How to detect heel strike and toe off from left/right vertical force data?

Hello:

I'm stacked in identifying HS and TO of my data. In the attachment data, you will find the right and left force. Also, there's the left and right contact. In the left and right contact columns 1 means contact and 0 means no contact. When the value changes from 0 to 1 = heel strike, and when the data is changing from 1 to 0 = toe-off. How can I identify when data is changing?

Thanks very much for the help!!!

readtable("3kmFES_001a.xlsx")

Answer 1

[William Rose]

@Mario, yuou might want to check out this article on this topic. (I am one of the authors.)

https://pubmed.ncbi.nlm.nih.gov/20478742/

Comparison of methods for kinematic identification of footstrike and toe-off during overground and treadmill running

We compared various methods for measuring heel strike and toe-off in the gaitlab, for runners on treadmill and not.

[William Rose]

@Mario,

I see that you have 10 seconds of L and R vertical force data collected at 1 kHz rate. (Split belt instrumented treadmill?). The spreadheet also has columns of 0/1 data for right and left contact and for single and dual support. The right and left contact columns data appears to be =1 if corresponding force is>0, otherwise contact=0.

Find the times t(i), wheere contact(i)=1 and contact(i-1)=0.

Assuming you have read in the file data and that you have placed the contact data (0's and 1') in vectors cR and cL (right and left contact), and the time values (0 to 9999) in vector t, then try the following. I will demonstrate with simulated cR data:

t=0:9999;                           %time (msec)
cR=round((1+cos(2*pi*t/1000))/2,0); %contact (0 or 1) (period=1 second)
nto=0;                              %toe off counter
nhs=0;                              %heel strike counter
for i=2:length(t)
   if cR(i)==1 && cR(i-1)==0        %if heel strike occurred
       nhs=nhs+1;                   %increment HS counter
       ths(nhs)=t(i);               %record HS time
   end
   if cR(i)==0 && cR(i-1)==1        %if toe off occurred
       nto=nto+1;                   %increment TO counter
       tto(nto)=t(i);               %record TO time
   end
end
fprintf('%d heel strikes, %d toe offs.\n',nhs,nto)

10 heel strikes, 10 toe offs.

fprintf('First HS at t=%.1f, first TO at t=%.1f.\n',ths(1),tto(1))

First HS at t=751.0, first TO at t=251.0.

Good luck.

[Mario]

@William Rose thanks so much!! It works well!! With respect of your question; It is not a split belt instrumented treadmill, but i have the chance to split the vertical force with the software of the force platform.

I changed the cR for the left_contact column of the data and it works :D

clear all
t=0:9999;                           %time (msec)
steps = importdata("3kmFES_001a.xlsx");
steps1 = steps.data;
left_contact = steps1(:,7)
right_contact = steps1(:,8)
nto=0;                              %toe off counter
nhs=0;                              %heel strike counter
for i=2:length(t)                   % 2 because the first line is the tittle
   if left_contact(i)==1 && left_contact(i-1)==0 %if heel strike occurred
       nhs=nhs+1;                   %increment HS counter
       ths(nhs)=t(i);               %record HS time
   end
   if left_contact(i)==0 && left_contact(i-1)==1        %if toe off occurred
       nto=nto+1;                   %increment TO counter
       tto(nto)=t(i);               %record TO time
   end
end
fprintf('%d heel strikes, %d toe offs.\n',nhs,nto)

fprintf('1° HS at t=%.1f, 1° TO at t=%.1f.\n',ths(1),tto(1))
fprintf('2° HS at t=%.2f, 2° TO at t=%.2f.\n',ths(2),tto(2))
fprintf('3° HS at t=%.2f, 3° TO at t=%.2f.\n',ths(3),tto(3))
fprintf('4° HS at t=%.2f, 4° TO at t=%.2f.\n',ths(4),tto(4))
fprintf('5° HS at t=%.2f, 5° TO at t=%.2f.\n',ths(5),tto(5))
fprintf('6° HS at t=%.2f, 6° TO at t=%.2f.\n',ths(6),tto(6))
fprintf('7° HS at t=%.2f, 7° TO at t=%.2f.\n',ths(7),tto(7))
fprintf('8° HS at t=%.2f, 8° TO at t=%.2f.\n',ths(8),tto(8))

Is it possible to plot HS and TO on the vertical force of the left_Fz(N)?

Again, thanks for the help!! have a nice week

Mario N.L.

[William Rose]

@Mario,

You are welcome. I am glad to hear that this will assist your research.

You added the comment "%2 because the first line is the tittle". Actually that is not the reason. The loop starts with i=2 because it accesses left_contact(i-1). If the loop started with i=1, then left_contact(i-1) would be left_contact(0) and that would be an error, since Matlab arrays start with element 1. (Labview arrays start with 0... )

Yes it is possible to include HS and TO on a plot of force versus time.

clear all
t=0:9999;                           %time (msec)
steps = importdata("3kmFES_001a.xlsx");
steps1 = steps.data;
Fleft=steps1(:,5);
left_contact = steps1(:,7);
right_contact = steps1(:,8);
nto=0;                              %toe off counter
nhs=0;                              %heel strike counter
for i=2:length(t)
    if left_contact(i)==1 && left_contact(i-1)==0 %if heel strike occurred
        nhs=nhs+1;                   %increment HS counter
        ths(nhs)=t(i);               %record HS time
    end
    if left_contact(i)==0 && left_contact(i-1)==1        %if toe off occurred
        nto=nto+1;                   %increment TO counter
        tto(nto)=t(i);               %record TO time
    end
end
fprintf('%d heel strikes, %d toe offs.\n',nhs,nto)

9 heel strikes, 8 toe offs.

%fprintf('1° HS at t=%.1f, 1° TO at t=%.1f.\n',ths(1),tto(1))
%fprintf('2° HS at t=%.2f, 2° TO at t=%.2f.\n',ths(2),tto(2))
%fprintf('3° HS at t=%.2f, 3° TO at t=%.2f.\n',ths(3),tto(3))
%fprintf('4° HS at t=%.2f, 4° TO at t=%.2f.\n',ths(4),tto(4))
%fprintf('5° HS at t=%.2f, 5° TO at t=%.2f.\n',ths(5),tto(5))
%fprintf('6° HS at t=%.2f, 6° TO at t=%.2f.\n',ths(6),tto(6))
%fprintf('7° HS at t=%.2f, 7° TO at t=%.2f.\n',ths(7),tto(7))
%fprintf('8° HS at t=%.2f, 8° TO at t=%.2f.\n',ths(8),tto(8))
plot(t,Fleft,'-b');
hold on; grid on
xlabel('Time (ms)'); ylabel('F_z (N)'); 
title('Left G.R.F.')
plot(ths,zeros(1,nhs),'vr',tto,zeros(1,nto),'^g')
legend('F_z','HS','TO')

Try the above.

[William Rose]

@Mario, why did you un-accept the answer?

[Mario]

Ohhh sorry! It was a mistake

[Mario]

@William RoseThanks for the plot answer!! It's great!! have a nice weekend!

[William Rose]

@Mario, you're welcome.

You could consolidate the two plot() commands into one, and remove "hold on":

plot(t,Fleft,'-b',ths,zeros(1,nhs),'vr',tto,zeros(1,nto),'^g');
grid on; xlabel('Time (ms)'); ylabel('F_z (N)'); 
title('Left G.R.F.')
legend('F_z','HS','TO')

Good luck with your research.