Dumbbells can't thin arms. Lifting dumbbells is mainly to exercise hand muscles. It is possible that the muscles will increase and the hands will be thicker. Now there are some movements to exercise your arms, so you can keep practicing. You can learn from Keep or some fitness experts, mainly by persistence. Dumbbells can't thin arms. Lifting dumbbells is mainly to exercise hand muscles. It is possible that the muscles will increase and the hands will be thicker. Now there are some movements to exercise your arms, so you can keep practicing. You can learn from Keep or some fitness experts, mainly by persistence.