I think answer should be D. If we assume the amount one trains does not influence one's VO2 max, the argument falls apart. In the case of aerobic activity, if one runner had a heart rate of 146 and the other had 156, definitely their rate of activity is different. Now, since their heart rate is 168 beats per minute, we see an increase which will result in change of VO2 max.

Hi everyone,

For the conclusion to hold true,it must be proved that the intensive training sessions have an equal effect on both the athletes.
The argument can be attacked by saying that Runner B performance increases during the intense training exercises and that of A falls.To shield the argument from this avenue of attack,it is necessary to have this defender assumption

Hope I am clear.

Cheers

if A>B, then A+x>B+x

Because x the same

B

Simplify: VO2 measurement between A &B
engaged in conditions: mod activity and 145-154 beats/min
Results : Vo2(A) > Vo2(B)
some missing assumption
Conclusion : if identical training imparted, definitely Vo2(A) > Vo2(B)

Solution : Use negation method.
A) Runner A and Runner B did not have similar VO2 maxes upon entering the study --> This doesn't affects the conclusion in any way .

B) Regarding their VO2 maxes, runners respond differently to intensive training --> IF this was the case, then conclusion falls apart. It might be that due to difference in response, Vo2 B might be greater than Vo2 A. This is the answer.

C) Intensive training doesn't involves sessions in which athletes maintain a heartbeat over 168 beats per minute --> This tells about the the consistency of heartbeat, but in no way it affects the conclusion as to why Vo2(A) should be greater than Vo2(B).

D) The amount one trains influence one’s VO2 max. --> The argument says that “both will train with similar intensity” and will engage in “identical intensive training”.

E) During the experiment, Runner A always have the greater VO2 max than Runner B --> This mentions that there was no affect of identical training conditions, that there was by default some great powers in A. so this too doesn't affect the argument as to why Vo2(A) should be greater than Vo2(B).

Official Explanation:

Premise #1 – A > B (VO2 max) after moderate aerobic activity.

Conclusion: Runners will begin identical intensive training, A will continue to have greater V02 max.

Assumption: The effects of intensive training on the two runners are equivalent to the effects of moderate aerobic training.

(A) directly contradicts what is stated in the passage: Runner A had a greater VO2 max than B.

(B), if it is not true, represents a possible flaw in the conclusion. Say Runner A responds to intensive training differently than Runner B, then it is possible that Runner A will NOT have a greater VO2 max than runner B.

(C) just quantifies what is meant by intensive training. It doesn’t relate to the argument as a whole.

(D) is tempting but remember the argument says that “both will train with similar intensity” and will engage in “identical intensive training”.

(E) is somewhat of a weakener. That is, it points to the possibility that the VO2 max fluctuated throughout the experiment and Runner A just happened to have the higher VO2 max at the very end of training.

An assumption, however, doesn’t weaken the conclusion, but is the very foundation upon which the conclusion rests. That’s why we negate assumptions. In other words, if I pull the foundation out from under the house and that house still stands, then the original assumption was not one that supported the conclusion. However, if I negate the assumption and the conclusion then totally falls apart, we know the original assumption is one upon which the argument depends.

By negating (E), “Runner A always had the greater VO2 max…”, we actually strengthen the conclusion. Therefore, (E) is not the answer.
_________________

Thanks!
Do give some kudos.

Simple strategy:
“Once you’ve eliminated the impossible, whatever remains, however improbable, must be the truth.”

Best Gmat Resource:
GmatPrep CR|GmatPrep SC|GmatPrep RC

Want to improve your Score:
GMAT Ninja YouTube! Series 1| GMAT Ninja YouTube! Series 2

My Notes:
Reading comprehension | Critical Reasoning

The answer is definitely B - the assumption that with regards to VO2 maxes, runners respond similarly regardless of intensity. D is a close answer but that's in the future and the argument does not suppose that. However, B is just extending a known fact and that's a concrete assumption.