Interval Training: How Long Should I Rest?

One of the hardest things to evaluate as a runner and coach is how much rest is needed between running intervals. Indeed, just like every individual will be able to run the intervals at different paces, each individual's recovery capacity is also unique. So why are so many workouts using a one-size-fits-all approach to recovery breaks between intervals? I believe runners should be able to customize their rest breaks to get the most from their workouts.  To help you with doing that, I have listed the most common types of interval workouts, their purpose, and how to tune in to your body and evaluate your rest.


1. Very Short Intervals Faster than Mile Pace/Sprint Intervals Workout

The intervals are less than 1k each or 4 minutes long each. The total distance covered during the intervals is less than a mile. Each interval should be run at a pace equal to or faster than your personal best for the mile.

Example: 6x100m or 4x30 seconds .

Purpose
Sprint intervals workouts lead to improvements in muscular efficiency and energy production that can also benefit endurance athletes. They do not aim at improving cardiorespiratory or cardiovascular fitness.

Evaluating Your Rest
Start with a recovery time about 8 times longer than your sprint. This means 4 minutes of rest after 30 seconds of sprinting.  Paradoxically, the better you get at sprinting, the closer to your true all-out speed you will be able to get, and the bigger your sprint/rest time ratio will be. For example, a typical competitive sprinter would need rests of 10 minutes to do 5x150m intervals at goal pace (over 90% of all-out effort). You are better off resting too much than not enough. You are also better off walking, or even just standing, during your recovery in order to replenish your muscles’ supply of phosphocreatine (a fuel used for explosive efforts). You should not be breathing hard when about to start your next interval. Studies have shown that these workouts are not good at improving cardio, so do not try to turn them into a cardio workout. Trying to sprint without proper recovery can also put you at a high risk of injury.

2. Intervals Faster than 5k Race Pace

Workout
Intervals are less than 1k each or 4 minutes long each. The total time spent running (recovery included) is between 30 and 45 minutes. The intervals should be run faster than your goal 5k race pace. If you have a heart rate monitor, you would be approaching your maximum heart rate.


Example: 8x200m or 6x1 minute at your mile pace.

Purpose
You can only become faster by running faster.  If all your workouts are done at paces equal to or slower than your most recent race pace, you cannot expect to become faster.  The purpose of this type of workout is to make your stride more efficient and, eventually, your goal 5k race pace feel easier.  These workouts can also help you increase the amount of oxygen your body utilizes when running hard: your VO2 max.

Evaluating Your Rest
Start by jogging for about the same distance that you were running. This way, you will be able to adapt to the accumulating fatigue by simply running slower, or even walk, between the intervals. Keep track of your rest times, though. It will allow you to see when you are really starting to get tired and also help you see your progress when you do the same workout again.

3. Long Intervals Faster than Race Pace for a Half-Marathon/Cruise Intervals

Workout
The intervals are usually between 800m and 3k each.The total distance covered during the fast intervals would be between 6k and 10k. The pace is your threshold pace or an approximation of it. You should feel like you would be able to hold your interval's pace for about 50 minutes (10k or a little more if your 10k PB is under 50 minutes). The perceived effort would be between 6 and 7 on a scale of 1 to 10 (10 being an all-out sprint at the end of a race). If you have a heart rate monitor, your heart rate would be between 88 and 92 percent of your maximum heart rate. 


Example: 6x1,600m at Threshold Pace.

Purpose
These are great workouts to improve your physical and mental ability to maintain and endure a greater effort intensity for progressively longer periods of time: i.e. your stamina. You will get used to the sensations linked to lactic acid buildup and learn to continue to push through that burning sensation.  Your body will learn to better deal with lactic acid and even to use it as a fuel. The benefits of these workouts are similar to that of Tempo runs, but they are mentally easier and also easier to recover from.

Evaluating your Rest
Try 1 minute of recovery for every 5 minutes spent running at your goal interval pace first. If you prefer to measure your rest in terms of distance, then jog for a third of the distance of your interval. Your rest should be short and active enough for your breathing and heart rate to be close to what it is during a half-marathon race when about to start your next interval. Keep track of your pace during your recovery. As you get better, you should be able to run faster during your recovery breaks.

4. Long Intervals Faster than Race Pace for a Marathon

Workout
These workouts are an alternative to tempo workouts. The intervals are usually longer than 1k and the total distance between 3k and 10k.

Example: 5 x 1,500m at half-marathon pace.

Purpose
When training for a marathon, you still need to regularly remind your body what it feels like to run faster than your Long Run Pace. This is essential to maintain your running efficiency and to be able to finish strong. Because these intervals are long, they also help you improve your stamina.

Evaluating your Rest
If you are used to this kind of interval training you will need about 1 minute of jogging for every 1.5k spent running at your goal interval pace. If this type of workout is new to you, you might need to double that time between intervals. Still, your rest should be short enough for your breathing and heart rate to still be close to what it is during a half-marathon race when about to start your next interval.

5. Intervals at Race Pace/ Intervals at Race Effort

Workout
The total distance covered during the fast intervals would depend on the race you are training for and where you are in your training cycle. Usually, the total distance covered and the length of each interval would increase week after week and, for 5k and 10k training, match the distance of the race a few weeks before race day. If training at 5k race pace with a heart rate monitor, your heart rate would be between 94 and 100%. For 10k race pace , your heart rate would be between 92 and 94%.

Example: 3x3.2k at 10k pace. 5x4 minutes at 5k race effort.

Purpose
Goal pace workouts a race simulations that prepare you both physically and mentally for the race. They are very important if you are about to race a new distance or a distance you have not raced in a while. They will help you remember what your stride, cadence, and breathing should feel like when going at the right pace.  If you have a good idea of the kind of effort you can maintain for 5k, doing this kind of workout based on effort (without checking your pace while running) can help you evaluate your goal pace before a race.  When you first try the goal-pace-mile workout, do two to three intervals followed by a three-to-five-minute recovery jog. As you get closer to your goal race, add more repeats and decrease the recovery period. To fine-tune your timing, include this workout in the final three weeks of training.

Evaluating Your Rest
Try a rest of about 3 minutes per 5 minutes of interval running (e.g. 2min30s of jogging after 4 minutes at 5k race effort). If you prefer to measure your rest based on distance, try jogging for about a 3rd of the distance of your interval (e.g. 200m of jogging after 600m done at 5k race pace). Your rest should become shorter and/or goal pace intervals longer workout after workout.  Indeed, this workout is preparing you to run the whole distance at that same pace without any rest at all on race day.

Conclusion

One rule that applies to all type of interval workouts is that your rest between intervals should allow you to run every interval at your goal pace until the end of the workout. If you start slowing down significantly after less than half of the workout, you will not get the expected benefits.

If you have things to add or things you disagree with, please post in the comments. I am always open to discussions.

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