Small Steps for Big Changes

Changes in cardiorespiratory fitness (VO2peak), an objective measure of fitness and habitual activity, will be used as an integrative measure of exercise adherence (and overall health) at 6-month and 12-month follow-up. Specifically, peak oxygen uptake (VO2peak) will be assessed by a maximal cycling exercise test. Power output will begin at 30 W and increase by 15 W/min until volitional exhaustion. Expired gas samples will be collected continuously and VO2 measured by a metabolic cart (Parvomedics TrueOne 2400). The mean of the two highest 30 s average values will define VO2peak. VO2peak will be confirmed using standard criteria110. A Polar chest strap, which is integrated to the metabolic cart and cycle ergometer (Lode Excalibur), will capture Heart Rate. Peak power output will be recorded as the highest value attained.

Self-reported adherence will be measuring using an online exercise log book, which participants will be asked to fill in following each exercise session. Adherence will be measured using raw exercise prescription bouts completed. Proportion achieved based on the amount prescription will also be calculated.

Changes in total time spent in moderate-to-vigorous physical activity in bouts ≥10 minutes (MVPA10+) will be assessed over 7 days using tri-axial accelerometers at baseline and 3, 6-, 9- and 12-month follow-up.

Changes in participants exercise efficacy beliefs, self-regulatory efficacy beliefs, concurrent self-regulatory efficacy beliefs, and self-monitoring efficacy beliefs will be measured at baseline, post-intervention, 6-month follow-up and 12-month follow-up. Efficacy measures will be context specific and will utilize a confidence scale ranging from 0%-100%.

Body composition will be assessed using the Hologic Discovery A device. DXA is a standard tool in the measurement of body composition and bone density in adults and children throughout multiple institutions.

Changes in insulin sensitivity and inflammation will be examined. Specifically fasting blooding samples will be taken to assess markers of insulin sensitivity (glucose, insulin, HOMA-IR) and inflammation (C-reactive protein [CRP], interleukin [IL]-6, tumor necrosis factor [TNF]-alpha).

The acute affective response to exercise will be assessed using the 1-item Feeling Scale (FS). The FS is the most frequently used measure of in-task exercise feelings of pleasure/displeasure. Consistent with our established laboratory protocol for assessing and comparing affect in intermittent and continuous exercise bouts, feeling scale will be assessed immediately pre- and post-exercise, and at the beginning (2.5%), middle (42.5%), and end (92.5%) of workout completion. These time points correspond to the midpoint of the first, fifth, and tenth interval within the HIIT protocol. Measurements of affect will be taken in Day 1, Day 6 and Day 9 of the 10-day intervention.

The Physical Activity Enjoyment Scale (PACES) will be used to assess perceived enjoyment at baseline and post intervention. This 18-item measure is scored on a 7-point bipolar scale based on the instruction; "Please rate how you feel at the moment about the physical activity you have been doing:". Example items are "it's not very refreshing/It's very refreshing" and "I would rather be doing something else/there is nothing else I would rather be doing". Items are summed to produce an overall enjoyment score out of 126.

Changes in average blood glucose from baseline to day 9 of the intervention will be measured using the CGMS iPro2 (Medtronic, Northridge, CA). The CGM records glucose values in a blinded fashion using a small microneedle inserted into the subcutaneous abdominal adipose tissue that is connected to a recorder that quantifies interstitial glucose values every 5 minutes for up to three days. Finger stick blood glucose samples, taken four times per day, are used as calibrators to create a 24-hr blood glucose curve, which are downloaded upon device removal and analyzed for: i) average blood glucose, ii) 2 hr postprandial area under the glucose curve, iii) post-meal spikes, and iv) overall glycemic stability. Participants wearing the CGM will be provided a standardized diet (~24 kcal/kg, 60% carbohydrates, 27% fat, 13% protein) to consume during each 24 hr monitoring period. CGM data will be collected at baseline and day 9 of training.

Affective attitudes towards physical activity will be assessed using the procedures outlined by Ajzen (2002). Specifically, a 7-point semantic differential scale will be used, with anchors including "Enjoyable-Unenjoyable", "Pleasant-Unpleasant", "Interesting-Boring". Previous research has found support for both the internal consistency and predictive utility of scores derived from this instrument.