I find that 41″ yellow, red, black, and purple band are the standard 41″ resistance bands to have for large group fitness camps. Now you have to always consider gender, age, strength level, what exercises you want to do, the resistance band set ups you plan to use and where are you going to be training with your Quantum Bands. This chart and questionnaire may assist with your decision. However I know personally I dislike buying a training product and finding out after the fact it isn’t even close to providing me a challenge or is so intense I can’t use it. To eliminate issue, let us assist. Email us your question at email@example.com and we will respond back to you ASAP to assist you with your decision.