Gaithersburg Mayor Sidney Katz joined city residents in a Zumba dance class at the International Fitness Party in the Park on Friday. The event brought a variety of fitness and dance classes together for local residents to sample at the City Hall Concert Pavilion. Zumba, belly dancing, tai chi and Bollywood moves were on the schedule at the fitness party. The 15-minute classes concluded in a cool-down period at the end of the event around 9 p.m.