The following question contains a sentence with a blank. Choose the most appropriate word or phrase from the given options that can most suitably replace the blank in the sentence.

The athlete's rigorous training and unwavering determination _________________ to their remarkable success.

To determine the most appropriate word to fill in the blank, we need to analyze the context and meaning of the sentence: "The athlete's rigorous training and unwavering determination _________________ to their remarkable success."

Let us evaluate each of the given options:
1. contributed: To contribute (usually followed by "to") means to help to cause or bring about a result. "Rigorous training" and "determination" are positive attributes that logically lead to or help bring about "remarkable success." Therefore, "contributed to" fits perfectly.
2. detracted: To detract (usually followed by "from") means to diminish the value, importance, or quality of something. This contradicts the positive relationship between training/determination and success.
3. underestimated: To underestimate means to estimate something to be smaller or less important than it actually is. This does not fit grammatically or contextually with the preposition "to."
4. isolated: To isolate means to place apart or alone. This does not make sense in the context of achieving success through training and determination.

Thus, the most suitable word that logically and grammatically completes the sentence is contributed.