A European Space Agency study in Berlin, Germany, in which young men spent eight weeks in bed, showed that an absence of load on spinal support muscles can sometimes be just as debilitating as a physical injury.
Ultrasound studies have shown that in most cases of lower-back pain, either the lumbar multifidus muscles, which keep the vertebrae in place, or the transversus abdominis, which holds the pelvis together, or both, are inactive. Normally the muscles work continuously to support and protect the lower back.
Heavy lifting, whiplash or other injuries can damage and inactivate these support muscles. This increases the risk of long-term back pain, as people are then more likely to suffer sprains, or damage to the discs or other tissue in the back. However, only between 10 and 15 per cent of cases of back pain begin with such an injury. For the rest, the cause is often a mystery.
Now a team from the University of Queensland in Australia has shown that the support muscles of the bed-rest volunteers were inactivated in a very similar way to those of lower-back pain patients.
Using magnetic resonance imaging, they showed that after eight weeks, the multifidus muscles of all 19 young male volunteers in the bed-rest study had wasted and become inactive.
“This is the first study to show that these muscles that protect your spine are switched off in de-loading,” says Julie Hides, one of the researchers. Slumping for hours in front of a computer or TV could have exactly the same effect, she suggests.
The bed-rest study also shows that switching these postural muscles back on is not simply a matter of getting up and walking around. Some of the volunteers have been monitored for the past six months and their multifidus muscles have still not recovered, even in those who exercised.
But people can be taught to reactivate the support muscles using visual feedback from ultrasound scans. In an earlier study by the Queensland team, this therapy reduced the recurrence of lower back pain by half (Spine, vol 26, p e243). The work should also benefit astronauts, who often suffer from back pain.
The conclusions sound reasonable to Robert Moore of the Adelaide Centre for Spinal Research in Australia. “We know that bones and soft tissues need physical stresses to maintain vitality,” he says.