Say there is 10" of snow on the ground outside, and I have an indoor area where I need to perform my GPP. I cannot use hills, yet this is the most important first step in GPP Essentials. We have big and small sleds and anything else you can suggest.
Weighted vest during running A’s, and plyometrics with weight vest on or holding dumbells.
Get your weight lift poundages higher.
I realize that hills are used for technique and power. Well, plyo"s and tech drills with weights vest can improve tech and power.
Remember that improved power can ofcourse improve technique.
A good core/mid section program involving flexion, extrension, rotation, compression and lateral flexion can do a lot more for technique and power than hills can in my experiance and opinion.