Analysis of the effectiveness of the use of instep weights (Powerinstep) in everyday runners
The use of weights when training is very common, especially in compensatory work and in performing supplementary exercises. A new type of weight appeared in the market in 2015 with the name of Powerinstep. It is a weight placed on the instep of athletes running shoes (Padullés & Rius, 2015). The goal of this study was to analyse the effectiveness of the use of these weights (Powerinstep) regarding the effect of biomechanical and certain athletic performance variables on two everyday runners groups with similar training methods. The sample used was composed of 19 subjects (9 male and 10 female). The control group (without weight) was made up of 4 subjects and the experimental group had 15 subjects (4 had 50 gram weights on each foot, 5 had 100 grams on each foot, and 6 had 150 grams on each foot). The weight given to each athlete depended on their body weight. There was a pre-test and a post-test done to each athlete with a training period of 14 weeks in between. These tests were: the Bosco test (SJ, CMJ, and ABK) and the Léger test (UMTT). The analysed variables were: height (cm) in SJ, CMJ, and ABK; time (s) in the Léger test; maximum and average heart rate (bpm); contact, flight, and passing times (s) of both left and right feet; step length (m) both left and right feet; stride length (m); the elevation of the centre of mass (cm) during left and right steps and the strides. Both the experimental group and the control group trained under the same time and schedule conditions, with the same work volume, and used the same training system. The only thing that varied between the groups was the whether they used weights or not. Given the sample characteristics, the statistical analysis method was non-parametric (Wilcoxon test). A comparative analysis of the variations between the pre-test and the post-test was done, both in the intergroups (control vs. experimental) and the intragroups (between the 3 subgroups of the experimental group). The differences found in the variations of the control group were not statistically significant (p<0.05). Neither were they in comparing the variations of the intragroups between the subgroups of 50g, 100g, and 150g weights (p<0.05). With this, it can be deduced that the weights given to each athlete regarding their body weight were correct. Statistically significant differences were found in the variations of the experimental group regarding the length of the stride (p=0.05), increasing this one, as well as the length of the left step (p=0.04). However, it has to be taken into account that the length of the step can be considered an improvement, but only if it is regulated to fit each athlete’s ideal step length in relation to their trochanteric length, and if it is also associated with an increase of their driving force. Likewise, given the limitations of the sample for significant changes to be given over time, tendencies of the changes in the average percentages were analysed. Even if they did not offer statistically significant differences, they did offer results to take into consideration. This way, variations with higher percentages were found, and they were technically positive for the experimental group in 12 of the 18 analysed variables. The most noteworthy ones were: SJ (increase in the height of the flight (5.99%), Léger test (increase in the time (5.78%), length of both right and left steps (increases 5.99% and a 10.85% respectively), and the length of the stride (increases 8.11%).
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