Will exercise worsen a fissure?

Yes it can. Any exercise that increases intra-abdominal pressure can worsen a fissure. Weight lifting and strenuous activity might cause this.
No. Typically not: aerobic exercise will not worsen condition. Strenuous resistance training with heavy weights may cause stress at anal canal maybe prolapse and should be avoided during active anal fissure.
Depends on exercise. Anal fissures are caused from passing large, hard stools. Poor diet (lack of adequate fiber and water intake) as well as inactivity can lead to constipation. Constipation leads to large hard stools. Moderate exercise, especially walking can help to regular the stools and actually improve problems with anal fissures. Exercises that cause straining could potentially aggravate the fissure.