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Posted: February 18, 2005
Science of Sport: Should You Use Active Or Passive Recovery Intervals?
By Owen Anderson, Ph. D. (copyright © 2003-2005)
During interval workouts, most runners jog or run easily during their recovery intervals, but is that really the right thing to do? Some coaches and runners believe that it is actually better to walk lightly during a recovery break; their contention is that walking (or even standing around in some cases) produces more complete recovery before the start of the next work interval, compared with actual running. In this view, the better recovery associated with passive intervals then leads to decreased levels of fatigue during work intervals, creating a situation in which either more work intervals can be performed per training session - or else the quality of work intervals can be improved.
While this thinking appears to be quite reasonable, it is also true that running or jogging during a recovery interval will generally keep an athlete's rate of oxygen consumption higher, compared with walking or resting. This is of course partially because muscles which are involved in running utilize oxygen at higher rates, compared with muscles which are being used to walk slowly. In addition, running during recovery might increase blood flow to key leg muscles, compared with walking, an effect which would make oxygen more readily available to the muscles during subsequent hard running. Overall, then, active recovery should lead to two very good things: (A) Oxygen consumption should shoot up to a loftier level during a work interval which follows an active recovery interval, since the rate of O2 consumption would be starting from a more-elevated point, and (B) Average oxygen consumption for the overall session should be greater with the active recoveries. Since the gain in VO2max which accrues from a specific workout is believed to be directly related to the magnitude of the oxygen consumption during the workout (1), active-recovery workouts might provide a greater stimulus for VO2max improvement.
It is sometimes said that active recovery (involving running or jogging) is great for improving workout quality because the higher level of muscular activity does a better job of decreasing blood-lactate concentrations, thus increasing the amount of time an athlete can continue working in a high-quality way. This is a red herring. It is true that active recovery seems to enhance lactate removal more effectively than passive recovery (2), and it is also true that high-blood-lactate levels are often present when an athlete becomes extremely fatigued during intense effort. However, it is not the high lactate concentrations which produce the exhaustion, and clearing the lactate away will not reduce fatigue to the slightest extent.
We know this thanks to an innovative study carried out several years ago by G. C. Bogdanis and his colleagues in the highly regarded physical-education department at Loughborough University in the United Kingdom. Bogdanis and co-workers simply asked eight male students to perform two 30-second, cycle-ergometer sprints, separated by six minutes of recovery, on two occasions (3). In one case, the subjects performed only the two bicycle sprints (the "legs" situation), and in the other the young athletes performed five minutes of very heavy arm exercise prior to engaging in the two sprints ("arms and legs"). As you might expect, the vigorous arm cranking caused blood-lactate levels to rise precipitously (to 11 mmol/Liter) just before the "arms-and-legs" sprints began. However, these lofty lactate levels had no significant effect at all on average power output during the two sprints; mean power output was just the same in the "legs" and "arms-and-legs" exertions. Lactate does not produce fatigue.
One final argument in favor of active recoveries is that since athletes do not stop running in competitions, they should not stop running during training, either. Some proponents of active recovery argue that it fosters an ability to "keep going no matter what" which ultimately improves the ability to "hang in there" during rough patches of races. This logic seems reasonable at first glance, although in truth the paces used for recoveries usually bear little resemblance to the velocities maintained in competitive situations; in this sense, active recovery really has very little specificity to racing.
There has been little good scientific research to guide us in selecting the proper type of recovery interval, but a recent study carried out by researchers from the University of Lille and the University of Artois in France offers some valuable information (4). In this French investigation, 12 young, physically active, well-conditioned (VO2max = 58 ml/kg-min) male subjects first performed graded tests to determine VO2max and vVO2max (running velocity at VO2max). They then carried out - on separate days, each time following at least 24 hours of rest - two key workouts. Both workouts involved the alternation of 15-second work intervals at 120% vVO2max (i. e., a speed which was 20-% faster than vVO2max) with 15-second recovery intervals. However, in one case the recovery intervals consisted of running at 50% vVO2max (active recovery), and in the other the recoveries involved just standing around or walking lightly (passive recovery). In both situations (active and passive recovery), the athletes attempted to complete as many work intervals as possible. Each workout was preceded by a warm-up consisting of 10 minutes of running at a speed of 10 kilometers per hour (a tempo of 9:40 per mile).
Average vVO2max of the athletes was 17.2 kilometers per hour, a pace of approximately 5:38 per mile. Thus, 120% vVO2max equaled 20.64 kilometers per hour, a tempo of about 4:41 per mile (69 seconds per 400 meters). As you can see, the athletes were covering about 84 meters during each 15-second work interval.
When the athletes utilized the passive recoveries, they were able to continue exercising for 745 seconds before they reached total exhaustion or could no longer maintain the required pace of 120% vVO2max. The 745 seconds included both the 15-second work intervals and 15-second recoveries, which meant that about 25 work intervals were completed (for over six total minutes of running at supra-vVO2max intensity).
In contrast, when the runners used the active recoveries (running their recovery intervals at 50% vVO2max, which worked out to be a rather inchmeal 2:48 per 400 meters), they kept going for only 445 seconds, completing just 15 work intervals (for less than four minutes at 120% vVO2max). The number of work intervals completed was significantly lower with the active recoveries, even though the active restorations involved running a rather paltry total of just 36 meters in 15 seconds).
Interestingly enough, both peak and average oxygen-consumption rates were not higher with active recoveries, compared with passive recovery intervals. Average oxygen consumption for the workout was 89.5% VO2max with active recovery and 85.5% VO2max for passive recovery, but this disparity was not statistically significant. Peak and average heart rates were identical for the two types of training session, and blood lactate was also very similar. The total distance run during the workout was 1763 meters with active recovery and 2077 meters with passive recovery, even though no running was carried out during the passive-recovery periods. Even more importantly, the total distance run at 120% vVO2max was vastly different, with just 1219 meters covered with active recovery and 2077 meters completed under passive-recovery conditions (a 70-% upswing). Each of the 12 subjects completed more work intervals using passive recovery, compared with active restoration.
The bottom line? For this kind of interval workout, passive recovery produced a much higher-quality session, compared with active recovery. With passive recovery, much more running was completed at the chosen, top-quality intensity (120% vVO2max), and passive recovery - contrary to expectations - did not lead to a reduction in peak or average oxygen-consumption rates or to a fall-off in heart rates. Utilizing passive recoveries is clearly the right way to carry out this workout.
Why exactly was passive recovery better? This may seem a bit perplexing, since passive recovery did not offer the runners any "breaks," as far as oxygen consumption and heart rate were concerned. A simple answer is that perhaps the passive-recovery intervals made the workout feel easier to the 12 French athletes. Perceived exertion was not measured in this study, but it is not hard to imagine a situation in which the athletes, when tired, would feel psychologically more comfortable pushing themselves to the limit for another 15-second work interval - if they knew that they could rest completely at the end of the interval, albeit for a relatively short time. The prospect of continuing to run (during recovery) after a near-maximal 15-second blast may have been tougher to handle psychologically, causing perceptions of fatigue to be magnified.
While this explanation seems plausible enough, there is an even better answer - one which is founded on basic cellular physiology. As it turns out, much of the energy required for short (for example, 15-second), near-maximal efforts is supplied within muscles by a high-energy compound called phosphocreatine. Without going into all of the gory biochemical details, we can say that phosphocreatine donates a high-energy phosphate to a chemical called ADP to make ATP, and then ATP is used directly to supply the energy for muscle contraction. Naturally, if you have a lot of phosphocreatine lying around inside a muscle, this process can occur at a high rate; energy needed for muscle contraction is thus also supplied at a high rate, and muscular power output can be great.
Now, an important thing to remember is that 15 seconds of 120-% vVO2max running will nearly wipe out the leg-muscles' stores of phosphocreatine (actually, it will probably reduce them to 15 to 20% of normal). During recovery, the muscles will struggle valiantly to restore their normal levels of phosphocreatine, so that the next work interval can be managed in a productive and powerful way. Scientific research strongly supports the idea that phosphocreatine re-synthesis is critically important for the recovery of power during repeated bouts of high-intensity exercise (5).
However, the rate of restoration of phosphocreatine probably depends on what the muscles are actually doing during recovery. If they are humming along during an active recovery period, they will be using phosphocreatine to provide the energy for jogging or moderate-speed running at the same time that they are trying to re-supply the stuff. If the muscles are allowed to be quiescent (as during a passive recovery), phosphocreatine concentrations should be restored more completely, and a runner will feel better (have more energy and power) during subsequent work intervals.
But what about those studies in which active recovery appeared to be better than passive recovery? In one such investigation, 13 male subjects carried out two maximal, 30-second, cycle-ergometer sprints, with four minutes of recovery in between, on two separate occasions (6). In one case, the recovery consisted of active cycling at 40% of VO2max, while in the other the recovery was completely passive. The active recovery resulted in a significantly higher average power output during the second sprint, compared with passive recovery; the difference was 603 Watts vs. 589 Watts, a 2-% boost. This difference was totally attributed to a 3.1-% higher generation of power during the initial 10 seconds of the second sprint; power output during the final 20 seconds of the second sprint was identical in the passive- and active-recovery cases.
So, active recovery looked better, right? One problem, though, is that the workout consisted of just two 30-second work intervals; the researchers didn't check to see how many intervals could actually be completed in the passive- and active-recovery cases. Furthermore, the comparison made in this study was not really a fair one. Since the active-recovery subjects were cycling at 40% VO2max at the ends of their active-recovery intervals, and the passive-recovery athletes were resting at perhaps just 20% VO2max at the ends of their passive-recovery intervals, the active-recovery athletes could get up to peak power much more quickly than the passive-recovery folks. This raised power output during the first 10 seconds of the work intervals for the active-recovery cyclists and made the active-recovery workout look better. However, there was nothing about passive recovery which made cyclists less able to perform their work intervals; indeed, power output over the most-fatiguing (last-20-second) portions of the work intervals was exactly the same for passive- and active-recovery athletes. If the research had been changed a little bit so that the cyclists had to cycle a fixed distance in 30 seconds, for example, the passive-recovery cyclists probably would have done just as well as the active-recovery people (or might even have done better, as in the French research). With a fixed distance to cycle, the passive-recovery cyclists would only have had to accelerate a little bit more during the first part of the work interval, compared with the active-recovery case. In fact, this is exactly what the French runners did during their 15-second work intervals at 120% vVO2max.
Note that we don't know whether passive recovery would have been superior if longer work and recovery intervals had been tested. If the athletes were using three-minute intervals at vVO2max and three-minute recoveries, would the use of passive recoveries have allowed the athletes to squeeze in one more work interval, or at least part of an additional interval? The answer to this question is unclear. The problem here is that while passive recovery should again permit greater re-synthesis of phosphocreatine, longer intervals place less of a demand on the phosphocreatine system, putting more stress on the aerobic energy-delivery system instead (the donation of phosphate from phosphocreatine to ADP to make ATP is "anaerobic," or - better stated - independent of oxygen). The key during a longer interval might not be phosphocreatine synthesis but rather the ability to deliver oxygen to the muscles and the capacity of the muscles to utilize the delivered oxygen.
There is also uncertainty about what would happen in situations in which interval workouts are not open-ended. In an open-ended interval workout, you simply perform as many work intervals as you can at a specified intensity and then quit for the day. However, many interval workouts are planned with a specified number of intervals to perform (for example, 3 X 1600 meters, 4 X 1200 meters, 6 X 800 meters, etc.). When the number of work intervals is clearly defined ahead of time, is there an advantage associated with utilizing passive recoveries, instead of active ones?
The answer is: It depends on the intensity and duration of the intervals. In the French case, for example, the runners would have failed to complete an interval workout planned as 25 X 15 seconds at 120% vVO2max if active recoveries had been part of the plan; they would have succeeded with passive recoveries. In general, as the intensity of work intervals increases (and the duration of intervals necessarily decreases), passive recovery becomes more important.
This is particularly true when work-interval intensity roams above vVO2max. At work levels above vVO2max, the phosphocreatine system becomes particularly important, since it is relied upon to supply the extra energy needed to run extra fast (oxygen can't pitch in any more energy than it already has, since vVO2max has been exceeded). Thus, the success of a workout revolving around 15- to 30-second work intervals at 120% vVO2max probably hinges on passive recoveries. On the other hand, if you lowered the intensity to 80% vVO2max, it probably wouldn't matter whether you used passive or active recoveries; the same number of work intervals could be completed.
In practical terms, any interval lasting longer than three minutes will most likely be completed at vVO2max or lower, suggesting that passive recovery will no longer be very important. In addition, any workout for which the intensity is set at vVO2max or lower will reduce the advantage associated with passive recovery.
As always, however, be sure to study yourself. Although it is not an especially common occurrence, you may find that you can perform well-defined workouts more effectively with passive recoveries, as opposed to active ones, even when the intensity of the work intervals is below vVO2max or the work-interval duration is three minutes or more ("more effectively" means that you are better able to maintain your desired pace throughout the entire work interval). Since the ability to run at a certain pace in competitive situations depends to a certain extent on the efficiency with which you run at that pace, and since such efficiency is enhanced by practicing the pace during workouts, passive recovery may be viewed as desirable if it allows you to zero in on a specific velocity.
What about RRN's very popular, lactate-stacker workout? Should passive or active recovery be used for this session?
Remember that the lactate stacker consists of going all-out for one-minute work intervals, with two-minute recovery periods consisting of easy jogging. The workout can be planned with a fixed number of work intervals (some athletes start with about six and progress to a larger number of work intervals over a period of several weeks) or on a "need-to-know" basis, in which you don't stop running until your legs tell you they can't take any more.
If you are performing the session correctly, you will be above vVO2max during your work intervals, a fact which would seem to favor passive recoveries. However, the recovery interval is twice as long as the work interval in this case, allowing more time for phosphocreatine synthesis. In addition, there's that body of scientific evidence which suggests that lactate clearance is greater during active recovery, compared with passive, and lactate clearance is certainly a good thing. Anecdotally, it appears that jogging during the two-minute recoveries does not decrease the number of one-minute work intervals which can be completed, compared with standing around, walking lightly, or reading the latest edition of The New York Times. We favor active recovery for the lactate stacker, even though it is above vVO2max. ©
(1) "The Interactions of Intensity, Frequency, and Duration of Exercise Training in Altering Cardiorespiratory Fitness," Sports Medicine, Vol. 3, pp. 346-356, 1986
To learn about Owen-Anderson's running camps in California, please send a note to Owen at firstname.lastname@example.org.
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