Efficiency in Exercise

I hear the word ‘efficient’ tossed around a lot in the gym, on the internet, in articles etc and I just want to be sure I’m understanding it correctly.

If someone was to become a more ‘efficient’ long-distance runner, this means that they would be expending less energy running the same distance as a less ‘efficient’ person. If they wanted to expend the same amount of energy/calories, they would have to either run faster or longer.

I think that part I have down, I think I just become a little confused when this is applied to sprinting / weightlifting, so if someone could correct me on this it would be appreciated:

An efficient/better sprinter (Say a 100 or 200m dash) is better able to tap into their short-term energy supplies and has better form than a less efficient sprinter. I suppose I am just confused here because energy seems less of a factor in these short-duration events.

An efficient weightlifter is more experienced and so is better able to recruit all their muscle fibers at once to push a maximal load, has better form and the movement pattern locked down. If their 1RM squat was say, 400lbs, a 200lb squat would not require them to expend much energy…though I’m not sure if this is the case and I’m not sure why that would be, aside from better form. A novice weightlifter would have to expend much more energy to perform that same 200lb squat.

I think my wondering about this first came up when I first heard my friend talking about P90x - He was saying that constantly varying what exercises they do makes sure that they don’t become too ‘efficient’ in any one of them and so they’re making sure that they continually get the most out of their workouts by ‘confusing’ their muscles. (which sounds pretty dumb)

I’m sorry if my question isn’t really clear, I’m not the best at articulating things. If anyone could correct me, or point me in the direction of somewhere I could learn more about this, it would be very, very appreciated.

more work in less time = efficiency

PX90 is based on “muscle confusion” theory. Nothing to do with efficiency.

The rest has been answered by bluecollar.