I bought a set of dumbbells which consisted of 2 bars, array of weights, 2 sleeves. 4 locks. but my dog eat one of the locks that keeps the weights on the dumbbell, i dont want to go out and buy a new set and you cannot buy the lock in single form, if i do a set of 20 reps on one arm and then change to a set of 20 on the other arm and keep on changing would that affect anything like muscle growth or would it work the same as if i were using 2 dumbbells? (hope you understand this )

plus i am lifting 20lb dumbbells i can do about 10 reps on one arm with a 20lb(er) and i cannot do any more, is this freakishly weak, if i carry on lifting these weight doing 4 sets of 10 will this improve my strength?

switching hands is fine (using 1 dumbell for both arms, swapping arms).

Tough to say if that's insanely weak or not, given that you didn't mention such crucial factors as the exercise in question, your bodyweight, or your level of experience. If you're new, don't worry about being weak, it can be fixed.

If you're intermediate and only doing 10 reps with 20lbs, that's a problem unless the exercise in question was one of a very select few (clean form reverse flyes, and clean/strict form lateral raises... those are about all that should be putting an intermediate lifter down with 10 reps or less)

you need to start increasing the weight to achieve real gains in both size and strength, maybe you need to buy some more weight. good luck !!!

Dumbbell exercise is a form of strength training exercise targeted towards working specific or group muscles. You can do a myriad dumbbell exercises at home or in the Gym. All you need is serious dedication and inexpensive pair of dumbbells. You can start with as little as two 15-20 minutes a week and gradually maintain at 30 minutes.

For the most noticeable improvements have rests between sets of reps. This allows the muscles to relax and the most growth happens in the first few reps when the muscles go from rest to working hard.