Bodyweight Exercises
If you're going to do bodyweight exercises, you will benefit from doing them in the most intense and explosive way possible. I went without lifting weights for nearly 3 months once, and kept my lean mass by doing plyometric-style bodyweight exercises. Granted, my maximum strength decreased somewhat, but my speed, agility, and "explosive" strength actually increased, while maintaining my muscle mass.
So, try doing:
Clap pushups - always go all the way down, then explode up as hard as you can, clapping while in the air. Some people get to where they can do two claps, one behind the back, one in front, for reps. But if not, one clap is fine. Just be sure to always focus on quality over quantity, which means doing the FULL MOTION, all the way down with the bottom of your sternum touching the floor to get a stretch in the chest, then exploding up, aiming to go as high as possible. Your chest, shoulders, and triceps will feel the burn, and if you're anything like me, your "fast-twitch" muscles will become even faster.
Squat Jumps - squat all the way down, as if performing an "ass to the grass" squat movement, then explode up, leaping as high as you can. You should come up on the balls of your feet before leaving the ground (this will give the calves a decent workout), and you should never land hard. Rather, you should use the downward momentum of the landing to ease back into the low squat position. I put my hands behind my head just to keep my arms out of the way. You should feel the burn in your hips, glutes, hamstrings, and of course, quads. However, if you feel it only in your quads, it's likely you're not going down far enough, or exploding up hard and fast enough. If you're inflexible like I am, it may help to point your feet outw@rds somewhat.
Pull-ups - if you don't have access to a pull-up bar, then you can simply drape a towel over a sturdy door, and then use that to perform pull-ups. It will feel a bit awkward at first, but it gets the job done. As always, focus on quality; go all the way down, and all the way up. You're stomach/chest will kind of slide against the door, but it won't hurt anything. Towards the end, when you're tired, feel free to jerk a little in order to give yourself that extra kick, but only on the last few reps. Just be sure you choose a sturdy door that won't fall out of its hinges.
Those three exercises should cover the core of any at-home, bodyweight workout. The main strength decrease that I experienced was in my lower back, as a result of not doing squats/deadlifts. My bench max went down of course, but at the same time, my quickness improved, and I could perform more reps. Not a bad deal considering I went without access to a gym for so long.
In fact, these days I incorporate plyometric bodyweight exercises into my lifting routine, just for the quickness/explosiveness they develop.
Good luck with the workouts.
