Almost all people who run 100 mile races on trails do squats in their training. If you ask them why, some will point out someone else who's successful who does them, some will say they tried it and it seemed to help and one or two might point out the few scientific articles that address the subject. The real reason is that they don't live next to a ski hill. These races often have a series of very long, very steep and very technical hills and these, if one is not prepared for them, can lead to the dreaded "dead quads." The way to train for them is to run hills, but that's not always possible; here, the few available hills are not runnable in winter, so some other training has to compensate. Squats and lunges simulate some of the stresses of running downhill and they don't entail the risks of barreling downhill all-out on rugged terrain - but for that same reason, they're not as useful as hill running.
The basic rules of cross-training and injury rehab are the same as they are for running:
1) Test yourself regularly, to see what you need to work on.
2) Train as specifically as possible.
3) Don't do anything you don't have to do, as you need rest as well as exercise.
Those three simple statements cover a lot. Many people race so rarely or challenge themselves in workouts so rarely that they miss point #1. Nothing helps running like running, but there are a few aids to training that one should keep in mind, but usually only are thought of when injured (#2). And you really need to ask yourself if an hour's exercise class is doing more than staying busy (#3).
My next post will be about how to decide what you need to work on and will focus on flexibility and mobility, as that's the very furthest removed from running and the first thing one needs to address in rehabbing injuries.
Lost in Space
2 days ago