Exercise variation is used by all coaches. Very seldom will you see an athlete performing exclusively competitive movements during the training process. Most trainees use a wide variety of exercises in their preparation, especially beginner to intermediate athletes.
While variation is certainly necessary, it is often used with an instinctive approach as opposed to being applied with a solid understanding of the training process.
Three main variables affect the magnitude of training impact: volume, intensity and novelty of exercises. Exercise variation then, is an interesting tool to enhance training stimulus without having to drastically increase volume and intensity over time.
However, new exercises must fit within the context of training. That is, the training transfer from the exercises to the competitive movements must be positive. Positive training transfer may be sought through sport-specific biomotor and/or technical improvements from the exercises utilized. While a wide variety of exercises might be used for improvements of biomotor abilities, the case is very different for gains in technical skills, where the exercises have to be extremely similar in form and execution to the competition movements to be effective.
As long as these conditions are respected (i.e. the exercises used are specific enough to yield improvements in sport-specific technical or biomotor abilities), exercise variation should be extensively used to prevent excessive increases in volume and intensity of competitive movements in training throughout the developmental process. With appropriate variation, the athlete’s motivation is less likely to falter and injury risks decrease drastically as well.
It is important to make sure that the degree of variation corresponds with the training phase. As a general rule, the further away in time the athlete is from a competition, the more variation he will use. Moreover, in his off-season, the athlete might even use very little exercises that have positive transfer in technical skills for competitive movement execution, but focus mainly on making proper sport specific morphological and physiological improvements through a wide range of exercises (i.e. exercises that will promote biomotor abilities enhancement). These exercises are usually termed general preparatory exercises. On the opposite side of the spectrum, as competition grows closer, a good portion of training time should be allotted to progress in technical execution of competitive movements. As we mentioned before, exercises with positive technical skill transfer are very limited so training variety will become naturally restrained, as it should at this time of the preparation. These exercises are coined special preparatory exercises.
An interesting remark can be made in regards to exercise variation and training experience. If you’ll recall, we’ve already brushed on this subject regarding the training of several motor abilities at the same time for advanced athletes, but haven’t examined it from the angle of exercise variation. As an athlete grows more experienced and amasses several years of sports training, the exercises he uses will have to become more and more specific to the sports he competes in to be effective. That is, the more closely the exercise resembles what he does on the field or the platform, the better it will transfer to competition performance. Exercises that are too far off in correspondence to the sport will not only be a waste of time, they will usually also interfere with the adaption process by mobilizing some of the recovery resources of the body. Beginner athletes, on the contrary, can make remarkable improvements by employing a broad range of exercises, and they should, as to ensure the establishment of a solid foundation of general physical preparedness on which to build on in upcoming years. This is what we call the funnel effect, where the amount of exercises with positive transfer reduces as the athlete’s qualification increases.
 “[…] the process by which improving performance in certain exercises/tasks affects the performance in other exercises or motor tasks.” Issurin, Vladimir. Building the Modern Athlete: Scientific Advancements & Training Innovations. 2016, UAC. P.94
 On the concurrent development of hypertrophy and maximal strength in our article on directed adaptation.