Why Size Matters For Special Forces

You need to be strong and run fast to pass Special Forces Assessment and Selection and become a Green Beret.

But in many cases, the biggest obstacle to your success is not your training, it’s actually your body composition.

After all, how many fat soldiers run a 12 minute 2 mile? And how many skinny guys can squat 315?

In this article, I will share body composition data from Special Forces Assessment and Selection and guide you step by step on how to apply it to your training and nutrition.

What the Data Shows

In 2022, Military Medicine published a study looking at 795 candidates at SFAS between 2015 and 2017. The purpose of the study was to analyze the extent to which anthropometrics and body composition affected selection success.

The top predictors in order from greatest to least

1. Lean mass (Cohen’s d = 0.71)
2. Body fat percentage (d = 0.70)
3. Bone mineral density (d = 0.60)
4. Body mass (d = 0.40)
5. Fat mass (d = 0.39)
6. Bone mineral content (d = 0.37)
7. Height (d = 0.35)
8. Body mass index (d = 0.21)

Lean Mass

Candidates with lean mass in the top 25% of their class had six times higher odds of being selected than those in the bottom 25%. 

This makes sense because lean mass is highly correlated with ruck march times, and fast ruck march times are the greatest predictor of selection success.

It is worth calling out, though, that lean mass was not positively correlated with any other performance metric. In fact, sit-up numbers actually went down as lean mass increased. 

But don’t dwell on the fact that your sit-ups may go down because situps and calisthenics do not play a large role in predicting selection success.

Here is the lean mass data:

You can read the lean mass table as saying, that within 13 lbs of 119.3 lbs have a 20% selection rate, candidates within 3.3 lbs of 136.5 lbs have a 27.6% selection rate, and so on.

The grey on this chart represents selected candidates and black non selected candidats. As lean mass increases, a candidate’s chances of getting selected go up.

Total Body Mass

One important caveat to this data is that lean mass does not control for height. Lean mass is your total body weight minus your weight in fat. So taller people are going to have more lean mass and bias the data.

Unfortunately, the researchers didn’t control for height with lean mass, but they did for total body mass (which is another word for total body weight). 

Here is the data where they controlled for the class average height of 5’10.

What you can see here, is that a candidate standing

5’10 and about 158lbs has an 18% chance of getting selected

Being 175lbs bumps that up to 30%

At 189lbs he peaks at 36%

And all the way up to 211lbs his chances remain around 35%

The Importance of Muscle Mass and Strength

If you have any doubts about whether you should be strength training and building muscle mass, this should ameliorate those concerns. But before you buy mass gainer to bulk up, I want to put these numbers in context.

First, everyone at selection has already been screened through a few layers of endurance checks, starting from the day enlisted with an 18X contract, submitted a package, or went to SFRE.

So, the pool of candidates is already filtered down to those who have a decent level of fitness and can move their bodies. 

If you’re slow or borderline in terms of your running, adding more weight is only going to slow you down. For every pound you put on, it’s going to add about 2 seconds to your mile time. So, you better be improving your endurance faster than you’re putting on weight. 

Body Fat Percentage

While you want to have a good amount of lean mass, the data backs up that you don’t want to carry dead weight. In fact, the candidates with the lowest body fat percentages are 4 times more likely to get selected than the fattest.

How is it the case that having more lean mass is good, but more fat mass is bad?

Lower body fat percentage is correlated with better physical performance across every measure – including the APFT, calisthenics, land navigation, runs, obstacle courses, and rucking. 

The weight you have from lean mass, which is largely muscle, can generate force and be an asset to improve performance.

An Encouraging Note to The Overweight

I’ve told this to many overweight guys who are training and discouraged about their run or ruck times. If you’re carrying an additional 30 lbs of fat and running a 9-minute mile that’s actually not bad. At that weight, you’re basically ruck running with 30 lbs. Once that dead weight is gone, you will be so much faster and lighter on your feet.

Warning about Overdieting

But just remember, your body composition and nutrition should serve your performance, not an arbitrary aesthetics goal. Some of you may be at 12% body fat and think about how much better you’ll perform at 9%.

But that’s not always the case. We all have different natural setpoints for our body fat, and the more we deviate from the setpoints, the more our hunger cues and body work to pull us back to our setpoint. So, if you’re performing well at 15 or 17% body fat, don’t diet to the extent it disrupts your performance, recovery, or well-being.

Bone Mineral Density

One aspect of training I am interested in is bone mineral density, which is an indicator of bone strength. Bone mineral density was strongly correlated with selection success, with candidates in the top 25% having double the probability of being selected compared to the bottom 50%.

What’s interesting though is bone mineral density was not correlated with any performance improvement in running, rucking, or any other measure.

Additionally, the study authors did not share insights or a hypothesis on why this was the case. I’m throwing out an idea here, which is that those with lower bone mineral density had a higher incidence of injuries which resulted in voluntary withdrawal or medical drops.

That said, I don’t have data to back it up.

How to Improve Bone Mineral Density?

There are ways we know of to improve bone mineral density. The most effective is heavy strength training.

Your bones are in a constant state of breaking down and building up. Up until your mid to late 20s, the scale is tilted heavily in favor of building up your bones. That’s why it’s so important to be lifting heavy weights during your early years to accumulate more bone tissue.

After age 30, your bone mineral density will plateau, and then it’s about maintaining and staving off future losses, rather than building more.

For most men in their 30s, especially those who are inactive, they’ll lose between .5 and 1% of their bone mineral density each year. That percentage loss only goes up as you get older.

How do you prevent losing bone mineral density? Again, do your strength training.

Height

While we can take steps to improve bone mineral density, reduce body fat, and increase muscle mass, you can’t change your height.

When we look at this chart and table, we do see an association between increased height and selection success.

In terms of physical performance, shorter stature was associated with better performance on push-ups and pull-ups.

And being taller was associated with faster run and ruck times.

But, if we control for total body mass being 183lbs across all heights, the association between being taller and improved selection odds mostly goes away, except for those 5’8 or shorter. 

In other words, if you’re 183 lbs, being 6’2 didn’t help you any more than if you were 183 lbs and 5’9. However, being 5’8 or under and 183 lbs reduced your odds of success.

What to Make of This Data

If you’re a little chubby, or if you’re skinny, or if you’re shorter, I’m sure you didn’t like hearing that other candidates in your position today performed worse.

But now that you’ve heard this data, which 99% of other people haven’t, you can take proactive steps towards your goal and to be better.

Evaluate Your Body Composition

Are you chubby, skinny, muscular, or skinny fat? Write down where you want to be, and I mean literally put it down on paper.

Evaluate Your Lifestyle

What are the simple changes you can make to maximize your progress? Consider cutting out soda, not buying sugary breakfast cereal, or eating more lean protein. The most common lifestyle change to improve performance is good sleep.

Evaluate Your Strength and Endurance

Next, what’s your mile time, squat, deadlift, and overhead press? There’s a good chance if you’re overweight, your running needs work. Or, if you’re skinny you need to spend time in the gym.

But getting your body composition in check is going to massively help, so the results of your training are revealed more quickly.

Next Steps

Now you know how body composition affects success at Special Forces Assessment and Selection. Your next step is to learn how to prepare for selection. Check out my article on The Smartest Way to Train for Special Operations.