A surprising number of casualties on the battlefields of Afghanistan and Iraq involved fractures, strains and musculoskeletal problems, many of them related to the heavy combat loads for soldiers and Marines on the front lines.

Indeed, a 2010 Johns Hopkins University study, published in the medical journal the Lancet, found that the most common reasons for medical evacuation of military personnel from war zones in Iraq and Afghanistan between 2004 and 2007 were fractures, tendonitis and other musculoskeletal and connective-tissue disorders, rather than combat injuries. And many of those injuries, particularly those involving the spine, prevented soldiers from ever returning to combat.

Johns Hopkins researchers looked at the records of more than 34,000 servicemembers who were sent to the military’s medical center in Landstuhl, Germany, according to the university. The top three grounds for medical evacuation were musculoskeletal or connective-tissue disorders (24 percent), combat injuries (14 percent) and neurological disorders (10 percent). There wasn’t much change in those percentages over the course of the four years analyzed, according to the research.

“The additional weight is clearly having a toll on service members in knee injuries and back injuries and injuries that arise out of repeated effect of weight on agility,” said Michael R. Turner, R-Ohio, chairman of the House Armed Services Subcommittee on Tactical Air and Land Forces.

A lack of agility causes a host of problems, including an inability to quickly get in and out of vehicles or move across a battlefield.

Aside from simply lightening the load of infantry men and woman, the Army and Marine Corps are working to improve physical training and nutrition.

“Physical conditioning is something simple,” said Sen. Jack Reed, D-R.I., chairman of the Armed Services Subcommittee on Seapower. “It seems so obvious. You have got to be in superb condition. The military is much more focused on physical conditioning.”

The cost of neglecting this type of injury is clear.

“A notable finding is the low occurrence of return to duty for musculoskeletal and connective tissue disorders, and especially spinal pain,” wrote Steven Cohen, the study’s author.