Most people believe that slow, controlled contractions during weight training activate the muscle fibers best. Spanish researchers found the opposite – at least on one abdominal exercise. They measured abdominal muscle activation 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.
Researchers measured muscle activity while the subjects did curl-ups at four different speeds, ranging from 4 seconds to maximum-speed curl-ups (1 second). They found that activation levels increased in each muscle as speed increased. The researchers concluded that doing curl-ups at fast speeds was best for overloading the abdominal muscles and building dynamic spinal stability.
But remember – don’t do ab exercises so fast that you can’t maintain good technique.
Source: Journal Strength Conditioning Research, in press; published online May 2008)