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Walter, AA, Smith, AE, Kendall, KL, Stout, JR, and Cramer, JT. Six weeks of high-intensity interval training with and without β-alanine supplementation for improving cardiovascular fitness in women. J Strength Cond Res 24(5): 1199-1207, 2010-The purpose of the present study was to evaluate the effects of cycle ergometry high-intensity interval training (HIIT) with and without β-alanine supplementation on maximal oxygen consumption rate (o2peak), cycle ergometer workload at the ventilatory threshold (VTW), and body composition. Forty-four women (mean ± SD age = 21.8 ± 3.7 years; height = 166.5 ± 6.6 cm; body mass (BM) = 65.9 ± 10.8 kg; o2peak = 31.5 ± 6.2 ml·kg−1·min−1) were randomly assigned to 1 of 3 groups: β-alanine (BA, n = 14) 1.5 g + 15 g dextrose powder; placebo (PL, n = 19) 16.5 g dextrose powder; or control (CON, n = 11). Testing was conducted at baseline (week 0), after 3 weeks (week 4), and after 6 weeks (week 8). o2peak (ml·kg−1·min−1) and VTW were measured with a metabolic cart during graded exercise tests on a corival cycle ergometer, and body composition (percent fat = % fat and fat-free mass = FFM) were determined by air displacement plethysmography. High-intensity interval training was performed on a corival cycle ergometer 3 times per week with 5 2-minute work intervals and 1-minute passive recovery with undulating intensities (90-110% of the workload recorded at o2peak) during each training session. o2peak increased (p ≤ 0.05) in the BA and PL groups at weeks 4 and 8, but did not change (p > 0.05) for the CON group. VTW increased (p ≤ 0.05) for all groups at weeks 4 and 8. Body mass increased (p ≤ 0.05) only for the BA group at weeks 4 and 8, whereas %fat decreased (p ≤ 0.05) and FFM increased (p ≤ 0.05) at weeks 4 and 8 for all groups (BA, PL, and CON). Although it is unclear why β-alanine supplementation increased BM, there was no additive effects for increasing o2peak beyond the PL. Overall, these results suggested that HIIT may be an effective and time-efficient method of training to improve maximal oxygen uptake.