Kunkel SD et al. mRNA expression signatures of human skeletal muscle atrophy identify a natural compound that increases muscle mass.
Cell Metab. 2011 Jun 8;13(6):627-38.
"An apple a day keeps the doctor away," the saying goes, but can it also keep away muscle loss?
In this study, researchers discovered that a natural compound from apples possessed the opposite signature to that which is associated with muscle-atrophy-inducing mRNA. Put simply, this means that apples may contain a compound that helps protect your muscles from breaking down during periods of disuse or damage.
The compound is called ursolic acid and is present in the wax-like coating of apples, pears, cranberries, prunes and other fruits; it's also found in high concentration in seaweed, Greek sage (Salvia triloba), oleander (Nerium oleander), rosemary (Rosmarinus officinalis) and periwinkle (Vinca minor).
When up to 0.27% of a mouse's daily energy intake was provided in the form of ursolic acid for five weeks, the researchers observed increases in IGF-1 signaling, muscle mass, and strength.
Researchers also noted decreases in fat mass, fasting blood glucose, plasma cholesterol and triglycerides, not to mention a decrease in atrophy-associated (muscle-wasting) skeletal muscle mRNA expression.
If ursolic acid does indeed prevent atrophy and promote muscle hypertrophy (growth), it's possible that Adam and Eve were just trying to put on more mass!

The Bottom Line:
Fuji and Smith variety apples were found to contain approximately 50 mg of ursolic acid per medium-sized apple.
Based upon the mouse data, a human would need to consume about 7.5 mg of ursolic acid per pound of bodyweight every day. For a 180-pound male, this equates to 27 Fuji apples daily. Not exactly practical.

Practical Application:
Eat a Fuji or Smith apple with your pre-workout snack to try and harness some of ursolic acid's many benefits! Even if the benefit is minor, the apple still provides training fuel. (Note that Smith and Granny Smith apples are not the same. Look specifically for Smith.)