I read with great interest the recently published paper providing a comprehensive and critical review of the results of meta-analyses (MAs) of exercise on cognition in healthy individuals.  The findings suggest that the effect of physical exercise training on improving cognition is small, and this small effect becomes even more ineffective with some key moderators.  I appreciate the meticulous work that has been done in conducting this review and presenting the findings.

The findings of this study are unexpected, as the current literature reveals a strong link between exercise and cognition, which can be supported by the results of most meta-analyses included in the review (22 out of 24).  Moreover, previous studies have reported that exercise reduces the risk of dementia characterised by cognitive decline.  Accurate interpretability of results is therefore very important for clinical and public health implications.

Although it is reported that a small part of large heterogeneity is reduced by key moderators, a moderate heterogeneity of 57% with unknown source makes it difficult to reach conclusive results.  Different exercise types, wide age range, and different outcome measures could be the reasons for avoiding showing robustly that physical exercises do have a small positive effect on cognition.  Moreover, some methodological limitations of the study should not be overlooked.  The fact that the search strategy is not comprehensive enough, that specific exercise types are not used as keywords, and that some large databases such as CENTRAL, CINAHL and Embase are not included may make it questionable that all eligible MAs in the literature have been included.  Another important point is that the methodological qualities of both the included reviews and the primary RCTs included to the MA were not mentioned, and the results were not interpreted accordingly.

I appreciate that the authors consider the results from different perspectives and examine the influence of moderators.  However, more clearly reporting the intensity, type, and duration of the included workouts would have further clarified the reasons behind these unexpected results.  In conclusion, the paper provides a thought-provoking insight into the effectiveness of physical exercise on cognition.  It is important to note that the findings should be interpreted cautiously due to the methodological limitations of the study.