There may be many reasons for arm trembling, one of which may be that your muscle strength decreases after a period of no exercise, which leads to muscle fatigue and instability when you do bench press. This doesn't necessarily mean that your physical fitness level is getting worse, but it does mean that you need to gradually increase the intensity and frequency of exercise to maintain the adaptability and stability of your body.

In addition, other possible reasons include: lack of sleep, inadequate diet, malnutrition, fatigue, tension or anxiety. Therefore, in addition to increasing the intensity and frequency of exercise, you also need to pay attention to maintaining good living habits and mentality.

Finally, if this happens frequently, it is recommended to consult a doctor or fitness instructor to learn more about muscle jitter and how to prevent it.