MCRD SAN DIEGO -- When the first-ever platoon of female Marine recruits landed here at the Corps' West Coast recruit depot earlier this year, their training was just as difficult as that of their male counterparts -- but differed in one small, important way.
Lima Company, the platoon's parent unit, was one of two recruit companies selected to participate in a study assessing a progressive approach to hiking under a combat load, a key component of training. The two companies each swapped out one high-impact running event, such as a track-style workout, for a hike. The length of the hike and the weight of the load progressed stepwise: As the weight increased, the length would decrease temporarily to allow recruits' bodies time to adapt.
Behind this study was Dr. Karen Kelly, a research physiologist at the Naval Health Research Center's Department of Warfighter Performance in San Diego.
Kelly, who has been studying musculoskeletal injuries in Marines since 2010, said she'd previously worked to bring down troubling injury rates at boot camp by educating drill instructors on best practices for injury prevention. Science supported a training change as well, she said.
"It's one of the fundamentals of exercise physiology," she said. "We progressively increase in intensity or duration of an event, right, and then ... you have to train specifically to what are types of movements and events that you're wanting to be successful in."
The progressive training plan also allows for greater pack familiarization, Kelly said, giving recruits a chance to develop comfort in how to carry their gear. It provides, too, space to build greater cardiovascular endurance.
In all, about 758 recruits from Golf and Lima companies participated in the study. About 70 of them, representing all fitness levels, also wore a Polar Grit X physiological monitoring watch to track everything from sleep cycles to caloric burn 24 hours a day.
Since recruits are typically barred from having any electronic devices, this posed an interesting logistics challenge for Kelly's researchers: They had to visit the recruits' barracks complexes periodically to charge the watches, and manually download all the data that typically syncs to a phone app.
Anecdotally, the data it reveals is fascinating. Recruit Training Regiment Commander Col. Matt Palma told Military.com that recruits wearing the watches burned between 4,300 and 5,000 calories per day. They walked between six and 10 miles per day on average -- up to two miles more for recruits whose barracks were farther from the dining facility. And though recruits are technically given eight hours each night to sleep, Palma said data showed they were getting an average of just six hours.
As to the question of injury prevention, early data is promising. The all-male Golf Company sustained fewer injuries, Kelly said, than Hotel, another all-male company that did not undergo the progressive hike program. Data from Lima Company, which had the female platoon, has not yet been analyzed, she said.
If the trend bears out, it could have implications for all Marines.
"Female Marines have a propensity to sustain lower-extremity injuries," Palma said. "Their male counterparts, to be quite honest with you, also sustain injuries. Maybe not at the same rate, but the injuries are identical. ... What we do here is hard, and it puts the body under tremendous stress."
A 2019 study in the journal Military Medicine showed Marines at boot camp had injury rates of up to 14%. Strains, sprains and stress fractures made up some 40% of all injuries, and hiking was the activity most likely to result in injury.
A version of progressive hike training, albeit with longer distances and heavier loads, is also taking place in the Infantry Marine Course pilot program up the coast at Camp Pendleton. As that 14-week program wraps up, leaders say they've seen a dramatic drop in musculoskeletal injuries and reduction in the attrition rate from 12% to just 4%. Kelly said she plans to equip the next pilot rotation, starting in June, with wristwatch monitors so she can capture more data.
Palma said he's nearly ready to order all recruits to switch to the progressive program.
"I'm almost 100% confident that, once I get Lima Company's results in, I'm going to direct the training change across the regiment," he said.
Lima Company is set to graduate in early May, and Palma said he expects a brief with new data this week.
Kelly said Marine Corps Commandant Gen. David Berger was behind the push for a way to train better and smarter.
"He has a vested interest in this, you know. That was a question he posed to us years ago. He was really breaking his guys, and what he could do," she said. "He really seems to care about the human performance side of it and properly treating them, which is great having a leader that has that vision. So I think it's trickling down, you know, but it's just changing mindsets."
-- Hope Hodge Seck can be reached at email@example.com. Follow her on Twitter at @HopeSeck.