroneal muscles to a sudden inversion tilt in recurrently sprained and in normal ankles was measured. The results indicated that the reaction time of these muscles in the injured ankle was significantly slower. These findings were disputed by others"3 who conducted a similar measurement procedure and found an almost equal reaction time in both peroneal muscles.The ability to maintain balance during standing on a single leg or both legs depends on the integrity of the visual, vestibular, and nervous systems. In the presence of an intact vestibular system, standing with eyes closed depends mostly on the normal function of the various proprioceptive receptors.4 14 An inversion ankle sprain that results in injury to the proprioreceptors of capsule and ligaments may impair standing balance on the affected limb, especially when eyes are closed.8"'.4Several research methods are used to assess ankle proprioception during upright standing. All subjects, with right lower limb dominance, reported a past history of at least three inversion injuries to one ankle only, which required protected weightbearing and immobilisation. A manual evaluation for anteroposterior stability of each ankle was performed. In all eight affected ankles, the anterior drawer sign was positive, as shown by the greater forward excursion of the injured compared to the uninjured foot. Four suffered right ankle sprains; four left ankle recurrent sprains. The sprains were never accompanied by a fracture of the ankle osseous elements. During the four months before testing, all subjects were fully weightbearing, pain-free, and the functional use of the ankle was unimpaired. EQUIPMENTPostural sway was evaluated by means of a force measuring system, which consisted of a force plate (Kistler Z-4305, Winterthur, Switzerland). The foot-ground reaction forces in the anteroposterior ...
Orchestra musicians are at high risk of neuro-mechanical disorders due to the intense stresses their body withstand, leading to pain and injury. This review presents a comprehensive account of the works on the circumstances and types of playing related mobility disorders of upper strings players, as well as on the relevant neuro-mechanical factors and perspectives to those disorders. The following aspects are considered: asymmetry and imbalance in the musculo-skeletal system, muscle-bone-joint interactions, repetitive overloading and fatigue. An additional factor relates to neuro-muscular redundancy in the motor system, whereby more muscles and tendons than strictly necessary are engaged in performing a motor task, thus making the system indeterminate, with no unique solution. This same task can be performed with different muscle combinations. It is thus of interest to verify whether playing disorders may be alleviated by considering alternative techniques of performance.
The present study deals with stabilizing aspects of a hand-held dish filled with liquid while walking steadily. This is an attempt to decipher the neuro-muscular strategies employed and the mechanical responses of the arm during certain tasks of manual materials handling. The experimental configuration included a cup and the test-subject’s hand as an ‘end-effector’ of a serial three-link system representing the upper limb. These links are connected together by the wrist, elbow and shoulder joints. The tested subjects walked at constant speed on a treadmill while aiming to minimize liquid spillage from the cup. The motion of the limb and shoulder girdle served as inputs to a model to reveal the impedance adjustments during the simultaneous control of grasping and walking under ordinary conditions, and when one of the joints is affected. A regressive function used to express stiffness, included first-order dependence on angle and on angular velocity. The function used for damping included first-order dependence on angular velocity. Redundancies in the numerical solution were eliminated using multicollinearity diagnostic algorithms. The results revealed that the wrist joint was found to have constant stiffness and damping and no regulation of these coefficients was necessary during gait. Both in the elbow and shoulder joints stiffness included a constant coefficient as well as an angular velocity-dependent coefficient. Although all tested subjects demonstrated ability to prevent spillage of liquid, there was a considerable variability among the results obtained, indicating that the compensatory mechanisms employed by each subject to regulate the mechanical impedance were subjective. These results can help in the optimization of manual materials handeling tasks in industrial settings as well as future design of prosthetic arms, robotic appliances and man machine interfacing devices.
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