Chin up bar
Tabata intervals, done once every other day, are a great time-efficient way of gaining many of the benefits of cardiovascular exercise, in a much shorter space of time – 4 minutes.
Choose any exercise, for example squats with bodyweight.
Find a Tabata Timer on Youtube or download an app.
Do 20 seconds of squats, rest 10 seconds, then repeat 8 times.
This gives 4 minutes of high intensity exercise.
I like to do these with MMA specific exercises like sit-throughs.
If you can spare another 10-15 minutes, here are a couple of workouts you can do at home for muscle-mass or just muscle-maintainence.
Remember that ‘return on investment’ in terms of exercise and ‘gains’ in strength and muscle mass is not proportional. In fact, there are a lot of fitness professionals who argue that 1 set of exercise to failure, is all that is required per body part. See Mike Mentzer and Dorian Yates’ training philosophies (not 1-set training, but certainly an in-and-out of the gym mentality)
Most importantly, do something, and form the habit of exercising whenever possible. Even if it’s just doing squats whilst the kettle is boiling!