why an athlete would need to be concerned about twitches or contractions is because, whenever they perform, and such thing happens, it will most likely distract the athlete, and cause the athlete doing his/her performance to not be as good, and may lead to failure, for example, when someone is running very fast for a sprinting race, and he has a contraction in his leg it will cause him to react by showing signs of pain by slowing down or even tripping and falling, causing him to lose the race.
If one or two bases are deleted the translational frame is altered resulting in a garbled message and nonfunctional product. A deletion of three or more bases leave the reading frame intact. A deletion of one or more codons results in a protein missing one or more amino acids. This may be deleterious or not.