Midstance Knee Flexion

Why this matters

Midstance is the moment of peak load — the body's centre of mass is directly over the stance foot and gravity plus running speed are compressing the leg. The knee flexion at this moment determines how much of that load is absorbed (by spreading the deceleration over a few milliseconds and a few centimetres of joint travel) versus transmitted (as a stiff impact pulse straight up the kinetic chain).

A well-flexed knee at midstance acts as a leaf spring — quadriceps and patellar tendon load eccentrically, then unload concentrically into push-off. A stiff knee (>150° included) bypasses that absorption and the load lands on the bones and connective tissue instead of the muscle. A collapsed knee (<125° included) loads the muscle far beyond its efficient range, which fatigues the quadriceps quickly and tends to recruit hip flexors as a substitute.

What good looks like

The knee is clearly bent — the calf is approximately under the knee, the thigh slopes back from the knee to the hip. The leg looks "loaded" but not crumpled.

Common faults

• Stiff knee (>150° included) — common in beginner runners who haven't built the eccentric quad strength. Looks like running on stilts; high impact transmission.
• Collapsed knee (<125° included) — over-bent. Often paired with weak glute medius (so the hip drops onto the stance leg) and a forward trunk lean compensation.

Coaching cues

• "Soft landings." Conscious cue to bend the knee on contact.
• Strength: single-leg squats and step-downs build the eccentric quad capacity that gates the angle.

Related measurements

• Pelvic Drop — excessive knee flex often pairs with a contralateral hip drop; both point at a weak gluteus medius.
• Foot Strike Angle — stiff-knee runners almost always heel-strike (the heel strike forces the leg to extend in front).