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The Science of Performance |
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Running and Muscle Damage
It is well known that running can cause muscle soreness, muscle damage, and reduced muscle function. From the newest beginner to the most experienced of runners, virtually all runners frequently experience the muscle pain associated with running. It is also well known that unaccustomed exercise and intensity causes the most pain and discomfort, while repeated exercise bouts provide protection against the extremes of muscle soreness and pain. Repeating a workout generally results in either significantly less or no post exercise soreness. These facts are generally interpreted to mean that the ability to withstand a particular load increases with training and that recovery time is subsequently shortened. From a training perspective this means that a beginning runner will be able to handle much less volume and intensity than a more experienced runner. For example, a beginner might struggle to run 20 miles per week while a seasoned veteran runner might routinely run 60+ miles per week. There is no doubt that the body’s capacity increases with training. A training load that initially is very hard becomes much easier with improvements in fitness and capacity. As the body improves with training, runners are typically advised to gradually increase the total training volume. Indeed, modern training wisdom generally suggests that a primary training goal should be to increase weekly mileage to as much as 100 miles per week in order to maximize performance. Modern training wisdom does not suggest that simply running 100 miles per week will result in maximum performance - it does recognize that other factors are necessary for best performance. However, conventional wisdom does suggest that performance cannot be maximized in the absence of high weekly running mileage. Said another way, conventional wisdom suggests high weekly training mileage is necessary but insufficient for maximum performance. This raises the question as to whether the body recovers faster as its capacity increases. Does recovery time decrease with increases in capacity and fitness? Does little to no post run muscle soreness indicate that the running muscles have been stressed less? Can runners safely increase training volume over time due to both increases in capacity and shortened recovery time? This is the subject we will be addressing today. Research Does your body recover faster as your performance improves? To examine this question, let’s take a look at two studies in particular that examined muscle damage and running. In the first study, researchers examined the changes in muscles of 29 runners during an 18-20 month training period (1). The second study examined the effect of running distance on muscle damage in 24 untrained subjects (2). Here is what they discovered. In the first study, researchers recruited 29 subjects who had never before run further than 12 km. Additionally, none of these subjects had ever competed in a distance running race either. The subjects commenced an 18 month training program that culminated with the running of a marathon. Training was divided into 3 phases of 6, 5, and 7 months respectively with training distance gradually increased during the entire training period. During the first training period of 6 months the subjects never ran further than 12 km in training and the period concluded with a 15 km road race. In the second period of 5 months the maximum distance run in training was 22 km (3 times) and the period concluded with a 25 km road race. During the final training period of 7 months the training distance and intensity were increased in a wavelike manner and in the last 6 weeks the subjects twice ran 32 km at a mild intensity. This period ended with the subjects running a standard 26.2 mile marathon. Five days before, shortly after, and 8-9 days following each race a muscle biopsy was taken from the thigh muscles of the subjects and examined for indices of muscle damage. In the second study, researchers divided 24 healthy, untrained subjects into two groups who ran either 10 or 20 km. Muscle biopsies were taken from the thigh muscles of the subjects one week before, 15 minutes after, and 48 hours following the run and examined for indications of muscle damage. Additionally the subjects were also tested for thigh muscle strength prior to, immediately after, and 1,2,3,7, and 14 days after the run. Eight of the subjects in the 10 km run group then entered a 10 week training program. Training consisted of running 3 days per week, beginning at a weekly run distance of 12.5 km in the first week and peaking at 29 km in week 10, an average increase of just 1.65 km per week. The subjects completed 10 km runs at least twice in the last weeks of the training program. At the end of the training program the subjects completed another 10 km run and underwent additional muscle biopsies and thigh muscle strength tests. Results Both research studies revealed some interesting findings. In the first study that examined runners during an 18 month marathon training program, muscle damage increased steadily throughout the training program. The first evidence of muscle damage showed up following the 15 km race. As the training and racing distance increased, the incidence of muscle damaged increased also, reaching its highest level at the end of the final phase. This is not to say, however, that all the runners experienced the same amount or timing of muscle damage. Only one runner exhibited muscle damage after the 15 km road race. After the 25 km road race, 13 runners had evidence of muscle damage. By the time the runners had completed the marathon, all 29 runners exhibited evidence of muscle damage. Additionally, the type of muscle damage was not the same for all runners, with different runners showing different abnormalities. Interestingly, the amount of muscle damage just prior to a race was equal to the damage observed immediately following the race, despite the higher intensity of running during the road races. Also, damage was found in all muscle fiber types with no single fiber type showing a greater percentage of damage than the other fiber types. The researchers concluded “that long-distance running is associated with transient minor pathological changes in skeletal muscle, which are related to the total distance covered per week rather than the intensity of the exercise.” The second study, which compared the extent of muscle damage resulting from a 10 or 20 km run and muscle damage following a 10 week training program, had several significant findings. Muscle damage was evident from both the initial 10 and 20 km runs. However, there was significantly more muscle damage in the 20 km runners than those who ran just 10 km. Additionally, thigh strength, which was tested prior to and up to 14 days following the runs, decreased the same amount for both groups after the run – approx. 15%. Thigh strength did not return to pre-run levels until 3 - 7 days following the run (at 3 days the 10 km group had recovered to approx. 96% pre-run strength, while the 20 km group had recovered to approx. 93% of pre-run strength. At day 7 the 20 km group had recovered to approx. 98% pre-run strength). Upon completion of the 10 week training schedule, the subjects were tested again for running performance, muscle damage and thigh strength. 10 km run time decreased an average of 4:15 min:sec. Despite the significant improvement in 10 km performance, there was no significant decrease in the amount of muscle damage or the loss of thigh strength. Muscle damage and strength loss were very nearly the same at the end of the 10 week training program as they had been at the beginning of the training program. In addition to muscle damage and strength loss being the same pre and post training, it also took the same amount of time to recover muscle strength. Muscle strength took 3 days to return to pre-run levels, the exact same amount of time it took to recover strength prior to the 10 week training program. The conclusion reached by the researchers? “The degree of muscle damage depends on running distance and a significant Ca2+ accumulation in muscle is seen after 20 km (author’s note: Ca2+ is an indicator of muscle damage). Ten weeks of endurance training does not influence Ca2+ homeostasis and muscle damage after 10 km running.” In other words, training did not decrease the amount of muscle damaged incurred by running 10 km. Discussion The first thing we learn from these studies is that muscle damage is more a function of running distance than intensity. An increase in either the weekly running distance or in the distance of the single longest run results in an increase in muscle damage. Increasing muscle damage with increasing long run distance provides a muscular explanation for a common training recommendation. In distance running, especially in marathon training programs, the recommended timing between long runs increases with the length of the long run. For example, an average runner training for a marathon would typically be advised to complete a long run each week until the length of the long run reaches 12 miles. At distances of 12 miles and further the runner is advised to complete a long run every two weeks. At distances beyond 18 miles the runner is then advised to run long once every three weeks. The reason for this advice is that from experience runners and coaches have learned that the longer the run the more time it takes to recover from that run. These studies show us that as the running distance increases, so too does the incidence of muscle damage. In both studies longer running distances resulted in more muscle damage. The more damage done, the longer it takes to recover, hence the recommendation for increasing the timing between increasingly longer runs. The second observation is the seemingly surprising result that the 10 week training program did not provide any protection from muscle damage. I say this is surprising because most training programs suggest that runners can safely increase their weekly training distance if it is done gradually, plus some research studies have also suggested that training provides some protection against muscle damage. This study seems to contradict both of these. A possible explanation for this contradiction is that a high intensity of effort was maintained between the initial 10 km run and the final 10 km run. The 10 week training program resulted in a 4:15 min:sec improvement between the initial 10 km run and the final 10 km run after 10 weeks of training. The amount of muscle damage following both the initial 10 km run and the final 10 km run was equal Intensity of effort was held high for both runs, though the speed of the two runs was different. This indicates that intensity of effort (and perhaps speed) plays a role in muscle damage and could off-set any training-induced protective effect. Of perhaps even more significance is the observation that muscle strength decreased the same amount and for the same length of time before and after the 10 week training program. The significance of this event is that I propose that changes in muscle strength levels are an indication of recovery status. If strength falls following an event, then recovery from that event is not complete before muscle strength has at least returned to pre-event levels. While it seems likely that there is a connection between loss of muscle strength and muscle damage, the exact relationship between these two has not been definitively established. It is probable that, in addition to muscle damage, other factors contribute to strength loss. In any case, if running muscle strength level changes are a reliable indicator of recovery status, this study shows that recovery time does not decrease significantly with time. A third observation is that different runners experience different levels of muscle damage. Clearly the amount and timing of muscle damage is different in different runners. While some experience damage at relatively low mileage and intensity, others can run significantly further and harder before the on-set of any damage. This is not too surprising a finding though since in every human endeavor we find a distribution of capability with this physical characteristic being no different. The important point to take from this observation is that each individual is just that – an individual. Assuming that muscle damage is not a beneficial thing, then clearly runners who experience damage at lower mileages should exercise some caution when deciding whether or not to emulate the training distances of those less susceptible to muscle damage. An important question not addressed by these studies is what happens if a runner increases mileage to a new high level and then maintains that mileage? In both studies, mileage was slowly increased for the duration of the training programs, with a concurrent increase in muscle damage. Would the amount of muscle damage have decreased if mileage was then plateaued at the new higher level while intensity was maintained? It is certainly possible. However, my personal bias, based on studies of overtraining and injury, is that if weekly mileage is plateaued and intensity is held high that the level of muscle damage plateaus, but does not decrease. I do not believe that muscle damage decreases if intensity is held high. Certainly more research needs to be done to definitively answer this question. Summary These two studies teach us several important things. First, muscle damage increases with both increases in weekly training distance and increases in the longest distance run. Second, runners have varying levels of susceptibility to muscle damage, with some runners experiencing muscle damage at much lower training distances than other runners. Third, if intensity is held high training does not seem to provide much if any protection against muscle damage. Fourth, if intensity is held high recovery time does not decrease significantly with changes in training status. Lastly, though these studies do not address this subject, my belief is that muscle damage and recovery do not decrease with plateaus in weekly training volume if intensity is maintained at a high level. Reference: 1. Kuipers H., Janssen G., Bosman F., Frederik P., Geurten P.; Structural and Ultrastructural Changes in Skeletal Muscle Associated with Long-Distance Training and Running; Int J Sports Med, 1989, 10(Suppl 3), 156-159. 2. Overgaard K., Fredsted A., Hyldal A., Ingemann-Hannsen T., Gissel H., Clausen T.; Effects of Running Distance and Training on Ca2+ Content and Damage in Human Muscle; Med Sci Sports Exerc, 2004, 36(5), 821-829. .
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