+My flexibility training for climbing has primarily focused on two areas: groin
+(side splits) and hamstring.
+
+I've seen really fast gains from *strength-at-range* training, which basically
+attempts to strengthen the muscle at the limit of its range of motion. The
+reasoning I've heard for why this is effective is twofold:
+
+1. Your central nervous system will hold you back from stretching beyond where it
+ feels strong to prevent you from hurting yourself, so *strength* is somewhat
+ surprising limiter on flexibility. I should note that this is effectively
+ hearsay: while I've heard this from a few reputable sources, I'm not aware
+ of any scientific way of proving this.
+2. It doesn't matter for your climbing if you're able to get your foot into a
+ certain position if you're then unable to pull from that position. This is
+ analogous to problems with out-of-context finger strength, where you
+ may be able to grip a hold but not move off it, because the arm system as a
+ whole is unable to maintain strength while changing position.
+
+Because strength at range exercises stress the muscle as it lengthens, they are
+particularly likely to cause delayed onset muscle soreness. You can see
+[DOMS](delayed-onset-muscle-soreness) for more information, but the takeaway is
+to start with low weights, and do a light version of the workout a day or two
+after; the chemical reactions which cause DOMS also have a preventive effect
+which treats existing DOMS and prevent further DOMS.
+
+# Side Splits
+A key here for me has been understanding a particular gotcha of the side splits.
+There's a bony protrusion on the outside of the femur, and when toes are forward
+and pelvis vertical, splitting the legs causes this bony protrusion on the femur
+to run into the pelvis long before you reach the full range of motion of the
+muscles. Before I knew this I ran up against this for a while, seeing no progress
+in my side split and even causing a bit of pain which would cause me to stop
+stretching at times.
+
+The solution to this is to bring the pelvis into a right angle with the femur,
+which puts the bony protrusion behind the femur. There are two ways to do this:
+
+1. Point the toes and knees out instead of forward. It's really the knees that
+ are connected to the femur, but the knee is not a ball joint so if you don't
+ align the knee with the foot you're going to have problems.
+2. You can also tilt the top of the pelvis forward. Note that this doesn't
+ necessarily entail tilting the entire upper body forward.
+
+There are three exercises which I use:
+
+1. **Butterfly** which hits the muscles of the groin which are most active
+ when the knee is bent (TODO: get the names of the muscles and maybe some
+ pictures?). With your butt against a wall, place dumbbells (starting at
+ around 10lbs or 5kg) on your knees in butterfly position. Extend to your
+ range for 3 seconds relaxed, then flex the muscle, bringing the weight
+ up just a tiny bit, for 3 seconds. Do this for 2 sets of 20 reps each.
+
+ Progressing this exercise is a bit tough: raising the weight is easy but
+ I've quickly gotten to the point that my knees are resting on the ground
+ while not fully extended. Elevating by sitting on a 45lb barbell plate
+ has allowed my to drop my knees further, but now my shins are running into
+ the plate and I'm haven't found a good narrower surface to sit on. I'm
+ not too worried about it at the moment because I can still progress
+ strength without progressing range (higher dumbbell weights), and this isn't
+ the position which is most relevant to climbing.
+
+2. **Wide squats** This hits all the muscles of the groin in a position which
+ is somewhat relevant to climbing. You can "heel-toe" your feet out to get
+ a rough measure of width, then holding a dumbbell (starting at 10lbs or 5kg)
+ squat down as far as you can, remembering to tilt the pelvis to avoid the
+ femur colliding with the pelvis. When your femurs are horizontal, you can
+ go wider. Hold for 3 seconds at the bottom of each squat, and do 2 sets of
+ 20 reps each.
+
+3. **Unsupported splits** Hits the muscles of the groin which are active with
+ straight knee. With the body upright-ish, spread the legs straight to a
+ position with a light stretch: you can spread the toes to avoid the
+ femurs colliding with the pelvis, but for balance purposes it may be
+ beneficial to tilt the pelvis forward a bit and keep the toes pointed partly
+ forward. Then, importantly, don't support your hips with your arms: keep
+ your hands away from your hips, legs, and lower torso. Instead, support
+ your weight with the muscles of the groin.
+
+ You should aim for a width where you can hold the position for about 45
+ seconds: if you're able to hold it for 60 seconds, you can go wider,
+ if you're only able to hold for less than 30 seconds, you should ease off
+ a bit. Do this twice.
+
+ Tracking progress isn't strictly necessary unless you believe you are
+ hitting a plateau and want to verify this. You can track progress by
+ taking photos and measuring angles, or measuring foot width on the ground
+ with tape. However, if you just go to the end of your range and hold there,
+ you'll probably find holding this challenging.
+
+ It's also not necessary to add weight to this, because as your feet
+ go wider, your muscles are at a greater biomechanical disadvantage due to
+ the lever physics. It's quite common for an increase in range to greatly
+ decrease how long you can hold the position, as the strength required
+ increases greatly with even a small increase in range.
+
+# Hamstring
+A peculiarity of the hamstring is that it's difficult to isolate since it works
+in conjunction with the entire posterior chain. The glutes and calf can loosen
+as you stretch the hamstring, causing you to have to increase the intensity
+of the stretch midway through, so it's beneficial to stretch these muscles before
+you stretch the hamstring. It may also be beneficial to stretch the distal hip
+flexors (pigeon pose) and/or the groin for similar reasons.
+
+I've been doing offset-leg good mornings to work these, however I'm not as happy
+with the results. I've experimented with good mornings on one leg with the other
+ankle tucked above the knee; these seem only slightly more effective and have balance
+issues. I'd like to experiment with nordic leg curls but these require a barbell.
+
+# Opposing muscles
+It's worth noting that while the groin and the hamstring do the lengthening and
+then pulling at that range, the opposing muscles (distal hip flexors and psoas,
+respectively) have to be strong enough to get the leg into position. To work
+these I occaasionally do fire hydrants and standing forward leg lifts.