Patterns of Free-Living Physical Activity and Posture: Objective Measurement and Relation to Coronary Risk

  • William Wiewatenni Tigbe

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

It has been generally assumed, that physical inactivity is causally involved in the aetiology of coronary heart disease (CHD) and other major chronic diseases. The threshold of physical activity (PA) needed for health benefits may be lower than previously believed and possibly achievable by low intensity activity for longer times. Objective measures of PA in the free-living environment would make the relationship clearer. The present study aimed to investigate the relationship between objectively measured free-living PA and CHD risk.

An objective PA monitor (the activPAL™) was validated against direct observation for measuring time spent sedentary, standing and walking, as well step count and rate of stepping. There was good agreement between observation and the activPAL™, absolute error of 1%. The monitor was also tested in the free-living environment against the Bouchard activity diary and the RT3 activity monitor and reasonable agreement (mean difference [95% Cl] of < 2.3 [-2.4 to 7.7]) was found.

118 healthy non-smoking postal workers (15 women) wore the activPAL™ activity monitor for seven days. The sample consisted of 59 delivery postal workers (active) and 59 office postal workers (inactive). The technology of the activPAL™ allowed for quantification of both PA and sedentary behaviour, and detailed analyses of pattern and intensity of PA. Socioeconomic strata were obtained. Anthropometric and blood pressure measurements used standard WHO protocols. Diet was measured using the Diet Q food frequency questionnaire. Cardiorespiratory fitness was assessed using the 3-minute step test. Fasting blood samples were obtained for lipid profile, glucose, CRP, IL6, adiponectin and ICAM levels. Comparison was made between the groups for differences, and relationships between PA measures and CHD risk factors were explored.

The delivery workers were more active (p < 0.001) during work hours only but did not compensate with inactivity when not working, and they were also fitter on the step test. No significant differences in risk factors were found between the two groups. From reverse power calculations, a sample size of 355 and 187 are required to exclude significant differences between the two occupation groups in the biochemical values and Procam risk score, respectively. Even short bouts of moderate and light intensity PA, but not vigorous intensity PA, were associated with coronary risk reduction. Diet, socio-economic and familial factors showed weak associations with CHD risk.

Longer time spent upright was cardio-protective - reducing waist, triglycerides, LDL and VLDL while increasing HDL and adiponectin. Increasing daily time spent in upright posture by one hour is associated with 19% reduction in 10-year Procam risk. An additional 30 min a day walking reduces 10-year Procam risk by 15 %, while an extra 30 min a day standing yields another 12% risk reduction. These findings, probably limited to healthy non-smokers, give some support for modifying current PA recommendations. They also open a new opportunity for PA prescription.
Date of Award2009
Original languageEnglish
Awarding Institution
  • Glasgow Caledonian University
SupervisorMalcolm Granat (Supervisor)

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