Many studies show the benefit of exercise for people with knee osteoarthritis. But pounding the pavement (walking) can increase pain. Aquatic therapy in a pool of warm, supportive water is one way to get the needed exercise without the added stress.
In this study from the University of Florida, the effects of walking on a treadmill underwater were compared with walking on a land treadmill. It was a small study with 14 adults in ages ranging from 43 to 64. All participants had been formally diagnosed with knee osteoarthritis (OA). A few had OA of the hip or ankle as well.
Everyone was treated with a 20-minute session on a treadmill at zero incline (flat). The 20-minute period was broken into four stages each lasting five minutes. Pace or speed of walking increased slightly with each stage. By the last five minute segment, the patients were walking at a moderate-to-somewhat hard level of perceived exertion.
Three sessions were completed in one week on the aquatic treadmill with water temperature holding steady at 86 degrees Fahrenheit. Then there was a one-week rest period and the same protocol was used on a land treadmill. Some patients did the land treadmill the first week while others were assigned to the aquatic treadmill first. Who did what first was randomly assigned using a computer program.
It should be noted that walking on a treadmill in water is not the same as walking in water without a treadmill. When using a treadmill in a pool, only the lower half of the body is underwater (which makes it easier to walk). Walking without the benefit of a treadmill places the feet on the bottom of the pool so more body is submerged making it more difficult to move.
The more body that is underwater, the greater the “fluid drag,” which slows a person down. Studies comparing energy required to walk on an aquatic treadmill versus a land treadmill show similar energy requirements. In other words, it is not more difficult or exhausting to walk on a treadmill underwater compared with a land treadmill.
Aquatic treadmill walking has also been shown to decrease the impact on the knee. The buoyancy of the water reduces the force from the ground starting at the foot and traveling up to the knee (called the ground reaction force). It was hypothesized that decreasing the joint load by using an aquatic treadmill would reduce pain and improve exercise quantity and quality. Let’s see if that is what happened in this study.
Results were measured within 24 hours of completing the three sessions (on either treadmill). They used two main outcomes: change in pain level and joint kinematics. Kinematics refers to how the joints move (speed or velocity, joint angle, step length, step rate).
Changes in pain and kinematics can affect a person’s gait (walking) pattern. Joint kinematic measurements were taken while the patients walked on land in a biomechanics lab. The researchers measured angular velocity for knee extension during stance (weight on that leg) and knee extension and internal rotation during swing (leg moving forward).
The angular velocities measured did improve more after aquatic therapy. Angular velocity gain for left knee extension during stance improved significantly (38 per cent) after aquatic walking. Gain for knee internal rotation was 65 per cent and 20 per cent improved for knee extension during leg swing. Pain was significantly greater (100 per cent more) after land exercise. The number of steps taken and the length of steps did not change with either form of exercise.
The authors point out that these kinds of changes in angular velocity indicate that the pattern of movement of the arthritic knee is improved during walking. That is important for restoring normal gait (walking), improving balance, and preventing falls. The actual mechanism for increasing angular velocity and joint kinematics remains unknown. It is thought that the combination of increase in fluid resistance, warmth and pressure of the water, and unloading of the joints work together to create these beneficial effects.
With only three sessions each (aquatic and land) on the treadmill, these outcomes are considered short-term. But evidently there was enough effect on the neuromuscular system to create these changes. Future research will be needed to see if the changes last (and for how long) and whether a longer period of time with more sessions would enhance the benefits even more.
The authors concluded that aquatic therapy may be a good alternative to walking on land for patients with painful and limiting knee osteoarthritis. This treatment approach can help patients experience pain relief and improve walking ability.