My impression is that it is definitely not as demanding as when you were plowing feilds with a team of oxen... but it is still physicall demanding. Sure, machinaty automates a lot, but that just means you are more productive and end up doing more of the labor the machine doesn't automate. Also from what I've heard, a lot of the work of modern farming is fixing and maintaining the machines that do the heavy lifting - which is also fairly taxing physical labor.