If the muscles of the throat are stiff, then your rhythm will get worse when are singing.
This is the same with dancing. You can’t dance well if your muscles or joints are stiff, making it hard to move your shoulders or knees.
The rhythm of the voice is relevant to the movements of the muscles, such as the cricothyroid muscle, vocal muscles and the lateral cricoarytenoid muscle. Those muscles are especially important.
Additionally, controlling your breathing is also important. This is relevant to the diaphragm’s role of vocalization, which inlcude the internal and external intercostal muscles.
Therefore, if the muscles of the throat or diaphragm are stiff, in turn your rhythm will be noticeably off or bad when singing. Being aware and understanding the connection between all the vital muscles used for vocalization will improve your ability to sing.
Note:For acquiring great breathing when singing, the costovertebral joints(C3 to C10) need to move smoothly.