I am trying to model a tibia with all the muscles, and have successfully run a kinematic analysis with C3D data. The forces acting on the muscles are clear in the .txt output file, however at the end of each time step there is this data:
Force[200]:
Name=Main.Studies.HumanModel.BodyModel.Left.Leg.Jnt.Ankle.Constraints.Reaction;
Class=AnyMainFolder.AnyFolder.AnyFolder.AnyFolder.AnyFolder.AnyFolder.AnyFolder.AnyRevoluteJoint.AnyKinEq.AnyReacForce;
SegmentName=Main.Studies.HumanModel.BodyModel.Left.Leg.Seg.Shank;
SegmentID=0;
Pos=2.184840997582162e-001;3.583288886075099e-001;9.238602960012199e-002;
RefFrame=Main.Studies.HumanModel.BodyModel.Left.Leg.Seg.Shank.AnkleJoint;
Components(5):
F[0]=-3.880546956050098e+002;5.206948822593242e+002;2.911534693467337e+001;
M[0]=-1.227857718873354e-013;-1.062635454592254e-013;1.522328092655277e-013;
F[1]=2.389406214326639e+002;6.438579518092851e+001;2.033177767369161e+003;
M[1]=9.124717602895251e-013;7.691144643413068e-014;-8.225498122554138e-014;
F[2]=-2.067952776520482e+002;-1.557516098234094e+002;2.923501542987227e+001;
M[2]=4.940819547203546e-014;-4.407633982645868e-014;9.367698735337497e-014;
F[3]=-0.000000000000000e+000;-0.000000000000000e+000;-0.000000000000000e+000;
M[3]=1.139961886794873e+001;-1.490975680055883e+001;1.202965849181227e+000;
F[4]=-0.000000000000000e+000;-0.000000000000000e+000;-0.000000000000000e+000;
M[4]=3.364935112869899e-001;7.880604704807493e-001;6.578650744057997e+000;
Force[201]:
Name=Main.Studies.HumanModel.BodyModel.Left.Leg.Jnt.Knee.Constraints.Reaction;
Class=AnyMainFolder.AnyFolder.AnyFolder.AnyFolder.AnyFolder.AnyFolder.AnyFolder.AnyRevoluteJoint.AnyKinEq.AnyReacForce;
SegmentName=Main.Studies.HumanModel.BodyModel.Left.Leg.Seg.Shank;
SegmentID=0;
Pos=2.095240217143745e-001;3.290492659076498e-001;4.965972300644907e-001;
RefFrame=Main.Studies.HumanModel.BodyModel.Left.Leg.Seg.Shank.KneeJoint;
Components(5):
F[0]=-3.653418460596454e+002;7.884208993164433e+002;-3.132144030975129e+002;
M[0]=-1.066781144826532e-013;-1.066781144826532e-013;-1.066781144826532e-013;
F[1]=4.388483250988131e+002;-1.209476653512677e+003;-3.556370068172439e+003;
M[1]=-5.731253090233312e-014;-5.731253090233312e-014;-5.731253090233312e-014;
F[2]=5.688697108036275e+002;2.567975616891561e+002;-1.713633131203234e+001;
M[2]=-5.954509488418671e-014;-5.954509488418671e-014;-5.954509488418671e-014;
F[3]=0.000000000000000e+000;0.000000000000000e+000;0.000000000000000e+000;
M[3]=2.470942356951964e+001;-5.415931250420806e+001;8.663654055934352e+000;
F[4]=0.000000000000000e+000;0.000000000000000e+000;0.000000000000000e+000;
M[4]=-2.566365007274727e-001;1.059214718073798e+000;7.353442382830600e+000;
My question is why are there 4 separate forces for each of these points, and what are these forces representing exactly? It seems like these are the forces that are acting on the shank from the ankle and knee, so to properly model a tibia these forces would be applied to the proximal and distal heads. However, is it necessary to apply each force separately at different points, or should they all be summed and applied to the singular point given in the data?