Marketer: While running is one of the most efficient forms of exercise

Option E

Weaken claim - new reduced gravity thread mill will lessen joint pain so folks can run and reduce weight

(A) Most avid runners greatly prefer running outdoors to running on a machine - not relevant

(B) Experts believe that swimming, not running, is the most effective form of exercise for those looking to lose weight. - not relevant

(C) A reduced-gravity treadmill can alter one’s natural running stride, leaning to muscle and tendon strain issues. - we are talking on this this treadmill will help loose weight not bring in a new issue.... also maybe the muscle strain will aid in weight loss.. we don't know

(D) While reduced gravity can lessen the severity of joint pain, those who experience pain from prior injuries will likely feel some joint pain while using a reduced-gravity
treadmill. - not a useful premise

(E) Much of the weight-loss benefit from running is derived from a runner having to carry his own body weight across a long distance. - Yup, proves why the old method is better and ols one might not help and weakness the process of the argument

I was confused between options C and E.
But then option E seemed clearer and more directive in terms of the focus more on "weight loss" but NOT "joint pain"

Option C introduces a new problem (muscle and tendon strain) but does not directly challenge the claim that the treadmill allows people to achieve the weight-loss benefit of running without joint pain. It suggests a different kind of risk but doesn't associate with the claim about "joint pain". So it's fruitless and unnecessary to bring a new topic to the argument.

Whereas option E suggests that the treadmill might reduce the effectiveness of the exercise because it diminishes the runner's workload, which is crucial for losing weight.

Thus OPTION E it is.­

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Veritas Prep Official Explanation

In any Strengthen or Weaken question, remember that the specificity of the conclusion is king. Here the details matter quite a bit in the conclusion, which is that those who suffer joint pain when running normally can, by using this treadmill, realize the full benefits of weight loss from running without the severe joint pain. Note that the strongest part of the conclusion is the "full weight loss benefits" - if those benefits are compromised at all by the treadmill, the conclusion is weakened.

Choice (E) does exactly that: if much of the weight-loss benefit of running comes from having to carry one's full body weight, then lessening that burden will lessen the weight-loss effect. (E) shows that this product will not likely achieve the lofty "full benefits of weight loss" standard set in the conclusion.

Among the other choices:

(A) misses the scope of who will be using the treadmill. Avid runners already run, so they are not the profile of people who are "unable to run due to joint pain." Their preference is then irrelevant to this study.

(B) also shifts the scope of the argument: even if swimming is better for weight loss, this argument is only about whether people can derive the same benefits from running on this treadmill that they would from running in general. Beware the always-popular "better plan" answer choice on many Weaken questions - just because a better plan exists (swimming) that does not mean that this particular plan (the treadmill) cannot accomplish its goal (achieving the same weight loss benefit as regular running).

(C) again misses the specific scope of the conclusion, which only addresses joint pain. Muscle and tendon strain introduces another type of potential injury, but the conclusion is specific that these people can achieve running benefit without joint pain in particular.

And (D) misses the specificity of "intense" joint pain in the conclusion. By saying that some people might experience some joint pain, (D) does not go far enough to show that people in general would experience intense joint pain.­