There’s been a lot of research on the optimal levels of arousal for various athletic activities. The simple answer is that a moderate level of arousal is best. If you’re too relaxed, you won’t perform as well, but if you’re too aroused, you won’t perform as well either. Basically, a U-shaped dose-response function.
But, the optimal location at the top of the U also depends on other factors such as the type of athletic activity, the skill of the athlete, etc. Activities requiring a high level of accuracy or fine-motor control, such as figure skating, have lower optimal levels of arousal. Weightlifting is at the other end of the spectrum, with one of the highest optimal levels of arousal.
This suggests that it’s better to increase your arousal before lifting than to decrease it. But there are individual differences that are not the focus of this type of research; so you have to find what works for you. If you experience a lot of mental anxiety during the day at work, for example, meditation may help reduce the anxiety that could well inhibit neural signals to cause muscular contractions. But if you’re already feeling happy and relaxed, you may do better to blast some pumping music, splash your face with ice water, etc.
I found it interesting that there are many more ways to DECREASE arousal than to INCREASE it. It also seems easier to decrease arousal than to increase it. One of the few documented ways of increasing arousal is listening to specific kinds of music.