I’d have to agree with Prof X. that “there’s not much difference” to a certain point. What I mean is that if you expose your muscles to an increasingly intense resistance they will adapt. One of these adaptations is increases in muscular size, another is increases in neuromuscular activation and coordination.
What I mean is that if you train for strength you will build some muscle. If you train for improving muscle you will build strength. Now, the extent to which you get a carry over will vary depending on many factors.
One factor that I’m surprised no one has mentioned (and if someone did mention it and I missed it I apologize) is diet. Your body needs surplus calories to build muscle as muscle is a very metabolically active tissue. If you don’t have any surplus calories, than your body is not going to add tissue that it can’t support.
In regards to the question about limits in terms of strength and muscular size; both are limited. If this weren’t true, then we’d see 80 year old bodybuilders, powerlifters, strongmen, etc… winning every competition out there. Why? Because if there were no limiting factor on an athletes strength/mass capabilities except time, then the oldest athletes would dominate.
Everyone has a genetic limit to their strength/mass building capabilities. I think we’d all like to wish that this weren’t true and that through determination and hard work we can indefinetely improve our bodies. But it’s simply not true.
Sure, improvements in training methodologies, supplements (either legal or illegal), nutrition, etc… will mean that the athletes of tomorrow will probably outdue the athletes of today. But, even then there will be a limit.
That being said, I don’t really agree that in order for someone to continue gaining strength they will reach a point where mass must also be built. Now, would they necessarily reach the same strength levels as they could if they gained mass? No, most likely not. But they will still improve in terms of strength.
I also don’t agree people who cite examples of strength athletes who compete in sports that contain weight classes to support the argument that you don’t need to build mass to get strong. Do you think those athletes would weigh as much as they do if they didn’t train? Or, more specifically; would they have the same levels of muscular development? No. Their bodies have build muscle to allow them to reach those strength levels.
But, they also train with the specific purpose of minimizing their bodys’ mass building tendencies (probably through a combination of training protocol and dietary restrictions).