Latissimus dorsi muscle strength testing.
Before going into further detail of test itself we have to understand why the lats are such an important muscle group.
It has several important origin sites which include thoracic spine T7 on spinous process all the way down to the sacrum, the Thoracolumbar Fascia (fascial connection located in lower back), last 3 or 4 ribs, inferior angle of scapula and posterior external lip of iliac crest (back top part of pelvis). It inserts on intertubercular groove of humerus (upper portion of humerus). It functions to extend, adduct and internally rotate the humerus
Based on origin sites having adequate strength for lats is necessary for proper arm movement and especially spinal stability. Also the lats are involved in a contralateral fascial connection comprising of opposing gluteus maxmius the Thoracolumbar fascia and lats. This connection is called the Posterior Oblique Sling that is ment to create optimal rotational movements and proper gait. I won't go into more detail about the POS for this post.
A dysfunction in the lats can cause a multitude of issues in the body and weakness on one side can potentially cause scoliosis as weak muscles tend to elongate. To connect this with the previous posts weakness will also cause the scapula to shift upward causing dominance in upper traps.
As for the test itself position the client in a prone position with the tested arm facing thumbs down and right by the torso. The assessor extends the clients arm as shown in the video and places their hand on forearm near the clients hand. Once ready the assessor attempts to abduct and slightly flex the arm in downward diagonal fashion and the client must resist. Since this is a subjective test use your best judgement to determine whether the muscle is weak or not. Generally if little resistance is required to move the arm the muscle is categorized as weak. Test both sides and see if there is a difference. Also notice how the clients elbow bends in the video? This means the long head of triceps presents weakness as it can't keep the elbow in extension. Always pay attention to see if there are other compensations