Being regularly physically active, defined as exercising at least 3-days/wk for 30-min provides essential and seemingly unlimited health benefits. To emphasize the importance of the health benefits of physical activity (PA), the United States government recently provided us with The Physical Activity Guidelines for Americans (PAG) 2nd edition. This recommended PA prescription for improving and maintaining health includes 150-min/wk of moderate intensity aerobic PA plus 2-days of muscle-strengthening PA. Yet, an estimated 26% of American adults and 36% of college students do not perform any leisure-time PA. A novelty of the PAG 2nd edition is the updated research acknowledging that PA exists on a spectrum where any and all movement is beneficial to health. This update emphasizes that the steepest decrease in relative risk of all-cause mortality among physically inactive individuals occurs with the substitution of sedentary behavior for light intensity movement, inherently encompassing lifestyle activities as healthy, meaningful PA. The 2018 Physical Activity Guidelines Advisory Committee Scientific Report (PAGACSR) conceptualizes this important public health message with the creation of a heat map relating PA with all-cause mortality, creatively depicting the dose-response effect of increased PA on health. The Office of Disease Prevention and Health Promotion contends that this new emphasis on all PA counting towards health can serve as a method of increasing PA in physically inactive individuals as demonstrated by the launch of the Move Your Way initiative. The all movement counts message can encompass the Integrated Behavior Change Theory (IBC) which attributes increased PA to perceived behavioral control due to higher autonomy.

HEAT is a Randomized Controlled Trial (RCT) comparing the PAG exercise prescription (ExRx#1) of 150-min/wk of moderate intensity aerobic PA plus 2-days of muscle-strengthening PA to a new method of exercise prescription (ExRx) using the everything counts message depicted by the heat map (ExRx#2) to prescribe exercise to physically inactive individuals. ExRx#1 uses the Frequency, Intensity, Time, and Type or FITT principle of ExRx to relay the PAG; and ExRx#2 will be founded in the Integrated Behavior Change Theory (IBC) and emphasize that all PA counts to relay the message of the heat map. ExRx#1 communicates the PAG ultimate weekly goal ExRx using an image adopted from the PAG website that depicts the 150-minutes of aerobic and 2 days of muscle strengthening exercise and provides a weekly prescription on the FITT of how to accomplish this weekly goal. ExRx#2 uses the heat map image to communicate the ExRx of all movement counts and that exercise can be done along any FITT.

Both ExRx were created by an expert panel of exercise professionals including the principal investigator Linda S Pescatello, PhD, who was senior editor of the American College of Sports Medicine Guidelines for Exercise Testing and Prescription 9th edition and one of the 17 Advisory Committee members of the PAGACSR which provided the scientific foundation for the PAG 2nd edition.

1. ExRx #1: The ExRx given to participants each week represents the ultimate weekly goal of 150-min of aerobic PA plus 2-days of muscle-strengthening PA to support optimal health. For example, the ExRx on week 6 suggests 3-days/wk of 50-min of aerobic PA plus 2-days of 30-min of muscle-strengthening PA in the form of resistance or neuromotor exercise. The ExRx then gives examples of taking a 50-min moderate intensity Zumba class on one day to fulfill part of the weekly aerobic PA guideline and 2-3 sets of 8-12 reps of resistance exercises for 30-min of muscle-strengthening PA on another day.
2. ExRx #2: The ExRx given to participants each week represents the ultimate weekly goal of moving more throughout the day across all intensities in order to achieve optimal health as represented by the deep green color on the bottom right of the heat map image that represented high amounts of activity and good health. For example, the ExRx on week 6 suggests including a variety of moderate intensity physical activities and light intensity physical activities to achieve the deep green color on the bottom right of the heat map. The ExRx then gives the examples of taking a Zumba class and weight training.

Subjects will be randomly assigned to receiving either ExRx#1 (n=30), or ExRx#2 (n=30). All subjects will participate in a 12-week unsupervised ExRx program that will safely progress them from being physically inactive to becoming physically active. Each week subjects of both groups will be sent an ExRx in the form of PA recommendations for the week that will be matched in terms of intervention setting, behavior change strategies, mode of intervention delivery, suggestions for types of PA to do, action planning, goal timeframe, and feedback. The difference between the two ExRx methods is the messaging of the specific frequency, intensity time, and type to follow in ExRx#1 versus giving only suggestions of exercises to do and no frequency, intensity, time or type restriction as "all movement counts" is emphasized in ExRx#2. Both groups will be given the main goal of the guidelines they are randomized to along with the same information on the definitions of aerobic, resistance, neuromotor, flexibility and concurrent exercise along with how to measure intensity of PA using the talk test and the Borg Ratings of Perceived Exertion 6-20 scale. Each participant will be verbally explained the overall goal of the ExRx and walked through the definitions to ensure complete understanding of each mode of PA and how to monitor intensity of activity. Both groups will be instructed that the guidelines will progress them from being physically inactive to meeting the overall goal of the ExRx from weeks 1-6; then the guidelines will stay consistent in prescribing the overall goal of the ExRx from weeks 6-12. In both groups, the ExRx is described as effective for improving and maintaining health and that all PA participation is at their own discretion and they can do whatever PA type they would like. Participants in both groups will be given the same exercise compendium of aerobic and resistance exercises to choose from in case they are unsatisfied with the example types of PA recommended in the weekly guidelines. Researchers will stress the goal of accurately recording PA and exercise regardless of if the recommendations given to them are met or not.

Currently 36% of University students are physically inactive. Due to barriers such as lack of time, exercising 150-min/wk+ and accomplishing a specific FITT such as the ExRx#1 provides may seem unattainable. In contrast, the ExRx#2 demonstrates a simple message to move more however you can, allowing for practical uptake of increased PA and using the IBC to connect the intention to exercise with the behavior through increased self-efficacy and autonomy. We hypothesize that ExRx #2 will elicit greater increases in PA volume from baseline (BL) to post-test at the end of the 12 weeks of guidelines (12W) compared to ExRx#1. We hypothesize that ExRx#2 will produce greater improvement in autonomy and self-efficacy compared to ExRx#1 at 12W.

Anthropometrics, health-fitness assessments, PA tracking and questionnaires will be administered at BL, 6W and 12W. All questionnaires will be administered in person using Qualtrics Secure encrypted database and will be compared between groups at BL, 6W and 12W to measure changes over time. Age will be assessed in years. Height (cm) and weight (kg) will be measured and used to calculate body mass index in m2/kg. Waist circumference will be measured at the height of the iliac crest with a Gulick tape measure in cm. Cardiorespiratory fitness will be assessed using a modified and validated Harvard Step Test protocol where participants step up and down on a 30cm box at a rate of 30 steps/min for 3-min and recovery heart rate (HR) is recorded. Muscular endurance will be measured via the push-up test with males performing repetitions until failure in the standard position and females in the modified kneeling position. Handgrip strength is a validated measure of overall muscular strength and will be measured using a validated protocol in the dominant hand with the Jamar Hydraulic Handgrip Dynamometer. Flexibility will be measured in cm using a Sit and Reach Flexibility Box. Timeline Follow-Back for Exercise (TLFB-E) is a self-report calendar diary method for logging daily exercise and PA, and sitting and sleeping time. Participants will record daily PA frequency, type, duration (min) and intensity using the Borg 6-20 scale. Researchers will assess the TLFB-E weekly to ensure students are actively participating in reading the ExRx guidelines and logging activity. Paffenbarger Physical Activity Questionnaire Question 8 will measure duration (min) in each intensity of PA plus time spent sleeping and sitting for a typical weekday and weekend day. PA volume will be calculated in MET.min/wk. Actical® accelerometers will be given to participants to wear on their hip for 4 consecutive days including 2 weekdays and 2 weekend days as an objective measure of PA volume in MET.min/day, steps/day and time spent in light, moderate and vigorous intensities. Transtheoretical Model Stage of Change will assess readiness to take action to exercise regularly and measures transitions in this readiness. Motivation for Physical Activity will determine type of motivation for PA (e.g., intrinsic vs external) and self-perceived autonomy. Marcus Self-Efficacy questionnaire will measure confidence for exercising when 5 different perceived barriers present. Task Self-Efficacy will measure confidence for exercising 3 times/wk at increasing durations. Barriers to Self-Efficacy will assess confidence in exercising 3days/wk for the next 3 months in the presence of possible barriers to exercise.

Group descriptive statistics will be presented as mean±standard deviation and ANOVA will be performed to determine if there are BL differences between the groups. All BL, 6W and 12W measures of PA and the psychosocial questionnaires will be analyzed with repeated measures ANCOVA using gender as a fixed factor and age, BMI, WC and other baseline descriptive characteristics as possible covariates. Post-hoc analyses will be used to test differences in groups and for 3 time points if there are significant time, group or time\*group interactions. Methods such as multiple imputation and estimated means algorithm will be used to carry out statistical inferences in the presence of missing data. All analyses will be set at the alpha level of .05 and will be carried out using SPSS Version 25.

ExRx #1 utilizes the widely-used gold standard FITT principle of ExRx to promote achieving the PAG. ExRx #2 uses updated research on the benefits of light intensity movement and the all movement counts message founded in the IBC to inherently support autonomy and higher self-efficacy to connect the intention to exercise with the behavior. This RCT will inform practitioners about which message resonates more with physically inactive students so we can more effectively promote healthy, active lifestyles.