Jakob Ingebrigtsen BMI of 21

Agree with everything here. Just wish some (NCAA) coaches would read this post as well …

Jakob's body type will work fine for middle distance, but it's probably a bit of a disadvantage in the marathon.

BMI is based solely on height and weight?

Makes no sense.

You can have an NFL running back who is 5" 8" with basically no body fate and weighs 200 lbs as he is all muscle while you can have a couch potato at the same height and weight with little muscle and lots of fat -- same BMI?

if so, a worthless measure

I agree it's pretty worthless for comparing sedentary people to fit people, or even for comparing fit people in very different types of sports (as in your NFL running back example). However, it's probably a fairly useful measure for comparing the degree of skinniness of runners of different heights. I think the OP's point is that Jakob is not particularly skinny for a runner, and that seems to be serving him well.

For your sake, I hope you're trolling.

BMI is a rule of thumb measure. It never aimed to be a perfect tool. BMI doesn't work for very muscular or very old people and that is mentioned in all the small print.

A worthless measurement.

% of body fat is a far better measurement.

The limitation of BMI is that this measurement does not distinguish fat from muscle. According to some research, more than half of Americans have a normal BMI but a high body fat percentage, which is known as normal weight obesity. A person who has normal weight obesity is just as unhealthy as someone with a high BMI.
Body Fat Percentage
Research on body fat percentage has improved in recent years, and in some cases, this measurement may provide a better picture of an individual’s risk of weight-related diseases than BMI. Body fat percentage distinguishes fat from muscle and calculates the percentage of body fat in the body. While BMI is a rough estimate of body fat, body fat percentage is a more accurate number.
Using body fat percentage, we might find that a highly trained athlete is overweight, according to the
BMI, but not overfat. Likewise, a person of normal weight on the BMI scales may still be overfat and at risk of weight-related diseases.

If BMI is so worthless, what is your recommendation for an efficient measurement that nursing can use to screen for clinical malnutrition/underweight that would automatically signal the dietitian to access that patient?

Not really. You could have 2 6'2/163 lb guys and one could be 15% BF and the other 5%. And things like frame size matter a ton. I have lined up against a Kenyan guy who was the same height as me. His legs were 2" longer and his shoulders were 1" narrower. It didn't matter how low my BF went, I wasn't going to weigh less than him.

This stuff only matters for that last 5-10lbs which is well beyond what any sane person using BMI for..

Body fat percentage of course.

I would say both variables are equal important. Yes, it's more unhealthy to have a "normal range" BMI but high % body fat then someone who has an "overweight" BMI but low % body fat.

The olympic Triathlon gold medalist Kristian Blummenfeldt is a good example. He has a BMI wich would be classified as overweight. But that guy is a beast! A real muscle pack with an extremely high VO2-max. However, having too little % body fat is negative for hormone levels as well (Estrogen in women, Testosteron in men). Chasing to low % body fat isn't optimal as well.

Everyone can see that Jakob Ingebritsen is lean, but has a fairly high muscle mass compared to many others athletes. I always find it fascintating to see when Jakob pulls away from the field without looking as he was putting in some extra gear. Everything looks so smooth!

Whilst most elite marathoners are tiny framed individuals, there are a few notable exceptions that could give Jakob hope. Vincent Kipchumba being a current example of a world class marathoner who looks massive compared to his rivals:

His body type would defiently not have a disadvantage at distances up to Half marathon, that'sfor sure! He is already running 180km/115miles per week. Marathon? Hard to say. Jakob has such a high anaerobic treshold and utilization rate wich would makes speeds @2.50-55min/km feeling fairly comfortable for him. It's more about enduring 42.2km. Think it's more about chanching a little bit in his training schedule (a few longer runs >30km). Everything else he already has. If he loses some "extra kilos" changing to Marathon is not because of cutting down on calorie intake but because of adaption to Marathon training.

I think the key thing that bothers me with Salazar or the others obsessed is the fixation on weight/looking like a certain runner (eg Sifan Hassan). Sure some runners look like the prototypical stick figure but there’s no one size fits all for mid-distance or distance runners.

What?!?!?!

You expect a nurse to use bodyfat percentage as the methodology for screening for underweight protein/calorie malnutrition? Do you really think that would be efficient? You expect the nurse to just whip out the calipers, but he doesn't already have a thousand other things to do.

On the other hand, if you use BMI, Height and weight are entered into the system, BMI is automatically calculated and if the BMI is under 18.5, a clinical dietitian is automatically ordered to access the patient more closely. Then the dietitian can document all the data points that are necessary for diagnosis for such as: BMI, handgrip strength, temporal muscle wasting, extremely poor PO intake....

Now I know you are trolling.

Preaching to the choir? Why not post this to r/running instead

Just because it has flaws doesn't mean it's worthless. No, you can't use it to compare an average person to a body-builder, but so what? Most of us aren't body-builders. If you want to grab people out of the general population (or, better yet, measure the population as a whole) then it does a good job.

The triathlete Kristian Blummenfelt tried losing weight, but learned that his VO2max decreased at a higher rate than his weight. Thus resulting in a lower relative VO2max and inferior performance ceteris paribus.

But that's not all. Nutrition deficiency has other 'benefits', like increased risk of injuries, overtraining, etc.

Because having a BMI @21 is considered as "unorthodox" among many runners and coaches, who thinks that a BMI >18.5 (the limit of underweight) is considering as unadvantage due to more mass to carry. If that's not a training advice/discussion then your are more than welcome to post anything that contradict my argument. As you (hopefully) understand, without properly (and enough) nutrition & recovery, all training hours your putting in would not be nearly optimal! If that´s not a training advice, then what is it?