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The Science of Performance |
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How Much Can You Improve? Part 3
Through the first two parts of this series we have established there is a large variation in response to training. Some people, the high responders, enjoy a tremendous improvement in capacity while others, the low responders, suffer from no improvements at all or, even worse, a decline in performance, despite following the same standardized training program as the high responders. The study we examined revealed the range of variation in aerobic capacity to be 61%, while other research has shown a range of 41% to 100%. Research on changes in muscle size and strength have shown a range of response of 250% in muscle strength and 61% in muscle size. The fact that some individuals lose aerobic capacity and muscle size and strength from the same program that other individuals improve from 60% - 250% provides evidence that a standardized training program is not suitable for all individuals. The results of these studies bring up perhaps the most significant issue of all on the topic of how much can you improve. That issue is, what factor or factors make one a high, average, or low responder and, most importantly, are these factors modifiable? If you are a low or average responder are there things you can do to improve your trainability? This most important of questions will be addressed here in part 3 of this series. Research Scientists have researched the answer this very same issue. One particularly illuminating study on this topic was conducted using monozygotic twins. A monozygotic twin is a type of twin derived from a single fertilized egg that splits into 2 embryos. Since both twins come from the same fertilized egg, they share the same DNA or genetic structure. You could say this is nature's own cloning process. Monozygotic twins are commonly called identical twins. By training individuals with the identical genetic structure scientists can determine how much of the response to training is due to genetic factors and how much is due to other factors. If both individuals that comprise a pair of twins respond exactly or very similarly to each other, then this would provide evidence that genetics play a primary role in response to training. If both individuals comprising a pair of twins respond differently to training, then this provides evidence that other, non-genetic factors are primarily influencing response to training. In this study researchers recruited 10 pairs of monozygotic twins and trained them for 20 weeks with an endurance training program to test the influence of genetics on response to training. (1) Training consisted of 4-5 cycling workouts per week, for 40 minute per session, with an intensity range of 60% - 85% of heart rate reserve. Subjects were tested for a variety of fitness indices, including maximum aerobic power, pre and post training. Fourteen healthy subjects served as non-training controls. Results
As in previously reviewed studies, there was a broad range of improvement in aerobic capacity in this study too. The average improvement in aerobic capacity was 12% but the range of changes was 0% - 41%. Importantly, the researchers noted that "These differences in training responses were not distributed randomly among the twins..." There was a significant within-pair similarity in response to training but little similarity in across-pair response to training. Basically, the two members of each set of twins responded very similarly to each other. However, there was little similarity in response to training across all the different twin groups, hence the range of 0-41%. Discussion In agreement with the previous studies examined in this series, there was a large variation in response to training in this study also. The total variation of response was just 41% in this study, which is on the low end of the range shown in other studies and likely due to the lower number of subjects involved. The most important finding of this study though is the evidence it provides for a strong genetic influence on response to training. The researchers write, "...75-80% of the variance in response to training are associated with genotype differences." What the researchers are saying is that genetics account for 75-80% of the response to training. Other factors account for the other 20-25% of response to training. Presumably these factors might be related to age, sex, previous training history, and diet amongst others. Training Implications What training implications can we draw from our investigation into range of response to training. First, as noted in the first 2 parts of this series, humans exhibit a broad range of response to training. Depending on the variable being measured, the range can be as large as 0-250% within the muscles and 0-100% in aerobic capacity. Second, the vast majority of response to training is determined by your individual genetics, which are not altered with training. If life has blessed you with superior athletic genetic talent, then thank your lucky stars because no amount of training will allow someone to overcome low genetic talent. No known training techniques or methods can alter a person's genetic structure. Genetics do not completely control response to training though. As much as 25% of an individuals response to training is due to factors other than genetics. Presumably then, an individual can alter their trainability to some degree with optimal training, recovery, nutrition, and other factors. I suggest that, based on the data, it is a reasonable to conclude that optimal training is not the same for all individuals. In all of the studies there were some number of subjects who either did not improve fitness or, worse, actually lost fitness. For beginner trainees a plateau in fitness and especially a decrease in fitness are associated with a training load in excess of what the individual can adapt to. In light of this fact, it is quite possible that differences in genetic talent also strongly influence the amount and intensity of training that is optimal for any individual. In support of this belief is a study that correlated performance in a 10 mile race with average weekly mileage for the previous year.(2) This study divided runners into fastest, middle, and slowest thirds based on finishing time and found that the average weekly mileage that produced the fasted performance in the slowest 1/3 of runners was significantly lower than the average weekly mileage that produced the fastest performance in the fastest 1/3 of runners. Combining the data from all of these studies leads me to suggest that the range of optimal training is likely very large, just as the range of response to training is very large. My hunch is that the range of optimal weekly mileage for runners ranges from 0 - 100 miles per week, depending on genetic response to training. However, much work remains to be done to prove or disprove my hypothesis. The title of this series is "How Much Can You Improve?". The answer is no one knows, at least not in advance of training. Your individual response to training can not be predicted in advance and will only be revealed after you have trained for some period of time. The odds are low that you have either elite level genetic talent or below average genetic talent. Instead, the odds are very good that you will fall somewhere in the middle of the bell curve in terms of genetic talent. The only way to confirm what your genetic talents are is to measure your actual performance following a training program. Summary Twenty weeks of endurance training by 10 pairs of monozygotic twins (identical twins) revealed both a wide variance in response to training (0-41%) and a significant genetic influence on response to training. The results of this study show that genetics are by far the most dominant influencer of response to training, accounting for 75-80% of changes observed from training. Other factors account for 20-25% of response to training. These factors presumably include age, sex, previous fitness experience, current fitness level, diet, and other unidentified factors. Reference:
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