So....I was chugging round as usual, and about 3k in, my arms just said they'd had enough. My arms.
So there was a bit of that weird bickering you sometimes do with your body parts...what do you mean you're tired you haven't done anything, I want to go home, shut up...and I sort of hauled myself and my knackered arms round.
What was that all about? Has anyone else had this?
Yup funnily enough today no idea why - it's never happened before see the ‘A” in knackered...
jancanrun.com/2018/02/16/16...
But seriously a couple of things to consider - were you running with your arms relaxed more or less at 90 degrees - going back and forwards not cross-body? That makes a difference to your balance and really adds to fatigue.
Were you carrying anything in your hands - again being off-balance on weight can make a difference.
Think of yourself as a Formula One car - your aerodynamics count a lot - lose your rear spoiler and the downdraft isn’t good enough and it's the same with your body’s symmetry.
If a bit of you is out it is surprising how that makes a difference.
Failing those reasons sometimes bits of your bod decide to have bolshy days....
Don't think there's much chance of me losing my rear spoiler!
But I like the idea I'm a formula 1 car...all that fine tuned engineering.
I may have been a bit cross body with the arms. I'll experiment. Thanks!
Maybe ...holding yourself tensely... ?
Was it cold ..? Maybe you were not, for whatever reason, relaxing the shoulders and arms when you ran.
If you were tense... your arms would ache...Focus on keeping relaxed. If they start to ache, slow down the pace until you can run comfortably . Try to keep the movement natural. Even if it's just your shoulders that are tight, this will run right down the arms.
My legs would probably love my arms to have a bad day just for a bit of payback (legs= " I've carried you and your poncy swishing to-and-fro, get over yourselves!" or "Having a bad day? Get down here and walk a handstand for a few miles and get back to me!" ). 
Good news that your legs are all good. That's the business end of all things joggy.
I habe had the odd arm ache too!!!
Sounds odd, but there's some good advice on here. Love the Formula 1 comparison from Hidden . It's just that sometimes I feel like an old go-cart, cobbled together by an enthusiastic father and son, held together with frayed bits of string and with decidedly wonky wheels!
Yep when I’m not thinking about my legs, knees ankles posture head up etc then the arms take a turn. Some times I suddenly realize that I’ve tensed right up and have the look of tyrannosaurs Rex (big lumbering body and weeny little arms somewhere under my chin) then there’s the paddle steamer effect that occurs when I seem to be trying the roll myself forward with them, not forgetting the “let’s try just dangling them for a while” till they become like out of control ropes whipping me . Oh ‘tis endless the amusement you can have with your arms! Mind whilst all this is going on the legs are just plodding away and thankful to have the focus off them.
One day, one day I may just be out there running with nothing on my mind but the view.
Arm or Waist?
broken arm! 
Mobile phone holder (Arm Band)
broken wrist - arm in plaster - GUTTED
Armed and No Longer Dangerous 
