WE ARE NOT CLOUDS.
For dancers, muscle building is key for professional development. I'm not talking about RRRRGGGGHHHH LOOK AT MY ARMS THEY'RE 5 TIMES AS BIG AS MY HEADDDDD. Dancers develop different muscles than many other sports and performing arts, ones that are more sculpted and sleek, less big and bulgy. Many of the muscles developed by dancers are inner muscles, such as the inner thigh, deep in the leg, or the core. Muscle development varies directly to how many days (not hours) per week you are in the studio.
I only take classes on Monday, Thursday, and Saturday, a total of 6 hours per week. Not a professional schedule, I know, but I appreciate not being locked up every day all day with no contact with sunlight. This upcoming year, because my schedule will stay the same, I am planning on taking a higher level class on Tuesday, and any other classes I can the rest of the week, even if they are levels below me. Dance development has nothing to do with how many hours per week you train, but everything to do with how many days per week you dance. Even if you cannot dance every day, there is nothing stopping you from giving yourself your own dance workout at home.
When selecting a dance workout, be careful as to what muscles they are building. Watch or read the instructions carefully and think about what muscles they may be building. It is best to warm up with a barre. I suggest Pure Barre videos, or Finis Jhung videos found on DVD and YouTube. Or you could use your own barre from class. Maybe create your own.
I also suggest teaching yourself a variation from a famous ballet. This improves your teaching, choreography, and dancing skills. You will learn how to adapt a dance from a video, which will come in very handy in the future. Well-known variations include The Sugar Plum Fairy from the Nutcracker, The Lilac Fairy from Sleeping Beauty, and Swanhilda's variation in Coppelia
Core strength is extremely important for a dancer. Without core muscles, extensions would drop, leaps would be barely off the ground, balance would be nearly impossible, and pirouettes absurd. This expressed, you can NEVER have too much core strength. Crunches, 100s, sit-ups, planks, and the like must be on your workout schedule.
Yoga and Pilates are considered very healthy for a ballerina, increasing balance, strength, and stamina. Try joining a club such as Groupon to get updates on special deals for yoga and Pilates classes. Special offers on Kindles are also very common. The other day I received coupon that included ten 90-minute yoga classes with a choice of a 15-minute massage or a 30-minute personal training session for only $30! Yoga is a very inexpensive and stress-relieving way to build muscle.