Fitness apps on mobile devices are gaining popularity, as more people are engaging in self-tracking activities to record their status of fitness and exercise routines . These technologies also evolved from simply recording steps and offering exercise suggestions to an integrated lifestyle guide for physical wellbeing, thus exemplify a new era of``quantified self"in the context of health as individual responsibility . There is a considerable amount of literature in science, technology and society (STS) studies looking at this phenomenon from different perspectives, linking it with the sociology of self-surveillance and neoliberal regimes of health . However, the human-technology interface, through which the micro- (behavioral) and macro- (social) aspects converge, still calls for extensive examination . This paper approaches this topic from the postphenomenological perspective, in combination with empirical studies of design analysis and interviews of fitness apps, to reveal the human-technology link between the design elements and people's perception through the direct experiences and interpretations of technology . It argues that the intentionality of self-tracking fitness app designs mediates the human-technology relations by``guiding"people into a quantified knowledge regime . It shapes the perceptions of fitness and health with representations of meanings about a``good life"of individual success and management . This paper also gives a critique of current individual, performance-oriented fitness app designs and offers the possibility of seeking alternatives through the multistable nature of human-technology relations—how altering interpretation and meaning of the design with a cultural or social context could change the form of technological embodiment.