An exercise pen includes an elongated body having an elongated upper body and an elongated lower body where a lower end of the upper body and an upper end of the lower body can be releasably coupled together, and a resistance tube extending within lumens of said upper and lower bodies, the resistance tube having a first end coupled to a lower portion of the lower body and a second end, opposite the first end, coupled to an upper portion of the upper body. A method of exercising using the exercise pen includes decoupling the upper body from the lower body; and stretching the resistance tube by moving the upper body away from the lower body. Other embodiments, including an exercise kit having different resistance tubes of different moduli of elasticity are disclosed.