Physical activity and the strength of the lumbar spine.

The cadaveric lumbar spines of nine young men killed in road accidents were subjected to a range of mechanical tests, and the results compared with the men's occupational and recreational histories. It was found that the compressive strength of the spines tended to increase with the level of physical activity in life, but the increase was significant only in the eight spines aged 18 or over. Compressive failure usually occurred in the vertebral body, but in three cases, the disc prolapsed into the vertebral canal; these discs came from three of the four most physically active individuals. It is concluded that physical activity strengthens both the vertebrae and the discs. A high level of activity can cause vertebral strength to exceed that of the discs.