“Brittany Runs A Marathon” (**1/2 out of four) was an agreeable comedy about an overweight young woman named Brittany (Jillian Bell) who decides to get her life together and start training for the New York City marathon but finds this is harder than she initially thought. Uneven movie has enough laughs and surprisingly tender moments to make it overall worthwhile. Bell’s first-rate performance holds the script together and keeps you watching even through periodic lulls.