FIRST Training Plans & Cross Training

[Deleted User]

I have heard good things about FIRST training plans on improving PBs and am quite tempted to use one of their plans. 

One thing though - what is meant by cross training in the plan?

 For me this could mean anything from weights to Martial Arts to cycling to hill walking.

I was planning on using this as gym time.

Any thoughts would be, as always, appreciated.

 Cheers