Moving the same thing (your body) from the same starting point to the same end point will accomplish the exact same amount of work, and therefore require the same amount of effective energy to accomplish, so it boils down to biomechanical efficiency of which movement more efficiently accomplishes work, and wastes less energy.

That’s going to depend on the individual, as everyone’s limb length and muscles and tendons will affect how efficiently the body maintains forward momentum once in motion, how much energy is wasted on each step, etc., so that the ideal step size is different from person to person, and the ideal speed is different from person to person. The answer will change for the same person with training, too, as the biomechanics of a particular movement tend to get more efficient when that movement is trained over time.

You may be able to estimate the right answer by just doing it both ways and seeing what a smartwatch tells you. The gold standard would be to hook you up to a machine that measures your oxygen consumption, but that wouldn’t be very practical.

Depends on the height of the steps and the person’s height and weight. At a certain point it begins to take significantly more effort to push down due to leverage, the position of the muscles, weight distribution, aerobic thresholds, etc. But this typically happens in an average person about when your knee passes the height of your waist, especially repeatedly. This is also why children or shorter people tend to get more tired climbing the same steps as taller people.

The standard height of stairs in most building code was typically designed to be ideal for the height of the average healthy male. But that isn’t exactly 100% perfect especially considering that it’s more important that every step is the same height all the way up a flight, or people will trip, and you can’t always divide the height exactly evenly as not all flights of stairs are the exact same height. But there also are a lot of steps that are out of code or are single steps or groups of single steps that have to fit a specific, uneven slope.

But in general, with steps in a modern building that is to code, your knee will have to come up to a height where you need to use more than twice as much effort on a two stair hop.

Depends on how tall you are. Over a certain height skipping every other step becomes more efficient.

You train your legs more.

The distance is the same, so that is the same work. But there is probably more effort in two steps at once just from how the muscles have to work. If your heart rate is higher even a little bit after getting to the top, then it’s more.

If the velocity is the same (rate of change) then I think work is the same (Physics was a long time ago).

That’s from a basic physics perspective.

Biologically I would assume 2 steps requires more calories as we don’t go slower, and I suspect the mechanics of motion don’t work as simply as a basic physics experiment.

Think of it in terms of the size of each stair and the size of the person.

If each stair is > the size of my leg, each step is plenty of work. Doubling it engages more muscle groups. In this case obviously more energy.

If each stair is < the sole of my shoe, each step is barely any work. Doubling it is negligible, no new muscles are engaged, they just work slightly harder for double the gain.

So, the answer is both, and it depends on the size of the person and the size of the stairs.

Assuming standard 7 3/4in height and 10in tread depth.

Most people go much slower when taking two at once. So I say, less calories. The human body is incredibly efficient with slow motions.

Long time ago, I have made a personal excercise out of it, by taking two at once, but with the same frequency of my steps, so it was effectively double speed. That was fun and it used many more calories of course.

Skipping steps is faster. The height and distance energy burn is roughly the same whether you walk up normally, backwards, skipping steps, or crawling (within reason). However your baseline metabolism is constant, so the faster method burns fewer calories.

Let’s say you were walking up stairs for 10 miles. That’s about 40,000 stairs. I would estimate that would take about 10 hours to do. But skipping steps you’d be done in maybe 6 hours. So in either case the stairs burn say 5000 calories. But going slower you have like 1000 calories of baseline metabolic burn, and skipping steps only 600. So skipping steps might be about 7% more efficient overall.