My upper-body is very tight restricting my arm action. What exact muscles are involved in the arm swing? How can I get them and keep them loose?
Swing from the shoulders
Please elaborate. I have tried the hands-down cue but the result seems to be something like what Marion does: elbow stays relatively static with arm flexing at the top and opening at the bottom. How do you get the elbow moving for full arm action? 
400m, have you tried arm swinging using light dumbells?
400m firstly if your arms are tight then whats your leg action like? more than likely you are restricting yourself thus leading to numerous problems.
ask yourself why is my arm action tight?
is it because i’m not relaxed leading to tightness in my traps causing my shoulders to raise or is it a flexibilty issue.
if you are running tense i would cut the effort down to the point were you are running relaxed and getting a better stroke with the arms.as you get accustomed to the action,slowly raise the effort until the feeling is carried to full speed.
don’t forget that tempo is good for helping an athlete run more relaxed.an athlete who remains tense during tempo will not finish the way he started using energy on tension rather than the run.
also practise your arm action in the mirror.this is something i practiced all the time and before i knew it i was getting the same range throughout my actual runs
many people that i train with have the same problem, and our coach has done/said the same things that X-Man has said. Also our training group has seen good results in these new methods while incorporating a chiropractor that deals with athletes. Helps to get things set.
Thanks for the replies guys - some great suggestions.
X-Man
If flexibility is an issue how can/should it be addressed? Therapy is a good start but $$$ is tight! Any good stretches that will help flexibility in traps, upper body?
Thanks.
Tell the athlete to not think about hands, just think about bring the elbows back - straight back liek you are trying to elbow someone standing behind you
Try that and get back to me
400 if flexibilty is the issue there are hundreds of approaches to stretching the upper body.i always have a therapist band with me,the blue/black are the strongest which i think are great and very inexpensive way of stretching out by yourself.
flexibilty in the uppper body is easily addressed and flexibilty will improve with stretching and proper stretching
What muscle groups are we looking at to improve arm range?
Chest (pecs), Traps, Upper Back? Can anyone reccomend some good stretches???
Thanks 
400m, I find that the upper chest is more involved. You should concentrate on incline presses as well as flat bench press.
Thanks for the tip
Inclines will help to strenghten but what about lossening. Any good methods?
I just do the normal, rotating the arms like you would do in swimming. Do you know the other stretch where you hold on to a wall with your arm straight and then turn your body so that it is facing the opposite way. It’s hard to explain in words but if anyone else knows what I mean then please try and explain further if you can.
The other one is what Bruce lee used in his film, way of the dragon (i think that’s the films name). You lie on your stomach, rasie your torso and move your shoulders in a cicular motion. Both back and foward.
Hope that helped.
what did i do to fix it?good old fashion push-ups.that right.i dont understand why it works but it does for me.
It seems resistance/weight training often improves flexibility. Atleast to a point.
The key is to see quantification of resting lenght and use of various methods to increase ROM.