The Right Leg Drive (RLD) amplifier can reduce the common-mode voltage
interference that typically affects biopotential measurements. For enhanced
performance a three electrode solution is recommended (where the third
electrode is the output of the RLD amplifier).
A performance somewhere in between the two and three electrode solutions can be
achieved with a two electrode system where the RLD amplifier instead of driving
its own electrode, drives the input pull up resistors where VIN+ and VIN- are
connected to (see Figure 62 in the datasheet).
Heart Rate monitors (for peak detection) with short cables, such as a chest
strap may not need to use the RLD amplifier. Applications with long cables will
benefit the most.