Temporality
Two prospective studies published in 2012 investigated the temporal relationship between changes in cardiorespiratory fitness and incident hypertension[15, 23]. In the ACLS study, improvements in cardiorespiratory fitness were associated with a lower risk of incident hypertension. When individuals were stratified according to how their fitness levels changed, those who maintained or improved fitness had a 26% and 28% lower risk of incident hypertension, respectively, compared with those who lost fitness[23]. Similarly, in a population of South Korean men, individuals whose cardiorespiratory fitness decreased over follow-up had an increased risk of incident hypertension compared to individuals whose cardiorespiratory fitness increased