Hello, biceps brachii, triceps brachii and forearm muscles all belong to small muscle groups, so it is normal for you to feel tired during training. However, in some cases, your biceps brachii and other muscle groups may be tired during training: 1) If you are a novice, you may not be used to the weight of your training equipment, so it will take you some time to get used to it and then return to normal after a long time. A person's muscle fibers determine his sports attributes. Human muscle fibers can be divided into fast muscle fibers and slow muscle fibers. The former is explosive power, the latter is endurance. Maybe you are explosive. Its characteristics are: heavy muscle load, less exercise times and easy fatigue (limited number of words in mobile phone plus QQ thank you)