JOINT MOMENTS AND NEUROMUSCULAR FUNCTIONING IN DROP JUMP EXERCISES

INTRODUCTION: Drop jump (DJ) exercises from different dropping heights are often used to obtain important data about the degree of adaptability of the locomotor system to increasing amounts of mechanical load. The purpose of this study was to analyze the adaptation of the neuromuscular system to mechanical load increases. These neuromuscular adaptations where related to the joints’ moments of force and to relative changes in the length of the leg extensor muscles. METHODS: Ten elite sprinters (height: 182±5.0 cm, body mass: 75.3±4.5 kg, best performance over 100 meters: 10.4±0.2 s) performed 6 DJs from 25, 40, 55 and 70 cm. EMG signals and ground reaction forces were recorded at 1000 Hz. EMGs from the tibialis anterior (TA), soleus (SOL), gastrocnemius (GAS), rectus femoris (RF), vastus medialis (VM), biceps femoris (BF) and gluteus maximus GM muscles were full wave rectified and integrated (iEMG) across different functional phases: pre-activation (PRE) (100 ms prior to contact), reflex induced activation phase (RIA) (from 20 ms to 100 ms after contact) and late EMG response phase (LER) (from 100 ms to the finish). Vertical peak and vertical net impulses were calculated. Simultaneously, angular kinematic data on the ankle, knee and hip joints were calculated using a video analysis system (120 Hz). Joint net moments from the hip, knee and ankle were calculated using an inverse dynamics method. Student’s T-tests were used to analyze the effects of drop jump height. RESULTS: The stretching and shortening velocities increased in all muscles with an increase in DJ height. Nevertheless, no differences were found in vertical jumping performance between DJs executed from different heights. The subjects were able to reduce the increasing stretching load, producing higher vertical net impulses during the downward movement. The percentage of total length changes of GAS, RF, VM and SOL increased with stretching load, average values increasing from 4.7% at DJ25 to 7.8% at DJ70; these values are inside the short range elastic stiffness. The iEMG of the RIA phase increased slightly with the increase of dropping height for VM, RF, GAS, SOL. For these muscles, the RIA phase presented higher iEMG values when compared with LER. For the four jumping heights, the peak values of hip, knee and ankle joint moments were similar. Nevertheless, a different joint moment/time curve pattern was obtained. On DJ70, the peak values of joint moments of the three joints were obtained earlier, coinciding with the stretching phase of the muscles studied. For DJ70, a decline in the value of the moments of force on the three joints was observed during the ascending phase. CONCLUSION: The athletes studied were able to resist increasing stretching speeds and forces during the braking phase. This ability was related to the increased capability of maintaining high levels of stretch reflex during the RIA phase, revealing the importance of the stretch reflex effect on increasing muscle stiffness

JOINT MOMENTS AND NEUROMUSCULAR FUNCTIONING IN DROP JUMP EXERCISES

INTRODUCTION: Drop jump (DJ) exercises from different dropping heights are often used to obtain important data about the degree of adaptability of the locomotor system to increasing amounts of mechanical load. The purpose of this study was to analyze the adaptation of the neuromuscular system to mechanical load increases. These neuromuscular adaptations where related to the joints’ moments of force and to relative changes in the length of the leg extensor muscles. METHODS: Ten elite sprinters (height: 182±5.0 cm, body mass: 75.3±4.5 kg, best performance over 100 meters: 10.4±0.2 s) performed 6 DJs from 25, 40, 55 and 70 cm. EMG signals and ground reaction forces were recorded at 1000 Hz. EMGs from the tibialis anterior (TA), soleus (SOL), gastrocnemius (GAS), rectus femoris (RF), vastus medialis (VM), biceps femoris (BF) and gluteus maximus GM muscles were full wave rectified and integrated (iEMG) across different functional phases: pre-activation (PRE) (100 ms prior to contact), reflex induced activation phase (RIA) (from 20 ms to 100 ms after contact) and late EMG response phase (LER) (from 100 ms to the finish). Vertical peak and vertical net impulses were calculated. Simultaneously, angular kinematic data on the ankle, knee and hip joints were calculated using a video analysis system (120 Hz). Joint net moments from the hip, knee and ankle were calculated using an inverse dynamics method. Student’s T-tests were used to analyze the effects of drop jump height. RESULTS: The stretching and shortening velocities increased in all muscles with an increase in DJ height. Nevertheless, no differences were found in vertical jumping performance between DJs executed from different heights. The subjects were able to reduce the increasing stretching load, producing higher vertical net impulses during the downward movement. The percentage of total length changes of GAS, RF, VM and SOL increased with stretching load, average values increasing from 4.7% at DJ25 to 7.8% at DJ70; these values are inside the short range elastic stiffness. The iEMG of the RIA phase increased slightly with the increase of dropping height for VM, RF, GAS, SOL. For these muscles, the RIA phase presented higher iEMG values when compared with LER. For the four jumping heights, the peak values of hip, knee and ankle joint moments were similar. Nevertheless, a different joint moment/time curve pattern was obtained. On DJ70, the peak values of joint moments of the three joints were obtained earlier, coinciding with the stretching phase of the muscles studied. For DJ70, a decline in the value of the moments of force on the three joints was observed during the ascending phase. CONCLUSION: The athletes studied were able to resist increasing stretching speeds and forces during the braking phase. This ability was related to the increased capability of maintaining high levels of stretch reflex during the RIA phase, revealing the importance of the stretch reflex effect on increasing muscle stiffness

RELATIVE JOINT MOMENT CONTRIBUTION TO THE POWER GENERATED IN A MARTIAL ARTS KICK – INFLUENCE OF SKILL LEVEL

The purpose of this study was to analyse whether athletes of different skill level present different relative joint moment contributions to the power generated in a martial arts kick. This investigation was carried out using the induced power analysis, a method based on the dynamic coupling inherent to ultiarticulated systems. The comparison was done among three male karatekas, considered to be experienced, intermediate and novice. The results show that the hip extension moment was the major contributor in the production of mechanical energy in the kicking foot at impact. Similarly the hip internal rotation and ankle dorsiflexion moments worked to build up the foot’s energy for most of movement. The experienced athlete seems to benefit more from these by potentiating the moments produced in these joints

KINEMATICS OF THE HAND AND KEY ROTATION IN A TENNIS FOREHAND DRIVE OF TENNIS PLAYERS

The purpose of the present study was to quantify kinematic variables of the hand of dominant arm and the main responsible rotation of the upper limb to the racket head velocity in an attack tennis forehand drive. Three elite tennis players and three highperformance tennis players were recorded with inertial measurement units (IMUs) with a frequency of 120 Hz during a cross-court (CC) and an inside-out (IO) forehand drive. The six fastest strokes in both directions were selected for analyses. Differences between two directions were shown in the follow through with a higher wrist abduction when playing in the inside-out direction (cross-court: 13.9 ± 17.2°; inside-out: 16.9 ± 18.6°). Results demonstrated that the horizontal flexion of the upper arm were the main responsible for the racket head velocity (48.1% CC and 45.2% IO)

Evaluation of upper limb joint contribution to racket head speed in elite tennis players using IMU sensors: comparison between the cross-court and inside-out attacking Forehand Drive

This study aimed to quantify and compare the upper limb angular kinematics and its contributions to the racket head speed between the cross-court (CC) and inside-out (IO) attacking tennis forehand of elite tennis players in a competitive environment. A new approach was used to study the forehand drive with mini-inertial sensors of motion capture to record the kinematic data. Six strokes in each direction per participant (72 shots in total) were chosen for analysis. Upper limb kinematics were calculated in the Visual 3D platform (Visual 3D Professional V5.01.21, C-motion, Germantown, MD, USA). The method used to calculate the upper limb’s contributions was performed with MATLAB software and used the segment’s (upper arm, forearm and hand) angular velocities and their respective displacement vectors obtained through the inertial sensors. Upper limb kinematics demonstrated a higher shoulder rotation in the IO direction with significant differences at the end of the backswing, which could be a key factor in distinguishing the two directions of the shot. Results also demonstrated that the horizontal flexion of the upper arm (around the shoulder joint) was primarily responsible for the racket velocity in the anteroposterior direction (48.1% CC and 45.2% IO), followed by the extension of the forearm (around the elbow joint) (17.3% CC and 20.9% IO) and the internal rotation of the upper arm (around the shoulder joint) (15.6% CC and 14.2% IO). No significant differences were shown in the contributions of upper limbs to the racket head velocity between the two directions of the shot. Tennis coaches and players should develop a specific training programme to perform higher angular velocities in these specific joint rotations.info:eu-repo/semantics/publishedVersio

COMPARISON OF INDIVIDUAL MUSCLE CONTRIBUTIONS TO GROUND REACTION FORCES DURING JUMP AND CHANGE OF DIRECTION TESTING AFTER ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION

The purpose of this study was to identify the main muscle contributions across a battery of different tasks commonly used to evaluate an athlete’s readiness to return to sport after anterior cruciate ligament injury (ACL) and following ACL reconstruction. These injuries are mostly related to landing and change of direction movements and, due to its high incidence, efforts must be made to better understand the knee soft tissue mechanisms during these types of tasks. Data from a single athlete were analysed for this study. Scaled generic musculoskeletal models, consisting of 12 segments, 23 degrees of freedom and 92 musculotendon actuators were used in OpenSim. The quadriceps were the main contributors to ground reaction forces along the anterior/posterior direction, and, aided by the soleus and gastrocnemii, counteracted most of the effects applied by gravity along the vertical direction. The main contributors to the ground reaction forces during all the tasks are the same muscles that are intimately related to ACL loading, thus making these tasks useful for injury rehabilitation programs

ANGULAR KINEMATICS AND JOINT MOMENTS ANALYSIS IN LOWER LIMB AND PELVIS DURING GAIT IN SAGITTAL PLANE IN PREGNANT WOMEN

This study compared sagittal plane lower limb range of motion (ROM) and joint moments of force (Mf) during gait in pregnant (second trimester) and non-pregnant women. Kinematic data were collected with an optoelectronic motion capture system (Qualysis, Ocqus 300) synchronized with two force platforms (Kistler AG, Winterthur, Switzerland) which collected ground reaction force values. The study revealed that the gait pattern in the second trimester of pregnancy is similar to the non-pregnant women pattern, in what concerns to the variables studied. Lower dorsiflexion and higher plantar flexion angles in the ankle joint in pregnant women, and higher values of hip flexion for the same group, were observed. With respect to the joint moments of force, there were higher knee flexor and hip extensor peak moments in pregnant women

An Informational Algorithm as the Basis for Perception-Action Control of the Instantaneous Axes of the Knee

Traditional locomotion studies emphasize an optimization of the desired movement trajectories while ignoring sensory feedback. We propose an information based theory that locomotion is neither triggered nor commanded but controlled. The basis for this control is the information derived from perceiving oneself in the world. Control therefore lies in the human-environment system. In order to test this hypothesis, we derived a mathematical foundation characterizing the energy that is required to perform a rotational twist, with small amplitude, of the instantaneous axes of the knee (IAK). We have found that the joint’s perception of the ground reaction force may be replaced by the co-perception of muscle activation with appropriate intensities. This approach generated an accurate comparison with known joint forces and appears appropriate in so far as predicting the effect on the knee when it is free to twist about the IAK

Perception of olive oils sensory defects using a potentiometric taste device

The capability of perceiving olive oils sensory defects and intensities plays a key role on olive oils quality grade classification since olive oils can only be classified as extra-virgin if no defect can be perceived by a human trained sensory panel. Otherwise, olive oils may be classified as virgin or lampante depending on the median intensity of the defect predominantly perceived and on the physicochemical levels. However, sensory analysis is time-consuming and requires an official sensory panel, which can only evaluate a low number of samples per day. In this work, the potential use of an electronic tongue as a taste sensor device to identify the defect predominantly perceived in olive oils was evaluated. The potentiometric profiles recorded showed that intra- and inter-day signal drifts could be neglected (i.e., relative standard deviations lower than 25%), being not statistically significant the effect of the analysis day on the overall recorded E-tongue sensor fingerprints (P-value=0.5715, for multivariate analysis of variance using Pillai's trace test), which significantly differ according to the olive oils sensory defect (P-value=0.0084, for multivariate analysis of variance using Pillai's trace test). Thus, a linear discriminant model based on 19 potentiometric signal sensors, selected by the simulated annealing algorithm, could be established to correctly predict the olive oil main sensory defect (fusty, rancid, wet-wood or winey-vinegary) with average sensitivity of 75±3% and specificity of 73±4% (repeated K-fold cross-validation variant: 4 folds×10 repeats). Similarly, a linear discriminant model, based on 24 selected sensors, correctly classified 92±3% of the olive oils as virgin or lampante, being an average specificity of 93±3% achieved. The overall satisfactory predictive performances strengthen the feasibility of the developed taste sensor device as a complementary methodology for olive oils defects analysis and subsequent quality grade classification. Furthermore, the capability of identifying the type of sensory defect of an olive oil may allow establishing helpful insights regarding bad practices of olives or olive oils production, harvesting, transport and storage.This work was financially supported by Project POCI-01–0145FEDER-006984 – Associate Laboratory LSRE-LCM, Project UID/QUI/ 00616/2013 – CQ-VR, and UID/AGR/00690/2013 – CIMO all funded by FEDER - Fundo Europeu de Desenvolvimento Regional through COMPETE2020 - Programa Operacional Competitividade e Internacionalização (POCI) – and by national funds through FCT Fundação para a Ciência e a Tecnologia, Portugal. Strategic funding of UID/BIO/04469/2013 unit is also acknowledged. Nuno Rodrigues thanks FCT, POPH-QREN and FSE for the Ph.D. Grant (SFRH/BD/ 104038/2014).info:eu-repo/semantics/publishedVersio

Using a multifactorial approach to determine fall risk profiles in portuguese older adults

The aim of this study was to use a multifactorial approach to characterize episodic and recurrent fallers risk profiles in Portuguese older adults.info:eu-repo/semantics/publishedVersio