After lifting weights for two weeks, joe finds that the weights he has been lifting do not feel very heavy to him anymore. this is an example of
a. exercise specificity principle
b. law of reversibility
c. overload principle
d. muscle adaptation principle

After lifting weights for two weeks, Joe finds that the weights he has been lifting do not feel very heavy to him anymore. This is an example of Muscle adaptation principle - D.

D. Muscle adaptation principle

Explanation:

After lifting weights for two weeks, Joe finds that the weights he has been lifting do not feel very heavy to him anymore. This is an example of Muscle adaptation principle. He has been working out, and thus he needs to get heavier weights.