Interval training is characterised by breaking your session into periods of higher intensity for certain durations followed by periods of recovery. The simple premise of interval training is that by breaking your training session up into periods of higher intensity exercise and recovery, you can accomplish more work at the same or higher intensity. For example, you can run 5 x 1km faster and with more intensity than you can a steady 5km with no rest.
In the late 1930s a German running coach, assisted by a cardiologist, began implementing periods of high intensity training followed by a period of recovery into their athletes’ training programs. These ‘interval’ trained athletes were soon shattering world records and the popularity of interval training was born.
But what adaptions in the athletes led to these significant improvements? The answer seems to lie within the recovery period. Immediately following a period of intense exercise your heart rate declines rapidly, however a large volume of blood in your working muscles is still returning back to your heart which results in greater filling of the left ventricle (one of the large chambers of the heart). This extra blood in the left ventricle results in an increase in stroke volume (amount of blood pumped by your heart with each beat) placing additional load on your heart and in turn, making it stronger.
With a number of recovery periods during an interval training session stroke volume peaks many times, providing a stimulus for improving maximum stroke volume and thus the capacity of the oxygen transport system.
During this recovery period there is also reduced demand for blood to the working muscles, which enables these muscles to be cleared of metabolic waste products quickly due to the elevated rate of blood flow.
Image: Rest between intervals is important
So what prescription of interval training is most effective in achieving these adaptions and improved performance? The key seems to lie in the intervals being performed at high intensity.
In 2007 Helgerud et al tested 4 different training programs in moderately trained runners;
- Long slow distance running (LSD): The first group performed a continuous run at 70% HRmax for 45 min.
- Lactate threshold running (LT): The second group performed a continuous run at lactate threshold (85% HRmax) for 24.25 min.
- 15/15 interval running (15/15): The third group performed 47 repetitions of 15-s intervals at 90– 95% HRmax with 15 s of active resting periods at warm-up velocity, corresponding to 70% HRmax between.
- 4 x 4-min interval running: A fourth group trained 4 x 4-min interval training at 90–95% HRmax with 3 min of active resting periods at 70% HRmax between each interval.
The findings… Groups 3 and 4 (high intensity intervals) improved their VO2max and stroke volume more than Groups 1 & 2 - by 7.2% in VO2max and 10% in stroke volume!
Each group was matched for the same amount of total work, leading to the conclusion that not only do you need to keep the intensity high but also that intensity of training cannot be compensated for by longer duration.
This was a study on moderately trained runners, but is interval training as effective for well trained runners? Well, yes… read on.
Image: Peter Bol in full flight training intervals
Midgley et al (2006) studied interval training in well trained runners and reported that VO2max of well trained runners can be enhanced when training protocols known to elicit 95–100% VO2max. This further supports the premise that high-intensity training may be effective or even necessary for well-trained distance runners to enhance VO2max.
No matter how well you run, if you are looking to run a new PB break up your training into shorter periods of time and go hard (95-100%)!
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A.W. Midgley, L.R. McNaughton and M. Wilkinson Is there an Optimal Training Intensity for Enhancing the Maximal Oxygen Uptake of Distance Runners? Sports Medicine. (2006) Feb. Volume 36, Issue 2, pp 117–132
Helgerud, K. Hkydal, E. Wang, T. Karlsen, P.L Berg, M Bjerkaas, T. Simonsen, C. Helgesen, N. Hjorth, R Bach, and J Hoff. Aerobic High-Intensity Intervals Improve VO2max More Than Moderate Training. (2007) Med. Sci. Sports Exerc., Vol. 39, No. 4, pp. 665–671.