Nothing boosts a runner’s confidence quite like logging a huge track session. Its flashy, its
technical, and it makes you feel like you’ve accomplished a great deal with one workout. In all honesty, it’s not unreasonable to think “if I want to run faster, I should just run faster in practice, right”?
While speed work can be an important part of your running, it is only one facet in a much larger picture of fitness. Though it serves an important function, there are several reasons why speed work is not as important as your think.
#1- You Need Aerobic Fitness
First and foremost, it makes up a relatively small percentage of your overall fitness. It is the icing on the cake. The peak of the pyramid. Your running is not pulled up by your top speed the same way a mountain is not formed from the peak down. It is pushed up from the bottom, through a strong aerobic base and highly-conditioned lactic threshold. As a distance runner, focusing on 400m speed makes little difference if you don’t have the aerobic capacity to run strong over the entire race distance as well. Aerobic fitness is the summative fitness of multiple metabolic systems or “zones”, with each relying heavily on its related antecedent systems. The better fitness you have in each prior zone, the higher the potential for each subsequent zone becomes, including top-end speed. Sprint work can make an impressive difference, but only if you have built the appropriate aerobic base to support it. It should serve as a way to refine and build on aerobic strength rather than a way of making up for an insufficient base. In other words,
speed should be done in addition to, not in place of.
#2- Law of Diminishing Returns
Additionally, it is not beneficial to work speed for more than 30 or 40 days. While athletes doing speed work may see considerable improvement in the first few weeks, for most athletes it only takes 3-4 weeks of focused speed work to maximize the benefits to these systems. Though there is not a hard, fast expiration date on speed, the fact remains the same that you can only work these systems for a relatively short amount of time before you simply stops seeing improvement. Beyond this point, the narrow margin of returns simply do not justify the added stress of the work and trying to force additional speed sessions can lead to chronic fatigue, injury, and burnout.
#3- Better Workout Options
Conversely, high-end aerobic work like long runs, steady states, and
progressive tempos can be done practically year round while continuing to see progress. Even threshold work like tempos and cruise intervals can be done for several months while continuing to see improvement. This type of work builds your aerobic base, improving efficiency, strength, and running economy while pushing the vLT (lactic threshold) up from the bottom. Focusing the majority of your training on building a strong aerobic engine will yield better results than focusing on speed, especially as your race distance increases.
#4- Specificity Matters: Train The Right Systems
The types of runs you do should revolve around the race(s) you intend to run. Each race
distance places unique energy demands on your body, requiring it to use multiple metabolic systems in specific ratios in order to meet the demands of the distance. In other words, each race is going to place a different emphasis on different training zones. This means that our training should reflect the energy demands of our races. The fact of the matter is speed work may not even be relevant to your race distance! The ratio of work we do in our build up to a race should mimic the ratio of energy pathways used in that race, so if 90% of your race is aerobic the vast majority of your work should focus on improving aerobic strength. There is little benefit in spending any focused amount of time working outside that energy system as it accounts for such a small percentage of your race (in other words, a small amount of time). You will shave significantly more time by being able to hold a faster pace aerobically than by trying to kick it in hard the last mile or so. For example, while running repeats at Vo2Max pace or faster would be useful for someone whose focus is mile to 5k, a marathoner would see little to no benefit from this type of work because they simply do not utilize that system during their race. Instead of relying on speed, marathoners rely on a massive aerobic engine and so nearly all of their work should focus on building aerobic strength and efficiency through high-end aerobic work like steady states, tempos, and long runs. Additionally, working systems which have little-to-no benefit to your race takes away time which could otherwise be spent working the more relevant systems.
While speed work can be an important part of your running, it is only one facet in a much larger picture of fitness. Perhaps the best way to explain the role of speed work is this: speed work helps us to squeeze the most out of our training to hit short-term targets while high-end aerobic work gives us the strength to achieve long-term goals.