Regular exercise, such as CrossFit and running, is not directly harmful to fertility. In fact, staying active is important for overall health. However, it is important not to overdo it. Extreme energy expenditure, such as through a severe diet causing rapid and excessive weight loss, can lead to a condition called amenorrhea, where menstruation stops. In these extreme cases, ovulation may also cease, affecting fertility. Overall, a balanced and healthy exercise routine tailored to your personal limits should not negatively impact fertility.