Hi Lin
Welcome to the AnyScript forum!
You say you have a predefined curve of the muscle strength. And you are interested in time dependence of muscle strength.
The error that you are seeing is due to the use of AnyMuscleModel, which expects F0 to be a constant. You can use AnyMuscleModelUsr1 to define your own function for muscle strength, which can also be a function of time. So, you would be able to implement your function within AnyScript without needing the Python hook. Further, if you have predefined values of strength, you can create an interpolation function using AnyFunInterpol and AnyInputFile. Please see the reference manual for more information on these classes and demo examples.
Please also see the tutorial on muscle modeling.
I hope that helps.
Best regards,
Dave