Flexion - Extension

Image result for knee flexion extension definition

Flexion is the bending of a part, or decreasing the angle between two parts. You flex your knee when you bring your leg up toward your thigh. 
Range of motion: 140°.

Extension is the opposite of flexion, describing a straightening movement that increases the angle between body parts. When standing up, the knees are extended.
Range of motion:  0°.


Image result for knee flexion extension muscles

Extensors: (quadriceps femoris, rectus femoris, vastus medialis, vastus lateralis and vastus intermedius); tensor fasciae latae.)
Flexors: hamstrings (biceps femoris,semitendinosus, and semimembranosus); popliteus; gracilis; sartorius.

Evaluating movement dysfunction

Mobility tests: Knee    Identify if caused by 1- or 2-joint muscles.
Strength tests: Knee
Posture Evaluation:  Poor alignment of the knee is likely caused by problem in the joint below or above it.
FMS: Deep Squat, difficulty to get back up will indicate a lack of strength.
        Inline Lunge: same as for the Deep Squat.
        Hurdle Step:  Identify lack of mobility.
        Active Straight Leg Raise:  look for lack of mobility at knee level.

Flexion - Extension

Running Low

Most of the time, running low, with a small angle of the knee (should be around 150°) is not cause by a limited range of motion of the knee extension but it can be.
Corrective measures:
        Mobility:  Standing Hamstring Stretch,    Sitting Hamstring Stretch.

Hurdle Movement (Front Leg)

Hurdling requires a rapid extension of the knee of the attacking leg.  Lack of strength and/or flexibility would results in poor performance or injuries.  The knee flexors (hamstrings) are rapidly stretched at the knee level at the same time the hip is flexed, compounding the stress on these muscles (remember that they are 2 joints muscles, dlexing the knee and extending the hip).
Corrective Measures
        Mobility:  Standing Hamstring Stretch,    Sitting Hamstring Stretch.


Image result for knee hyperextension

Knee hyperextension can be diagnosed with a posture evaluation.  While it might not affect negatively performance of T&F athletes, it should be addressed if that position is seen while performing.  Bounding and running with the knee in hyperextension drastically increase the possibility of getting injured.