I was working out with some friends today and during one of the exercises (jump squats) I jokingly said to my buddy (who is 5'4" with a normal proportioned frame, I have a lean build) when he was cheating on the exercise a bit, "Hey man, these are harder for me because I'm taller and weigh more, so no excuses!" and laughed. I said it in jest, but then this girl scoffs at me with an attitude and says, "That's BULL**! Obviously height and weight don't make a difference! Read a science book!" (lol?)
The fact that she missed that I was clearly joking notwithstanding (it's called pep talk, lady), after thinking about it some more in the locker room with my buddy I actually wasn't even sure what the answer to the question was. That is:
What are the (intrinsic*) factors which influence how challenging a particular exercise is?
*intrinsic to the nature of the body as opposed to how one uses it
I like to think that I have a very solid foundational understanding of biology, but this goes beyond the basics into ATP expenditure, muscle fiber theory, etc.
What is "challenging"?
First, we have to define what it means for an exercise to be "challenging". While there is certainly a psychological aspect to this, I would prefer to avoid that and stick with the pure biological definitions. Perhaps, an exercise is more challenging for person A than it is for person B if person A has to expend more energy proportional to their size than person B. I'm not sure this is the best way of looking at it but I obviously can't use something like "If person B expends more energy" because a bigger person will always use more energy than a smaller person quite naturally. The question is whether the bigger person's naturally bigger muscles 100% make up for the additional weight they have to lift to counter their own body...
Intrinsic factors vs non-intrinsic factors
I'm not looking for factors which affect how challenging an exercise is which are not innate to the biological system itself. Stuff like whether I had enough sleep the night before or are eating a proper diet — these factors are not relevant here. I'm assuming all these factors (which are relatively controllable) are otherwise equal in all comparisons of performance.
My current thoughts:
Height—on the face of it—doesn't seem like it would too significantly affect an athletes performance, but I'm not totally sure. Yes, the oxygen is thinner up there, but that's insignificant, but my heart has to pump blood further to reach distant parts of my body. Is this somewhat of a factor? Unless heart strength scales proportionally with height (does it?), this seems viable.
Number of muscle fibers
It wasn't entirely clear to me reading basic skeletal muscle articles whether people vary significantly in the number of muscle fibers they have, and whether this has something to do with height or build.
Type of muscle fibers
Do taller people have, on average, a particular type of muscle fiber more than another (fast twitch vs slow twitch)?
Cardiac muscle strength vs body size
It is not clear to me whether the heart muscles increase in strength proportionally with body size. In fact, that so many large individuals (not simply fat, but big tall and otherwise healthy individuals) tend to have cardiac issues seems to attest to the fact that larger people put more strain on their hearts than smaller individuals (on average).
Other factors I'm missing
I'm sure there are other factors involved. If I think of others off the top of my head I'll add them to the list.
That's all I got. Help me out here. Thanks :)