Laser Hiking Notes (email)
Date: Thu, 1 Feb 1996 17:29:29 -0600
From: Shona Moss <smoss@gpu.srv.ualberta.ca>
To: Multiple recipients of list <laser@cali.kentlaw.edu>
Subject: Re: Knee Problems
This is in partial response to Derek Jackson's questions about knee
problems while hiking and training techniques on a hiking bench.
Hi!
I once did a study (for a biomechanics class - I'm just completing a
Masters degree in Exercise Physiology now) that calculated out the moment
torques around the knees and hips and the righting moment exerted on the
boat by hiking on a Europe dinghy. I inserted the calculations on a
spreadsheet so that I could input various sizes of people in various
hiking positions (straight leg, bent leg, etc - i.e. I could change the
hip and knee and neck angles). The results were not surprising to me.
The loads on the knees were very large in, obviously, a separating
direction (upwards of 200 Newtons at an angle of 33 degrees from the
vertical in the direction towards one's head - imagine a side profile view
of someone hiking. This is for someone of 155 lbs). Four ligaments per
knee take up this force (and one of them will be slack) when the
quadraceps muscle is slack (which is fairly often).
The knee moment or torque calculated was around 155 Nm for this same 155
lb person in the straight legged person. Therefore, for one knee the
quadriceps had to exert a force of 155 Nm / 2 = 77.5 Nm around the centre of
axis of the knee in order to maintain the straight legged position. By
the way, for the bent legged position, the moment for one knee was 40
Nm. Then, this subject did a measured maximal isometric contraction for
knee extension. The maximal voluntary contraction was ~220 Nm for one
knee. Therefore, while straight legged hiking, the force that the
quadriceps has to contract at to maintain the position is 35% of its
maximal voluntary contraction force. For the bent legged position,
the quadriceps has to contract at 18% of its maximal voluntary
contraction to maintain that position. Keep in mind though that this
is only one person who at the time was NOT doing any leg strength
training.
In the isometric exercise physiology literature several
papers have looked at how long one can maintain isometric contractions
of muscles at various percentages of maximal voluntary contraction (MVC).
In isometric contraction, blood flow to the muscle tissues is greatly
impeeded and even halted in many cases. For example, isometric
contraction at an intensity above 60 to 70 percent of MVC will block
circulation as if "artificially blocked by a tourniquet". Combining
the results of several papers shows that even at isometric
contractions of 10 to 15 % there still is a mismatch between
contraction and blood flow. One study measured time to exhaustion for
a load corresponding to 10% of MVC; near exhaustion occurred in 25
minutes. In another study, mean time to fatigue was 3.6 minutes for an
isometric contraction at 30% of MVC. Another study showed that time
to exhaustion was just over 4 minutes for a contraction of 20% of
MVC. To hold an isometric contraction for over an hour, the
endurance limit of force may be as low as 8% of MVC.
Anyways, what this told me (it was not too earth shattering!)
was that this particular subject (I guess that I should say here that
it was me - yup, me and my not very strong quadriceps! :) ) could not
hold the straight legged position for very long. This was no
surprise to me! Considering that I would have to hold a 35% of MVC
contraction to maintain the position, I would not be in that position
for long.
Many of you know that you can bent leg hike without any quadriceps
contraction at all. I've done that lots! With the help of friction
of the back of your pants on the side of the boat AND with those knee
ligaments taking up all the knee reaction forces (all 200 N of them)
I can "hang" on the side of the boat. This is also where knee
cartilage takes a bit of a beating. Especially pounding over
waves...... By the way, cartilage does not grow. It is not
supplied by any blood circulation. It is kept spongy only by the
synovial fluid it sits in. Therefore, if you damage it, it will
not repair itself as muscle will. Food for thought.
So, what did I learn from all of this?
- Do work out properly to strengthen all the muscles around the
knee. I would suggest heading to a gym to do the bulk of your
strenth work and then use the hiking bench for specific training
(i.e. specific muscles and isometric contraction). Make sure you
include general stregth work (typically, 3 sets of 8 to 10 reps -
this is very general - but works - talk to the staff at your gym.
THey can help you out with rep intensity, warm up set of reps,
exact number of reps done, etc.). This way your MVC will
increase. Make sure that you work on all the major muscle groups: Quads.
Hamrstrings, Gastrocnemius and Soleus, Gluts, Tibialis Anterior (on front
of shin), back, and stomach. These are all really important for hiking.
- The forces imposed on the knee and the forces required to be exerted
by the quadriceps muscles are large and should one feel pain in the knee
joint, go to the doctor first and then start a strengthening program to
remedy the problem.
- When hiking, try to relax your quadriceps muscles while
hiking every so often. Waves make this easier because you move your body
around. THis will allow more blood flow in and out of the working muscles.
- Do add aerobic training to your schedule. It is debatable whether
aerobic training helps in recovery from anaerobic work (which isometric
contraction is) but sailboat racing has a real aerobic element to it
(but certainly does not look like it relies on it or is limited by it as
shown in the ONE scientific paper that I've found that gave the
physiological and performance stats on the Australian Laser racing team
from the early 1990s) considering races last longer than 5 minutes.
Wow, this is WAY too long! But, I thought someone might be interested in
the information obtained from the little project I did. Straight legged
hiking is not always feasable to do for a whole race if leg strength is
not adequate enough. Although, sitting and hanging on your knee
ligaments and the friction of your pants is not always so good either.
Strong legs are important!
Enough of my crap!
Bye,
Shona Moss Lovshin