Fit for action? Mark LoMoglio/Icon Sportswire via Getty Images

Head injuries are more than just a headache. Athletes who get concussed are more likely to later tear a knee ligament or sprain their ankle – and stiffer hips and looser legs may be to blame.

Sportsmen who sustain a concussion have an increased likelihood of getting a musculoskeletal injury in their lower limbs for up to three months after the head injury. “We knew they were more likely to get hurt but we didn’t know why,” says Dominique DuBose at the University of Florida, in Gainesville.

To find out, her team examined 39 college American football players. Of these, 13 went on to have head injuries. DuBose and her colleagues discovered that for an average of 50 days after a head injury, these athletes had stiffer hips, but looser knees and legs.


“Stiffness is one of those ‘Goldilocks’ measures: too much is not a good thing, too little and you’re not stabilising your lower extremity,” says Daniel Herman, a member of the team.

Return to play

The athletes’ altered limb stiffness could be a sign of changes in muscle control prompted by a concussion, but what causes this is unclear. One theory is that concussion has lingering effects on the brain areas involved in movement, even after other symptoms have gone.

“I think some part of brain processing, disrupted by the concussion, affects your motor programming, which leads to problems in muscle activation and consequently your movement pattern,” says team member Terri Chmielewski. “When you have an altered movement pattern, that can make you at risk for injury.”

Problems in other brain systems, like vision, might also increase athlete injury risk, says Alison Brooks at the University of Wisconsin, in Madison. But she warns that the underlying relationship between concussion and other injuries is unclear. “How do we know these athletes weren’t different to begin with? Maybe the reason they got a concussion in the first place is that there’s something different about them,” she says.

Even so, the association between concussion, stiffness and injury may ultimately lead to changes in how athletes recover from concussion. They may need to undergo more thorough assessment of their muscular control and meet stricter health criteria before being allowed to play again, says Herman.

Journal reference: Medicine & Science in Sports & Exercise, DOI: 10.1249/MSS.0000000000001067

Read more: Brain damage in American football linked to head trauma