That's an interesting one - and you will probably get different answers, depending on who you ask! On the surface, preparing for two disciplines (cycling and running) eliminates the need for swimming (which itself is quite a technical sport and difficult to master, especially if you are starting later in life). That said, many - and we would agree - feel that Duathlon races can feel harder than a Triathlon. With no impacts in swimming, your speed is often limited by your own technical skills (or lack of!), rather than simply physical effort. Starting a race with a run, heart rate can be very high from the start and combined with the physical impacts of running (with a cycle and a second run still to come), many find the overall impacts of Duathlon racing harder.