There are two schools of thought concerning tempo runs, aka extended runs done at or above your lactate threshold, the point at which your muscles produce too much lactic acid for your muscles to absorb + clear, causing your muscles to feel weary (among other tired effects).
As your fitness improves, the pace at which you hit your lactate threshold should get faster. This can allow you to run farther at faster paces. For any race distance beyond a sprint this is of course very important.
The traditional school of thought is that tempo running at or above the threshold strengthens your muscles’ ability to clear excess lactic acid, and therefore your threshold will increase over time.
Another school of thought is that a lot of aerobic running at a sub-threshold pace over time will increase that threshold, plus higher intensity running at shorter bursts will improve your running economy and in turn that threshold.
Who’s right? To some extent both camps are right. The question is which camp’s approach is most beneficial.
