WRT stretching, there is some pretty useful research (can't recall the references at present) that indicated that stretching before exercise makes little or no difference to muscle strain/pain, and there has been evidence for quite some time that stretching on cold muscles can cause inflammation of tendon sheaths and subsequently can inflame the tendon. Some work has been carried out on 'microtears' of the tendons, but this is still a contentious area because most athletes rely on microtears and irritation of the muscle fibres as part of training - this is how muscles get larger and more efficient.
Again, it's the force involved (and with tendons it's often the repetition) that contributes to things like tendonitis and tenosynovitis. Rupture of the tendons requires really high impact although complete rupture (eg of achilles tendon) may occur after there has been partial rupture for some time then it may take a lesser force to achieve the full rupture.
Stretching over two joints really only increases the amount of force that is applied to the muscle/tendon/ligament unit, so a little less force is needed compared with when stretch is applied over one joint.
And tendons have less blood supply, so take longer to settle than muscle.
Sorry to have confused OA and tendon/ligament problems... although the result is quite similar, we're pretty hardy animals except where we ignore discomfort and persist with inefficient biomechanical movements or don't allow sufficient recovery period between training sessions.
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