Muscles
Your muscles cannot function right without collagen. Muscles, similar to cartilage, attach to the heads of bones and your muscle ache may indicate a lack of collagen.
Hair
Hair can tell a lot (if not everything) about your current state and condition. Collagen deficiency will reflect on your hair. Collagen plays a great role in delivering nutrients to the hair follicles. If there is no collagen, you hair becomes brittle, dry, weak and dull. You need collagen to help your hair protect itself from free radicals that affect the hair texture, its growth and thickness.