Today, let us “Start With Why” movement is not only recommended, but highly beneficial when hurt or injured.
Common practice and well-intentioned advice typically lead to stopping our activities when pain appears or when injury shows its ugly face. This approach, however, omits a few important physiological concepts that clearly go against the idea of staying idle.
Movement has shown time and again to help reduce both pain after trauma or injury, as well as long lasting, persistent pain. This can be moving the whole body, the painful or injured areas or even distant ones.  
Doing some intervals on a stationary bicycle while we are reconditioning a painful shoulder or yet again doing a full seated upper body and “core” workout in the days following an ACL surgery are good ways to keep the blood flowing as well as reducing pain.
Stimulating the painful or injured area supports healing. In fact, properly exercising the hurt area helps the tissues become resilient and avoids weak scars being laid down.
An individualized program of gradual loading of the injury site is a great way to insure this.
Training the body also has general, systemic effects. Overall blood flow is increased, growth and healing encouraging hormones are secreted and the brain is stimulated in a way that helps both brain and body learn faster.  
It has been shown that low intensity aerobic (cardio) activities help increase the brain’s plasticity or ability to change, adapt and learn. This is a great way to help learning new abilities and movement patterns.
One reason why we stop training even painless areas of our bodies is that we are afraid of contributing to an asymmetry between our limbs: think “Rafael Nadal”! (https://tinyurl.com/ycbhkgm5)
Contrary to popular belief, training the opposite side of the body for a short period will not lead to such changes and will even lead to performance benefits to the side that isn’t being exposed to training.  This also allows us to train during injury in a way that minimizes training gaps and time away from training.
A single leg activity would be a great choice while the other limb is immobilized or very limited because of injury.
Seeing the positive in an event, like an injury, is never easy. However, working on our weaknesses (mobility, strength, conditioning, mental preparation, etc) can help not only get back to how we were, but allows us to get better than we were. Hitting the ground running is the goal, both figuratively and literally. 
Having an outside perspective helps on this front as we tend to overly focus on the site of pain or injury.
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