Long-term implications of acutely increased cardiorespiratory fitness following short-term exercise interventions in older adults are unknown. In this study, we examined peak oxygen uptake (VO_2peak) four 'free-living' after a high intensity interval training (HIIT) intervention. Seventeen lifelong exercisers (LEX) and 17 previously sedentary (SED) males (55-74 years of age in 2012) were tested four years (phase D) after our previous experiment which included 6-weeks of aerobic moderate intensity exercise (phase B), followed by 6-weeks of HIIT (phase C). At all stages, a standard incremental exercise protocol on a cycle ergometer was completed to determine VO_2peak. SED (P = 1.000, Cohen's d = 0.01) and LEX (P = 1.000, Cohen's d = 0.11) VO_2peak at phase D was not different from phase A (enrolment). SED experienced a large decrease in VO_2peak from phase C to phase D (32 ± 6 ml·kg·min^-1 to 27 ± 6 ml·kg·min^-1 [P 2peak from phase C to phase D (42 ± 7 ml·kg·min^-1 to 39 ± 9 ml·kg·min^-1 [P 2peak than SED (P 2peak over the four years from 39 ± 7 ml·kg·min^-1 to 36 ± 9 ml·kg·min^-1 (N = 25, P 2peak from 30 ± 7 ml·kg·min^-1 to 25 ± 9 ml·kg·min^-1 (N = 9, P = 0.003, Cohen's d = 0.62). Four years after completing a brief period of aerobic exercise and HIIT, older males demonstrated a preservation of VO_2peak, irrespective of training status (LEX or SED). However, LEX exhibited greater VO_2peak than SED after 4-years of unsupervised 'free-living'. Finally, those who discontinued exercising experienced a greater reduction in VO_2peak. These findings infer that to maintain aerobic capacity, 6 weeks of HIIT every four year may be sufficient, but to attenuate the decline, exercise should be maintained.