I understand you had question of how we determined the biceps’ role of the involvement of the bent-over row:
https://exrx.net/WeightExercises/BackGe ... entOverRow
The biceps brachii classification as dynamic stabilizer or a synergist is dependent upon the specific movement pattern of a given exercise. It is largely effected by how the biceps brachii is attach to the scapula. In many upper body pulling exercises, the biceps lengthens slightly around the shoulder as it shortens through the elbow, rendering it a dynamic stabilizers. However, In other moments, the biceps are not effected by certain shoulder motions and are therefore considered synergists.
First you must understand all possible functions of the biceps on this page:
Then you must understand the concept of a dynamic stabilizer. The most classic example of a dynamic stabilizer is the hamstring during a squat or leg press where the hamstrings shorten at the hip but elongate at the knee.
Here’s more about Dynamic Stabilizers (aka fixators)
During the wide grip pulldown the biceps are indeed a synergist. This is because the biceps do not have the ability to abduct the shoulder even when the shoulders are externally rotated. This means during the wide grip pulldown, the biceps do not lengthen through the adducting shoulder as the elbow flexes.
However since the biceps has the ability to flex and/or transverse flex through the shoulder they are classified as dynamic stabilizers in the underhand pulldown, wide grip underhand row, and even the rear delt row. This means during these movements, the biceps lengthen slightly through the shoulder as they shorten through the elbow. This is why they are classified as dynamic stabilizers during the bent-over row and underhand pulldown, but not the wide grip pulldown.
Many of our Kinesiology references are listed here:
Back in 1996, I first included a similar analysis in my master’s report entitled "An Interactive Multimedia Computer Database of 250 Weight Training Exercises and Muscular Analyses". If memory serves, the most relevant references pertaining to the potential articulations of the biceps brachii are likely in the following texts:
21) Kreighbaum, E., Barthels KM (1996). Biomechanics; A Qualitative Approach for Studying Human Movement, Allyn & Bacon, 4.
22) Moore KL (1985). Clinically Oriented Anatomy, Williams & Wilkins, 2.
I hope that clears things up for you.