Question

If i was standing on a log and I was stepping down with one leg what movement is occurring at the knee joint? Is it knee extension?

What is the main muscle active during this movement?

What is the origin and insertion of this muscle?

what position is it crossing relative to the joint?

Answer 1

The movement occuring is knee extension.

Knee extension involves straightening the knee or decreasing the angle of knee flexion as opposed to knee flexion in which your leg (and knee joint) is bent.

The primary muscle involved is Quadriceps femoris.

The quadriceps muscles consist of four large muscles at the front of the thigh: the rectus femoris, vastus intermedius, vastus lateralis, and vastus medialis.

Origin : The rectus femoris has its origin on the iliac spine of the hip bone. The other quadriceps muscles have their origins on the femur.

Insertion :  All four quads insert at Tuberosity of the tibia via the patellar ligament.

The quadriceps femoris muscle group (rectus femoris, vastus lateralis, vastus medius, and vastus intermedius) crosses the knee via the patella and acts to extend the leg.