Just run. As hard as you can.
As hard as you can today may not be as hard as you did the other day.
Maybe you stayed up late last night, or ate a bunch of food that your body is still digesting, or both.
Every day isn’t going to be your fastest, or strongest.
That’s not what’s important.
What’s important is that when it’s time to run, or lift, or jump, that you do those things to the best of your ability in the moment.
That you get your butt into the gym (or outside, etc.) and get working.
Never let the notion that ‘you might not be at your best’ stop you from trying your best.