The Reality of Muscle Atrophy
San Francisco 49ers defensive end Nick Bosa recently drew attention during training camp when observers noted a visible discrepancy in the size of his thighs. Addressing the topic on Tuesday, September 8, the 28-year-old athlete confirmed that the change is a direct result of his recovery process.
Following an ACL surgery in October 2025, Bosa experienced significant muscle atrophy in his right leg. «Atrophy is real,» Bosa explained. «I don’t remember the specific measurements, but the difference was drastic following the procedure. It’s going to take a couple of years to regain those last few centimeters.»
Performance Over Aesthetics
Despite the visible imbalance, Bosa remains unbothered by his appearance. He emphasizes that his primary objective is functional readiness rather than physique goals. «It’s not really a focus for me,» he stated. «I’m not going to change my training just to gain size. I don’t train like a bodybuilder—I train like an athlete. I won't incorporate exercises that aren't conducive to athletic performance just to increase leg circumference.»
He reassured fans and staff that his physical function is not compromised, noting, «My leg is performing just as well as the other one. That’s all that really matters to me.»
Returning to the Field
General Manager John Lynch has expressed no concerns regarding Bosa’s readiness for the upcoming Week 1 kickoff, despite the defensive star missing nearly a year of game action. Bosa is no stranger to this recovery path, having successfully returned to the field for the start of the 2021 season after a 2020 ACL tear.
Reflecting on his past rehabilitation, Bosa noted that he is taking a slightly more relaxed approach this time. «I don’t know if I’ll be that strict again,» he admitted, referring to his previous intense diet. «It was a bit over-the-top, especially regarding cutting out carbohydrates.»
Feeling Faster
Although his leg size is different, Bosa feels that his overall speed has returned to form. He compared his current state to his previous recovery year, remarking, «I definitely feel some similarities to that year—I'm a bit leaner in the lower body. I’m moving very well, and we’ll see how that translates when I get back on the field.»