Endurance performance: can a short, sharp shock work wonders?

There’s an old adage that says “If you do what you’ve always done, you’ll get what you’ve always had.” But many endurance athletes employ the same one-pace training day in, day out only to be surprised that they (inevitably) fail to make progress. The problem is that grinding out steady-state, one-pace workouts only tend to produce performance gains in the earlier stages of training – ie in novice athletes. Once the muscles and cardiovascular system have adapted to a steady-state routine, an inevitable performance plateau that one-paced training brings is reached.

More intense option

Once adaptation to a steady-state one-pace training regime has occurred, something different is needed for further performance gains. Increasing the pace of steady state training is of course an option, but the risk is that it leaves the athlete both exhausted and injury-prone. What’s needed is a way of maintaining base endurance but lifting maximal aerobic capacity for those all important races and competitions, and one of the very best ways of achieving this is by incorporating interval sessions in a training program.

As almost every athlete and coach knows, interval training’ is a method of training that intersperses intervals of high-intensity exercise, with short periods of rest. Done right, interval training allows athletes to get larger fitness gains, faster than simply ploughing along endlessly at a steady intensity. Until comparatively recently however many interval sessions recommended by coaches were fairly daunting – for example, 8 x sets of 4 minutes on the bike performed at 90-95% maximum aerobic capacity (hard!) or 6 x 800m on the track at near race pace. Perhaps this explains why comparably few club and recreational athletes incorporated these sessions into their own programs!

Short intense intervals

In the past 10-15 years however, a large body of evidence has accumulated showing that club and recreational athletes can have most of their cake and eat it. This is thanks to the use of sessions of shorter duration, high-intensity intervals, typically employing 8-10 intervals of around 30-60 seconds’ duration often dubbed ‘high-intensity interval training or HIIT for short^(1-3).

A number of scientific studies have shown that per unit of time invested, HIIT is very effective at producing the necessary changes in muscle biochemistry for fitness and performance gains than training at a constant, one-speed pace (steady-state training). For example, one study demonstrated that 2.5 hours of sprint interval training produced similar biochemical changes in muscles to 10.5 hours of endurance training and similar endurance performance benefits⁽⁴⁾.

Meanwhile, a 2010 study found that performing 7 x 30-second sprint intervals was just as effective at increasing markers of aerobic fitness as 3 x 20-minute hard efforts despite the fact that during the latter, the total work performed was 8 times greater and the exercise duration 17 times longer than during the sprint intervals⁽⁵⁾. And just to underline the value of short intervals, a Canadian study found that a HIIT program consisting of sessions consisting of 6 intervals of just 10 seconds sprinting was still able to produce significant gains in measures of aerobic fitness⁽⁶⁾!

A short HIIT shock

There no doubt that compared to steady-state, one-pace training, the addition of HIIT to a training program brings very significant performance benefits. This is not surprising; there’s good evidence that HIIT can improve maximal oxygen consumption (VO2 max – one of the best indicators of aerobic fitness) more effectively than doing only traditional, steady-state long aerobic workouts^(7-10).

But how effective is the inclusion of HIIT for athletes who are already possess good levels of fitness and who are training using a variety of training intensities to develop even higher fitness levels? Could the addition of short burst HIIT result in additional fitness and performance gains? Specifically, could the addition of a short training segment consisting of 1-2 weeks (often referred to as a ‘microcycle’) of HIIT boost aerobic fitness and lift performance even further?

The evidence is somewhat mixed; adding a short HIIT microcycle has been observed to improve endurance performance-related variables in tennis and soccer players when that HIIT training included more high-intensity work than the control group^(11-13). In addition, studies on skiers and cyclists have shown that a HIIT microcycle can produce significant gains in maximum aerobic capacity (VO2max)^(14-16).

By contrast however, other studies investigating changes in VO2max after a HIIT microcycle have reported no significant changes compared to control conditions (where the athletes simply continued their normal training)^(17,18). But to complicate matters further, remember that VO2max, while very important, is not the only determinant of endurance performance. A key factor is the % of VO2max that athletes can sustain for long periods (ie without significant lactate accumulation in the muscles)^(19,20).

As an example, consider athlete A with a VO2 max of 64mls/kg/min who can sustain 95% of VO2 max for long periods. He/she can therefore sustain an oxygen uptake of 0.95 x 64 = 60.8mls/kg/min. Compare that to athlete B with a higher VO2max of 70mls/kg/min but who can sustain only 85% of VO2max. In that case, sustainable oxygen uptake is 0.85 x 70 = 59.9mls/kg/min. In this case, athlete B could be expected to outperform athlete A in a sustained maximal effort event.