Hiking Hills

A few years ago, I posted on the challenges of maintaining low weight as one ages.  I have managed to  stay near my target weight, with the occasional excursion in either direction, though admittedly more often up than down.  My suspicion that maintaining weight would prove 90% as difficult as losing it has proven to be all too well founded.  As has the observation that exercise is inherently damaging to muscles (see for example here), especially as one's body's ability to repair itself decreases inexorably with age.

It can be helpful to refer back to those old college physics courses.  One helpful formula is the well-worn Newtonian formula for kinetic energy, which is equal to half your mass times the square of your velocity.  Now, the human body does not maintain precisely the same speed while moving (that is after all what bicycles are for), and the faster you are going, the more energy your body must absorb when decreasing your velocity by a set amount on each footfall.  In fact, this amount of energy increases linearly with your average velocity.  So you can reduce the energy absorption (and thus the muscle and joint damage) by decreasing your speed.  And here you were wondering why old people often move much more slowly than do young people!

But moving more slowly decreases the quality of the exercise, for example, requiring more time to gain the same cardiovascular benefits.  One approach is to switch from (say) running to hiking uphill, thus decreasing velocity while increasing exertion.  This works quite well, at least until it comes time to hike back down the hill.

At this point, another formula comes into play, that for potential energy.  The energy released by lowering your elevation is your mass times the force of gravity time the difference in elevation.  With each step you take downhill, your body must dissipate this amount of energy.  Alternatively, you can transfer the potential energy into kinetic energy, but please see the previous discussion.  And again, this is what bicycles are for, at least for those retaining sufficiently fast reflexes to operate them safely under those conditions.  (Not me!!!)

The potential energy can be dissipated by your joints or by your muscles, with muscular dissipation normally being less damaging.  In other words, bend your knee and hip before, during, and after the time that your foot strikes the ground.  This gives your leg muscles more time to dissipate that step's worth of potential energy.  Walking backwards helps by bringing your ankle joint into play and also by increasing the extent to which your hip and knee can flex.  Just be careful to watch where you are going, as falling backwards down a hill is not normally what you want to be doing.  (Me, I walk backwards down the steepest slopes, which allow me to see behind myself just by looking down.  It is also helpful to have someone else watching out for you.)

Also, take small steps.  This reduces the difference in elevation, thus reducing the amount of energy that must be dissipated per step.

But wait!  This also increases the number of steps, so that the effect of reducing your stride cancels out, right?

Wrong.

First, longer stride tends to result in higher velocity, the damaging effects of which were described above.  Second, the damage your muscles incur while dissipating energy is non-linear with both the force that your muscles are exerting and the energy per unit time (also known as "power") that they are dissipating.  To see this, recall that a certain level of force/power will cause your muscle to rupture completely, so that a (say) 10x reduction in force/power results in much greater than a 10x reduction in damage.

These approaches allow you to get good exercise with minimal damage to your body.  Other strategies include the aforementioned bicycling as well as swimming.  Although I am fond of swimming, I recognize that it is my exercise endgame, and that I will therefore need to learn to like it.  But not just yet.

To circle back to the subject of the earlier blog post, one common term in the formulas for both kinetic and potential energy is one's mass.  And I do find hiking easier than it was when I weighed 30 pounds more than I do now.  Should I lose more weight?  On this, I defer to my wife, who is a dietitian.  She assures me that 180 pounds is my target weight.

So here I am!  And here I will endeavor to stay, despite my body's continued fear of the food-free winter that it has never directly experienced.