The more serious the anatomic deficiency, the smaller the margin for falling into a training error becomes. Anatomic factors work in another way. Particular types of anatomic factors tend to predispose a known array of possible injury manifestations. Acquired anatomic factors usually are represented by loss of flexibility, loss of strength, or malalignment as a result of a prior injury. These factors arise either due to neglecting to rehab after an injury or because rehab failed to restore the anatomic part to its pre-injury state.
Shoes work in the injury formula in much the same way that anatomy does.
If the shoes are optimal, the margin for falling into a training error becomes larger. If one or more of the shoe factors is present, then the margin for training error becomes smaller. Like anatomic factors, shoe factors may also predispose certain types of injury. Excessively worn out shoes fail the runner in at least two ways. First, and most obvious, is that they have lost a significant portion their shock absorbing capacity.