Assessment of individual anaerobic threshold and stroking parameters in swimmers aged 10-11 years

The assessment of blood lactate concentration is considered essential for the physiological diagnosis of swimming performance. But for a more detailed and complete analysis of a swimmer's strengths and weaknesses, it is also important to examine his or her technical characteristics. However, few studies have combined physiological and technical evaluation in child swimmers. The aim of the present study was to assess the metabolic anaerobic threshold (blood lactate concentration and corresponding swimming velocity) of 10- to 11-year-old swimmers (n=15) using an individualized intermittent incremental protocol. Comparison was made with the traditionally used 4 mmol center dot l-1 lactate threshold. In addition, stroke rate, stroke length, and stroke index were measured throughout the experimental protocol for assessment of the anaerobic threshold. Each swimmer performed a front crawl 5x200 m test, in which the swimming velocity was controlled by an acoustic signal each 50 m. Blood samples were collected from the ear lobe (Lactate Pro, Arkay, Inc., Kyoto, Japan), at rest and after each step. Stroke rate was registered by a Seiko base 3 chronofrequencemeter; stroke length, stroke index, and velocity were calculated at the end of each 200 m. The individual anaerobic threshold occurred at 2.3 mmol center dot l-1 (s=0.59), and the corresponding velocity was 1.026 m center dot s-1 (s=0.053), much lower than the traditionally used 4 mmol center dot l-1 value (or even 3.5 mmol center dot l-1). The velocity corresponding to 4 mmol center dot l-1 and 3.5 mmol center dot l-1 was 1.081 m center dot s-1 (s=0.056) and 1.067 m center dot s-1 (s=0.055), respectively. Stroke rate increased and stroke length decreased throughout the incremental protocol (i.e. with increasing velocity). The stroke index showed a tendency to increase throughout the protocol, with a significant difference from the first to the second step. The velocity corresponding to 4 mmol center dot l-1 (and 3.5 mmol center dot l-1) does not represent the metabolic individual anaerobic threshold in trained swimmers, independently of their age, and age-group swimmers prefer to increase their velocity through an increase in stroke rate. Thus, given the importance of developing swimming technique in age-group swimmers, coaches should implement the lengthening of swimmers' stroke cycles in their training practice routines, so that they limit the effects of reduced stroke length when velocity increases.