Thanks Panoramix I'll pay more attention to that. I'd previously been trying to follow
http://www.youtube.com/v/eqVmMd7FdAA&rel=1 but while the straight back is mentioned it's not so obvious as in
http://www.youtube.com/v/l8IsN_nOQYc&rel=1 which is helpful.
I'm struggling to see how this will make me quicker though. As well as preventing injury, I can see that better technique might enable me to maintain a given stroke rate for a given time at a higher resistance (thus improving speed) but I just can't figure out how it'll make me quicker while reducing the stroke rate at a low resistance given that if anything it will shorten the length of the stroke. This is what leads me to believe I need to use a higher resistance but get the technique right so I don't hurt my lower back.
The logic behind is that if you push the seat backward by a certain amount with your legs, you want your shoulders travel the same distance. If you don't have a "strong" back, back flexes reducing the travel of your shoulders so you have say 3 inches left and the rest is lost in deforming your back.
To train the best is to start at say 15 strokes per minutes. Seat on the machine, flex your legs, sit up (seat is forward) then push on your legs making sure your body is completely rigid (except the legs of course), once your legs are straight, use you stomach muscles to lean backward - by now arms and legs stay straight - and once you feel like you are close to fall backward finish the stroke by pulling on your arms. Keep the leg, stomach muscle and arm actions separate don't worry about the split time, focus on keeping the three actions separate and feel the force in the chord travelling from your hands to your feet.
Once you are a bit more confident carry on with the same motion pushing as hard as you can as if you were trying to break the foot rests; you should see the split time going down dramatically (with the same stroke rate).
Once you master this, up the rate; at some point you
will loose the coordination, don't panic just go down a few strokes per minutes and everything will go back together. After a few months 35 strokes per minute will feel "natural".
You may have attended one of these H&S training when they teach you to avoid back injuries by lifting with a straight back pushing on your leg, the feeling is somehow similar. When you feel the pressure under your feet it means you are doing things right.
My PB in 2003 for a 2k was 7:05 after just 6 months of serious training and having just stopped smoking so I guess that the coaching was good! I have stopped because of other commitments but I am sure that I would eventually have broken the 6:50 barrier when people start to actually want you in their boat!