Purpose: A self-paced maximal exercise protocol has demonstrated higher V˙ O 2 max values when compared against traditional tests. The aim was to compare physiological responses to this self-paced V˙ O 2 max protocol (SPV) in comparison to a traditional ramp V˙ O 2 max (RAMP) protocol in young (18–30 years) and old (50–75 years) participants. Methods: Forty-four participants (22 young; 22 old) completed both protocols in a randomised, counter-balanced, crossover design. The SPV included 5 × 2 min stages, participants were able to self-regulate their power output (PO) by using incremental ‘clamps' in ratings of perceived exertion. The RAMP consisted of either 15 or 20 W min−1. Results: Expired gases, cardiac output (Q), stroke volume (SV), muscular deoxyhaemoglobin (deoxyHb) and electromyography (EMG) at the vastus lateralis were recorded throughout. Results demonstrated significantly higher V˙ O 2 max in the SPV (49.68 ± 10.26 ml kg−1 min−1) vs. the RAMP (47.70 ± 9.98 ml kg−1 min−1) in the young, but not in the old group (>0.05). Q and SV were significantly higher in the SPV vs. the RAMP in the young (<0.05) but not in the old group (>0.05). No differences seen in deoxyHb and EMG for either age groups (>0.05). Peak PO was significantly higher in the SPV vs. the RAMP in both age groups (<0.05). Conclusion: Findings demonstrate that the SPV produces higher V˙ O 2 max, peak Q and SV values in the young group. However, older participants achieved similar V˙ O 2 max values in both protocols, mostly likely due to age-related differences in cardiovascular responses to incremental exercise, despite them achieving a higher physiological workload in the SPV.