My friend and I take 5-15 minute breaks every hour while studying. We like to be productive during these breaks. Most of the days, we do push-ups during these breaks. However, on days when our upper body muscles are sore from push-ups, we'd like to do some sort of quick/easy leg workout.
What's a suggestion for a "push-up like" leg workout that we could do during 5-15 minute breaks without any equipment?