Downloadable computer application software and computer hardware that detects, tracks and monitors an individual's motions, body movement, body positioning and physical activity during strength and flexibility exercises; downloadable computer application software and multiple electronic sensors sold as a unit for detecting, tracking and monitoring an individual's motions, positioning and physical activity for use in fitness instruction and for providing real-time personalized feedback based on an individual's body movement and positioning during strength and flexibility exercises; portable electronic device, three-dimensional electronic sensors and a touchscreen display sold as a unit that capture and communicate an individual's movement, performance and fitness data during strength and flexibility exercises in real-time; downloadable computer application software for use in taking fitness classes, receiving fitness instruction, sharing information with others, tracking and monitoring fitness goals and calories burned during strength and flexibility exercises; downloadable computer software for accessing live and on-demand fitness classes featuring strength and flexibility exercises