Often on rounds with medical students or housestaff we will review why a serum creatinine of 0.8 mg/dl in a 40 year old athlete…
may mean a much higher creatinine clearance than a creatinine of 0.8 mg/dl in a sedentary 74 year old grandfather…
due to the much lower muscle mass and subsequent lower creatinine production in the older individual.
The beautiful cross sectional MRI images above are a stunning visual reminder of muscle mass differences that we only guess at from external appearances.
The good news is that aging alone does not relegate one to inevitable muscle mass decline and frailty. The images are taken from an interesting study in The Physician and Sportmedicine examining muscle mass and function in men and women in each of four age categories: 40s, 50s, 60s and older than 70. The subjects were all considered masters level athletes engaging in training exercise 4-5 times per week.
In these individuals muscle mass and function did not decline with age though they did gain body fat. Compare the muscle area and appearance of the 74 year old sedentary male above to the 70 year old male athlete below…
The lesson: Stay active, keep your kidneys healthy and keep that creatinine of 0.8 mg/dl reflecting the same creatinine clearance at 70 years old as it did at 40!
It's known that "old" (experienced) athletes are good for competitions with extreme aerobic practice.
For instance, an italian athlete 67 or 68 year old won three years in a row the french alpine Mont Blanc ultratrail : 200 km running, 2 days, 8000-9000 m of positive change in altitude.
I read the interview of a sport physiologist who commented it, with the notion of a increased resistance with age of the striated muscles (if regular training), to the traumatisms, especially the concentric contraction during the down run.
That same notion applies to a patient with limb amputation where "normalization" of serum creatinine has everything to do with muscle mass loss and not kidney function.
Great post, I'll be using these pictures in the future