Uphill Athlete coaches, led by Carolyn Parker, put together 24 free body-weight only strength workouts that are designed to be done at tempo. So your heart rate should be in your zone 1 or 2 throughout. Even for those sheltered-in-place in an urban apartment will be able to maintain most, if not all, of their aerobic conditioning by doing one of these workouts each day, or alternate with a treadmill walk or run and do one of these every second day.
The workouts are highly varied to help you fend off boredom. We recommend doing one of them every second day. We have divided the series into 3 levels: Rainier, Denali, and Everest. Rainier is the easiest series and Everest is for well-conditioned athletes only. You can also start with Rainier workout number 1, progress through all 8 in the Rainier series, move to the Denali series, and so on.
Here are our free at home strength and conditioning workouts
Be sure to read and bookmark our definitive article, Strength Training for the Mountain Athlete