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? (we’ll tackle the converse question of endurance training affecting sprint performance some other time!) 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, as we saw in last week’s Toolbox, Paton and Hopkins (3) found 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 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% 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, Ma’am
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%) and muscle glycogen content (26%) 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% VO2peak power output, which jumped 100% 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 (2), this improvement in ride time to exhaustion was pretty amazing! Also, remember that the control group had zero changes to their performance.
Now probably the first objection most of you are going to raise to this study, especially if you’ve read last week’s Toolbox, 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?
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. McLellan TM, Cheung SS, and Jacobs I. Variability of time to exhaustion during submaximal exercise. Can J Appl Physiol 20: 39-51, 1995.
3. 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 at Dalhousie University, with a research specialty in the effects of thermal stress on human physiology and performance. Stephen’s company, Podium Performance, also provides elite sport science and training support to provincial and national-level athletes in a number of sports. He can be reached for comments or coaching inquiries at email@example.com.