20kg backpack rucking - good for cardio?

For strength it works even if you walk very slowly

For cardio I think you need to get into zone 1 (>60% of max HR)

If you run 60km/wk it will be no problem to walk fast enough to exceed >60% of max HR and still enjoy the walking. With a 20kg bp it is hard to NOT exceed it at least if the terrain is not flat.

I once did a lot of golfing, carrying the bag. I was amazed how little running I needed to be in a decent shape for racing. That proved that walking with extra weight can be more effective than anticipated. I did not walk as briskly as I would recommend you so obvisously even lower intensity has an effect. I could not call walking efficient (it takes a lot of time), but it is obviously effective.

Seemed like a good Idea to me--at the time. Did it for a year or so. 10-20 lbs. 8 mi rum home with backpack. Later, I showed up with displaced L3, 4, and 5.

I used to hike and climb all summer at Mt. Rainier National Park during the summers back in the mid-70's. Carried a lot of loads between 50-75lbs for weeks on end. I usually had about a week to 10 days before high school started. I wasn't in the best of running shape but could run up hills well and could keep going for a long time. As the season progressed my times dropped and my placings were higher.

Running with weights can only be performed to develop speed and strength capabilities. Such exercises are performed with maximum power and for a very short time. In fact, they are accelerations of no more than 100 meters. Running with weights for long distances will not bring anything but injuries. The biomechanics is broken, the load on the musculoskeletal system is significantly increased, and the emphasis is shifted from sharpness and ease of movement to breakage force, which contradicts the laws of economical running. You can use it as a weighting agent https://www.amazon.com/Mato-Hash-Drawstring-Promotional-1PK-100PK/dp/B076VSDHM3?th=1.

Training this way will definitely get you fit for backpacking and overall fitness but I doubt it will do anything to help with improving oh, say, your 5k time. If you’re only considering overall fitness then, yes, it’s a good idea.

Used to go hiking with a guy that hiked a lot. Had done the Appalachian Trail etc. He was a pretty tall guy and not a great runner but could really hike. I had just gotten out of college and was probably a sub 30:00 10k runner at the time and he would consistently leave me in the dust.

So I backpack all the time and my pack is usually 40 to 50 pounds for a weekend or long weekend trip. It is great for cardio fitness especially if you are going up hill. Going uphill without weight is helpful but with weight it will definitely get your heart rate up and is also good for developing your glutes and quads and helps with core strength and balance.

If you are just planning on filling a backpack with weight I think you can go lighter than 45 pounds and still get benefits. I have a weight vest I use for similar purposes and I usually max out at 30 to avoid back strain and fatigue.

Good luck