Most people know that muscle and joint pain, particularly in the lower back, can be linked to chronic sitting, a weak core, lazy glutes and poor form in the gym. But the very thing that is supposed to restore and regenerate our bodies (sleep) can also contribute to pain and injury. Poor positioning of the legs can further compress already tight hip muscles. Twisting of the spin or pelvis can cause fussy muscles like the quadratus lumborum to become hypertonic. And acrobatic-like arm contortions can restrict blood flow or put pressure on the brachial plexus causing nerve pain and restricted range of motion.
I've known my personal sleep tendencies could use some tweaking for years. I sleep on my side (alternating) with my top knee pulled high toward my chest and my bottom arm extended (often hanging off the edge of the bed) under my head which is usually flexed into my chest. Last year I embarked on a self-guided experiment to switch to back sleeping because I heard it's the "best". I ended up with a stiff neck and my hands falling asleep because I had my elbows bent and hands on my chest (vampire style) and for some reason tended toward laterally flexing and twisting my neck to one side. So I called in reinforcements.
I asked my physical therapist and friend what the "best" position is for sleeping for most people. Ideally sleeping on your back with pillows underneath your knees (to support your lower back, just like during a professional massage) and enough pillow support under your neck to keep it neutral. Too many pillows under your head can cause your neck to flex and tuck (ouch) and too few can cause it to extend (chin toward ceiling, also ouch). This position can also ward off acid reflux as long as your stomach is below your esophagus to prevent food or acid from coming up your digestive tract. This image should help (if this hand position doesn't work for you, like it didn't for me, try placing your hands at your side in the anatomical position). This article has some good tips for how to become a back sleeper.
Better: Left Side
The problem with back sleeping is that everyone (or roughly 92% of the world) can't stand it. And for people who snore or have sleep apnea side sleeping may actually be better. However, just like back sleeping, neutral is the name of the game. Try not to hike up one knee and twist your spine/internally rotate your top hip. Instead try to keep your legs relatively straight and your hips neutral by putting a pillow between your knees so they are about standing distance apart versus touching. Try to avoid resting your head or neck on your arm, especially if you feel numbness, tingling or nerve pain. Rather, try to position the palm of your downward arm near your face and tuck your top hand onto your bottom bicep. Say what? Here's a picture that should help. Note, it's generally accepted that sleeping on your left side is most beneficial.
The good old fetal position is probably the most popular. And it can be a good one for pregnant women, especially if you lay on your left side because it improves circulation in your body and in the fetus, and it prevents your uterus from pressing against your liver, which is on your right side. And some yogis will tell you that the fetal position can calm the sympathetic nervous system. The advice above can still improve this position: watch your arm positioning, don't over tuck your chin, ensure your neck is supported and try putting a pillow between your knees.
Pretty much there's nothing good to say about this position other than it can be good for reducing snoring and apnea. But other than that it can lead to joint pain, crunched muscles and angry nerves. Best to try to switch to another position.
Note of Caution
I'm not a doctor, sleep specialist or physical therapist. I'm a personal trainer with a solid knowledge of the body, a desire to sleep better and a computer. Defer to your medical professionals in all matters including sleep. The information above is simply general and publicly available knowledge that I'm sharing in hopes of helping my clients and readers toward rest and regeneration. If you have any muscle or joint issues, sleep pathologies, or are pregnant seek professional advice from your medical community.