If you’re training right it never gets any easier, but you do get faster.

Having said that, most people when they first start can’t run slow enough to maintain a stable aerobic heart rate. The solution is alternating run / walk, building up to progressively more running between walk breaks.

As an example, right now I can maintain 11:00 mi / mile at, my threshold heart rate, where I can maintain a conversation, and feel like I can keep going indefinitely. So I run 80% of my runs at that speed, and the rest at faster speeds over shorter distances. Great.

But 2 years ago when I restarted running after a break, my aerobic pace was more than 13:00 / mile. That’s a problem because at that speed I can’t physically maintain the running mechanic. It breaks down. So the only options are to run faster than optimal, which means you’re not getting aerobic training (instead it’s anaerobic training); or to slow down into the walking mechanic.

Research suggests that slow running in the aerobic zone is the key to improving aerobic pace and endurance. And if that aerobic pace is not possible because of mechanics, then alternating run / walk is a good way to average out the heart rate.