The notoriously difficult viral fitness challenge may leave you feeling underwhelmed at the end of your 75 hard days, according to one exercise expert. The 75 Hard Challenge is the fitness trend that has united Hyrox heads, couch to 5K alumni, New Year’s resolution makers and first-time gym goers alike. The 11-week challenge is a grueling test of resilience, discipline and mental and physical health that has swept TikTok in 2024, with thousands of new recruits jumping head-first into the fitness experiment every week. However, some experts in the field are unconvinced about the effectiveness o…