Q. Should I lock my feet when doing a sit up?
A. Some ways of doing a sit up can hurt your low back. The old way of doing sit-ups with your feet locked under a bar or held by a partner can be unsafe because it allows your larger and more powerful hip flexor muscles to take over if you have weak abdominal muscles. If the large hip flexor muscle, which attaches to the front and sides of your lumbar spine, overpowers your abdominal muscles, your low back can hyperextend. Overworking the hip flexors can lead to a muscle imbalance of tight hip flexors, tight back extensors, and weak abdominal muscles. This can lead to a back problem and may make an existing back problem worse. It is recommended that a "crunch" exercise be used instead. To do this, keep your low back in a safe, mid-line position. Do not secure your feet, and only do a "partial" sit-up.