Common Muscular Weaknesses

Abdominal Weakness Increased risk of lower back injury can occur 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 tilt the 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 are put at a mechanical disadvantage (active insufficiency) further placing additional stresses on these very same lower back muscles. Iliopsoas can pull on the spine during hip flexor activities if the abdominal muscles are weak. Risk is compounded when abdominal weakness is combined with hip flexor inflexibility. Examples of affected exercises: Squat Deadlifts Military Press (standing) Lying Leg Raise (full extension): hands may be placed under lower portion of glutes to decrease tilt of pelvis and subsequent hyperextension of spine. Example preventative / corrective exercise: Crunch Hamstrings Weakness Increased risk of knee injury (instability) occur during knee extension activities, specifically when knees are flexed more than 90°. When hip and knee are simultaneously extending during a compound movement, hamstrings counter the anteriorly directed forces of Quadriceps. Also see Knee Stability and Angle of Pull for force vector explanation. Hamstrings / Quadriceps strength ratios should be greater than 56% to 80% depending on the population tested. Examples of affected exercises: Squat Leg Press Example preventative / corrective exercises: Leg Curls Straight Leg Deadlift Supraspinatus Weakness Increased risk of shoulder injury during shoulder flexion and abduction activities, specifically when the elbow travels below the shoulder during shoulder abduction. Risk is compounded with a winged scapula condition. Paradoxically, avoiding full range of motion (i.e. not initiating deltoid exercises from a fully adducted position) may not allow the Supraspinatus to be fully strengthened since it is more fully activated at these initial degrees of shoulder abduction/flexion. Once an injury has occurred, however, range of motion is typically restricted on the shoulder press. See shoulder abduction force vector diagram. Examples of affected exercises: Shoulder Press Upright Row Lateral Raise Example preventative / corrective exercises: Front Lateral Raise Lying Lateral Raise

Infraspinatus Weakness Increased risk of shoulder injury occurs during throwing and shoulder transverse flexion and transverse adduction activities, particularly when the elbow travels behind shoulder. Risk is compounded with a protracted shoulder girdle. The strong stabilizing and dislocating forces of the Pectoralis Major (Sternal and Clavical) is counteracted by the Infraspinatus, Teres Minor, and to a lesser extent, the rear deltoid and long head of the triceps brachii. This counter force is most crucial during: initiation of a transverse adduction/flexion elbows behind shoulders stabilizing force during the end of a throwing movement high deceleration dislocating forces required of the posterior cuff can cause breakdown in their tendons near their humeral attachment. External rotation-muscular endurance / internal rotation-muscular endurance should be greater than 70%. Examples of affected exercises with suggestions for high risk individuals: Bench Press: Bring bar lower on chest, keeping elbows closer to sides. Chest Press: Elevate seat so elbows are closer to sides Range of motion may need to be limited so elbows do not go behind shoulders Example preventative / corrective exercises: Lying External Rotation Rows Erector Spinae Weakness Increased risk of lower back injury occur 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 lower 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. Examples of affected exercises Straight Leg Deadlift Squat Deadlift Example preventative / corrective exercises: Back Extension (novice) Cable Row (with spinal articulation) (novice to intermediate) Stiff Leg Deadlift (advanced) Vastus Medialis Weakness Increased risk of knee injury (chondromalacia) occurs 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 patellar surface. Greater pain is usually experienced during leg extension activities in which the knee is a greater than a 20 to 30 degree angle. Avoiding full range of motion (i.e. not locking out) during Quadricep exercise may not allow the Vastus Medialis to be fully strengthened since it is more fully activated at these final degrees of knee extension. Examples of affected exercises: Leg Press Squat Leg Extension Example preventative / corrective exercises: Single Leg Extensions (last 20 degrees of extension) Leg Press (last 20 degrees of extension) Hip Abductor Weakness One hip can sag when weight is shifted to one leg. Possible increase risk of Iliotibial band friction syndrome (ITBFS) when combined with Gluteus Maximus and/or Tensor Fascia Latea Inflexibility (Fredericson, et. al. 2000). Examples of affected exercises: Lunges | Step-Ups Running | Stair Climber | Gauntlet | Elliptical Example preventative / corrective exercises: Lever Seated Hip Abduction All effected exercises in a progressive manor