Practicing and applying knee strikes
As part of your personal defense tool box you should include the use of knee strikes. One of the most common methods of training with them is to have a partner hold a striking shield and then holding your partner, you knee the bag, step back and then fire off another strike.
You may want to try this in your next work out. Instead of hitting with the knee and then stepping back, try throwing your full body weight into the knee in an attempt to knock your partner back and then step forward with the leg you kneed with. This will change the dynamics from a stationary drill to a walking drill.