Testing the activitystat hypothesis: a randomised controlled trial protocol

Background: The activitystat hypothesis proposes that when physical activity or energy expenditure is increased or decreased in one domain, there will be a compensatory change in another domain to maintain an overall, stable level of physical activity or energy expenditure. To date, there has been no experimental study primarily designed to test the activitystat hypothesis in adults. The aim of this trial is to determine the effect of two different imposed exercise loads on total daily energy expenditure and physical activity levels. Methods. This study will be a randomised, multi-arm, parallel controlled trial. Insufficiently active adults (as determined by the Active Australia survey) aged 18-60 years old will be recruited for this study (n=146). Participants must also satisfy the Sports Medicine Australia Pre-Exercise Screening System and must weigh less than 150 kg. Participants will be randomly assigned to one of three groups using a computer-generated allocation sequence. Participants in the Moderate exercise group will receive an additional 150 minutes of moderate to vigorous physical activity per week for six weeks, and those in the Extensive exercise group will receive an additional 300 minutes of moderate to vigorous physical activity per week for six weeks. Exercise targets will be accumulated through both group and individual exercise sessions monitored by heart rate telemetry. Control participants will not be given any instructions regarding lifestyle. The primary outcome measures are activity energy expenditure (doubly labeled water) and physical activity (accelerometry). Secondary measures will include resting metabolic rate via indirect calorimetry, use of time, maximal oxygen consumption and several anthropometric and physiological measures. Outcome measures will be conducted at baseline (zero weeks), mid- and end-intervention (three and six weeks) with three (12 weeks) and six month (24 week) follow-up. All assessors will be blinded to group allocation. Discussion. This protocol has been specifically designed to test the activitystat hypothesis while taking into account the key conceptual and methodological considerations of testing a biologically regulated homeostatic feedback loop. Results of this study will be an important addition to the growing literature and debate concerning the possible existence of an activitystat. Trial registration. Australian New Zealand Clinical Trials Registry ACTRN12610000248066

The relationship between curriculum time for physical education and literacy and numeracy standards in South Australian primary schools

Etude comparative entre les volumes horaires en EPS, enseignements littéraires et mathématiques. Leur croisement avec des caractéristiques démographiques et socio-économiques ne donne pas de résultats significatifs sur les influences possibles en terme de réussite académique

Reliability of the 5-min psychomotor vigilance task in a primary school classroom setting

This study evaluated the reliability of the 5-min psychomotor vigilance task (PVT) in a single-sex Australian primary school. Seventy-five male students (mean age = 11.82 years, SD = 1.12) completed two 5-min PVTs using a Palm personal digital assistant (PDA) in (1) an isolated setting and (2) a classroom setting. Of this group of students, a subsample of 37 students completed a test–retest reliability trial within the classroom setting. Using a mixed-model analysis, there was no significant difference in the mean response time (RT) or number of lapses (RTs ≥ 500 msec) between the isolated and the classroom setting. There was, however, an order effect for the number of lapses in the isolated setting, with the number of lapses being greater if the isolated test was conducted second. Test–retest intraclass correlation coefficients (ICCs) in the classroom setting indicated moderate to high reliability (mean RT = .84, lapses = .59). Bland–Altman analysis showed no systematic difference between the two settings. Findings suggest that the 5-min PDA PVT is a reliable measure of sustained attention in the classroom setting in this sample of primary-aged schoolchildren. The results provide further evidence for the versatility of this measuring device for larger interventions outside the laboratory.

Validation of DXA Body Composition Estimates in Obese Men and Women

The aim of this study was to determine the accuracy of dual-energy X-ray absorptiometry (DXA)-derived percentage fat estimates in obese adults by using four-compartment (4C) values as criterion measures. Differences between methods were also investigated in relation to the influence of fat-free mass (FFM) hydration and various anthropometric measurements. Six women and eight men (age 22–54 years, BMI 28.7–39.9 kg/m2, 4C percent body fat (%BF) 31.3–52.6%) had relative body fat (%BF) determined via DXA and a 4C method that incorporated measures of body density (BD), total body water (TBW), and bone mineral mass (BMM) via underwater weighing, deuterium dilution, and DXA, respectively. Anthropometric measurements were also undertaken: height, waist and gluteal girth, and anterior–posterior (A–P) chest depth. Values for both methods were significantly correlated (r2 = 0.894) and no significant difference (P = 0.57) was detected between the means (DXA = 41.1%BF, 4C = 41.5%BF). The slope and intercept for the regression line were not significantly different (P > 0.05) from 1 and 0, respectively. Although both methods were significantly correlated, intraindividual differences between the methods were sizable (4C–DXA, range = -3.04 to 4.01%BF) and significantly correlated with tissue thickness (chest depth) or most surrogates of tissue thickness (body mass, BMI, waist girth) but not FFM hydration and gluteal girth. DXA provided cross-sectional %BF data for obese adults without bias. However, individual data are associated with large prediction errors (4.2%BF). This error appears to be associated with tissue thickness indicating that the DXA device used may not be able to accurately account for beam hardening in obese cohorts.