mainline

The Case against Perfectionでサンデル教授は遺伝子操作による問題を色々な角度から検証し、比較をするので、内容は分かり易い。
Whatever the means, the push for supersized players is degrading to the game and to the dignity of those who transform their bodies to meet its demands. A retired NFL Hall of Fame lineman laments that the overgrown linemen of today, too big to run sweeps and screens, are capable only of high impact "belly-bumping": "That's all they're doing out there. They are not as athletic, not as quick. They don't use there feet." Enhancing performance by mainlining cheeseburgers does not cultivate athletic excellence but overrides it in favor of a bone-crushing spectacle.
上の個所は日本のお相撲さんの事を連想させますが、それはともかく "mainlining cheeseburgers" は「チーズバーガーばかりを食べる」と言う様な意味に見えますが、"mainline" の意味は何でしょう。辞書を見ます。
・Macmillan Dictionary: to do, eat, or take too much of something: We stayed up mainlining junk food and watching TV.
・Dictionary.com:
a. to use or enjoy something without restriction: to mainline on TV movies.
b. to use, enjoy, or imbibe (something) without restriction: mainlining coffee all day long
上の辞書には引用文とピッタリの意味と用例がありましたが、この意味を載せていない辞書も多くありました。多分比較的新しい用法なのでしょう。