Author(s): JEAN-BENOIT, M., FUBIANI, C., GONZALEZ, S., CRESPEAU, S., Institution: UNIVERSITÉ DE SAINT-ETIENNE, Country: FRANCE, Abstract-ID: 1156

INTRODUCTION:
Vertically-oriented plyometric tasks are often used in sports training, allowing to assess and develop fast, high-intensity actions involving the muscle-tendon “stretch-shortening cycle” [1,2]. From a mechanical output perspective, a plyometric task such as a rebound jump can be described by both a very high ground reaction force (GRF) production and a very short contact time [1]. Sprint biomechanics studies have consistently shown that maximal and submaximal speed (90% of maximum) running induced single-leg stretch-shortening actions on the ground with both very high GRF output and very short contact time [e.g. 3]. Thus, we hypothesized that submaximal and maximal-speed sprinting could be considered as efficient vertical plyometric stimuli, based on single-leg force-time outputs, in comparison to other classical plyometric tasks.
METHODS:
After familiarization, sixteen participants used to sprinting and plyometric training volunteered to perform a session including a maximal-speed 30-m sprint, a standardised submaximal sprint (90.1±0.4% of top speed) and the following vertical plyometric tasks: double-leg drop jump, hurdle jump, foot-ankle rebounds and in-place single-leg skipping. All tasks were performed with maximal intensity on a multiple force plate system sampling force-time data at 2000 Hz. Repeated-measure analysis of variance was used to compare average vertical GRF and contact time for the same leg (single, dominant) output across tasks.
RESULTS:
Significant differences were found between both sprint conditions (maximal and sub-maximal) and other plyometric tasks tested, towards a greater average vertical GRF output during the contact phase and/or a shorter contact duration. For example, the mean GRF in sprinting (about 1400 N) was significantly higher than during skipping (1186 N) and foot-ankle rebounds (1048 N), and the contact time (about 130 ms) was significantly shorter than during hurdle jumps (207 ms) and drop jumps (244 ms). No significant difference was found in the main mechanical outputs tested between the maximal and submaximal sprint conditions.
CONCLUSION:
When compared for the same leg, maximal and submaximal sprinting led to the highest levels of vertical GRF and the shortest contact times. In comparison with the drop jump, sprinting induced about 20% greater single leg GRF and about 50% shorter contact times. Added to the established high-quality mechanical stimulus of the hamstring muscles, submaximal and maximal sprinting, when programmed and performed correctly, can be considered as efficient plyometric stimuli, from a mechanical output standpoint.