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The Science of Performance |
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Power Runningsm Part 6: Intensity
Imagine for a moment that you spent 10 weeks building up your fitness level through 40 minutes per day of running or cycling, 6 days a week. Then for the next 15 weeks, you continued to run and cycle for 40 minutes per day, 6 days per week. Would you expect your fitness level to improve during the additional 15 weeks of exercise? I think it’s safe to say that most of us would expect to either maintain or increase fitness. What would you say if I told you that you could easily lose fitness even though you continued to work out regularly? That’s exactly what happened to a group of subjects in a research study conducted by Dr. Robert Hickson and colleagues at the University of Illinios.1 In this study, participants built up their fitness levels by working out 40 minutes per day, 6 days per week, for 10 weeks. Then for the next 15 weeks they maintained exercise volume and frequency (40 minutes per day, 6 days per week) but the intensity of training was reduced by either one-third or two-thirds. Just a small one-third decrease in intensity caused a measurable decrease in fitness! The group that decreased intensity by two-thirds lost even more fitness, despite continuing their 40 minutes per day exercise routine. How is it possible that maintaining exercise volume fails to maintain fitness? Why did small decreases in intensity result in large decreases in fitness? Homeostasis Your body works hard to maintain homeostasis. Homeostasis is the scientific word for saying that your body tries to keep things in balance. That it resists change. That it works to maintain its internal equilibrium. For example, if your core body temperature begins to rise significantly, you body compensates by increasing its sweat rate and redirecting the flow of blood closer to the body’s surface. Or if you get dehydrated, your body responds by turning on its thirst mechanism and making other changes in its physiology to conserve its existing water stores. These and thousands of other processes are occurring all the time as our bodies work to maintain homeostasis. Nature has built this into us as a survival mechanism. Disrupting Homeostasis While homeostasis is obviously a good thing in terms of helping you survive, it works against you when you are trying to improve your performance. Your body is going to resist getting faster and stronger, just like it resists any other change. In order to overcome the body’s natural resistance to change, you have to provide a potent stimulus. That stimulus is intensity. You must train with sufficient intensity in order to cause an adaptive response in your body. If you don’t train with sufficient intensity your body will not change. Instead, it will maintain its existing state. The reason strength training and speed work are so potent is because they are, by their very nature, intense workouts. Insufficient intensity explains why steady state running programs do little to improve performance; the intensity is too low to cause much of an adaptation in the body. Intensity is critical in improving or maintaining performance. Its importance can’t be overstated. If there is any attribute that you want to improve, your training program must be set up to train that attribute and then you must train with a high enough intensity level in order to force the body to change. If you decrease the intensity of your training program, your performance will drop, just like the performance of the subjects in the study by Hickson. Intensity Defined We need a good working definition of intensity so that we can ensure that our workouts are providing the stimulus our bodies need to grow stronger and faster. Intensity: the percentage of momentary possible capability at which you are working If you are maximally capable of sprinting 100 meters in 14 seconds and you run that 100 meters in 14 seconds you are performing at your maximum capacity and are therefore training with high intensity. If you were to run 100 meters in 28 seconds you would be training with much lower intensity, 50% in this example. Intensity is not defined by how much work you do; it is defined by how close to your momentary maximum capability you are working. In the case of running, intensity would be how close to your maximum sustainable speed you are running and for how long you maintain that pace. Let’s say you are capable of running a 5k at a maximum pace of 6 minutes per mile. If you run 5k at your maximum sustainable pace of 6 minutes per mile for 3.1 miles you are training at high intensity level. On the other hand, if you run 5k at only 8 minutes per mile, your intensity level is much lower. Included in the definition of intensity is the length of time you maintain your work rate. Let’s say you are capable of bench pressing 200 lbs a maximum of 10 repetitions. If you perform 5 repetitions with 200 lbs, then you would not be training with high intensity. True, you are using a heavy weight, but since you terminated the exercise at 50% of your capacity, by definition the intensity is low. The same thing applies to running. Using the example from above, let’s say you can run 5k at the maximum average pace of 6 minutes per mile. If you run at your 6 minutes per mile pace, but instead of running 5k you stop at 2k, your intensity level was low. Again, intensity is defined as how close to your momentary maximum capacity you are working at – and that definition includes a time element. A simple way to think about intensity is that it is a measure of how hard you are working. The harder you work, the higher the intensity. How Much Intensity? This brings us to the question of how much intensity is required to affect a change in performance. Think of intensity as a continuum, with zero effort at the far left of the scale and maximum intensity at the far right of the scale. What level of intensity is required in order to stimulate growth? 50%? 60%? 100%? Unfortunately, physiologists cannot definitively answer the question. We do have some clues though. First, any level of intensity greater than that to which you are accustomed will cause an adaptive response in your body. It doesn’t matter what level of intensity you are training at, if you increase it you will provide a stimulus to which your body will need to adapt. If you are used to doing all your runs at a particular pace and you then speed up that pace your performance will improve. Conversely, if you routinely conduct some faster paced / harder effort runs and then drop those workouts from your routine, your performance will drop – just as it did in the study by Hickson. What if you are accustomed to higher intensity work already? Do you need to continuously increase the intensity of your workouts until you are at 100% intensity for every workout? While science hasn’t definitively answered this question, I believe the answer is no. High intensity is required to reach your maximum, but it is not necessary to train at 100% intensity all the time. Additionally, it has been my experience that most people cannot handle all-out 100% intensity all the time. It is just too hard on both the body and the mind. I believe that an intensity level of about 80% is sufficient to provide a benefit. An intensity level below about 80% or so will likely not be sufficient to maintain performance; recall that in the study by Hickson performance declined when intensity was decreased 33%. Lastly, it is not necessary or recommended to suddenly increase the intensity of your workouts to a high level. Sudden spikes in intensity levels are likely to cause extreme soreness and may quickly lead to overtraining. Give you body time to adapt to increasing intensity levels. Make haste slowly. Coax your body into improving with gradual increases in intensity. Summary So, to sum up, intensity is what causes adaptation. If the intensity is low, the response will be small too. As intensity increases, the magnitude of response increases. When intensity decreases, so does performance. In order to maximize your performance, you have to train with sufficient intensity. Not all workouts need to be at 100% intensity. It is likely that there is a range of intensity that you can work at and still improve. I suggest that an intensity level of about 80% or higher is required once a runner has progressed beyond the beginner stage. Lastly, start gently and advance slowly to avoid overtraining and/or injury. Till next time keep on running. Reference: 1. Hickson, R., Foster, C., Pollock, M.L., Galassi, T.M., Rich, S., Reduced training intensities and loss of aerobic power, endurance, and cardiac growth. J.Appl. Physiol. 58(2): 492-499, 1985.
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