explain why more energy is expended by walking downstairs than by walking horizontally on the same speed.?

Answer 1

Because our muscles don't have the ability to store energy while coming down from a higher potential energy. Our muscles require energy to tense up, which it has to do going either up coming down, although it's easier coming down. As an analogy, imagine that you are on a rocket-powered car that has no brakes. In order to slow down, you can point the rocket in the opposite direction, which will slow you down to a stop. But that takes just as much energy as it took in getting you up to speed.

Answer 2

Answer 1

As you walk downstairs you tend to almost come to a halt on each step.

Your body or leg acquires a downward velocity during the step down which your leg muscles have to remove before you come to a halt. They do this by pushing upwards, which expends energy.

I suspect that running downstairs or walking down a slope is less inefficient than walking downstairs.

Alternative Answer 2

Consider a spaceship accelerating towards its destination then decelerating to a stop on arrival. Its energy expenditure is essentially equivalent in both acceleration and deceleration. Friction does not slow it down, so it has to push just as hard to stop as it did to start.

Your legs aren't as energy efficient as a spaceship and some friction loss (largely air resistance) does occur.

However, gravity is accelerating you downwards and giving you kinetic energy. You have to fight that somehow. You don't have brakes to turn it into heat, although of course that does happen to some extent in your joints and muscles. So you have to do it by pushing upwards, which expends energy.

The same is true when simply standing still - you are constantly pushing against gravity - but locking your knees means you aren't actually pushing with your muscles.

Answer 3

Another way to look at is potential energy. When you r walking horizontally, there is no potential energy term. However, walking down stair or up stair with the same speed as you walk horizontally, the potential energy has to be considered. That how energy is expended.
E = 1/2mv^2 + mgh (mgh is potential energy)

Answer 4

not to my experience i let gravity take over and clonk down the stairs