   What Forces come into play during Running?
  I would like to simulate Running in a simple Way in my Soccer Game. I just want to keep Track of the Angle of the Thighs.How do I calculate the Force Forward based on the Angle of the Thighs?How do I calculate Resistance to Movement?Any other Forces I should care about?   
  I am not an expert here, although I hope I can point you in the right direction.  Searching for 'kinetics' (the study of motion/movement) and possibly adding 'human body kinetics' or something might help.As far as my theories go; I would guess you can assume the player is always standing up, <0,1,0> (if that is your UP vector).  And that the angle of the thigh is always computed from the up angle; however there is point where this will be parallel as you run.Force Based on AngleTypically when the thigh angle is in front of the player there is little, or even no forces being exerted to the player; I just went out running down the driveway to get the mail while thinking about this problem.  The most force applied is as the leg is behind, pushing against the ground and just before it lefts off the ground.  In essence, running is more about pushing than it is about pulling.Likely this could be simulated with some form of sine-wave or response chart/look-up table; where forces are only added if foot is on ground, and less pull force, more push force.Resistance to MovementObviously you have air resistance.  But to simulate a player stopping by 'muscle" forces I can only say that the angle of the thigh would be changing at a slower rate than the player is moving.  You can calculate this though I can't describe how at this moment.  It may actually be the way to simulate the force of running as well, just in that case the angle of the thigh would change _more_ than what the ground did; ie it moved faster.-----------------------------------My thoughts; unless you are making some for of simulated soccer game that dives into a high level of physical details like how real people run, I would say move the player more traditionally, and play an animation that matches the player run speed.  Could require a few animations as well to look smoothly.Sounds interesting though, keep us updated!   ;  walking and run are controlled acts of falling, when your feet are on the ground they being used as pivot points for a fall where you then transfer your forward momentum to your other foot to pivot your self back up ready for the next fall.   ;  Simulating body mechanics of something as complex as running is going to be really bloody difficult.If you want to do it properly then try starting here and following the references to get something you can use.http://w4.ub.uni-konstanz.de/cpa/article/download/900/818Alternatively, cartoonify it and make your job much easier :). Realistic running animation without motion capture data is going to be in the order of man months worth of work. Particularly without access to certain journals (Medicine & Science in Sports & Exercise)   ;  Just for clarification, hiigara, please tell us, if you actually had a 3D animation in mind. Because you write the angle of the thighs and not the angles I read it as a 2D-problem.   ;  Thank you for your replies all.davetyler thanks for that Doc, it is exactly what I was looking for. Although I don't want to simulate running to that Extent of Accuracy, I was looking for a good Bed reading to help me understand the Real Mechanics so I can then devise a trimmed simplified Model.Background of my Project:it is a Soccer Manager Game. I simulate running in 2D. The Player has a Position (x,y) and a Velocity (Vx, Vy).The Z Dimension is cosmetic, like in a 2.5D Game.Since Z is cosmetic, there is no vertical Gravity Force and the Players are Dots without any Volume or Area (For Kinetics purposes. Although they will have Area for collisions). Sure I can add an Horizontal Force to simulate the Gravity push when the Athlete leans forward to gain Acceleration.All I want is to keep track of (Leftthighangle, Rightthighangle) and connect those Parameters with the Forward applied Forces.Why?If this was an Arcade Game where the User is controlling the Players I would not care much about Realism. In such Games fake Physics is more fun.But in this case the User is a passive Watcher of a Match, like a Movie, so adding Realism will help me stand out from the Competition.Soccer is all about Legs (Although there is a good amount of Heading too). The fact that a Player has taken a longer or shorter Stride determines with which Leg will he be able to kick the Ball or Tackle the Opponent. The Leg used as Support Leg on the Last stride cannot perform the Kick. The Fact that you use the Left or Right Leg in a Kick makes a lot of Difference, specially in a Management Simulation. The most common Fouls in Soccer is when you Tackle the Support Leg of your Opponent without touching the Ball first. Want to simulate that. And there is also the Cosmetic effect of Realistic Brutal Accelerations.blackbird your Speculations are very interesting. I also did my own Speculations and I will share them with you in the next few Days.I am coding those Speculations, and I will have a small App to show.   ;Quote:Original post by unbirdJust for clarification, hiigara, please tell us, if you actually had a 3D animation in mind. Because you write the angle of the thighs and not the angles I read it as a 2D-problem.Yes, it is 2D. The Angle in the Plane that cuts the Player in 2 symmetric Pieces, in the Direction he is facing.;Quote:Original post by hiigaraSure I can add an Horizontal Force to simulate the Gravity push when the Athlete leans forward to gain Acceleration.When running, leaning forwards doesn't give you any acceleration, especially due to gravity. The reason people lean forwards when they run is to balance - to stop the fact that all the force is coming from their legs and feet making them fall over backwards.The only time gravity would come into is is if you were running up or downhill.   ;Quote:Original post by BattleMetalChrisQuote:Original post by hiigaraSure I can add an Horizontal Force to simulate the Gravity push when the Athlete leans forward to gain Acceleration.When running, leaning forwards doesn't give you any acceleration, especially due to gravity. The reason people lean forwards when they run is to balance - to stop the fact that all the force is coming from their legs and feet making them fall over backwards.The only time gravity would come into is is if you were running up or downhill.Whilst I understand the point you are trying to refute, you are not correct. Leaning forward is imperative in the acceleration phase of sprinting.http://www.sport-fitness-advisor.com/sprintingtechnique.htmlThe above is a relatively simple link that justifies that claim.As far as the OP's problem goes. I don't think that the user will feel like the game is more realistic if tackles sometimes take out the standing leg because of a running model you have in place. That could be essentially random (based on a tackling stat) and provide the same feel to the user...assuming that you aren't graphically displaying the tackles.Still it sounds like an interesting problem so feel free to ignore my advice and try and work it out anyway. I would probably ignore my advice as well ;)   ;Quote:Original post by davetylerWhilst I understand the point you are trying to refute, you are not correct. Leaning forward is imperative in the acceleration phase of sprinting.I didn't say people don't lean forward when they sprint, I said that leaning forward doesn't cause gravity to accelerate you.You lean forward to help gravity counteract the fact that all the force is coming from a point far below your centre of mass; you'd fall over backwards otherwise, as your feet tried to run out from underneath you. What it doesn't do is cause gravity to accelerate you forwards.   