Typically when a runner suffers an injury, they back off their running volume and intensity until the injury subsides, or worse, they stop altogether, and when the injury heals jump back in risking further injury. Both methods don't lend themselves to consistency and long-term development. Then they begin to add in more miles gradually until they reach the previous levels before introducing intensity. This could take several weeks to months to bring you back to pre-injured levels.
The idea behind the run load continuum is that during an injury, you maintain the same running volume in minutes but decreased the amount of stress being placed on the body by manipulating the amount of load/stress that are occurring during the run. This will allow you to maintain fitness as you gradually increase stress to rebuild the affected area.
There are several ways we can manipulate the loading, and these can be used in combination to manage the mechanical stress placed on the body. This can also be used to bump up the volume in preparing for longer races. One way I used to do this in preparing athletes for marathons, was to do a long run and then get in the water right after and do 20 to 30 minutes of a deep water running. This would allow for a bit more volume in active recovery. I'll outline this process and then give me some examples of how you can use it.
Guidelines
1. Keep running volume ( minutes) the same as you had for the past 4 weeks.
2. Don't run back-to-back days to allow your body to recover from the stress of the workout.
3. Gradually increase the load by adjusting the type of activity in the amount of minutes you are doing.
Run load continuum (from least stressful to more stressful)
A. Deep water running
B. Walking
C. Waist-deep water running
D. Incline walking on a treadmill
E. Treadmill running (cushioned deck)
D. Outside running
Here is an example of how you can use this format.
You're coming off of an injury and your run is usually 45 minutes. Run for 20 minutes before the pain starts, stop at 20 minutes, and do the remaining 25 minutes in waist-deep water. Gradually shift the minutes on the road and lessen the waist-deep running provided you are progressing and adapting properly.
Run training does not need to be all or nothing, by having a pool and treadmill access you can keep a running volume the same interest and manipulate the stress to help you recover quicker while maintaining run fitness. A water running belt is always good to have in your tool box.