You must not push yourself too hard and neither should you undergo overexertion. Every person’s limit is different when it comes to bearing the level of discomfort. So you must exercise during menstruation only up to the level you think is permissible for yourself.
Physiologically, there is no evidence that suggests against working out on the first day of period. So the decision to hit the gym is completely personal and based on how you are feeling on that particular day.
On day 1 of menstrual cycle, start with stretching. It is a safe way to kickstart your work out and also assists the body in easing out the cramps. Some of the common gym exercises that can be useful in such cases are walking, aerobics, dancing, stretches and light weight training. All of these provide you with the required exercise while helping you relax. Cardio training like walking specifically helps during cramps and when you are feeling irritable. Aerobics also helps you relieve other symptoms of periods. Avoid jogging specifically when you are suffering from pain due to menstruation. Light weight training is also advisable if you feel your body would be comfortable doing it.
Pay special attention to your posture at all times, especially on the first day of your period. If you feel bloated and tired all the time, it would definitely affect your posture and you will sit in a slouchy manner. This can happen more during strength training. Check out the strength training for beginners to learn about how to perform strength training effectively without injuring yourself.
When you are exercising, you are prone to dehydration. So you must drink water at regular intervals during the workout and even post that. Ideally, it is advisable to drink 10-12 glasses of water daily during the menstrual cycle. Regularly hydrating yourself ensures that your body doesn’t bloat up during menstruation.