How is Heavier Faster?

Yesterday we wrote about some Army researchers’ finding that, in a long, heavy ruck march, the guys who march fastest are the most muscular ones. Not necessarily the strongest, but the most muscular.

How can that be? If you beef up for a long ruck with an extra 20 lbs. of muscle, you’re schlepping an extra 20 lbs. What compensates for all that extra weight if not strength? And maybe bigger legs and glutes would make sense, or even bigger traps, but what will I gain from heavier arms, shoulders, chest, and lats? Those muscles don’t even do much work in rucking. 

In those respects Knapick’s finding are hard to understand, but I have a three guesses.

When you pick up a weight, you and the weight share a common center of gravity. The heavier the weight is in relation to your body, the more it’s in charge. You’ll have to lean over to keep it centered over your feet without toppling over. The lighter you are, the more you have to lean.

Center of gravity. Imagine two guys each carrying a huge, 100-lb. backpack of bricks. They’re equally tall, but one guy weighs 150# and the other weighs 300#. Since each guy is wearing a huge bag of bricks behind him, that shifts his center of center of gravity back. Light Guy must lean hard into his straps to try to balance the load over his feet, and he doesn’t have much bodyweight to lean with. His own center of gravity doesn’t count for very much against the backpack of bricks; basically the bricks are in charge. But Heavy Guy isn’t pulled off balance as much because he’s counterbalanced by an extra 150# of meat that Light Guy doesn’t have. In the battle against the backpack of bricks, his center gravity weighs twice as much as Light Guy’s and isn’t too impressed by all the bricks. He can stay on his feet just fine.

But this can only be part of the story, because it would apply just as much to a 300# fat guy as to the beefcake. But there’s one other attribute the muscular guy has working for him.

Squat for high reps and grow. Strength-endurance makes for big muscles.

Strength-endurance: The Army researchers were measuring absolute strength, i.e. “one-rep max” (1RM). And that’s the kind of strength they concluded didn’t help the men ruck faster. But there’s a distinct attribute called “strength-endurance,” which is your ability to exhibit strength for a long time. It’s the difference between, say, squatting 500# for one rep and squatting 250# for 20 reps.

Big muscles are particularly associated with strength-endurance. In fact, squatting for 20-rep sets will make you HUGE. And every gym rat since the Coolidge administration has known that you get biggest by lifting in sets of 8-15 reps with restricted rest periods. That is solidly in strength-endurance territory. It won’t improve your 1RM much and powerlifters will talk down to you, but you won’t care because you’ll be swole and get all the girls.

So carrying a rucksack shares more in common with bodybuilding than powerlifting, namely moving sub-maximal poundages repeatedly with little rest.

What about squats and deadlifts? I wonder what would happen if Knapick had measured soldiers’ strength differently, with some of the big exercises like squats and deadlifts instead of isolating one joint at a time. See, Knapick’s team tested how good the subjects were at extending just the knee, flexing just the knee, extending just the ankle, and so on. In other words, they tested what are called “isolation exercises” (working just one joint at a time), and isolation exercises are notoriously bad at building or testing real-world strength. 

Not a very meaningful test in the real world.

What Knapick didn’t do in this study was point to a huge barbell and order the soldiers, “Try to deadlift that.” That would have told us a lot more about the pure strength of the guys who marched faster or slower. (It is even conceivable that the faster, more muscular test subjects had grown that extra muscle by having big squat poundages. You don’t know much about someone’s musculature just by knowing that it’s big. You’ll find big thighs on weightlifters, bodybuilders, and cyclists, but they have completely different attributes.)

Researchers now are trying to study squat and deadlift maxes among military trainees, but the results are messy. The Canadian military studied the soldiers who tried out for Canadian special forces and tested each guy’s squat max. The guys who squatted less were much, much more likely to drop out of training. But when the SEALs estimated their applicants’ deadlift maxes, they decided that in order for a sailor to make it through Hell Week it would be enough if he could just deadlift 1.75x bodyweight, which is nothing. A middle-of-the-pack weightlifter or powerlifter could deadlift that in stiletto heels on laughing gas. 

“Can” does not imply “should.” Advanced lifter on closed course with Olympic-grade stilettos. Do not try this at home.

The methodology is messy too. It’s hard to take a guy off the street, casually test his one-rep max in something like a squat, and get a meaningful result. For one thing, a little experience makes a huge difference, and so does technique. Give me a 98-lb. weakling and a couple sessions to improve his technique, and I can help him test better against stronger people just by optimizing his form. Also, testing somebody’s true one-rep max in a squat or deadlift is physiologically a huge deal and, even for an experienced competitor, your max varies up and down by a big margin over the course of a year. If you’re overtrained or you just peaked, you’ll be wiped out and your squat might be in the toilet. And the Navy researchers had to estimate their subjects’ deadlifts—maximal deadlifts are hugely stressful to the body and take months to recover from fully—using a questionable rep-max formula, which they acknowledge is a crude measure and makes the results hard to interpret. 

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