In people who have not previously trained, performing 8 weeks of traditional weightlifting exercises for the biceps leads to greater increases in muscle size and strength compared to performing...

We analyzed one assertion on this topic and found that in people who have not previously trained, performing 8 weeks of traditional weightlifting exercises for the biceps led to greater increases in muscle size and strength compared to exercises that involve holding a weight in a stretched position without moving it [1]. This single assertion suggests that isotonic exercise — which involves moving a weight through a full range of motion — may lead to more noticeable gains in muscle and strength than eccentric quasi-isometric exercise — which means holding a weight still while the muscle is stretched, without changing joint position. We did not find any studies or assertions that contradicted this finding. However, our analysis is based on only one assertion, and it does not include data on other muscle groups, longer training periods, or different intensities. The evidence we’ve reviewed so far leans toward isotonic exercise being more effective for building muscle and strength in untrained individuals over an 8-week period, but we cannot say this applies to everyone or every type of training. The difference may be due to how each method stresses the muscle: isotonic movements involve both stretching and contracting the muscle under load, while quasi-isometric holds focus only on the stretched phase. For someone just starting out, moving weights through their full range might provide a broader stimulus. What this means for you: if you’re new to training and want to build muscle and strength in your arms, doing traditional bicep curls or similar movements that involve lifting and lowering the weight may give you better results than holding a weight in a stretched position. But more research is needed to know if this holds true for other muscles, longer timeframes, or different goals.