Here's why you WILL NOT build unwanted muscle as a Dancer...
Number ONE question I am asked on a daily basis... "Will I build muscle?"
"But I do not want my legs to get bigger..."
There are many factors to considered in physical preparation of Dancers and not as many of them revolve around the barbell and heavy weight as you might think. Plus, there are many ways to build "strength" for Dancers and not all of them are defined in the same way. For example, a strong Dancer, as defined by a Dance Teacher or Coach, may not be definitively strong in the eyes of the Physical Prep Coach or Strength Coach or Physio and Vice Versa.
What must we consider? and what are the reasons visible muscle mass increases are fairly non-existent?
Bigger muscle are only stronger muscle up to a point.
Strength can be represented at a variety of speeds (Athletically Strong, Strong in Balancing, Strong in Fine Control and slow movement, Strength Endurance)
Strength gains are not just the result of increases in muscle size.
Its not Squatting that increases Muscle Size, it is the repetition ranges and intensity of the squats that determine the adaptation. Squat for Strength, Size, Muscular Endurance, Power... It very much depends on the programming.
Strength to Weight Ratio (Relative Strength) is more a predictor of performance (in general) than absolute strength.
The way we train Dancers to be strong and robust does not revolve around training that creates changes in Muscle Mass.
Dancers do too much other forms of exercise and movement throughout the day to allow for effective hypertrophy (muscle fibre growth)
Gaining Muscular Size can be heavily determined by nutrition. Positive energy balance and caloric surplus is essential for hypertrophy. Dancers tend to eat in calorie maintenance or balance and thus this does not promote fibre size changes.
Muscle Size increases require a large training volume isolated to muscle groups and compound movements and due to the volume and intensity already seen in Dancers' schedules this volume will not be accumulated.
Gains in Strength and the athletic goals for Dancers surround fine control, neuromuscular efficiency, dynamic stability, muscular and anaerobic endurance, movement skill and relative strength in certain muscle groups/functions. These goals do not lend themselves to training to hypertrophy. Hence you do not see bodybuilders in gymnastics or jumping in the long jump pit.
Of course... There are some small gains in muscle fibre size, even changes in muscle fibre type. However, these small increases may be in type 1 fibres which are more in use during slow or continuous movement. Their size is significantly smaller than your typical Type 2A fibre which is simply involved in Raw Strength and Power activities and fatigues much more rapidly.
So we must consider what we are training for and the muscle actions that are used for Dance. Correct Physical Preparation for Dancers must be guided the demands of Dance and the Genre. For example in Ballet, we may focus on slow and controlled movement, movement efficiency and movement capacity. Or in Break Dancing we may focus on Upper Body Strength and Power, Or even in Contemporary methods such as "Flying Low" we may ensure Dancers have the capacity and robustness to land and jump from a variety of positions and therefore joint strength and health will be prioritised over fine control or other modes of training.
Strength training must be guided by the needs analysis of the individual. Mistakes can be made where Dancers simply train in a traditional way without guidance.
Training under S&C specialists will ensure that the desired attributes of "Strength" are maximised.
Here is an example of Exercises that do not focus on Muscular Size Changes.
Yielding Isometric Split Squat
Copenhagen Groin Exercise
Nordic Hamstring Drop