"Rest" has to be the most grossly over-recommended and oversimplified advice when it comes to healing and recovering from injuries, and here is why.
Temporal characteristics of an injury:
Time Factor: Is this an acute injury that popped up on 1-2 runs with no prior warning? An area that has bothered you for 2-6 weeks? Or is it a chronic issue that you've struggled with for years and never seems to get better? Each of these issues needs to be treated differently.
An acute injury (<2 weeks) is the type that may recovery (more) fully from a few days of relative rest and deloading, allowing irritation and inflammation to calm down and allowing someone to resume training soon thereafter.
However, even during this time, an injured person should be using other concurrent rehabilitation strategies such as gentle active and passive movements, cross training, and perhaps modalities to help if the injury is quite painful. If the injury was purely a matter of training errors and/or overloaded tissues, then adjusting the training load upon resumption may be the only necessary step (no strengthening, stretching, balance exercise, etc needed).
Note: When I use the phrase 'relative rest', I don't mean no activity at all, I mean a reduction in the aggravating activity if you can identify one- while potentially performing cross training or specific exercises and stretches (such as from a PT) to improve the area of concern. Full rest is rarely the best strategy.
Subacute issues (2-6 weeks) will likely also benefit from relative rest, as there is often an overtraining component to them. However, if an issue has been there for >2 weeks of resting -or- the issue came back soon after re-engaging in the activity, there are likely other factors to be addressed. These factors may include limited mobility or flexibility, weakness in the kinetic chain, impaired balance, lack of neuromuscular control (inability to express muscle strength in a coordinated and accurate fashion), or poor form/technique during an activity. Each of these issues can be improved with appropriate rehab exercises, retraining, and education. Helping to improve these impairments is a physical therapist's wheelhouse. Manual therapy can help decrease pain and improve range of motion which then allows a home exercise program to be more effective. Prescribed strengthening and balance exercises can help improve impairments and get someone back to performing (sometimes better than before the injury).
The more chronic the issue (6+weeks), the more likely it is that other rehab strategies such as progressive exercise and loading are going to be necessary for a full recovery. If rest was going to 'fix' these issues, it would have already. The factors listed in the subacute stage are likely still at play here, but there now may be additional complications such as: decreased activity tolerance, deconditioning, decreased motor cortex space corresponding to injured body area (poorer proprioception), hypersensitivity in the affected area, lack of trust in one's physical ability and feeling that issue is now permanent state of being, and being generally sad and frustrated.
An injury can start to feel permanent after 6 weeks (...months...years) but often times people are simply unaware the depth of impairments and coping/compensation strategies they've developed so they aren't able to assess themselves objectively. It may be that an ankle or achilles issue seems to always pop up, but the client hasn't realized that they have half the range of motion compared to the opposite side, or decreased strength- so each time they're 'rested' enough to resume activity, they run into the same wall they ran into last time and injury returns. A stiff ankle is going to put more load on the achilles, and if the ankle remains stiff it doesn't matter how long you 'rest', it will still be stiff. Same goes for weakness of a muscle or tendon. In fact, prolonged 'rest' can worsen these factors and put someone further away from being able to tolerate their activities.
As a complicating factor to self-rehab, with certain chronic conditions, pain is no longer an accurate indicator of injury. For example, a tendinitis (inflammatory process) that has been present long enough will actually affect the quality of tendon tissue even after the inflammatory process has ended. Exercise and tissue remodeling can be a painful- but necessary- process to improve tendon tissue quality and enable resumption of desired exercise. If one thinks pain=injury with this, they will never perform enough remodeling exercise to actually fix the problem and alleviate the pain. This is not to say that you should push all injuries to pain in the hopes it will get better- but if you don't know when to push or not, when to allow pain or not, you may stop yourself short of eliciting the improvements necessary to finally get over the injury.
When to be more cautious with rest vs relative rest plus rehab?
Some injuries- such as a bone stress injury- are more highly volatile to overload and we need to be more careful. Even so, giving the blanketed advice of 'just rest' is lazy (or rushed) and sub-optimal, as the person can continue movement and exercise in ways that don't stress the injured bone; i.e. cross training and rehab exercises. This may be swimming instead of running in the acute phase and then progressing to strength training and cross training while weight-bearing, even before clearance for return to run.
There is always something active that can be done to speed up recovery faster than bed rest will.
Often times, activity is necessary on the path to recovery from injury.
So if you've been told by your physician or healthcare/rehab clinician that you 'just need to rest' without any further detail or direction, and this doesn't sit right with you. Contact us and find out what you can do now to get back to the things you love.