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The purpose of the present study was to examine the influence of 3 different high-intensity interval training regimens on the first and second ventilatory thresholds (V[T.sub.1] and V[T.sub.2]), anaerobic capacity (ANC), and plasma volume (PV) in well-trained endurance cyclists. Before and after 2 and 4 weeks of training, 38 well-trained cyclists ([Vo.sub.2]peak = 64.5 [+ or -] 5.2 ml*[kg.sup.-1*[min.sup.-1]) performed (a) a progressive cycle test to measure [Vo.sub.2]peak, peak power output (PPO), V[T.sub.1], and V[T.sub.2]; (b) a time to exhaustion test ([T.sub.max]) at their [Vo.sub.2]peak power output ([P.sub.max]); and (c) a 40-km time-trial (T[T.sub.40]). Subjects were assigned to 1 of 4 training groups (group 1: n = 8, 8 x 60% [T.sub.max] at [P.sub..max] 1:2 work-recovery ratio; group 2: n - 9, 8 x 60% [T.sub.max] at [P.sub.max], recovery at 65% maximum heart rate; group 3: n = 10, 12 x 30 seconds at 175% PPO, 4.5-minute recovery; control group: n = 11). The T[T.sub.40] performance, [Vo.sub.2]peak, V[T.sub.1], V[T.sub.2], and ANC were all significantly increased in groups 1, 2, and 3 (p < 0.05) but not in the control group. However, PV did not change in response to the 4-week training program. Changes in T[T.sub.40] performance were modestly related to the changes in [Vo.sub.2]peak, V[T.sub.1], V[T.sub.2], and ANC (r = 0.41, 0.34, 0.42, and 0.40, respectively; all p < 0.05). In conclusion, the improvements in T[T.sub.40] performance were related to significant increases in [Vo.sub.2]peak, V[T.sub.1], V[T.sub.2], and ANC but were not accompanied by significant changes in PV. Thus, peripheral adaptations rather than central adaptations are likely responsible for the improved performances witnessed in well-trained endurance athletes following various forms of high-intensity interval training programs. Key Words. ventilatory threshold, anaerobic capacity, plasma volume, endurance performance, short-term training

The purpose of this study was to examine the accuracy of the American College of Sports Medicine (ACSM) walking equation at low walking speeds, altitude (1,550 m), and higher grades. Twenty men and women (mean [+ or -] SD, age, 28 [+ or -] 6 years; height, 171 [+ or -] 13 cm; weight, 67.8 [+ or -] 18.1 kg) completed 2 randomized testing sessions under altitude (AL) ([P.sub.1][O.sub.2] = 123.1 mm Hg [20.93%]) and sea level control (SLC) ([P.sub.1][O.sub.2] 147.3 mm Hg [25.00%]) conditions. Steady-state oxygen uptake ([Vo.sub.2]) was measured while subjects walked at 50 m*[min.sup.-1] at 8 separate grades (0, 5, 10, 15, 18, 21, 24, and 27%). Steady-state [Vo.sub.2] measurements from the last 2 minutes of each grade in AL and SLC were compared to the predicted [Vo.sub.2]. of each grade according to the ACSM walking equation. Mean [Vo.sub.2] differences between predicted and AL values ranged from -0.5 to 1.4 ml*[kg.sup.-1]*[min.sup.-1], averaged 0.1 ml*[kg.sup.-1]*[min.sup.-1] across all grades, and were significant (p < 0.051 at 0 percent grade. Mean [Vo.sub.2] differences between predicted and SLC values ranged from 0.6 to 3.0 ml*[kg.sup.-1]*[min.sup.-1], averaged 1.4 ml*[kg.sup.-1]*[min.sup.-1] across all grades, and were statistically significant (p < 0.05) at 0 and 5 percent. The standard error of the estimate (SEE) for the prediction of [Vo.sub.2] under AL and SLC were 2.2 and 2.0 ml*[kg.sup.-1]*[min.sup.-1], respectively. Total errors for the prediction of [Vo.sub.2]max under AL and SLC were 2.3 and 2.6 ml*[kg.sup.-1]*[min.sup.-1], respectively. Overall, the findings indicate that the current ACSM prediction equation for walking is appropriate for application at low speeds, moderate altitude, and higher grades. Key Words. oxygen consumption, prediction of [Vo.sub.2], sea level