Regeneration of SP

[Handsome Jack]

Well, yes. That is the traditional way of going about it. Using SP via Power-Ups. But that doesn't "put a strain" on your body. Think Kaio-Ken, or a similar ability from other media. Where a person actually injures themselves to increase their power.

Edit: Which is why I put out the second proposal of "spending" HP instead of SP to activate SP-related abilities, rather than regenerating SP via hurting yourself.