Interval training is a key part of successful endurance training program.
It’s received a lot of attention from researchers. And research has been unequivocal with regards to its benefits…
Interval training improves many health and performance measures: cardiovascular fitness (VO2max), metabolic rate, blood sugar levels, blood pressure, fat oxidation, neuromuscular coordination, exercise economy and performance.
Through research we know a lot more about how to structure intervals to maximise their effectiveness.
We know which intensities work best. How they produce different training effects. We’ve learned how to optimise interval duration and volume. And we know that how we structure the recovery periods — passive recovery vs active recovery, work to rest ratio etc — is also important. I’ve covered many of these areas, on the following page: high intensity interval training (HIIT).
Whilst this provides us with insights into how to structure interval training. It’s less obvious whether all athletes gain the same benefit.
One factor is how aerobic fitness affects the effectiveness of interval training sessions? For instance:
- Do highly and moderately trained athletes gain the same benefit from intervals?
- Should they exercise at the same “relative” exercise intensity?
- And should they utilize the same recoveries?
In this article we take a look at the recovery between intervals:
- How aerobic fitness (VO2max) affects the effectiveness of interval workouts
- The implications for interval training
- How this can affect group training sessions
- Ways to assess aerobic fitness
VO2 Max and Recovery During Interval Training
One study, published in The Journal of Sports Medicine and Physical Fitness, looked to answer some of these questions. Here, researchers looked at how athletes VO2 max affected the interval training workout (Panissa et al., 2014). They wanted to know whether the runners VO2 max affected the effectiveness of the interval workout. And whether using the same interval training approach worked equally for athletes irrespective of their VO2max.
So, how did they do this?…
The athletes completed a high-intensity interval running session, comprising 1-minute intervals at the velocity of VO2max (vVO2max), separated with 1-minute standing recoveries.
During the interval workout the researchers recorded oxygen uptake to see how much time each athlete spent above 90% VO2max. They then analysed whether there was a relationship between aerobic capacity and the effectiveness of the workout — more time at near to VO2max indicated a more effective workout.
What did the researchers find?…
Runners with a high VO2 max recovered more quickly
The main finding of the study was that the runners with the highest VO2max scores accumulated less time above 90% VO2max.
The key point here is: this was despite all the athletes training at the same ‘relative’ intensity and using exactly the same interval duration and recovery.
In terms of interval intensity, they were all working as hard as each other. It’s just that the athletes with a high VO2 max were recovering more quickly than the other athletes. Here, the athletes with the highest aerobic fitness were not gaining the same training benefit (in terms of time spent near VO2max) despite the workouts being identical in terms of intensity.
The enhanced recovery is not surprising, since a high VO2 max means you can transport larger amounts of oxygen around your body. And therefore speed up the recovery between intervals.
Whilst improved recovery is an important training adaptation. Here it meant the interval workout was less effective for runners with the highest VO2 max scores.
When your fitness improves, reduce interval recovery time
In short, the recovery was too long for the runners with greater aerobic fitness. And to achieve the same training effect, they needed to use shorter recoveries.
So, in the same way that you would increase interval running speed — or power (if you’re a cyclist) — when you get fitter, you also need to adjust (reduce) the recovery duration.
Implications for Interval running training:
What does this mean for interval training?…
Firstly, a one size fits all approach isn’t the best approach. We must recognize individual differences in aerobic fitness when planning interval workouts.
For example, I like to use 1km intervals run at 10k pace, in the build up to important 10k races.
Since I have a high VO2max, I gain more from these when I keep the recoveries quite short. See 1km 10k pace running intervals for examples.
I find this works really well. And as my fitness (or 10k conditioning) improves, I look to reduce the recovery period to achieve the same training benefit. For example, I might start a training block by running the 1km intervals off a 200m recovery in 60-65seconds. And by the end of the training block i’ll run the same intervals off a 50-55 second 200m recovery.
The important point here is your fitness level — this won’t work for all runners and for some a longer recovery would work better.
With this in mind, we should tailor interval sessions — especially group interval workouts — to reflect individual differences in fitness.
Second, some interval sessions are more effective for athletes with a high VO2 max and less effective for those who maybe have a lower aerobic capacity but greater efficiency.
In practical terms:
Athletes with greater aerobic fitness should use either shorter recoveries, or use active recoveries.
If aerobic fitness is lower, then a longer recovery, or a standing recovery may be more appropriate.
Whilst this research looked at VO2max intensity, the same is likely true (and probably more so) for intensities run below VO2max, such as 5k training and 10k pace running intervals.
In particular, this has implications for group interval workouts.
Group running interval workouts
Group interval sessions often form the main quality workout for many club runners. They’re a great way to get the most out of your training.
There’s only one problem… not everyone get’s the same training benefit.
During these sessions, athletes of varied abilities often run the same intervals. And often using the same recovery duration. Whilst this works for many athletes. The research demonstrates that not all athletes will gain the same benefit. If you’re on either end of the fitness spectrum — high aerobic capacity, or lower — the training effect will be different.
For athletes, with a large aerobic capacity, the sessions often end up being too easy. And if your aerobic capacity is smaller, then these may end up too intense. With this in mind, we should try to adjust recovery periods based on individual aerobic fitness — not a straightforward task!
An important consideration… Just because two athletes have the same performance level, it doesn’t mean they have the same aerobic capacity. They might have similar race times, but one may have greater aerobic fitness, whilst the other has greater running economy.
Here, paying attention to heart rate recovery between intervals, can prove useful for checking whether recovery periods are appropriate.
Improving Group Interval Workouts
So, how can you improve group training sessions?
One approach is to get the athletes with a greater aerobic fitness, to use active recoveries. And those with lower aerobic fitness can use a standing recovery.
For example, during a group session of 800m intervals, some runners could use a standing recovery, whereas others could jog 100m down the straight and back as their recovery.
Another option is to increase the interval length for athletes with greater aerobic capacity.
How do you know if you have a high or low aerobic capacity?
As mentioned, one way is to keep a check on recovery heart rates. Athletes with greater aerobic fitness will recover more quickly (their heart rate will decrease more rapidly during the recovery period) — providing they are training at the same relative intensity.
The gold standard is a VO2 max test at an accredited sports science laboratory. This can be quite expensive, and in 2021 is currently not an option for many athletes.
Another approach is to use tests such as Jack Daniels’ VDot test, or the Cooper run test. One consideration here is these can overestimate VO2max for athletes with greater running economy. And underestimate it for those with lower running economy.
Many GPS watches now provide an estimation of VO2max, based on the relationship between running speed and heart rate. Again, this is affected by running efficiency and also training status. For example, these estimate my VO2max as higher during high volume training. This happens because of reduced exercising heart rates during high volume training. And normally returns to normal following a couple of rest days.
Another option is to consider resting and maximum heart rates — athletes with higher VO2 max scores often have lower resting heart rates and higher maximum heart rates. The following formula provides an estimation of VO2 max using the relationship between VO2 max and the ratio of maximum heart rate to resting heart rate (Uth et al., 2004).
VO2max (ml.kg.min-1) = 15 x (Maximum HR/Resting HR)
To sum this up…
Aerobic fitness plays a key role in the effectiveness of interval training.
Often the recovery gets overlooked in favour of interval intensity. By adjusting the recovery period we can increase the effectiveness of interval workouts.
To get the most out of interval training — especially when there’s an aerobic focus to the workouts — we can reduce the duration of the recovery, or switch to an active recovery. This will help to maximise the training time at VO2 max. Here, it’s important to consider an athlete’s fitness level.
For athletes with a high level of aerobic fitness, reducing the recovery period, can be the best way to increase the overall intensity and effectiveness of the workout. Helping to ensure you achieve the greatest aerobic training benefit.
For athletes, with a lower aerobic capacity, it’s crucial that recovery is long enough to maintain the correct interval intensity or speed. In this instance, passive recoveries may prove more effective.
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Panissa VL, Julio UF, Pinto-E-Silva CM, Andreato LV, Schwartz J, Franchini E. (2014) Influence of the aerobic fitness on time spent at high percentage of maximal oxygen uptake during a high-intensity intermittent running. J Sports Med Phys Fitness. 2014 Dec;54(6):708-14.
Uth N, Sørensen H, Overgaard K, Pedersen PK. Estimation of VO2max from the ratio between HRmax and HRrest–the Heart Rate Ratio Method. Eur J Appl Physiol. 2004 Jan;91(1):111-5. doi: 10.1007/s00421-003-0988-y. Epub 2003 Nov 18. Erratum in: Eur J Appl Physiol. 2005 Jan;93(4):508-9. PMID: 14624296.