This is an excerpt from Daniels' Running Formula-3rd Edition.
Racing a 5K is very different from racing a 10K, but training can be similar for both these events. In fact, racing some 5Ks will help performance in a 10K, and 10K races make a 5K seem short. As I tend to feel about all race distances, the race actually starts about two-thirds of the way through that particular event. So, in a 5K, you need to be ready to race after the first couple miles, and in a 10K the race really begins at about the 4-mile mark. Up to that two-thirds point, you need to see how relaxed you can be while still sticking with the pace (or competitors) that your plan calls for.
Both the 5K and 10K are primarily aerobic events, with most 5K races performed at about 95 to 98 percent of V∙O2max and 10Ks at about 90 to 94 percent of V∙O2max. To be sure, these are not fun intensities to hold for prolonged periods, and the mental aspect of these distances is certainly important.
In chapter 3 I discuss the physiological systems involved in running, including V∙O2max, running economy, lactate threshold, and heart rate. Both 5K and 10K runners need to make sure their training maximizes aerobic power, economy of movement, and lactate threshold, which requires a good mix of R running, I training, and T running. These types of training are all important, but some runners find more success by concentrating on one of these systems, while others may be better off emphasizing another approach. This means runners must spend a fair amount of time emphasizing each of these systems, with the idea of learning which brings the most return for the time spent doing it.
Figure 3.2 in chapter 3 shows the profiles of three female runners who all raced at about the same speed in a middle-distance event yet varied a great deal in V∙O2max and running economy. Sometimes the difference in physiological values between two runners is a function of inherent capabilities, and other times it is a result of the training that has been emphasized. In any case, each type of training must be included in the program to make sure nothing is being overlooked or underemphasized.
In the past, it was typical for runners training for a 5K or 10K race to have already spent a fair amount of time training for shorter distances before deciding to move up to a longer track event or road race. That has changed a fair bit in recent years. Many people taking up the sport today register for a 5K or 10K race, or even a marathon, as their first serious event. With this in mind, I present a couple of approaches to training for one of these longer track or popular road races.
When training for any running event, you should schedule some weeks of relatively easy running before taking on more specific workouts, and this initial period of training may have to involve a combination of walking and running. Chapter 14 outlines a conservative approach to training for a first-time marathon that also works well for a runner preparing for her first 5K or 10K event; therefore those who fit into this beginner category should consider the approach outlined in chapter 14. The programs presented in this chapter (chapter 11) apply to runners who have some running background and are interested in moving up to a slightly longer event.