This is CNBC's Morning Squawk newsletter. Subscribe here to receive future editions in your inbox. Happy Tuesday. I did my workout studio's Hyrox-themed class yesterday, which not only left me sore but also with a better understanding of what all the hype in the fitness business is about. S&P 500 futures ticked higher this morning. The stock market is coming off a winning day. Here are five key things investors need to know to start the trading day: Billionaire entrepreneur Elon Musk is