Running Science

by Owen Anderson

  When endurance runners do not recover properly during training, their overall fitness is not optimized and competitive performances are subpar. Reaching an optimal state of fitness is always the result of high-quality training combined with outstanding recovery from that training. Beneficial, long-term adaptations to strenuous exercise only occur during recovery periods, not during exertion itself, and some recovery strategies increase adaptation while others slow down or even retard positive physiological changes. Furthermore, inadequate recovery can increase the risk of injury.1

  Cool-Downs

  Historically, runners and coaches have believed that a postworkout cool-down (i.e., jogging easily for 1 or 2 miles), is an important element in immediate recovery from training. According to conventional thinking, cooling down properly after a heated effort clears lactate from the blood most effectively, smoothes out the decline in body temperature associated with the cessation of training, and mellows nervous system activity so that it will be possible to rest more completely during the remainder of the day and sleep more soundly at night. Some exercise researchers have also suggested that cool-downs can enhance immune system functioning, leaving runners less vulnerable to respiratory system infections during periods of tough training.

  It is certainly correct that a cool-down produces a more gradual decline in body temperature after a strenuous exertion than does resting.2 However, no research has ever demonstrated that more temperate reductions in body heat optimize recovery processes or lead to better performances. Similarly, the link between cool-downs and stronger immune system activity is quite tenuous. There is an indication in the scientific literature that good cool-downs can lead to improved sleep.3 (See the section on sleep later in this chapter for more information.)

  The key question, however, is whether cool-downs can actually modulate recovery in a way that is performance enhancing. To find out, Thomas Reilly and M. Rigby took a look at various postexercise strategies used by two groups of university athletes.4 One group conducted an active cool-down after a soccer match and then used the same strategy during training over the course of the week leading up to a second match. No cool-down was conducted after this second match or during the following week. The second group, which had not used cool-downs after the first match or during the week following, cooled down after the second match and then used cool-downs as a recovery technique during a second week of practice.

  The cool-down contained three phases:

  Five minutes of easy jogging

  Five minutes of stretching

  Two minutes of lying in a prone position while the legs were shaken down by another player. Shaking down a leg involves gripping it by the ankle and moving it quickly in a variety of directions while the athlete relaxes and provides little resistance to movement; the goal is to reduce tightness and improve the leg’s dynamic flexibility.

  During the weeks without active cool-downs, the players simply rested in seated positions for 12 minutes after the match or following workouts.

  Immediately after competitions, performance during vertical and standing long jump tests was down for both groups compared with pregame results, presumably because of the muscle stress and lingering fatigue associated with the matches. However, the drops in jumping ability were smaller in the group that had cooled down. Athletes who didn’t cool down after a game were still unable to jump normally 48 hours afterward, while players who had cooled down returned to normal functioning during that time.

  Similarly, the deterioration in 30-meter (98 ft) sprint performance following a match was almost 50 percent greater for the group that had no cool-down compared with the group that used cool-downs. Forty-eight hours after the game, performance during a sprint-fatigue test, which included seven 30-meter (98 ft) sprints with 20 seconds of jog recovery in between, was fine for the athletes who had cooled-down but still subpar for the individuals who had only rested. Muscle soreness had almost completely disappeared in those who had cooled down within 48 hours after the match, but muscle pain increased on successive days following competition for those who had just rested after the match.

  Unfortunately, the exact mechanisms involved in producing the superior recoveries for those who had cooled down are unknown. In this study, three different cool-down techniques (jogging, stretching, and shaking) were used, and the specific role played by each of these recovery strategies is unclear.

  Myths About Cool-Downs and Lactic Acid

  A traditional view is that cool-downs are beneficial because they remove lactic acid from the blood and muscles at a more rapid rate than does rest. This supposition is based in part on research carried out by lactate researcher Arend Bonen and his colleague Angelo Belcastro who monitored blood lactate levels in well-conditioned runners after fast, 1-mile runs.5 When the athletes cooled down by jogging continuously, blood lactate concentrations returned to nearly normal levels within 20 minutes. In contrast, intermittent exercise, consisting of light calisthenics and jogging, or complete rest had much more modest impacts on lactate levels over a 20-minute postexercise period. Full rest cleared just half of the excess lactic acid in the blood in 20 minutes; intermittent exercise fared only slightly better.

  Similar results were obtained in a separate study in which athletes either jogged lightly or rested after an intense workout.6 Athletes who rested after a strenuous workout needed 25 minutes to clear half of the above-normal lactic acid from their bloodstreams, while the easy joggers need just 11 minutes to eliminate a similar quantity of lactic acid.

  Such data inspired some exercise experts to recommend rather prolonged, active cool-downs. For example, physiologist Edward L. Fox concluded that intense workouts should be followed by a minimum of 30 minutes of what he called “exercise recovery” (e. g., slow, continuous jogging).7 Fox believed that active, 30-minute recoveries could remove at least 80 percent of the excess lactic acid appearing in the blood in response to challenging running.

  Such recovery recommendations hinge on a very shaky proposition: that elevated postworkout blood lactic acid is a bad thing and thus that its rapid removal is beneficial. The truth is that unusually high blood levels of lactic acid are not deleterious in any way (refer to chapter 10 for more on the role of lactic acid during running). Lactate is a great fuel for skeletal and cardiac muscles, and thus an increased blood lactate concentration can be viewed as a good thing—an indication that fuel will be distributed widely throughout the body, to the heart, muscles, and liver, for example. Postexercise blood lactate is increased simply because the net release of lactate by the muscles during exercise has been greater than the net uptake of lactate by the sinews. This is a natural consequence of exercise conducted at an intense level (i.e., above the lactate-threshold velocity). It is not a sign that muscles are in a perilous physiological position or that lactic acid will suddenly begin attacking muscles and preventing good recovery.

  Thus, it is not logical to suggest that cool-downs are good because they reduce blood levels of lactic acid. In the two studies mentioned earlier, active cool-downs drove lactate downward because the cool-downs were carried out at an intensity below lactate threshold, leading to a situation in which lactate uptake by the muscles was greater than lactate output. In effect, the muscles were using the blood lactate as a source of energy to sustain jogging as the centerpiece of the cool-down. There is nothing about this process that would optimize recovery.

  Cool-Downs and Potential Harm to Recovery

  Exercise physiologist Dave Costill of Ball State University argued that in many cases active cool-downs can hurt the recovery process and decrease performance potential in subsequent workouts or competitions.8 Costill’s hard-to-refute reasoning is as follows:

  Runners cannot complete high-quality workouts in the best possible way unless their leg-muscle glycogen concentrations are ample.

  Many runners have trouble keeping their leg-muscle glycogen depots full on a day-to-day basis during periods of challenging training.

  A thorou
gh, active cool-down following a quality or prolonged workout will significantly expand total glycogen breakdown in the leg muscles, making it more difficult to return glycogen to top levels for subsequent training sessions.

  In contrast, inactivity (i.e., rest) following a strenuous workout accentuates glycogen storage and thus increases the likelihood that future training sessions will proceed in an optimal way.

  In fact, Costill and his Swedish research colleague Bengt Saltin discovered that up to 75 percent of the glycogen burned during a difficult workout could be restored fairly quickly to leg muscles when runners rested rather than jogged after such a workout.9 Since adequate levels of muscle glycogen are required for high-quality training and top running performances, Costill concluded that extended cool-downs should be avoided during repeated days of demanding training, meaning either intense or prolonged work.

  How is it possible to square such findings with Reilly’s research showing that cool-downs seem to boost recovery? Reilly’s cool-downs involved just 5 minutes of active effort, not enough time to put a significant dent in muscle glycogen stores. Costill’s concern was that the more extended cool-downs, such as Fox’s 30-minute sessions, could deplete large stores of carbohydrate. The take-home message for runners and coaches is that Reilly’s 5-minute cool-downs are optimal during periods of strenuous training; they produce beneficial effects with little risk of glycogen depletion. In addition, it is quite likely that an expansion of the stretching phase of Reilly’s cool-downs would be advantageous. Stretching prepares muscles for the postworkout state without using up precious glycogen fuel; in fact, some research has suggested that stretching boosts intramuscular glycogen synthesis.

  Cool-Downs and Cardiac Arrhythmia

  Some runners are concerned that the lack of an appropriate cool-down can increase the likelihood of a potentially dangerous condition called cardiac arrhythmia. However, research has shown that from a health standpoint it is perfectly acceptable to exercise lightly after an intense workout—or lie on one’s back! The real problem can occur if a runner elects to simply stand around after training ends. During strenuous exercise, blood concentrations of the key hormone noradrenaline can increase significantly. Noradrenaline is an important regulator of blood pressure; it tends to increase pressure by stimulating the heart. Noradrenaline levels can peak dramatically once intense exercise ends as a way of preventing blood pressure from falling rapidly. Unfortunately, high levels of noradrenaline have been linked with an increased risk of irregular heartbeats. Standing still after a tough workout is a bad idea because it decreases blood pressure (i.e., the leg muscles stop pushing blood upward toward the heart). More noradrenaline is released to raise blood pressure, and thus the chances of arrhythmia increase.

  In contrast, jogging, walking, or lying on one’s back during cool-down helps maintain blood pressure: Jogging and walking keep the heart rate up naturally and allow the leg-muscle pumps to do their job, while lying down makes it easier for blood to slip back to the heart since it doesn’t have to travel uphill. As a result, less noradrenaline is released following intense work, and the risk of arrhythmia is reduced.10

  Thus, brief cool-downs do not seem to increase the chances of heart problems as long as runners avoid standing around in one position following intense exercise. The available evidence suggests that abbreviated cool-downs, with 5 minutes of jogging, 5 minutes or more of stretching, and perhaps even 2 minutes of leg shake-downs, are beneficial for recovery.

  Deep-Water Running

  A nonimmediate, between-session recovery technique that has been linked with improved restoration of muscular function after intense training is deep-water running. The logical support for deep-water running as a recovery strategy is as follows: Many runners recover from demanding workouts by jogging easily on their rest days. However, this jogging, as easy as it may be, places an additional burden on already stressed muscles because sinews must still deal with the impact forces associated with jogging. Muscle membranes and filaments, already frayed from a prior, intense workout, may undergo further fraying or may be blocked from repairing damage even though the chosen running pace is quite easy.

  In contrast, there are no impact forces during deep-water running (unless the unlucky deep-water runner smacks into a pool wall during an exuberant water-sprint). The normal eccentric strains associated with running are quite mild since water resists and thus controls leg movements, preventing muscles from being stretched out explosively as they are trying to shorten. Perhaps this protection from strain allows muscles to devote more of their energies to adapting positively instead of repairing additional traumas incurred by land-based training.

  In one study carried out with 30 individuals, deep-water running was better at reducing muscle soreness and restoring muscle strength following plyometric exercise than were a variety of other recovery-enhancing strategies.11 The plyometric workout used to induce muscle soreness and dysfunction involved a series of drop-jumps from a platform 50 centimeters (20 in) high, performed once every 7 seconds until exhausted. Five different 3-day recovery strategies were used following the plyometric sessions:

  Three days of complete rest

  Complete rest on day 1 followed by 2 days of deep-water running

  Complete rest on day 1 followed by 2 days of treadmill running

  Treadmill running on all 3 days

  Deep-water running on all 3 days

  For the treadmill and deep-water recovery exercise periods, intensity was set at about 75 percent of maximum heart rate. As it turned out, the most effective way to recover exercise capacity occurred when deep-water running was undertaken on all 3 days following the plyometric workout. Deep-water running for 3 days was more effective than pure rest and also better than 1 day of rest and 2 days of deep-water running.

  Deep-water running did not prevent the delayed-onset muscle soreness that is almost certain to occur after an exhaustive plyometric session, especially when little plyometric training has been previously conducted. However, 3 days of deep-water running did lead to a quicker disappearance of overall soreness, and it produced a faster restoration of muscle strength compared with the other four strategies. Creatine kinase is a muscle cell enzyme, the appearance of which in the blood often signals muscle damage; concentrations of this enzyme peaked earlier—and at a lower value—when deep-water running was carried out for 3 days compared with the other four strategies.

  The subjects in this study reported that muscle soreness disappeared completely while they were actually running in deep water. Some soreness returned after they climbed out of the pool, but these results suggest that on the days following a very rugged workout, it might be possible to sustain higher-quality exercise while running in deep water than by running more stiffly and with more pain on a treadmill or on regular ground. The researchers reported that deep-water running allowed study participants to maintain better range of motion at the hip while working out within the time frame during which muscle soreness was present.

  The fact that muscle pain disappeared during deep-water running only to return when subjects ventured back onto dry land suggests that soreness is to at least some extent a neural phenomenon without a muscle base, that is, an array of sensations created by the nervous system primarily to curb an athlete’s appetite for and tolerance of strenuous exercise and thus prevent significant muscle damage from occurring. When the nervous system senses that no damage related to impact force will occur during an exertion, it may then turn off the pain and stiffness sensations and thus allow an athlete to exercise more strenuously.

  This study found that easy treadmill running was a poor recovery technique because it probably added additional injury to leg muscles on top of the stresses that were already present as a result of the plyometric exertions. In contrast, deep-water running, with its lack of impact forces, allowed the muscles to begin the adaptive process after the plyometric challenge.

  It is not clear why deep-water running was superior to rest, howe
ver. The subjects in the study were relatively untrained, so it is possible that the deep-water running simply constituted above-normal training, which could have increased muscular strength. This is somewhat unlikely, however, given the short duration of the study. In addition, it is not clear why deep-water running led to lower creatine kinase levels compared with rest, unless deep-water exertion upgraded creatine kinase clearance from the blood, or why deep-water running produced a reduction in overall pain levels during routine, daily activities undertaken outside of the pool.

  Nonetheless, it appears that deep-water running can be useful in many runners’ training programs. On the day(s) following a high-quality or prolonged workout, for example, a period of regular running, even at an easy pace, might augment muscle damage and block basic recovery processes. Regular running could also be psychologically taxing since it would be completed with sore, throbbing muscles and a fair amount of mental worry. On the other hand, relatively pain-free deep-water running might not interfere with recovery because it should produce no further damage. Since the deep-water running could be carried out at a fairly high intensity without interference from perceived pain, it might also lead to larger long-term gains in fitness. This possibility needs further checking by exercise scientists. It will also be interesting to see whether deep-water running has a positive effect on joint mobility during regular running.