You know that the muscles in the body are arranged by antagonistic pairs, right? That is to say, each muscle has a partner that contracts in contrary direction. It is when both muscles are working opposite each other in proportion that balance is achieved. In Yoga we train to accomplish the fullest range of motion, such that each muscle may be allowed by its partner to contract fully. When one contracts fully, the other releases fully and vice versa. So in your stretch, one muscle was not allowing the stretch. It was too tightly and inflexibly contracted. It also means that the counter-muscle was weak, not able to contract and help that muscle release. Your very strong arms were in a position to help the weak muscle and thereby encourage the stretch. The the tight muscle gets the message that it needs to give a little.
The concept of muscular antagonism was not foreign to me. I was introduced to it in Vocal Pedagogy 101 a long time ago. But it is different when one is at a level to understand physically how that actually feels in the process of singing. Poor antagonism is when one muscle dominates excessively as in falsetto or the reverse, a "loose" heavey chest voice. Good antagonism is when the two muscles are doing their part, preventing one muscle from being two active. An organized balance between the two main phonation muscle groups, CT and Vocalis is the goal. It is precisely that: a question of balance! And balance means that one will tip off of center a few times before achieving stability.
Luciano Pavarotti often refers to his voice as an elastic voice. He meant flexible, able to traverse his entire range almost seamlessly. The goal used to be a state of balance that gives the impression that there are no registers. One young, professional tenor told me a while back that his goal was to keep the registers. He wanted the sensation of a sudden shift from low to high. For him the drastic change was a virtue. How things have changed.
If the goal were simply to stretch thin towards the top then falsetto would be hallmark of a great singer. A coordinated tone requires the CT to stretch the folds thin out but with simultaneous opposition from the Vocalis to prevent the folds from thinning out too much. This longitudinal tension makes for a much more efficient vibration process. Elasticity is when the CT has the strength to stretch effortlessly to the top with appropriate opposition from the Vocalis to create a full voice tone. Not two-thirds voice, not three-fourths but a full voice! This takes time! The modern singer's nemesis!
One can listen to my clips over the three years I have been writing this blog and documenting my progress and hear a gradual leaning out of the voice. Many listened to my falsettone high C about a year ago and celebrated my having found my tenor voice. But it was not a true high C. I have a real one now that is becoming viable, but I also have three former baritones who can stretch to Eb5 or higher. High notes are not everything, but a well-coordinated high note is a sign of a voice that has been truly developed. I have found that singers who sing high notes that are too thin, often have difficulty in the passaggio. One short aria I find to be a remarkable test, is Arturo's short one minute arioso, "Per poco fra le tenebre" from Donizetti's Lucia. I have heard more than a few otherwise able tenors, literally crash-and-burn on that little aria. I would encourage all tenors regardless of category to try to master that little one-minute challenge:
Here is a clip of my attempt at it. It is an interesting clip in that one can hear when the voice is truly balance and when it deviates a tiny bit. One can hear very successful stretches in the passaggio but one has the feeling it can all become stretchier, more elastic! That is the goal, and elasticity is possible without losing the fullness of the tone.