Exercisers choose their own fitness adventure at Studio Twenty Inc., where the class schedule brims with opportunities to stretch, dance, and pedal. Star Trac spinning bikes welcome cyclists of different sizes and skill levels with grippy, adjustable seats ideal for treks over imaginary hills and under imaginary limbo poles. Four types of Zumba classes, including options for kids and seniors, melt calories with Latin-inspired dance moves set to salsas, merengues, and cumbias. Class sizes are small, which lets students soak up personal attention from the instructors.