What you’re describing — a lump that only becomes visible when you flex your calf muscle, is painless, and feels soft or pressible — is most often consistent with a benign (non-dangerous) condition rather than something serious. I know it can be unsettling to notice something like this, especially at your age, but the pattern you describe is actually fairly reassuring. A few possibilities commonly fit this presentation: Most commonly, this turns out to be a muscle herniation. This happens when a small portion of muscle bulges through a natural weak spot in the surrounding fascia (the connective tissue covering the muscle). When the muscle is relaxed, you may not see anything. When you flex, pressure increases and a small bulge appears. These are usually harmless and often painless. A lipoma (a benign fatty growth) is another possibility, but lipomas are typically visible and palpable all the time — not just when flexing — and they usually don’t change much with muscle contraction. A vascular bulge or vein prominence can also become more noticeable with muscle contraction, though these often have a slightly bluish tone and may flatten when you elevate the leg. Features that are reassuring in your description: Appears only with flexing Painless Soft/pressible Symmetric contour with movement No rapid growth reported Features that would be more concerning — and would warrant prompt evaluation — would include rapid enlargement, firmness, persistent visibility at rest, skin changes, pain, or neurologic symptoms. If you want a definitive answer, an ultrasound is usually the simplest and most useful first imaging test for this type of finding. It can quickly distinguish between fat, muscle, and vascular causes. Based on your description alone, this sounds much more likely to be benign than dangerous.