Strength / Weight Training

The long and the short of it is that if you are lifting weights in a challenging way, which gets you close to failure, on a regular basis, with some kind of progressive overload, you will stimulate hypertrophy / muscle growth. This is why you see results from different methodologies as long as they follow some basic principles. Obviously there's more optimal ways to do things, but the kind of "definitive" way is that most of it works.

The other component is food. You have to eat in a caloric surplus to gain significant amounts of muscle and "use" the stimulus from the workouts. You also have to eat a good amount of protein. You also generally have to do these things for an extended period of time. If you want to gain muscle, bulk for 6 months plus.

There is also the aspect of hormone profiles and the way they impact your ability to build muscle. You can get these checked via places like medichecks and see if there's anything that needs addressing.

If you really want to gain muscle and are struggling, consider going full hardgainer and just accepting that you will develop some fat. You probably just need to eat more.

Little improvement in size, appearance or strength?
2 kg of extra muscle spread on your frame might not appear dramatic because of your height, but keeping up the consistency, volume and food will get you there.

Lift hard, recover well, eat loads.
Then cut some of the excess fat.

Yeah, I was thinking this a few weeks ago too. Wish there was an answer. People still can't decide if the last three-five reps of a set are the ones that create hypertrophy or not (here's a four hour podcast saying they clearly aren't the only factor. It really delves into why hypertrophy isn't a simple dose/response relationship in the first hour or so)

Like Zooey said, the fact that people have had success with such a wide variety of training programs shows that most things will work. And even if you could find an 'optimal' for you, it'd change as you got stronger/bigger/heavier/lighter/increased work capacity/sick anyway.

For what it's worth, I've found going really, really hard, controlling reps so that muscles hurt instead of joints and eating everything over Christmas has worked pretty well lately.

There must be a definitive way to build muscle.

Well yes and no. The variability of individuals makes having a unified process hard to define, as the same stimulus will have different outcomes based on the individual.

The other other component is....

SLEEP

With regard to working out. There seems to be so much variation out there. There must be a definitive way to build muscle.

Im with @zooeyzooey in that as long as youre lifting challenging weights, you will grow.

I do feel there is a case for specialisation or specifics, but that would be for the advanced to elite in whatever you speaking of.

All these programs are designed for specific things, and each has its pros and cons. And will either take you or someone like a coach to find whats right but youre talking the top, "im trying to add 5cm to my jump, or 10lbs to a deadlift." At that stage youll be more in tune with your body.

Edit: nothing wrong with picking one to work through. It can give you focus and direction! Also, they have loads of experience so its a good place to learn stuff.

BTW, one of the big things about getting bigger, is simply long term consistent challenging weight lifting. Theres a few of us who have been lifting for years and size and bulk comes with long term exposure.

You body needs to grow and adapt to get stronger. Bones will get denser, tendons and fibres stronger, and then your muscles will get stronger.

Unless youre doing the otc enhanced route, its not going to happen overnight.

What is your goal? - Deadlift strength? Overall size? Overall strength? Speed? Power? Endurance?

For me, i struggle to follow set programs. in my youth, I didnt get passed the simple stage of the various day splits. Bro split, full body, upper/lower split. These days, im happy to train roughly everything every day for 4-5 days a week. But im very fluid with it. If my elbows are hurting, i concentrate on legs. If i cant bear the thought of leg day, i do upper.