Centripedal forces and the calf muscle pump

[Gerrard Farrell]

Re: Centripedal forces and the calf muscle pump

Hi Joakim ,
Many thanks for responding .

Yes ,you are quite right , the question should say the upper end is hinged at a revolute joint (representing the hip joint) . The "acceleration " I mean relates to change in speed of the free end as it moving along its curved trajectory .

Say you were sitting in a car going round a bend and the speedometer said a constant 30 miles an hour . The car would have constant angular acceleration .

But what if you were going around the same corner whilst increasing speed from 30 mph to 60 mph (as measured by the speedo ) . How would you calculate the angular acceleration in that instance .

Actually , I suppose you would be trying to find the rate of change in angular acceleration .

But what does this mean for the force produced by the fishing weight (mass 100g ) on the seal .



Gerry

[Gerrard Farrell]

Re: Centripedal forces and the calf muscle pump

Still on the same general theme , is venous return from the lower limb easier to achieve in a tall individual with long legs or a smaller individual with proportionally shorter legs ? Intuition would say its more difficult with longer legs but this might not be the case in some instances .

Let's say we take an imaginary couple where the man is six four and the woman is four ten . He has legs 85cm long and hers are 57 cm long .

Now let's say they go out for a jog together and run at 3m/s . For the woman this would give a centrifugal effect at the ankle of 3x3/.57 =15.7 . Add in gravity and we have about 2.5 Gs acting on the blood in this section when the reference foot is on the ground . ( it would be much higher during the swing phase 6x6/.57=63 , so 7.3 Gs )

For the man we have 3x3/.85 =10.58 , so about 2 Gs during stance phase . ( swing phase 42.3+ 10 giving 5.2 Gs - less chance of reflux than in the case of the woman's leg ? )

Now the column of blood is longer in the male's leg , but is the higher centrifugal effect in the woman's lower leg enough to be the determining factor when considering the initial question " is venous return from the lower limb easier to achieve in a tall individual with long legs or a smaller individual with proportionally shorter legs ? "


On a slightly different tack , cardio vascular fitness clearly involves not just the heart and lungs but the peripheral muscle pumps as well . So is peak cardiovascular fitness for swimming the same as that for running with regard to the peripheral pumps ? Probably not
. Swim fit does not necessarily mean run fit for the cardiovascular system .

Note ; the figure of 6m/s in the bracketed material comes from the parts of the swing phase just prior to ground contact and just after toe off but not the period between , when the velocity of the foot relative to the hip can be viewed as being back to about 3m/s . I got the 6 from looking at the foot relative to a static running track as a person runs down the track but in treadmill studies it represents the stance foot going from 3m/s backwards relative to the body to 3m/s forwards ,a transient velocity change of 6m/s (this bit might be wrong )

. The centrifugal effect is generated by the foot/leg moving relative to the torso at the hip joint , so perhaps the best way to look more closely at the effect is by treadmill studies using markers and a bit of soft wear .