The Smart Trac 2000 allows you to perform the lunge exercise and several other lower body and abdominal exercises while maintaining correct form. This allows maximum targeting of the hip, thigh, buttocks, hamstring, and abdominal muscles without stressing or straining your knees, arms or back. First and foremost, you should always consult your doctor before you begin any exercise program. Lunges are simply the most effective way to shape and tone the lower body, trouble is, until now the lunge has been somewhat difficult and even harmful if not done properly. The Smart Trac 2000 allows you to do this incredibly effective exercise easily - with perfect form and with no stress or strain to your joints. Something called a resistance & assistance mechanism. While doing a lunge, the Smart Trac provides just the right amount of resistance working targeting those major muscle groups in your lower body. Then as you bring your leg back, the Smart Trac gives you just enough assistance to get back up and ready to go again! The result is a perfectly executed lunge all the time every time; with absolutely no stress or strain to your joints. Not only will you have a more effective workout, you'll be working out smarter!