The purpose of the study was to compare the blood lactate accumulation and other metabolic responses by trained swimmers with varying degrees of controlled frequency breathing (CFB). Fourteen (eight males, six females) trained collegiate swimmers performed peak and submaximal tethered swim tests during which breathing was restricted to one breath every two (BR2), four (BR4), six (BR6) (N = 13), and eight (BR8) (N = 9) strokes. All submaximal swim tests were of 4-min duration, with tethered swim resistance at a constant 80% of peak resistance. Measures included oxygen uptake (VO2), carbon dioxide production (VCO2), tidal volume (TV), ventilation (VE), estimated alveolar partial pressure of O2 (PAO2) and CO2 (PACO2), respiratory exchange ratio (RER), stroke rate (SR), heart rate (HR), and change in blood lactates (delta LA). Significant differences were associated with increases in CFB for all variables except HR and delta LA. Although CFB was associated with reduced VE, compensatory adaptations resulted in increases in TV, PACO2, and SR and decreases in PAO2 and RER. VCO2 was greater for BR2 than all others, and VO2 for BR2 was greater than BR8. The results indicate that CFB does not affect blood lactate accumulation but does enhance oxygen extraction. CFB may impede proper stroke mechanics.