A question about biceps and rotational equilibrium I know that as the angle of the elbow increases, the force of the bicep increases. i.e. when angle is 180, arm is fully extended and there is 0 force from bicep. When the elbow angle is smaller there is more force from the bicep. So would shorter forearms be the answer, because the angle would be smaller?
 A: The thing about the force exerted by our bodies when muscles contract is that it strongly depends on where the muscle attaches to the joint. Consider the left side of the following image:

Notice that the muscle does not attach to the hinge directly, but rather is attached slightly below it. When the muscle contracts, the lower bone swings upwards, similar to a lever. 
To a crude approximation, the force at the edge of the limb is given by the usual lever equation
$$F=\frac{Tr_2}{r_1}$$
where $T$ is the tension of the muscle while contracting, $r_1$ is the length of the limb and $r_2$ is the distance from the joint to where the muscle is attached.
Since $r_2<r_1$, the force exerted by the limb is less than the tension $T$. However, the upside is that the limb can move farther.
Now suppose that we increased $r_2$, so that the muscle attached further down. $F$ would increase, but there's a downside: if the muscle can only contract its length by a certain distance $\Delta$, then the limb will have a decreased range of motion. In particular, if the top end of the muscle is arbitrarily defined to be attached at coordinate $(-x,0)$, and the other end it attached near the limb at $(d_2\cos(\theta),d_2\sin(\theta))$, then one can show that the range of angles your arm can swing through is given by
$$\Theta=\cos ^{-1}\left(\frac{-2 \Delta  \left(d_2+x\right)+2 d_2 x+\Delta ^2}{2 d_2
   x}\right)\rightarrow \cos ^{-1}\left(1-\frac{\Delta }{d_2}\right) \text{ as }x\rightarrow\infty.$$
Here is a representative plot of the angular range as a function of tendon connection distance $d_2$:
Plot[Re@ArcCos[1 - \[CapitalDelta]/d2] /. \[CapitalDelta] -> 1, {d2, 
  0, 10}, PlotRange -> {0, \[Pi]}]


So if you make $d_2$ too large, you could wind up in a regime where the ratio $\Delta/d_2$ is such that you can't fully flex your arm!
By similar geometric considerations, you can also show that making your limbs shorter (ie, reducing $d_1$ rather than $d_2$) will have a somewhat similar disadvantage: namely, while it will not reduce the angular range of motion, it will reduce the length of the arc your arm traces when it flexes. 
So while it is conceivable that we might have developed differently, there are tradeoffs involved, and the question of why we have the particular configuration we do today is more a matter of evolution than physics.
Minor note: Without the Re command the plot is the same, except that at the derivative discontinuity near $d_2=0.5$ the trace vanishes because $\cos^{-1}$ takes on complex values there, but it's visually obvious that in that regime the range of motion is just $\pi$, and the real component of the $\cos^{-1}$ evaluates to exactly that in the short-length regime.
