There are a number of things which can cause frequent urination
. While there is no direct evidence that exercise itself causes a significant increase in urination, there are some factors which may exacerbate the need to go to the bathroom. The most common is also the simplest, that being an increase in fluid intake. If you drink a lot during your workouts, your body absorbs what it needs but then needs to get rid of anything extra, and this is done in the form of urination. Sometimes decreasing fluid intake will solve the problem. That said, you need to find a happy medium between getting yourself dehydrated and overloading yourself. Other mechanisms exist as well. Especially in overweight individuals, the elevated heart rate from exercise can cause temporarily high blood pressure. One of the body's first defense mechanisms for high blood pressure is to decrease blood volume, hence fluid is excreted as urine. Another mechanism is that certain exercises (especially lower body and abdominal) can increase pressure on your bladder giving you the sensation that you need to go, even if your bladder is not full. Lastly, if you are taking any supplements when you work out, many of these have diuretic properties which means they will induce urination.
Moving your workouts to earlier in the day may prevent you from feeling like you have to urinate at night, and this is something you may want to experiment with. However, while all of the above causes may be benign reasons for your increased urination, it can also be caused by more significant issues, including diabetes, hypertension, pregnancy, hormonal imbalance, urinary tract infection
, etc. If your frequent urination does not seem to be related to your exercising and persists, you should discuss this issue with your primary care physician
who will evaluate you for causes of your condition.