It has become the accepted standard if one trains in the style of the military that training involves wearing weighted packs and weighted vests. Does this training really help? Does the long distance endurance training military personnel typically engage in help if no weighted packs are involved? And, is there a way to train accuracy with weaponry while also training conditioning and under physical duress?  

A recent study conducted by Old Dominion University and published in the Journal of Strength and Conditioning Research examined these very questions. In the study, two groups of students were enrolled and underwent physical training similar to that used in the Marine Corps. One group did all the training “under load,” meaning while carrying weight, and one group trained without a weighted load. In the weighted group, men carried 30kg and women carried 20kg in the form of backpacks loaded with sandbags and weighted vests. These loads were considered comparable to the weights carried by actual troops recently in Iraq and Afghanistan.
Tests were completed before and after a ten week training periods. The assessments at the beginning and end of training were based on standard military tests administered by the Navy and Marines. Subjects were tested for physical aptitude and also for their marksmanship ability with an AR-15 rifle. The nine-week training period consisted of a regimen modified from Marine recruit training. Subjects trained for one hour a day for four days a week. Sessions included running, stair climbing, calisthenics, and specific military exercises like low and high crawls, partner carries, and sprinting while holding ammunition cans. Both men and women in the loaded group started with only a 5kg load in week one and worked up to their full loads of 30kg and 20kg by weeks eight and nine.
Breaking Muscle Shop
After final testing was completed it was determined both loaded and unloaded groups demonstrated significant improvements in running, calisthenics, and military drills. When administered the standard Navy and Marine Corps physical tests, both men and women passed at a similar rate. Both the loaded and unloaded groups also passed at a similar rate. The same held true for the marksmanship tests.
The results of this study are perhaps counterintuitive. Most people would imagine training with a weighted backpack and vest would lead to greater physical adaptation than training without them. Instead, it may be that training infrequently with a load is enough to prepare military personnel for real life situations and training in general otherwise without the weight will lead to a decreased incidence of injury.