More than 180,000 Americans enlist in the military each year. And their first assignment is to spend several weeks completing rigorous boot camp training – which can easily lead to injuries if they aren’t prepared.

We asked Dr. A. Brion Gardner, a veteran of Operation Iraqi Freedom and recipient of several military awards for his care of wounded Marines and Navy Sailors, to share how – and why – new recruits can prepare for the physical demands of the military. Dr. Gardner is a sports medicine and total joint replacement specialist in the Prince William Orthopaedics, Hand Surgery & Sports Medicine care center.

Is it common for new recruits to experience injuries during boot camp?

Absolutely. The majority of boot camp-related injuries are overuse injuries, such as a sprain, tendonitis or stress fracture. That’s because if anyone has been inactive prior to boot camp and they go into the rigorous, repetitive, high-impact activities of training, their body is simply not prepared to adapt to that impact and it’s going to break down.

Why are boot camp and other “get fit fast” programs challenging for the body?

The main reason is that you essentially overload your body. It’s like your digestive system, where if you consume a lot of food when you haven’t before, you’re going to feel fatigued and almost sick because your digestive system isn’t used to consuming that many calories. Your musculoskeletal system is exactly the same.

If you’re inactive, your muscles are used to processing a certain amount of glucose and oxygen to maintain your muscle metabolism at a certain level based upon activity. If you have never run 10 miles, and you haven’t even been running in several months but find yourself running or walking 10 miles, your muscles have not been preconditioned to handle that stress on them. They don’t have enough local glucose stored within the muscle cells and aren’t able to process the oxygen exchange in the cells. That’s when you’ll build up lactic acid and have local muscle breakdown, which leads to pain, poor mechanics and often overuse injuries. It’s the same with your tendons. They are very elastic, and there is memory within that elasticity. The more you stretch and improve elasticity, the more you’ll be able to perform at that sustained level. But if you ask for that impact and demand without preconditioning, you’ll be at risk for sprains, strains, tendonitis and muscle pulls because the local cellular metabolism hasn’t been ramped up.

How early should new recruits begin their conditioning?

If anyone is planning to go to boot camp, at a minimum they should engage in an exercise program for six weeks prior to going. It would be even better if they began conditioning themselves three to six months in advance.

What types of exercises should they prepare?

I’d recommend a balance of aerobic activity, stretching – especially hamstring and quad stretches – and exercises to maintain your core. This will help to prevent injuries that could occur in the training environment. The time to get into shape is not during training – it’s prior, so that you can minimize the risk of developing an overuse injury or more catastrophic fracture because you’re not used to running on uneven terrain or participating in other activities. Your adaptability to unique environments would be better if you trained beforehand.

Should they continue this personal conditioning after boot camp?

After boot camp, depending on their specialty, service men and women may go on to an additional school of training, whether that’s with the infantry, surface warfare with the marines, or something else. Every school has a physical fitness component to it, and there’s always going to be running, push-ups and sit-ups. There will be organized training during those school periods, but I still recommend maintaining stretching, aerobic exercises and core workouts on your own and in advance of additional trainings.

Dr. A. Brion Gardner is a sports medicine and total joint replacement specialist at the Prince William Orthopaedics, Hand Surgery & Sports Medicine care center in Manassas, Virginia. Dr. Gardner has expertise in arthroscopic ankle, knee, shoulder and hip surgeries, fracture care, robotic-assisted surgery and war extremity injuries. Dr. Gardner received the Navy and Marine Corps Commendation Medal for his care of critically wounded Marines and Navy Sailors in Iraq and Afghanistan. He has been a contributor to WashingtonPost.com in the NFL Forum “The League,” writing a weekly analysis of sports injuries, and has also served as a contributor to television and radio sports talk shows as a medical analyst.