system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: When lifting weights, why is it easier to do the last few reps if a spotter places a finger under the bar?

Is it actually the miniscule amount of weight they are taking off or is it a placebo effect thing?

edit: Thanks guys for all the great answers.
gpt
Physics. The weight of the bar is applying a downward force, and your muscles are pushing a force upwards. If the force you apply upwards is greater than the weight pushing down, the bar will accelerate upwards. The last few reps, we find it harder and harder to recruit the necessary muscle mass to accelerate the bar, so often times you'll have the bar start losing momentum at a certain sticking point and possibly stop in it's path. For that moment the force you're applying to the bar and the weight of the bar are equal, so the bar will hover at that sticking point. The spotter can come in and place a finger under the bar to apply just enough extra upward force to start accelerating the bar out of that sticking point. Remember, the forces at the sticking point are equal, which is why the bar is not moving, so only a little bit of extra force applied is necessary to give the bar upward momentum. It is much easier to maintain momentum, than to accelerate a stationary mass - this is also why paused sets are much more demanding.