The History of Interval Training: From Gerschler and Zatopek to Modern HIIT

Interval training is often presented as a modern invention, a product of time-poor athletes and research showing that short bouts of hard work can rival hours of steady effort. In fact, the structure is older than that. The practice of alternating hard efforts with recovery was in use, and producing world-class results, decades before the physiology that explains it was formalized. This article therefore traces that development: what the early coaches understood empirically, how laboratory science later confirmed and refined it, and how the current HIIT literature connects back to methods that are nearly a century old.

Before the Science: Fartlek and Empirical Practice

The earliest structured approach resembling interval work came from Sweden in the 1930s. Coach Gosta Holmer developed fartlek, or “speed play,” an unstructured method in which runners varied pace continuously across a run, alternating faster surges with easier running over natural terrain. It was intuitive rather than prescriptive, with no fixed work or rest periods, but it established the core idea that varying intensity within a session produced results that steady running did not.

Notably, fartlek worked without a physiological account of why. This is the pattern that recurs throughout the early history of interval training: practitioners arrived at effective methods through observation and competition results well before laboratory science could explain the mechanisms. In other words, the explanation followed the practice, not the other way around.

Gerschler and Reindell: The Freiburg Method

The first genuinely systematic interval method came from the partnership between German coach Woldemar Gerschler and cardiologist Hans Reindell at the University of Freiburg in the 1930s. Gerschler wanted a training method grounded in physiological principle rather than tradition, and Reindell provided the cardiac expertise to build one.

Their method was specific and heart-rate controlled. A runner performed efforts of roughly 30 to 70 seconds at an intensity that raised the heart rate to around 180 beats per minute, then recovered until it dropped to about 120 before beginning the next effort. The recovery was not incidental. Gerschler and Reindell believed the primary training stimulus occurred during the recovery period, as the heart rate fell from its elevated value, rather than during the effort itself. It was this emphasis on the interval between efforts that gave the method its name.

Notably, the scale of their evidence was unusual for the period. Gerschler and Reindell studied heart rate responses across roughly 3,000 subjects, each completing a defined period of heart-rate-controlled training, and reported measurable increases in heart volume within weeks. As a result, their most successful athlete, Rudolf Harbig, set world records at 800 and 400 metres that stood for years, giving the method competitive validation to match its physiological reasoning.

Zatopek: Volume and the Popularization of Intervals

If Gerschler formalized the method, it was Emil Zatopek who brought it to the world’s attention. The Czech runner trained on a high-volume interval approach, repeating fast segments many times over with short recoveries, at a training load that struck contemporaries as excessive. His response to the criticism was characteristically direct: running 100 metres twenty times amounted to two kilometres, which was no longer sprinting.

Even so, the results were difficult to argue with. At the 1952 Helsinki Olympics, Zatopek won the 5,000 metres, the 10,000 metres, and the marathon, the last on his first attempt at the distance, a feat no runner has repeated. Consequently, his success established interval training as the dominant preparation method for distance running, and demonstrated that the approach scaled to volumes far beyond what Gerschler had originally prescribed.

Meanwhile, Hungarian coach Mihaly Igloi developed his own system of running sets of short, fast repetitions, reinforcing the idea that a large accumulated volume of interval work could build both speed and stamina. By the 1950s, then, the empirical case for intervals was well established across multiple national traditions, even though the physiological case was still catching up.

Astrand and the Laboratory Confirmation

The formal physiological validation arrived in the 1960s, when Swedish physiologist Per-Olof Astrand studied interval work under controlled laboratory conditions. Using a stationary bicycle, Astrand demonstrated what coaches and runners had already established in practice: by dividing a fixed quantity of work into smaller segments separated by recovery, an athlete could complete a greater total volume at a higher intensity than continuous effort allowed.

The observation sounds self-evident, but its formalization mattered nonetheless. It gave coaches a principled basis for manipulating work duration, intensity, and recovery to target specific outcomes, rather than relying on tradition or trial and error. This, then, is the point at which interval training shifted from an empirical practice to one with an explicit physiological rationale, roughly three decades after Gerschler had first built a method around it.

The Modern Research Era Begins

The contemporary HIIT literature begins in earnest in the 1990s. Rather than replacing the older structure, it largely refines it, narrowing in on which combination of intensity, duration, and recovery best serves a given physiological target.

Tabata and the Four-Minute Protocol

In 1996, Izumi Tabata studied Japanese speed skaters and reported that a protocol of eight rounds of 20 seconds near-maximal effort with 10 seconds rest, four minutes of work in total, improved both anaerobic capacity and maximal oxygen uptake, the latter by a meaningful margin. Consequently, the Tabata protocol became shorthand for very short, very intense interval work, though it is often applied far more loosely today than the original study specified.

Gibala and Sprint Interval Training

A decade later, Martin Gibala’s group examined sprint interval training, showing that a small number of brief all-out sprints could produce metabolic and performance adaptations comparable in some respects to much larger volumes of traditional endurance training. This finding drove the popular interest in time-efficient exercise, the idea that minutes of hard work could substitute for hours of steady effort.

The Norwegian 4×4

Running parallel to the sprint-based research, the Norwegian 4×4 method developed by Jan Helgerud and Jan Hoff took a longer-interval approach aimed specifically at raising maximal oxygen uptake: four intervals of four minutes at 90 to 95 percent of maximum heart rate, separated by three minutes of active recovery. In a 2007 study, Helgerud and colleagues found this method improved maximal oxygen uptake more than moderate continuous training of matched total work, and the 4×4 remains one of the most studied protocols for developing aerobic ceiling.

Taken together, these protocols differ mainly in their targets. Short sprint work develops anaerobic capacity through very high intensity, whereas the 4×4 sustains a high but submaximal intensity to maximize time near peak oxygen uptake. Even so, both are recognizably descendants of the same principle Gerschler built his method on: alternating hard efforts with recovery produces adaptations that continuous effort does not.

What the History Shows

Overall, the through-line across nearly a century is that the structure of interval training has been remarkably stable, while the understanding of why it works has deepened in stages. First coaches established the practice empirically, then laboratory physiology confirmed and explained it, and more recently research has refined the specific combinations of intensity, duration, and recovery for particular outcomes.

For coaches, this history has a practical implication. The core variables Gerschler manipulated, namely effort intensity, work duration, and recovery, remain the levers that define an interval session today. What has changed is the precision with which their effects can be matched to a goal, whether that is anaerobic capacity, maximal oxygen uptake, or repeatable race-pace work. In short, the method has not been reinvented so much as progressively clarified.

References

1. Billat LV. Interval training for performance: a scientific and empirical practice. Special recommendations for middle- and long-distance running. Part I: aerobic interval training. Sports Med. 2001;31(1):13-31. DOI: 10.2165/00007256-200131010-00002. PMID: 11219499
2. Tabata I, Nishimura K, Kouzaki M, et al. Effects of moderate-intensity endurance and high-intensity intermittent training on anaerobic capacity and VO2max. Med Sci Sports Exerc. 1996;28(10):1327-1330. DOI: 10.1097/00005768-199610000-00018. PMID: 8897392
3. Gibala MJ, Little JP, van Essen M, et al. Short-term sprint interval versus traditional endurance training: similar initial adaptations in human skeletal muscle and exercise performance. J Physiol. 2006;575(Pt 3):901-911. DOI: 10.1113/jphysiol.2006.112094. PMID: 16825308
4. Helgerud J, Hoydal K, Wang E, et al. Aerobic high-intensity intervals improve VO2max more than moderate training. Med Sci Sports Exerc. 2007;39(4):665-671. DOI: 10.1249/mss.0b013e3180304570. PMID: 17414804
5. Seiler S, Tonnessen E. Intervals, thresholds, and long slow distance: the role of intensity and duration in endurance training. Sportscience. 2009;13:32-53.

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