How to specify a fixed intercept for linear model

Hi,

Im fitting some simple linear models to data from the olympic running events
with lm(Logtime~Logdistance), the models contain an intercept and one slope
parameter. 

I have fitted a separate model for each years data and as the intercept
changes very little between years i am trying to simplify the models so that
they all have the same intercept (calculated from the mean of the previous
intercepts).

I have seen a few posts relating to zero intercepts but cannot figure out
how to set to a specific value to the parameter.

Any help would be greatly appreciated.

Thanks.

Chris.