The long-running series in which readers answer other readers’ questions on subjects ranging from trivial flights of fancy to profound scientific and philosophical concepts

Is running up and down a hill better for you than running on the flat? Or does the downhill bit being easier counteract the uphill bit? What about running down a hill and then up, when you’re already tired? Steve Henderson, Wythenshawe

Send new questions to nq@theguardian.com.

A sample of 10,000. That’s quite a lot, should be enough to get a reasonable result.

– Hello, yes, could I have a word with the grand old duke of York please? bricklayersoption

I think the days of him being called “grand” are in the past nowadays. asparagusnextleft

Top tip: take your shoes off and throw them in the lake, and you can run uphill with no problem. (Although Ron from Sparks thinks you should have known that.) Mobilepope

Mr Henderson’s question is something a lot of runners have wondered about. I’ve written a scientific paper on the topic, combining treadmill data with data from races: From Treadmill to Trails: Predicting Performance of Runners. For the relatively small slopes that most runners spend most of their time running on, the uphills and downhills come very close to cancelling out. However, on very steep mountain trails people aren’t efficient enough at running downhill to make up for the climbing. I’ve written an open-source web-based app that will do a calculation for your GPS track. Ben Crowell

In my case, a 66-year-old man with a total knee replacement, running uphill is the only easy way to get cardio besides cycling. I can’t subject my new knee to too much impact or it will wear out prematurely. When running uphill I have way less impact due to the ground in front of me being higher than the ground I’m on. Also with more exertion I hit my desired cardio level faster and end up taking fewer steps. All Denes

I recently tripped running down a hill, shattered both the bones in my arm, and ended up in emergency surgery to put a metal plate in my arm. Based on my experience I’m going to say running down a hill is not good for you! Georgia Willox Dunant

Michael Moseley deals succinctly with this issue here. Alan Coady

How strange, I was just thinking about this. As someone who has suffered with a knee injury this year, I can tell you that running downhill is far, far tougher on your knees than running uphill – it’s the constant braking force running downhill that kills your knees. For the immediate future, all my training will be uphill. PtolemyHanshaw3

Yes, as anyone who has hiked on hills will tell you the knee pain coming down is worse than the muscle pain going up. Over time, that sort of trauma will lead to surgery, and running puts tremendous forces on the tendons and joints. To be avoided. nancyjt Downhill is particularly effective at highlighting anterior knee problems. Cuthberto

We have a fast flat parkrun course that I generally do in 23mins or so. There is also one where you run up a steep hill and back down it – I can’t get below 26mins on that. Yet on the latter I’ll be sweating more and feel a bigger difference in my legs afterwards. PeteTheBeat

Homo sapiens developed as an endurance hunter, we’re built to be able to efficiently lope along on the flat all day long. Clearly running uphill is harder work than running on the flat just on the old Newtonian weight x vertical distance moved. However, running downhill isn’t all rest, it requires effort, specifically eccentric contraction of the quads as a sort of shock absorber, to stop us “running away” down the hill, along with contributions from other muscles recruited to an unusual biomechanical pattern, as anyone who has ever suffered the dreaded Doms after a day in the hills can attest to. So yes, running up and down hills takes more effort than running on the flat. Whether it is “better” brings us to the question of joints. Everything in moderation. Ringstone

One thing I know. When you get in to your mid-70s, if you don’t walk up a hill for a while, then go up a steep one, your hips feel as if they are going to drop off your body. Busch

Not sure of the science etc but as a frequent runner, and I’m sure any other runner would agree, running hills is without doubt much harder than running flats. If you are used to running hills and then run a completely flat course, it hardly feels like a workout, so not sure why anyone would think running flats is equivalent to running a hilly course james187

If running the flat isn’t a workout you aren’t running fast enough! langers9

Running hills will make you fitter and makes flats seem effortless. I can almost effortlessly run up steep hills that leave most walkers and others panting and sweating; I feel as if I can run endlessly on flats. In fact, because I trail run in very hilly terrain every day, I find long flats boring. Even running at full speed, flats just aren’t a challenge. I like the variety of extreme trail-running. SueBBlue

To the extent that the objective of exercise is to raise your heart rate, running uphill is better for you than running on the flat, as your heart needs to work harder. That being said, running both up and downhill risks playing havoc on your knees (as I’m now finding in my 50s). DrJWCC

Running downhill is actually harder on the body than running flat. It forces the leg muscles to extend further in negative repetitions, which makes them feel more sore, and the impact of each step is greater, which can jolt the whole body more and can give you stitches or abdominal pain. The natural instinct is also to lean backwards to avoid the risk of toppling head over heels, which leads to more heel striking, resulting in lower efficiency and yet more jolting. The best advice for running downhill is to lean into the decline and go as fast as possible, which can sometimes feel scary if it’s a big downhill stretch.

All of which means hill running is significantly tougher on the body than flat running. It will definitely make you fitter and stronger than running flat, but comes with an increased risk of injury. A good recommendation is to mix up the two. FesLerdinand

In South Africa they is an annual endurance run, called Comrades. It is a 90km run between Pietermaritzburg and Durban – for mad people. In even years it is run between Pietermaritzburg and Durban. In odd years it is the other way round. Going down to Durban by the sea is considered harder than going up to Pietermaritzburg in the mountains because of the strain on the legs. I don’t know if this is true, because I still have my sanity and would not entertain the idea of trying it! Squeakysquirrel

The records for the two directions are quite interesting.

The record for the “up” run (87 km) is 5hr 24min 39sec. The record for the “down” run (90.2 km) is 5hr 18min 19sec.

So roughly six minutes faster to go 3km further. Looking at a map showing the gradients, I would have expected the “down” to be considerably faster. Troy_McClure

Always run up the hill, never downhill. Give it a few weeks and you’ll be amazed at your fitness levels. luce83

Sooner of later, you will run out of hill to go up, and that point you will have to go down, or just stay on top of the hill for ever. MonsterX

Running uphill definitely improves your strength and fitness, but the gradient naturally forces you to take shorter strides than you would on the flat, so keep running on relatively flat routes for the majority of your weekly distance to keep your form sound.

Lots of people here rightly saying that running downhill places lots of stress on the joints and ligaments. However, running down a gentle decline is useful practice for speed, as it gets your body accustomed to a longer stride. Just don’t do it too often and don’t go haring down anything too steep like a lunatic. You should still be able to land mid-foot. If you have to land on your heels to stop yourself going totally out of control, you are asking a lot of your knees and will probably regret it. fisheye

Whether or not it is better for you depends on your objective. But running up and then downhill is certainly harder work.

When you run uphill you are gaining potential energy as you put in more effort to overcome gravity. But when you run downhill you are not able to make much use of that potential energy you have stored, because you still need to keep your balance and control your speed. So over all, you expend more energy to run, say, 1km uphill and then 1km downhill than if you run 2km on the flat. And that is without the risk of injury, which many people have posted about.

As a comparison, if you were to cycle up a hill for 1km and then freewheel down for 1km there would be much less difference in overall energy usage compared with cycling 2km on the flat. That is because a lot of the potential energy you store when climbing the hill can be used to descend the hill, and the bike has low friction. You won’t quite get all the energy back as wind resistance opposes you (consuming energy) whichever direction you are going in. Mark_MK

Some people run for pleasure, others for exercise. I’ll stick to running from predators, as nature intended. Sotired42