Objective: To change implicit and explicit bias so that active obese people are regarded as more fit and normal weight sedentary people as less fit. Design: Study one created a questionnaire that measured perceptions of active obese persons and sedentary normal weight persons on fitness-related items. Study two used a modified visual probe task to retrain perceptions regarding active obese persons and sedentary normal weight persons. Main outcome measures: Self-reported explicit bias was measured with a questionnaire and implicit bias was measured with response times collected during a visual probe task. Results: The questionnaire reliably measured 'fitness and fatness' perceptions. In study two, pairing images of active obese persons with positive activity-related words resulted in active obese persons being explicitly rated more fit; pairing images of normal weight sedentary persons with negative words associated with sedentary lifestyles increased endorsement of normal weight people as unfit. There were no changes in implicit bias. Conclusions: Bias regarding how body weight is thought of relative to fitness can be altered by pairing images of obese persons being active with words such as 'health' and 'fit'. This is evidence that representations of persons of all body weight should be used when promoting physical activity.