After doing slow calf exercises for six weeks, six young people saw their calf muscles get slightly thicker and their muscle fibers angle differently—this might help their muscles push force to their tendons more efficiently.

We analyzed one assertion on slow-speed calf training and found it supports the idea that this type of exercise may lead to small increases in calf muscle thickness and changes in muscle fiber pennation angle. The evidence comes from a study involving six young people who performed slow calf exercises for six weeks, during which their muscles showed slight structural changes that could affect how force is transferred to their tendons [1]. We did not find any studies that contradict this observation. However, the sample size was very small, and the results are based on a single group of participants under specific conditions. Because of this, we cannot say whether these changes would happen in older adults, athletes, or people with different activity levels. The term “pennation angle” refers to the angle at which muscle fibers attach to the tendon — a change in this angle might influence how efficiently the muscle pulls on the tendon, but we don’t yet know how meaningful this change is for performance or injury prevention. What we’ve found so far suggests that slow-speed calf training might influence muscle structure in a way that could improve force transmission, but the evidence is limited to one small study. More research with larger groups, longer timeframes, and different populations is needed to understand how consistent or lasting these changes might be. If you’re doing slow calf raises and noticing your calves feel stronger or look slightly fuller after several weeks, that’s consistent with what this one study observed — but don’t assume it’s the only way to build muscle or improve function.