Calculating Formula from Plot Points Ok, so it's been a very long time since I've done anything like this. I've got a big table of data to enable you to look up a certain $X$ value (bodyweight) and get a $Y$ value (co-efficient for weightlifting). I want to condense this down into a formula, no matter how complex, that I can put into an Excel spreadsheet to track some training. I've grabbed a few data points from the table, that look something like this:
X    Y

40   1.32435
50   1.0099
60   0.83285
70   0.72625
80   0.6578
90   0.61185
100  0.5813
110  0.5625
120  0.55095
130  0.54032
140  0.53117
150  0.52318
160  0.51588
170  0.509075
180  0.5023
190  0.49582
200  0.4903
210  0.48581
220  0.48231
230  0.47891 

Any help is greatly appreciated.

Taking a look at your data, I guessed that maybe a function of the form $f(x)=a/x^p+b$ might work.  If we then parameters $a$, $b$, and $p$ to minimize
$$\sum_{(x,y)\in \text{data}} (f(x)-y)^2,$$
we find $f(x)=\frac{2106.91}{x^{2.11436}} + 0.463718$.  The sum of the squared errors is $0.000480789$, which seems pretty good.  The graph of $f$ with the data looks like 

