Training smarter: when less is more

Time is a major limiting factor for people seeking to perform exercise, regardless of whether they are sub-elite athletes seeking to produce their best performance in competition or sedentary individuals seeking to start an exercise programme to improve their health. Therefore a training paradigm that produces rapid improvement in both performance and health outcomes is extremely desirable. Low volume, high intensity interval training (HIT) is such a training paradigm and has been shown to induce similar metabolic and health adaptations as traditional high volume, low intensity endurance training. This is despite greatly reduced total exercise duration and energy expenditure.

14 By Dr John Babraj PhD

What is HIT? HIT is generally characterised by brief periods of repeated bursts of all-out exercise interspersed with longer periods of either passive or active recovery. The training stimulus associated with HIT, such as intensity of the interval, duration of the interval or number of repetitions, can be continually changed to suit the needs of the participant. A typical progressive two-week training regimen that has been used repeatedly in research literature (1) is shown in table 1. The total exercise duration when using this type of protocol is only 15 minutes over two weeks with a total time commitment of between 17 and 25 minutes. As well as the extremely low duration of exercise there is also extremely low energy expenditure when performing this type of exercise – approximately 250 kcal per week. A typical 30-second cycle sprint can be seen in the video. The participants bring the cycle speed up as high as they can before any resistance is added, and the aim is to maintain the speed for the full 30 seconds. As can be seen in the video, the participant’s power output decreases from approximately six seconds into the sprint as the skeletal muscles’ ability to fuel the exercise decreases. During repeated sprint training the peak power produced by the participant drops from sprint to sprint as skeletal muscle fuel stores are not fully recovered. This drop in peak power is dependent on the recovery period and evidence suggests that a minimum recovery period of four minutes is required to produce power outputs closer to the first sprint. When fuelling a high intensity sprint the skeletal muscle uses a variety of fuel stores (Figure 1). In the first six seconds of the cycle sprint the phosphocreatine and glycogen stores are predominantly used. After six seconds the phosphocreatine contribution rapidly decreases with the muscle supplying most of the energy from stored glycogen. After 15 seconds the heart has started to respond to the demands of the

TABLE 1: TYPICAL PROGRESSIVE HIT PROGRAMME Training Sprint

Session Number duration

1 2 3 4 5 6

4 4 5 5 6 6

30 sec 30 sec 30 sec 30 sec 30 sec 30 sec

Sprint Resistance Recovery (% body weight)

period

between sprints

7.5% 7.5% 7.5% 7.5% 7.5% 7.5%

240 sec 240 sec 240 sec 240 sec 240 sec 240 sec

The REPs Journal 2012;24(May):14-19