An Evolving Approach to Assessing Cardiorespiratory Fitness, Muscle Function and Bone and Joint Health in the COVID-19 Era

Cardiorespiratory fitness (CRF) is now an established vital sign. CRF, along with muscle function and bone and joint health is related to functional independence and a higher quality of life. Wasserman and colleagues proposed a gear model illustrating the integrated role of the respiratory, cardiovascular, and skeletal muscle systems during aerobic exercise; in 2015, a revision to the original model was proposed. Our understanding of the effects and challenges associated with the coronavirus disease 2019 (COVID-19) are rapidly evolving. Initial evidence indicates higher levels of CRF, and muscle function protect individuals infected with COVID-19 from a complicated medical course. Moreover, for those individuals infected with COVID-19, there are initial signs of a reduction in CRF following the initial phase of recovery. We are also gaining an understanding of long COVID syndrome, where individuals who have recovered from the acute phase of viral infection present with lasting symptoms, which include but are not limited to reduced CRF, shortness of breath, and fatigue. Clearly, these individuals will require rehabilitation to restore and/or improve CRF, muscle function, bone and joint health, functional capacity (ie, the ability to perform activities of daily living), and quality of life. The importance of assessing the synergistic function of systems essential to performing activities that require physical exertion is a health care imperative. This graphical narrative provides an update to the gear model initially proposed by Wasserman and updated to a gear and circuit in 2015. External CRF, muscle function, and bone and joint health influencers and an approach to clinical assessment are also introduced.