I admit to being shamelessly biased about the benefits of hydrotherapy for the treatment of a large number of conditions. And when it comes to hydrotherapy some of the best results I see are from those who do deep water running. This form of running has no impact, and can have tremendous benefit in strengthening the core muscles in particular (so important in low back pain). A number of studies have found that deep water running is just as effective as treadmill running to improve fitness, but without the load on the joints. http://www.ncbi.nlm.nih.gov/pubmed/9407747
Initially when I started my hydrotherapy training, deep water running was mainly used by athletes to either use for cross-training along with other exercise, or for keeping their fitness while rehabilitating. However I found through working at the Wesley Hydrotherapy (now closed) that it was excellent for a large number of medical conditions. These included cardiac rehabilitation patients (because of the water pressure, there is improved cardiac output in water, so the heart rate doesn’t tend to rise as quickly ie the heart pumps out more blood rather than having to go faster -very good for those who have just had a heart attack although need to be carefully supervised and medically screened). We also started using it for people who had had strokes, arthritis and for weight management. It was also very effective for lymphoedema and swelling reduction, aided by the hydrostatic pressure and the moderate-to-vigorous exercise getting the circulation going. I had clients unable to walk 50m due to arthritic pain who could work in the pool at intensities similar to treadmill running for an hour and a half. All without as much sweating, soreness and load on the joints!
There are a number of techniques for deep water running (best determined for you by your physiotherapist -often not easy to see your own technique) I find the easiest for most people to start with that supported by either a deep water running belt, or sitting on a noodle, breastroking movement with the arms and a cycle with the legs. The spine should be straight but not too straight (around a 10 degree forward lean is usually recommended) Another style is running with alternate arms and legs, in a more traditional “running” style. This can be achieved by imagining you are dragging a piece of paper behind you with your feet pointing and your hips fully extending (very good for gluteal strengthening). Cross country skiing is the same thing except the elbows and knees stay straight throughout (propulsion is achieved via turning the hands pushing with the palm each time) This one is quite hard to master but gives some of the best resistance by creating water movement in both directions. One of my favorites is “hands up” running, which as the name implies has the hands up and just using the legs. The equivalent for the upper body is “breastroke arms” where the arms breastrokes but the legs don’t move. The legs can be either bent (easiest) or out straight in front of you (hardest)
You are really only limited by your imagination and fitness/mobility level on what you can come up with. You can run with leg or arm weights, try tethered running (where a belt is tied to the wall and you run away from it), or run without a belt or noodle at all (very hard work! You do by pushing down VERY hard like you are climbing a ladder) You can alternate your speed, do interval training, endurance work -all tailored to your individual needs.
If you have your legs too far out behind you though you will find it hard to stay straight and you will lean forward excessively (and this is why deep water running not great idea initially for those who aren’t that confident in the water because you need to be able to get yourself up off your tummy and either swim to the side or right yourself)

Pool noodles also known as "woggles"
The cheapest way to do deep water running is to just sit on a noodle (can get from many discount stores for around $3) These are fine for most people. When you start getting better at deep water running, or if you need additional back support, the deep water running belts are best. You will sit lower in the water than you do with the noodle, and there is also more of a tendency to lean forward, so you will also work harder than if you are on the noodle.
Features of our AquaJogger running belts

Aqua Jogger deep water running belt
Resilient closed cell foam won’t absorb water, dries quickly, and resists chlorine damage.
Patented contoured design supports and strengthens the lower back.
Soft, flexible foam narrows at the waist for comfort and freedom of movement.
Easy-to-operate quick-release buckle ensures a hassle-free fit.
Active has a custom-woven non-elastic web belt
The AquaJogger design tones the abdominal muscles without doing a single sit-up due to the continual use of abdominal muscles to maintain correct posture.
To accomodate different body shapes, belt can be worn upside down or with the foam in front of the body.
Soft, durable, and comfortable
COST - $65 See our equipment page on how to order