The maximal oxygen uptake (V̇O₂peak) test is an approved pre-operative examination tool, in a clinical setting: Both V̇O₂peak and anaerobic threshold indicate a patient’s physiological tolerance for major surgery and post-operative mortality, with cycle ergometry being routinely used for V̇O₂peak tests in clinical settings, in many European countries. Nevertheless, the opportunities to assess populations with restricted mobility of the lower limbs are limited, as alternative methods (such as an arm-crank test protocol) to assess V̇O₂peak are yet to be established. Twelve sedentary middle-aged adults (55.1 ± 5.0 years) performed two incremental protocols on an arm crank and cycle ergometer on separate occasions. During exercise, gas exchange was collected and analysed by an online breath-by-breath analysis system. Regression analysis showed that the model with dependent variable cycle ergometer V̇O₂peak (CEV̇O₂peak) in ml·kg^-1·min^-1 and independent variables arm crank V̇O₂peak (ACEV̇O_2peak) in ml·kg^-1·min^-1, lean body mass lower limbs (LBMLL) and total lean body mass (TLBM) fitted the population the best, with r² = 0.87, adj. r² = 0.82 and SEE = 3.14. The equation estimated with this model is: CE V̇O_2peak = 11.776 + 1.418 X ACE V̇O_2peak(ml·kg^-1·min^-) – 1.454 x TLBM + 3.967 X LLLBM. Our study suggests that arm cranking could be an alternative mode of exercise for sedentary middle-aged adults (and potentially in clinical settings) to assess the cardiorespiratory fitness of people with restricted lower-limb mobility.