Introduction and purpose: Our aim was to determine a morphometric relation between the long head of the brachial biceps and the bicipital groove with respect to the subscapular tendon, and its repercussion on functional imbalance of the shoulder.

Materials and methods: For this analytical observational crossover study we took a sample of 30 right-handed, sedentary, duly informed male subjects. The morphometric study was carried out with ultrasonography using a cross-section of the long head of the brachial biceps.

Results: In the dominant limb: 1. Bicipital groove (depth 2.6 mm, width 13.4 mm, internal angle 149.8°); 2. Long head of the brachial biceps (area 1.35 mm, internal angle 152.53°, echogenicity 97.95); 3. Subscapular thickness 4.53 mm. In the non-dominant limb: 1. Bicipital groove (depth 2.9 mm, width 12.5 mm, internal angle 145.73°); 2. Long head of the brachial biceps (area 1.07 mm, internal angle 141.32°, echogenicity 112.72); 3. Subscapular thickness 4.12 mm.

Conclusions: The greater the thickness of the subscapular tendon: 1. Bicipital groove (greater width and internal angle, less echogenicity and depth); 2. Long head of the brachial biceps (greater area and internal angle, less echogenicity). Therefore, there is a greater risk of dislocation of the long head of the brachial biceps and functional instability of the shoulder.