PHP RPG algorithm

hey folks,

i'm developing a mmorpg game in php. in this game in addition to battling other players a player can train their character at a 'gym', the factors that influence how much stats they gain are

1. Amount of energy used Max:100.
2. Their Level.
3. The value of the stat they are currently training.
4. Their total stats
5. Their will ranges from 0 - 5000 depending on the property the character has.

I've been trying hard to get something that works, some algorithms work for lower level players but not for higher level ones, and vice - versa for others.

I would appreciate any help/ suggestions you guys have to offer.

Thanks in advance.