**Core Concept**
Energy in muscles is stored in the form of high-energy phosphate bonds, primarily in the molecule ATP (adenosine triphosphate). This energy is stored in the form of phosphate bonds between the phosphate groups of ATP.

**Why the Correct Answer is Right**
The high-energy phosphate bonds in ATP are broken down to release energy, which is then used for muscle contraction. This process is mediated by the enzyme myosin ATPase, which hydrolyzes ATP to ADP (adenosine diphosphate) and inorganic phosphate, releasing energy that is then used to drive muscle contraction. The energy stored in ATP is essential for muscle function, as it allows muscles to contract and relax.

**Why Each Wrong Option is Incorrect**
**Option A:** Creatine phosphate is a high-energy molecule that stores energy in the form of phosphate bonds, but it is not the primary storage form of energy in muscles.
**Option B:** Glycogen is a complex carbohydrate that stores energy in the form of glucose molecules, but it is not the primary storage form of energy in muscles.
**Option C:** Lactic acid is a product of anaerobic glycolysis and is not a storage form of energy in muscles.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that ATP is the primary energy currency of the cell, and its breakdown is essential for muscle contraction. This process is mediated by the enzyme myosin ATPase, which is sensitive to calcium ions and is activated during muscle contraction.

**Correct Answer:** C.