What does "120-pound weakling’s" mean ?

Here is the sentence: " I highly doubt an NFL linebacker’s body deals with protein intake in exactly the same way as a 120-pound weakling’

Here is the sentence: " I highly doubt an NFL linebacker’s body deals with protein intake in exactly the same way as a 120-pound weakling’s."

or:Here is the sentence: \" I highly doubt an NFL linebacker\u2019s body deals with protein intake in exactly the same way as a 120-pound weakling\u2019s.\"

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