A common recommendation of someone that is obese is to begin an exercise program. The type of exercise that is often recommended is a brisk walking program. Since the main preventable risk factor in large joint osteoarthritis is obesity it makes sense for obese individuals to exercise. This recommendation of brisk walking may make sense of helping to manage obesity but it may be increasing the risk of injury especially in the knee. With the knee being the primary site for obesity-related osteoarthritis, it creates a tough dilemma.
The Facts on Obese Clients Doing Brisk Walking
– Peak ground reaction forces (GRF) were 60% greater in obese (BMI of 30 to 43) group compared to normal weighted individuals. This is how it broke down per walking speed:
o 1.0 to 1.75 m/s / 63%
o .75 m/s / 71%
o .5 m/s / 85%
– GRF was significantly smaller for obese subjects versus normal-weighted subjects walking at 1.0 m/s
– Body mass was 48% greater in obese subjects versus normal-weight subjects, whereas the tibial articulation area was only 8% larger. How you can visualize this is like have dined amount of surface if you are 100 lbs and a penny amount of surface area if you are 148 lbs. This would lead to obese individuals having greater mechanical loads across tibial articulating surfaces.
– During normal walking, the resultant GRF causes an external adduction moment at the knee which puts greater force on the medial aspect of the knee. An increase in external adduction correlates to osteoarthritis severity and progression.
– Obese adults walk with externally rotated leg or maybe valgus knee alignment which acts to reduce external knee adduction.
– Preferred walking speed in normal-weighted adults is 1.4 m/s (3.1 mph) and obese adults 1.1 m/s (2.46 mph). With the slower walking speed, obese individuals have the same GRF as normal weight individuals walking at a higher speed.
– Bonus Note – After 4 minutes of treadmill walking or a familiarization period, the kinematics of walking on a treadmill are the same as ground walking.
The Take Home Message on Brisk Walking for the Obese
Brisk walking may not be the best weight loss solution for obese individuals. Having your obese clients walk at a slower speed which is often preferred by obese individuals is the solution to decreasing stress on the knee joint. Other weight loss strategies will need to be explored in order to manage BMI in order to decrease the risk of osteoarthritis and osteoarthritis progress.
If you are a fitness professional and would like more confidence in working with clients with osteoarthritis and a great variety of knee rehabilitation exercises, I would suggest attending Exercise Rehabilitation of the Knee Course.
For More Details:
Browning RC, Kram R. (2007). Effects of obesity on the biomechanics of walking at different speeds. Med Sci Sports Exerc. 2007 Sep;39(9):1632-41.