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
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