Propulsive Impulse Research Articles

Hierarchical Optimization for Control of Robotic Knee Prostheses Toward Improved Symmetry of Propulsive Impulse.

Automatically personalizing complex control of robotic prostheses to improve gait performance, such as gait symmetry, is challenging. Recently, human-in-the-loop (HIL) optimization and reinforcement learning (RL) have shown promise in achieving optimized control of wearable robots for each individual user. However, HIL optimization methods lack scalability for high-dimensional space, while RL has mostly focused on optimizing robot kinematic performance. Thus, we propose a novel hierarchical framework to personalize robotic knee prosthesis control and improve overall gait performance. Specifically, in this study the framework was implemented to simultaneously design target knee kinematics and tune 12 impedance control parameters for improved symmetry of propulsive impulse in walking. In our proposed framework, HIL optimization is used to identify an optimal target knee kinematics with respect to symmetry improvement, while RL is leveraged to yield an optimal policy for tuning impedance parameters in high-dimensional space to match the kinematics target. The proposed framework was validated on human subjects, walking with robotic knee prosthesis. The results showed that our design successfully shaped the target knee kinematics as well as configured 12 impedance control parameters to improve propulsive impulse symmetry of the human users. The knee kinematics that yielded best propulsion symmetry did not preserve the normative knee kinematics profile observed in non-disabled individuals, suggesting that restoration of normative joint biomechanics in walking does not necessarily optimize the gait performance of human-prosthesis systems. This new framework for prosthesis control personalization may be extended to other wearable devices or different gait performance optimization goals in the future.

A Review of Biomechanical and Physiological Effects of Using Poles in Sports.

The use of poles in sports, to support propulsion, is an integral and inherent component of some sports disciplines such as skiing (cross-country and roller), Nordic walking, and trail running. The aim of this review is to summarize the current state-of-the-art of literature on multiple influencing factors of poles in terms of biomechanical and physiological effects. We evaluated publications in the subfields of biomechanics, physiology, coordination, and pole properties. Plantar pressure and ground reaction forces decreased with the use of poles in all included studies. The upper body and trunk muscles were more active. The lower body muscles were either less active or no different from walking without poles. The use of poles led to a higher oxygen consumption (VO2) without increasing the level of perceived exertion (RPE). Furthermore, the heart rate (HR) tended to be higher. Longer poles reduced the VO2 and provided a longer thrust phase and greater propulsive impulse. The mass of the poles showed no major influence on VO2, RPE, or HR. Solely the activity of the biceps brachii increased with the pole mass.

Influence of unilateral and bilateral knee extension fatigue protocols on inter-limb asymmetries assessed through countermovement jumps

ABSTRACT This study explores the sensitivity of jump type (unilateral and bilateral) and output variable (mean force, propulsive impulse, and jump height) to detect the changes in inter-limb asymmetries induced by unilateral and bilateral fatigue protocols. Thirty-eight individuals performed two testing sessions that consisted of (I) nine “pre-fatigued” countermovement jumps (CMJs; three bilateral and six unilateral [three with each leg]), (II) fatigue protocol and (III) nine “post-fatigued” CMJs. The testing sessions only differed in the fatigue protocol (five sets to failure against the 15-repetition maximum load using either the unilateral or bilateral knee extension exercise). The magnitude of all CMJ-derived variables (mean force, impulse, and jump height) decreased following both unilateral (p ≤ 0.002) and bilateral fatigue protocols (p ≤ 0.018). However, only unilateral protocol accentuated inter-limb asymmetries, which was detected for all variables during the unilateral CMJ (from −4.33% to −2.04%; all p < 0.05) but not during the bilateral CMJ (from −0.64% to 0.54%; all p > 0.05). The changes in inter-limb asymmetries following the unilateral and bilateral fatigue protocols were not significantly correlated between the unilateral and bilateral CMJs (r s ≤ 0.172). The unilateral CMJ should be recommended for the testing purposes over the bilateral CMJ due to its greater sensitivity to detect the selective effects of fatigue.

Development and Reliability of Countermovement Jump Performance in Youth Athletes at Pre-, Circa- and Post-Peak Height Velocity

The purpose of this study was to determine the intrasession reliability of countermovement jump (CMJ) braking and propulsive phase variables in youth athletes. Thirty youth athletes between the age of 10- and 16-years volunteered to take part in this study. All participants performance 3 CMJ trials on a force platform. Thirteen of 16 CMJ variables were found to have acceptable absolute reliability in the pre-PHV group (CV% = 3.51-9.96) whilst the circa-PHV group contained 10 variables demonstrating acceptable absolute reliability (CV% = 2.37-9.67). Almost all variables (14 out of 16) in the post-PHV group were found to have acceptable absolute reliability (CV% = 2.59-9.61). Mean and peak braking RFD displayed poor absolute reliability in all maturity groups (CV% = 10.89-21.55). Time to take-off, braking and propulsive phase time and propulsive impulse demonstrated the largest differences between pre- and circa-PHV groups (p &lt; 0.005; d &gt; 0.95). Braking phase time, peak and mean braking force, mean braking power and RSImod demonstrated the biggest differences between the circa- and post-PHV groups (p &lt; 0.001; d &gt; 1.81). The poorest reliability scores were found in the circa-PHV group, demonstrating the need for additional familiarisation at this stage of maturity.

Different functional networks underlying human walking with pulling force fields acting in forward or backward directions

Walking with pulling force fields acting at the body center of mass (in the forward or backward directions) is compatible with inclined walking and is used in clinical practice for gait training. From the perspective of known differences in the motor strategies that underlie walking with the respective force fields, the present study elucidated whether the adaptation acquired by walking on a split-belt treadmill with either one of the force fields affects subsequent walking in a force field in the opposite directions. Walking with the force field induced an adaptive and de-adaptive behavior of the subjects, with the aspect evident in the braking and propulsive impulses of the ground reaction force (difference in the peak value between the left and right sides for each stride cycle) as parameters. In the parameters, the adaptation acquired during walking with a force field acting in one direction was transferred to that in the opposite direction only partially. Furthermore, the adaptation that occurred while walking in a force field in one direction was rarely washed out by subsequent walking in a force field in the opposite direction and thus was maintained independently of the other. These results demonstrated possible independence in the neural functional networks capable of controlling walking in each movement task with an opposing force field.

Acclimatization of force production during walking in persons with Parkinson's disease

Individuals with Parkinson’s disease walk slowly, with short strides resulting in decreased mobility. Treadmill walking assessments are utilized to understand gait impairment in persons with Parkinson’s disease and treadmill-based interventions to mobility have become increasingly popular. While walking on a treadmill, there is a reported initial acclimatization period where individuals adjust to the speed and dynamics of the moving belt before producing consistent walking patterns. It is unknown how much walking time is required for individuals with Parkinson’s disease to acclimate to the treadmill. We investigated how spatiotemporal parameters and ground reaction forces changed during treadmill acclimatization. Twenty individuals with idiopathic Parkinson’s (15 Males, 5 Females) walked for a five-minute treadmill session on an instrumented treadmill while motion capture data were collected. The measures of interest included ground reaction force measures (peak propulsive force, peak braking force, propulsive impulse, and braking impulse) and spatiotemporal measures (stride length, stride time, or double support time). Analyses demonstrated significantly increased propulsive impulse (p <.001) after the first minute, with no significant difference for the remaining minutes (p ≥ 0.395). There were no significant changes in the spatiotemporal measures (P =.065). These results quantify the stabilization of ground reaction force during the treadmill acclimatization period. Based on our findings, if steady-state gait is desired, we recommend participants walk for at least two minutes before data collection. Future clinical investigations should consider ground reaction force as sensitive parameters for evaluating gait in persons with Parkinson’s disease in treadmill-based assessments or interventional therapies.

Effect of a High-Intensity Handball-Specific Fatigue Protocol Focused on the Leg Contralateral to the Throwing Arm on Interlimb Asymmetries.

Janicijevic, D, Pérez-Castilla, A, Miras-Moreno, S, Ortega-Becerra, M, Morenas-Aguilar, MD, Smajla, D, Sarabon, N, and García-Ramos, A. Effect of a high-intensity handball-specific fatigue protocol focused on the leg contralateral to the throwing arm on interlimb asymmetries. J Strength Cond Res 37(7): 1382-1389, 2023-This study aimed to elucidate which countermovement jump (CMJ) variant (unilateral or bilateral) is more sensitive to detect the decrement in kinetic CMJ-derived variables of the leg more actively involved in a handball-specific fatigue protocol. Seventeen female handball players (age: 20.6 ± 2.5 years) performed a fatigue protocol consisting of 8 repetitions of the following circuit separated by 10 seconds: 10 m sprint, 180° change of direction with the leg contralateral to the throwing arm, 10 m sprint with ball reception at 7 m, and handball throw preceded by a jump over a 40 cm hurdle with the leg contralateral to the throwing arm. Before and after the fatigue protocol, 6 unilateral CMJs (3 with each leg) and 3 bilateral CMJs were performed on a dual Kistler force platform (model 9260AA6). Bilateral CMJ height was reduced by 5.4% after the fatigue protocol (p < 0.001). However, the fatigue protocol did not promote any significant change in peak force, mean force, and propulsive impulse or in their asymmetry values (17 of 18 comparisons). The decrement of 6.1% during the unilateral CMJ in the propulsive impulse developed by the leg ipsilateral to the throwing arm (less involved in the fatigue protocol) was the only variable that reached statistical significance (p = 0.038). The pre-post fatigue changes in asymmetry values presented negligible correlations between both CMJ variants (rs = 0.01 to -0.19). These results suggest that neither unilateral nor bilateral CMJs are able to detect changes in interlimb asymmetries after a high-intensity handball-specific fatigue protocol.

Cross-Sectional Analysis of Ground Reaction Forces During Jumps in Professional Baseball Players.

Amonette, WE, Vazquez, J, and Coleman, AE. Cross-sectional analysis of ground reaction forces during jumps in professional baseball players. J Strength Cond Res 37(8): 1616-1622, 2023-This study described and compared force plate kinetics in major (MLB) and minor (MiLB) baseball players while performing vertical jumps (CMVJ), squat jumps (SSJ), and depth jumps (DJ). Second, comparisons were made between playing positions. Data were collected on 101 professional baseball players. Peak force, eccentric and concentric impulses, peak power, and jump height were determined from each test. Reactive strength index was computed from the DJ. Data were compared using factorial analysis of variances, alpha was set at p ≤ 0.05, and effect sizes were reported using Cohen's d . During CMVJ, MiLB players generated more force ( p = 0.04; d = 0.48), power ( p = 0.02; d = 0.42), and jumped higher ( p = 0.03; d = 0.32) than MLB players. Pitchers generated higher propulsive impulses than catchers ( p = 0.004; d = 0.93). Outfielders generated more power ( p = 0.02; d = 0.98) and jumped higher ( p = 0.049; d = 1.08) than catchers and infielders ( p = 0.025; d = 0.32). Minor league baseball players generated more force ( p = 0.002; d = 0.62), power ( p = 0.001; d = 0.84), and jumped higher ( p = 0.02; d = 0.48) than MLB players in SSJ. No differences were observed by position in SSJ. Minor league baseball players jumped higher than MLB players in the DJ ( p = 0.01; d = 0.57) and outfielders generated more power in the DJ than pitchers ( p = 0.05; d = 0.43) and catchers ( p = 0.007; d = 1.61). Reactive strength index was greater in outfielders compared with catchers ( p = 0.01; d = 1.20). These data indicate that MiLB players were generally more powerful and jumped higher than MLB players in the 3 performance tasks. The difference observed by playing level were likely related to physical preparedness at the beginning of spring training; positional differences were the result of athletic skill sets required for tactical excellence at each position.

Frontal Plane Neurokinematic Mechanisms Stabilizing the Knee and the Pelvis during Unilateral Countermovement Jump in Young Trained Males.

(1) The unilateral countermovement jump is commonly used to examine frontal plane kinetics during unilateral loading and to identify athletes with an increased risk of lower limb injuries. In the present study, we examined the biomechanical mechanisms of knee and pelvis stabilization during unilateral vertical jumps. (2) Healthy males performed jumps on a force plate with the dominant leg. Activity of the dominant-side gluteus medius and the contralateral-side quadratus lumborum and erector spinae muscles was recorded with surface EMG. The EMG data were normalized to the EMG activity recorded during maximal voluntary isometric hip abduction and lateral trunk flexion contractions. During jumps, the propulsive impulse was measured, and the pelvis and thigh segmental orientation angles in the frontal plane were recorded and synchronized with the EMG data. (3) The magnitude of knee valgus during the jump did not correlate with hip abduction force, but negatively correlated with gluteus medius activity. This correlation became stronger when gluteus medius activity was normalized to hip abduction force. Propulsive impulse did not correlate with any neuromechanical measurement. (4) We conclude that hip abduction force itself does not regulate the magnitude of knee valgus during unilateral jumps; rather, the gluteus medius should be highly activated to increase frontal-plane knee joint stability.

Comparison of the Reliability of Four Different Movement Thresholds When Evaluating Vertical Jump Performance.

Analyzing vertical jumps performed on a force plate can be useful for the strength and conditioning professional in managing neuromuscular fatigue. The purpose of this study was to compare different movement thresholds when analyzing countermovement (CJ) and squat jump (SJ) performance. Twenty-one college-aged participants (9 female, 12 male) performed five CJs and five SJs. Movement initiation was identified when the vertical ground reaction force (VGRF) deviated five standard deviations (5SD), four standard deviations, (4SD), 2.5% of system weight (2.5%SW), and 10% of system weight (10%SW) from their starting position. For CJs, movement was determined when the VGRF deviated either above or below these thresholds (5SDAB, 4SDAB, 2.5%SWAB, 10%SWAB) and was compared to when VGRF deviated below these thresholds (5SDB, 4SDB, 2.5%SWB, 10%SWB) in terms of peak force (Fmax), net impulse (netIMP), braking impulse (brIMP), propulsive impulse, jump height (JHT), peak power (Pmax), peak velocity (Vmax), and RSImod. For SJs, movement was determined when VGRF initially rose above these thresholds (5SD, 4SD, 2.5%SW, and 10%SW) for Fmax, netIMP, JHT, and Vmax. Significant differences were observed among several methods except for Fmax. However, these differences were small. All CJ measures demonstrated good-to-excellent relative reliability (ICC: 0.790-0.990) except for netIMP for 2.5%SWAB (ICC: 0.479). All methods demonstrated good absolute reliability as measured by percent coefficient of variation (CV%) except brIMP and RSImod. This may be due to instructions given to each jumper as well as skill level. For SJs, no differences in Fmax or netIMP were found across all methods. Small differences were seen for JHT, Pmax, and Vmax across several methods. All methods produced acceptable CV% (&lt;10%) and excellent ICCs (0.900-0.990). However, some jumpers produced CV% that was greater than 10% when determining JHT for 5SD, 4SD, and 2.5%SW methods. This could be due to our method of obtaining system weight. Based on our findings, we recommend using the 10%SW method for assessing SJ performance on a force plate.

Laser ablation induced impulse study for removal of space debris mission using small satellite

In recent years, many plans have arisen for building constellations in low Earth orbit, some of which have already provided commercial services. The number of satellites that form these constellations will exceed 10^4, and a number of these could become space debris due to accidental failure, leading to serious problems for human activities in space. Laser ablation-induced propulsion achieved by remote irradiation from the service spacecraft has been proposed as one effective method to remove such space debris and it involves effectively generating a propulsion impulse from a laser. Because most of the high-power lasers currently utilized in space applications are Nd:YAG lasers, in this study, we evaluate the characteristics of second harmonic generation (SHG), which can be generated using nonlinear crystals. The momentum coupling coefficient may be dependent on the irradiated laser wave length which has a significant difference in the ablation process such as plasma generation and heating. These effects have been investigated using an impulse measurement instrumental setup with a KD*P nonlinear crystal. As an efficient impulse generation method, the irradiation of the fundamental and SHG beams of the Nd:YAG laser at the same point was found to be more effective than the fundamental beam with the same total energy. SHG does not require additional power-consuming equipment such as additional exciters or amplifiers, but requite temperature-controlled nonlinear crystals, and impulses can be increased with minimal additional power. It turned out to be advantageous for space applications, which will require minimum power operation. Additionally, we found an additional nonlinear laser-induced impulses through the interaction of the beams.

The Effect Of Pronated Versus Non-pronated Feet On Jump Parameters In Female Collegiate Athletes

Foot pronation is characterized by a reduced or absent medial longitudinal arch. The presence of pronated feet is thought to contribute to alterations in ankle-foot complex and hip and knee joint kinematics. There is little evidence analyzing the role of pronated feet in jump performance. PURPOSE: To investigate the effect of pronated (PR) and non-pronated (NP) feet on jump performance. METHODS: Thirty female collegiate athletes (20.2 ± 1.3 yrs, 70.4 ± 12.2 kg, 172.9 ± 8.8 cm, BMI 23.4 ± 2.6 kg/cm2) from various sports completed a pre-screening questionnaire and 7 subjects were excluded due to a history of lower-limb injury within the past year. Twenty-three subjects underwent ankle-foot evaluation and drop-countermovement jump (CMJ) testing using a force plate and integrated software. The subjects were categorized as either NP (n = 8) or PR (n = 15) based on the navicular drop (ND) test. Participants with ND > 10 mm were classified as having PR feet. Subjects with at least one foot classified as pronated formed the PR group while those with neither foot classified as pronated formed the NP group. Subjects performed a total of 9 drop-CMJ tests [3 bilateral (BL), 3 unilateral left limb (LL), 3 unilateral right limb (RL)]. RESULTS: With respect to BL CMJ performance, no significant differences (p > 0.05) between groups were observed for peak force (2412 ± 751 vs 2172 ± 467 N), propulsive impulse (340 ± 86 vs 339 ± 55 N/s), rate of power development (28009 ± 18705 vs 20270 ± 16647 W/s), take-off velocity (8.65 ± 1 vs 8.37 ± 0.6 ft/s) and peak positive power (3206 ± 795 vs 2966 ± 869 W). Significant correlations (p ≤ 0.05) between body weight (BW) and jump performance were observed for BL peak force (r = 0.59), RL peak force (r = 0.74), BL propulsive impulse (r = 0.83). LL propulsive impulse (r = 0.74), RL propulsive impulse (r = 0.80), BL peak positive power (r = 0.83), LL peak positive power (r = 0.80), RL peak positive power (r = 0.83). CONCLUSIONS: We observed no differences between the groups on BL jump performance. However, moderate to strong positive correlations between BW and CMJ performance were observed. The observed correlations between BW and CMJ performance may reflect an underlying relationship between lean mass and CMJ performance. Further investigation of the effect of foot posture on other components of sport performance is needed.

Force plate analysis of ground reaction forces in relation to gait velocity of healthy Beagles

To evaluate changes in ground reaction forces (GRFs) in relation to gait velocity using 2 force plates (FPs) for healthy Beagles. 18 healthy Beagles were included (body weight, 10.45 ± 1.28 kg; age, 26 ± 11 months). Ten GRF parameters were measured at three gait velocities (walk, 0.9 to 1.2 m/s; trot 1, 1.6 to 2.0 m/s; and trot 2, 2.1 to 2.5 m/s): peak lateral force (PLF), peak medial force (PMF), lateral impulse (LI), medial impulse (MI), peak propulsive force (PPF), peak braking force (PBF), propulsive impulse (PI), braking impulse (BI), peak vertical force (PVF), and vertical impulse (VI). As velocity increased, the PVF of all limbs increased, the VI of all limbs decreased, and the PPF of the forelimbs increased. At all velocities, PBF and BI were significantly higher than the PPF and PI in forelimbs; however, PBF and BI were significantly lower than the PPF and PI in hindlimbs. There were no significant differences in the PLF, PMF, LI, and MI of the forelimbs and hindlimbs among all velocities. The PLF was significantly higher than the PMF of forelimbs during trot 1 and trot 2. These results may be useful when comparing healthy Beagles with diseased ones when premorbid data are not available. Because the forelimbs are mainly responsible for the braking force, it is suggested that weight bearing is more stable in the forelimbs than in the hindlimbs, which are mainly responsible for the propulsive force, and that a greater force is generated laterally than medially during trot.

Energy Flow And Impulse Predictors Of Bat Speed During Baseball Tee Batting Using The Least Absolute Shrinkage And Selection Operator (LASSO) Regression

Unlike baseball pitching, there currently is limited research on baseball batting to explain which biomechanical factors can best predict bat speed. Furthermore, an observational analysis has not been conducted to understand how ground reaction forces (GRF) and energy flow through the kinetic chain influence bat speed. PURPOSE: To understand how energy is generated, absorbed, and transferred through the kinetic chain and identify the best model of GRF and energy flow predictors of bat speed in the baseball swing. METHODS: Nine collegiate baseball players performed tee batting while their movements and GRF were recorded using a 3D motion capture system and two force platforms. Bat speed was recorded using an inertial measuring unit (IMU) sensor fixed to the knob of the bat. Biomechanical metrics were extracted from a total of 33 swings for energy flow and impulse analysis. A total of 27 energy flow and impulse discrete variables were inputted into a regression based on the LASSO regularization to determine the best model that predicts bat speed. Model performance was assessed using the root mean square error (RMSE) in units of m/s and an ordinary least squares (OLS) coefficient of determination. RESULTS: Players hit off the tee with a measured bat speed of 30.4 ± 1.3 m/s. The LASSO model predicted bat speed with a RMSE of 1.0 m/s (r2 = .597, p < .001) and included the back leg vertical impulse, lead leg propulsive impulse, lumbosacral (L5S1) energy absorption and transfer in the acceleration phase, and the lead hip energy absorption during follow-through. CONCLUSION: This study provides evidence that suggests that the key factors of determining bat speed during tee batting involve the momentum generated by the legs and the energy absorbed by the L5S1 and lead hip joints along with the energy transfer to and from the pelvis through these joints during the phases immediately before and after ball contact.

The Influence of Competitive Level on Stretch-Shortening Cycle Function in Young Female Gymnasts.

This cross-sectional study investigated how stretch-shortening cycle (SSC) function and kinetic variables differed between young female gymnasts of varying competitive levels. Drop jump (DJ) force–time profiles were examined in 118 female gymnasts, sub-divided by competitive level (n = 21 recreational, n = 41 regional and n = 50 elite). DJ force–time data were analyzed to calculate performance and kinetic variables. Participants’ SSC function was categorized as poor, moderate, or good, depending on the presence of an impact peak and spring-like behavior. A high proportion of gymnasts across each group were categorized as having “good” or “moderate” SSC function (i.e., >94.8%), with a trend of increasingly better SSC function observed with competitive level. Significant differences in reactive strength index, contact time, time of landing peak force, relative propulsive peak force, impulse, and ratio of braking: propulsive impulse were found between the elite and recreational group (p < 0.05). While SSC function was generally good to moderate, elite gymnasts had a more desirable kinetic jump-landing strategy than recreational level gymnasts. Drop jump kinetic variables appear to distinguish between elite and recreational gymnasts but not between regional standard gymnasts. Practitioners should consider the kinetic profile of gymnasts when benchmarking and setting training objectives.

Ground reaction forces and muscle activities during anteriorly-loaded overground walking: Preliminary results

Anterior-load carriage is common and has been identified as a fall risk factor in occupations. However, there is a lack of investigation of how anterior-load carriage influences kinetics and muscle activities. This study examined how anterior-loading affects ground reaction forces (GRFs) and leg/trunk electromyography (EMG) during level overground walking among young adults. Thirty young adults were randomly distributed into three groups: no load, 10% bodyweight (bw), and 20% bw. Each participant walked on a walkway at self-selected speed while holding the assigned load (assembled by a fitness sandbag) with both hands and anterior to the abdomen. Dependent variables included the kinetics (the peak GRF in vertical, forward, backward directions, rate of loading, and braking and propulsive impulses) and EMG magnitudes of six leg/trunk muscles (tibialis anterior, gastrocnemius, vastus lateralis, biceps femoris, gluteus maximus, and oblique). The results did not show significant group-related differences in any kinetic parameters or the EMG magnitudes except for the gluteus maximus. Both loaded groups displayed significantly higher gluteus maximus EMG magnitude than the unloaded group during anteriorly-loaded walking. Greater activation of the gluteus maximus may reflect the body's effort to stabilize the posteriorly leaned trunk, which was the main strategy to offset the anteriorly shifted body-load system's center of mass caused by the anterior load and to maintain dynamic balance during gait. The findings of this study could contribute to reducing the risk of falls in the industrial environment by providing insight into the kinetic control of the human body during anteriorly-loaded walking.

Kinetic and kinematic changes during resisted sprinting due to towing three common parachute sizes.

Different sized parachutes may alter applied resistance during parachute towing (PT), changing results of resisted sprint training interventions. Thus, it was hypothesized that there may be significant net anteroposterior ground reaction force and impulse differences due to parachute size towed. Fifteen male sprinters completed control and PT sprints over a 50 m force platform system. Estimated aerodynamic drag, ground reaction forces and kinematic differences during the maximum speed phase were compared between control (no parachute) and PT trials with small (0.39 m2), medium (0.54 m2) and large (0.72 m2) parachutes, using One-way ANOVA (significance set at P<0.050) with Tukey's HSD post-hoc (critical Q value = 3.746) tests. No significant (P>0.050) step length, step frequency, propulsive mean force, vertical mean force, or vertical impulse differences between trials. There was a significant anteroposterior impulse difference (P<0.001, Q=4.574) between small and medium PT, but no differences between medium and large PT. Compared to the control trial, all PT trials increased anteroposterior net mean force (P<0.001), anteroposterior net impulse (P<0.001), and propulsive impulse (P<0.001). However, only PT with the large parachute significantly reduced running speed (P<0.050, Q=3.792), braking mean force (P<0.050, Q=4.130) and braking impulse (P<0.001, Q=5.987), compared to the control trial. A large parachute may be most effective for PT (compared to control trial) to overload the body during the maximum speed phase in a single session.

Single-leg mechanical performance and inter-leg asymmetries during bilateral countermovement jumps: A comparison of different calculation methods

BackgroundThe possibility to selectively assess the force exerted by each leg during bilateral jumps has allowed sport scientists to explore inter-leg asymmetries, this metric being a rich source of research due to its potential applications to improve sports performance and reduce the risk of injury. The purpose of this study was to explore the reliability and agreement of single-leg mechanical performance and inter-leg asymmetry variables obtained by two procedures of analysis (Synchronous [simultaneous jump detection for both legs] and Asynchronous [specific jump detection for each leg]) during bilateral countermovement jumps (CMJs). MethodDuring a single testing session, 74 participants performed 5 maximal height bilateral CMJs on dual force platforms (Kistler, model 9260AA6, Winterthur, Switzerland), and the 2 trials that differed the least in terms of squat depth and jump height were considered for statistical analyses. The following mechanical variables were calculated separately for each leg using the Synchronous and Asynchronous procedures: mean force, peak force, and propulsive impulse. ResultsThe procedures showed comparable reliability, except for mean force and propulsive impulse of the left leg (higher for the Asynchronous procedure). The agreement between the procedures was very high, while the most reliable mechanical variable was mean force (CV≈2.9%, ICC≈0.98), followed by peak force (CV≈4.4%, ICC≈0.96) and propulsive impulse (CV≈6.4%, ICC≈0.91). Reliability of inter-leg asymmetries was greater using mean and peak force (ICC range=0.74–0.82) than using propulsive impulse (ICC range = 0.65–0.66). SignificanceBoth Synchronous and Asynchronous procedures can be used to evaluate single-leg mechanical performance (mean force, peak force, and propulsive impulse) and asymmetries, whereas mean force should be used to evaluate single-leg mechanical performance and mean or peak force to assess asymmetries.

Positive Impulse Phase versus Propulsive Impulse Phase: Correlations between Asymmetry and Countermovement Jump Performance.

The relationship between asymmetry and performance is still undetermined in the literature. Methods of assessing asymmetry have been inconsistent and focused on the analysis of jumping asymmetry. Dual ground reaction forces are prevalent in athlete monitoring, though underutilized in asymmetry research. The purpose of this study was to assess the relationship of countermovement jump (CMJ) impulse asymmetry to performance in collegiate soccer athletes. Male and female athletes were selected from an ongoing athlete research repository database of NCAA D-I soccer athletes. All athletes contributed two maximal effort unweighted (CMJ0) and weighted countermovement jumps (CMJ20) using the mean for calculations. Propulsive phase asymmetry scores (PrPAS) and positive impulse asymmetry scores (PIAS) were calculated to determine the magnitude of asymmetry for each prospective phase. Statistically significant correlations were found between CMJ0 jump height and unweighted PIAS (r = −0.43) in females. Males had statistically significant correlations between CMJ20 jump height and weighted PIAS (r = −0.49). Neither unweighted PrPAS nor weighted PrPAS produced statistically significant correlations (r < 0.26) to their prospective jump heights. When assessing CMJ asymmetry, it is recommended to conduct both weighted and unweighted CMJ testing, utilizing PIAS as the metric to be assessed.

Countermovement Jump Force-Time Curve Analysis between Strength-Matched Male and Female Soccer Players.

The purpose of this study was to compare countermovement jump force–time measures between strength-matched male and female soccer players. Males (n = 11) and females (n = 11) were strength-matched via isometric mid-thigh pull testing, whereby peak force values were normalised to body mass. Subjects performed three maximal-effort countermovement jumps (CMJs) on a force platform from which a range of kinetic and kinematic variables were calculated via forward dynamics. Thereafter, differences in gross measures were examined via independent t-tests, while differences in force–, power–, velocity–, and displacement–time curves throughout the entire CMJ were analysed using statistical parametric mapping (SPM). Jump height, reactive strength index modified, propulsion mean force, propulsion impulse, and propulsion mean velocity were all greater for males (d = 1.50 to 3.07). Relative force– and velocity–time curves were greater for males at 86–93% (latter half of the concentric phase) and 85–100% (latter half of the concentric phase) of normalized movement time, respectively. Time to take-off, braking phase time, braking mean velocity and impulse, propulsion phase time and centre of mass displacement were similar between males and females (d = −0.23 to 0.97). This research demonstrates the strength of SPM to identify changes between entire force-time curves. Continued development and the use of SPM analysis could present the opportunity for a refined comparison of strength-matched male and female CMJ performance with the analysis of entire force–time curves.