ENERGY TRANSFER: DO WE REALLY WANT THIS?


When talking about ski boots, the big buzz word in the industry is energy transfer. According to the experts, the better the boot, the more energy it will transfer inferring that transferring energy is both desirable and beneficial. But is it? And what is meant by energy transfer? It is not clear what the objective of energy transfer is or how it relates to effecting control of a ski.  As far as I know, no one has offered an explanation. Yet it is consistently stated as the broad objective of a ski boot. In addition, there seems to be consensus among the experts that the foot functions best when it’s joints are immobilized in the ski boot. Presumably this would serve to maximize energy transfer.

Definitions

  • energy |ˈenərjē|noun ( pl. energies ) – Physics, the property of matter and radiation that is manifest as a capacity to perform work (such as causing motion or the interaction of molecules).
  • transfer |noun |ˈtransfər|  – an act of moving something or someone to another place.

It follows from the above definitions that energy is a general capacity to perform work with no particular sense or control over the process. Therefor, energy transfer is the act of moving energy from one place to another. If energy transfer is the primary function of the ski boot as the experts seem to agree on, then the boot will act to transfer energy from the skier to the snow surface. In accordance with Newton’s Third Law, the snow will transfer an equal and opposite amount of energy back to the boot. Where does this energy go? Up the vertical column of the body.

What follows is an excerpt from a letter of support offered by G.Robert Colborne for my nomination for the Gold Medal in Applied Science & Engineering in the 1995 British Columbia Science & Engineering Awards. Dr. Colborne’s area of expertise is the human lower limbs in particular quantifying mechanical moments of force (ergo; torques) around the joints of the lower limb, and the mechanical power generated or absorbed by the muscle group crossing these joints. At the time he wrote his letter, Dr. Colborne was the assistant Professor of Anatomy at the University of Saskatchewan, Canada

“Recent considerations of safety in skiing highlight the importance of dissipating (NB; preventing the transfer of energy) ground  reaction forces (i.e.; snow reaction forces) through the joints of the foot and ankle, which are multi-axial and able to absorb significant energy without sustaining injury. The next more proximal joint (ergo; closer to the torso) is the knee, and this structure is implicated all too often in skiing injuries, where forces are transmitted (ergo; energy is transferred) by rigid boots that restrict ankle and foot movement”.

  • dissipate |ˈdisəˌpāt|verb1 [ no obj. ] disperse or scatter: the cloud of smoke dissipated.• (with reference to a feeling or other intangible thing) disappear or cause to disappear:

Dr. Colborne went on to state:

“Mr. MacPhail’s design enables toe musculature of the lower limb to absorb these forces before they are directed (ergo; transferred) into the ligaments of the knee, thus protecting these relatively stiff tissues from injury.”

In summary, the lower limbs protect the knee by dissipating ground reaction forces through the joints of the foot and ankle. The stated objective of the ski boot is to immobilize the joints of the foot and ankle and transfer energy. Where doe the transferred energy manifest itself? in the knee joint. There are other implications of restricting movement of the joints of the foot and ankle that I will discuss in future posts.