TrainingThe Science of Performance |
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Easy Runs and Recovery
You completed a hard run yesterday and this morning when you awoke, you instantly could feel residual fatigue and soreness in your legs. No doubt about it, that was a tough workout yesterday and you know that you will be moving slow today because you are still sore and tired. “No worries though”, you think to yourself, “today and tomorrow I have easy runs scheduled and they will help me recover”. The belief that easy paced runs assist in recovery is fairly common. For example the 2nd edition of The Competitive Runner’s Handbook defines an easy run this way. “Easy pace is recovery running. It equals approximately 60 to 70 percent of maximum heart rate. Use these runs the day after hard workouts and races, the day before races, and whenever you’re tired and want to take it real easy.”(1) Is the belief that easy runs enhance recovery well founded? Do easy runs truly help speed recovery? Surprisingly, while conventional wisdom promotes this belief, there is little actual research on this topic. That is not to say there is not any research though. In fact, noted physiologist Dr. David Costill and a team of researchers examined this very topic in a research study on marathoners (2). Let’s take a look at this particular study and see what we can learn. Research The researchers had two objectives in mind with this particular study. First they wanted to examine what effect running a marathon had on leg strength and work capacity. Second, they wanted to investigate the effect of either resting or conducting an exercise-recovery regimen (i.e. easy runs) on rate of recovery. To study these two things, the researchers recruited 10 trained male runners and tested them pre and post marathon. These runners were experienced runners and had been in training for at least 5 years. All had previously run marathons, but none had run a marathon in the previous six months (this ensured there was no residual fatigue from a recent marathon). During the final three months before the marathon all the runners intensified their training and were running an average of 104 km per week. All ten runners ended up setting personal records in the marathon, with an average time of 2:55 hr:min. Prior to the marathon all of the runners were tested for knee extensor (quadriceps) strength and work capacity using a Cybex II system. Strength was determined by measuring maximal peak torque achieved during a maximum leg extension at three different extension velocities. Work capacity was measured by the total accumulated work achieved from 50 repeated maximum leg extensions. Upon marathon completion the subjects were randomly assigned to either a rest group or an exercise group. Random assignment resulted in the two groups possessing similar physical, anthropometric, and physiological characteristics as well as performance times. The rest group performed no exercise and emphasized slow walking in the week following the marathon. The exercise group performed daily runs of gradually increasing duration for 20, 25, 30, 35, 40, and 45 minutes during the 6 days post marathon. The runs were performed at an easy pace corresponding to 50% - 60% VO2max and were conducted in the afternoons. Leg strength and work capacity was measured 15-20 minutes following the marathon and then 1, 3, 5, and 7 days post marathon. Leg strength and work capacity tests were conducted in the morning. Results Not surprising, the marathon caused a significant decrease in leg strength at all three contraction velocities. Similarly, work capacity was decreased, on average, 47% immediately following the marathon. The subjects were tested for leg strength and work capacity on days 1, 3, 5, and 7 post marathon. By day three, the rest group had recovered significantly more overall than had the exercise group. On day five the rest group’s rate of recovery remained above those of the exercise group. On day seven, the rest group’s recovery continued to exceed that of the exercise group, even though both groups’ strength levels remained below their pre-marathon level. Overall, the rest group recovered faster and to a greater extent than did the exercise group. Table 1: Leg strength and work capacity % loss post marathon
Notes: Pre marathon strength and work capacity equal 100%. Values in table 1 are estimated from figures 1 & 2 in the research study. Discussion Two questions must be addressed from the results of this study. First, what accounts for the loss of muscle strength and work capacity? Second, what caused the differences in recovery rate between the rest group and the exercise group? One possible explanation for the loss of muscular strength and work capacity is lowered post marathon glycogen levels. This particular explanation is unlikely because the researchers measured glycogen levels pre and post marathon and noted “…muscle glycogen levels had returned to normal levels days 1-7 postmarathon in the presence of reduced maximal peak torque (leg extensor strength) throughout the week postmarathon. Thus muscle glycogen levels could not account for the reduced maximal peak torque directly after the marathon and during the week postmarathon” Similarly, dehydration probably did not play a role in strength and work capacity reduction. The researchers noted that the runners’ body weight had returned to pre-marathon levels 1-day post marathon while muscle function continued to be impaired. Having eliminated glycogen and hydration levels as possible reasons for the loss of strength and work capacity, two other explanations are possible - central nervous system fatigue and muscle fiber fatigue or damage. Central nervous system fatigue simply means that the brain fatigues and therefore recruits fewer muscle fibers. As muscle fiber recruitment drops, so too does performance. New research has indicated that central nervous system fatigue plays a major role in the immediate loss of muscle strength and power during and immediately following exercise (3). However, there is no evidence that the central nervous system remains in a fatigued state in the days following an event. More research on this theory remains to be done. Several research studies have noted increasing amounts of muscle damage occurring as the distance to be run increases, with evidence of muscle damage occurring at distances as short as 10k (4,5) ((see the article, ,Running and Muscle Damage in the physiology section of this web site for a discussion of these research studies)). The evidence is clear that, at a minimum, muscle fibers are damaged during exercise resulting in a loss of contraction ability. Muscle fiber damage could completely explain the loss in strength and performance that persist in the days after an event. This brings us to our second question – namely what accounts for the differences in recovery rate between the rest and exercise groups? If muscle damage is solely responsible for the decrease in strength and work capacity then this easily explains why the rest group recovered faster than the exercise group. After all, stressing a damaged cell with additional stress (exercise) is not a proven method for increasing the healing rate of that cell. This would be akin to continuously reopening a cut to see if you could cause it to heal faster. By fully resting their damage muscle cells, the rest group allowed their cells the maximum opportunity to recover. Conversely, the exercise group continued to stress their damaged muscle fibers with additional exercise, delaying their recovery despite the relatively easy pace of exercise in the days following the marathon Additionally, if central nervous system fatigue is partially or fully responsible for muscle strength and work capacity loss in the days following an event, it seems equally unlikely that additional stress will cause the system to recover faster. This would be akin to saying that as fatigue sets in near the end of a race that increasing your pace, or in effect increasing the stress on the system, is likely to reduce the amount of fatigue you are experiencing. Lastly, if muscle damage and/or central fatigue are the root causes of the strength and capacity loss observed in the marathon, these two factors would similarly play a role at any distance run. In other words, additional stress in the form of easy runs following any exercise that caused muscle damage or central nervous system fatigue is unlikely to cause a faster rate of recovery and will likely slow the overall rate of recovery. Certainly shorter or less intense runs will result in less muscle damage or fatigue and the length of time to full recovery will probably be less as compared to events that are longer or more intense. However, even if muscle damage and/or central fatigue are less severe, it does not follow that easy runs will hasten recovery. Conclusion This particular study casts serious doubt on the belief that easy paced runs promote recovery from hard or long runs. Despite the fact that many runners continue to exercise following an event or hard workout, this study indicates that even easy paced efforts may impede or slow the recovery process. In the words of the researchers, “Rest during the week postmarathon allowed recovery of work capacity but did not result in recovery of maximal peak torque. Exercise during the week postmarathon did not facilitate the recovery of marathon-induced reduction in maximal peak torque and work capacity. Therefore, if exercise recovery is selected the week postmarathon, exercise intensity and duration must be judiciously selected.” Reference:
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