In addition to rock climbing, I also go to the gym for strength training with free weights and machines. I know some muscle groups are crucial to rock climbing, such as arms, back and core. I also know there exist some "antagonist workouts". Practicing these "antagonist workout" can be help maintain a healthy posture. I wanted to know more systematically which muscles are important, and what are the most efficient workouts and antagonist workouts. Thanks!
There a few muscle groups that are heavily used while climbing:
- Lats: The side muscles of your back. Also termed as wings.
- Forearms (one of the first to tire out).
- Calves (for most of your tiny toe holds, these play a crucial role).
- Core (these are more like a link between the whole body).
There are literally hundreds of exercises for each of the above mentioned ones. However, I'll state the basic and the foundational ones for each of these. There are variants and different exercises that can't be covered comprehensively in a single answer (I'll be posting only body weight exercises).
Workouts that help you strengthen your lats:
- Pull-ups, chin-ups and pull-up, chin-up holds. These allow you to train your lats to take the weight of your entire body.
- Pull-up variants - Typewriter pull-ups, muscle ups et al. (There are lots of them).
- Bar hangs - helps to strengthen your grip strength.
Workouts for biceps and forearms:
- Push-ups and push-up variants (diamond, archer, typewriter et al)
Squats and variants of squats (helps with your thigh muscles as well).
- Plank and plank variants.
- Leg raises.
- Elbow lever.
Apart from all these, some of the key things in climbing which are often neglected by non-professional climbers are:
- Flexibility. Without flexibility you struggle big time on problems. Most of the times, it's more the flexibility than the strength that gets you through. As a climber, you'll have to use your body to retain tension. Strength alone can't get you through this.
- Wrists and finger strengths: Most of us part time climbers do not spend enough time on strengthening our wrists or fingers. Static holds like elbow lever, advanced techniques like tucked planches, and exercises like pullups and bar hangs help with the wrist and to some extent finger strengths. However, developing finger strength is much longer a process. Crimps, pinches, pocket holds are difficult and scary initially. There are static holds that you can use like these that help with the finger strength.
NOTE: In case you want to do dynos, you'll need dynamic strength as well. These are more related to the explosive power that you'll have to develop once you are more comfortable with static moves.
Ricketyship's answer gives a great outline of training the climbing specific muscles, so I would like to add several other points (especially as the question asked about antagonist training).
First off, the ability to generate and modulate tension is a key skill in climbing (particularly bouldering). Arguably the best exercise for training the ability to "flip the switch" and try hard is heavy deadlifts (3 rep or 1 rep max). For reference, the climbing coach Steve Bechtel considers a 2 rep max deadlift at 2X bodyweight for men and 1.5X bodyweight for women a guideline for high performance climbing. Properly executing a heavy deadlift requires almost every muscle from fingers to toes and has a large neurological component. Lifting large weights, however, does pose risk---get instruction on proper form before going heavy!
As for antagonist workouts, one of the largest problems to avoid would be "Climber's Back", i.e., the common hunched over position with forward rotated shoulders adopted by many climbers. To a large extent, this can be countered by stretching and mobility exercises, but working on building your chest (e.g., pushups) doesn't hurt!
After finger injuries, shoulder and wrist injuries are the most common in climbing. Doing exercises focused on strengthening and stabilizing these joints would be another excellent use of a non-climbing day at the gym. I's Y's & T's are a common exercise for shoulders and wrist extensor exercises and reverse wrist curls for wrists.
Taking a slightly different tact here, I'm going to recommend 3 exercises (or types of exercise), rows, squats and Turkish get-ups.
A lot of the rounded shoulder postural issues you see in strong climbers I believe is from disproportionately strong lats. Climbers love pull ups, and I've known several who trained pull ups (and pull up variations) in the gym as well as campusing up every overhanging route they could find.
The forward, rolled shoulder posture issue is generally a sign of a tight chest (mainly seen in your typical bench bross, office workers and office working bench bros) and weak upper back, particularly the rhomboid muscles, which help to pull the shoulders back and stabilise the scapula.
The way to reverse this, and help protect your shoulders is full range of motion rows (inverted rows are great for this) or a favourite of Dan John, batwings.
"But I climb!" I hear you cry, "Why do I need to work my legs?". It's true, it's not immediately obvious, and I have heard the ideal climbing physique described as the upper body of a silverback gorilla and the legs of a stick insect, and this does fit the typical image of a climber that most people seem to have, but I think there's a couple of reasons to include them.
First, you do need leg strength to climb. The ability to pull yourself up by your arms will only carry you so far, how do you tackle climbing on crimps on a slab when you can only get a couple of fingers on the hold? How about standing up from a rock-over move? You need leg strength!
Secondly, a couple of years back Alex Puccio, arguably one of the best boulderers in the world, had to pull out of the bouldering world cup after suffering a severe knee injury, during a slip while warming up.
Squats help keep the knees healthy. Several years back, I was dropped by my climbing partner from around 8m up. I hit the floor, feet first, dropped into a squat and rolled onto my back to absorb the impact and suffered only a bit of muscular soreness the next couple of days. I attribute this entirely to consistently including goblet squats in my training program. I suggest you do the same.
One of the main issues I've seen with climbers (and boulderers) is shoulder issues. When we slip, we don't always do the (usually) smart thing and let go, we can clamp down on the hold, which can shock load the shoulder joint and cause issues (spoken from personal experience).
Though definitely not gym specific advice, one of the main issues I see with new climbers (particularly men) is too much reliance on brute strength and upper body power, and not enough on technique and footwork.
If you want to become a better climber, learn to use your feet more. If you learn to use your feet and legs more (leg strength can help here), then you're being more efficient, using less energy and tiring your upper body less.
I've seen big guy climbers who can barely manage 5 pull ups able to easily lead 7a sport climbs because of excellent footwork and body positioning.