(AP) -- American soldiers in Iraq and Afghanistan were more likely to be medically evacuated for health problems such as a bad back than for combat injuries, a new study says.
Researchers also found psychiatric disorders rose during the period studied - 2004 to 2007 - despite an increased focus on treating mental health problems.
The research was published Friday in the British medical journal, Lancet.
Steven Cohen of the Johns Hopkins School of Medicine in Baltimore and colleagues analyzed data from about 34,000 American military staff medically evacuated from Afghanistan and Iraq during those years, or about 6 percent of the service personnel.
In previous wars, including World War II, and the Korean and Vietnam conflicts, combat injuries also were not the top cause of soldier hospitalizations; illnesses such as respiratory and infectious diseases were.
Twenty-four percent of the evacuations from Afghanistan and Iraq in 2004 to 2007 were due to muscular problems such as back pain, tendinitis, and repetitive stress injuries.
Combat wounds came in second at about 14 percent.
That was followed by neurological disorders (10 percent), psychiatric disorders (9 percent) and spinal pain (7 percent).
The remaining 36 percent of the medically evacuated service members fell into many separate categories, including gastrointestinal problems, infectious or respiratory diseases, chest or abdominal pain, congenital anomalies, benign tumors, pregnancy, and hormonal disorders.
The study was paid for by the John P Murtha Neuroscience and Pain Institute and the U.S. Army.
Cohen said chronic pain was almost unavoidable for active troops.
"It's the nature of being a soldier," he said in an interview with The Associated Press. "If you're in an infantry unit for a year, you will have overuse injuries. Back pain is the rule, not the exception."
Cohen said the findings should spur military health authorities to tweak their strategies.
"I don't think the military prepares (its doctors) for the types of injuries they see," he said. "Very few people have to perform complicated procedures like tracheotomies (windpipe surgery), but what they will see a thousand times more is overuse injuries and tendinitis."
Dr. Michael Kilpatrick, director of strategic communications for the U.S. Military Health System, said officials are investigating how best to protect troops on the front lines from physical wear and tear. To do that, they are examining how much soldiers need to wear heavy protective body armor and carry water and food supplies, and the length of their rotation times, said Kilpatrick, who was not involved in the study.
Cohen and colleagues also found troops evacuated for psychiatric reasons increased 32 percent during 2004-2005 and 62 percent during 2006-2007. That might be due to the stress of longer tours of duty, he said, since troops often are more susceptible to mental illness the longer they serve.
"This is a new era for us with multiple deployments," Kilpatrick said. He said mental health programs were increasing in the military and that about 1,000 specialized staff had been added to address psychiatric issues.
Experts said the large number of soldiers with chronic physical pain was likely masking an even bigger problem with psychiatric illnesses such as Post-Traumatic Stress Disorder, or PTSD.
"It would be astonishing if that were not the case," said Simon Wessely, director of the Centre for Military Health Research at King's College London. Wessely also was not connected to the Lancet study.
"Many people have nonspecific symptoms like back pain, but when you need to evacuate them because of that, it's usually a marker that something else is going on," he said.
Explore further: US health care: Does more spending yield better health?
More information: http://www.lancet.com