How Does Strength Training Improve Body Composition? [A Complete Guide]

Do you need to be strong to build muscle? It’s the age old question with many interpretations.

Let’s skip the bro science and dive into the actual studies:

In a 2014 study, Akagi, et al., concluded that the size of the pectoral muscle (chest) is tightly correlated with 1RM strength on the bench press.

It’s a small study with only 18 people, but the results were consistent and linear… the bigger your bench press, the bigger your pecs. And the athletes were trained, with many of the subjects bench pressing around 225, a feat less than 1% of people on earth can do.

Another study in 2016, by Jones, et al., found a similar (almost perfect) relationship with Free Fat Mass (FFM) and conventional deadlift with r=0.965. An r value of exactly 1 is a perfect positive linear relationship.

For a more in-depth discussion of many more studies on this subject, see Greg Nuckols paper on Size vs. Strength: How Important is Muscle Growth For Strength Gains?

Of course there are outliers, genetics does play a role in strength and hypertrophy, my personal 23andMe data tells me that “your genetic muscle composition is common in elite power athletes.“

But at the end of the day, there are very few people benching 315 with small pecs. Same goes with any other muscle group, there are very few females squatting 2x bodyweight with small glutes.

If the end goal is a better body composition, you should be training to get stronger.

“That’s great, but I’m not trying to be the World’s Strongest Man”

The question becomes, where do you begin?… And where do you want to end?

Well, it depends.

Pick the physique that you admire the most, or aspire to have, and then work from there. More often than not, you’ll have to build lean tissue. Most people have a goal in mind, to gain or lose weight. But that’s the wrong approach, what most really want do is improve body composition by reducing body fat.

For me, I was in precarious position. I was skinny fat. I started my fitness journey at 165 pounds, and a tad over 30% body fat.

Jay Soriano (Las Vegas Personal Trainer). 5’6″, 165 pounds in both photos. Before: 30% body fat measured by BodPod (arguably the gold standard). After: Estimated 12-14% via skin calipers.

I opted to cut down to a body fat percentage that I could be somewhat happy with and then transitioned to bulking to gain size, and repeated the process essentially for the last decade.

For me, a physique I admired was Mike Tyson in his prime. Relatively short for his weight class, he was a physical specimen.

Alright, so let’s breakdown exactly how I am trying to achieve a physique like Mike Tyson’s (and how you can calculate yours).

Let’s say, for the sake of argument that Mike Tyson in his prime was 5’10” and 216 pounds at about 10% body fat. That would bring is Fat Free Mass Index (FFMI) number to 28, many agree that a number over 25 is difficult to attain for a natural athlete. Of course, there are genetic freaks out there and Mike Tyson is very likely one of them, certainly a one-of-a-kind athlete. While the “25 FFMI Rule” is generally accepted as true, this data comes from a 1995 study by Kouri, et al., titled Fat-Free Mass in Users and Nonusers of Anabolic-Androgenic Steroids, a summary concluded:

“In an examination of 157 athletes, comprising 83 steroid users and 74 nonusers, we calculated normalized FFMI using height, weight, and body fat based on skinfold measurements. With this simple measurement, we found that athletes who had not used steroids all had values of less than 25, whereas a large proportion of steroid-using athletes easily exceeded this limit.”

Of course there are limitations, 157 athletes is the grand scheme of things is a relatively small number when you consider professional athletes are one-percenters. There’s also a selection bias, you only had to be 16 years old with two years of lifting experience to participate. At that age, you haven’t even had the chance to grow into your body. Hypothetically, the same 16 year old who measured at a 22 FFMI during the study could be an FFMI of 28 when he’s 26 years old.

The study was also from the 1990’s, a lot has changed in training and nutrition since then. Many professional athletes today are higher than a 25 FFMI. Just look at Francis Ngannou, UFC Heavyweight Champion in a sport with arguably the strictest drug testing with USADA (the team that took down Lance Armstrong, Barry Bonds, among others). If we guesstimate his body fat to be 10-13%, at 6’4″ he cuts down to the heavyweight limit of 265 pounds. That would bring his FFMI to around 28-29.

I’m not a one-percenter though. My NBA dreams were squashed at 13 years old when I realized I wasn’t going to be taller than 5’6″. I’m certainly not a genetic anomaly either, unless you count being genetically pre-disposed to to developing type 2 diabetes. So far all intents and purposes I’ll assume that 25 FFMI is my natural limit (and if I could ever get to Mike Tyson’s 28, all the better).

At my height (5’6″), I would need to be 166.4 pounds at 10% body fat to achieve a FFMI of 25. For reference, I would need to be 187 pounds at the same level of leanness to achieve a FFMI of 28. Most advanced lifters are happy with gaining 2-4 pounds of lean tissue in a year… another 20 pounds sounds almost crazy to me. At my height I feel like ~165 pounds offers my best physique.

I’m sitting here in a Covid world, and I’ve certainly put on the Covid-19 pounds. So far I’ve cut down to about 173 pounds at about 15% body fat. So to get down to 10% I’ll need to lose about 8.65 pounds of body fat. I do tend to lose some muscle during a cut, so I estimate I’ll have to cut down to 160 pounds at slowly bulk up to 165-170 and then repeat the process.

Stay tuned.