Walking vs HIIT Efficiency

Try the 7 minute workout (or similar). It's much more efficient than running.

Not saying walking is not good for you, but walking is very energy efficient. Your heart rate is probably higher reading HN, at least for me. Doing some sprints and other movements, like playing football, or moving the lawn, will give you a good workout though.

Surprising how few calories it burns, seems like a simple 30 minute walk would be better and have less of an impact.

Yes, but you won't gain much cardiovascular health from that.

What is it about walks that help? Would 30 burpees every hour have a similar effect? Is it heart rate? Duration?

The problem is that it takes time; for the same amount of time you can have a better "training effect". For less time you can have the same training effect. An hour sauntering around the city takes as much time as an hour biking at your lactate threshold. But your heart works a lot harder for that hour of biking compared to standing around waiting for traffic lights to change.Both are better than an hour spent replying to comments on HN, though!

It's burried in the article, but it's there: exact type doesn't matter, higher intensity / making you breath harder is better, dimminishing returns above 2.5 hours per week.

For calorie burning short intensive work outs are better. For example, deadlifts or playing squash for 30minutes is comparable to multiple hours of jogging.

what sort.. does this really work? Doesn't seem overly cardio to me...

Walking is not time efficient, you're better off doing 10 mins of HIIT than an hour of walking.