An electronic fitness device comprises an optical transmitter, a first lens, an optical receiver, and a second lens. The optical transmitter is operable to transmit an optical signal. The first lens covers at least a portion of the optical transmitter and is operable to direct the optical signal into the skin of a user in a first direction outward from a center of the electronic fitness device. The optical receiver is operable to receive optical signals modulated by the skin of the user and to generate a photoplethysmogram (PPG) signal resulting from the optical signal. The second lens covers at least a portion of the optical receiver and is operable to receive a modulated optical signal from the skin of the user in a second direction inward toward the center of the electronic fitness device and to direct the modulated optical signal toward the optical receiver.
