High-intensity interval training is one of the best ways to improve fitness, health and endurance exercise performance.
To optimise intervals, we put a lot of thought into the intensity, duration and volume of the work intervals.
However, interval training is far more than just how hard you push the interval. And it’s easy to overlook one crucial part… the recovery interval.
The simple truth is:
If you want to get the most from interval training, then you must pay attention to the recovery interval. Not only will this enhance your workout, but you will achieve greater gains in aerobic capacity (VO2max) and improve exercise performance.
The problem: often I see athletes completing really high-quality intervals only to stand around for a few minutes between intervals. And most cases they’re fully recovered well before they start the next interval.
Standing recoveries have their place, and can be really beneficial during faster sprint intervals, but for most endurance workouts they are not the best approach.
One area where they can limit training is during aerobic interval training.
As you will find shortly, the way you structure your recovery can directly affect factors such as VO2max and the velocity at VO2max.
In this article we look at:
- Why the between interval recovery is so important
- Different approaches: Active vs Passive recovery
- Consider which is the best approach for different interval workouts
- The best method for different sports
- Practical implications for training
What is the recovery interval?
High-intensity intervals are structured workouts, comprising two parts:
- Work intervals
- Recovery Intervals
The recovery interval is a period of low-intensity exercise, or rest, that separates the high-intensity work intervals.
They provide a period of physical and mental recovery between the work intervals — allowing you to work harder during your work intervals.
Here, we have two different approaches:
- Passive recoveries — complete rest
- Active recoveries — low intensity exercise.
We’ll come back to those in a second.
Why is the recovery interval important?
By splitting the workout into smaller intervals, we can exercise harder than during one continuous effort.
We can also perform more total work.
Two Key points:
- The way we structure the recovery interval affects the intensity of the work intervals.
- It also influences the training effect.
One crucial factor is the intensity of the work interval — higher intensity intervals result in greater training benefits.
Meaning, we gain more from the interval workouts.
Interval intensity vs workout intensity
Here, it’s important to recognise that there’s two ways we can view the intensity of an interval training workout:
- Interval intensity — the intensity of each interval
- Average Workout intensity — the combined intensity of the interval and recovery
Both are important components that affect workout effectiveness. And both are influenced by the recovery interval.
Key point: by adjusting the recovery period, we can manipulate both the work interval, and the average intensity of the workout.
Why is that important?… Well, by modifying the recovery we can alter the training effect. And the training benefit.
- Sometimes we use longer recoveries so we can exercise harder during intervals.
- Whereas, sometimes we use quick recoveries, which increases the overall workout intensity. This is really crucial when the focus is on aerobic capacity.
Here, the duration/intensity of the recovery interval can be as important as the work interval.
One question often comes up: are active or passive recovery best for interval training?
Before taking a look at that…
What is an active and passive recovery?
- An active recovery is where you continue to exercise at a low intensity during the recovery.
- Whereas, a passive recovery involves complete rest — standing, sitting, etc.
Both have advantages and disadvantages.
Here, there are two schools of thought:
- Those in favour of passive recoveries believe they allow greater work during the intervals. The idea being more rest = higher interval intensity.
- Whilst those in favour of active recoveries believe, they speed up recovery and boost the aerobic training effect.
Regardless, there are situations where each approach is more effective — we’ll come back to that in a second.
Active recovery vs passive interval recoveries
So, what does research tell us about using an active or passive recovery during interval training?
The first point to note is the benefits of each method vary depending on the intensity, the purpose of exercise (developing speed, aerobic fitness, etc), and also the exercise type (running, cycling, swimming, etc).
Here, we’re going to look at:
- High Intensity VO2max intervals
- Short Sprint Intervals
We will start with the Aerobic Intervals.
Active Recovery is Optimal For VO2max Intervals
With high-intensity aerobic intervals, research has found active recoveries to be the most effective option because they boost the aerobic training benefit.
Why active recoveries work best for aerobic intervals…
First, researchers have shown active recoveries to increase interval performance and the aerobic energy contribution during exercise (Dorado et al., 2004).
Here, the 3 studies all used a similar training method — sets of repeated 30-second intervals at 105% maximum aerobic velocity (MAV), with either an active (50% MAV) or passive recovery.
The researchers found active recoveries were more effective for increasing VO2max and maximal aerobic velocity. This was despite completing 1/3 fewer intervals than the passive recovery group (2 sets of 10 x 30secs vs 2 sets of 15 x 30secs).
Third, active recoveries are more beneficial for increasing levels of testosterone, HGH, VEGF (a signalling protein that stimulates new blood vessel growth) than passive recovery (Wahl et al., 2014). Leading the researchers to suggest that an active recovery promotes key anabolic processes.
One point to note:
Active recoveries are physically and mentally more demanding. They lead to increased levels of the stress hormones adrenaline and noradrenaline (Abderrahmane et al. 2013). Therefore, it’s important to consider the increased training stress when using active recoveries.
- Aerobic intervals work best with active recoveries
- Active recoveries lead to greater increases in VO2 max and the maximal velocity at VO2max
- Effective approaches include repetitions of 30seconds at just above the speed, or power, at VO2max (e.g. 105-110% of vVO2max), combined with short active recoveries at 50% of VO2max.
- Example workouts include 2 sets of 10 x 30secs at 105% VO2max, 30 secs at 50% VO2max.
What about sprint intervals?…
Sprint Interval Recovery
With sprint intervals, both passive and active recoveries can be beneficial. However, the benefit depends on the sport.
We also need to consider that the primary focus of sprint intervals is to produce a high work rate during the interval.
Here, we’re not concerned about the average workout intensity.
Since sprint cycling requires significant recovery, you might expect a passive recovery to be superior.
15-30second cycling sprints
Researchers have shown that passive recoveries allow cyclists to complete more work during repeated 30 second sprints (Spierer et al. 2004; Bogdanis et al. 2016) and 6 x 30 second sprints (Lopez et al. 2014).
One caveat: passive recoveries appear to work better when completing just two sprints, whereas active recoveries work better when there are multiple sprints (Lopez et al. 2014).
Researchers (Connolly et al. 2003) observed similar results — increased peak and average power — when using 15second sprints with 3 mins of either active or passive recoveries.
5-6second cycling sprints
With very short sprints (5-6s), researchers have found contrasting results:
- In one study, very short (5s) sprint performance was lower following active recoveries (Ohya et al. 2013). Here, sprint performance was increased with short passive recoveries (25-50s). However, the researchers found that active recoveries were equally effective with longer (100s) recoveries.
- In another study (Signorile et al. 1993), short sprint performance (repeated 6s sprints, with 30s active or passive recovery) was greater when using an active recovery. The researchers commented that active recoveries were superior to passive recovery during repeated high intensity power activities.
- 15-30second sprints benefit from active recoveries
- With very short sprints (5-6s), both passive and active recoveries can be effective. However, for trained cyclists active recoveries are preferred.
With running, the limited research suggests that passive recoveries may be more effective with very short supra-maximal intervals.
Research published in the European Journal of Applied Physiology (Dupont et al. 2003), compared the effects of a passive and active recovery, on a running sprint interval session.
The research involved:
- Repeated 15 seconds intervals run at 120% maximal aerobic speed (MAS)
- The recoveries were: 15seconds of (1) passive recovery, or; (2) run at 50% of MAS.
Here, passive recoveries allowed runners to complete significantly more running intervals before exhaustion.
One point to note: Oxygen uptake was over 20% higher with the active recoveries — highlighting a much greater aerobic training benefit with the active recoveries.
We should also note that the recovery was extremely short. So we cannot say whether passive recoveries would be better when using longer recoveries.
- With running, passive recoveries are more effective for sprint intervals — especially maximum velocity and speed endurance running intervals.
- You can also combine active and passive recoveries. For example, you can combine a jog and standing recovery: jog half the recovery, then use a standing recovery for the rest.
With swimming, passive recoveries are most effective for short intervals.
Two separate studies looking at the effects of active and passive recoveries on 8 x 25m sprints (Toubequis et al. 2005; Toubekis et al., 2006), found that active recoveries decreased 25m sprint performance.
In both cases, the researchers recommended using passive recoveries for sprint swimming intervals.
Whilst a passive recovery works better between repetitions, researchers suggest that an active recovery may be effective as part of the between set recovery (Toubekis et al., 2008).
Therefore, if you’re completing multiple swimming sets, e.g. 4 sets of 5 x 100m, 30secs recovery, then the best approach appears to be:
- A passive recovery between repetitions
- Active recovery between sets
- Passive recoveries are better with swimming intervals.
- Active recoveries appear useful when used between sets.
Further Considerations: Aerobic Capacity and Interval Recovery
A further consideration is your fitness level/training experience. It turns out, your aerobic capacity (VO2max) is a crucial consideration.
As a general rule:
- Active recoveries are a better choice if you have a high VO2max.
- Passive recoveries are sometimes more suitable if you have a lower aerobic capacity.
I’ve covered this in more detail here: Why athletes with a high VO2max need shorter recoveries.
Novel approaches for different sports
Recommendations for swimming
With swimming, active recoveries are not practical. Here, we consider passive recoveries the best approach.
When the focus is on aerobic conditioning and muscular endurance, we keep the recovery periods much shorter. This helps to push up the overall workout intensity.
Whilst active recoveries are less effective between repetitions, they may be beneficial between sets.
Recommendations for cycling
In cycling, active recoveries appear to be the best and most practical option, regardless of the length or intensity of the interval.
The real advantage with cycling is its very easy to manipulate the intensity of the recovery, from very low to moderate.
- For sprint intervals, we should reduce the recovery intensity to around 30-40% of maximum aerobic power (MAP).
- With aerobic intervals aim for approximately 50% of MAP.
Recommendations for running
With running, we can use either active or passive recoveries depending on the length and the intensity of the interval. If the workout involves shorter intervals with a quick recovery — such as 12 x 200m, off 25-30secs recovery — then a standing recovery is often best.
If you’re running longer race pace intervals — such as 6 x 1km at 10k pace — then an active recovery, often works better.
The advantage here is that by using the active recovery, we increase the average intensity of the workout. This better replicates the physiological demands of racing.
Similarly, VO2 max intervals work best when combined with, active recoveries completed at 50% of the velocity at VO2max. This increases the aerobic component, boosts VO2max, and increases the velocity at VO2max.
Interval intensity is also a factor
- Active recoveries work well with aerobically focussed intervals — VO2max, 5k, 10k, Lactate Threshold, etc.
- Passive recoveries work best with faster intervals — maximum velocity, speed endurance, 800m, etc.
And with aerobic intervals, it’s not just about the interval intensity…
The average workout intensity is also crucial
This is where the choice of active and passive recovery can have a significant impact.
To illustrate just how much, look at the table below…
Here, I’ve shown how an active or passive recovery affects the average workout intensity. In this example, I’ve viewed workout intensity as the average workout pace (see column 4) — the average combined running pace of the interval and recovery.
|Interval session||Interval pace||Recovery|
Active vs passive
|Avg pace (inc recovery)|
Active vs passive rec
|6 x 1km (10k pace)||3:20/km||200m jog (60s) vs rest (60s)||3:34/km vs 4:10/km|
|5 x 1km (5k pace)||3:12/km||200m jog (90s) vs rest (90s)||3:47/km vs 4:24/km|
|5 x 1km (3k pace)||3:02/km||400m jog (180s) vs rest (180s)||4:07/km vs 5:07/km|
Active and passive recoveries are both effective during interval training.
- Active recoveries more suited to aerobic focussed intervals, longer intervals, and where the recovery duration is longer. They are also more beneficial for those with higher levels of aerobic fitness.
- For sprint intervals, passive recoveries can be a better option. Although this must be considered on a sport by sport basis.
For me, I’ve always found active recoveries to be most effective. The exception being when running sprint intervals and swimming workouts.
During cycle training, I only ever use active recovery — whether that’s with short sprints, VO2max intervals or longer threshold training intervals.
With swimming, I have only used passive recoveries — this just works better. You just need to reduce the recovery time if you’re using aerobic intervals. That said, active recoveries can work well between sets.
And as mentioned, with running training I favour active recoveries for nearly all sessions, except during sprint training, such as hill sprints, and speed endurance workouts
A crucial factor is to account for individual differences in aerobic fitness.
The key takeaways are:
- If the focus is purely on interval intensity, then use either a passive, or very low intensity active recovery.
- When the focus is on aerobic capacity, active recoveries provide the additional training stimulus to increase VO2max and the velocity or power at VO2max.
- The velocity at VO2 max
- High Intensity Interval Training
- Athletes with a higher VO2 max need shorter recoveries between intervals
- Physiology of Endurance
- Training to Improve Endurance
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