Similarly, surfaces such as rocky or pothole-ridden trails, soft sand, hard cement and asphalt, as well as canted roads all impose some added injury risk. In the case of canted roads, the limb on the high side of the cant is forced into greater pronation, while the low side is forced into less pronation than on completely flat surfaces. Furthermore, the cant creates pseudo limb length inequality. That temperature extremes can cause injury and illness is well known. The same holds true for other environmental factors, such as acute exposure to altitude, and exposure to smog.
Most runners know well enough to protect themselves from acute exposure.
However, runners must also take care to ward off the cumulative effects of repeated sub-acute exposure to some environmental factors. The foregoing has been an introduction to the factors that create injury and illness in runners. Knowing these factors is a good part of the battle in fending off injury and illness, training consistently, and improving your performances. However, translating this knowledge into specific preventive measures can potentially be an even more powerful weapon.