Larry started a fitness program about 8 weeks ago. He runs 2 miles every day and does some weight training. He likes to use weight machines and focuses on 1 or 2 muscle groups each day. He could initially do 6 repetitions of most exercises in his program, and he can now do 15-20. Larry likes the initial improvement in his energy level and appearance since starting the program. He has noticed that his work in construction seems a little easier, too. However, Larry doesn't think he is getting as much benefit out of his program now as he did at the start of his fitness program.
Larry isn't seeing as much improvement as he did initially because
a) he has reached his optimal level of fitness
b) his body isn't as responsive to the level of exercise as it was initially
c) his body is conserving energy
d) his diet isn't compatible with his fitness program