Dell'Antonio, E, Ruschel, C, de Brito Fontana, H, Haupenthal, A, Pereira, SM, and Roesler, H. Effect of immersion on ground reaction force and contact time during drop jump exercise. J Strength Cond Res 30(12): 3443-3449, 2016-This study analyzed the effect of water immersion on vertical ground reaction force (GRF) peaks and contact times during the braking, propulsion, and landing phases of drop jumps (DJs). Twenty-five healthy male athletes of volleyball and track and field (age 18.0 ± 2.4 years) participated in this study. Peak vertical GRF during braking, propulsion, and landing phases; time duration of braking and propulsion phases; and total contact time were measured during maximum DJs performed on land and in water at 4 levels of immersion (tibia, knee, thigh, and hip). A force plate was used to collect GRF data, and the braking and propulsion phases of contact were determined by using an electrical goniometer placed on subject's knee. The effect of immersion level on variables was analyzed through the use of a repeated measures analysis of variance (p ≤ 0.05). The results showed that increasing immersion leads to a decrease in peak force during the braking phase, landing phase, and in the propulsion phase of the DJ, with the decrease in peak forces between immersions being greater as the immersion level gets deeper. Concerning the contact times, increasing immersion levels caused an increase in total contact time and in the duration of the braking phase. No differences were found for the duration of the propulsion phase between the conditions. Our results have shown that temporal features of the DJ were not preserved in water, and this must be taken into account when choosing the aquatic environment as an alternative for plyometric training. If the rationale of performing plyometric training in water is the reduction of GRFs, then hip immersion seems to offer an interesting combination of significantly lower GRF but without further modification of important temporal features when compared with the other water conditions analyzed.

This study aims to analyze and summarize the biomechanical (kinematics, kinetics and neuromuscular) differences between shod and barefoot running, through a literature review. Searches were conducted for complete articles published between 2013 and November 2018 in the Web of Science, PubMed, Scopus and SPORTdiscus databases. The search terms used were Biomechanics, Kinetics, Kinematics, Electromyography, “Surface Electromyography”; and Unshod, Barefoot, Barefeet and Running. The search resulted in 687 articles; after excluding duplicates and selecting by title, abstract and full text, 40 articles were included in the review. The results show that there are important differences in the biomechanics of running when shod or barefoot. In general, studies indicate that in barefoot running: a) individuals present forefoot or midfoot foot strike patterns, while in shod running the typical pattern is the rearfoot strike; (b) greater cadence and shorter stride length are observed; and (c) there is greater knee flexion, lower peak vertical ground reaction force and greater activation of the medial gastrocnemius. In addition, barefoot runners contact the ground with greater plantar flexion, possibly as a strategy to reduce impact when stepping without footwear. These differences, as well as runners’ individual characteristics, should be considered in the prescription of the barefoot running, in order to minimize injuries resulting from the practice. Level of Evidence II; Review.

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Introduction: Pilates is a physical exercise method that uses the resistance of springs to modulate the over-

This study aimed to analyze the effect of aquatic plyometric training (APT) on jump performance in volleyball players. Twelve female athletes (16.6 ± 0.9 years) were assessed through the following jump tests: spike height (SH), squat jump (SJ), countermovement jump (CMJ) and CMJ with an arm swing (CMJA). Jump height in each test and the eccentric utilization ratio (EUR) were the outcome measures. APT consisted of sets of drop jumps for 6 weeks (2 sessions/week) at a water depth of 0.75 m. Tests were performed at the beginning of a five-week pre-season period, before and after APT, and four weeks later for the follow-up. Repeated measures ANOVAs were used to analyze data and Hedges’ g to estimate effect size (ES). Performance of all jumps did not change from baseline to Pre-APT. Performance improved in SH (p < 0.001, ES: 1.09), the SJ (p = 0.045, ES: 0.76) and the CMJA (p < 0.001, ES: 0.78) after APT when compared to Pre-APT. No changes were observed after the follow-up period. In conclusion, including six weeks of APT in the training routine of youth volleyball players improved performance of a sport-specific task (SH), the SJ and CMJA, with gains preserved after a four-week follow-up.