Are the fittest Canadian adults the healthiest?

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Jonathon Fowles, Joel Roy, Janine Clarke and Shilpa Dogra

The link between fitness and disease and disability is well established.Note1-3 Accordingly, fitness assessments are used to estimate health risk in the general population. Although such assessments are typically less strenuous than those employed to ascertain performance-related fitness, the results allow for an individual’s fitness level to be placed in categories such as poor, fair, good, very good or excellent.Note4 It is gener ally assumed that people in the highest fitness categories are the healthiest.

Epidemiological studies that have found fitness to be associated with morbidity and mortalityNote5-7 typically divide fitness scores of the sample into quintiles or quartiles rather than using normative data for placement into categories. Such research is, therefore, unable to determine if people who have excellent or very good fitness are, in fact, healthier than people in lower categories.

The present analysis examines associations between the results of a standard fitness appraisal and selected health outcomes among Canadians aged 15 to 69 (see The data). The aim is to determine if people in higher fitness categories are, indeed, healthier than those in lower categories.

Cardiorespiratory fitness

Cardiorespiratory fitness is a strong and independent predictor of morbidity and mortality.Note5-7 In the present study, respondents whose cardiorespiratory fitness scores were in higher categories generally had better health outcomes.  All outcomes except lung function (FEV1/FVC) were significantly better among those whose cardiorespiratory fitness was “Excellent,” compared with those whose scores put them in the “Needs improvement” category; this was also true for most health outcomes among those whose cardiorespiratory fitness was “Very good” (Table 1). With further adjustment for waist circumference, systolic blood pressure was no longer significantly lower among respondents with “Excellent” cardiorespiratory fitness, compared with “Needs improvement” (Table 2). Few differences in health outcomes emerged between respondents in the ”Needs improvement” cardiorespiratory fitness category and those in the “Fair” or “Good” categories.

Grip strength

Grip strength is associated with functional autonomy among older adults.Note16 However, according to data from the CHMS, results for waist circumference, total cholesterol/high-density lipoprotein (TC/HDL) and lung function were not as favourable among respondents whose grip strength was “Excellent” versus “Needs improvement” (Table 1). For instance, respondents whose waist circumference was large enough to be associated with increased health risksNote17 had significantly greater (p < 0.005) grip strength (73 kg versus 70 kg) than did those with a smaller waist (data not shown).

These results may reflect the association between grip strength and body mass. Since Force = Mass*Acceleration, a higher body mass (as indicated by a larger waist) would mean greater grip strength. When waist circumference was taken into account, glycated hemoglobin (HbA1c) results were better, and the prevalence of positive self-rated health was higher, among respondents with “Excellent” grip strength, compared with those whose grip strength was categorized as “Needs improvement”; lung function, however, was still worse for those in the “Excellent” category (Table 2).

Results of grip strength assessments should be interpreted cautiously and in the context of waist circumference, which is negatively associated with some health outcomes.

Trunk flexibility

Trunk flexibility is associated with low back painNote18 and other musculoskeletal morbidities.Note19 When age group and sex were taken into account, results for waist circumference, HbA1c, TC/HDL, and positive self-rated health were significantly better among respondents who had “Excellent” sit-and-reach scores, compared with those whose scores were in the “Needs improvement” category (Table 1). However, when further controlling for waist circumference, no significant associations remained between trunk flexibility and any of the health outcomes (Table 2).

Thus, when waist circumference is taken into account, trunk flexibility does not seem to be associated with the health outcomes examined in this study.

Abdominal muscular endurance

Like trunk flexibility, abdominal muscular endurance is related to low back painNote20 and musculoskeletal morbidities.Note19CHMS data adjusted for age and sex suggest that respondents with “Excellent” abdominal muscular endurance had better outcomes for waist circumference, HbA1c, TC/HDL and self-rated health than did those whose muscular endurance was categorized as “Needs improvement” (Table 1). But when waist circumference was also considered, only HbA1c and the prevalence of positive self-rated health differed significantly between those whose abdominal muscular endurance was classified as “Excellent” versus  “Needs improvement.”

It should be noted that the distribution of the results of the partial curl-up assessment were bimodal—most respondents were either in the “Needs improvement” or “Excellent” categoriesNote21,Note22; this may be explained by the complexity of the test (technique and/or cadence). Because of the bimodal distribution and the lack of association with health outcomes, this testing protocol has been removed from the updated CSEP manual.Note4 Other protocols such as the front plank or side-support may be better-suited for assessing abdominal muscular endurance in the general population; however, further research is required.

Composite scores for back fitness and musculoskeletal fitness

Among respondents whose back fitness was “Excellent,” results for all health outcomes except diastolic blood pressure were better than among those whose back fitness was categorized as “Needs improvement” . Similarly, respondents with “Excellent” musculoskeletal fitness had better results for waist circumference, HbA1c and self-rated health than did those whose musculoskeletal fitness was categorized as “Needs improvement”; the relationship with HbA1c and self-rated health remained when adjusting for waist circumference.

Conclusion

The current analysis generally indicates an association between measured fitness levels, particularly, cardiorespiratory fitness, and various health outcomes. However, the association seems to hold only at the highest levels of fitness (“Excellent” or “Very good”), not at intermediate levels (“Good” and “Fair”), when compared with people in the “Needs improvement” category. The study suggests that fitness assessment results must be contextualized for specific health outcomes; higher fitness scores may be positively associated with some health outcomes, but negatively associated with others. These negative associations may be mediated by body composition.

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