Cardiac Autonomic Responses To Repeated Shuttle Sprints

Team sport match play requires athletes to perform a number of repeated shuttle sprints. However, the acute effects of these repeated sprint sequences on lactic acidosis and resulting autonomic state perturbation are not known. PURPOSE: to observe and compare the blood lactate and post-exercise cardiac autonomic responses of a repeated shuttle-sprint ability test (RSSA test) with the 30-15 Intermittent Fitness Test (30-15IFT); the latter test representing a standard for exhaustive supramaximal effort. METHODS: Thirteen adult team sport players performed the RSSA test and 30-15IFT on separate days in a counter-balanced order. The RSSA test consisted of six repetitions of maximal 2 × 15 m shuttle sprints (∼5 s) departing every 20 s, while 30-15IFT involved progressive 30 s shuttle runs interspersed with 15 s of passive recovery until exhaustion. Blood lactate was measured before and after the tests, while autonomic responses were assessed using immediate heart rate (HR) recovery (e.g., HRR60s) and heart rate variability (HRV) indices. RESULTS: Peak blood lactate (10.6 ± 2.1 vs. 10.2 ± 2.8 mM) and HRR60s (36.4 ± 7.8 vs. 39.3 ± 7.9 bpm) were similar after both the RSSA test and 30-15IFT. With the exception of the vagal-related time-varying root mean square of successive R-R interval differences at each 30 s, which recovered earlier after the RSSA test compared with 30-15IFT, all HRV indices decreased similarly after both tests in comparison to baseline values. CONCLUSIONS: the RSSA test was shown to induce comparable levels of lactic acidosis and post-exercise autonomic state as the 30-15IFT. These levels of metabolic and autonomic states are likely to occur during team sport match play.