title: Tripping people up for science.
abstract: Tytell reports the work of several researchers who have used a safety harness to watch people's reaction when a hidden box pops up in front of their foot to trip them. They found that the upper body pitches forward and the person responds by bending their knees and pushing up with the other leg as if hopping. This lifts them higher than a normal step and buys them some time in which they may be able to recover from the imbalance. The effectiveness of this measure depends on the force that can be exerted by calf muscles and the speed with which the muscle reaches its maximum force. Older people's muscle takes longer to reach maximum force but exercises like dancing and skipping can increase muscle strength at any age.