The most basic component of training is the balance between workout duration and workout intensity. Whether you are an Olympian or a novice "how long" and "how hard" are the only two variables that can be used to produce a workout within a given sport. How these are balanced is at the heart of preparing for competition. It seems this should be simple, but it’s not. Many athletes get it wrong in their training and it’s evident on race day.
In the first couple of years that athletes are in their sport they discover that increasing workout durations and therefore volume (the sum total of workout durations for a period of time such as a week) improves their performance. They get faster by simply training with longer durations or more miles/kilometers. In fact, the rate of performance improvement at this stage is so steep that if continued long enough the athlete would eventually break a world record in their sport. But that’s rare. Something changes in these first few years.
It’s easy to think in terms of duration (and therefore weekly volume). One can determine a personal hours number and assume this is the key to building their fitness. That’s evident by how most athletes think and talk about training. Unfortunately, this way of viewing training continues well beyond the novice stage. After several years in the sport if you ask an athlete how training is going he or she will still nearly always cite volume: “Last year at this time I was training 8 hours per week and now I’m training 10.” The key to their performance simply becomes doing more duration and more volume. “If next year I can train 12 hours per week and then 14 the following year and 16 after that then I will be unbeatable.” Nearly all athletes, regardless of their levels of performance, think the key is “train longer.” After all it worked really well for the first few years so why not continue down that same path? More weekly volume becomes their focus. They reconfigure their lives in order to fit in more and longer workouts.
Very few athletes talk about their performance as a product of workout intensity. There’s a good reason for that oversight. How do you put a number on intensity? I can say I ran for one hour. That’s easy to measure and quite understandable by everyone. But how is the intensity of that one-hour run measured and expressed? That’s hard to do without getting bogged down in the details of the warm-up, work intervals, recovery intervals, and cool down. Most seem to understand that intensity is some how important, but it’s not easy to express so it’s largely ignored or at best given limited credit with a long-winded explanation. Instead, more weekly volume continues to be the key to success throughout the athlete’s career—with obvious limitations as time passes.
In the first few years in a sport there is no doubt that increased duration is effective. Train more; within the boundaries of one’s physical, mental, and time constraints; and better performances are a common result. I came to realize quite early in my coaching that an ever-increasing weekly volume was not the path to take. At some point the return on investment plateaus and may even turn downward. I found that for the advanced and experienced athlete – usually starting around the fourth year of dedicated training – the focus needs to shift toward intensity. Making such a shift often keeps the positive performance slope steep for a few more seasons.
Of course, by all of this I don’t mean that duration is unimportant. You can’t train a total of two hours per week with high intensity only and expect a personal best performance in a marathon simply because you’re in the fourth year of training. You’ve still got to put in a certain amount of volume. How much? I’ve come to think of the duration-intensity relationship as proportions of training that must somehow be balanced. To be more clear, I believe that performance on race day is roughly 60 percent determined by recent training intensity and about 40 percent by workout durations (weekly volume). That’s just my opinion from a few years of competing and coaching. I know of no research that substantiates that ratio. But there is research that supports the notion that intensity is a better predictor of performance than is duration or volume, especially in the more experienced and advanced athletes. I’ve listed some below. By clicking on the references you can read the abstracts. These studies are all around 10 to 20 years old as there seemed to be more scientific interest in the topic then (it’s now shifted more toward the balance, or “polarization,” of training intensities).
The bottom line here is that for the advanced athlete with about four or more years of dedicated and consistent training, the key to performance improvement shifts toward intensity as duration plays a somewhat lesser, but not unimportant, role. Getting that balance right is more complicated than simply doing more weekly volume. This is determined by the type of event you're training for. Getting that balance right is the key to success.
(This is also a good time to point out that on TrainingPeaks you can express the intensity of a workout just as easily as you can its duration. It’s called the Intensity Factor (IF) and is simply the workout’s normalized power/pace/speed or average heart rate divided by your functional threshold power/pace/speed/heart rate. Also by knowing the workout’s duration and IF the session’s training stress score (TSS) can also be expressed. That means that a single number gives you a pretty good idea of how much you accomplished in the workout relative to your current level of fitness. These breakthrough training metrics all come from the work of exercise physiologist Andrew Coggan, PhD.)
Lehmann, M, H. Mann, U. Gastmann, et al. 1996. Unaccustomed high-mileage vs intensity training-related changes in performance and serum amino acid levels. International Journal of Sports Medicine 17 (3): 187-192.
Midgley, A.W., L.R. McNaughton, and M. Wilkinson. 2006. Is there an optimal training intensity for enhancing the maximal oxygen uptake of distance runners?: empirical research findings, current opinions, physiological rationale and practical recommendations. Sports Medicine 36 (2): 117-132.