
Hello, I'm Jay, a sex-positive, friendly fellow from Nova Scotia. In this post I'd like to talk about positions and equipment people can use to make sex more comfortable, especially when it comes to our tender backs, knees, hips, and shoulders.
Preparation
The key to success is preparation. When you go for a run or visit a gym you stretch before exercising. When you're dealing with sore joints and muscles, it makes sense to take care of them before sex too. I'm not suggesting you take a time-out from passionate kissing to do some yoga, but I do think it makes sense to work some body care into foreplay.
As an example, it feels good to share a bath or warm shower with your lover. Get soapy, touch each other, kiss under the shower. Rub each others backs (and fronts). This is a good way to put both people in the mood and loosen up tense muscles. In a similar fashion, a wonderful way to bond and feel close is to give your partner a massage. Get out some lotion, take off each other's clothes and take turns rubbing shoulders, backs, and feet. It's a good way to connect and it works out sore muscles.

Comfortable positions
Once we've moved passed the preparation phase and on to sex itself, there are a few things we can do to make sex more comfortable and less painful. One is to find comfortable positions. Which position will feel best will vary depending on which muscles or joints you're trying to protect. However, usually the key factor to being comfortable in these situations is to either avoid moving or tensing up the sore area, or avoid putting weight on it.If you have a tender back, you're probably better off holding still under your partner than being on top during intercourse. If you have delicate knees, being on your hands and knees probably isn't ideal for you. Many people report that one of the more comfortable positions is to place both people on their sides with the man tucked up behind his partner. It's a fairly natural position, one many people sleep in, and this position allows both people to relax most of their muscles during intercourse. As a bonus, finding new or better angles during sex is often a matter of sliding slightly up or down on the bed.

Special gadgets
There are a number of items which can help make sex more comfortable. Placing thick pillows under your back or ass while on your back can ease back and hip pain. Having a Liberator Wedge tucked under your body (especially under your chest when on your hands and knees) will take strain off your elbows and shoulders. Indulgence carries a Doggy Style Strap which will make one particular, popular sexual position feel better.
Following up on my comments about positions - if you can't avoid putting weight on a sore part of your body, you can still take away the worst of the discomfort with some strategically placed pillows and aids.
Rearrange the furniture
Another thing you and your partner can do to make sex feel better is to rearrange the furniture. Beds are typically comfortable places to sleep and are often a convenient place to have sex, but the flat surface isn't always comfortable. Guys, try standing next to the bed, behind your partner, and bending your partner over it, stacking pillows underneath the two of you as required to get comfortable. Ladies, have your man sit on a chair and lower yourself down on him. Try spooning and screwing on the couch. Guys, if sex is hard on your knees most of the time, ask your partner to lay on her back by the edge of the bed so you can stand while entering her. Ladies, if your man has lower back problems, lay him flat and climb aboard.

The idea here is to find a way to have the furniture act as a support. We're so accustomed to making love on flat surfaces that people often overlook the possibility of using chairs, pillows, wedges, and foot stools in ways that take pressure off our bodies. Experiment, find surfaces that feel nice under your body, or soft items you can place under your sore muscles.