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  1. #35
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    agree with cooler about the thumb thing, it's just spasm from your active movements. something to do with adrenaline too.

    about that knee, I have friends that play volleyball and have the same problem when they land after hits. But for them, it's because they have some natural defect with their knees. one has one leg longer than another and another guy just has a weird knee connection. they both dealt with it with knee guards so I guess that will be a good way to go.

  2. #36
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    Anybody notice that most threads started by Joanne are often more than 1-page long?

    Anyway, I think intensity does have a bearing on your knees. I wear a knee-guard nowadays as in badminton we do plenty of moves that need knee action.

    Funny though, the soreness for me seems to come more from the left knee than the right (I am right handed) when most people here speak of the racket leg instead. I wonder why is that? Any comments for me? It began ever since I started applying 'scissor-kick' to my jump smashes - resulting in landing on my left foot. Any suggestions on landing in relations to knee health?

    With kneeguards, I feel so much more 'secure' as I know I get support from the transfer of force from the soles of the feet to the knee. The other thing I can say is that I felt less impact on the entire leg with the kneeguard in place, making my stance more stable.
    Last edited by wilfredlgf; 07-01-2003 at 08:54 PM.

  3. #37
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    Originally posted by jwu

    about that knee, I have friends that play volleyball and have the same problem when they land after hits. But for them, it's because they have some natural defect with their knees. one has one leg longer than another and another guy just has a weird knee connection. they both dealt with it with knee guards so I guess that will be a good way to go.
    Natural defect? Uh-oh... Okay. I'll try and measure my legs afterward. Weird knee connection? What does that mean?

  4. #38
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    Originally posted by wilfredlgf
    Anybody notice that most threads started by Joanne are often more than 1-page long?

    Anyway, I think intensity does have a bearing on your knees. I wear a knee-guard nowadays as in badminton we do plenty of moves that need knee action.

    Funny though, the soreness for me seems to come more from the left knee than the right (I am right handed) when most people here speak of the racket leg instead. I wonder why is that? Any comments for me? It began ever since I started applying 'scissor-kick' to my jump smashes - resulting in landing on my left foot. Any suggestions on landing in relations to knee health?

    With kneeguards, I feel so much more 'secure' as I know I get support from the transfer of force from the soles of the feet to the knee. The other thing I can say is that I felt less impact on the entire leg with the kneeguard in place, making my stance more stable.
    Lol. I DID NOT notice that. Surely there are other threads with 1+ pages too.

    And this is my left leg too, and I'm a right handed.

    Aren't knee guards just a piece of hard cloth? Or something like that? How come it's so good? Oh yeah, I know it's probably more then that, just don't know how it works.

  5. #39
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    Originally posted by wilfredlgf
    Funny though, the soreness for me seems to come more from the left knee than the right (I am right handed) when most people here speak of the racket leg instead. I wonder why is that? Any comments for me? It began ever since I started applying 'scissor-kick' to my jump smashes - resulting in landing on my left foot. Any suggestions on landing in relations to knee health?
    suggested reasons(in random order):
    a) lose weight
    b) left knee may not be used to the new movement and needs readjustment
    c) landing of the left foot after scissor kick may be incorrect.
    d) not turning hips properly.


  6. #40
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    Originally posted by Joanne
    Natural defect? Uh-oh... Okay. I'll try and measure my legs afterward. Weird knee connection? What does that mean?
    weird knee connection as in the tibia of my friend's leg (one of the lower leg bone) doesn't connect correctly to the knee, it's slightly off where it suppose to be.

    I mention the two instance because I think both of my friends have more severe problems than what you have. Just be careful with it and I think you've been doing that after reading some of the threads above.

  7. #41
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    Originally posted by jwu
    weird knee connection as in the tibia of my friend's leg (one of the lower leg bone) doesn't connect correctly to the knee, it's slightly off where it suppose to be.

    I mention the two instance because I think both of my friends have more severe problems than what you have. Just be careful with it and I think you've been doing that after reading some of the threads above.

    Lol. I see.

    Cheung, how does losing weight help to avoid the soreness? Just wondering.

  8. #42
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    Anybody notice that most threads started by Joanne are often more than 1-page long?

    coz kids ask the darnest questions

    Regarding your thumb trembles, it goes away when used because the major nerve pulse override the weak pulse that was causing the trembling. For now, don't worry about it, i sometime get some too on my index finger after doing some hard labors.
    Last edited by cooler; 07-01-2003 at 09:51 PM.

  9. #43
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    Originally posted by Joanne
    Aren't knee guards just a piece of hard cloth? Or something like that? How come it's so good? Oh yeah, I know it's probably more then that, just don't know how it works.
    That's what I thought initially but the thing is actually quite flexible. You will feel some tightness there but you're knee can actually bend pretty well.

  10. #44
    Regular Member wilfredlgf's Avatar
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    Originally posted by Joanne
    Lol. I see.

    Cheung, how does losing weight help to avoid the soreness? Just wondering.
    Pressure on a surface, P = Force, F / Area, A

    In badminton (esp in jumping):

    F = the force in which your body exert when it falls
    If you are 45 kgs, the simple (Read : Simple) calculation of the force your body exerts downwards = 45kg x 9.81 ms- = 441.45 Newtons (N)

    A = the area of both the soles of your feet
    Say... a rough estimation for a size 7 foot = 0.25 m x 0.08 m = 0.02 m
    Total area of both soles = 0.02 x 2 = 0.04 m

    Pressure applied to the soles of your feet = 441.45N / 0.04m
    = 11036.25 kgms-

    As this 11036.25 kgms- is applied to your soles, it is also transferred to your knees as part of energy transfer in the form of impact vibration.

    As of Newtons' 3rd Law "For every action, there's an equal reaction".
    So, as you land, the force that is exerted on the floor as you touch down fully will also general force that hits it upwards (in the opposite direction). This will tranfer a force upwards to your knees.

    So, the heavier you are, the stronger the force that will punish your knees (your legs in whole).

    Pressure, P = Force, F / Area, A
    Force, F = Mass, m * Acceleration, a

    Notice for F, it is governed by the value of m, which is roughly your weight.
    'a' is very much fixed; gravitational acceleration = 9.81 ms-

    Otherwise, hold a pencil upside down, put your forefinger on the pointed end, then gently knock the butt of the pencil on a surface. You will feel that the harder you hit the surface, the more you feel the point poking your finger.

    And notice that if you exert the same amount of force on a blunt pencil (bigger area of impact in comparison to sharp pencil) the feeling will be less.

    Oh gosh, it's been years since I played with Physics.
    It's likely to be wrong up there, but you get the idea.

    Maybe some of you engineer guys could fix this?
    Last edited by wilfredlgf; 07-01-2003 at 11:08 PM.

  11. #45
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    Originally posted by Joanne
    Yep... I'm 12 this year. Why the 2 ??
    Just a thought. You are 12 and your body is developing. Many instances kids of your age feel pain in their joints before a growth spurt - heels, knees, hips, etc. Not sure if this is your case, best is to consult a doctor, preferably one especialized in sports medicine.

    Doing the ' invisible' chair is good for making your knees stronger, but in your situation may not be advisable until you get an opinion from a specialist. Some coaches say this exercise is not recommended for kids in developing phase - under 16 year old.

  12. #46
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    Originally posted by wilfredlgf
    Oh gosh, it's been years since I played with Physics.
    It's likely to be wrong up there, but you get the idea.

    Maybe some of you engineer guys could fix this?
    You accounted for two soles of feet. People usually initially land on one foot first.

    Also, there is the height of the jump which has not been accounted for.

    And the situation in which the knee problem occurred for Wilfred was the scissor kick - I presume the scissor kick movement occurred during a leap backwards, so since the force is directed to the ground at a tangent, some playing around with vectors probably will be needed as correction factors.

  13. #47
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    and the force on your body when landing is not necessarily the same as that of gravity on your body.
    What I'm trying to say is that 9.81 ms-2 is the rate that gravity accelerates you.
    What we need to consider is the rate of deceleration involved in the landing.

    The higher you jump the greater your velocity on landing.
    The more you bend your knees on landing, the greater the amount of time to decelerate to zero velocity. More time decelerating means a smaller rate of deceleration.

    Inevitably, you have to put as much energy into landing as you do in jumping.
    Your calves might play a greater part in the jump than the landing I expect.

  14. #48
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    People, didn't I add "(read:simple)"?

    If someone would go and calculate the wind resistance, lost of energy (from bouncing), sole rubber elasticity... be my guest.

  15. #49
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    Originally posted by wilfredlgf
    People, didn't I add "(read:simple)"?

    If someone would go and calculate the wind resistance, lost of energy (from bouncing), sole rubber elasticity... be my guest.
    Sorry Cheung and Mark Nicholls. I'm still feeling the after effects of yesterday's migraine and I tend to get 'irritated' pretty easily today. Your additions to the calculations I did earlier is most appreciated.

    Darn, I really hate it when the 'aura patterns' begin to grow in my eyes, then as soon as it's over, the vomitting feeling takes over, half of the head hurts bad for the entire day.

    I humbly apologize, gentlemen.

  16. #50
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    Originally posted by viver
    Just a thought. You are 12 and your body is developing. Many instances kids of your age feel pain in their joints before a growth spurt - heels, knees, hips, etc. Not sure if this is your case, best is to consult a doctor, preferably one especialized in sports medicine.

    Doing the ' invisible' chair is good for making your knees stronger, but in your situation may not be advisable until you get an opinion from a specialist. Some coaches say this exercise is not recommended for kids in developing phase - under 16 year old.
    Well, I hope you mean I might get my growth spurt? Waiting for it... still not yet happened and beginning to doubt it'll happen. Lol.

    My coach does it with us all the time... guess it's okay.

    Wilfred, great post. But truth is... I only understood... 1/4 of it. And don't try making it simpler anyhow, my simple brain won't even BOTHER to try to process it.

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    no problem wilf, no offence taken.

    using v^2 = u^2 + 2 g s (where g is gravity 9.81, s is height of jump)
    and v = u + at (where a is the deceleration on landing)
    and F = ma

    v^2 = u^2 + 2 g s where u = 0 (at top of jump) becomes
    a^2 t^2 = 2 g s substitute F/m for a
    F^2 t^2 / m^2 = 2 g s
    F^2 = 2 g s m^2 / t^2
    F = m (2 g s)^0.5 / t

    I reckon the force experienced on landing (in Newton) is

    F = ( Body Mass in kg * (2 * 9.81 * height of jump in metres)^0.5) / time taken to land

    with a bit of jumping up and down with a stopwatch (don't laugh) I reckon landing takes about 0.1 seconds (from first contact with floor to zero downward velocity)

    rather than calculate the actual Force, which depends on each individuals mass, I will express it as a ratio to the force your body experience due to gravity.

    So landing in 0.1s from a 0.3m jump subjects your body to approx 2.5g
    (2.5g sounds a bit high so I reckon 0.1 seconds to land is too short)

    double the landing time and you halve the g-force
    double the height of the jump and you multiply the g by square root of 2 (approx 1.4)


    Again, that's a simplistic view because I doubt if the rate of deceleration is constant, and it is only considering a jump that is straight up and straight down.

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