Strategy Page outlines the dilemma facing the designers of modern infantry protective gear.
The U.S. Army finally (in 2017) agreed to do a study of the impact of the weight American infantry carry into combat and the impact of that weight on performance. The troops have been complaining about this weight issue for some time. The average weight carried is 54 kg (119 pounds) and while about a third of that can be dropped in an emergency, most of it (weapons and protective gear) cannot. The IOTV (Improved Outer Tactical Vest) and helmet account for a third of the weight. Worse the IOTV restricts movement and this is a major shortcoming in combat.
Because of this, the U.S. Army is having second thought about its IOTV and current body armor designs in general.
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What the army has not tweaked is the weight and, to a lesser extent, the restrictive nature of the vest. While the troops appreciate changes that make it easier to move about while encumbered by the vest, what was bothering troops most, especially the infantry who have to run around on foot wearing IOTV while fighting, was the weight ... Marine and Army experts point out that the drive (created mainly by politicians and the media) for "better" body armor resulted in heavier and more restrictive (to battlefield mobility) models. This has more than doubled the minimum weight you could carry into combat. The report agreed with troop complaints that the excessive weight caused increased fatigue, reduced speed in combat and made it difficult to use weapons quickly and effectively when the enemy was encountered. The report also pointed out that a third of the troops shipped out of the theater for treatment of injuries were suffering from weight-related problems (musculoskeletal injuries) and that was twice as many suffered from enemy fire.
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This weight issue is a relatively recent problem. Until the 1980s, you could strip down (for actual fighting) to your helmet, weapon (assault rifle and knife), ammo (hanging from webbing on your chest, along with grenades), canteen and first aid kit on your belt, and your combat uniform. Total load was 13-14 kg (about 30 pounds), which is as much as the IOTV alone weighs. You could move freely and quickly while carrying only 14 kg and you quickly found that speed and agility was a lifesaver in combat. But now the minimum load carried is at least twice as much (27 kg) and, worse yet, more restrictive to mobility and speed.
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The enemy has also adapted, knowing that the more heavily encumbered Americans were not as agile or as fast and that could be exploited. The frustration of being slower than your foe often led U.S. troops to exertions that brought on musculoskeletal injuries. The new body armor may protect from bullets and shell fragments but it does nothing for over exuberant troops.
So the soldiers and marines are getting louder in their demands for relief from protection they don't need and restrictive protective vests that can get them killed.
There's much more at the link. Recommended reading.
It's great that the new protective gear has reduced serious injuries and deaths as much as it has: but my own memories of running around in an operational zone, carrying all the weight of a 1970's and 1980's serviceman, are not happy ones. Weight is not your friend at the best of times, and in extreme climatic conditions, it's even more so. You can become so exhausted that you can't react quickly enough to the stimulus of gunfire or an ambush, can't return fire accurately or fast enough to stop someone hitting you or your buddies, and can't get your mind into gear to deal with injuries or other problems to your buddies that require instant attention. It's like your mind is wading through molasses in its efforts to respond - usually unsuccessfully. It's terrifying to experience.
I hope the US Army's study bears fruit. An infantryman carrying up to 120 pounds of gear is not capable of responding and reacting as fast as he should. It's as simple as that. When it comes to women in combat, it's even worse, because in general they don't have the muscle mass to cope with that burden. It's almost guaranteed to get them killed or injured at far higher rates than male soldiers.