I recommend acquiring the text Starting Strength (3rd edition if possible) by Mark Rippetoe. It's a strength program for novices and most of the text is spent explaining how to execute the key lifts of the program with the correct form - those lifts being, squat, deadlift, bench press, shoulder press and the power clean.

I recommend it because I like doing a lot of the things you listed, and I've spent a lot of time doing conditioning work with things like body weight exercises, sand bags, ropes, kettle bells, etc. I was really fit and in great condition, however I didn't put any noticeable muscle on - not that was a goal of mine at the time.

However doing the Starting Strength program my strength rapidly increased and I packed on the muscle. To build muscle you need to provide the stimulus to force adaption, and lifting heavy is by the far the most efficient way of achieving this.

Also you'll want to eat a lot, you'll need a calorie surplus. If you handle dairy I'd recommend consuming raw a2 milk, milk being very anabolic, it seems to aid strength gains better than anything else that isn't a drug.

Once you reach the strength level you desire, it will be easy to maintain with less work, and you'll be able to do other things you enjoy and hopefully be able to perform a little better at them as well.

Here is some good info:

http://www.marksdailyapple.com/gain-weight-build-muscle/

Eat calorie dense hyper-palatable foods. Fatty seasoned meat, some nuts, guacamole, buttered cinnamon covered mashed taters, coconut milk smoothies etc.

Hi and welcome!

(You’re in a similar boat to me back when I started weight training; I feel I have a lot to offer regarding this particular question, so although I’ll try and be as succinct as possible, feel free to ask anything else or for further explanation).

First off, I agree with 2 of your statements; (1) you’re underweight (or at least, nowhere near your ‘natural muscle’ potential), and (2) weight-training, or weight-training style exercises are the best way to go about addressing (1) – at least to begin with (further detail below).

To put your ‘stats’ in context, I am 5’7” (168cm), 170lbs (75kg), and around 10-11% BF, with a BMI of around 28 (just to highlight the uselessness of BMI!). So were pretty much the same except I’m 50lbs heavier. It only took me around 9-12months in a gym to go from 60kg->75kg in the same lean state.

Rather than reeling off a list of vanilla (but largely true) statements like ‘do compound moves’, ‘keep intensity high’, ‘eat more calories’, I’ll point you towards some useful online/ paper resources, and invite you to do some reading:

If you take the advice of (what I assume) 99.9% of people will give you (i.e. hit the gym). I recommend you check out all the following resources even if you have no intention of joining a gym; the information around how/why/when to train, and how to best go about it is invaluable:

Specific training methods: stronglifts.com (beginners training, recommended); elitefts.com (& 531 ebook download $19.99); book: SuperSquats by Randall Strossen (brutal, not recommend for at least 6 months, but by far-and-away the best training method for getting big and strong fast)

general resources (my list after years of sifting through rubbish): t-nation.com book: Power to the People! By Pavel Tsatsouline google search: ‘Greasing the groove Pavel Tsatsouline’  READ THIS!

while stronglifts 5x5 is a bit of a bland method of training, this is great for ‘gym newbies’ as it keeps the volume relatively high, enabling you to focus on muscle size, endurance, correct form, and keeps the strain off your joints and ligaments.

Jim Wendler’s 5-3-1 e-book is fantastic and my preferred method of training. Whether you use the system or not, the reading around assistance exercises, their purpose, and how many you need and when, is again invaluable.

If this is the route you decide to go, I also recommend asking this sort of question on a forum like sugdenbarbell, uk-muscle, or even myprotein (whilst studiously avoiding anything body-building.com related).

If you stick to ‘other activities’ and some home-exercise, good on you (probably healthier in the long run!), but progress will be considerably slower. If possible, I recommend you consider gymnastics.

The issue with gymnastics is it also requires a base-level of conditioning; but once you get there you'll get hooked. And things like planches, tucks, leg raises, human flags, hand-stand pushups et seq are, in my opinion, the ideal exercises for paleo-enthusiasts and general health.

All of the above is linked to STIMULATING muscle growth. As mentioned by plenty of others; to actually ACHEIVE muscle growth, simply stuff your face with more food. The more, the better, simple as. I'll leave the question of diet to the resident experts; since my answer would be to start drinking lots and lots of milk (paleo or not :P)

As a final thought: and yes I did promise I wouldn’t give generic recommendations, but I can’t stress enough the benefit of one particular exercise: deadlifting. Even at home, all it takes is a concrete floor, a few hundred kilos of Olympic plates, and a bar. Including deadlifting into whatever you choose, will increase you progress exponentially.

Hope some info linked here you find useful :)

I wouldn't get too bogged down in the numbers while you're changing things, pretty much all measurements for body composition that'll be easily available to you are too variable in the short-term. Focus on how you feel, and understanding when/if you're hungry, what your energy levels are etc.

Hiking, kayaking and rock-climbing are all excellent things to be doing, but I expect it would take a while to see significant muscular development. Your body is more interested in increasing efficiency, and between that and improved technique, you'll find it difficult to gain the progression you really want with those activities. So I'd say it's definitely worth utilising high-intensity weight workouts. These can be bodyweight based, and endlessly modifiable so that 15-30 minutes once a week is sufficient if you go for maximum intensity. In fact it should be all you can manage.

So low volume, high weight is the way to increase muscle size. The fundamental movements to work with are pushups, pullups and squats. There's variation in the recommendations but it's mostly detail - you should be creating a good environment to build. Don't hold back on the steaks. If you're not progressing try eating more. There's no particular reason to load up on carbs for the sake of it - if you only have one 'intense' workout a week then 100g carbs should be plenty. But if you're out every other day trekking or on the river then you might as well eat as much as you possibly can of solid whole foods. And really make sure you get good sleep every night, and don't push your muscles hard while in recovery. It doesn't take much if you give your body the opportunity.

I would like to stick with exercise that uses natural movement--hiking, kayaking, rock climbing, sports, etc. rather than going to the gym and lifting weights; though I wouldn't mind some pointers to a half hour routine I could do at home 2-3 times a week that might include weights.

While there are good bodyweight exercises such as dips and pullups, your task would be far, far easier if you joined a gym or had access to one...

Yes, eat dairy. Don't do intermittent fasting, as it will be tough to get enough calories in to really gain weight - instead eat many LARGE meals a day, push yourself. If you tolerate lactose then drink milk post-workout, if not you can still consume large quantities of cheese, an extremely protein and calorie dense food.

Starting Strength (startingstrength.com) is a great training plan to follow until you are normal weight with muscular build. Its basically three working sets of five reps of each basic compound barbell lift (deadlift, squat, benchpress, overhead press, and power cleans).

Lift heavy with your biggest muscles. ALso continue the exercise you mention. Lots of protein and dairy (eggs, meat, whey protein and cottage cheese).

Can I suggest you look up "Convict Conditioning". It's. A great body weight training manual, even with the slightly off-putting title.