Human Muscle Stretch Reflexes: The Effects Of Stimulus Properties, Muscle State And Subject Intention
Funder
National Health and Medical Research Council
Funding Amount
$170,604.00
Summary
The best known muscle reflex is the tendon jerk, which is usually evoked by tapping the muscle tendon with a small hammer. This tap imposes a very rapid stretch on the muscle, which produces a stretch reflex. Different stretch responses, however, can be observed to slow or fast stretches, or to vibration of muscle. Normally, when the muscles of a relaxed person are stretched, no active response is observed. However, when the person is engaged in a task and contracting their muscles, then stretch ....The best known muscle reflex is the tendon jerk, which is usually evoked by tapping the muscle tendon with a small hammer. This tap imposes a very rapid stretch on the muscle, which produces a stretch reflex. Different stretch responses, however, can be observed to slow or fast stretches, or to vibration of muscle. Normally, when the muscles of a relaxed person are stretched, no active response is observed. However, when the person is engaged in a task and contracting their muscles, then stretch modulates the muscle activity such that an increase in contraction of the muscle opposes the stretch and defends the position of the joint against the external disturbance. This is the everyday situation in which stretch reflexes operate. Despite extensive investigation for over a hundred years, there is still no consensus among researchers about the behaviour of stretch reflexes nor about their role in the control of movement. Even the demarcation of reflex from voluntary muscle activity is not always certain. One of the outstanding features of stretch reflexes is the variability of their behaviour, which depends on the particular muscle involved, its level of contraction, the type of stretch and the task in which the person is engaged. This variability has made it difficult for researchers to determine the role of reflexes in the control of movement. In order to study stretch reflex behaviour in human subjects, we will measure the electrical activity of elbow muscles, the elbow position and the force generated at the joint under a variety of conditions. A series of five experiments will investigate specific unresolved issues such as the effect of subject intention on the modulation of muscle activity and how altered modulation of muscle activity may change the stiffness of our limbs. The objective of the experimental series is to fill in important gaps in the picture of the behaviour of the stretch reflex.Read moreRead less
Physiology And Pathophysiology Of Trunk Control Mechanisms
Funder
National Health and Medical Research Council
Funding Amount
$168,958.00
Summary
The overall aim of this series of experiments is to understand how the spine is controlled and how this changes in disease. Altered control has been identified in people with low back pain, yet we still know very little about the normal mechanisms for protection and support of the spine. Back pain is a common affliction that affects about 5% of Australians each year and is the most common and expensive work-related injury in western society. An understanding of normal control and the mechanism o ....The overall aim of this series of experiments is to understand how the spine is controlled and how this changes in disease. Altered control has been identified in people with low back pain, yet we still know very little about the normal mechanisms for protection and support of the spine. Back pain is a common affliction that affects about 5% of Australians each year and is the most common and expensive work-related injury in western society. An understanding of normal control and the mechanism of dysfunction is critical for identification of risk factors and development of strategies for rehabilitation and prevention. The experiments are divided into two series. The first series addresses normal spinal control. The questions to be asked deal with how the brain copes with the challenge of using trunk muscles for breathing and spinal control at the same time, how the activity of the trunk muscles is affected by input from sensory receptors in the joints, ligaments and muscles of the spine, and whether intra-abdominal pressure can support the trunk. The second series deals with clinical populations. The first aim is to identify whether people with respiratory diseases use trunk muscles for spinal control and breathing at the same time. If they cannot, we predict that they will be more prone to low back pain. We will test this in a large study of incidence of low back pain in people with and without respiratory disease. The second study will investigate the pelvic floor muscles which are important for continence and assist with spinal control. We will investigate whether people with incontinence have poor spinal control and whether this leads to back pain. The final experiment will identify whether people with low back pain interpret sensory information from the spine differently. By answering these questions we hope to intervene in the enormous personal, social and economic consequences of LBP which affects between 60-90% of the population at some stage in their life.Read moreRead less