Aerobic Gains: Sprint vs. Endurance Training

Adding high-intensity training during the off-season appeared to improve endurance performance, but not replace endurance training.

Whether it's tapering and peaking for a key event, a busy schedule or the approaching winter, we often need to ramp down the volume of training but worry about the loss of endurance capacity. Can short bursts of high intensity training help to maintain our endurance?

Mixing intensity

It has been a long-standing argument in both laboratory exercise research and coaching circles: How much cross-transfer is there between high-intensity training and endurance performance? And how does this happen? For a long time, the two extremes have been thought of as being mutually exclusive. Like the wings of an aircraft, if one goes up, the other must go down.

However, we find that adding high-intensity training during the off-season appeared to improve endurance performance even in elite athletes. Specifically, the survey suggested that efforts near or beyond power output at VO2max were most beneficial overall, possibly because they stimulated all the major metabolic pathways (alactic, anaerobic and aerobic.)

Hammering in Hamilton

With this theme in mind, a research group at McMaster University in Hamilton, Canada, tested the effects of very short bouts of maximal-intensity exercise on aerobic performance (1). This was an "extreme" study in that the eight subjects were relatively untrained (recreationally active) and were given an exercise program that was very minimal. At only six sessions of 4-7 maximal (Wingate) 30-s sprints spread out over 14 days, this is much less exercise than that provided in traditional exercise studies. Indeed, total exercise time over the two weeks was only about 15 min!

Before and after the 14 days, subjects were tested for their levels of citrate synthase (a key marker of aerobic metabolic activity) and the amount of muscle glycogen (another strong indicator of aerobic capacity). Both of these values are derived by taking a small muscle sample from their thighs. Their aerobic power (VO2peak) was tested, along with their time to exhaustion at a power output equal to 80 percent of their pre-study VO2peak.

Equally importantly, another eight subjects served as a control group, doing the VO2peak and ride to exhaustion before and after 14 days of their normal activity. No muscle samples were taken for ethical reasons (it's fairly obvious that no changes would be expected.)

Just the facts

As expected, no changes were observed in the VO2peak or tolerance time in the control group. However, dramatic increases in both citrate synthase activity (38 percent) and muscle glycogen content (26 percent) were seen in the experimental group despite the small dose of actual exercise.

The increase in these metabolic indicators of aerobic capacity was pretty impressive. But the biggest change was in the time to exhaustion at 80 percent VO2peak power output, which jumped 100 percent from 26 up to 51 min. This happened despite no change in VO2peak, often (and falsely) used as the key aerobic indicator in other studies.

Even given the variability in the time to exhaustion test that I reported in one of my very first scientific papers (3), this improvement in ride time to exhaustion was pretty amazing! Also, remember that the control group had zero changes to their performance.

Subject group

Now probably the first objection most of you are going to raise to this study is that this study has no relevance to competitive or elite cyclists because they used recreationally active athletes with no background in structured training. As is the case in many studies, the simple addition of ANY exercise to untrained subjects will generally result in an improvement.

No argument there, just some food for thought. In general, it is usually preferable to study elite athletes, but the primary purpose of the study is to investigate the mechanism behind the improvements that have already been previously reported, and the best way to tackle this question is to study individuals who were at a "stable" baseline of training. Oftentimes, elite athletes experience far too many fluctuations in their training status to permit a true baseline, and the effects of the experiment can easily be masked by such changes.

So the moral of this story is that there's a time and place for everything, and the best research design depends on the question being asked!

On the road

This unique aspect of this study is its use of such a small amount (15 min) of high-intensity training, spread over a relatively long (14 d) period of time. Keeping in mind that every bit of training still counts, the training in this study was so small as to be almost non-existent in the way we traditionally think of training. So what lessons from this study can we take onto the road?

  • I feel that this study further supports the previous review by Paton and Hopkins (4) that there IS a place for high-intensity training to both complement and improve endurance training. Therefore, I think we should get away from the traditional mindset that the two are exclusive and somehow harm each other.
  • The use of short high-intensity efforts is especially relevant, I feel, for situations where your training volume is decreased suddenly and for a short term. For example, if work or school smacks you with a really crazy week, you may consider focusing on maintaining the intensity of your workouts and sacrificing endurance rides.
  • Similarly, this work supports the newer idea of tapering for a big race, where the quality of the intensity training is maintained while cutting down on the total training volume. Overall aerobic capacity should not be affected by this decrease in endurance work over the short term.
  • The big caveat is that intensity work is not meant to replace endurance training over the long-term. Cycling remains an endurance-based sport, and that remains the foundation for long-term improvement and progression.

Update: Gibala et al 2006

One of the limitations of the Burgomaster et al. 2005 study (1) was that it compared one group who did the short intense training (SIT) and another group who did no exercise. While it did demonstrate that the SIT was effective compared to sitting on the couch, how does it stack up compared to a "typical" endurance training program?

In the September 2006 issue of the very prestigious Journal of Physiology, the same McMaster research group (2) set out to compare the efficacy of a two-week SIT style of training (total 2.5h spread over six sessions) with a 10.5h endurance training program. Total work performed was 630 versus 6500 kJ!

In addition to similar muscle metabolic testing as their previous study, Gibala et al. 2006 altered the style of performance testing, from a ride at set intensity to exhaustion in Burgomaster (1), to a time trial-based effort where subjects were told to complete 50 and 750 kJ of work (approximately five and 60 min efforts) as quickly as possible. I think this is a much nicer performance test, as it replicates real-life time trialing and is less affected by motivational variability. It was also nice to have two distinct efforts and different pace selection.

To summarize the findings, all tested measures (muscle glycogen, muscle buffering capacity, aerobic enzymes, time trial performance) improved with both SIT and endurance training, with essentially no differences observed when comparing the two styles.

Summary

So the McMaster group's latest study strongly confirms their previous 2005 study, and the points I made in the "On the road" section above still hold. So as we're looking towards the off-season and lots of indoor riding for many of us, keep in mind that there is a time and place for short and intense workouts.

References

    1. Burgomaster KA, Hughes SC, Heigenhauser GJ, Bradwell SN, and Gibala MJ. Six sessions of sprint interval training increases muscle oxidative potential and cycle endurance capacity in humans. J Appl Physiol 98: 1985-1990, 2005.
    2. Gibala MJ, Little JP, van Essen M, Wilkin GP, Burgomaster KA, Safdar A, Raha S, and Tarnopolsky MA. Short-term sprint interval versus traditional endurance training: similar initial adaptations in human skeletal muscle and exercise performance. J Physiol
    3. McLellan TM, Cheung SS, and Jacobs I. Variability of time to exhaustion during submaximal exercise. Can J Appl Physiol 20: 39-51, 1995.
    4. Paton CD and Hopkins WG. Effects of high-intensity training on performance and physiology of endurance athletes. Sportscience 8: 25-40, 2004.


Stephen Cheung is an Associate Professor of Kinesiology and a Canada Research Chair in Environmental Ergonomics at Brock University, with a research specialization in the effects of thermal stress on human physiology and performance. He can be reached for comments at thermal.doc@gmail.com.

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