Answer
The difference in maximum stored energy is $~~9.8~J$
Work Step by Step
We can find the maximum stored energy for sprinters:
$U_{max} = \frac{1}{2}kx^2$
$U_{max} = (\frac{1}{2})(33\times 10^3~N/m)(0.041~m)^2$
$U_{max} = 27.7365~J$
We can find the maximum stored energy for nonathletes:
$U_{max} = \frac{1}{2}kx^2$
$U_{max} = (\frac{1}{2})(33\times 10^3~N/m)(0.033~m)^2$
$U_{max} = 17.9685~J$
We can find the difference in maximum stored energy:
$\Delta U_{max} = (27.7365~J)-(17.9685~J)$
$\Delta U_{max} = 9.8~J$
The difference in maximum stored energy is $~~9.8~J$