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  • Dr. Vidlock

Physiology of Recovery

There is nothing like finishing a long training run, better yet, discussing it with your running buddies. But there is no joy in talking about the run where your legs feel like concrete blocks.  What is the trick to recovering well? Recovery is essential in allowing your body to increase mileage, build speed and strength.  How does the recovery process of training work?  What can we do to maximize our recovery?  It turns out those high school biology classes are useful here.  (If the thought of biology makes you want to stop reading – just skip ahead a few paragraphs)  Endurance exercise especially running causes adaptation in many systems of our bodies, including cardiac, skeletal muscle, bone and respiratory.  Cardiac response to exercise depends on the skeletal muscle demand for oxygen.  With increased mileage and intensity, the oxygen uptake of skeletal muscle increases. The cardiac output (dependent on heart rate and volume of blood in each beat) increases accordingly up to its maximal point.  Endurance exercise can increase the amount of blood flow to the cardiac muscle, allowing the heart muscle to beat more efficiently, sending a larger amount of blood with each beat.  Oxygen consumption in the heart is directly related to heart rate, the pumping ability of the heart and the stress on the heart walls, and these all elevate with exercise.  With repeated exercise the heart muscle builds stronger tissue which can allow more stress, and becomes more effective at pumping.  Without proper recovery, the muscle cannot adapt to training and athletes will feel fatigued. The respiratory systems adapts to endurance exercise similarly.  During exercise ventilation increases due to muscle and brain stimulation.  The increase in carbon dioxide from exercise as well as increase in temperature also causes ventilation to increase.  Over time with repeated endurance training and proper recovery, the oxygen content entering the blood increases. Endurance training leads to positive changes in bone, ligaments and tendons.  Bone density increases with repeated endurance weight bearing exercise.  Ligaments and tendons become stronger with endurance training.  Skeletal muscle adaptation plays a major role in allowing progression of endurance training.  Humans have two types of muscle fibers, fast twitch and slow twitch, named for the speed of contraction.  Slow twitch fibers contract slowly, are more efficient with utilization of oxygen, lower need for glucose and resist fatigue.  Fast twitch muscle fibers contract faster, have a low capacity for holding oxygen and fatigue easily.  Most elite runners training for marathons and ultras have at least 90 percent slow twitch fibers. Genetics appear to be the determining factor in fiber type and training will not likely alter the percentage of fiber types. In sprinters the main energy source is ATP, and with vigorous exercise the demand for oxygen will exceed supply.  At that point there is need for glycogen to produce ATP, however this system also produces lactate, which lowers the pH of the blood, stopping ATP production.  Slow twitch muscle fibers rely on mitochondria to use oxygen and produce ATP.  Training and appropriate recovery allows increase in mitochondria and increased capacity for oxygen and ATP production. Myoglobin content in muscles increases with training, allowing more oxygen stores. In addition with training, fat is more easily utilized as an energy source. Maximal oxygen uptake (VO2) increases with vigorous exercise until it reaches a point where it cannot increase any longer (VO2 max).   VO2max is in part genetic and somewhat variable with training.  Lactate threshold is when the lactate content of the blood increases over resting state (due to body’s inability to clear it as fast as it is produced).  Most distance runners set their pace at or slightly above their lactate threshold. With training the lactate threshold can be increased and occur at a high percentage of the VO2 max. Muscle soreness after exercise is common with both endurance exercise and resistance training.  Delayed onset muscle soreness (DOMS) occurs after eccentric muscle exercise, such as running downhill making quads sore.  Endurance training can damage muscle fibers and cause inflammation.  The muscle tissue undergoes a damage-regeneration cycle starting within hours of the exercise. Regeneration of new muscle fibers occurs and with exercise these new fibers are stronger and better organized compared to sedentary individuals.  The new fibers contain more mitochondria, greater blood flow and increased metabolic activity, allowing more vigorous exercise.  So, recovery is important to allow increases in muscle strength and efficiency in the lungs and heart.  What if we do not allow the body to recover?  It is good training at times to run on tired legs- that may help prepare for a race.  However, constant running on tired legs leads to breakdown of muscle fibers and doesn’t allow for the hormones and immune system to keep up.  This leads to overtraining.  Symptoms of over training include: persistent muscle soreness, constant fatigue, elevated resting heart rate, increased infections, increased injuries, irritability, depression and burnout.  Many of these symptoms can also be attributed to other conditions, so overtraining may be hard to detect especially at an early stage.  The whole issue of lactic acid should be brought up here.  For years it was thought that buildup of lactate or lactic acid caused fatigue and eventually overtraining.  This is not true, but is a misconception held by many.  The body does not produce lactic acid, but it does produce lactate.  Lactate is a byproduct of anaerobic respiration.  When a runner goes beyond their aerobic capacity the body relies more on anaerobic respiration and produces energy from sugar without using up oxygen but it produces hydrogen ions (acid) and pyruvate. Aerobic respiration can get rid of the pyruvate and hydrogen by using oxygen, but in the absence of oxygen pyruvate and hydrogen ions will make lactate.  Lactate prevents the buildup of acid.   The muscle fatigue is from the acid- not lactate.  By building muscle fibers we can allow more mitochondria and oxygen production.  What can we do to aid recovery?  There always seems to be something new to try, but what is the evidence?  Is there a placebo effect?  Are there harmful products? Let’s take a look at some common recovery methods. Nutrition is a mainstay in recovery and could easily be a separate article in and of itself.    Basically the evidence shows benefit in consuming some carbohydrate and protein within an hour after running longer distances.  There are so many products claiming to aid recovery.  While few have any evidence, most are not harmful.  It may be worthwhile to try a new recovery meal/snack if you want variety or feel your current foods are not helping.  Antioxidants get a lot of press as helping to stop damage to cells.  Some studies have shown that boosting antioxidants may help with immune function.  However, the cell damage that occurs is a part of the recovery process; it triggers new stronger muscle fibers to develop. Could antioxidant use prolong this recovery and growth of new muscle fibers?  There are some studies showing just that.  As more evidence emerges, there will likely be a clearer picture of where and when antioxidants fit into training. Rest is the biggest component in recovery.  How much do you need and why does your running buddy need more or less?  Everybody is different, and again there is not a lot of research into how much rest is optimal.  One of the best ways to gauge rest/recovery is checking resting heart rate.  Remember that running on tired legs with every run might seem like a good idea short term, but soon injury and fatigue will win. Ice baths are a popular topic among runners.  The first time I tried one my kids though it was fabulous to dump ice all over their mom in the tub.  But it was only fun for them as I was miserable during the bath.  Afterwards I felt good though.  This goes along with the studies showing that while ice baths can make athletes feel better there are inconsistent results regarding muscle recovery.  However, there really isn’t evidence to show harm, so if a runners swears by the ice bath- then go for it! Studies on massage do show some benefit in reducing inflammation with in muscles and many runners feel amazing after a recovery massage.  It is not known if the reduction in inflammatory markers causes a prolonged recovery and hampers the growth of stronger muscle fibers.  Most runners would cringe at the thought of taking away their massage and at this point there really isn’t enough evidence to stop. Compression items are seen at every race.  Some runners swear they run faster and more efficiently but there is no scientific evidence to back this claim.  Wearing compression AFTER a long run may help the DOMS.  Again these are not harmful, so even if there is a placebo effect- does it matter? There are so many other products out there and I find myself intrigued, even knowing the lack of evidence.  My latest favorite is a hot pepper lotion to apply right after a long run and shower.  It may feel even better in the winter as the thought of hot pepper lotion when it is 90 degrees out is a bit crazy.  There isn’t one shred of evidence behind it, and my scientific background leads me to believe it can’t absorb enough to get to those deep muscle fibers.  But placebo or not, I continue to lotion up.  The bottom line as usual is listen to your body, get appropriate rest and don’t’ be afraid to try some new things as long as they aren’t harmful.



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