I played some open hockey yesterday, and spent the better part of my bench time explaining the significance of resistance training to another old fart complaining about his knees and knee pain. Hockey, you see, like running, swimming, and racquet sports is just plain tough on the joints.
So I thought I would share with you some specifics on how, and why resistance training is critical for good joint stability ... PARTICULARLY if you do a lot of 'pounding' cardio work.
Within the context of joints, exercises can, basically, be separated into two types: closed chain exercises and open chain exercises. Not surprisingly, the analogy is derived from the links on a chain (bike, necklace, bondage, whatever ;-). The links of a chain are closed when there is tension on the chain; open when the tension is relieved.
At the joint, there is a lot going on:
- Ligaments connect bones to other bones;
- Tendons (attached to muscles) attach to bones and
- There is a soft tissue that functions as padding, or bushing between the bones
And during an exercise like running, an individual knee joint undergoes the repetitive process of opening and closing. First, it is supporting the load of your bodyweight as you land and push off of it, and then it dangles somewhat freely as you extend your foot forward to take your next stride.
Thus, this is what we call an open chained exercise: just as the links in a chain 'open' when tension on the chain is relieved, the link between the tibia (lower leg) and femur (thigh bone) is 'opened' when you run (or walk). Then, the tibia and femur are quite literally 'smashed' together (closed) upon your foot's impact with the ground. Only the soft tissues (meniscus), ligaments, and tendons keep the bones from contacting each other under this load.
So, while something like running is terrific and necessary for your heart health, it is actually quite abusive on your joints. Repeat this movement over years and years (or a marathon or two) and you are virtually guaranteed knee, hip and back problems later in life.
Conversely, an exercise like leg curls is considered a closed chain exercise: during the complete range of motion of the exercise, there is never any 'open relief' between the chain of bones at the knee joint. The tendons, ligaments, and muscle groups are constantly 'pulling' and 'tightening' the joint. The Chain link is Closed without opportunity for impact.
The moral, of course, is that balance and variety is the key: strength training and cardio cannot be safely separated. Anyone who runs a lot, plays hockey, or otherwise performs a lot of open chained exercises simply needs to incorporate additional closed chain resistance training to help maintain good strength and stability around the joint. Depending on your age and fitness levels, this type of strength training should be performed at least two days per week.
Additionally, proper form on closed chain resistance exercise also helps assure good skeletal alignment ... particularly for you cardio beasts. Because even the slightest skeletal MISalignment is magnified with thousands of open chained repetitions.
Finally, muscle mass, bone density, and flexibility all decrease significantly once adults turn 30 ... and then accelerates with age. So not only will you help ensure the soundness of your joints through resistance training, but you'll hold on to your lean mass and strength!
Resistance training is the ONLY way to reverse this degradation.
And it's not just the knees. Racquet sports (tennis, racquetball), softball, and swimming does the same thing for the shoulders. These open chained exercises are terrific for you heart and lungs, but not so gentle on the joints. Even something as potentially harmless as bowling or curling can cause knee, shoulder, and lower back problems without strong joints.