Browsing by Author "Cook, Ian"

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    Open Access
    Development of a four-item physical activity index from information about subsistence living in rural African women: a descriptive, cross-sectional investigation
    (BioMed Central Ltd, 2009) Cook, Ian; Alberts, Marianne; Lambert, Estelle
    BACKGROUND:We investigated the criterion validity of a physical activity index (PAI) derived from socio-demographic variables obtained from convenience samples of rural African women. METHODS: We used a sample (N = 206) from a larger dataset which surveyed adult rural Africans during 1997, and data collected during 2003/4 from 138 adult rural African women. A three-point PAI (low-, medium- and high-subsistence) was constructed from four socio-demographic questions related to electricity, cooking methods, water collection and availability of motorized transport. Criterion measures included measures of adiposity, blood biochemistry, resting blood pressure (RBP), physical fitness (VO2max) and single-plane accelerometry (ACC). RESULTS: Age, educational level and health status were not related to PAI level (p > 0.1). There was a significant negative, linear trend between the PAI level and adiposity level (p < 0.04), and fasting blood glucose concentration (p < 0.0001), while VO2max was positively related to PAI level (p = 0.0190). The PAI level was positively and linearly related to ACC output, namely counts.day-1 (p = 0.0044), steps.day-1 (p = 0.0265), min.day-1 of moderate-to-vigorous activity (p = 0.0040), and the percentage of subjects adhering to physical activity public health guidelines (p = 0.0157). Other criterion measures did not reach significance, but were in the expected direction (sedentary behaviour: p > 0.08, RBP: p > 0.07). CONCLUSION: The PAI derived from a socio-demographic questionnaire is a valid instrument for broadly categorizing levels of physical activity for this specific population of rural African women. As the epidemiological transition progresses, validity will need to be re-established.
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    Open Access
    Effect of body mass and physical activity volume and intensity on pedometry-measured activity energy expenditure in rural black South Africans in the Limpopo Province
    (2010) Cook, Ian; Alberts, Marianne; Lambert, Estelle V
    Objectives. We developed a novel approach to investigate patterns of pedometry-measured total weekly activity energy expenditure (EEAct) in rural black South Africans in the Limpopo Province. Design. We analysed 7-day pedometry data in 775 subjects (female: N=508; male: N=267). Variance components models for EEAct were used to estimate the variance explained by body mass (BM), total weekly steps (volume) and estimated intensity (kcal. kg-1.step-1). Univariate General Linear Models, adjusting for age, BM and physical activity (PA) volume, were used to determine if EEAct was primarily affected by volume or intensity. Results. BM (13.1%), PA intensity (24.4%) and PA volume (56.9%) explained 94.4% of the variance in EEAct. Adjusted EEAct did not differ between sexes (78 kcal.week-1, p =0.2552). There were no significant differences across activity categories (sedentary to very active) for adjusted EEAct (62 - 287 kcal.week-1, p>0.1). Adjusted EEAct for 6 - 7 days of compliance (≥10 000 steps.day-1) differed significantly from 1 - 2 days of compliance (266 - 419 kcal.week-1, p<0.04). Obese (body mass index ≥30 kg.m-2) and normal weight (body mass index 18.5 - 24.9 kg.m-2) women did not differ significantly across activity categories for EEAct (200 - 592 kcal.week-1, p>0.30). Conclusions. We have highlighted an intensity effect for days of compliance and at very active ambulatory levels (≥12 500 steps. day-1). A volume effect appeared to dominate between sexes, across activity categories and weight-by-activity categories. It is important that post hoc statistical adjustments be made for body mass and PA volume when comparing EEAct across groups.
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    Sources of variance and reliability of objectively monitored physical activity in rural and urban Northern Soto-speaking blacks
    (2008) Cook, Ian; Lambert, Estelle V
    Objectives. We investigated the sources of variance and reliability in an objective measure of physical activity for a 14- hour and 4-day monitoring period. Design. A convenience sample of rural (N=31) and urban (N=30) adult, Northern Sotho-speaking blacks was recruited. Physical activity was assessed for 8 consecutive days using a uni-axial accelerometer. Physical activity indices were total counts, average counts, inactivity (<500 counts) moderate-1 activity (500 - 1 951 counts), moderate-2+vigorous activity (≥1 952 counts), and were expressed per hour or per day as required. Results. Accelerometry data from 41 subjects (23 males, 18 females) complied with selection requirements and were analysed for variance distribution and reliability (intraclass correlation coefficients (ICCs)). For the 14-hour monitoring period variance was distributed as follows: intra-individual (71 - 82%), inter-individual (3 - 18%) and hour-of-day (2 - 14%). Attenuated ICCs ranged from 0.31 to 0.75 (median: 0.70). Variance for the 4-day monitoring period differed from the 14-hour monitoring period: inter-individual (47 - 58%), intraindividual (43 - 51%) and day-of-week (0 - 6.5%). Attenuated ICCs ranged from 0.27 to 0.84 (median: 0.79). Irrespective of the monitoring period, total counts, average counts and moderate-2+vigorous activity tended to be the most reliable measures requiring the fewest number of monitoring periods. Conclusions. These findings provide an insight for understanding how variance is distributed in objectively measured activity patterns of a South African sample and show that reliable measures of adult physical activity behaviours require 18 - 128 hours and 3 - 44 days, depending on the monitoring period, physical activity index, residence status and sex.
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    Voluntary physical activity : measurement and relationship to selected health parameters in rural black South Africans resident in the Limpopo Province, South Africa.
    (2012) Cook, Ian; Lambert, Vicki
    The use of objective measures of physical activity in addition to, or in place of, subjective or self-report measures of physical activity, is being increasingly promoted in Physical Activity Epidemiology research. This thesis investigates methodological issues related to the use of objective measures of physical activity and presents pioneering objectively measured physical activity survey results from a rural South African setting. In this series of studies, we firstly explored the sources of variance in the objective measure of physical activity (uni-axial accelerometer) as a function of residence and also movement monitor placement. Secondly, we highlighted the importance of Non-Exercise Activity Thermogenesis (NEAT) in a rural African setting and the importance of considering the full spectrum of accelerometer counts when contrasting rural and urban populations. Thirdly, we demonstrated novel approaches to pedometry data from a rural African setting, such that volume-intensity effects could be inferred, and using estimated energy expenditure whether current physical activity guidelines are met. Finally, we indentified that the current recommendations for physical activity and health, applied in a rural African setting, may miss important and possible health-promoting physical activity.