José Luis López Elvira

Effects of Sled Towing on Peak Force, the Rate of Force Development and Sprint Performance During the Acceleration Phase

Abstract Resisted sprint training is believed to increase strength specific to sprinting. Therefore, the knowledge of force output in these tasks is essential. The aim of this study was to analyze the effect of sled towing (10%, 15% and 20% of body mass (Bm)) on sprint performance and force production during the acceleration phase. Twenty-three young experienced sprinters (17 men and 6 women; men = 17.9 ± 3.3 years, 1.79 ± 0.06 m and 69.4 ± 6.1 kg; women = 17.2 ± 1.7 years, 1.65 ± 0.04 m and 56.6 ± 2.3 kg) performed four 30 m sprints from a crouch start. Sprint times in 20 and 30 m sprint, peak force (Fpeak), a peak rate of force development (RFDpeak) and time to RFD (TRFD) in first step were recorded. Repeated-measures ANOVA showed significant increases (p ≤ 0.001) in sprint times (20 and 30 m sprint) for each resisted condition as compared to the unloaded condition. The RFDpeak increased significantly when a load increased (3129.4 ± 894.6 N·s−1, p ≤ 0.05 and 3892.4 ± 1377.9 N·s−1, p ≤ 0.01). Otherwise, no significant increases were found in Fpeak and TRFD. The RFD determines the force that can be generated in the early phase of muscle contraction, and it has been considered a factor that influences performance of force-velocity tasks. The use of a load up to 20% Bm might provide a training stimulus in young sprinters to improve the RFDpeak during the sprint start, and thus, early acceleration.

Respuestas, adaptaciones y simetría de la huella plantar producidas por la práctica de la marcha atlética. (Answers, adaptations and symmetry of the track to plant produced for the practice of the athletic march).

The purpose of this paper was to determine the effect of the race walking exercise on the structures of the foot, so much in the immediate responses to the practice as in the long term training adaptations. Footprints were recorded tree times using the photopodogram methodology on a sample of 17 young race walkers. The first one and second footprints were carried out in both feet at the middle of the season, in rest and after 30 min race walking respectively. The third was taken in rest on the dominant foot 3 months later, at the end of the season. The re- sults indicate that there are not differences among the right and left foot, neither before nor after the exercise. However, the re- sponses showed different behaviour. While the right foot showed significant increments in the width of the forefoot and midfoot (P < 0.05), the left foot showed an increment in the length of the foot. This different behaviour can be due to the characteristics of the circuit on which the race walk was car- ried out, circular with turn to the left. This takes us to suggest that, to avoid overloads and muscular unbalances the race walk- ers should train in circuits balanced in curves to either sides, or if in circular circuits frequently change the turning sense. The adaptations followed a similar pattern to that of the responses of the right foot. There were significant increments in the width of the forefoot, although the length of the foot also increased significantly. Anyway, we believe that the last could be due to the intrinsic characteristic of the athletes, since many of them were in age of growing.