"Stretching always helps me start my day in a good way." Nyjah Huston
Whether it’s with an ironclad fist, waking up and French kissing the morning (thanks Bon Jovi ;)), a preparatory mantra of movement before launching into the sporting arena, a calming flow of exploring the ends of your physical range as you slow your mind, or a routine performed as a religiously repetitive element of a rehabilitation program ~ stretching feels like a good thing. An absolute no-brainer. However, nailing down the why and how of that “goodness” is something else.
As a scientist, stretching is a bit of a quagmire to investigate as there are just so many variables!! I can hear Lorimer Moseley saying, “We are fearfully and wonderfully complex”. So very true!
Oodles of research has been done on stretching and how it impacts the body. Which tissue is being stretched? What method of stretching to use? Before or after exercise, or both? Duration of stretch hold? Dynamic (with movement) or static (still) stretching? Impact on muscle/ligament/tendon? Value of stretching to attain muscular balance across the body (e.g. pectoralis vs rhomboids > hunched upper back and forward head movement (read more here), or abdominals vs gluteal muscles > poor lumbar curve and lower back pain)? Provides potential protection from sporting injury, or not? How does it impact joints? What about the fascia? Even how the ambient temperature of the space you’re 
stretching in impacts outcome (think hot yoga)? Does it help with recovery from acute injury? How does it affect how people feel chronic pain? And there’s much more….
Here’s a potted history on the current understanding:
lifting) dynamic stretching is more effective than static hold stretches.How much are we really changing the tissues when we stretch? Like the duality in human development between nature and nurture, we seem to have a duality in physical intervention when it comes to stretching. A duality between: (a) structural/functional change at the level of the musculoskeletal tissue, and (b) plasticity in the sensing organs in those musculoskeletal tissues and in the neurology of the brain. The biggest impact seems to be on joint ROM and anti-inflammatory effect in the tissues. Both of these land firmly in the "pro" column on the stretching ledger.
Stretching also has an impact through mindful movement. Consciously focussing on how your body is moving (including your breathing) allows the brain to release the worries of the day. This feeds back into the autonomic nervous system to reduce the prevalence of flight/fight and promotes a transition towards a calmer headspace (read more here). This provides an avenue for everyone to wind themselves down when there is a need. Stretching is
a great tool in the repertoire for those working on maintaining a good headspace.
Stretching aids circulation ~ of your blood and the interstitial fluid (or your extracellular matrix). This helps cells in every part of your body stay healthy ~ a happy side product of movement generally (…but don’t let me digress to the pitfalls of sedentarism yet again. Motion is lotion!! ;)).
We also know stretching promotes a better awareness of where we are in space through triggering more feedback to the brain. This has subsequent benefits when it comes to our sense of balance.