second. but with qualification. sloooooowwww squat and keep both feet flat on the ground. those systema buggers have a brutal way of doing squat. see how slow can you do 1 squat.
Yep. Squats are a great way to build core strength - but they're also a great way to get hurt if you're not careful, so get a trainer to teach you how to do them right. Squats and other complementary core strength exercise, and then don't forget the aerobic conditioning. A foundation of good fitness will do more to advance your aikido training than trying to practice techniques at home that you've only just been exposed to for the first time.