Physiological responses to shuttle repeated-sprint running.

This study investigated the influence of 180 degrees changes of direction during a repeated-sprint running test on performance, cardiorespiratory variables, muscle deoxygenation and post-exercise blood lactate ([La] (b)) levels. Thirteen team-sport athletes (22+/-3 yr) performed 6 repeated maximal sprints with (RSS, 6 x[2 x 12.5 m]) or without (RS, 6 x 25 m) changes of direction. Best and mean running time, percentage speed decrement (%Dec), pulmonary oxygen uptake ( V O (2)), vastus lateralis deoxygenation (Hb (diff)) and [La] (b) were calculated for each condition. Best and mean times for both protocols were largely correlated (r =0.63 and r =0.78, respectively), and were 'ALMOST CERTAINLY' higher for RSS compared with RS (e. g., 5.30+/-0.17 vs. 4.09+/-0.17 s for mean time, with the qualitative analysis revealing a 100% chance of RSS time being greater than RS). In contrast, %Dec was 'POSSIBLY' lower for RSS (2.6+/-1.2 vs. 3.2+/-1.3%, with a 79% chance of a real difference). Compared with RS, V O (2) (40.4+/-4.2 vs. 38.9+/-3.8 mL x min (-1) x kg (-1), with a 90% chance of a real difference) and [La] (b) (10.0+/-1.7 vs. 9.3+/-2.4 mmol.L (-1), with a 70% chance of a real difference) were 'POSSIBLY' higher. Conversely, there were no differences in Hb (diff) (11.5+/-3.2 vs. 10.9+/-3.0 microM, with the comparison rated as 'UNCLEAR'). To conclude, the present results suggest that the ability to repeat sprints can be considered as a general quality. They also suggest that repeated shuttle sprints might be an effective training practice for eliciting a greater systemic physiological load, but perhaps not a greater loading of the vastus lateralis.