## 2 Methods
### Baseline Measures  
Trait mental and physical energy and fatigue: Using the second section of the State and Trait Mental and Physical Energy and Fatigue survey [41], the trait aspect (long-standing pre-disposition) of mental and physical energy and fatigue was collected during a familiarization visit. The trait component references how the respondent usually feels and contains a 12-item scale with 3 items for each of the 4 trait outcomes. Representative statements include \"I feel I am full of pep\" and \"I have feelings of being worn out.\" Participants are asked to mark how they normally feel on a 5-point scale ranging from \"never\" to \"always.\" In previous studies, [PERSON]'s alpha coefficients range from 0.73 to 0.94 [41,42]. With the current data, the alpha coefficients ranged from 0.79 to 0.86 (Trait Physical Energy = 0.81, Trait Physical Fatigue = 0.79, Trait Mental Energy = 0.86, Trait Mental Fatigue = 0.85).  
Sleep quality and quantity: The Pittsburgh Sleep Quality Inventory (PSQI) was used to measure self-reported sleep quality and quantity over the last 30 days. The 19-question survey assesses seven dimensions of sleep: sleep quality, latency, duration, habitual sleep efficiency, sleep disturbance, use of sleep medication, and daytime dysfunction. The scores for each dimension range from 0 to 3 and are summed to create an overall sleep quality score, with higher scores indicating worse sleep quality. Previous studies have defined poor sleep quality as PSQI scores > 5 [43]. For the current study, we used data from the sleep duration component of the PSQI to identify the participants' self-reported average night sleep to determine if participants had received adequate sleep the night before the study.  
Physical Activity: The International Physical Activity Questionnaire--Short Form (IPAQ-SF) was administered to assess self-reported physical activity levels and sitting behavior [44]. Respondents were asked to report how many days they perform vigorous (i.e., heavy lifting, digging, aerobics, or fast bicycling), moderate (i.e., carrying light loads, bicycling at a regular pace, or doubles tennis) and light (i.e., walking at work or at home, walking to travel from place to place) physical activity and the number of hours and minutes per day engaged in each of these types of activities. Physical activity levels are calculated by multiplying the number of days per week of physical activity performed by the number of minutes. Results for this study are presented in hours per week. Respondents are also asked to identify the days per week, in addition to the number of hours and minutes per day spent sitting (including time spent sitting at a desk, visiting friends, reading or sitting or lying down to watch television) on a typical weekday and weekend day. Sitting time for this study was calculated by multiplying the number of self-reported weekdays spent sitting by the time spent sitting on weekdays, multiplying the number of hours and minutes spent sitting on a typical weekend day by two, then adding the weekday and weekend results for total sitting time. Results are presented as number of hours per day of sitting time.  
Caffeine consumption: Respondents completed a questionnaire that asked them to identify their consumption of different caffeinated beverages and edible products containing caffeine. Consumption of caffeinated products was standardized to 8 oz servings [42] and the total amount of caffeine in servings per day was calculated for each participant.