Body Center Of Mass Displacement Research Articles

Test-retest reliability of lower limb muscle strength, jump and sprint performance tests in elite female team handball players.

This study aimed to assess the reliability of lower limb muscle function (knee extensor/flexor peak torque, rate of torque development (RTD), impulse, and countermovement jump (CMJ) performance) and sprint performance (acceleration capacity). CMJ performance was evaluated on a force plate. MVIC, RTD and impulse variables were investigated using a portable isometric dynamometer and sprint performance was assessed with dual-beam photocells in elite female athletes. CMJ test variables maximal vertical jump height, peak and mean power, concentric work, and body center of mass displacement demonstrated good-to-excellent test-retest correlations between Test 1 and Test 2 (ICC ≥ 0.70, CWw-s = 3.4-11.0%). Peak MVIC torque for the knee extensors and flexors demonstrated excellent test-retest correlations (both ICC = 0.84) along with CVw-s values of 6.8 and 6.0%, respectively. Late-phase (0-100ms, 0-200ms) RTD for the knee flexors demonstrated excellent test-retest correlations (ICC = 0.89-0.91, CVw-s = 4.8-8.5%). Sprint times at 10- and 20-m demonstrated excellent test-retest reproducibility (ICC = 0.83 and ICC = 0.90, respectively) with CVw-s values of 1.9 and 1.5%. For 5-m sprint times, test-retest reproducibility was good (ICC = 0.71) with CVw-s of 2.8%. Sprint testing performed while dribbling a handball improved (p < 0.05) from test to retest at 5-, 10- and 20-m. In conclusion, the force plate, the mobile isometric dynamometer, and dual-beam photocells provide reproducible tools for field-based testing of countermovement jump performance, knee extensor and flexor strength and sprint performance.

Dual vs single force plate analysis of human drop jumping

The aim was to develop a Drop Jump (DJ) protocol on dual force plate recordings (Dual Force Plate method: DFPM) to assess lower limb power production and quantify impact loading, and range of body center of mass (BCM) excursion during human DJ, and to examine if single-plate analysis (Reverse Integration Method: RIM) was a valid alternative. Nineteen male subjects performed DJs from an elevated platform (48 cm). Kinematic (BCM displacement and velocity, rebound jump height) and kinetic (BCM power, work, rate of force development (RFD), lower limb stiffness (LLS)) variables were obtained by force plate recording during the drop take-off phase (DFPM) and rebound phase (RIM, DFPM). DFPM and RIM did not differ at the group level for any outcome parameter. However, large intra-individual differences in BCM displacement were observed between DFPM and RIM (CV 9-10%) as well as for rebound jump height, LLS, and work performed on BCM (CV 9.8-14%). A majority of the remaining variables demonstrated low intra-individual variability between the two methods (r= 0.73-0.96, CV 1-5%). In conclusion, No systematic differences were revealed between DFPM and RIM, suggesting that RIM is a valid approach for assessing DJ performance. Substantial between-method intra-individual variability was noted for key outcome parameters.

Effects of constrained arm swing on vertical center of mass displacement during walking

The purpose of this study was to determine the effects of constraining arm swing on the vertical displacement of the body's center of mass (COM) during treadmill walking and examine several common gait variables that may account for or mask differences in the body's COM motion with and without arm swing. Participants included 20 healthy individuals (10 male, 10 female; age: 27.8±6.8 years). The body's COM displacement, first and second peak vertical ground reaction forces (VGRFs), and lowest VGRF during mid-stance, peak summed bilateral VGRF, lower extremity sagittal joint angles, stride length, and foot contact time were measured with and without arm swing during walking at 1.34m/s. The body's COM displacement was greater with the arms constrained (arm swing: 4.1±1.2cm, arm constrained: 4.9±1.2cm, p<0.001). Ground reaction force data indicated that the COM displacement increased in both double limb and single limb stance. However, kinematic patterns visually appeared similar between conditions. Shortened stride length and foot contact time also were observed, although these do not seem to account for the increased COM displacement. However, a change in arm COM acceleration might have contributed to the difference. These findings indicate that a change in arm swing causes differences in vertical COM displacement, which could increase energy expenditure.

Metabolic Cost, Mechanical Work, and Efficiency During Normal Walking in Obese and Normal-Weight Children

Purpose: This study aimed to investigate the influence of childhood obesity on energetic cost during normal walking and to determine if obese children choose a walking strategy optimizing their gait pattern. Method: Sixteen obese children with no functional abnormalities were matched by age and gender with 16 normal-weight children. All participants were asked to walk along a nearly circular track 30 m in length at a self-selected speed. Spatiotemporal data, kinematics, and ground reaction force were collected during walking using a three-dimensional motion analysis system. Metabolic cost was collected by a portable gas analyzer simultaneously. Results: The mechanical energy expenditure (MEE) was 72.7% higher in obese children than in normal-weight children. The net metabolic cost was 65.7% higher in obese children. No difference was found in the metabolic rate (J·kg− 1·m− 1), normalized MEE (J·kg− 1·m− 1) and mechanical efficiency between the obese and normal-weight groups. The obese children walked with a 0.15 m/s slower walking speed, 10.0% shorter cadence, and 30.9% longer double-support phase compared with normal-weight children. In addition, no differences were found in the mediolateral and vertical body center of mass displacement. Conclusion: Body mass played a dominant role in the total metabolic and mechanical cost per stride. Obese children may adopt a walking strategy to avoid an increase in the metabolic cost and the mechanical work required to move their excess body mass.

Kinematic and Kinetic Analysis of the Forward Lunge During Four External Load Conditions

PURPOSE: To determine the effects of external load on ankle, knee and hip joint kinematics and kinetics during the forward lunge METHODS: Sixteen recreationally active college-aged adults (8 men, 8 women) completed forward lunges under four external load conditions, 0% (control), 12.5%, 25%, and 50% body mass, in a between-subject randomized order. Three dimensional kinematics and ground reaction force data were used to quantify ankle (AN), knee (KN) and hip (HI) kinematics, net joint extensor moment impulse (NJMI) and eccentric (ECC) and concentric (CON) work during the interval when the stepping limb (dominant limb) was in contact with the ground. Additionally, four lunge characteristics, repetition time, stepping limb contact time and vertical and anterior total body center of mass displacement, were calculated. RESULTS: No significant (P>.05) condition effects were realized for the lunge characteristics or peak flexion angles. For NJMI, post hoc analyses of a significant condition by joint interaction (P<.001) revealed HI to be dominant across all conditions with AN>KN for 25 and 50. The addition of weight had no significant effect on KN NJMI, while significant AN & HI NJMI increases were not evident until 25% body mass was added (0 & 12.5<25<50). Similar to NJMI, a significant condition by joint interaction (P<.001) was revealed with the hip performing significantly greater work for both phases (ECC: HI>AN and KN; CON: < HI>KN>AN). Within joint comparisons revealed AN CON=ECC, KN CON>ECC, and HI ECC>CON. Additionally, a significant phase by joint interaction (P<.001) was demonstrated with the hip producing approximately 50% of the total work across all conditions. Although the additional weight prompted significant work increases at the HI (0 & 12.5<25<50) and AN (00<50) and no significant KN changes, the proportion of total work contributed by each joint remained nearly constant. CONCLUSION: The forward lunge is HI extensor dominant exercise. The addition of external weight prompted no significant changes in KN NJMI or work. These results can assist clinicians in deciding whether the characteristics of the forward lunge match a patient exercise needs during rehabilitation and performance enhancement programs.

Changes in power and force generation during coupled eccentric–concentric versus concentric muscle contraction with training and aging

Age-related decline in maximal concentric muscle power is associated with frailty and functional impairments in the elderly. Compared to concentric contraction, mechanical muscle output is generally enhanced when muscles are rapidly pre-stretched (eccentric contraction), albeit less pronounced with increasing age. Exercise has been recommended to prevent loss of muscle power and function and recent guidelines indicate training program for increasing muscle power highly relevant for elderly subjects. This study examined the differences in muscle power, force and movement pattern during concentric-alone and coupled eccentric-concentric contraction and selected functional motor performances before and after 36-week multicomponent training including aerobic, strength, balance, flexibility and coordination components in elderly males. Vertical force, excursion, velocity, power and acceleration of the body center of mass were measured in two standardised vertical jumps (squatting jump, SQJ; countermovement jump, CMJ). Pre-stretch enhancement during CMJ did not improve performance [i.e., no enhanced maximal muscle power (Ppeak) and jump height (JH)] compared to concentric-alone muscle contraction (SQJ). Nevertheless, pre-stretch enhancement occurred as for similar SQJ and CMJ maximal performance, elderly people employed lower mechanical work, higher mean muscle power (Pmean), shorter concentric phase duration and shorter body center of mass displacement during CMJ. Post training, CMJ Ppeak, Pmean and JH increased in training group (P<0.05) while Ppeak and JH decreased in control group during the CMJ and SQJ (P<0.05). In conclusion, long-term training counteracted the age-related decline in muscle power and functional performance observed in the control subjects, while substantial gains in muscular performance were observed in the trained elderly.

Postural responses triggered by multidirectional leg lifts and surface tilts

The aim of the present study was to investigate the relationship between proactive and reactive components of postural control. We contrasted the kinematic and electromyographic (EMG) responses to multidirectional voluntary leg lifts with those elicited by unexpected surface tilts. In particular, we addressed the role of trunk stabilization following either a voluntary or forced weight shift from double to single limb support. Nine young female subjects stood with a standing posture of 45 degrees toe-out and their arms abducted to shoulder level. On the experimenter's signal, subjects either (1) lifted one leg as fast as possible in one of six directions (R/L side, R/L diagonal front, R/L diagonal back) to a height of 45 degrees or (2) maintained standing as the support surface tilted at a rate of 53 degrees /s to a height of 10 degrees in one of six directions (R/L-up, R/L diagonal toes-up, R/L diagonal toes-down). For both tasks, our results showed that the center of pressure (COP) displacement began before or in conjunction with displacement of the center of mass (COM), after which the COP oscillated about the horizontal projection of the COM. In addition, the muscles were recruited in a distal-to-proximal sequence, either in anticipation of the voluntary leg lift or in response to the sudden surface tilt. Thus, the COP was being used dynamically to control displacement of the COM. The axial postural strategy comprising head, trunk, and pelvis movements was quantified by means of principal component analysis. More than 95% of the variance in the data could be described by the first two eigenvectors, which revealed specific coordination patterns dominated by pelvis rotation in one direction and head/trunk rotation in the opposite direction. Unexpected surface tilting elicited an automatic response strategy that focused on controlling the orientation of the head and trunk with respect to the vertical gravity vector while trunk verticality was compromised for movement generation and the recovery of postural equilibrium during leg lifting. In conclusion, regardless of the type (voluntary versus involuntary) or direction of perturbation, the strategy employed by the central nervous system to control the body COM displacement concerns mainly trunk stabilization.

Total body centre of mass displacement estimated using ground reactions during transitory motor tasks: application to step ascent

A double integration technique is presented that estimates whole body centre of mass (CoM) displacement from signals of a single force platform, compensating for the drift and low frequency noise inherent in the signals. The technique is composed of two different integration techniques, which may also be used separately, and is applied to transitory motor tasks with known initial and final conditions such as step ascent and descent, single step, etc. First, the lowest frequencies within the force platform signals and considered not to be associated with actual movement are filtered out. Second, a regular and a time-reversed double integration are performed and weighted against each other. The technique’s accuracy was assessed using computer generated force platform signals that were artificially perturbed. Experimental data were used to compare the estimated CoM displacement to that obtained from a regular double integration and from segmental analysis performed on stereophotogrammetric data. It was shown that the proposed technique’s CoM displacement estimates were more repeatable and up to 50% more accurate than those of a regular double integration. Moreover, the CoM displacement estimated using a single force platform and the proposed technique was found to be not statistically different from that obtained with more demanding measurement and processing techniques such as stereophotogrammetry and segmental analysis.

Postural control during a sit-to-stand task in individuals with mild Parkinson's disease.

Individuals with Parkinson's disease (PD) typically have difficulty rising from a chair. A major contributing factor may be altered anticipatory postural control; this hypothesis has been fueled by reports of altered function of the supplementary motor area in PD, an area linked to the preparation of movements. This study tested the hypothesis that individuals with PD would exhibit altered anticipatory postural control which would include a reduced preparatory hip flexion and decreased forward displacement of the COM prior to lift-off of the buttocks from the chair. Ten male subjects with PD and ten male age-matched controls were instructed to rise from a chair without the use of their arms at their comfortable pace on two separated days during on and off-medication states. Body movements were recorded with an optoelectronic device, in addition to forces under the buttocks and each foot to calculate lower extremity joint angles, joint movements and net body centre of mass displacement (COM). The sit-to-stand (STS) duration was the same for the PD-on and controls, but greater for the PD-off group. The PD groups (on and off) used a hip flexion strategy (greater preparatory hip flexion displacement and forward COM displacement, reduced knee extensor moments) compared to the controls. Contrary to predictions, subjects with PD exaggerated, rather than reduced, the movement preparation of the STS using a hip flexion strategy. Possible underlying causes of this flexion strategy could include compensation for poor lower extremity muscle strength and a need for greater postural stability during the lift-off phase.

Evaluation of Four Vertical Jump Tests: Methodology, Reliability, Validity, and Accuracy

Vertical jump performance tests can give considerably different results, even when different methods are used to analyze the same jump trial from the same subject. To evaluate and compare 4 different methods commonly used to measure vertical jump performance, 52 physically active men each performed 5 maximal vertical jumps. Kinetic and kinematic data were used to analyze each trial using the 4 methods: a criterion test based on body center of mass displacement (VJPT), 2 methods based on vertical takeoff velocity as calculated from the force platform, and 1 method based on time in the air (JUMPAIR). All 4 methods showed excellent reliability (R > .97). Using VJPT as the criterion, the other 3 methods showed excellent coefficients of validity (R > .95) but poor accuracy: The obtained vertical jump height scores were statistically different among all methods (p < .01). JUMPAIR is considered a relatively simple and inexpensive method to obtain valid and reliable measures of vertical jump performance without an arm swing, provided the appropriate adjustments are made to the jump results.