Muscle activity when walking downstairs

Question

Amanda is walking downstairs. Explain what muscle(s) are involved at the knee of the descending lower extremity: what is the prime mover(agonist) and what type of muscle contraction is utilized (concentric, eccentric or isometric)? What muscle is inhibited? What muscle(s) might be a synergist? Is walking downstairs considered a power or control motion?

Answer 1

When Amanda is stepping down (descending), the quadriceps muscle group is the prime mover, particularly the rectus femoris and vastus lateralis. These muscles are eccentrically contracting, thus lengthening the muscles. The gastrocnemius is a synergist, also contracting eccentrically. Descending stairs is considered to be a control movement because the eccentric contractions of the muscles mentioned above decelerate the lower extremity stepping down, preventing Amanda from collapsing and falling down the stairs. Also, note that the vastus medialis of the quads is important in controlling tracking of the patella during motion at the knee.