In order to gain a clearer understanding of factors which influence the physiological testing of senior and veteran cyclists this thesis:- assessed the validity and reproducibility of the Kingcyc1e ergometer; the reproducibility of laboratory based assessments of cycling performance; investigated cross sectional age-related declines in selected metabolic, cardio-respiratory and performance related variables; examined the effect of age and testing protocol on the determination of threshold exercise intensity; studied the effects of age on laboratory and field based cycling performance; and identified correlates to endurance cycling performance. One hundred and fourteen well trained competitive male endurance cyclists participated in these studies and selected groups of subjects performed laboratory based and field based tests. These consisted of:- Kingcycle peak power (PP) and peak aerobic capacity (PAC) tests; lactate minimum (Lac_min); ramped lactate threshold (LT_ramp); continuous lactate threshold (LT_inc); discontinuous lactate threshold (LT_dis), laboratory based 16.1-km time trial (LTT) and field based 16.1-km time trial (FTT). Power output recorded using Kingcycle was significantly higher than SRM (P < 0.001). Ratio limits of agreement between SRM and Kingcycle showed a bias of 0.90 (95%CI = 0.89-0.91) with a random error of x/+ 1.07. Mean coefficient of variation for peak power (W_peak) and average power recorded using SRM during PP and LTT trials were 1.3% (95%CI = 1.0-2.0%) and 2.8% (1.6-4.9%) respectively. Age was a modest predictor of peak physiological variables assessed during PAC. The decline in W_peak with age was between 25 and 30 W, (~ 6 to 9%) per decade. Regression analysis provided a prediction of the decline in peak heart rate (IIR_peak b.min⁻¹) [210-(0.66·age, yr), SEE 5%, P < 0.01]. Relative exercise intensity (%W_peak) maintained during LTT and at lactate threshold tended (P = 0.08 and 0.07, respectively) to be higher in the veterans and % W_peak at lactate threshold was affected by age (P < 0.05). Mean values for power, heart rate and oxygen uptake (V̇O₂) at designated blood lactate derived thresholds were affected by testing protocol (P < 0.05) with no interactive effect (P > 0.05) of age and testing protocol. Seniors and veterans maintained a similar (P > 0.05) relative exercise intensity (% W_peak, %IIR_peak and %V̇O₂_peak) and blood lactate concentration during LTT. Economy for LTT was higher (P < 0.05) in the seniors but was dependent on method of calculation.