Interval training: taking a more moderate approach

Over the past three decades, a large body of research has confirmed that interval training is an excellent method of improving fitness and that regular sessions of interval training can produce significant fitness gains in less time and with less effort than a higher volume of steady-state endurance training^(1-4). Even better, the benefits of interval training can also be realised by amateur and recreational athletes – not just elite athletes. Indeed, recreational athletes who introduce intervals to a training schedule stand to gain even more than more advanced level athletes (who will almost certainly already be utilizing interval training in their training programs)⁽⁵⁾.

High intensity intervals

In the early days of the interval training revolution, sessions were typically 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⁽⁶⁾. 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, following landmark research by a Japanese professor called Izumi Tabata of the National Institute of Fitness and Sports in Kanoya, Japan⁽⁷⁾, which found that just 8 x repeats of very high-intensity, shorter intervals of 20 seconds’ duration could achieve excellent gains in endurance fitness, the popularity of high-intensity interval training (HIIT) mushroomed! In the years following, subsequent research confirmed that HIIT training using short intervals can be a very effective method of sharpening endurance fitness in athletes^(8-10).

A more moderate option

The term ‘HIIT’ when talking about interval training actually covers a range of interval durations and workout structures. The positive findings obtained by sessions of Tabata’s 20-second intervals has been replicated with intervals lengths from 1 minute down to as little as 10 seconds⁽¹¹⁾! As a rule of thumb however, most HIIT sessions aim to generate a training intensity that is high enough to accumulate time spent at or close to 90-95% of maximal aerobic capacity. This is because research on this topic has concluded that accumulating time at this intensity is the best way to improve oxygen uptake and endurance performance^(12-14).

However, while undoubtedly effective, there are some circumstances where a more moderate approach to interval training intensity is preferred. Although there’s no strict definition, moderate-intensity intervals generally involve performing intervals of between two and four minutes at an intensity of around 70-85% VO2max^(15,16). One example of its use is where interval training is combined with blood flow restriction of the active limbs (see this article). The goal here is to use blood flow restriction in combination with moderate-intensity intervals to generate an equivalent training effect to that of HIIT but with less physiological stress, as has been demonstrated in runners and rowers⁽¹⁷⁾. Another example is the use of moderate-intensity interval sessions in sedentary novices those who are obese, or patients with cardiovascular conditions – a training method that is generally better tolerated than HIIT yet still produces significant benefits in these populations⁽¹⁸⁾.

Moderate-intensity intervals and athletes

Because HIIT is a very effective and time-efficient method of training, there’s been very little research into the use of moderate-intensity interval training in athletes. After all, if you can perform continuous moderate-intensity training for an hour or two uninterrupted at 70-85% of VO2max, why would you break that session up by adding add periods of rest? One possible reason is that (as with the blood flow restriction example), a session of moderate-intensity intervals imposes less physiological stress than HIIT sessions, or indeed, continuous steady-state sessions. In theory, this fact could be leveraged to allow athletes to perform a block of higher-volume moderate-intensity interval training without the same accumulation of fatigue that would occur with the same volume of continuous or multiple bouts of HIIT training. But is there any evidence for this theory from real-world studies on already well-trained endurance athletes performing a training program?

New research

To date, no studies have investigated the use of moderate-intensity interval sessions by athletes as part of a training program, but a brand new study on cyclists by a team of Norwegian scientists has provided some definitive answers⁽¹⁹⁾. Published in the prestigious journal ‘Medicine and Science in Sports and Exercise’, this study compared the physiological effects of a moderate-intensity interval training (MIIT) microcycle followed by a 6-day active recovery period, with a time-matched regular training program over the same period during the general preparation phase in well-trained cyclists (see figure 1).

Figure 1: Periodization phases in a cycling season*