When many athletes think of “doing intervals” in their triathlon training programs, they tend to have a very vague and narrow concept of what this means and limited view of how they can benefit. Typically, they believe the key to benefitting from interval sessions is simple—just push yourself as hard as you can. They also tend to narrowly associate these sessions with “speed work” that’s higher than threshold effort. Athletes with this vague and/or narrow view are missing out on huge performance gains that effective interval sessions can deliver.
Whether you’re a using a DIY triathlon training program or following one written by a coach, understanding what interval sessions are and how they’re beneficial is key to implement them correctly and reaping the rewards.
Broadly defined, interval training is a training session comprising multiple higher-intensity periods, or intervals, separated by lower-intensity recovery or rest periods. It's based on the concept that more and more effective work can be completed at the target intensity (the higher relative intensity) in interval sessions than during a constant effort at the same target intensity.
Interval training is highly productive for training at various intensities…not just super-threshold efforts. Properly constructed interval sessions can stimulate 30-100% more training response than constant-intensity sessions depending on the type of training response targeted.
Interval Session: An interval session designed to target the same training response could have been constructed like this: 4 intervals of 10-minute duration at Zone 3 effort with a 1-minute recovery between each interval. (Written as 4 x 10' (1') @ Z3 in TriDot System nomenclature.)
Comparing Sessions: In these simple examples, the short rest periods in the interval session allow the athlete to perform 6 additional minutes training at Zone 3. Considering it may take the first 20 minutes in each session training at Zone 3 to stress the athlete sufficiently to begin to trigger the desired training response, this additional 6 minutes in the interval session gives the athlete 20 minutes of productive Zone 3 training compared to just 14 in the constant-intensity session. That's nearly 50% more duration at the target effort!
• Minimum interval duration - How long must each interval be? An interval too short may not produce any stimulation at all. For example, oxidative energy production is triggered once the glycolytic system is depleted. If the session is targeting the oxidative energy system, each interval must be long enough to deplete the glycolytic system's capacity to produce energy. Only then will the oxidative system be tapped.
• Maximum interval duration - How long can (or should) each interval be? At what point do additional training stimuli (a longer interval) cease to produce a training effect? Your body only has the potential to absorb certain amounts of stimuli during each training dose. But the limits of this absorption potential shouldn't necessarily be pushed in each interval. Just because you can do longer intervals doesn't mean you should. The objective is to get the most training effect out of the entire session not just a few individual intervals. Interval durations that optimize the overall session are key.
• Minimum rest duration - How much rest is required between intervals? Depending on the training effect desired, rest periods of 10" or full recovery of up to 5 to 10 minutes may be appropriate. If rest durations are too short, your ability to perform subsequent intervals will be hindered and your training session will be cut short.
• Maximum rest duration - How much rest is too much? Many training responses require that you get your body in a specific state for the training response to be stimulated. Getting to this state may take 10-20 minutes or more. Too much rest can allow your body to fall out of that state and require an additional 10-20 minutes to resume training otherwise subsequent training will not achieve the desired training effect. In most cases such as this, once the athlete falls out of the desired physical state, the session cannot be continued but rather must be repeated at a different time.
• Rest intensity - Does the rest period consist of complete passive recovery or active partial recovery at a lower intensity? This is closely tied to the same physiological factors as minimum and maximum rest duration. For certain training responses, intensities during rest periods must be held at a specific level to maintain a physical state during the session. For others, total recovery is required for subsequent intervals to be performed at the desired level.
• Session load - How much training stimuli can your body absorb during a single session? Interval sessions that don't tax the athlete enough leave potential performance gains on the table. Those that stress the athlete too much not only fail to produce performance gains, they waste time and cause unnecessary muscle damage and hinder subsequent training sessions.
Each of these parameters is a critical factor in constructing interval sessions and vary based on the training response desired.
Here's an example of just how critical these factors are: An athlete may do 7 x 3 minutes at Zone 5 intensity thinking that they're getting 21 minutes in Zone 5 (super-threshold). Let's assume that rest periods are correct. Factor not considered: during certain super-threshold training sessions the first 2 minutes of each interval are spent getting your body to the physical state required for the training response to be stimulated. So, doing 7 x 3 minutes equates to only 7 minutes of Zone 5 training. 3 total minutes per interval – 2 minutes of priming in each = 1 beneficial minute per interval.
A better interval session construction would be 4 x 5 minutes at Zone 5. Removing the first two priming minutes from each interval, the session would equate to 12 minutes of Zone 5 training (4 x 3). This is almost double the training time at Zone 5 compared to the prior interval construction.
Using optimized interval sessions in your training is one of the key ways to produce greater gains in less time. Doing these highly effective sessions week after week produces performance gains that are otherwise unattainable.
Next time you head out for an interval session designed for you, trust that there is a method to the madness and a science to the specificity. Regardless of the session’s target intensity, implement it as written—not too hard, not too light, but just right.