Vertical Velocity Of Center Of Mass Research Articles

Effects of load increase on lower extremity kinetic and kinematic variables in the back squat exercise.

Squats are one of the most widely used weight training methods worldwide, and the single most ubiquitous with regard to multi-joint resistance training. The objective of the present study was to investigate kinematic and kinetic changes in the lower extremities as a result of load increases during a back squat exercise, and to propose an association between back squats and lower extremity injuries. Eight individuals with experience of back squat training were recruited. The subjects performed back squats with loads of 25%, 50%, 100%, and 125% of their body weight. During the performance, the center of pressure (COP) sway; vertical center of mass (COM) velocity; joint moment; joint range of motion (ROM) of flexion/extension and adduction/abduction; and rotation of the ankle, knee, and hip joints were measured. The participants' lower extremity joint ROM, vertical COM velocity, and COP variability did not change significantly with changes in weight loading. However, the moments applied to the lower extremity joints differed according to changes in barbell weight. The moments of plantar flexion (f= 54.362, p< 0.001), dorsiflexion (f= 8.475, p< 0.001), knee flexion (f= 12.013, p< 0.001), knee extension (f= 8.581, p< 0.001), hip flexion (f= 5.111, p< 0.001), and hip extension (f= 11.053, p< 0.001) increased in the sagittal plane (flexion/extension). There was also a significant increase in ankle eversion (f= 5.612, p= 0.004), hip abduction (f= 3.242, p= 0.037), and adduction (f= 5.846, p= 0.003) in the frontal plane (adduction/abduction). Among the moment variables in the transverse plane (rotation), there were significant differences in ankle internal rotation (f= 7.043, p= 0.001) and hip external rotation (f= 11.070, p< 0.001). As the barbell load increased, posture and performance were maintained, but rotational moments of the joints differed. It is expected that the joint directions that showed significant differences in this study are likely to be vulnerable to the risk of injury when an excessive load is applied to the body. Examples include the hip adduction moment, hip external rotation moment, and ankle internal rotation moment, and apply regardless of the increase in the rotational moments of joints from load increases.

Muscle Contributions to Take-Off Velocity in the Long Jump.

A key determinant of long jump performance is the ability to increase the vertical velocity of the center of mass (COM) while minimizing the loss in forward velocity (running speed) during the take-off phase, but exactly how this occurs is not fully understood. We combined a three-dimensional musculoskeletal model of the body with dynamic optimization theory to simulate the biomechanics of the long jump take-off and determine the contributions of the individual leg muscles to jump performance. The body was modeled as a 29-degree-of-freedom skeleton actuated by a combination of muscles and net joint torques. A dynamic optimization problem was solved to reproduce full-body motion and ground-force data recorded from experienced subelite jumpers. The optimization solution then was analyzed to determine each muscle's contribution to the ground-force impulse and hence the change in velocity of the COM during the take-off phase. The hip, knee, and ankle extensors dominated the change in velocity of the COM during take-off. Vasti (VAS) generated the highest support impulse and contributed one-third (33%) of the increase in vertical COM velocity generated by all the muscles. Soleus (SOL) and gluteus maximus (GMAX) also developed substantial support impulses and contributed 24% and 16% of the increase in vertical COM velocity, respectively. VAS also generated the highest braking impulse and contributed approximately one-half (55%) of the loss in forward COM velocity generated by all the muscles, whereas SOL and GMAX made much smaller contributions (12% and 7%, respectively). VAS, SOL, and GMAX contributed nearly three-quarters (73%) of the increase in vertical COM velocity at take-off, suggesting that these muscles ought to be prioritized in strength training programs aimed at improving long jump performance.

Young adults use whole-body feedback and ankle proprioception to perceive small locomotor disturbances

To prevent a fall when a disturbance to walking is encountered requires sensory information about the disturbance to be sensed, integrated, and then used to generate an appropriate corrective motor response. Prior research has shown that feedback of whole-body motion (e.g., center-of-mass kinematics) drives this corrective response. Here, we hypothesized that young adults also use whole-body motion to perceive locomotor disturbances. 15 subjects performed a locomotor discrimination task in which the supporting leg was slowed during stance every 8–12 steps to emulate subtle slips. The perception threshold of these disturbances was determined using a psychometrics approach and found to be 0.08 ± 0.03 m/s. Whole-body feedback was examined through center-of-mass (CoM) kinematics and whole-body angular momentum (WBAM). Perturbation-induced deviations of CoM and WBAM were calculated in response to the two perturbation levels nearest each subject's perception threshold. Consistent with our hypothesis, we identified significantly higher perturbation induced deviations for perceived perturbations in sagittal-plane WBAM, anteroposterior CoM velocity, and vertical CoM velocity and acceleration. Because whole body motion is not sensed directly but instead arises from the integration of various sensory feedback signals, we also explored local sensory feedback contributions to the perception of locomotor disturbances. Local sensory feedback was estimated through kinematic analogues of vision (head angle), vestibular (head angular velocity), proprioception (i.e., sagittal hip, knee, and ankle angles), and somatosensation (i.e., anterior-posterior & mediolateral center-of-pressure, COP). We identified significantly higher perturbation induced deviations for perceived perturbations in sagittal-plane ankle angle. These results provide evidence for both whole-body feedback and ankle proprioception as important for the perception of subtle slip-like locomotor disturbances in young adults. Our interpretation is ankle proprioception is a dominant contributor to estimates of whole-body motion to perceive locomotor disturbances.

Subtle alterations in whole body mechanics during gait following anterior cruciate ligament reconstruction

BackgroundClinically, normalization of gait following anterior cruciate ligament reconstruction (ACLr) is defined as the absence of observable deviations. However, biomechanical studies report altered knee mechanics during loading response (LR); a time of double limb support and weight transfer between limbs. It is conceivable that subtle adjustments in whole body mechanics, including center of mass (COM) velocity and ground reaction force (GRF) peaks and timing, are present. Research questionThe purpose was to compare limb and whole body mechanics during LR of gait in the surgical and non-surgical limbs post-ACLr. MethodsAnterior and vertical COM velocity at initial contact; knee flexion range of motion, peak knee extensor moment, peak vertical and posterior GRF, minimum vertical COM position and maximum anterior and vertical COM velocity during LR were identified for twenty individuals 112 ± 17 days post-ACLr without observable gait deficits. To assess differences in timing of COM variables, coupling angles (vector coding) were calculated for multidirectional coordination of vertical and anteroposterior COM velocities and GRFs and categorized as in-phase, anti-phase, vertical phase, or anteroposterior phase coordination. Paired t-tests compared peaks between limbs; non-parametric Wilcoxon signed-rank tests compared coordination pattern frequency. ResultsLess knee range of motion (5.6 °), 30% smaller knee extensor moment, 11% smaller posterior GRF, and slower anterior COM velocity at initial contact (2%) and peak during LR (1.3%; all p < 0.05) were observed in the surgical compared to the non-surgical limb. For COM velocity coordination, lesser anti-phase (7.38%) and greater in-phase coordination (2.88%) were observed in the surgical limb. For GRF coordination, less in-phase coordination (1.94%) was observed in the surgical limb. SignificanceDifferences in coordination patterns, suggest that individuals post-ACLr make subtle adjustments in timing of whole body mechanics; particularly in COM velocity during gait. These adjustments are consistent with reduced sagittal plane loading in the surgical knee.

Biomechanical analysis of the timed up-and-go (TUG) test in children with and without Down syndrome

BackgroundThe timed up-and-go (TUG) test consists of multiple functional activities of daily living performed in a sequence, with the goal to complete the test as quickly as possible. Considering children with Down syndrome (DS) have been shown to take longer to complete the TUG test, it is imperative to identify which tasks are problematic for this population in order to individualize physical interventions. Research questionIs the biomechanical pattern of each functional task during the TUG test different between children with DS and typically developing (TD) children? MethodsThirteen children with DS and thirteen TD children aged 5–11 years old completed the TUG test. Kinematic data was captured using a Vicon motion capture system. We visually coded the TUG test into five phases: sit-to-stand, walk-out, turn-around, walk-in, and stand-to-sit. We focused on the center-of-mass (COM) movement in the sit-to-stand phase, spatiotemporal parameters in the walk-out phase, and intersegmental coordination in the turn-around phase. Results and significanceChildren with DS took longer to complete the entire test, as well as each of the five phases. During the sit-to-stand phase, children with DS produced smaller peak vertical COM velocity, medial-lateral COM excursion, and peak knee and hip extension velocity compared to TD peers. Children with DS walked at a slower velocity during the walk-out phase. Both groups demonstrated a similar intersegmental coordination pattern between the head, thorax, and pelvis during the turn-around phase although children with DS had slower average and peak angular velocity at the head, thorax, and pelvis. Our results suggest that children with DS were less able to anticipate transitioning between motor tasks and took longer to initiate motor tasks. Our TUG analysis provides the detailed insights to help evaluate individual motor tasks as well as the transition from one task to another for clinical populations.

Transition versus Continuous Slope Walking: Adaptation to Change Center of Mass Velocity in Young Men.

During continuous uphill walking (UW) or downhill walking, human locomotion is modified to counteract the gravitational force, aiding or impeding the body's forward momentum, respectively. This study aimed at investigating the center of mass (COM) and center of pressure (COP) velocities and their relative distance during the transition from uphill to downhill walking (UDW) to determine whether locomotor adjustments differ between UDW and UW. Fourteen participants walked on a triangular slope and a continuous upslope of 15°. The kinematics and COPs were obtained using a force plate and a motion capture system. The vertical velocity of the COM in the propulsion phase, the horizontal distance between the COM and COP at initial contact, and the duration of the subphases significantly differed between UDW and UW (all p < 0.05). Compared with the results of UW, longer durations and the deeper downward moving COM in the propulsion phase were observed during UDW (all p < 0.05). Additionally, a shorter horizontal distance between the COM and COP at initial contact was associated with a slower vertical COM velocity in the propulsion phase during UDW. The reduced velocity is likely a gait alteration to decrease the forward momentum of the body during UDW.

Investigating the anticipatory postural adjustment phase of gait initiation in different directions in chronic ankle instability patients

ObjectiveThe main objective of the present study was to analyze how supra spinal motor control mechanisms are altered in different directions during anticipatory postural phase of gait initiation in chronic ankle instability patients. It seems that supra spinal pathways modulate anticipatory postural adjustment phase of gait initiation. Yet, there is a dearth of research on the effect of chronic ankle instability on the anticipatory postural adjustment phase of gait initiation in different directions. MethodA total of 20 chronic ankle instability participants and 20 healthy individuals initiated gait on a force plate in forward, 30° lateral, and 30° medial directions. ResultsAccording to the results of the present study, the peak lateral center of pressure shift decreased in forward direction compared to that in other directions in both groups. Also, it was found that the peak lateral center of pressure shift and the vertical center of mass velocity decreased significantly in chronic ankle instability patients, as compared with those of the healthy individuals. ConclusionAccording to the results of the present study, it seems that chronic ankle instability patients modulate the anticipatory postural adjustment phase of gait initiation, compared with healthy control group, in order to maintain postural stability. These changes were observed in different directions, too.

Biomechanical characteristics of an anterior cruciate ligament injury in javelin throwing

PurposeThe purpose of this study was to understand the mechanism of an anterior cruciate ligament (ACL) injury in javelin throwing and javelin throwing techniques relevant to this ACL injury. MethodsThe patient in this study was an elite female javelin thrower who completed the first three trials and sustained a non-contact ACL injury on her left knee in the fourth trial of javelin throwing during a recent track and field meet. Three-dimensional kinematic data were collected in the injury and non-injury trials. The kinematic data of 52 male and 54 female elite javelin throwers were obtained from a javelin throwing biomechanical database. ResultsThe patient had greater forward center of mass velocity and less vertical center of mass velocity after the first 25% of the delivery phase in the injury trial compared to non-injury trials. The patient had less left knee flexion angle and angular velocity but similar left knee valgus and internal rotation angles during the first 21% of the delivery phase in the injury trial compared to non-injury trials. The video images showed an obvious tibia anterior translation at the 30% of the delivery phase in the injury trial. The left knee flexion angle and angular velocity at the time of the left foot landing and the maximal left knee flexion angle during the delivery phase were not significantly correlated to the official distance for 52 male and 54 female elite javelin throwers. ConclusionThe ACL injury in this study occurred during the first 30% of the delivery phase, most likely during the first 25% of the delivery phase. A stiff landing of the left leg with a small knee flexion angle was the primary contributor to this injury. Javelin throwers may have a soft left leg landing with a flexed knee, which may help them prevent ACL injuries without compromising performance.

Emotional influences on sit-to-walk in healthy young adults

The purpose of this study was to investigate influences of emotional feelings on sit-to-walk (STW). Eighteen healthy young adults performed STW while feeling sadness, anger, joy and neutral emotion. Emotions were elicited using an autobiographical memories task. We used an optoelectronic motion capture system to collect motion data and assessed kinematics of STW. Emotion-related differences in STW kinematics were consistent with differences in movement speed. Compared to neutral emotion, sadness was associated with increased STW duration and phase durations, decreased peak forward and vertical center-of-mass (COM) velocity, increased drop in forward COM velocity, and increased forward and vertical normalized jerk score (NJS). Anger and joy were associated with decreased STW duration and phase durations, increased peak forward and vertical COM velocity, decreased drop in forward COM velocity, and decreased forward and vertical NJS compared to neutral emotion. Findings suggest that emotional feelings affect movement speed, hesitation, and movement smoothness during STW.

Body composition and kinematic analysis of the grab start in youth swimmers.

The purposes of this study were to compare the kinematic variables in youth swimmers during the grab start between sexes and to investigate the relationship between body composition and kinematic variables of the participants. Six female (Mage = 13.71 ± 0.49 yrs) and seven male (Mage = 14.00 ± 1.07 yrs) swimmers participated in this study. All participants were required to perform grab start tests in random order (three trials by each participant), while the best attempt was analyzed. Nineteen kinematic parameters consisting of block time, flight time, flight distance, total time, total distance, horizontal and vertical displacement of the center of mass (CM) at take-off, horizontal and vertical displacement of the CM at entry, height of take-off and entry, relative height of take-off, horizontal and vertical velocity of the CM at take-off, horizontal and vertical velocity of the CM at entry, angle of take-off, angle of entry and angle of knee at block were analyzed. Out of the 19 evaluated kinematic parameters, a statistical difference between the female and male group was found only in the total distance. Therefore, both female and male groups are considered as only one group and merged after analyzing the results. Statistical analysis showed positive and negative correlations between horizontal / vertical velocity of CM at take-off and several kinematic variables (e.g. angle of entry (rhorizontal = −.868, p=.000 / rvertical = .591, p=.02), total distance (rhorizontal = .594, p=.02 / rvertical = .54, p=.04), and height of take-off (rvertical = .888, p=.000), respectively). On the other hand, positive and negative correlations were found between somatotype components and several kinematic variables (e.g. horizontal displacement of CM at entry (rendomorphy = −.626, p=.013), angle of entry (rmesomorphy = −.686, p=.005 / rectomorphy = .52, p=.047), total distance (rendomorphy = −.626, p=.012), and height of take-off (rendomorphy = −.633, p=.011 / rectomorphy = .515, p=.05)). In conclusion, results show that in order to be successful at grab start performance, a swimmer should target to get higher horizontal velocity of CM at take-off and optimize the angle of take-off so this movement form supplies more total distance to the swimmer. Coaches should consider improving start performance and adding start training to regular training sessions. Moreover, youth male and female swimmers can participate together in the grab start training.

Effects of seat–thigh contact on kinematics performance in sit-to-stand and trunk flexion tasks

It has been shown that thigh–seat contact-surface influences performance of isometric push-force with upper-limbs. The push-force performance is higher when subjects are seated with partial ischio-femoral / seat contact than when they are seated with full ischio-femoral contact. This was ascribed to greater pelvis and spine mobility induced by the short thigh–seat contact-surface. The present study tested the generalization of this hypothesis during movements involving body segment displacement, namely trunk flexion (TF) and sit-to-stand (STS) motor tasks. Both motor tasks were carried out in similar conditions to those implemented in the isometric push-force tasks, i.e. full ischio-femoral / seat contact (100-IFC) and short ischio-femoral contact (30-IFC, i.e. 30% of full ischio-femoral / seat contact).Results showed that kinematic performances (maximal antero-posterior and vertical center of mass velocity and maximal backward displacement of center of pressure) in both motor tasks were higher in 30-IFC than in 100-IFC. In the sit-to-stand task, time of seat-off is shorter in 30-IFC. As the subject's initial global posture was comparable across the experimental conditions, it can be discarded as a source of performance change. It is discussed that it is the enhanced pelvis mobility induced by the sitting condition which is responsible for the increase of motor performance in both trunk flexion and sit-to-stand tasks. Our results highlight the role of joint mobility in motor performance.

Controlling Propulsive Forces in Gait Initiation in Transfemoral Amputees

During prosthetic gait initiation, transfemoral (TF) amputees control the spatial and temporal parameters that modulate the propulsive forces, the positions of the center of pressure (CoP), and the center of mass (CoM). Whether their sound leg or the prosthetic leg is leading, the TF amputees reach the same end velocity. We wondered how the CoM velocity build up is influenced by the differences in propulsive components in the legs and how the trajectory of the CoP differs from the CoP trajectory in able bodied (AB) subjects. Seven TF subjects and eight AB subjects were tested on a force plate and on an 8 m long walkway. On the force plate, they initiated gait two times with their sound leg and two times with their prosthetic leg. Force measurement data were used to calculate the CoM velocity curves in horizontal and vertical directions. Gait initiated on the walkway was used to determine the leg preference. We hypothesized that because of the differences in propulsive components, the motions of the CoP and the CoM have to be different, as ankle muscles are used to help generate horizontal ground reaction force components. Also, due to the absence of an active ankle function in the prosthetic leg, the vertical CoM velocity during gait initiation may be different when leading with the prosthetic leg compared to when leading with the sound leg. The data showed that whether the TF subjects initiated a gait with their prosthetic leg or with their sound leg, their horizontal end velocity was equal. The subjects compensated the loss of propulsive force under the prosthesis with the sound leg, both when the prosthetic leg was leading and when the sound leg was leading. In the vertical CoM velocity, a tendency for differences between the two conditions was found. When initiating gait with the sound leg, the downward vertical CoM velocity at the end of the gait initiation was higher compared to when leading with the prosthetic leg. Our subjects used a gait initiation strategy that depended mainly on the active ankle function of the sound leg; therefore, they changed the relative durations of the gait initiation anticipatory postural adjustment phase and the step execution phase. Both legs were controlled in one single system of gait propulsion. The shape of the CoP trajectories, the applied forces, and the CoM velocity curves are described in this paper.

BIOMECHANICAL DIFFERENCES BETWEEN JUMPERS AND SPRINTERS ON LONG JUMP PERFORMANCE

INTRODUCTION The running long jump distance is determined by the height of the center of mass (CM) at takeoff and horizontal and vertical velocity of CM at takeoff. Hay (1993) reported a positive relationship between approach velocity and jumping distance over a wide range of jumping abilities. However, comparing with long jumpers, sprinters have similar approach velocity but many cannot archive a longer jumping distance. The aim of this study is to investigate the biomechanical characteristics between sprinters and long jumpers when performing the running long jump.