Determinants Of Peak Oxygen Consumption In Older Adults: Function Or Fatigue?

Abstract

Maximal oxygen uptake (VO2max) is considered the gold standard of the functional limit of the cardiorespiratory system and may serve as a powerful indicator of an older adult's capacity to perform daily and recreational activities. Yet, it is challenging for many older adults to satisfactorily complete a maximal exercise effort, especially those age ≥75. PURPOSE: To examine the determinants of VO2peak and factors associated with ability to meet conventional benchmarks of maximal testing. METHODS: Thirty-four older adults mean age 78.2 ± 5.1 yrs and 59% female were enrolled in the Study of Energy and Aging (SEA) Pilot. V02 peak was measured on a treadmill using a modified Balke protocol. Ratings of Perceived Exertion (RPE) were measured at the end of each exercise stage. Physical function was assessed using the Short Physical Performance Battery (SPPB). Activity level was determined from the Physical Activity Scale for the Elderly (PASE) and perceived fatigue in the past 4 weeks (higher score = more energy) was measured using the Physical Energy Scale of the Motivation and Energy Index. RESULTS: Mean values of VO2peak and SPPB and PASE scores were 22.1 ± 5.6 ml/kg/min, 11.0 ± 1.3 and 136.2 ± 56.3, respectively. SPPB score, energy score and age independently explained 52% of the variance in VO2peak. Each 1.7 point increase in SPPB score and 0.55 point increase in energy score was associated with a 1 ml/kg/min greater VO2peak (p<0.02). Age was inversely associated with VO2peak (p<0.02). PASE score and sex were not significant predictors (p>0.07 for both). Only 5 (15%) met the standard respiratory exchange ratio (RER) cutpoint of ≥1.1 indicating maximal performance and only 41% (N=14) met the relaxed standard of RER ≥1.05. SPPB score was higher (p=0.05) for those with an RER ≥1.05, but no other predictor from the VO2peak model was related to having a "good test" using either cutpoint. There were no differences in RPE at VO2peak between those with an RER ≥1.05, 17.3 ± 1.7 and those with an RER <1.05, 17.4 ± 2.0, p>0.05. CONCLUSIONS: Mobility disability and perceived fatigue may be important limitations to performing maximal tests. When choosing a fitness test for older adults, researchers should consider other options, e.g. a submaximal test or 400m walk. Supported by the NIA with ARRA funds under grant number 1RCAG36594-01.