Common Muscular Weaknesses


Abdominal Weakness

Increased risk of lower back injury during hip flexion, extension, stabilization and back extension activities. Erector Spinae muscles can hyperextend lower back more than usual if abdominal muscles are weak. The abdominal muscles tilts pelvis forward improving the mechanical positioning of the Erector Spinae, specifically when the lumbar spine becomes straight. When abdominal strength/endurance is not adequate to counter the pull of the antagonist Erector Spinae under load, these low back muscles become situated in a mechanical disadvantage (active insufficancy) further placing additional stresses on these very same low back muscles. Iliopsoas can pull on spine during hip flexor activities if abdominal muscles are weak. Risk is compounded when abdominal weakness is combined with hip flexor inflexibility.

Hamstrings Weakness

Increased risk of knee injury (instability) during knee extension activities, specifically when knees are flexed lower than 90°. Hamstrings / Quadriceps strength ratios should be greater than 56% to 80% depending on the population tested.

Supraspinatus Weakness

Increased risk of shoulder injury during shoulder flexion and abduction activities, specifically when elbow travels below shoulder during shoulder abduction. Risk is compounded with a winged scapula condition.

Infraspinatus Weakness

Increased risk of shoulder injury during shoulder transverse flexion and transverse adduction activities, particularly when elbow travels behind shoulder. Risk is compounded with a protracted shoulder girdle. During the end of a throwing movement, high deceleration forces required of the posterior cuff can cause breakdown in their tendons near their humeral attachment. Strengthening of the rear deltoid and long head of the triceps brachii can also help stabilize shoulder, although to a lesser extent as compared the infraspinatus. External rotation-muscular endurance / internal rotation-muscular endurance should be greater than 70%.

Erector Spinae Weakness

Increased risk of lower back injury during lumbar spine extension or stabilization activities. Back extension exercises involving complete lumbar spine range of motion have demonstrated primarily excellent or good results for those with chronic low back pain. Excellent or good results by diagnosis: 76% Mechanical / Strain, 72% Degenerative, 78% Disc Syndrome, 75% Spondylo. In contrast, McGill condemns the use of isolated lumbar spine exercise apparatuses and argues erector spinae endurance is more important than strength. See Low Back Debate.

Vastus Medialis Weakness

Increased risk of knee injury (chondramalicia) during knee extension activities. The patella becomes laterally displaced with the pull of the vastus lateralis. This patella tracking problem can produce wear on the inferior petellar surface. Greater pain is usually experienced during leg extension activities in which the knee is a greater than a 20 to 30 degree angle.


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