ASSIGNMENT

Assignment

Assignment

Introduction

Reference to the case the effect of muscle mass and the level of force on the contraction-induced rise in heart rate. It is well documented that isometric contraction causes a rise in heart rate. However, the effect of contraction intensity and size of muscle mass involved is not clear (Fontana, 1993). Various investigators have suggested that the rise in heart rate is contraction-intensity dependent.

Muscles can contract isometrically — no change in length on contraction — or isotonically, where there Is a change in length. During an isometric contraction energy's consumed as the muscle generates a tension, with the muscle fibres contracting against the elastic elements such as tendons which are in series with the fibres. However, unlike an isotonic contraction no mechanical Work is performed as the muscle does not shorten, Isometric contractions are common for postural muscles but can occur in non- postural muscles, for example in arm muscles when carrying a heavy shopping bag. In this practical we Investigate the cardiovascular effects of isometric contraction of the forearm muscles. We d.o this by using a hand dynamorneter to measure the magnitude of muscle contraction whilst simultaneously measuring the subjects blood pressure and heart rate. Both types of muscle contraction have been reported to have cardiovascular effects, which is unexpected as normally physiological reflexes maintain constancy of these cardiovascular parameters in response to perturbations. The so-called baroreceptor reflex. Whilst, increases In cardiovascular variables might be predicted for dynamic exercise, e.g. increased cardiac output to meet increased metabolic demands, the modest changes in energy metabolism associated with isometric contractions would lead us to predict little alteration in cardiovascular functioning. One way of assessing this is to explore the consequences of varying magnitudes and periods of fatiguing and non-fatiguing contractions. It for example, blood pressure altered during the contraction then one consequence must have been the readjustment of the baroreceptor reflex. It is part of the reporting process for this investigation that you evaluate your observations in the light of known physiological processes using the primary literature (Potts, 1998).

Changes in heart rate (f c) and blood pressure (BP) were observed in eight healthy young men aged [mean (SD)] 20(l) years and ten healthy elderly men aged 65 (5) years, during electrically evoked contractions of the ankle plantar flexors and elbow flexors which were sustained for 2 min. There was no significant difference in the f c response to evoked contraction of the ankle plantar flexors or elbow flexors between young and elderly subjects. During contraction of the elbow flexors, elderly subjects produced an unexpectedly large rise in systolic BP which was significantly greater than that of the young subjects. The exaggerated response seen in the elderly group may be due to a more rigid arterial tree which is thought to occur with advancing age. Electrically evoked contraction of the slower contracting elderly ankle plantar flexors resulted in a significantly diminished diastolic BP response when compared with that of the young subjects. In contrast, during electrically evoked contraction of the elbow flexors, which ...