Marcel Hubert

Loading forces in shallow water running in two levels of immersion.

OBJECTIVE To analyse the vertical and anteroposterior components of the ground reaction force during shallow water running at 2 levels of immersion. SUBJECTS Twenty-two healthy adults with no gait disorders, who were familiar with aquatic exercises. METHODS Subjects performed 6 trials of water running at a self-selected speed in chest and hip immersion. Force data were collected through an underwater force plate and running speed was measured with a photocell timing light system. Analysis of covariance was used for data analysis. RESULTS Vertical forces corresponded to 0.80 and 0.98 times the subjects body weight at the chest and hip level, respectively. Anteroposterior forces corresponded to 0.26 and 0.31 times the subjects body weight at the chest and hip level, respectively. As the water level decreased the subjects ran faster. No significant differences were found for the force values between the immersions, probably due to variability in speed, which was self-selected. CONCLUSION When thinking about load values in water running professionals should consider not only the immersion level, but also the speed, as it can affect the force components, mainly the anteroposterior one. Quantitative data on this subject could help professionals to conduct safer aqua-tic rehabilitation and physical conditioning protocols.

Vertical reaction forces and kinematics of backward walking underwater.

The aim of this study was to compare the first and second peaks of the vertical ground reaction force (VGRF) and kinematics at initial contact (IC) and final stance (FS) during walking in one of two directions (forward×backward) and two environments (on land×underwater). Twenty-two adults (24.6±2.6 years) walking forward (FW) and backward (BW) on a 7.5m walkway with a central force plate. Underwater immersion was at the height of the Xiphoid process. Ten trials were performed for each condition giving a total of 40 trials where the VGRF and kinematic data were recorded. Two-way repeated measures analysis of covariance was used with a combination of environment and direction of walking: FW on land, FW underwater, BW on land and BW underwater (entered as between-subjects factor) and repeated measures of VGRF peaks (first and second) or angles (at IC and FS). Walking velocity was included as a covariate. Both VGRF peaks were reduced when participants walked underwater compared to on land (p<.001). For BW, in both environments, the second peak was lower than the first (p<.001; for both). During BW at IC the ankle is more dorsiflexed and the knee is more flexed, both on land and underwater. At FS, there was no difference between the ankle angle for FW and BW in both environments. At IC, in FW and BW the knee and hip are more flexed underwater. BW underwater involves a lower VGRF and more knee and hip flexion than BW on land.

Incidência de lesões em velejadores brasileiros de diferentes níveis técnicos

The first step to reduce the incidence of injuries in athletes is to assess the characteristics of occurrence, providing background for the structure and application of prevention programs. This study had the aim to investigate the incidence of injuries in sailing athletes of different technical levels. The sample was composed of 172 sailors, divided in three groups: 89 beginners, participants in the Optimist qualifying of the World Championship (group 1); 29 juvenile sailors, participants in the Youth Sailing Cup (group 2) and 54 national elite sailors, participants in the Pre-Olympic Sailing Week (group 3). The data collection instrument was a mixed questionnaire and the data were analyzed by descriptive statistics. Five athletes from group 1 (5.6%); five athletes from group 2 (17.2%) and 15 athletes from group 3 (27.8%) reported some kind of injury related with the modality. Higher incidence of injury was observed in the back and knee and the most reported diagnostic was muscular injury, followed by cuts, sprains and tendinitis. The incidence in sailing is low if compared with other sport modalities, despite the high physical demand required during the actions on the boat. It was verified that the professional athletes, who had higher age mean and time of practice, suffered the most injuries. On the other hand, the lowest incidence was among children and adolescents. Therefore, it is important that prevention programs start from the first years of practice in order to reduce the risk to future outbreaks, especially of chronic nature. Based on this information concerning kinds of injury, we suggest inclusion of exercises specific to musculature conditioning and compensation in the training programs, as well as stretching and relaxation sessions.

Kinematic, kinetic and EMG analysis of four front crawl flip turn techniques

Abstract This study aimed to analyse the kinematic, kinetic and electromyographic characteristics of four front crawl flip turn technique variants. The variants distinguished from each other by differences in body position (i.e. dorsal, lateral, ventral) during rolling, wall support, pushing and gliding phases. Seventeen highly trained swimmers (17.9 ± 3.2 years old) participated in interventional sessions and performed three trials of each variant, being monitored with a 3-D video system, a force platform and an electromyography (EMG) system. Studied variables: rolling time and distance, wall support time, push-off time, peak force and horizontal impulse at wall support and push-off, centre of mass horizontal velocity at the end of the push-off, gliding time, centre of mass depth, distance, average and final velocity during gliding, total turn time and electrical activity of Gastrocnemius Medialis, Tibialis Anterior, Biceps Femoris and Vastus Lateralis muscles. Depending on the variant, total turn time ranged from 2.37 ± 0.32 to 2.43 ± 0.33 s, push-off force from 1.86 ± 0.33 to 1.92 ± 0.26 BW and centre of mass velocity during gliding from 1.78 ± 0.21 to 1.94 ± 0.22 m · s−1. The variants were not distinguishable in terms of kinematical, kinetic and EMG parameters during the rolling, wall support, pushing and gliding phases.

Ground Reaction Force and Cadence during Stationary Running Sprint in Water and on Land.

This study was aimed at analyzing the cadence (Cadmax) and the peak vertical ground reaction force (Fymax) during stationary running sprint on dry land and at hip and chest level of water immersion. We hypothesized that both Fymax and Cadmax depend on the level of immersion and that differences in Cadmax between immersions do not affect Fymax during stationary sprint. 32 subjects performed the exercise at maximum cadence at each immersion level and data were collected with force plates. The results show that Cadmax and Fymax decrease 17 and 58% from dry land to chest immersion respectively, with no effect of cadence on Fymax. While previous studies have shown similar neuromuscular responses between aquatic and on land stationary sprint, our results emphasize the differences in Fymax between environments and levels of immersion. Additionally, the characteristics of this exercise permit maximum movement speed in water to be close to the maximum speed on dry land. The valuable combination of reduced risk of orthopedic trauma with similar neuromuscular responses is provided by the stationary sprint exercise in water. The results of this study support the rationale behind the prescription of stationary sprinting in sports training sessions as well as rehabilitation programs.

Método dinamométrico para avaliação da escora em barcos tipo Catamaran

This study aimed to propose and to validate a method for the measurement of hiking distance (Hd) and hiking moment (Hm) in Catamaran boats, through the use of force plates. This new method proposes the measurement by dynamometry, with the positioning of a force plate below each boat hoof to measure the Ground Reaction Forces (GRF). Based on the classic static equations Hd and Hm were determined. In order to validate the method a validation of competing was carried out through the comparison with kinematic values measured through the Peak Motus system. Intraclass correlation coeficient was used. Different positions in two different inclinations of the boat, simulating the boat heeling, had been analyzed. The results showed a high correlation (ICC > 0.99) and a small average error (1.00% for Hd and 0.96% for Hm) between the methods. Thus, the new method seems to be valid and efficient since it measured the variables in a fast and precise way, facilitating the analysis and assisting sailors and coaches on decision taking