Trevor Siemian is Tom Brady and Peyton Manning’s baby that never reached maturity.
But first, a few facts about the anterior and posterior neuromuscular systems.
These systems evolved first (and for a far longer time) among four-legged animals. Posterior muscular systems supply constant, enduring power, evolved to continuously oppose the force of gravity.
Anterior muscular systems channel this power into quick movements. In canids, the anterior system (termed ‘ventral’ in 4-legged animals, lining the inner-legs/ belly) is often loose, only firing regularly for small corrections, or for extra energy during hunting/ fight-or-flight.
Trevor Siemian’s anterior forearms are Tom Brady-esque in their efficiency (particularly medially), and he shows the mechanical learning rate of late-career Peyton Manning.
On the back-side, however, his posterior muscular system can generously be described as underdeveloped. His apparent lack of arm strength in college was due to this overall-deficient posterior thoracic system.
The good news is that Siemian shows a band of posterior efficiency extending medially through his thoracic region. This allows him to really ‘spin the ball’ in certain contexts, where he can organize his motions around his band of posterior medial efficiency.
This band on its own wouldn’t normally be enough to overcome Siemian’s physical limitations, But whether it’s Kubiak’s teachings, studying Manning’s routines in 2015, or just natural talent/ smarts, Siemian shows a mechanical learning/ adaptive rate that I’ve only ever seen in late-career Peyton Manning.
On the field, Siemian is still showing mixed results. On throws where he can naturally access his band of posterior medial efficiency, he can deliver a quick accurate ball via his anteriorally-efficient forearms (note the way he cocks the ball onto his forearms pre-throw). On throws where he is on the move or unable to organize his motions properly, he loses posterior strength, with the result being apparent in the fundamental trajectory of the ball. Likewise, he will sometimes be forced into a slow physical delivery of the ball, due to pre-throw posterior-focused mechanical adjustments.
Posterially, Trevor Siemian is backup-quality at best, with his band of medial thoracic efficiency being his only back-side qualifier for an NFL roster. But his learning and mechanical adjustment rates compare only to late-career Peyton Manning (trying to compensate for four neck surgeries), and his anteriorally-efficient forearms make his front-side delivery quick and accurate.
His need for pre-throw mechanical compensations means he will need to develop Peyton Manning-esque visual recognition skills to be able to consistently get the ball out quickly/ powerfully enough. But early-on, he is showing a truly remarkable learning rate, such that I won’t bet against his eventual success if it can continue.