Unique, roto-molded construction with multi-layer technology make these last 100 times longer than traditional rubber medicine balls. Won't split, crack, or lose shape after the most vigorous training. Full-bounce construction and can withstand continual slamming. Sets include UltraFit™ Endurance™ balls, all-steel UltraFit™ rack, and set of 3 laminated UltraFit™ charts.