Critical Reasoning

A recent longitudinal study of people who had successfully lost weight and implemented regular exercise routines in their twenties found that, by the age of forty, most of them had gained back the weight, stopped exercising regularly, or both. This finding alone is unremarkable, but the researchers were surprised to discover that, among the study's subjects who had hired personal trainers to help them lose weight and exercise in their twenties, an even higher percentage had regained the weight or stopped exercising than among subjects who had not hired such trainers. The researchers thus concluded not only that remaining on an effective weight management and exercise program is difficult, but also that personal trainers are largely ineffective in helping people do so.


Which of the following, if true, most weakens the argument in the passage below?

A. Most people who hire personal trainers do so, at least in part, because they lack sufficient motivation to remain on a diet or exercise regimen by themselves.

B. Some people hire personal trainers for sport-specific training or rehabilitate injuries, rather than to lose weight or implement a regular exercise program

C. The average person's metabolism slows significantly between the ages of thirty and forty, making it more difficult for people aged forty or older to avoid weight gain.

D. Many of the personal trainers hired by the people in the study were also dietitians who helped their clients design meal plans.

E. Subjects in the study who hired personal trainers had, on average, more free time to exercise than did those who had not hired such trainers.

Answer is A

I thought it was B.

Can someone please explain this?

Thanks!

This is a weaken question. First let's break the argument down into conclusion and evidence.

The conclusion is "The researchers thus concluded not only that remaining on an effective weight management and exercise program is difficult, but also that personal trainers are largely ineffective in helping people do so."

Focus in on the last portion - "personal trainers are largely ineffective in helping people do so [manage weight and exercise].

The evidence for this is that "among the study's subjects who had hired personal trainers to help them lose weight and exercise in their twenties, an even higher percentage had regained the weight or stopped exercising than among subjects who had not hired such trainers."

I think the gap for this one kind of jumps out. The people are gaining weight in their thirties after they had lost it in their twenties. It was in their twenties that some people used personal trainers to lose weight and exercise. How could those trainers be blamed for weight gained years later?

No where in the argument does it say that these people were still using personal trainers in their thirties. In fact, it seems to imply that they were not using personal trainers in their thirties. So the problem is not that personal trainers are ineffective, but that the people stopped using them!

This is what choice A says. People hire personal trainers because they lack the motivation. So the personal trainer was very helpful when the people used the trainer but years later - when they did not have the trainer - they gained the weight back and stopped exercising.

Choice B is not actually relevant to this conclusion. The conclusion is specifically about trainers successfully helping people manage weight and exercise. If the trainer is hired for another reason than it has nothing to do with weight management and exercise and does not apply. If you hire a tutor to help you with the GMAT and your MCAT score does not improve then you cannot say your tutor is ineffective!

What about option C. It says that in the forties, the metabolism doesn't allow to loose weight easily and thus provides us with a third reason. Also there is two parts of the conclusion and both should be answered, so not only the PTs are being questioned but also the general effectiveness of the program.
Option C gives the explanation to both the parts.