The length of your calf muscle fibers changes depending on how you bend your knee and point your foot. When your leg is straight and your foot is pointed up, the fibers are longer, but they shorten noticeably when your knee is bent and your foot is pointed down.

Our current analysis shows that bending your knee and pointing your foot changes the length of the muscles in the back of your lower leg. The evidence we have reviewed leans toward the idea that these calf muscle fibers stretch out when your leg is straight and your toes point upward, but they shorten when your knee bends and your foot points downward [1]. What we have found so far comes from reviewing 20 studies support, 0 studies refute. We want to be clear that this is a partial view. Our analysis improves over time as more research becomes available. The evidence we have reviewed suggests a clear relationship between joint position and muscle length. When you keep your leg straight and lift your toes toward your shin, the fibers lengthen. When you bend your knee and point your toes toward the floor, those same fibers shorten noticeably. We do not claim this is a final answer. We simply report what our current review of the available data indicates. The evidence we have reviewed focuses on basic joint positions. We do not have enough evidence yet to say how this changes during heavy exercise or long-term training. Our current analysis shows a consistent pattern in how joint angles affect muscle length, but we will update this as new data emerges. For everyday life, this means you can adjust your lower leg stretch by changing your knee position. If you want to feel a deeper stretch, try bending your knee while keeping your heel on the ground. If you want to target the upper part of those muscles, keep your leg straight. We will continue tracking new research to give you the most accurate picture over time.