Distance runners: should you be sprinting for performance?

As all regular SPB readers will know, the topic of interval training and how athletes can maximize its benefits is something we’ve reported on extensively in recent years. In short, a very large body of evidence has accumulated over the past couple of decades showing that performing regular bouts of high-intensity interval training is an extremely effective training tool for athletes seeking to maximize performance for a relatively low training workload⁽¹⁾.

In plain English, short sessions of high-intensity intervals are a great way of producing gains in aerobic fitness, enabling athletes to sustain a higher intensity/pace/workload for longer before fatigue sets in. And as we’ve also discussed in previous SPB articles, high-intensity, short-duration intervals are also a very time-efficient for the fitness gains achieved, easy to add to an endurance program, and psychologically less demanding to carry out – all of which explain why they have become so popular.

The power of sprint intervals

Traditionally, interval sessions have typically been modelled around interval lengths lasting from 2-10 minutes, with intervals of 3-5 minutes becoming a popular and well-documented method for athletes and fitness enthusiasts seeking to improve aerobic fitness and endurance performance⁽²⁾. The rationale for using 3-5 minute intervals is that there is a lag between starting a high-intensity effort and the cardiovascular system and muscles ‘catching up’ - a phenomenon that arises from the way the body responds to increase oxygen demand (more technically known as ‘oxygen kinetics’).

However, one of the key and more surprising findings to emerge from the more recent research on interval training is that very short, very high intensity intervals of 30 seconds or less duration can also be extremely effective for building fitness. This all stemmed from a landmark study by a Japanese professor called Izumi Tabata of the National Institute of Fitness and Sports in Kanoya, Japan⁽³⁾.

In short, Tabata discovered that sessions consisting of a 4-minute period of eight very hard intervals (170% of VO2 max) with a 2:1 ratio between work and rest (ie 8 sets of 20 seconds of work followed by 10 seconds of rest) was as effective at building aerobic fitness as a 1-hour session of steady-state, moderate-intensity (70% of maximum oxygen uptake - VO2 max) endurance training. Subsequent research has validated that short and intense intervals are indeed an effective tool for developing fitness, even when the interval length is as short as 10 seconds, and especially where athletes need to also develop anaerobic power⁽⁴⁾.

Sprint intervals for distance athletes?

There’s no doubting that high-intensity short (sprint) intervals are very time effective for developing aerobic fitness. But how relevant are these intervals for athletes performing over longer distances? The research here is rather unclear. A number of studies have suggested that endurance athletes can indeed significantly benefit from sprint type intervals. For example, studies show that multiple all-out sprints lasting no more than 40 seconds, with recovery periods five times longer than the sprint duration, can significantly improve the performance of endurance athletes⁽⁵⁾. Additionally, training using all-out sprints of varying durations is known to be a key loading parameter for developing aerobic power⁽⁶⁾. When using this approach, the most commonly used protocol involves performing 4 to 6 repetitions of 30-second all-out sprints, with a number of studies confirming the benefits for endurance athletes of this kind of interval session^(7,8).

Question marks

Despite these findings however, there remain doubts and question marks. It was only last month that we reported on new research comparing equal workloads of long duration interval repeats consisting of 4 x 3-minute intervals with short-duration interval repeats consisting of 24 x 30-second intervals⁽⁹⁾. Importantly, the intensities and total durations were matched between the two sessions. What emerged was that the time accumulated above 90% VO2max – a vital determinant of how effective a training session is for developing aerobic fitness - was significantly lower in the 30-second intervals compared to the 3-minute intervals (201.3 seconds in the short intervals vs. 327.9 seconds in the long), despite the intensity of the shorter intervals being higher than that of the longer intervals. Put simply, despite their lower intensity and same total interval work time, the long intervals were much more effective at generating oxygen uptakes above 90% VO2max. The ability (or lack of it) of short intense intervals to generate the high levels of oxygen uptake required for maximum development of aerobic power has also been questioned by other studies⁽¹⁰⁾.

There’s also uncertainty due to the relative lack of research on other parameters of the short/intense interval protocol, such as repetition rate, training frequency, and training period – ie what combination works best for athletes. Moreover, most high-intensity/short interval studies have been conducted in controlled laboratory environments, typically using equipment such as power bicycles or treadmills, which don’t reflect the real-world demands of athletes engaged in competition, and which also make it difficult to conduct research on a large number of subjects (what’s needed to draw more robust conclusions). As a result, there is a dearth of field-based studies that have investigated the effectiveness of short/sprint interval training protocols with real athletes in their natural training environments.

New research

To try and understand the benefits or otherwise of sprint-interval type sessions in training for distance runners in real world conditions, a team of Chinese scientists has just carried out a study investigating the effects of 6-week sprint interval training compared to traditional training on the running performance of 5,000m distance runners⁽¹¹⁾. Published in the journal Frontiers in Physiology, this study compared the effects of a carefully designed sprint-interval training protocol with traditional endurance training methods on maximum oxygen uptake (VO2max), oxygen cost of submaximal running (a measure of running economy), time to exhaustion (TTE), and timed running performance for the 100m, 400m, and 3,000m distances.