Age and gender related changes in the electromyogram and cardiovascular system during muscle fatigue in humans

Allahyari, Mansour (2003) Age and gender related changes in the electromyogram and cardiovascular system during muscle fatigue in humans. PhD thesis, University of Glasgow.

Abstract

Muscle fatigue can be defined as a failure to maintain the required or expected force. This is a complex process, which is still not fully understood. Three sites are commonly thought of as the major locations of fatigue: the CNS, transmission at neuromuscular junction and individual fibres. Muscle size and related neuromuscular function change dramatically across the human lifespan, initially showing rapid increases due to growth and then, later, more gradual decreases due to ageing. The physiological changes underlying the loss of muscle strength are not fully understood. Progressive muscular weakness is associated with a shrinking of muscle mass and muscle cross-section. This has been partially confirmed in the past, although, surprisingly, there has been little research on differences in fatigability between young and elderly subjects. The purpose of this study was threefold, firstly, to determine if there is a relationship between fatigue and sex. Secondly, if there is a significant association between fatigue and age. Thirdly, to determine if these relationships are dependent on the cardiovascular system. 108 volunteers participated in this study. There were 53 females and 55 males. The ages of the volunteers ranged from 5 to 65 years. A series of experiments were performed to investigate the fatigue process during grip contractions at 60% of maximum voluntary effort. To facilitate this, the volunteers were divided into 6 age groups. Blood pressure and heart rate were measured before and immediately after the contraction. The dominant or preferred forearm of the volunteer was always chosen for the experiments. Measuring the change in EMG signal during sustained and intermittent contractions assessed the state of fatigue. The mean endurance time of females was significantly longer than that of males. In both females and males there were substantial reductions in median frequency of the EMG spectrum and longer half relaxation times. This indicates a strong fatigue state. The reduction in median frequency and increase in half relaxation time were similar in both females and males. After both sustained and intermittent contractions there was no significant difference between males and females in systolic, diastolic blood pressure and heart rate. It was found that lowest maximum voluntary grip was in the age group 1 (5-9 years) and the highest maximum voluntary grip was seen in group 3 (20-29 years). There were significant differences between mean maximum voluntary grip in groups 1 & 2 compared to groups 3, 4, 5 and 6. There was a clear trend for longer endurance times in older groups. However, there were no significant differences in endurance time between the age groups. During sustained and intermittent contractions, the mean median frequency of the age group volunteers was not significantly different in the initial 5 seconds period. Neither were the median frequencies different in age groups at the end of the contraction. There was no significant difference between the mean half relaxation time in different age groups at the beginning or at the end of the series of intermittent contractions. The mean systolic and diastolic blood pressure before contractions and after both sustained and intermittent contractions show a progressive increase with age. These changes are what might be expected. It was found that the mean heart rate after sustained contraction in children was significantly faster than adults. There were no significant differences between the mean heart rate in other groups.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Kinesiology.
• Colleges/Schools: College of Medical Veterinary and Life Sciences
• Supervisor's Name: Baxendale, Dr. R.H.
• Date of Award: 2003
• Depositing User: Enlighten Team
• Unique ID: glathesis:2003-71465
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 10 May 2019 14:36
• Last Modified: 10 Jun 2021 09:26
• URI: https://theses.gla.ac.uk/id/eprint/71465