Interval Training 101 - Part Two!

If you are an endurance athlete perplexed about what to do, simply remember that if you are trying to improve VO2max, vVO2max and/or lactate threshold, you should attempt to keep recovery intervals as short as you reasonably can.

Keep Recoveries Short To Boost VO2max ///

If you are an endurance athlete perplexed about what to do, simply remember that if you are trying to improve VO2max, vVO2max and/or lactate threshold, you should attempt to keep recovery intervals as short as you reasonably can. Lengthening recoveries will tend to drive down average oxygen-consumption rates and mean levels of lactate production, effects which are counterproductive in terms of VO2max and lactate-threshold.

Let's say, for example, that a distance runner named Ben is doing a classic interval workout, 10 x 400m, and has chosen to carry out the session at a goal 5k race tempo which is four seconds per 400m faster than his current 5k pace. Since his 5k pace is 75 seconds per 400m, his interval pace will be 71 seconds per 400m. That's very reasonable, but should he use equal recoveries (71 seconds), short recoveries (30-60 seconds), or long recoveries (5-6 minutes)?

Of course, the long recoveries are attractive because they would drive down fatigue and help keep Ben on course with his planned pace during the work intervals, thus bolstering his economy at goal velocity.

The best advice, though, is that Ben should start with roughly equal - not long - recoveries and then try to shorten them a bit. By doing so, he'll produce considerably higher rates of oxygen use over the course of the workout than with the long recovery scenario, and blood-lactate profiles will also be better. Interestingly enough, he'll also be in good shape from an economy standpoint, as long as his pace doesn't drop off too much during those seventh, eighth, and ninth intervals. (We won't worry about the tenth one, since it is always - miraculously - the fastest interval of the whole workout.)

True, if Ben hits several intervals slower than 78 seconds-or-so during the second half of the workout, it's time for him to either increase his motivation and mental focus or add a little bit of fat to his recoveries. As long as he can complete the intervals in close to the planned time, however, he should hang in there with equal recoveries - and then shorten them as fitness improves and the workout becomes more manageable.

It's true that if you don't care about vVO2max and lactate threshold and simply want to improve economy, you should go ahead and use 5:1 (which in Ben's case would mean six-minute recoveries for each 71-second work interval). This would be great for the 400m runner, who has few concerns about aerobic capacity and lactate threshold. However, distance athletes do care about those key variables, and casting aside the training stimuli which help optimise them is not usually a sound practice.

Although I have focused so far on the impact of interval training on VO2max, lactate threshold and economy, it's important to recognise that interval training can also have a strong influence on the development of strength and power. I have assumed so far that interval workouts consist only of running, cycling, rowing, swimming or skiing segments at various speeds, but of course they can also include strengthening exercises.

The renowned running coach Percy Cerutty made great use of such muscle-bolstering activities, calling on runners like Herb Elliott and John Landy to carry out a variety of strengthening moves within the context of 'circuit' workouts, which also included hard-pressed runs up severe sand dunes. Elliott was never beaten in the mile or 1500m, ran a 3:59.9 mile at the age of 19 and a 3:54.5 mile just one year later, then in 1960 carried off four sub-four-minute miles in a three-week time span, just before winning the 1500m Olympic gold medal with a world-record time of 3:35.6!

Strength Movements Can Boost Race Times ///

That's anecdotal evidence, course, but Finnish researcher Laina Paavolainen recently provided strong evidence that workouts which combine high-speed running intervals with explosive strengthening movements (hops, jumps, bounds, presses etc) can significantly improve 5k race times (11).

In this study, runners who increased mileage from 45 to 70 miles per week failed to improve 5k times, while runners who remained at 45 miles but added explosive running and strength drills to their training bettered their 5k performances by around 30 seconds. In effect, the explosive group replaced 32% of the training volume of the 70-mile group with the explosive drills - almost exactly the percentage of training time which Cerutty had suggested reserving for strengthening work.

The explosively trained runners improved running economy and overall power on a high-speed treadmill test, while the 70-mile runners were unable to do so. Interestingly enough, Paavolainen's group found that max running velocity was a good predictor of 5k time, as was footstrike time (the amount of time a runner spends in the 'stance phase' of the gait cycle).

One special interval training technique involves carrying out intervals in two completely different aerobic activities within a single workout. For example, triathletes frequently perform both high-speed bike and running intervals within a single session, and even 'almost-pure' runners sometimes venture onto a bike during - or at least on the day of - a running interval workout.

The idea, of course, is that this accumulation of high-intensity aerobic work will have a greater-than-usual impact on VO2max and perhaps lactate threshold. This seems fairly sensible: for example, a 5k runner who has completed six 800m running intervals within a workout would baulk at the very idea of another leg-muscle-tearing running interval or - worse still - two or three more running intervals; but that same runner could clamber onto a bike after the sixth interval and knock off several 5-6-minute cycling intervals, without impact damage to the leg muscles and without impairing recovery.

So far research doesn't support the idea, though; in fact it suggests that such cross training is not a good way to try to boost VO2max (12). The research hasn't been carried out in an optimal way, however since it has really examined the effects of replacing one discipline with another - running training with biking, for example. Of course, when that happens the poor runner will make fewer gains in running capacity (adaptations to training are sport-specific, after all); the idea is to add intervals in a 'cross' sport to what one is already doing. Such additions have not been closely investigated but are anecdotally appealing.

If increasing the length of work intervals and reducing those of recovery intervals is a good idea, what about actual work interval intensity? Is there a certain speed which optimises fitness improvement? Should one carry out work intervals at vVO2max? At lactate-threshold speed? Halfway between vVO2max and lactate threshold? At race pace?

Do Some Workouts At Race Speed ///

These questions have been hotly debated by athletes, coaches and exercise scientists, and it is clear that it makes sense to carry out some interval workouts at - or around - actual race velocities. For example, a runner completing 1600m work intervals at her current 5k race pace will no doubt improve efficiency (economy) at this speed, making it more likely that she will be able to move up to higher velocities in future races.

In a similar vein, a runner performing work intervals at goal 5k pace (perhaps four seconds per 400m faster than current 5k pace), will find it easier to actually run at goal speed in a race because of the resulting gains in efficiency and confidence.

However, there are times when no racing is taking place, so there are no current race times available to govern training. In addition, many exercise scientists argue that it makes more sense to train at intensities which are judged optimal for producing selected physiological responses (for example, the improvement of lactate-threshold speed), since these physiological improvements will ultimately determine overall performance.

One such intensity, for example, would be vVO2max (an athlete's rate of movement when VO2max is attained). vVO2max is an outstanding predictor of performance, and a moment of reflection reveals why this is so: an athlete might have an extremely impressive VO2max but still perform rather poorly if somewhat mediocre movement speeds caused him to utilise almost all of that considerable oxygen-processing capability.

In other words, if the athlete were inefficient (ie using a lot of oxygen to sustain a mundane pace) the voluminous VO2max would be of little benefit.

Why High VO2max May Be A False Positive ///

By contrast, an athlete with a very high vVO2max can move very fast at her VO2max intensity and thus is obviously fairly efficient. In effect, the athlete enjoys the best of both worlds - a very high aerobic capacity and very great efficiency. vVO2max thus becomes a powerful predictor of performance, while VO2max and economy by themselves carry much less information and thus are less predictive. An athlete with great economy, for example, might have a poor VO2max and thus be unable to reach high speeds at VO2max; his terrific economy would thus give a 'false positive' test for good performance.

Since vVO2max is so tightly linked with success, it makes sense for endurance athletes to carry out interval workouts which have the greatest chance of optimising this variable. The noted French researcher Veronique Billat has been able to show that the best way to do this is by utilising vVO2max itself during training. Again, a moment's thought reveals why this is the case: by working at vVO2max, you improve neuromuscular coordination and efficiency while moving very fast. Most importantly, you are certain of attaining VO2max intensity within the training session, providing the optimal stimulus for VO2max to expand further.

But how do you determine your vVO2max? As I have pointed out in these pages before, you can do this quite easily: on a day when you are feeling great, simply run, cycle, swim, race-walk, row or ski as far as you can in six minutes and then compute your distance. For example, if you're a runner and you ran 2000m in six minutes, your vVO2max would be 2000/360 or 5.55m per second (72 seconds per 400m). If you ran 1600 meters in six minutes, your vVO2max would be 1600/360 = 4.44m per second (90 seconds per 400m).

In a recent study, Billat asked eight experienced runners to take part in four weeks of training which included one interval session per week at vVO2max. The athletes specialised in middle and long-distance running (1500m to half-marathon), their mean age was 24, and average VO2max was a respectable 71.2 ml/kg/min (13).

During the four-week period, the runners completed one vVO2max interval workout per week, consisting of five three-minute work intervals at vVO2max, with three-minute jog recoveries. The rest of the running during the week was easy, except for a 'lactate-threshold-improving' session, which consisted of two 20-minute work intervals at 85% of vVO2max, with a five-minute easy-jog recovery between the two intervals. Total distance covered by the runners per week was about 50 miles.

Billat's vVO2max and lactate-threshold intervals were simple - and simply devastating. After four weeks, vVO2max rose by 3% - from 20.5k/hour to 21.1k/hour. In addition, running economy improved by an astounding 6%, while heart rate at 70% VO2max dropped by 4%. Although lactate threshold held steady at 84% of vVO2max, since vVO2max was higher after four weeks, velocity at lactate threshold also increased. Almost all of the key physiological variables associated with performance had improved!

Note in particular the dramatic improvement in economy (6%) achieved by Billat's runners, an almost unheard-of increase in efficiency in well-trained competitors, especially within such a short time frame. The reason for this efficiency groundswell is that exercising at vVO2max increases leg-muscle strength and power, and enhanced strength tends to boost economy; since muscle cells are stronger, fewer need to be recruited to move at particular paces, and thus the overall 'cost' of movement is reduced.

In addition, vVO2max exertion boosts neuromuscular responsiveness and coordination far more than does lethargic pacing; and increased coordination also reduces energy expenditure.

Billat's 30-30 Regime ///

Bear in mind that Billat's interval training seems to 'bring things together' (ie boost economy, vVO2max and lactate-threshold speed simultaneously), so it's not too much of a stretch to say that it would be ideal training for the last four weeks before a major competition.

However, it is also important to do some vVO2max work at the beginning of the year, because it will kick-start fitness and improve the quality of the ensuing training. If things are proceeding correctly, of course, the speed of the vVO2max intervals will increase as time goes by. (You'll want to perform the six-minute test every six to eight weeks to obtain a new vVO2max for yourself).

Very recently, Veronique has formulated a pair of vVO2max interval sessions which lead to impressive gains in fitness. In one of the new workouts, the idea is to warm up thoroughly and then alternate just 30 seconds of moving along at vVO2max (instead of the classic but agonising three minutes) with 30 seconds of 'floating' at 50% of vVO2max (14).

In her new research on this 30-30 pattern, Billat studied eight well-trained male endurance runners whose average age was 34. Prior to the study, these athletes were running about 35-40 miles per week. Their average VO2max was a pretty decent 60 ml/min.kg-1, mean vVO2max was 18.5k/hr (a pace of 5:13 per mile), and their lactate-threshold velocity was 82% of vVO2max, or 15.2 k/hr (6:21 per mile).

Build Up To The Classic Interval ///

After these runners were evaluated for VO2max, vVO2max, and lactate-threshold running speed, they began to use the key workout: after warming up with 15 minutes of easy jogging, they alternated 30-second work intervals at 100% of vVO2max with 30-second recoveries at 50% of vVO2max, sustaining this pattern for as long as possible. For example, a runner who had a vVO2max of 20k/hr (5.55 meters per second) would run for 30 seconds at 5.55 m/second (166m) during the 30-second work intervals and about half that distance,thus achieving 50% of vVO2max, during the 30-second recoveries.

Incidentally, if you are wondering about the curious exactness of the recovery interval intensity, it is believed that hitting 50% of vVO2max 'right on the head' during recovery intervals is not that important, since the fitness gains associated with the workout come from the vVO2max work, not specifically from the recovery effort. It is important, however, for the recoveries to be run slowly and easily - at some speed reasonably close to 50% of vVO2max - so that 100% of vVO2max and not some lower intensity can be sustained during the work intervals.As it turned out, the somewhat unusual strategy of alternating 30 seconds at vVO2max with 30 seconds of floating produced an average of 19 intervals at vVO2max before exhaustion set in, 9mins 30secs of high-quality running, and a grand average of 7mins and 51secs at VO2max (83% of the total), which is considered to be excellent.

Interestingly enough, three individuals were able to complete 22-27 intervals during the 30-30 workout, with as many as 18.5 minutes completed at actual VO2max. If you are wondering how 27 30-second work intervals can lead to 18.5 minutes at VO2max (instead of 13.5 minutes or less), bear in mind that the runners often sustained VO2max during the 30-second recovery intervals, too, even though they were running at only half of vVO2max! Obviously, there was a 'physiological lag' occurring, with the runners' bodies taking longer than 30 seconds to downshift oxygen usage as running pace slowed.

The 30-30 workout is a powerhouse; and even though heart rate soars to near maximal near the end of the session, it is tolerated well even by rather inexperienced runners who tend to really struggle with the more-challenging 'classic' (5 x 3 minutes @ vVO2max). Indeed, Veronique has carried out new experimental work with modestly fit physical education students (VO2max = 54 ml/min.kg-1) showing that a twice-weekly regimen of 30-30 workouts can boost VO2max by a whopping 10% in just 8-10 weeks!

Veronique recommends using the 30-30 session early in the season to kick-start improvements in VO2max, vVO2max, lactate threshold, and running economy. Anecdotally, 30-30, even when it is carried out to the point of exhaustion (ie the point at which vVO2max can no longer be sustained for a 30-second work interval), appears to be a little easier on runners' muscles and tendons than the crueller '3-3' session (5 x 3 minutes at vVO2max, with 3-minute recoveries).

After a month or so, you can progress from 30-30 to another Billat workout, the '60-60' (60 seconds at vVO2max alternating with 60 seconds of floats, again until exhaustion). Once you have become a master of 60-60, you can then begin the classic (and much tougher) three-minute interval at vVO2max workout to further improve vVO2max, VO2max, lactate threshold, and economy - and also enhance another variable known as tlimvVO2max - the amount of time you can run continuously at vVO2max before fatigue stops you. tlimvVO2max also happens to be an excellent predictor of endurance performance in its own right.

That covers vVO2max, but which interval workouts are best for lactate-threshold improvement? Which ones are best for economy? How about pure strength?

Boosting Lactate Threshold ///

For boosting lactate threshold, you would go for interval sessions which allow you to reach VO2max for a considerable portion of the workout and which feature high rates of lactate production and appearance in the blood. Attainment of VO2max makes the heart - in the long run - a better pump and also forces muscle cells to make more energy-producing mitoc-hondria and synthesise new aerobic enzymes.

When there is a lot of lactate around, the muscles get better at clearing lactate from the blood. Combine these responses and you can achieve a dramatic lift-off in lactate-threshold speed. Interval workouts which fit the bill include Veronique's vVO2max session and another exertion in which two-minute, close-to-max bursts are alternated with about four minutes of 'coasting' at moderate intensity - recovery intervals which can be reduced in time.

For improving economy it is very hard to beat Veronique's vVO2max effort; other very good sessions would involve working at your current or goal race speeds for 2-6 minutes at a time, with initially equal recovery periods. Circuit workouts are terrific for building general and sport-specific strength, but the 'exercise intervals' within the circuits should progress over time, becoming more and more like the actual movements used in your particular sport.

Sessions which combine running and strengthening intervals can be used to promote power, too; the idea is to work not just on force production but on the rate of force production. The chosen exercises will have to be carried out at high speeds, and the running intervals will be very intense.

Part 1 | Part 2


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