And do not state the size of the effect.
Well, they do quote the size of the effect in the abstract. And the results clearly have no statistical "power".
This is part of the abstract. HR = hazard ratio. i.e. the relative ratio of dying for the joggers compared to the non-joggers.
And CI is a confidence interval. e.g. For the light joggers they can say with 95% statistical certainty that the risk of dying was
between 10% and 47% of the non-joggers.
The lowest HR for mortality was found in light joggers (HR: 0.22; 95% CI: 0.10 to 0.47), followed by moderate joggers (HR: 0.66; 95% CI: 0.32 to 1.38) and strenuous joggers (HR: 1.97; 95% CI: 0.48 to 8.14).
But see that for the strenuous joggers the range can be anywhere between 50% of the non-joggers death rate to 8x the death rate.
So, really nothing at all can be said about anything apart from either the light joggers, or considering all joggers together.
For those groups there is a benefit at the 95% confidence level.
(And, as a physicist, I don't really consider any result to be worth much at such a low level.)