Trail running - think of it as fell running's slightly friendlier cousin and road running's gnarlier, but easier on your legs, compadre - is a great way of staying fit for mountaineering or hill-walking, but also a cracking sport in its own right.
If you're already into the outdoors, there's a good chance that some of your kit will do double duty for running. But along with specialist trail-running shoes, clothing and packs designed to work on the run, will be more comfortable and capable and well worth looking at if you plan to run regularly.
So what should you look for in your trail running kit? Here are some guidelines to help you choose shoes, shorts, tops, shells and running packs or bum-bags complete with links to our reviews on each area.
You can of course just scroll on through or if you're interested in a particular area, use the quick links below to jump straight to that section. See you on the trails!
Trail Running Shoes
In really simple terms, choosing a trail-running shoe is all about balancing grip, cushioning and trail feel or nimbleness in a package that fits your foot comfortably. Your priorities will depend on both your running style and the conditions you run in.
As a rule, the more cushioned a shoe is, the more comfortable it will be on harder surfaces, but the less feel for the trail you'll have. You'll also find cushioned shoes more forgiving on longer runs. Light, nimble runners can often get away with less underfoot cushioning, but it's very much a personal preference.
Most mid-sole cushioning uses EVA, but several brands have developed their own variants that are bouncier or longer-lasting.
Two things determine grip levels: the rubber compound and the shape and size of the lugs on the sole. Softer rubber tends to grip better, particularly on wet rock and hard surfaces generally, but the pay-off is faster wear rates.
The other factor is the depth and aggressiveness of the outsole lugs and pattern. In general terms, the toothier the sole, the better it will cope with softer surfaces and mud in particular, but the more it will squirm on harder stuff.
The trick is to work out what matters most to you and choose your shoes accordingly. If you run a lot on rocky terrain then a shoe with soft rubber and medium tread is a good start, if you tend to be out on grassier, muddier stuff then prioritise a toothier sole.
Trail running shoe get a real kicking, particularly in the mountains, so its worth finding a shoe with lightweight reinforcement to the uppers or you may simply wear through them in double time. Toes get a particularly hard time, but watch out for insteps and other areas of the shoe too.
Modern shoes often use seamless uppers with bonded protective film to add lightweight abrasion protection. However in general, the more durable the shoe's construction, the heavier it's likely to be.
It seems logical that an off-road running shoe should be waterproof, but in reality, most trail runners prefer a fast-drying, non-waterproof shoe to one that fills with water and then takes ages to dry out.
A compromise solution is a waterproof sock, but our general advice would be to avoid waterproof liners except maybe used with gaiters in full-on winter conditions. As a bonus, it'll save you around £25 on purchase price.
For an overview of the best 2016/17 trail running shoes, see our Best Trail Running Shoes article. Finally, as with other outdoor footwear, we'd strongly suggest that you try carefully before buying.
Trail Running Shorts
The good news is that terrifying, split-sided, fell-running shorts are no longer compulsory. Instead both outdoor brands and running specialists are producing longer-cut, more aesthetically-pleasing shorts that don't make you look like a refugee from the 1970s.
Most specialist running shorts come complete with an integral liner and, increasingly, these are becoming longer and more supportive so you get the anti-chafing benefits of a Lycra-type short, but with more, er, casual looks.
Shorts from Salomon and Montane go even further and use a single inner panel to eliminate fabric bunching between the thighs. The only downside to a stretch lycra-type liner is that it can be warmer in hot conditions. Make sure the liner is snug enough to stop unwanted, erm, flapping about, an issue we had with Montane's otherwise excellent VIA shorts.
It's always handy to have a pocket to hold keys, an emergency tenner and maybe a gel or two just in case. The best place for these is out back unless you're planning to use a bum-bag, in which case you won't need them anyway.
Fabrics And Construction
Quick-drying and fast wicking polyester is a good outer short fabric. inner shorts will tend to use some elastane, which means they're stretchy, but lose a little breathability as a result - elastane is pretty much rubber...
Wider, comfortable, elasticated waistbands are the way to go. Make sure there's a back-up cord to keep fit snug. Generally you want shorts to be unrestrictive, but not too baggy or flappy.
Recent reviews include the Montane Trail 2SK - double construction, great colour. Patagonia Nine Trails, weighty, but comfortable and reliable. The Arc'teryx Adan short which is ultra-lightweight and airy thanks to a more minimal liner. And the excellent Salomon Fast Wing TW shorts which like the Montane, are a sort of hybrid lycra/baggy mutant.
Finally, when things get cooler, have a look at the affordable, but rather good Alpkit Koulin Trail Tights.
Trail Running Tops
Unless you run very cool, you'll be best of with a high-wicking, quick-drying baselayer-type top. A simple tee shirt will do just fine most of the time, maybe with the addition of long-sleeves for winter use.
The majority of running tees use polyester for its quick wicking properties. That said, in cold weather particularly, merino wool is an interesting alternative. It doesn't wick or dry as fast, but if you're not going to sweat outlandishly, it's comfortable against the skin and has natural anti-odour properties.
Most running tops are simply designed, but adding a zip will give venting options, while a collar can help protect the back of your neck from sunshine. Speaking of which, fabrics with a high UPF sun-protection factor are a good call in summer.
Other handy features include reflective details for night-time safety, flat-locked seams for comfort and anti-odour treatments to stop you reeking like an old sock...
Chances are you already own something suitable, but we liked this Salomon 1/2 Zip Agile Tee for summer running and the Rab Aeon Tee does a great basic gig with excellent Polygiene anti-microbial treatment helping it to keep smelling fresh.
Trail Running Shell Jackets
Although some races and events require you to carry a waterproof jacket, many runners prefer to simply use a windshell instead. The thinking is that you'll get wet from your own sweat anyway, so you may as well choose a more breathable, more comfortable windproof instead.
Even the most breathable modern waterproof fabrics are still going to be overwhelmed when you're working hard. If you run cool, you may be able to cope with a waterproof and if it's really wet, it simply feels more protective, but most days, a lightweight windproof will do the job.
What To Look For
Ideally you want a slim-fitting jacket that doesn't interfere with your running action or mobility generally and won't flap in the wind. Hoods need to stay put and move with your head - try carefully before buying. Some method of tabbing down the jacket when it's not being used is a really good idea and stops irritating flapping as you run.
We're happy with a single pocket to hold a phone or keys. Positioning is important to stop bounce and flap. And with waterproofs, some sort of venting option is a good call. The Montane Spine Jacket - above - has pit-zips, others use permanent vents.
If you're planning on carrying the jacket, you'll want something as light and compact as possible, ideally less than 100g but certainly no more than 200g.
On the windproof front, we're super impressed with the Arc'teryx Incendo Hoody and its women's specific counterpart, the Cita Hoody. Also very good is the Patagonia Houdini Windproof jacket, a versatile, no-nonsense windshell that won't weigh you down on the trail.
Trail Running Packs and Bum-Bags
The longer you're out, the more useful it is to have some extra carrying capacity to carry spare clothing, food - gels and bars are an obvious choice - and crucially, water.
There are two obvious contenders for your coin, bum-bags and lightweight running packs. Both have pros and cons.
Bum-Bags / Lumbar Packs
Bum-bags - also known as 'lumbar packs' or, in the US, 'fanny packs' - are a stable, convenient way of carrying small loads. They keep weight low and stable, plus leave your back free to breathe and sweat.
Points to look out for include a comfortable interface with wicking fabric, secure, wide-ish straps, a little stretch may help keep things in place. And easy access storage and compartments for anything you want to carry.
Some packs have gel loops, pockets for a phone and bottle holsters, but it's all down to personal preference. We like a separate phone pocket, but your mileage may vary.
And a rule, running-specific packs sit high on the back and use a stretchy harness or strap system to stay snug and stable without restricting movement or breathing. 'Race vests' like the Montane Fang 5 above are pretty much wearable, wrap-around items, half clothing, half pack and work very well, though they are warmer in hot conditions.
Features to look out for include easy-to-reach stash pockets for gels, bars, gloves and so on. Facility for a hydration system or bottles and enough storage space to cope with any spare clothing or items. The lighter your kit, the less capacity you'll need, but a built-in bungee cord system lets you stash extra kit if necessary.
Packs we've tried recently include the Montane Fang 5, a lightweight, comfortable race vest. The Osprey Rev 1.5 which mixes conventional and race vest features with some neat extras and the Nathan Fireball which we liked, but found a little low on capacity.
Finally the Camelbak Octane LR is a neat multi-sports pack that ingeniously carries fluids low down in the hip area for improved stability.
Trail Running Socks
Ideally trail running socks should minimise bulk but still provide decent cushioning in strategic areas around heel, the ball of the foot and the toe box. There's no 'right answer', but we've used running-specific socks from Bridgedale, Falke, Smartwool and Sealskinz successfully.
On longer runs, some hardened ultra specialists favour socks with individual toe compartments and lavish helpings of vaseline or similar lube to minimise blister issues.
One awesome sock for those with dodgy ankles is the Falke Stabilizer which reinforces your proprioceptor response to help prevent you from twisting your ankle again. In a nut-shell, it simply helps your brain to know what angle your foot is at relative to the rest of you. Sounds nuts but works really well.
Finally, we've had limited success with waterproof Sealskinz socks for running use. Yes, they keep water out to a point, but ultimately it always seems to get inside if it rains. Plus they're simply not cushioned or breathable enough. We'd save them for the bike.
Trail Running Accessories
Finally, there are plenty of extras that are worth a look. A good running head torch can make the difference between getting out on winter evenings and not. We prefer a broad light spread over a narrow spot, but even better is both.
USB charging is great for convenience and messing about with batteries, while simple, intuitive controls you can use with gloved or cold hands are more use than millions of complex settings. We'll be testing a whole raft for head-torches shortly, but for a good starter, have a look at our Ten best head-torches for running overview.
Don't get carried away though. One of the joys of trail running is the freedom that comes with moving fast and light across the hills.