Long-term stretching seems to occur mostly at a sensory level of the nervous system versus the mechanical properties of the muscle-tendon complex itself.
Neural Plasticity – Learning Posture and Movement Patterns
Neural Plasticity explains how the nervous system learns and patterns our postures and movement patterns, as well as our memories and sensitivity to pain.
What is Muscle Memory?
Muscle memory describes the concept that musculature contracts in patterns for both posture and motion, and these patterns reside in the nervous system.