New research looks at the physiological demands of low, medium high and very high-intensity training, and the implications for athlete recovery MORE
How red-hot interval training fires up performance in seasoned cyclists
Use a blend of these interval training techniques for maximum endurance gains
High-intensity interval training is known to boost endurance performance, but not much is known about which type of high-quality interval training produces the largest performance gains, especially in well-trained athletes. The optimal intensity and duration of intervals, as well as the length of the recovery period between intervals, have been largely unknown.
This lack of clarity around interval training has been particularly apparent in the field of endurance cycling. Only one published scientific study has taken a close look at interval training optimisation in endurance-trained cyclists, and the research produced somewhat perplexing results. In this lone investigation, carried out in South Africa, 20 endurance cyclists were split into five groups, each performing a different high-intensity interval workout twice a week for three consecutive weeks.
Surprisingly, this research revealed that sub-maximal intervals (8 x 4 minutes per workout at 85% of peak power output, with 90-second recoveries) produced the same improvement in 40k time-trial performance as a greater number of shorter but much more intense ‘supra-maximal’ intervals (12 x 30 seconds per workout at 175% of peak power output, with 4.5-minute recoveries). It was unclear why these supra-maximal, ‘anaerobic’ intervals improved endurance performance as much – in an event lasting about an hour – as traditional ‘aerobic’ intervals with longer duration, lower intensity and shorter recovery. And critics of the work suggested that the research needed to be repeated with a larger number of subjects in each interval-training group before they could be confident of the results.
More recently, researchers from the University of Queensland in Brisbane, Australia, have attempted to improve our understanding of the effectiveness of interval-training by examining the effects of three different high-intensity interval-training regimens on 38 highly-trained cyclists, triathletes, and duathletes. All the participants had been training for, and competing in, cycling events on a regular basis for six years, with an average weekly cycling training distance of 285k (177 miles).
In tests carried out before the actual training began, the researchers gathered information on the following variables for all athletes:
- VO2peak (the same as VO2max, measured in milliliters of oxygen consumed per kilogram of body weight per minute);
- PPO (the peak 30-second power output, in watts, produced during the VO2peak test);
- Pmax (the minimal power output – in watts – which elicited VO2peak during the progressive VO2peak-exercise test);
- Tmax (the maximal amount of time an athlete could exercise continuously at Pmax). The Tmax tests ended when athletes could no longer maintain a cycling cadence of at least 60 rpm, and the total amount of work completed during the Tmax test was calculated as the product of Pmax and Tmax;
- 40k time-trial performance.
The athletes were assigned to one of three groups, based on their 40k time-trial performances and VO2peak tests. All the athletes carried out their special high-intensity-interval workouts twice a week for four weeks, along with their usual training, and were reassessed physiologically after two and four weeks of the programme. The interval sessions were structured as follows:
- Group 1. For each interval workout, the eight cyclists in this group attempted to complete eight work intervals at Pmax (the minimal intensity that induced VO2max) for a work interval duration of 60% of Tmax, with a 1:2 recovery ratio. For example, if an athlete’s pre-training test showed he could maintain an exercise intensity of Pmax for a total duration (Tmax) of 360 seconds, his work-interval duration would be 60% of 360, ie 216 seconds. Using a 1:2 recovery ratio, his recovery intervals would last for 2 x 216 = 432 seconds. Thus, the workout would consist of 8 x 216 seconds at Pmax, with 432secs recoveries;
- Group 2. As Group 1, but with recovery time lasting only as long as it took the athletes’ heart rates to return to 65% of maximal;
- Group 3. The athletes in this group attempted to perform 12 x 30secs work intervals per session at a sizzling intensity of 175% of PPO, with 4.5-minute recoveries.
Subjects assigned to a fourth (control) group stuck to their usual moderate-intensity, base-training programme, with no added high-intensity interval training. The key differences between the three ‘active’ groups are shown schematically in the table below.
|High-Intensity Interval Workouts for Groups 1-3|
|Group||Intervals/Session||Intensity||Interval Length||Rest-Interval Length|
|1||8||Pmax||60% Tmax||120% Tmax|
|2||8||Pmax 6||0% Tmax||65% HRmax|
|3||12||175% PPO||30 seconds||4.5 minutes|
The work intervals in the active groups were so intense that the cyclists could not always complete the prescribed number of work intervals per session. In fact, Group 1 participants completed an average of just five work intervals per training session (instead of the prescribed eight), while Group 2 members finished approximately four per workout (instead of eight), and Group 3 an average of nine, rather than the recommended 12. Given that both the intensity and length of the intervals were strikingly different for Group 3, yet another variable (Wtrain – the amount of work actually completed per training session) became an important part of the analysis.
As it turned out, the athletes in Group 1 performed significantly more work over the course of the eight workouts (two per week for four weeks) than those in Group 2, who, in turn, completed significantly more than those in Group 3. These distinctions are important, because the volume of high-intensity work, which is, actually completed plays a strong role in determining how much fitness will be derived from any particular form of training.
Group 1 athletes also enjoyed considerably more recovery time between work intervals than those in Group 2 (a total of 2,028 seconds v 1,248 seconds for the eight workouts). This was, of course, because using 65% of heart-rate max as the end point of the recovery interval tended to produce shorter recoveries than using 120% of Tmax as the criterion. This could also be an important factor since, while shorter recoveries tend to keep oxygen-consumption rates higher during ensuing work intervals, the residual fatigue can make it more difficult to complete large amounts of high-quality work.
In the Tmax test completed after four weeks of training (cycling for as long as possible at Pmax), only the athletes in Group 1 were able to complete more work than in the pre-training period, possibly because of the increased amount of work they were able to complete during workouts. Athletes in Groups 2, 3 and, of course, the control group maintained their initial level of work output. By contrast, athletes in all three active groups significantly improved maximal oxygen uptake (VO2peak) in the course of the study. It might seem surprising that members of Group 3 were able to boost VO2max significantly, since their intervals were short and ‘anaerobic’ and their recovery durations long, leading to a situation in which average oxygen-consumption rates during the workouts were extremely modest.
Fast adaptation to training
However, bear in mind that the highest rate of oxygen consumption recorded during an incremental VO2max test is a function not just of the heart’s ability to work as a pump and the muscles’ ability to extract oxygen from the blood; it also reflects the ability of the neuromuscular system to generate high levels of muscular force in short periods of time – a process which can create an incredible demand for oxygen. If this concept is difficult to grasp, simply think of the heart and muscles as having reserve potential; in some cases, they may be waiting for an athlete to develop the capacity to generate unusually high muscular forces on a more-than-momentary basis, so that they can really ‘strut their stuff’ when it comes to oxygen consumption. Of course, this ability to reach very high levels of force production was enhanced by the type of supra-maximal training carried out by Group 3.
Naturally, what really matters to serious cyclists is competitive performance ability. So, how did they fare in their 40k time trials? Well, all three active groups improved on their original performances and pedaled faster over 40k than the controls at the end of the study period. In their final time trial, non-control cyclists managed to cycle about 2k per hour faster than they had done four weeks before. That represents an impressively fast adaptation, showing that the training techniques used in this research were highly productive.
So, what have we learned – and can we say that one interval-training program is really better than the others? The answer is, of course, that each type of training is associated with unique benefits. For experienced cyclists, conducting interval workouts twice a week at Pmax, with work-interval durations at 60% Tmax, can increase the amount of work it is possible to complete during high-intensity interval sessions (Group 1), boost the amount of work completed at Tmax (Group 1), boost VO2max by between 5% (Group 1) and 8% (Group 2), magnify PPO (Groups 1 & 2) and increase speed in a simulated 40k race by around 2k per hour (Groups 1 & 2) – all in just four weeks!
However, carrying out interval workouts at 175% of PPO (which happens to be about 185% of Pmax), with very abbreviated 30-second work intervals and extraordinarily long (4.5-minute) recoveries, can also provide a nice boost to seasoned cyclists. This training schedule, as performed by Group 3, increased VO2max by 3% in just four weeks, took PPO up by a similar amount in the same period of time and super-charged 40k time-trial speed by over 4%.
It is important to bear in mind, however, that the mechanisms underlying the various positive changes probably differed between the groups. We know, for example, that Group 2 athletes augmented maximal aerobic capacity slightly more than those in Group 3; yet both groups achieved equal improvements in 40k performance, suggesting that Group 3’s gains were achieved in a different way – perhaps via an enhanced muscular fatigue-resistance, improved intramuscular buffering capacity (ie an enhanced ability to soak up the surplus hydrogen ions which appear in muscle cells during very hard exercise), or an increased efficiency of exercise. Similarly, although Group 1 was able to carry out more work per workout and during the Tmax test than Group 3, the two groups performed in similar fashion.
Ditch the classic heart rate formula
Thus, it makes sense to believe that the best interval-training programme would involve blending elements of the different schemes used in this study. By combining the controlled, Pmax-type training with the close-to-maximal 175% PPO intervals, one might reasonably expect to achieve greater gains in VO2peak, PPO and performance speed than could be achieved with only one type of training. One might, for example, use a 4-6-week ‘block’ of Pmax workouts and then move into a similar-length phase of supra-max intervals; or you could simply alternate the two types of effort over a 10-12-week period. It is not clear which combined scheme would produce the greatest gains.
So what practical advice can be given to serious cyclists? There is debate about the average duration of Tmax for experienced cyclists, but in the Queensland study mean Tmax for the 38 highly-trained subjects was about 244 seconds. Thus, it would be reasonable for you to put your bicycle into a preferred racing gear, then ride as far as possible on a measured course for four minutes; (this should be done on a day when you are feeling well-recovered, and at a time when winds, rain, and other climatic problems are not likely to hamper your performance). Your average speed during this four-minute test will thus be your vVO2max (velocity at VO2max), which you can use as a surrogate for Pmax. You can then conduct intervals at this level of effort, using a work-interval duration of 60% of Tmax, or .60 x 240 = 144 seconds (2:24). Attempting eight of these intervals per workout, with double-duration (4:48) recoveries, or with recoveries that last as long as it takes to get your heart rate down to 65% of max, would be a reasonable thing to do.
At the same time, working at very close to your max intensity for 30-second work intervals (in a separate workout, of course), with long recoveries and around 12 work intervals per session, should also produce major benefits. Note that if you decide to use 65% of max heart rate to determine the duration of your recovery intervals, you must be sure what your max heart rate really is. One of the best ways to determine this is to throw away the classic 220-minus-age formula and proceed as follows: warm up thoroughly, cycle as intensely as possible for two minutes, recover with easy pedaling for one minute, and then go all-out again for another two minutes; your heart rate at the end of the second two-minute supra-max bout should be within a beat or two of maximal.
Try this simple four-minute test
As you contemplate whether to include Pmax interval training in your overall programme, it should be motivational for you to think about how large the benefits of Pmax training can be. In the study described above, the two Pmax groups hoisted VO2max by 5-8%, PPO by 5-6%, and 40k time-trial speed by 5 to 6% – in just four weeks! Over comparable time periods, other types of more-traditional (non-Pmax) interval training have generally produced 2-4% gains in PPO and 40k time-trial performance.
The high movement speeds and heavy rates of oxygen consumption associated with Pmax training are likely to be key factors underlying the hefty physiological and performance gains; it is reasonable to believe that training at VO2max is the most potent way to induce improvements in this key variable. It is also important to note that the athletes in the Queensland study performed a Pmax assessment after just two weeks of training (after only four Pmax sessions) and then adjusted their subsequent training to reflect the new and higher Pmax values. The ability to assess Pmax with a simple, non-disruptive four-minute test makes this form of training even more attractive for cyclists, since they can adjust their training every 2-3 weeks-or-so to reflect their higher states of fitness – and thus create a greater stimulus for physiological improvement.
Intervals pack a major fitness wallop
Research from other laboratories also suggests that such interval workouts pack a major fitness wallop. For example, in a study carried out in Australia and the UK, endurance runners improved Vmax by 4% and VO2max by 5% after just four weeks of Vmax training; (Vmax is the running velocity which elicits VO2max and it is thus directly comparable to Pmax, the power output which produces VO2max).
In this study, five well-trained, county-level, middle-distance athletes with good fitness (VO2max = 61 ml/kg-min) initially completed VO2max, Vmax, and 3k time trial tests and then undertook a four-week training programme consisting of two high-intensity interval workouts and one recovery run per week.
After four weeks, the same tests were repeated. The interval workouts were conducted at an intensity of Vmax, with six work intervals per workout and a recovery duration of between 60 and 75% of Tmax; (of the total of eight workouts carried out, two featured recovery durations of 60% of Tmax, three were set at 65%, one at 70% and two at 75%). The recovery run was a simple 30-minute affair, pitched at an intensity of 60% of Vmax. After four weeks of this kind of training, the athletes improved 3k time by 3% (from 10:17 to 10:00), increased Vmax itself by 4% (from 20.5 to 21.3 k/hour) and enhanced VO2max by 5% (from 61.5 to 64.5 ml/kg-min). This type of interval training was thus extremely effective: athletes should jump at the opportunity to improve Vmax by 4% with just eight quality workouts.
Memorable work by French exercise scientist Veronique Billat also provides support for the use of Vmax training. Billat found that completing just one Vmax workout per week (5 x 3 minutes at Vmax , with three-minute recoveries), along with easy running and one weekly ‘tempo’ workout (2 x 20 minutes at 85% of Vmax , with a five-minute recovery) caused Vmax to surge by 3% and running economy to improve by 6% – again in just four weeks!
In our focus on Vmax (Pmax) training, we have not intended to short-change the concept of supra-maximal training, which is also supported by scientific research. In an extremely interesting three-week study carried out at the University of Cape Town Medical School in South Africa, completing two interval workouts per week at an intensity of 175% of peak power generated a greater improvement in 40k time-trial performance (2.4%) than doing the same work at intensities of 100% or 80% of peak power.
So what’s the take-home message? A thorough understanding of the available scientific research suggests that a combination of the two types of interval training (Pmax and supra-max) will produce consistently excellent performance results for experienced cyclists and other endurance athletes. Inexperienced athletes would probably also benefit from these techniques, although they should be very careful about introducing the training into their programmes; the high speeds and intensities associated with Pmax and supra-max workouts can produce a significant amount of muscular soreness and stiffness in athletes who do not have a good foundation of sport-specific strength.
Experienced athletes, on the other hand, can use Pmax and supra-max interval workouts in almost all phases of their training – not just during the run-up to major competitions. The prudent use of Pmax and supra-max interval workouts fairly early in the training year can improve Pmax, VO2max and movement economy quite dramatically, leading to higher-quality training as the year progresses.