Peiffer, JJ, Abbiss, CR, Chapman, D, Laursen, PB, and Parker, DL. Physiological characteristics of masters-level cyclists. J Strength Cond Res 22(5): 1434-1440, 2008-Although a considerable amount of research is available describing the physiological characteristics of competitive young-adult cyclists, research describing these same characteristics in Masters-level cyclists is rare. Therefore, the purpose of this study was to describe and compare the effect of aging on physiological fitness parameters of Masters-level cyclists in an attempt to provide normative fitness data. Thirty-two male cyclists (35-73 years) completed one 15-minute economy test and one graded exercise test (GXT) on a cycle ergometer. During the GXT, maximal oxygen uptake (JOURNAL/jscr/04.02/00124278-200809000-00030/ENTITY_OV0312/v/2017-07-20T235344Z/r/image-pngo2max), maximal heart rate (HRmax), the first (VT1) and second (VT2) ventilatory thresholds, and peak power output (PPO) were recorded. For the purpose of analysis, subjects were allocated into three age groups (35-45 years, 45-54 years, ≥55 years). Maximal oxygen uptake and absolute PPO were significantly lower among subjects 55 years and older (45.9 ± 4.6 mL·kg−1·min−1 and 324 ± 51 W, respectively) compared with the 45- to 54-year group (54.2 ± 6.6 mL·kg−1·min−1 and 392 ± 36 W, respectively), and both were significantly less compared with the 35- to 44-year group (60.7 ± 5.1 mL·kg−1·min−1 and 434 ± 32 W, respectively). Maximal heart rate was significantly greater in both the 35- to 44-year and 45- to 54-year age groups compared with the ≥55-year group. The first ventilatory threshold was significantly greater in the subjects who were 55 years and older group compared with the 35- to 44-year and 45- to 54-year age groups, and VT2 was significantly greater in subjects 55 years and older compared with the 35- to 44-year group. Economy was not different amongst groups. In conclusion, increases in age resulted in a significant reduction in fitness parameters across age groups. The comparison of the fitness characteristics of Masters-level cyclists with established young-adult cyclist data should be avoided, because this may lead to inaccurate assessments of fitness.