I recently put up a post on recovery and regenration which lead to a question about the comparative benefits of compression garments and use of pool based recovery strategies. Hydrostatic pressure in a pool may offer more compression than some of the latest skin tight training gear that I see so many atheltes sporting. Anyway I needed to dig out a particular paragraph and figured I would share the whole article with the everyone as I really think that the pool is not used nearly as much as it should be. It's a bit of a beast so we will run the article in two parts.
Water Workouts - A Complete Guide to Pool Based Training for Training and Rehabilitation - Part I
'Pools are excellent environments in which to train....water provides buoyancy and resistance properties that allow the individual to undertake exercise with minimum impact on the body.'
Angela Calder (Performance Consultant for Australian Institute of Sport).
If the pool is such a great training environment why don't we make the most of it and incorporate it into our clients and athletes training, rehabilitation and recovery sessions?
The immediate response is that we don't have access to good pools, we don't have the right equipment, people look at me funny when I'm aqua running etc etc. Phooey - they're excuses, but they are not good excuses.
In my opinion the main reason that people don't include pool-based training into their training programme is ignorance. How can you use a training method if you don't understand how to use it? That was the position I was in 10 years ago when I started working at the Lilleshall Sports Injury and Rehabilitation centre. Up until this point the only reason I went to the pool was to swim, play on inflatables and do some top bombing from the diving boards. Whilst working at Lilleshall I had my first exposure to pool based training as part of the rehabilitation programme for footballers receiving treatment at the centre.
The extent of my knowledge was that you get injured and you can use the pool the get fit! It didn't even occur to me that you could use the pool even when you weren't injured. It wasn't until I started working with the England Netball team that I was exposed to the use of the pool as a training tool and not just something you do when you are injured. I soon started including a wide range of pool-based training with my athletes' programmes. Ten years on and I'm still using the pool for training and rehabilitation. If you want to learn a bit more about the applications of water workouts and how you can improve your body alignment, aerobic and anaerobic fitness, flexibility, strength and overall balance and coordination, read on, this is the article for you.
Movement In A Fluid
We could simply tell you about all of the great training sessions that you can complete in a pool but to truly understand the training methods you need to know how the body moves in water and some of the properties of water that help to create the training environment for various applications. In this section we will explain some of the science and biomechanics behind the training to give you a general understanding of the actions of fluid forces on the body. Here comes some science!
1. Buoyancy
Buoyancy is a fluid force that always acts vertically up and it was that clever Greek chap Archimedes that first explained the factors that determine the magnitude of a buoyant force (Archimedes' principle - physical law stating the buoyant force acting on a body is equal to the weight of the fluid displaced by the body) (5,6,8). Buoyancy is important because it can provide assistance for exercises, which is particularly useful during the rehabilitation of injuries. You can also increase the buoyancy of you athlete by using floatation devices (belts and vests).
2.Hydrostatic Pressure
The hydrostatic pressure in a fluid increase with depth and this pressure acts over the surface of any object (5,6). One of the reasons that the pool is such a useful training environment for people rehabilitating from an injury is because the increased pressure on the body can be used to reduce effusion and allow the individual to exercise an injured limb without the risk of further increases in effusion.
3. Fluid Dynamics - Flow
When an object such as a human hand moves through water, there is little apparent disturbance of the water surrounding it if the relative speed of the hand with respect to the water is low. Increase the speed of movement and you will create waves and eddies (5,6). Two different types of flow exist:
Laminar - characterised by smooth layers of fluid molecules flowing parallel to one another.
Turbulent - characterised by a mixing of the layers of fluid molecules. By manipulating the training techniques used in the pool we can alter the fluid dynamics and change the intensity of the training session. If we maintain a streamlined shape we will produce minimal disruption of flow, if we adopt an unstreamlined shape or use an object (e.g. floats) that is not streamlined we will create a disturbance of flow and increase drag which in turn will increase the intensity of the movement.
4. Water Depth
There is an inverse relationship between the depth of water and the amount of bodyweight that is supported by the musculoskeletal system. If you are standing on the bottom of the pool and you are up to your neck in it (so to speak), your body will only be bearing about 8% of its weight. Drop the water level to around mid chest and the body bears between 28%-35% of the weight, increasing to between 47%-54% when the water level is waist high (7). 
By manipulating the water level you can increase or decrease loading on the musculoskeletal system - great for rehab and injury prevention. It's important to note that these figures only reflect static weight bearing and increase with movement.
Physiological Response to Training in Water
Just as it's important to understand the properties of water you need to appreciate some of the physiological responses to training in water. One of the main things to consider is that there will be a decrease in respiratory function due to increased pressure on thoracic cavity. Individuals will experience a drop of up to 9% in their vital capacity (total volume of air forcefully expired after maximal inspiration) (4). There will be an increase in breathing rate but sub-maximal and maximal heart rates will tend to be 8-10% lower (10-20bpm) than those on dry land (9). Maximal oxygen uptake can decrease as well (~17%) (1,4,10). The take home message is don't expect to see the same physical and physiological responses during a pool session as you would on dry land. I learnt from experience that trying to get your athletes heart rate to similar levels to those seen during a land based session is not a good idea. They are not being lazy, there's a good reason why heart rate is low, breathing is rapid and they are about to start hyperventilating! The key is to be a good coach and adapt the session accordingly.
In the next part we will actually look at how to incorporate pool based training into your physical preparation programmes.