Statistical analysis
Participant characteristics were evaluated with descriptive statistics and presented as either frequency and percentage or median and first and third quartiles. Feasibility of HIIT was assessed at EOS. We considered our intervention feasible based on both the number of prescribed workouts completed throughout the intervention, and the rate of adherence to the individualized exercise prescription throughout the intervention. Our goal was ≥75% of prescribed workouts completed among participants, and ≥75% of participants adhering to their individualized exercise prescription. Adherence was defined as completing or exceeding ≥70% of the workouts in a manner that is consistent with the exercise prescription. We defined being consistent with the exercise prescription as maintaining HR within all prescribed zones or ±5 beats per minute outside of each zone throughout the workout. Change from baseline to EOS was calculated for the following variables collected during assessment sessions by the total sample and by group: body weight, fat mass, fat-free mass, body fat percentage, handgrip strength, SPPB, PROMIS physical function score, NTSS-6 score, and UENS score. Peak aerobic capacity data was not analyzed due to the limited number of participants able to complete both a baseline and EOS test due to research restrictions from the COVID-19 pandemic. Assessment session data is presented as mean and 95% confidence intervals (CI). Assessment session data was compared to established cut-points for minimal clinically important differences for the following: hand grip strength (+5–6.5kg) [