Tension in lower arm while playing trills.

[parishrut]

I have been playing the plastic keyboard for quite some time now for an inter school band competition. When I play a trill with any two fingers by my right hand, some stiffening or tension or whatever you call it, starts developing on the upper side of my lower arm and it slows down my trill till you can call it a trill at all. I can do this with my left hand ten times better. What is the correct technique which goes into playing trills? Has the light plastic keyboard got to do something with it? Why does this happen with the right hand only? I play trills by my fingers, the movement originating from the lowest knuckle with hardly any arm movement.
 

[keyboardclass]

Try my trill exercise (slowly at first):

Here's the notes:


...and before anyone comments - I know the elbows are low.  It was fine by Deppe!

[pianoplayjl]

So it's trilling with the 4th and 5th fingers?

[sucom]

When playing trills, try practising them as quavers, then triplets and then semiquavers, ensuring that your fingers, hands and arms are relaxed at all times.  If you press too hard with your fingers, they will naturally tense up, creating tension in all other areas.