Purpose <p>This study compared selected physiological and autonomic responses induced by swimming training sets.</p> Methods <p>Thirty male swimmers (19 ± 3 years) performed maximal efforts of 50- (s50) and 400-m (maximal aerobic speed; MAS) and an incremental test to determine the speed corresponding to lactate threshold (sLT). In part 1, 28 swimmers performed 8 × 200-m (intensity - passive recovery: sLT − 30&#xa0;s) and 8 × 100-m (MAS − 30&#xa0;s). In part 2, three groups of ten swimmers performed 8 × 50-m (90% s50–30&#xa0;s), 4 × 50-m (maximal − 2&#xa0;min), 8 × 25-m (maximal − 2&#xa0;min). Blood lactate (BL) was determined at start, middle, and end; area under the curve (BLarea) and rate of increase (BLrate) were calculated. Blood pH and heart rate variability (HRV) were determined pre- and post-sets. Internal load was quantified using session rating of perceived exertion and training impulse.</p> Results <p>BLrate was higher in 8 × 100-m vs. 8 × 200-m (0.37 ± 0.20, 0.18 ± 0.12 mmol⋅L^− 1⋅min^− 1, <i>p</i> &lt; 0.05) and in 8 × 50-m and 4 × 50-m compared to 8 × 25-m (1.42 ± 0.26, 1.54 ± 0.39, 0.57 ± 0.15 mmol⋅L^− 1⋅min^− 1 respectively, <i>p</i> &lt; 0.05). BLarea was higher in 8 × 200-m compared to 8 × 100-m (63.0 ± 36.1, 38.2 ± 20.0 mmol·L^− 1⋅min) and in 8 × 25-m compared to 8 × 50-m and 4 × 50-m (80.1 ± 20.9, 49.7 ± 14.0, 57.4 ± 17.3 mmol·L^− 1⋅min, respectively, <i>p</i> &lt; 0.05). Post-set pH was lower in 4 × 50-m compared to 8 × 25-m (7.16 ± 0.07, 7.25 ± 0.06, <i>p</i> &lt; 0.05). HRV was lower post-8 × 50-m compared to 8 × 25-m (1.69 ± 0.42, 2.41 ± 0.40 ms, <i>p</i> &lt; 0.05). In part 1, but not part 2, training load methods were correlated (<i>r</i> = 0.52, <i>p</i> = 0.01).</p> Conclusions <p>Despite similar BL, evaluating autonomic responses, BLarea, BLrate and acid-base balance are important to facilitate decisions on swimming training planning combined with internal training load assessment.</p>