Creating interval workouts with the appropriate amount of time-at-intensity and recovery between efforts is an essential skill for any athlete or coach designing training plans. Individual workouts are the small building blocks that build upon one another to create training stress that leads to physiological adaptations and improved performance. Workouts don’t have to be complicated to be effective, and the most effective are usually the simplest. But they still have to be designed correctly.
A training plan critique is one of the most important practices we have in the CTS Coaching College. A plan is put on the screen, the coach provides background information. This includes the athlete’s training history, some personal history, and goals (no names). Then the coach describes the rationale for the presented plan. At that point, the coaching staff critiques the plan and the rationale. They challenge the coach to defend their decisions and they provide constructive criticism. It’s challenging, and a crucial component of professional development.
One of the most important lessons for coaches is that there are many scientifically sound and effective paths to improve athletic performance. For instance, there are several ways to increase “time-at-intensity” or “time-in-zone” as an athlete gets stronger. When it’s time to decide whether to make intervals longer or add more intervals, here are some of the principles we use and recommend.
The fundamentals of interval duration
Interval duration determines the intensity of the effort and the physiology being stressed, not the other way around. Thinking about intervals in this manner, they are at the maximum intensity you can maintain for a given time. The maximum time an athlete can sustain an effort at VO2 max is about 8 minutes. An effort that’s 20 minutes long will not be a VO2 max effort because after about 8 minutes (or less depending on fitness) components of the energy production necessary to sustain a VO2 max effort are depleted. All efforts eventually become aerobic because that is the most basic and sustainable way we produce energy.
Similarly, the highest intensity achievable for intervals that are between 8-20 minutes in duration will be at or slightly above lactate threshold power output. This is because it takes that long for reliance on anaerobic glycolysis to drop so you reach a steady state condition. When people make lactate threshold intervals too short, too much of the energy for the effort is coming from anaerobic glycolysis (i.e. the effort is not aerobic enough).
Generally speaking, the range of durations for individual intervals are:
- 20-60 seconds: Anaerobic Capacity
- 2-5 minutes: VO2 max
- 8-30 minutes: Lactate threshold
- 20-60 minutes: Tempo & Sweet Spot Tempo
- 60+ minutes: EnduranceMiles (Zone 2, aerobic endurance)
Why we start with higher number of shorter intervals?
Newer athletes or those inexperienced at a particular type of interval need to learn how to pace their efforts. Jumping straight into a 20-minute lactate threshold interval is difficult. Athletes don’t know how to predict what they’ll feel like or be able to sustain 20 minutes later. Eight-minute efforts are more manageable (we’ll sometimes start with six-minute efforts, even). Don’t worry if your pacing is off in the beginning. Athletes using short threshold intervals have tremendous room for improvement. As a result, they make gains in lactate threshold power even if the pacing is a bit off.
Intervals at the shorter end of the range are also good because new athletes can achieve higher quality efforts. That increased quality comes from more effective pacing of short intervals, and having the fitness to ride powerfully for the full duration. To increase peak power at a VO2 max, I’d rather see 5 strong 2-minute efforts than 2 mediocre 5-minute efforts. The goal is “time-at-intensity”, so if two minutes is as long as you can maintain an effort that elicits VO2 max right now, more 2-minute intervals is the way to accumulate maximum time-at-intensity.
Add intervals or make each interval longer?
OK, so after a block of training and some recovery, you’ve adapted and improved. It’s time to add more training stress to your workouts, but how? Keep the intervals the same duration and add more efforts? Or, keep the number of intervals constant and make them longer? Generally, the harder the effort, the more we start by keeping interval duration constant and increasing the number of efforts. For instance, with VO2 max intervals for moderately fit cyclists, the amount of time-at-intensity within a single workout will max out at around 15-20 minutes. Early on we use small chunks of time to get to the point where you can do 15-20 minutes time in zone. Then we may reduce the interval number and increase the duration of each, in an effort to reach the point where you can do 5-minute VO2 max efforts.
With lactate threshold and challenging aerobic intervals (Tempo and Sweet Spot Tempo), the individual intervals start out longer. As a result, adding more intervals can represent a big jump in stress. Because of this, it is harder to make rule of thumb recommendations for interval progression at this intensity. If you start with three 6- to 8-minute efforts, add time to each interval to get to 10- to 12-minute efforts. Then, depending on the athlete, go to 4 efforts but knock them back to 8-10 minutes each. Alternatively, stick with 3 intervals and add time to get closer to the goal of 20-minute individual intervals.
We’ve established there are limits to how long athletes can sustain a single effort at given intensity. Cumulative time-at-intensity during a single training session is (or should be) also limited, too. Even once you can do effective 5-minute VO2 max intervals, you can’t do an endless number of them. So, as we build individual workouts for moderately fit cyclists using variations of interval number and duration, the maximum times-at-intensities we’re looking for are:
- 3-5 minutes: Anaerobic Capacity
- 15-20 minutes: VO2 max
- 45-60 minutes: Lactate threshold
- 75-90 minutes: Tempo and Sweet Spot Tempo
- 3+ hours: EnduranceMiles (Zone 2, aerobic endurance)
Perspective, Not Prescription
Knowing how intensities and durations work together to generate training load is good for gaining perspective on the principles behind the workouts on your training plan. However, it isn’t enough to create plans that account for training history, athlete phenotype, and strengths and weaknesses. Some parts of your plan and workouts also must be specific to the demands of your goal event. This is where working with a professional coach shows its value, especially a coach who has to defend your training plan before the entire coaching staff!
By Chris Carmichael, with Coach Adam Pulford