Military service is tough on the body. The U.S. Army, in fact, has lost 4.1 million days of productivity this year alone to limited duty related to injuries, 70 percent of which were characterized as musculoskeletal, or MSK, trauma.

So it comes as no surprise that the service wants to determine who is at risk for such injuries and how they can be prevented. What is unusual, though, is that Army researchers are not looking at traditional predictors of MSK workplace injuries like repetitive motion, weight, posture and weight-bearing loads, but at run times.

Run times? You bet. According to Dr. Bruce Jones, a senior Army Public Health Command physician, and Todd Hoover, operations division chief for the Army Wellness Center, males who can’t run 2 miles in less than 15 minutes and women whose 2-mile runs take longer than 18 minutes are at greatest risk for MSK injuries.

Add other factors, such as smoking, being below or above Army weight standards, or not getting enough sleep, and the risk climbs.

“The point is, this is preventable, so we can actually, through some targeted, precision programs, focus on soldiers who meet this risk criteria, refer them to Army Wellness Centers and then ... coach their behaviors to improve their performance and decrease the risk factors,” Hoover told reporters during a briefing at the Association of the United States Army annual meeting Oct. 16 in Washington.

The pressure for soldiers to be physically fit is high: their missions often depend on it and they must meet military physical fitness standards each year, including the new Army Combat Fitness Test, to be rolled out service-wide in fiscal 2020.

The traditional approach to getting soldiers in shape has been to increase their physical training — more miles spent on roads running or marching or increased trips to the gym.

But Jones and Hoover say these approaches usually don’t improve fitness, they only lead to injury.

“The more you do it, the more you get injured,” Jones said. “There are a couple of studies that suggest there are thresholds of training above which injury rates increase but fitness does not … you have to tailor this at the unit level and at the soldier level.”

And here’s where run times come in. Units — and the soldiers themselves — can identify who is at risk for injury if they don’t meet the 15-minute or 18-minute 2-mile run time criteria. Then, through the Army Wellness Centers, they can develop a plan to increase their aerobic fitness, not by adding more time in the gym, but through high-intensity interval training, HIIT, or other types of training.

“HIIT is a way of getting more fit with fewer footsteps. There's a bigger bang for your buck,” Jones said. “If you’re trying more and you’re not getting more fit, especially if you get injuries, those are the three cardinal signs. There’s a way to back off on training … We are not saying you should do less work, we are saying that it needs to be looked at more objectively and scientifically.”

The service operates 35 Army Wellness Centers worldwide that provide weight management and metabolic testing, exercise testing and prescriptions, stress management and biofeedback, body composition analysis, nutrition education and wellness coaching.

As part of the exercise testing and prescriptions, some facilities have a new device called the K5 wearable metabolic analyzer, which measures maximum oxygen uptake during exercise, heart rate, stress and other physical measures. Used alongside other tests such as body mass index measures and resting metabolic rate, Army Wellness Centers can guide troops to optimal fitness, the researchers said.

Sometimes, the trimmest soldiers or those with bulging muscles aren’t the fittest.

“We’ve been arguing for some time — it’s not necessarily the Army’s position — but we’ve been arguing that you need to look at fitness and fatness to decide which soldiers are optimally ready,” Jones said.

According to the APHC, knee injuries, caused by overuse, are the most common MSK condition among soldiers, followed by back problems related to physical training or vigorous operations.

The knee and other overuse injuries are the ones that can be addressed by increasing a person’s aerobic fitness, Hoover said.

Running slowly puts less stress on knees but the decrease in stress is negated by the increased number of steps slower runners take, actually adding more stress to the joints.

Increasing a runner’s aerobic fitness through HIIT or other training method, and the chance of developing an acute or chronic MSK injury declines.

"In the general population, we think to solve a problem we have to do more … but the reality is it sometimes takes more of a precision approach,” Hoover said.

Army Wellness Centers are designed to help soldiers, family members, retirees and anyone in the military health system whose health and fitness are affected by abnormally low or high body mass index, are unfit or could benefit from nutritional guidance and sleep issues that affect performance.

They are available to beneficiaries through a doctor, unit or self-referral.

The centers aim to improve health and fitness in the military community (AWCs are open to all branches of service) to increase readiness, decrease attrition and save the Pentagon billions. While the researchers did not have the current estimated cost to the Army of the monetary loss caused by decreased productivity or the medical costs of treating MSK injuries, Pentagon estimates in 2001 for all the services were between $12 billion and $20 billion.

The Army researchers said the service must develop new approaches to fitness that will improve readiness and save money, even if it means changing a mindset that believes more training leads to a fitter force.

“The data’s pretty clear that if you are in poor aerobic fitness — poor aerobic capacity — and either lower or high body composition, those are the risk factors ... The mindset [now] is you look at people aesthetically, you look at weight or the guys with the big muscles and you think they are physically fit … but the reality is that aesthetics really aren’t necessarily the best indicator,” Hoover said.

Locations of all Army Wellness Centers are located on the Army’s AWC website.