Critical velocity and lactate threshold in young swimmers

The purpose of the present study was to compare the critical swimming velocity (CV) in children, with the lactate threshold (LT) and the velocity corresponding to a blood lactate concentration of 4 mmol x l(-1) (V4). Twenty swimmers (ten females and ten males, mean +/- SD age: 12.9 +/- 1.1 years, body weight: 51.2 +/- 10.0 kg, height: 157.1 +/- 9.7 cm) performed four repetitions of 200 m swimming with increasing intensity (80, 85, 90 and 100% of their 200 m maximum velocity), interspersed with 15 minutes of passive rest. Blood lactate concentration was determined after each repetition. From the speed-lactate curve, the velocity corresponding to LT and V4 was calculated. In order to calculate CV, all swimmers were timed exerting maximum effort, on distances of 50, 100, 200 and 400 m. CV was expressed as the slope of the linear relationship of time versus distance and was calculated from combinations of four (CV4) three or two timed distances. Velocity on LT (1.079 +/- 0.114 m x s(-1)) and V4 (1.106 +/- 0.112 m x s(-1)) was comparable to CV4 (1.085 +/- 0.121 m x s(-1)). CV calculated from a combination including distances of 50, 100 or 200 m were higher compared to LT (p < 0.05). V4 was higher compared to CV of 100-200-400, CV of 200-400, CV of 100-400 (p < 0.05). The CV calculated from distances of 50 and 100 m was significantly higher than all other velocities (p < 0.05). These results confirm that the critical velocity seems to be a valid, practical and time-saving, non-invasive alternative method which can be applied in the swimming pool by a coach for the evaluation of the endurance capacity of young swimmers. For practical reasons, combinations of less than four distances can be used (i.e. 50-400 m, or 50-100-400 m).