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  • Author: James E. Mitchell x
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Wendy C. King, Jia Li, Kira Leishear, James E. Mitchell and Steven H. Belle

Background:

Accurately measuring physical activity (PA) with activity monitors requires sufficient monitor wear time which can be difficult to assess. Monitor sensitivity to movement and population characteristics (eg, children vs. adults) may dictate the duration of monitor inactivity indicative of nonwear. A standardized method for determining appropriate decision rules to identify wear time is needed.

Methods:

Several decision rules based on minimum durations of monitor inactivity (ie, 60, 90, 120, 150 minutes) to identify nonwear were applied to Stepwatch Activity Monitor data from 1064 adult bariatric surgical candidates. The frequency, pattern, and duration of resulting nonwear and wear periods were examined. Generalized Estimating Equations tested the effect of these decision rules on PA measures.

Results:

A 60-minute duration resulted in unreasonably large percentages of subjects with unlikely wear patterns [eg, ≥3 nonwear periods in a day (29.9%); ≥2 wear periods of less than an hour in a day (28.7%)]; 120 minutes appeared most reasonable. Wear time decision rules impacted PA measures.

Conclusions:

The methods described in this paper can be used to determine appropriate instrument and population specific wear time decision rules. Recognizing monitor wear time is estimated, PA measures least affected by wear time are preferable.

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L.P. Kilduff, E. Georgiades, N. James, R.H. Minnion, M. Mitchell, D. Kingsmore, M. Hadjicharalambous and Y.P. Pitsiladis

The effects of creatine (Cr) supplementation on cardiovascular, metabolic, and thermoregulatory responses, and on the capacity of trained humans to perform prolonged exercise in the heat was examined. Endurance-trained males (n = 21) performed 2 constant-load exercise tests to exhaustion at 63 ± 5 % VO2max in the heat (ambient temperature: 30.3 ± 0.5 °C) before and after 7 d of Cr (20 g · d–1 ’ Cr + 140 g • d–1 glucose polymer) or placebo. Cr increased intraccl-lular water and reduced thermoregulatory and cardiovascular responses (e.g., heart rate, rectal temperature, sweat rate) but did not significantly increase time to exhaustion (47.0 ± 4.7 min vs. 49.7 ± 7.5 min, P = 0.095). Time to exhaustion was increased significantly in subjects whose estimated intramuscular Cr levels were substantially increased (“responders”: 47.3 ± 4.9 min vs. 51.7 ± 7.4 min, P = 0.031). Cr-induced hyperhydration can result in a more efficient thermoregulatory response during prolonged exercise in the heat.

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Brian Cook, Trisha M. Karr, Christie Zunker, James E. Mitchell, Ron Thompson, Roberta Sherman, Ross D. Crosby, Li Cao, Ann Erickson and Stephen A. Wonderlich

The purpose of our study was to examine exercise dependence (EXD) in a large community-based sample of runners. The secondary purpose of this study was to examine differences in EXD symptoms between primary and secondary EXD. Our sample included 2660 runners recruited from a local road race (M age = 38.78 years, SD = 10.80; 66.39% women; 91.62% Caucasian) who completed all study measures online within 3 weeks of the race. In this study, EXD prevalence was lower than most previously reported rates (gamma = .248, p < .001) and individuals in the at-risk for EXD category participated in longer distance races, F(8,1) = 14.13, p = .01, partial eta squared = .05. Group differences were found for gender, F(1,1921) 8.08, p = .01, partial eta squared = .004, and primary or secondary group status, F(1,1921) 159.53, p = .01, partial eta squared = .077. Implications of primary and secondary EXD differences and future research are discussed.