I've been doing Jefferson curls for 3 - 6 months now and I've not noticed any improvement in terms of how far the bar can go below my toes.
I've been doing once a week and I was wondering if there was any harm in increasing the frequency to 2 or 3 times a week?
Admittedly I dropped the weight recently because I had to have a month off from doing them. I'm current using about 35 lbs but I was probably close to 50lb before my break. I would probably be happy to start building the weight back up too and I would be keen on advice on the frequency increasing the weight.
Finally I would be interested to know if it's ok to keep doing them after I've finished MN PE2>iM - I'm not sure what the next iM is for MN.