Although uphill hiking requires stronger core, upper legs and CNS (central nervous system), the main difference is in calves.
This post is about uphill hiking and how it is enhanced by calf training.
I want to make it clear that whether you'll be uphill, downhill or flat terrain hiking - benefits of compound exercises (in our case, squats and deadlifts) are always more than any other exercise. Do not sacrifice even 1 rep of any compound exercise to do more of calves. Simply add calf exercises to your routine while still focusing on compound exercise progressive overload the most.
As you'll read in a minute, when you're going to train calves you can forget about your entire lifting schedule and do them anytime without any gear.
Calves are used for feet movement and especially toe movement, which are more active on an incline. When you walk uphill or go upstairs, using your toes you active your calves more to be able to lift the heels that are down below. Things should be considered;
Muscle Fibers
There are two types of muscle fibers: fast twitch and slow twitch.
Fast twitch fibers
Fast twitch fibers are used for explosive performances (e.g. sprinters). They're very powerful in short period, but get exhausted quickly. That's why they respond better to high intensity, low volume training. When trained and backed up with a decent nutrition, they grow a lot. Usually they aren't involved in our everyday activities and hence unless practiced, our control on them are limited. Examples: Chest, hamstrings.
Slow twitch fibers
Slow twitch fibers are used for endurance (e.g. marathon runners). They're weaker in the short term, but can perform for very long period of time without getting tired. That's why they respond better to low intensity, very high volume training. When trained and even backed up with a decent nutrition, they remain in a slim appearance and don't grow a lot. Usually they're more involved in our everyday activities and hence adapted to regular tension. Examples: Deltoids, abs, calves.
Calves of most people have more slow twitch fibers. They're adapted to regular tension as they're used everyday, all the time.
Genetics
Another important thing you should know about calves is that they're one of the most genetic dependent muscles if not the most.
Generally speaking; the lower the calf (at right), the more fast twitch muscles and usually larger & more muscular appearance.
Their size are highly up to insertions.
This is why you can see a huge bodybuilder with baby calves (high insertions) and a skinny, untrained 18 year old fella walking with twice as big calves (low insertions). It's unlikely to see a similar trend in any other muscle.
Yes, it's true that the lower the calf, the more of fast twitch muscles. However, slow twitch muscles are always superior in number in our calves (soleus & gastrocnemius) [1].
And although they're very highly up to genetics (I'd say, around 90%) and hence tough to strengthen, there are things you can do to bring them up.
Routine
Exercise
Stand on a flat ground with your hip width stance.
Step 1: Slowly lift your heels as high as you can. When I say slowly, I mean it should take 2 full seconds to lift them completely.
Step 2: Squeeze your calves at the top for 2 seconds. No, don't just squeeze them, pretend as if God is pulling your heels from above with all his mighty power and making you stay there for 2 seconds.
Step 3: Lower your heels slowly for 2 seconds. DO NOT touch the ground.
Repeat 100 times.
It's 2 seconds concentric, 2 seconds squeeze and 2 seconds eccentric. 1 rep should last 6 seconds, and 100 reps 600 seconds, 10 minutes.
If you really want to reap the benefits of calf improvements, I recommend this routine everyday for 10 minutes. You don't need shoes, socks, stairs, certain time of the day etc. Just do them.
Cardio
When you're in the gym and will be doing cardio, going for inclined treadmill HIIT cardio will provide the best results for your calves and hence overall uphill hiking performance.
Step 1: Warm up. Walk on flat treadmill for 5 minutes.
Step 2: Up the incline to 15 degrees and walk at ~3.5 mph for 1 minute. Then rest walking at ~2 mph for 1 minute. Do not change the incline. Repeat 5 times.
Step 3: Cool down. Walk on flat treadmill for 3 minutes.