This thesis aimed to establish why the incidence of a V02-plateau is typically high (>80%) for a discontinuous test but not for a continuous test, how treadmill grade influences V02peak and the incidence of a V02-plateau for a speed incremented test, and whether it is possible to develop a continuous protocol for which the incidence of a plateau in the V02-running speed relationship is >80%. Study 1 was a large study that addressed several issues. Each subject (n = 10) completed a discontinuous test (DCT) in which running speed was increased every 3 min, a continuous test in which the speed was increased every 3 min (CT), a ramp test in which the speed was increased every 5 s (5%RT60), and a run to exhaustion at a.speed calculated to elicit 105% V02 peak (105%T). For each test, the treadmill grade was set at 5%, and the sampling period was set at 60 s. Each subject also completed 2 further tests: a ramp test (5% grade) for which the sampling period was 30 s (5%RT30); and a ramp test (60 s samples) for which the treadmill grade was set at 0% (O%RT). The peak V02 (mean ± SD) was higher for the 5%RT60 than for the DCT (59.9 ± 7.9 vs. 57.8 ± 8.1 ml.1 kg·.1 min; p < 0.05), but the incidence of a V02-plateau was higher for the DCT (80% vs. 50%). The incidence of a plateau was also higher for the 5%RT60 than for the O%RT (50% vs. 30%), as was the peak V02 (59.9 ± 7.9 vs. 57.8 ± 7.9 rnl.kg·1.min·1; p = 0.003). The peak V02 was lower for the 105% T than for the 5%RT60, and the difference between the two values was negatively correlated with the duration of the 105%T (r = -0.89, p = 0.001). The incidence of a plateau was lower for the 5%RT30 than for the 5%RT60 (20% vs. 50%); the reason for this appeared to be that the variability in V02 was higher for the 30 s samples. It was concluded that discontinuous tests should not be used for the assessment of V02m", and that factors which influence the variability in V02 might be important determinants of the incidence of a plateau. Study 2 evaluated the effect of sampling period and exercise intensity on the variability in V02. Eight subjects completed 4 runs at -70% V02P" during which 12 samples of expirate were taken over periods 000, 60, 90, or 120 s. In addition, V02 was determined over twelve 30 s periods during runs at -70 and -96% V02Peak (n = 6). The SD for V02 decreased as sampling period increased from 30 to 60 s (1.3 ± 0.7 vs. 0.6 ± 0.2 ml.kg·1.min·1; p < 0.05), but no further decrease was observed as the sampling period increased beyond 60 s. This SD also decreased as exercise intensity increased (1.1 ± 0.2 vs. 0.6 ± 0.3 ml.kg·1.min·1; p = 0.005), such that the SD for 30 s samples taken during the run at -96% was the same as that for the 60 s samples taken at -70% V02Peak (P = 0.96). It was concluded that the only valid approach to defining a V02-plateau is one in which the sampling period decreases as exercise intensity increases. Study 3 evaluated three ramp tests for the assessment of V02max in runners. Each subject (n = 12) completed 3 tests: a constant speed, increasing grade test (lOT); a constant grade, increasing speed test on a level treadmill (0% T); and a constant grade, increasing speed test conducted at a 5% grade (5% T). For each test, the sampling period decreased as the exercise intensity increased and the individual V02 data were fit to both a linear model and a (two-piece) plateau model. For each test, the SEE was lower for the plateau model than for the linear model (p < 0.0005) and a V02-piateau was observed in >90% of subjects. However, V02max, was higher for the 5%T (64.0 ± 4.7 ml.kg·1.min·1) than for the O%T (62.6 ± 4.6 rnl.kg·1.min·1), and higher still for the lOT (65.1 ± 4.3 ml.kg·1min·1) (p < 0.05). It was concluded that whilst an upper limit for V02 is typically reached when trained runners perform a treadmill ramp test, the V02 at which this limit is reached depends on the conditions under which the test is performed.