Modelling fatigue and recovery in static postural exercise.

Previous investigations of isometric exercise required information of both the forces exerted and the duration for which they were held to predict fatigue and recovery. This thesis investigates the hypothesis that measures of holding times and rest are sufficient to predict the effects of maintaining static postures. To test this 24 male subjects (aged 19-26 years) held a stooped posture for different percentages of their Maximum Holding Time (MHT), were given pre-determined rest periods and then reheld the posture for as long as possible. Four durations of holding time were investigated which corresponded to 25%, 50%, 75% and 100% of each subject’s MHT. The range of MHTs was 6.47-15.55 minutes. Subjects were provided with different rest pauses following each period of exercise. The duration of the pauses was calculated such that they were equivalent to 12.5%. _ 35%. 50%, 75% and 100% of the subject’s MHT. A mathematical model was developed from these results such that recovery could be predicted if the MHT for that posture is known. and the holding time and rest pauses for the task are measured. The form of the model agrees closely with current understanding of the physiological effects of sustained isometric exercise. The model was found to give statistically reliable values when tested with different subjects (two groups of six male students) on both the same and a different posture. Additions to the model meant it could provide accurate estimates of recovery following repeated bouts of postural exercise and rest. Further findings were that discomfort rating was linearly related to holding time, that heart rate and blood pressure failed to provide useful measures of postural load, and that control of the experimental task and the motivation it engendered are important if reliable results are to be achieved.