[DainBramage]

Measures of distance covered during a six-minute walk improved markedly between tests at baseline and four months in both the supplement and placebo group.

Both groups improved over 4 months because they were walking everyday.

[ConservativeMind]

You are correct to note that, but I neglected to pull one key item into my note. It is directly from the linked study's abstract:

Urolithin A, compared with placebo, significantly improved muscle endurance (ie, increase in the number of muscle contractions until fatigue from baseline) in the FDI and TA at 2 months (urolithin A: FDI, 95.3 [115.5] and TA, 41.4 [65.5]; placebo: FDI, 11.6 [147.4] and TA, 5.7 [127.1]).

There actually was a very sizable change with endurance.