jaguar1 wrote:
Yes, to handle higher mileage and do so consistently without breaking down, you have to slow down. Timothy Noakes wrote to someone I know and said something along the lines that 'long slow distance' is more sustainable over a lifetime than high intensity running. It's true-- it's what we're most adapted for.
Staying healthy is more intensity dependent than frequency dependent because of the greater stress imposed on muscle-to-bone with a higher intensity. The greatest stress to a bone is where the muscle inserts-- this can be both good and bad, depending on how it applied.
On the other hand, to esp. point out-- if you're not getting enough energy intake to counterbalance higher mileage (a likely overlooked factor), that's another issue in itself (~hormonal and catabolic effect on body tissue due to a negative energy balance). However, from a mechanical standpoint, low intensity/high mileage is less stressful and more sustainable than high intensity running.
It's how it's applied. Higher intensity/low frequency exercise induces change, whereas low intensity/frequency exercise helps with maintenance and recovery to allow for supercompensation. The body thrives on a balance between rest and stress, and supercompensates when you rest. Great quote related to this, "Rest or regeneration is the most essential part of training for inducing optimal biological adaptations."-- Jan Olbrecht in "Science of Winning"
Yes, the body likes to move frequently and get the blood flowing to the working muscles. This is why cross training is beneficial, but I would like to add walking to the mix, since it's weight bearing, natural, and the next closest thing to running. Then, to "move" twice a day (run/cross train/walk) is further beneficial.
This is the well supported thought. Look up research by Clinton Rubin at SUNY-Stoney Brook and David Burr/Alex Robling/Charles Turner at IUPUI. Burr/Robling/Turner did the research (2007?) that found that 4-6 hours between bouts is most anabolic. Rubin has done some interesting research with turkeys, who spend most of their daily time standing, which exhibits a low intensity/high frequency "vibrational force" of the muscles on bone. When you consider that our weight bearing, long bones are the strongest bones in the body (vs. the upper, non-weight bearing bones), how our bones are built/their strength/adapted is moreso influenced by this constant, low intensity/high frequency stress. Our lower legs are built to "endure"-- a high intensity stimulus is not something that evolutionarily we're meant to do a lot of.
I've sort of been putting all of this to the test with myself the past 10 years, having DXA data going back to 2002 and averaging over 100 mpw since Nov. 2006. My bone density continues to improve at all sites (hip/spine/whole body). When I was tested in '08 along with labmates, I had the best hip density of anyone, which they contributed to my running.