The reason why I feel lighter after practicing dumbbells may be because of muscle fatigue. When you do strength training, your muscles need to overcome gravity and the weight of dumbbells, which will make your muscles feel tired. When you finish the exercise, your muscles will feel relaxed and your arms may feel lighter. In addition, when you exercise your muscles, they will consume a lot of energy, which will also lead to muscle fatigue and relaxation.

In addition, the reason why shaking your arm feels more relaxed after practicing dumbbells may be because of the adaptability of your muscles. When you do strength training, your muscles will adapt to gravity and the weight of dumbbells. When you continue to practice, your muscles will gradually adapt and be able to overcome gravity and the weight of dumbbells more easily, which will make you feel more relaxed when shaking your arms.

In short, it is normal to feel lighter or more relaxed after practicing dumbbells, because muscles have adapted to gravity and the weight of dumbbells and need to consume more energy to keep their bodies stable. If you feel uncomfortable or painful, it is recommended to stop practicing and consult a doctor or professional coach.