Today I've got a confluence of ideas for you regarding joint health, strength, and endurance.
My friend Jon Hinds, owner of the fantastic Monkey Bar Gym in my old stomping grounds Madison, Wisconsin, recently posted this video of a video analysis of someone running in running shoes and the same person barefoot.
Listen to the video commentary about what happens to the bones and joints, and you don't have to wonder why most runners will end up injured. Running shoes with puffy heels simply don't let your feet contact the ground the way they should, thus joints above take a real beating and eventually injury will occur. It's that simple.
Likewise, in the gym I prefer people to wear as flat a shoe as possible. Other than barefoot training, which is common in many of the top gyms in the country, Vibram Five Fingers are a great choice, as is Nike Frees. Vans, Converse AllStars, or other flat shoes are also good.
Here is why: A flatter shoe will be more stable, and will allow you to sit back further on your heels which will aid in recruiting your posterior chain (glutes, hamstrings) i.e. the biggest muscles. Working your biggest muscles means you get better results. You'll get stronger where it counts.
Not to mention that wearing flatter shoes will put less shear force on your knees and low back.
But that's not all (joke). There is a book making headlines these days called "Born to Run" concerning the Tarahumara native peoples of Mexico famous for incredible distance running abilities. One of the reasons cited for the Tarahumara's legendary running is that they run barefoot or in sandals. They also rarely get injured despite running distances and over terrain we can hardly fathom.
Now, moving on to developing endurance I-let's look at a study done by Universities in Spain and the U.S. concerning the influence of strength and power on endurance.
The study (Journal of Strength and Conditioning Research 23(5) 1482-1488) took 14 firefighters that must perform endurance tests as a part of their job and in training specifically targeted their maximal strength and power, then looked at the effect on endurance. Across the board they found that just by increasing their maximal strength and power output the firefighter's performed better in endurance tests.
To put it another way, if you have hit a plateau in running, biking etc... then more running is not the answer. It's doubtful that cardio capacity or VO2 max is what's holding you back. Likely it is that your body is not able to produce enough power in order to propel you faster. Improving muscle strength means that running at a given pace will now be easier due to the fact that said effort requires less of a % of maximal strength and power output.
The most efficient way to do this is to get follow an intelligent strength & power program using resistance training. And one key to getting stronger is developing the largest muscles using proper biomechanics and technique - i.e. the stress should be placed across the proper muscles instead of the knees and low back.
The bottom line is do yourself a favor and lose the crosstrainer shoes with the puffy heels. Once you go flat you'll never go back.