You know that sore feeling the day after a workout? This is mainly due to the 'eccentric' phase of the exercises you did. When you put force on stretched or lengthened muscles, you are damaging and stressing the fibers of that muscle. This leads to a higher resting metabolic rate following the workout due to recovery and repair of those muscle fibers.
The energy cost of eccentric training is very low while the magnitude of the force produced is unusually high. Therefore, muscles respond to eccentric training with meaningful changes in strength, size and power (Lindstedt, LaStayo, and Reich, 2001).
So next time you're at the gym, don't just drop your weights and focus on the lifting phase only. Try contracting for one count and then lower for three counts. For example, during a bicep curl, count to one as you curl the dumbbell up, and then count to three as you lower the dumbbell back down to your sides or hips. For a barbell squat, count to three as you lower your body towards the ground, then count to one as you pop and squeeze back to standing.