RESUMO
BACKGROUND: Although the metabolic equivalents (METs) system is a common procedure to quantify the intensity of physical activity in older adults, it remains unclear whether the conventional METs intensity thresholds (CTs) used for this purpose are appropriate in this population. Therefore, this study aimed (i) to derive overall and fitness-specific METs intensity thresholds in older adults ≥ 60 years old (OATs) expressed both in standard METs (VO2/3.5 mL O2·kg-1·min-1) and older adults METs60+ (VO2/2.7 mL O2·kg-1·min-1), and (ii) to compare them with the CTs. METHODS: A total of 93 subjects were assessed for cardiorespiratory fitness. Graded exercise test protocols using indirect calorimetry were performed to calculate individual VO2max and categorize subjects as "very poor/fair" or "good/superior" fitness. Overall and fitness-specific OATs expressed in standard METs (OATsstandard) and METs60+ (OATs60+) were derived based on the %VO2max and the ventilatory thresholds (VTs) physical intensity categories. RESULTS: Significantly higher VO2max, VO2 at VT1 and VO2 at VT2 (p < 0.001) were obtained in the "good/superior" subgroup compared to the "very poor/fair" fitness subgroup. Accordingly, OATs were approximately 69% higher in individuals with a "good/superior" fitness compared to those with a "very poor/fair" fitness. Furthermore, this study showed that OATsstandard were approximately 21-24% lower than OATs60+, and 10-22% higher OATs were observed when following the VTs intensity categories (heavy-intensity physical activity [HPA] and severe-intensity physical activity [SPA]) compared to the %VO2max categories (moderate-intensity physical activity [MPA] and vigorous-intensity physical activity [VPA]). When compared with the CTs, similar or higher OATsstandard and OATs60+ for MPA, and HPA were obtained compared to the conventional MPA threshold (3.0 METs). Conversely, for VPA and SPA, lower, similar, or higher OATs were obtained depending on the METs derivation approach (OATsstandard or OATs60+) or the intensity categories (VO2max or VTs), compared to the conventional VPA threshold (6.0 METs). CONCLUSIONS: None of the derived OATs were concurrently similar to the CTs, suggesting that fitness-specific METs intensity thresholds adapted to the METs derivation approach should be used in older adults. TRIAL REGISTRATION: FenotipAGING (Non-health-care intervention study), PRO-Training (NCT05619250).
RESUMO
BACKGROUND: It is important for sport scientists and health professionals to have estimative methods for energy demand during different physical activities. The metabolic equivalent of task (MET) provides a feasible approach for classifying activity intensity as a multiple of the resting metabolic rate (RMR). RMR is generally assumed to be 3.5 mL of oxygen per kilogram of body mass per minute (mL O2 kg-1 min-1), a value that has been criticized and considered to be overestimated in the older adult population. However, there has been no comprehensive effort to review available RMR estimations, equivalent to 1 MET, obtained in the older adult population. OBJECTIVE: The aim of this review was to examine the existing evidence reporting measured RMR values in the older adult population and to provide descriptive estimates of 1 MET. METHODS: A systematic review was conducted by searching PubMed, Web of Science, Scopus, CINAHL, SPORTDiscus, and Cochrane Library, from database inception to July 2021. To this end, original research studies assessing RMR in adults ≥ 60 years old using indirect calorimetry and reporting results in mL O2 kg-1 min-1 were sought. RESULTS: Twenty-three eligible studies were identified, including a total of 1091 participants (426 men). All but two studies reported RMR values lower than the conventional 3.5 mL O2 kg-1 min-1. The overall weighted average 1 MET value obtained from all included studies was 2.7 ± 0.6 mL O2 kg-1 min-1; however, when considering best practice studies, this value was 11% lower (2.4 ± 0.3 mL O2 kg-1 min-1). CONCLUSION: Based on the results of this systematic review, we would advise against the application of the standard value of 1 MET (3.5 mL O2 kg-1 min-1) in people ≥ 60 years of age and encourage the direct assessment of RMR using indirect calorimetry while adhering to evidence-based best practice recommendations. When this is not possible, assuming an overall value of 2.7 mL O2 kg-1 min-1 might be reasonable. Systematic review registration: International Prospective Register of Systematic Reviews on 30 September 2020, with registration number CRD42020206440.