The Effects of Age, Organized Physical Activity and Sedentarism on Fitness in Older Adults: An 8-Year Longitudinal Study

Round 1

Reviewer 1 Report

The study was aimed at wide describing the changes in physical fitness during a 8 year follow

up in a large sample of Spanish adults aged 65 or over that are engaged in organized physical activity. The topic is of high importance since the European society is getting older and older and there are hardly any such broaden-organized and longitudal studies regarding this aspect of society aging. The Authors proved that organized physical activity and sitting time are critical to physical fitness in the elderly.

However, I have a few concerns I’d like to express.

1. My main concern is about the division of the participants in to NON-SEDENTARY and SEDENTARY groups (lines 109-113). According to the Authors’ description, e.g. “all participants who had never been sedentary or had showed a positive change (passing from sedentary at baseline to non-sedentary in the follow up)” were included into NON-SEDENTARY group. However, in what period of time the positive change was taking into account. We can imagine a person who was sedentary at the baseline and (for a number of reasons) showed positive change but a week (or less) before the follow up study. To avoid such concerns, the Authors should precise the methodology of their study – what time-frame was taken into account. The same is regarding the second question (lines 114-130).
2. The sentence “Variables showed a normal distribution when checked with histograms” (line 146) is not clear enough. Did the Authors check normality of the data only looking at the histograms or perform any statistical test? Please, clarify. What about the homogeneity of variances that is needed for t-tests?
3. Table 1 title should be completed: “Descriptive characteristics” of who/what?
4. Figure 5 needs to be corrected. The chart showing Balance results (top left corner of the figure) contains unnecessary fragment “…documento” (lower left corner of the chart).

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

This is a very interesting study.  It provides longitudinal data not often available, Such data is critical for us to understand the real long term impact of interventions such as the one described in the article.

I have two concerns that should be addressed before publication.

First, as the final sample is a sub-set of the original sample there is no indication as to whether the two samples (time one and time two) are systematically different in any way (age, sex, etc.)  Knowing if such differences exist is important to evaluate the results.

Second, there is only a small reference regarding whether any of the participants continued to exercise/be physically active on their own.  That is an important issue as for some people the socialization that comes with such activity could be a more important reason for continuing than the health effects of the exercise itself.  This distinction should be addressed throughout the article.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

General comments

This is a very interesting and worthwhile study. There are very few longitudinal studies in which physical activity and sedentary behaviour are evaluated. The analyses were generally performed well, with plausible explanations offered for the findings observed. The differences between sexes with age in terms of strength and balance are interesting and worthy of further study.

Specific comments

Introduction

• The introduction is clear with no changes required.

Methods

• There is very low retention at follow-up, with participant numbers falling from 2987 to 642. This should be reported as a percentage here and discussed later as a limitation.
• Why were sedentary to non-sedentary considered to be the same as people who were non-sedentary all the time? It would be interesting to compare these groups rather than combining them.
• The fact that all 642 participants at baseline were in organised physical activity needs to be explained. If being in OPA was a condition of selection in the original study, this needs to be clarified in the methods section.
• The use of another term rather than HEALTHY and UNHEALTHY should be considered for the four groups as there are other factors than physical activity involved in health.
• A test of normality should be sued, rather than visually inspecting histograms.
• Provide a reference for the choice of interpreting effect size magnitudes.

Results

• The screenshot used in Figure 5 has the word “documento” visible on the balance graph.

Discussion

• Although the different types of PA are noted as a limitation, if this information is available it should be included in the analysis.
• The poor retention rate of 21% over the eight years should be added as a limitation and discussed as this could have a major impact of the findings. Perhaps only those people who were still active were more likely to respond to the follow-up request?

Author Response

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Author Response File: Author Response.pdf