A study of Greek national calibre rowers doing 1000 m intervals was published this past March in the Journal of Sports Sciecne and Medicine
see the full text here
This is interesting because it shows us what happens when intervals are not used properly in training - and when they are used the way most athletes and coaches employ them. Only pure speed intervals are meant to be performed at 100% intensity. In this study the 1000 m repeats were at full intensity and we see the physiological result from such work.
For a more complete look at intervals and intensity see Stephen Seiler's Excellent Site
The authors looked at repeated 1000 m intervals with different rest intervals and examined the recovery after it in terms of power output and the heart rate response. Obviously power output is what we are looking for on the water and heart rate is of interest because many coaches and athletes use heart rate as an indicator of recovery and when to begin their next interval (depending upon the training effect that they are looking for).
Interval training comes in many flavours, with work to rest ratios varrying from 1:1 for aerobic intervals to 1:3 or more for anaerobic intervals.
This study used rest intervals of varrying lengths up to 6 minutes, which would work out to approximately 1:2 ratio. This is a length of recovery used by many coaches and outwardly it would appear that athletes are generally recovered after this period.
What a coach tries to accomplish in an interval session can vary. Traditionally, a 1:1 ratio is used for aerobic intervals. It is expected that recovery will be incomplete, but the athletes can work at a higher intensity that they normally would be able to doign steady state work.
Ratios may be manipulated so that athletes work at or just above the lactate threshold to work on their ability to clear lactate and maintan higher intensites duing sustained exercise.
Pure speed training on the other hand requires complete recovery. The goal is to deplete the system and train its abiltiy and capacity of recovery.
What did they find?
Recovery was incomplete even after 6 minutes of rest. In fact in the second 500 meters of the pieces there was NO EFFECT of the recovery time.
Unless the recovery was very short, no change was seen in the heart rate response during the next interfval.
What does this mean for me?
- Doing 1000-m intervals with 6 minutes or less rest will result in incomplete recovery.
- You can expect decreases in power output even in just the second interval.
- 6 minutes rest or less will not be pure speed work - it will train lactate clearance as recovery is incomplete.
- If your goal is complete recovery between intervals, more than 6 minutes rest is required.
This study did not examine the effect of the intensity of the interval. The intervals were "all-out" which is what many athletes do, but is not the preferred way to do interval training. This may be the key information here. Working at 100% - well above VO2 max - for intervals of 3 minutes duration and then trying for full recovery isn't focussed on anything in particular. Is it speed training? No - the recovery isn't enough. Is it anaerobic threshold training? No - the intensity is too high to come close to repeating performance even in the second interval.
More information is available:
Stephen Seiler's Site