All that research seemed to focus on endurance exercise but it was interesting to see Alex point to new research that indicates that there are similar ideas at play with respect to lifting weights.
What I thought was neat about the study was the distinction between "peripheral" and "central" fatigue: the former is the reduced ability of your muscle itself to contract, and the latter is a reduction in the signal from your brain to your muscle demanding contraction. If you pick up a heavy (above critical torque) dumbbell and lift it until you can't anymore, the limiting factor appears to be peripheral fatigue. Your muscles are simply no longer capable of contracting powerfully enough to lift the weight. In contrast, if you lift a lighter (below critical torque) dumbbell to failure, your muscles themselves fatigue to a much lesser extent, suggesting that fatigue somewhere in your brain or central nervous system is the problem.
The study is Distinct profiles of neuromuscular fatigue during muscle contractions below and above the critical torque in humans.