It is ok to use 3 kg dumbbells for a long time, but whether it is suitable for you depends on your physical condition and health goals. If you are a beginner or have poor physical fitness, a 3 kg dumbbell may be more suitable to help you gradually increase your muscle strength and endurance. However, for experienced bodybuilders, 3 kilograms of dumbbells may not be enough to effectively stimulate further muscle growth.

To choose the right dumbbell weight, you can consider the following factors:

1. Your fitness goal: If your goal is to increase muscle strength, you may need to choose a heavier dumbbell. If your goal is to build a figure or improve muscle endurance, 3 kilograms of dumbbells may be enough.

2. Your physical condition: If you are a beginner in fitness or have poor physical fitness, it is more appropriate to choose a lighter weight at first to prevent injury. If your body has adapted to lighter dumbbells, you can gradually increase the weight.

3. Your training plan: If you plan to do high-intensity weight training, 3 kilograms of dumbbells may not be enough to challenge your muscles. According to your own ability and training plan, choose the right weight to ensure that you can achieve your goal.

In short, using 3 kg dumbbells for a long time may be suitable for beginners and people with poor physique, but it may not be challenging enough for experienced bodybuilders. Therefore, when choosing the weight of dumbbells, we should comprehensively consider our physical condition and fitness goals, and gradually adjust the weight as needed.