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Alison Griffin, Tim Roselli and Susan L. Clemens

Background: Health benefits of physical activity (PA) accrue with small increases in PA, with the greatest benefits for those transitioning from inactivity to any level of PA. This study examined whether self-reported PA time in Queensland adults changed between 2004 and 2018. Methods: The Queensland government conducts regular cross-sectional telephone surveys. Between 2004 and 2018, adults aged 18–75 years answered identical questions about their weekly minutes of walking, moderate PA, and vigorous PA. Hurdle regression estimated the average annual change in weekly minutes of PA overall and by activity type, focusing on sociodemographic differences in trends. Results: The sample size averaged 1764 (2004–2008) and 10,188 (2009–2018), totaling 107,171 participants aged 18–75 years. Unadjusted PA increased by 10 minutes per week per year (95% confidence interval [CI], 8.8–11.1) overall, with increases for most subgroups. Adjusted PA increased by 10.5 minutes per week per year (95% CI, 9.4–11.7). Trends differed by employment—employed adults and those not in the labor force increased by 14.3 (95% CI, 12.8–15.8) and 2.2 minutes per week per year (95% CI, 0.4–4.0), respectively, with no increase for unemployed adults. The increases were due to both an increased prevalence of doing any activity and an increased average duration among active adults. Conclusions: Since 2004, PA time has increased for Queensland adults, with substantial variability by employment status.

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Daniel C. McFarland, Alexander G. Brynildsen and Katherine R. Saul

Most upper-extremity musculoskeletal models represent the glenohumeral joint with an inherently stable ball-and-socket, but the physiological joint requires active muscle coordination for stability. The authors evaluated sensitivity of common predicted outcomes (instability, net glenohumeral reaction force, and rotator cuff activations) to different implementations of active stabilizing mechanisms (constraining net joint reaction direction and incorporating normalized surface electromyography [EMG]). Both EMG and reaction force constraints successfully reduced joint instability. For flexion, incorporating any normalized surface EMG data reduced predicted instability by 54.8%, whereas incorporating any force constraint reduced predicted instability by 43.1%. Other outcomes were sensitive to EMG constraints, but not to force constraints. For flexion, incorporating normalized surface EMG data increased predicted magnitudes of joint reaction force and rotator cuff activations by 28.7% and 88.4%, respectively. Force constraints had no influence on these predicted outcomes for all tasks evaluated. More restrictive EMG constraints also tended to overconstrain the model, making it challenging to accurately track input kinematics. Therefore, force constraints may be a more robust choice when representing stability.

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Jillian J. Haszard, Kim Meredith-Jones, Victoria Farmer, Sheila Williams, Barbara Galland and Rachael Taylor

Although 24-hour time-use data are increasingly being examined in relation to indices of health, consensus has yet to be reached about the best way to present estimates from compositional analyses. This analysis explored the impact of different presentations of results when assessing the relationship between 24-hour time-use and body mass index (BMI) z-score using compositional analysis of 5-day actigraphy data in 742 children. First it was found that reallocating non-wear time to day-time components only (sedentary behavior, light physical activity, and moderate-to-vigorous physical activity [MVPA]) before normalization to 24 hours provided stronger estimates with BMI z-score than simply removing non-wear time before normalization. Estimates for sleep time were substantially affected, where associations with BMI z-score nearly doubled (mean difference [95% CI] in BMI z-score for 10% longer sleep were −0.20 [−0.32, −0.08] compared to −0.11 [−0.23, 0.002]). Presenting estimates in terms of a greater number of minutes in a component, relative to all others, showed MVPA to be the strongest predictor of BMI z-score, while estimates in terms of the proportion of minutes showed sleep to be the strongest predictor. Both presentations have value. However, presentations in terms of one-to-one “substitutions” of time may need careful interpretation due to the uneven distribution of time in each component. In conclusion, when analyzing relationships between 24-hour time-use and health outcomes, non-wear time and presentation of estimates can impact final conclusions. As a result, the current understanding of the importance of sleep for child health may be underestimated.

Open access

Amelia J. Carr, Philo U. Saunders, Laura A. Garvican-Lewis and Brent S. Vallance

Purpose: To quantify, for an elite-level racewalker, altitude training, heat acclimation and acclimatization, physiological data, and race performance from January 2007 to August 2008. Methods: The participant performed 7 blocks of altitude training: 2 “live high:train high” blocks at 1380 m (total = 22 d) and 5 simulated “live high:train low” blocks at 3000 m/600 m (total = 98 d). Prior to the 2007 World Championships and the 2008 Olympic Games, 2 heat-acclimation blocks of ~6 weeks were performed (1 session/week), with ∼2 weeks of heat acclimatization completed immediately prior to each 20-km event. Results: During the observation period, physiological testing included maximal oxygen uptake (VO2max, mL·kg−1·min−1), walking speed (km·h−1) at 4 mmol·L−1 blood lactate concentration [La], body mass (kg), and hemoglobin mass (g), and 12 × 20-km races and 2 × 50-km races were performed. The highest VO2max was 67.0 mL·kg−1·min−1 (August 2007), which improved 3.1% from the first measurement (64.9 mL·kg−1·min−1, June 2007). The highest percentage change in any physiological variable was 7.1%, for 4 mmol·L−1 [La] walking speed, improving from 14.1 (June 2007) to 15.1 km·h−1 (August 2007). Personal-best times for 20 km improved from (hh:mm:ss) 1:21:36 to 1:19:41 (2.4%) and from 3:55:08 to 3:39:27 (7.1%) in the 50-km event. The participant won Olympic bronze and silver medals in the 20- and 50-km, respectively. Conclusions: Elite racewalkers who regularly perform altitude training may benefit from periodized heat acclimation and acclimatization prior to major international competitions in the heat.

Open access

Joseph O.C. Coyne, Sophia Nimphius, Robert U. Newton and G. Gregory Haff

Open access

Lorenzo Lolli, Alan M. Batterham, Gregory MacMillan, Warren Gregson and Greg Atkinson

Open access

Jos J. de Koning