Just because your apartment gym only has dumbbells doesn't mean you have to limit yourself to them, bodyweight training is also a fantastic way to get yourself in shape.
An exact routine would depend on knowing your goals, but essentially movements break down into one of about 6 different movement patterns (I'm not going for the 7 primal movement patterns here, before anyone decides to contradict me). They are:
- Everything else
There are various ways of splitting these up, you could do a push / pull split, push / pull / legs split, upper / lower split, full body every day, it's entirely up to you. The most important things are consistency and progress (progress with dumbbells can be tough with the larger weight jumps, instead of trying to jump between bells to progress, you could also consider adding reps or sets to slowly increase the volume before jumping in weight, or decreasing your rest between sets).
This is when you extend your arms to push something, e.g.
- Dumbbell bench press
- Dumbbell overhead press
- Dumbbell floor press
- Press up
- Handstand push ups
And variations on all of the above. Dumbbell exercises can be either with one dumbbell (unilateral movement) or two (bilateral movement), using a single dumbbell can also be a nice challenge for your core.
Squat and some lunge movements can also be included in this is you just want to do a push / pull split.
This is bending the arms to pull things towards you, or yourself towards things, e.g.
- Dumbbell row variations
- Renegade row
- Inverted row (also known as an Australian push up by some)
- Chin / pull up
- Front / back lever
- Dumbbell high pull
Hinge movements and the lunge and reach can also be included in this if you want to do a push / pull split.
This group of movements involve hinging at the waist (like when you bend forward to touch your toes, or pick something up off the floor), e.g.
- Dumbbell deadlift variations
- Dumbbell swing
- Back extension
- Reverse hyper
This is probably where you're doing to see the greatest variation from traditional barbell exercises. Most people thing of deadlifts as being bar bending, massive weight pulling exercises. But try doing a few sets of high rep stiff leg deadlifts with the 50's and see how your glutes and hamstrings feel the next day.
As the name suggests, this is when you squat (think, the resting position quite commonly seen in parts of Asia and Africa), e.g.
- Dumbbell squat
- Goblet squat
- Rear foot elevated split squat
- Bodyweight squat
- Shrimp squat
- Pistol squat
As with deadlifts, these are usually thought of as having massive weight across your shoulders and squatting while your face goes the colour of beetroot, but try working up to a set of 10 pistol squats on each leg, you'll have pretty solid legs.
Possibly one of the most hated movements with anyone I've asked, from a position of one foot a few feet in front of the other, bend both legs until your back knee touches the floor, then stand up again. Simple.
- Bodyweight / dumbbell lunges (or split squats, same thing)
- Front / back lunges
- Walking lunges
- Lunge and reach
Think lunges are too easy? Grab the 50's and do walking lunges until either your legs give out or your grip does.
As the name suggests, this is everything that doesn't fall under the above. When thinking about a workout routine, you should base it on the above, and throw in a couple of exercises from here, normally at the end
- Core work
- Dumbbell farmers walks
- Bridging exercises
- Turkish get ups
- Direct arm work
- Grip work
So, a push / pull split could be:
- Heavy rear foot elevated split squat
- Bodyweight walking lunges
- Heavy dumbbell overhead press
- Press ups
- Hanging leg raise
- Dumbbell triceps extension
On one day, then
- Heavy dumbbell stiff leg deadlift
- Lunge and reach
- Pull ups
- Dumbbell bent over row
- Dumbbell swings
- Dumbbell curls
On the next.
Hopefully that'll give you some ideas, if all else fails and you're completely lost, look up a bodyweight workout routine, such as on http://www.reddit.com/r/bodyweightfitness and go with that.