Discussion: Tuning the foot pod
in: Orienteering; Gear & Toys
Jan 18, 2007 9:02 PM
#
After Tims posting yesterday I thought that this might interest some others today. Did hill training today on the same hill (i.e. always started from the same spot), so it seems quite obvious to me that the foot pod should measure the same distance up and down - well, see for yourself
Interval 1 up 755m down 784m (4 % diff)
Int 2 889 up and 936 down (5 % )
Int 3 1070 up 1102 down (3 %)
Int 4 1165 up 1235 down (6%)
Int 5 .... you get the point!
Additionally the altimeter always measured the start spot to less than 5 m (really accurate I would say)
Any comments, suggestions as to why this is so?
Interval 1 up 755m down 784m (4 % diff)
Int 2 889 up and 936 down (5 % )
Int 3 1070 up 1102 down (3 %)
Int 4 1165 up 1235 down (6%)
Int 5 .... you get the point!
Additionally the altimeter always measured the start spot to less than 5 m (really accurate I would say)
Any comments, suggestions as to why this is so?
Jan 18, 2007 9:17 PM
#
Foot pod is useless for the distance measure on the hills going up and down. Don't see any point to discuss issue.
Jan 18, 2007 10:37 PM
#
Given that the foot pod measures speed & distance off your stride, I imagine that the variation in the measurement is, at least partially, due to variations in your stride. Clearly your stride will be different on that way up compared to the way down, and it's quite likely that it changes as you get more tired with each interval.
Jan 19, 2007 1:35 PM
#
@ Speedy - not a very useful comment I think!
@ Mark - did a fairly extensive search on Polar.fi just to make sure I was correct in my assumption. The foot pod most definitely does NOT use your stride to measure distance, but rather acceleration and maths (see article http://support.polar.fi/PKBSupport.nsf/ALLDOCS/422...)
but I see reading the article further that it does use the foot angle for calculations as well, so maybe this could be an explanation!
So I guess now the question is which distance is more accurate? up or down :)
@ Mark - did a fairly extensive search on Polar.fi just to make sure I was correct in my assumption. The foot pod most definitely does NOT use your stride to measure distance, but rather acceleration and maths (see article http://support.polar.fi/PKBSupport.nsf/ALLDOCS/422...)
but I see reading the article further that it does use the foot angle for calculations as well, so maybe this could be an explanation!
So I guess now the question is which distance is more accurate? up or down :)
Jan 19, 2007 3:35 PM
#
Yes, the foot pod measures the acceleration of your foot as you run. I would have the said that acceleration of your foot is intrinsically linked to your stride or gait … as is the angle of your foot while running …
As your stride changes, I expect the angle of your foot does also (less less lift at the back of your stride, for example) and this will affect the measurement.
As your stride changes, I expect the angle of your foot does also (less less lift at the back of your stride, for example) and this will affect the measurement.
Jan 23, 2007 3:51 AM
#
As I understand it the foorpod has two accelerometers perpendicular to each other and does a double intergation to get distance. By having two accels it can resolve vertical and horizontal components.
The accels must be a DC type to be able to measure the accelerations, so I am thinking the reason you get differences between up hill and down hill is due to the DC gravity acceleration. On the up lift your foot is moving against gravity and on the downward motion it is going with gravity. On flat ground the two would cancel, but on a slope they don't.
One way to check would be to run up and down different gradients. The steeper the gradient the greater the difference between up and down.
The accels must be a DC type to be able to measure the accelerations, so I am thinking the reason you get differences between up hill and down hill is due to the DC gravity acceleration. On the up lift your foot is moving against gravity and on the downward motion it is going with gravity. On flat ground the two would cancel, but on a slope they don't.
One way to check would be to run up and down different gradients. The steeper the gradient the greater the difference between up and down.
This discussion thread is closed.