there's definitely something wrong with either the cables, levers or brakes if V-brakes require a lot of strength to work.
If it's in good working condition, they can be worked with one or two fingers.
In fact, that's what you should get for any proper brake setup.
If you require a lot of strength to get the brakes to work, then from what I've seen, it's an issue of using linear pull levers with short pull cantilevers or calipers.