When sparring another player you will adapt to their power. Many players call this "leeching". What it means is that while sparring a player if they are more powerful than you then you will gain power at a faster rate until you have matched a certain amount of their power.
Certain races have better adapt mods which cause them to adapt at a much faster rate. One of the fastest adapting race is Humans.
You can leech battle power, energy, gravity mastery, and perhaps some other minor things.