Waist of Time
Waist twists and side bends do not whittle your waist and if done too often or with too much weight, they may actually add bulk to your midsection. In addition, doing them too vigorously may lead to low back pain. A better exercise is to hold a weighted ball (2 to 4 pounds) at chest level, plant your feet firmly, tighten your abs, and slowly rotate from side to side, 8 to 15 times.
Squats are the best lower body toner but, if your go too low, you may get pain in your knees, hips, and lower back. Knees especially take a beating from deep squats due to overstretched ligaments and increased pressure on the joints. Never go lower than thighs parallel to the floor, make sure your heels stay firmly planted, and keep your knees are in line with your toes.
Big Bad Bend
Standing and flopping forward to touch your toes is another invitation to back pain, especially if you do it quickly and with fully straightened knees. If you are prone to lower back issues, it is best to avoid this move. Those with no back problems who do this stretch should do it slowly with softened knees get a decent stretch through the back of the thighs and lower spine.