The primary aim of this study is to evaluate if a single bout of AM vs PM resistance exercise has different effects on insulin sensitivity and sleep. A randomized cross-over trial be used to compare resistance exercise at two different times of the day. Each condition will take place in a laboratory setting. Each condition will consist of exercise, overnight sleep, and oral glucose tolerance tests the following day. The AM exercise will occur \~1.5 hours after habitual wake, and PM exercise will occur \~11 hours after habitual wake. After a 2-6 week washout, participants will complete the other condition. The hypothesis is that PM exercise will be more beneficial than AM exercise in improving insulin sensitivity. This study could identify if there is a better time of day to perform resistance exercise to decrease risk of developing Type 2 Diabetes Mellitus.
Men and women, all ethnicities, aged 50-74 years
BMI ≥25 kg/m² and <45 kg/m²
Weight stable (less than 5% change in the past 6 months)
Generally healthy individuals
Uncontrolled cardiovascular, metabolic, renal, or pulmonary disease
Cancer treatment in the past 5 years
Untreated thyroid disease or other medical conditions affecting weight or energy metabolism
Current use of weight loss medication or other medications likely to impact energy balance
Crossover
Resistance Exercise Timing
Behavioral1 resistance exercise session consisting of 3 sets, 10 repetitions per set, on 12 different exercises
Insulin sensitivity
Insulin sensitivity will be calculated using the Matsuda Insulin Sensitivity Index
Sleep Duration
Sum of time spent in stage 1, stage 2, stage 3 and rapid eye movement stage (REM) as assessed via polysomnography.
Sleep Staging
Time spent in stage 1, stage 2, stage 3 and REM sleep assessed by polysomnography.
Sleep Quality
As assessed via Pittsburg Sleep Quality Index Questionnaire (scale:0-21, higher scores=worse outcome) and polysomnography
Sleep Efficiency
Ratio of time in bed vs time asleep
Muscular Strength
Muscular strength as assessed via 10 repetition maximum test
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