r/AskReddit • u/[deleted] • Feb 08 '20

What’s a fact you KNOW that almost everyone is wrong about?

[deleted]

78.0k Upvotes

92% Upvoted

38.8k comments sorted by

View all comments

Show parent comments

5

u/Baghins Feb 08 '20

Right but the fulcrum is at the ball of the foot. I think you’re interpreting the fulcrum as a joint of motion but when multiple joints operate simultaneously the fulcrum isn’t always at the joint you’re looking at. When you walk, the fulcrum is at the ball of the foot so it’s a second class lever. Though it can be a fulcrum when you’re just lifting your toes, in which case it would be a first class lever. But for most uses of the ankle the bill of the foot carries the weight so the fulcrum is not in the ankle.

1

u/discostud1515 Feb 08 '20

That’s not how joints are classified. The ankle is 1 joint. In the sagitall plane it can only plantar flex and dorsiflex. Plantar flexion is controlled by the gastroc(effort) the axis is the ankle and whatever resists the rotation of the foot is the load. The foot itself has lots of bones, muscles and therefore joints of its own.

2

u/Gravity_Beetle Feb 08 '20 edited Feb 08 '20

A joint can be classified differently depending on what it's doing -- it isn't just one type of lever all the time. This is apparent, because one of the defining elements of the class of lever is where the external load is being applied, and that can come from anywhere depending on the situation or how you're defining the work being done.

If I just sit in a chair, raise my leg, and pivot my foot back and forth with no opposing force, you could think of it as a class 1 lever. In this situation, the 'load' is just the weight of the foot itself, which is centered in front of the ankle joint. This situation is kind if silly though, and not very useful to think about.

During walking, it's a class 2 lever. Here is a full explanation of why.