To target specific muscle groups with a mini exercise bike, you can adjust the resistance level and position of your body while cycling. For example, to target your quadriceps, increase the resistance on the bike and pedal in a standing position. To target your hamstrings, lower the resistance and pedal in a seated position with your feet placed further back on the pedals. To target your calves, pedal with the balls of your feet on the pedals and focus on pushing through your toes.