A new book, finite element analysis for biomedical engineering applications, will be out on April 3, 2019 by CRC Press. **20% OFF**

http://www.feabea.net/bookflyer.pdf

]]>http://www.feabea.net/bookflyer.pdf

Hello,

I have recorded some movement data with Vicon and would like to know the relative movement of certain markers (i.e. breast markers) in their respective segment coordinate system (i.e . trunk coordinate system).

For this, I would like to normalize the segment orientation to the calibration pose.

I followed the description in 'Research Methods in Biomechanics' 2nd ed. in constructing the orientation/rotation matrix (pg. 40).

According to the book: "the rotation matrix that defines the relative orientation of a segment, Rseg, with reference segment Rref, can be expressed as" (pg. 57)

R = Rseg * transpose(Rref)

To my understanding, if I want to apply it to my case, Rseg would be the rotation matrix i.e. of the trunk at each instant and the reference segment, Rref, the rotation matrix of the trunk of the static trial.

However, the book further states that "for a normalized joint angle, the rotation matrix must include the orientation of the segments in the calibration pose Rcalseg and Rcalref and is expressed as follows:

R = (transpose(Rcalseg)*Rseg) * transpose(transpose(Rcalref)*Rref)

As I am only interested in the normalized rotation matrix without referencing it to a further segment, I am now confused if I have to calculate my rotation matrix either

a) R = R_trunk_dynamic * transpose(R_trunk_static)

or

b) R = transpose(R_trunk_static) * R_trunk_dynamic

Also, as the rotation matrix is made up of the unit vectors of the local or segment coordinate system (LCS) I would now like to have a normalized LCS with reference to the static trial.

Therefore, I assumed that R has now the unit vectors of my normalized LCS. However, I am wondering if now the columns or the rows of R will be the unit vectors in x, y and z direction? Assuming Rseg and Rref originally had their unit vectors as rows.

Any advice is greatly appreciated.

Thank you,

Janina

]]>I have recorded some movement data with Vicon and would like to know the relative movement of certain markers (i.e. breast markers) in their respective segment coordinate system (i.e . trunk coordinate system).

For this, I would like to normalize the segment orientation to the calibration pose.

I followed the description in 'Research Methods in Biomechanics' 2nd ed. in constructing the orientation/rotation matrix (pg. 40).

According to the book: "the rotation matrix that defines the relative orientation of a segment, Rseg, with reference segment Rref, can be expressed as" (pg. 57)

R = Rseg * transpose(Rref)

To my understanding, if I want to apply it to my case, Rseg would be the rotation matrix i.e. of the trunk at each instant and the reference segment, Rref, the rotation matrix of the trunk of the static trial.

However, the book further states that "for a normalized joint angle, the rotation matrix must include the orientation of the segments in the calibration pose Rcalseg and Rcalref and is expressed as follows:

R = (transpose(Rcalseg)*Rseg) * transpose(transpose(Rcalref)*Rref)

As I am only interested in the normalized rotation matrix without referencing it to a further segment, I am now confused if I have to calculate my rotation matrix either

a) R = R_trunk_dynamic * transpose(R_trunk_static)

or

b) R = transpose(R_trunk_static) * R_trunk_dynamic

Also, as the rotation matrix is made up of the unit vectors of the local or segment coordinate system (LCS) I would now like to have a normalized LCS with reference to the static trial.

Therefore, I assumed that R has now the unit vectors of my normalized LCS. However, I am wondering if now the columns or the rows of R will be the unit vectors in x, y and z direction? Assuming Rseg and Rref originally had their unit vectors as rows.

Any advice is greatly appreciated.

Thank you,

Janina

Hi All,

I am currently trying to calculate RFD but this is something I have never done before; I would like to calculate it at various points i.e. 0-30 ms, 0-50 ms etc... I originally differentiated force and time but realised this will only give me instantaneous RFD at that time point, therefore I am currently struggling to calculate these intervals, any help would be greatly appreciated as this is a technique I am eager to learn. Thank you in advance!

]]>I am currently trying to calculate RFD but this is something I have never done before; I would like to calculate it at various points i.e. 0-30 ms, 0-50 ms etc... I originally differentiated force and time but realised this will only give me instantaneous RFD at that time point, therefore I am currently struggling to calculate these intervals, any help would be greatly appreciated as this is a technique I am eager to learn. Thank you in advance!

Hi there,

I am trying to synchronize the data from a Walkway system and IMU sensors. I have seen some options using external trigger device, but not sure how to implement them. It would be great if you could share any working examples/ideas that could be implemented easily.

Thanks much..

]]>I am trying to synchronize the data from a Walkway system and IMU sensors. I have seen some options using external trigger device, but not sure how to implement them. It would be great if you could share any working examples/ideas that could be implemented easily.

Thanks much..

Hi Everyone

We have completed an experiment measuring impact acceleration at both the tibia and sacrum (using Shimmer inertial sensors, Dublin) while recreational runners ran for 15 minutes on a treadmill. The sensors were attached with double sided tape, elastic tape over the sensors onto the skin and with an elastic belt wrapped firmly around the runner's waist. The sensors were aligned with the longitudinal axis of the segment (tibia, sacrum)

While for the majority of runners the impact acceleration at the sacrum was lower than at the tibia, for a few individuals we found the opposite, the sacrum acceleration is actually higher.

No studies to date appear to have reported this phenomenon, in stead suggesting the signal will always be lower because it is dampened as it propagates through the body.

for example:

Reenalda, Jasper, Erik Maartens, Jaap H. Buurke, and Allison H. Gruber. "Kinematics and shock attenuation during a prolonged run on the athletic track as measured with inertial magnetic measurement units." Gait & posture 68 (2019): 155-160. (measured at the tibia and sacrum)

Shorten, Martyn R., and Darcy S. Winslow. "Spectral analysis of impact shock during running." International Journal of Sport Biomechanics 8, no. 4 (1992): 288-304. (measured at the tibia and head)

We have filtered the signal at 60 Hz (with a bidirectional fourth-order Butterworth filter) and we removed any linear trend from the signal (Shorten and Winslow, 1992)

Has anyone else experienced this situation in assessing runners?

or/and

Does anyone have an explanation to why the impact acceleration would be greater at the sacrum?

Many thanks

Kieran

SHORTEN MR, WINSLOW DS: Spectral analysis of impact shock during running. Int J Sport Biomech 8: 288, 1992.

]]>We have completed an experiment measuring impact acceleration at both the tibia and sacrum (using Shimmer inertial sensors, Dublin) while recreational runners ran for 15 minutes on a treadmill. The sensors were attached with double sided tape, elastic tape over the sensors onto the skin and with an elastic belt wrapped firmly around the runner's waist. The sensors were aligned with the longitudinal axis of the segment (tibia, sacrum)

While for the majority of runners the impact acceleration at the sacrum was lower than at the tibia, for a few individuals we found the opposite, the sacrum acceleration is actually higher.

No studies to date appear to have reported this phenomenon, in stead suggesting the signal will always be lower because it is dampened as it propagates through the body.

for example:

Reenalda, Jasper, Erik Maartens, Jaap H. Buurke, and Allison H. Gruber. "Kinematics and shock attenuation during a prolonged run on the athletic track as measured with inertial magnetic measurement units." Gait & posture 68 (2019): 155-160. (measured at the tibia and sacrum)

Shorten, Martyn R., and Darcy S. Winslow. "Spectral analysis of impact shock during running." International Journal of Sport Biomechanics 8, no. 4 (1992): 288-304. (measured at the tibia and head)

We have filtered the signal at 60 Hz (with a bidirectional fourth-order Butterworth filter) and we removed any linear trend from the signal (Shorten and Winslow, 1992)

Has anyone else experienced this situation in assessing runners?

or/and

Does anyone have an explanation to why the impact acceleration would be greater at the sacrum?

Many thanks

Kieran

SHORTEN MR, WINSLOW DS: Spectral analysis of impact shock during running. Int J Sport Biomech 8: 288, 1992.

https://www.sciencemag.org/news/2019...costs-and-open

Univ of California is "boycotting" Elsevier, publisher of the Journal of Biomechanics.

Is this the first domino?

Should ASB, ISB and other Biomechanics societies sever their loose associations with J Biomechanics?

Should we join the UC system by not submitting manuscripts to J Biomechanics?

Or, perhaps we should stop reviewing for J of B after some date? (I would not want to screw colleagues who have manuscripts in the pipeline)

The institutional subscription rate for the printed journal is >$US 8000 (though I think they offer better rates if your university buys into the whole Elsevier "family" of journals).

Note: I have never had a problem with our colleagues who are on the editorial staff at J Biomechanics. I find them to be fair and professional (if under/unpaid!?)

]]>Univ of California is "boycotting" Elsevier, publisher of the Journal of Biomechanics.

Is this the first domino?

Should ASB, ISB and other Biomechanics societies sever their loose associations with J Biomechanics?

Should we join the UC system by not submitting manuscripts to J Biomechanics?

Or, perhaps we should stop reviewing for J of B after some date? (I would not want to screw colleagues who have manuscripts in the pipeline)

The institutional subscription rate for the printed journal is >$US 8000 (though I think they offer better rates if your university buys into the whole Elsevier "family" of journals).

Note: I have never had a problem with our colleagues who are on the editorial staff at J Biomechanics. I find them to be fair and professional (if under/unpaid!?)

Dear colleagues.

In the past few years a number of pedal-based cycling-powermeters were introduced to the market (cf. https://www.dcrainmaker.com/2018/11/...yers-2018.html). Some of them claim to measure pedaling efficiency. This would require the collection of at least tangential and radial forces at the pedal. While these pedals and their software (to my knowledge) only report "overall" power and efficiency with low temporal resolution, for biomechanics research raw-data with reasonable frequency would be essential. I am aware of some custom-made force measuring pedals which unfortunately are far off my budget.

Hence my question: Is anyone of you aware of commercially available pedal based powermeters which allow the recording of forces in a reasonable temporal resolution? This might not be possible with standard software, so the additional question is: Has anyone had experience with a company offering pedal-based power meters which supports Higher Education Institutions to gather raw-data?

Thank you in advance for your replies and effort.

Happy to share the results with the community.

Kind regards from Vienna

Stefan

]]>In the past few years a number of pedal-based cycling-powermeters were introduced to the market (cf. https://www.dcrainmaker.com/2018/11/...yers-2018.html). Some of them claim to measure pedaling efficiency. This would require the collection of at least tangential and radial forces at the pedal. While these pedals and their software (to my knowledge) only report "overall" power and efficiency with low temporal resolution, for biomechanics research raw-data with reasonable frequency would be essential. I am aware of some custom-made force measuring pedals which unfortunately are far off my budget.

Hence my question: Is anyone of you aware of commercially available pedal based powermeters which allow the recording of forces in a reasonable temporal resolution? This might not be possible with standard software, so the additional question is: Has anyone had experience with a company offering pedal-based power meters which supports Higher Education Institutions to gather raw-data?

Thank you in advance for your replies and effort.

Happy to share the results with the community.

Kind regards from Vienna

Stefan

I wanted to experimentally verify the step frequency’s (SF) dependence on Body Mass (BM). It appears in an equation I use to estimate leg-stiffness (kleg) for scenarios that I run through the model.

The expression is for the frequency of a mass bouncing vertically on a spring. This is similar to a subject running in-place with close to zero aerial phase.

The equation,

SF=(1/(2*PI))*SQRT(kleg/BM)

implies that if the BM increases, the SF should decrease according to 1/SQRT(BM).

If a subject while running very slowly, adds 20% to their BM using a weight jacket, then their step frequency should decrease by SQRT(1/1.2) or 8.7%. .

I have tried this myself, but I don’t have access to a weight jacket. I could only hand-hold an additional 10% of my BM while I ran slowly. Then, my SF dropped by 3%; I expected it to decrease by 5%.

I have looked for research on this issue, but I could not find any. Has anyone ever worked in this area? Or, are there any published articles on this topic?

Ted

]]>The expression is for the frequency of a mass bouncing vertically on a spring. This is similar to a subject running in-place with close to zero aerial phase.

The equation,

SF=(1/(2*PI))*SQRT(kleg/BM)

implies that if the BM increases, the SF should decrease according to 1/SQRT(BM).

If a subject while running very slowly, adds 20% to their BM using a weight jacket, then their step frequency should decrease by SQRT(1/1.2) or 8.7%. .

I have tried this myself, but I don’t have access to a weight jacket. I could only hand-hold an additional 10% of my BM while I ran slowly. Then, my SF dropped by 3%; I expected it to decrease by 5%.

I have looked for research on this issue, but I could not find any. Has anyone ever worked in this area? Or, are there any published articles on this topic?

Ted

Our Kinesiology program in exploring increasing our physics and math requirements for our Kinesiology undergraduate degree. Our undergraduate program relies on enrollment numbers to be sustainable to a certain extent, so there is a concern that increasing our physics and math requirements will negatively impact our enrollment numbers. Therefore, I am posing these questions here.

]]>- For those that belong to a kinesiology program that has increased, or decreased, math or physics requirements:

- Did you see an impact on enrollment numbers, and what was that impact (increase or decrease)?
- What did you change your math requirement from and to?
- Were there any other impacts, negative or positive?

- I have read a lot of math advocates opine that math requires one to think, or learn to think, differently (in more logical fashion) as compared to other subjects. However, i have not seen any scientific evidence of this. Does anyone here know of any evidence of this, or to the contrary?

Hi,

I've been discussing new marker cluster construction. Based on the works by Cappozzo (see Surface-marker cluster design criteria for 3-D bone movement reconstruction. IEEE Trans Biomed Eng. 1997 Dec;44(12):1165-74) does anyone have a nice matlab/python/excel sheet to calculate these parameters. Or a procedural outline if someone wanted to investigate minimal cluster size construction to satisfy optimal performance in their specific lab environment.

Or do many people prioritize this at all?

Thanks,

Jereme

]]>I've been discussing new marker cluster construction. Based on the works by Cappozzo (see Surface-marker cluster design criteria for 3-D bone movement reconstruction. IEEE Trans Biomed Eng. 1997 Dec;44(12):1165-74) does anyone have a nice matlab/python/excel sheet to calculate these parameters. Or a procedural outline if someone wanted to investigate minimal cluster size construction to satisfy optimal performance in their specific lab environment.

Or do many people prioritize this at all?

Thanks,

Jereme

I read somewhere that the venous foot pump can be viewed as priming the calf pump in a fashion that resembles the atria priming the ventricles .

With regard to how the foot pump functions , the idea that the vessels of the plantar venous plexus are stretched during weight bearing , and that this stretching empties them , still persists . I believe that this idea is demonstrably wrong .

An article published in 2012 ,E Lindsay et al ,(see below ) lays out the argument for a vessel stretch mechanism very well .

Here are 2 quotes from the article -

1 When weight is applied to the sole of the foot, the plantar arch is flattened. The resulting longitudinal stretching of the veins allows the blood to be pumped along the long and short saphenous veins into the deep calf veins, even when the patient is in the upright position.

2 Gardner and Fox also found that ‘weight bearing on a flaccid hemiplegic leg with the knee locked also caused flow in the femoral vein’, indicating that the foot pump may be functional in paraplegic legs. It has also been suggested that stretching the arch without weight bearing may be sufficient to empty the veins (Gardner and Fox, 1983).

The problem with the stretch to empty theory is that veins are viscoelastic and stretching them will not effectively empty them .

Here is a simple experiment that is even cheaper than my previous HP sauce efforts .

I filled a simple latex glove with cold water . Then I got someone to hold the fingers whilst I pulled up on the open end of said glove to stretch it . Far from the glove emptying ,more room was created for addition water .

I was pretty certain of what would happen before I started but thought I would check anyway .

Any thoughts ?

**Short-stretch compression bandages and the foot pump - Nursing Times**

https://www.nursingtimes.net/.../030624Short-stretch-compression-bandages-and-the-f...

by E Lindsay - Cited by 2 - Related articles

9 Nov 2012 - leg, focusing on calf-**muscle** function and the action of the **foot pump**. They discovered that the plantar venous plexus fills when the foot is ..

]]>With regard to how the foot pump functions , the idea that the vessels of the plantar venous plexus are stretched during weight bearing , and that this stretching empties them , still persists . I believe that this idea is demonstrably wrong .

An article published in 2012 ,E Lindsay et al ,(see below ) lays out the argument for a vessel stretch mechanism very well .

Here are 2 quotes from the article -

1 When weight is applied to the sole of the foot, the plantar arch is flattened. The resulting longitudinal stretching of the veins allows the blood to be pumped along the long and short saphenous veins into the deep calf veins, even when the patient is in the upright position.

2 Gardner and Fox also found that ‘weight bearing on a flaccid hemiplegic leg with the knee locked also caused flow in the femoral vein’, indicating that the foot pump may be functional in paraplegic legs. It has also been suggested that stretching the arch without weight bearing may be sufficient to empty the veins (Gardner and Fox, 1983).

The problem with the stretch to empty theory is that veins are viscoelastic and stretching them will not effectively empty them .

Here is a simple experiment that is even cheaper than my previous HP sauce efforts .

I filled a simple latex glove with cold water . Then I got someone to hold the fingers whilst I pulled up on the open end of said glove to stretch it . Far from the glove emptying ,more room was created for addition water .

I was pretty certain of what would happen before I started but thought I would check anyway .

Any thoughts ?

https://www.nursingtimes.net/.../030624Short-stretch-compression-bandages-and-the-f...

by E Lindsay - Cited by 2 - Related articles

9 Nov 2012 - leg, focusing on calf-