Many trainers believe that slow, controlled contractions during weight training activate the muscle fibers best. Spanish researchers found the opposite-at least for curl-ups. They measured abdominal muscle activations levels during fast and slow curl-ups by electromyography (EMG). They attached electrodes to the rectus abdominis (six-pack muscle), internal and external obliques (side abs) and the erector spinae (spinal) muscles. They measured muscle activity while the subjects did curl-ups at four different speeds ranging from 1rep per 4 seconds to maximum-speed curl-ups. TActivation levels increased in each muscle as speed increased. They concluded that doing curl-ups at fast speeds was best for overloading the abdominal muscles and building dynamic spinal stability. Don’t do ab exercises so fast that you can’t maintain good technique. (Journal Strength Conditioning Research, in press; published online May 2008