Muscle is in a state of tension and congestion after exercise, and at this time, blood is filling muscle fibers, making them feel moderate swelling and oxidation at the same time. When your muscle fiber has not reached that level, but the strength is over, blood can't complete oxidation and metabolism well in muscle tissue and expand circulation well in muscle fiber, because the muscle space you provide for it is not enough, that is, it is not developed enough. So there will be this involuntary trembling. Normal, as long as it is not excessive in the future or with the improvement of muscle development, it will improve.