The reason why music tracking can only be up to 138 seconds is because under normal circumstances, people's attention and memory can effectively follow the rhythm of music in a short period of time. Long-term music tracking may cause distraction and fatigue, affecting the accuracy and quality of tracking.

In addition, the time limit for music tracking is also related to the structure and rhythm of the music. Most musical works have a clear musical structure, including introduction, theme, chorus and other parts. Usually, the main rhythm and melody of the music will be repeated in a short period of time, so it is easier to keep consistent with the rhythm of the music in a short period of time.

In addition, long-term music tracking may also cause physical fatigue for ordinary people. Performing movements to the rhythm of music, especially more complex and fast movements, requires a certain amount of physical strength and endurance. Therefore, limiting the time of music tracking is also to protect your health.

It should be noted that the time limit for music tracking is not absolute. It can vary according to personal musical understanding and physical fitness. Some people may be able to follow the rhythm of the music for a longer period of time, while others may need a shorter period of time. Therefore, when tracking music, you should make appropriate adjustments according to your own situation to ensure the accuracy and comfort of tracking.