Vertical Center Of Mass Displacement Research Articles

Neuromechanical stabilisation of the centre of mass during running

BackgroundStabilisation of the centre of mass (COM) trajectory is thought to be important during running. There is emerging evidence of the importance of leg length and angle regulation during running, which could contribute to stability in the COM trajectory The present study aimed to understand if leg length and angle stabilises the vertical and anterior-posterior (AP) COM displacements, and if the stability alters with running speeds. MethodsData for this study came from an open-source treadmill running dataset (n = 28). Leg length (m) was calculated by taking the resultant distance of the two-dimensional sagittal plane leg vector (from pelvis segment to centre of pressure). Leg angle was defined by the angle subtended between the leg vector and the horizontal surface. Leg length and angle were scaled to a standard deviation of one. Uncontrolled manifold analysis (UCM) was used to provide an index of motor abundance (IMA) in the stabilisation of the vertical and AP COM displacement. ResultsIMAAP and IMAvertical were largely destabilising and always stabilising, respectively. As speed increased, the peak destabilising effect on IMAAP increased from −0.66(0.18) at 2.5 m/s to −1.12(0.18) at 4.5 m/s, and the peak stabilising effect on IMAvertical increased from 0.69 (0.19) at 2.5 m/s to 1.18 (0.18) at 4.5 m/s. ConclusionTwo simple parameters from a simple spring-mass model, leg length and angle, can explain the control behind running. The variability in leg length and angle helped stabilise the vertical COM, whilst maintaining constant running speed may rely more on inter-limb variation to adjust the horizontal COM accelerations.

A forefoot strike pattern during 18° uphill walking leads to greater ankle joint and plantar flexor loading

BackgroundThe ankle joint is one of the most involved joints in uphill walking. Furthermore, it is well known that toe walking increases the external dorsiflexion moment in the first half of stance during level walking. However, the effects of different foot-strike patterns on plantar flexor muscle forces, ankle joint forces, and other lower limb joint and muscle forces are unknown. Research questionDo foot-strike patterns during 18° uphill walking affect lower limb sagittal joint angles and moments, as well as joint contact and muscle forces? MethodsThis study was based on a data subset from previous publications, analysing uphill walking on an 18° ramp at a preset speed of 1.1 m/s in 18 male participants (34 limbs analyzed, 27 ± 5 years). Participants were divided into two groups based on their foot-strike pattern at initial contact: heel (HC) and forefoot (FC). Lower limb sagittal joint angles and moments as well as joint contact and muscle forces were assessed. Differences between the groups were assessed using two-sample t-tests. ResultsFC showed increased soleus and gastrocnemius muscle forces as well as ankle joint forces during loading response and mid stance compared to HC. The soleus muscle force impulse was 51.1% higher in the FC group than in the HC group (p < 0.001). On the other hand, FC had a lower absolute centre of mass vertical displacement and reduced knee and hip joint, as well as iliopsoas and hamstring muscle force impulses. SignificanceIn terms of plantar flexor and ankle joint loading, it is advantageous to exhibit a heel strike pattern. The current results can be used to recommend foot-strike patterns for uphill walking, particularly in the presence or prevention of musculoskeletal issues.

Estimation of running biomechanical parameters using magneto-inertial sensors: a preliminary investigation

Many runners perform training sessions outdoors and on varying surfaces (e.g., track, paved path, trail). Training surface has been shown to influence running spatiotemporal measures and stiffness [1]. However, applied research in understanding training surface influence has been limited by lack of robust methodology to capture biomechanics in-the-field. The increasing availability of wearable magneto- inertial sensors (MIMUs) is now making it possible to perform in-field assessment of running biomechanics [2]. Validation of new inertial-based methods is vital to widespread field use. In this study, we compared inertial-based methods for running biomechanical analysis and against gold-standard stereo-photogrammetric system (SP). Ten recreational male runners (age: 32.3 ± 10.0 years) were enrolled and asked to run on a treadmill at 14 km/hr for 8 trials lasting 6 minutes. We simulated changes in surface in a controlled lab setting by using 8 different footwear conditions. Participants were instrumented with MIMUs (mod: Opal v2, APDM, Portland, USA; fs=200 sample/s) attached on the pelvis (L5) and the instep of both feet, and retroreflective markers on heels, toes, and each MIMU (recorded with a 9-camera Vero system, Vicon, Oxford, UK; fs=200 sample/s). The estimated relevant biomechanical parameters included: stride/stance/swing duration, stride rate, vertical oscillations of the center of mass (CoM), and vertical/leg stiffness. Gait events (initial and final contacts) were estimated using a modified version of the MIMU-based method proposed by Benson et al. [2]. CoM vertical displacement was estimated as the vertical component of the L5 MIMU trajectory. Vertical and leg stiffness were computed starting from CoM displacement, stance interval, and swing interval [3]. For each participant and trial condition, errors with respect to SP were computed (80 values for each parameter) and root mean squared errors (RMSE) across participants and conditions were then calculated. In addition, a Bland-Altman analysis was used to quantify the agreement between MIMU and SP outcomes in terms of 50% limits of agreement interval (LoAI). Differences between MIMU-based and SP-based parameters over all the runners are reported in Table 1. Results showed high accuracy especially in the estimation of stride duration, stride rate and CoM vertical displacement. The level of uncertainty associated to each biomechanical variable, as provided by the LoAIs, can be used to detect differences in surface conditions (footwear conditions). Future analysis and development of field methods will investigate the influence of unconstrained movements (outdoor, no treadmill) in addition to varying surface conditions and the influence of running speed on inertial-based method accuracy.

Grizzlies and gazelles: Duty factor is an effective measure for categorizing running style in English Premier League soccer players.

English Premier League soccer players run at multiple speeds throughout a game. The aim of this study was to assess how well the duty factor, a dimensionless ratio based on temporal variables, described running styles in professional soccer players. A total of 25 players ran on an instrumented treadmill at 12, 16, and 20 km/h. Spatiotemporal and ground reaction force data were recorded for 30 s at each speed; video data (500 Hz) were collected to determine footstrike patterns. In addition to correlation analysis amongst the 25 players, two groups (both N = 9) of high and low duty factors were compared. The duty factor was negatively correlated with peak vertical force, center of mass (CM) vertical displacement, and leg stiffness (kleg) at all speeds (r ≥ −0.51, p ≤ 0.009). The low duty factor group had shorter contact times, longer flight times, higher peak vertical forces, greater CM vertical displacement, and higher kleg (p < 0.01). Among the high DF group players, eight were rearfoot strikers at all speeds, compared with three in the low group. The duty factor is an effective measure for categorizing soccer players as being on a continuum from terrestrial (high duty factor) to aerial (low duty factor) running styles, which we metaphorically refer to as “grizzlies” and “gazelles,” respectively. Because the duty factor distinguishes running style, there are implications for the training regimens of grizzlies and gazelles in soccer, and exercises to improve performance should be developed based on the biomechanical advantages of each spontaneous running style.

Optimizing Template Models to Quantifiably Assess Center of Mass Kinematic Reconstruction.

The center of mass (COM) plays a fundamental role in human ambulation, but the redundant nature of the human body adds complexity to mathematically modeling its dynamics. Template models like the Bipedal Spring Loaded Inverted Pendulum (B-SLIP) and the Virtual Pivot Point (VPP) address this complexity by removing the redundancy while retaining desired salient characteristics, such as the COM evolution. However, template models for the COM during human walking have mostly been used for qualitative analysis due to issues such as overestimation of COM vertical displacement. This paper considers a quantifiable template-based analysis of human walking by using an optimization framework to set the model parameter values for matching both explicitly and implicitly considered gait characteristics. Furthermore, it is shown that allowing the leg stiffness of the B-SLIP and VPP model to vary throughout the gait cycle better matches vertical COM trajectories with 54%-63% error reduction. These optimized template models show promise in retaining ground reaction force (GRF) information, which is not explicitly considered during the optimization process. Future work looks to incorporate these optimized trajectories as a reference for control of a lower-limb knee-ankle prosthesis.

Efekti promene visine vertikalnog sunožnog skoka na elektromiografske, kinematičke i kinetičke varijable

Countermovement jump (CMJ) is an element of many sports techniques and has an important role in the overall performance, both when performed at maximal and submaximal intensity. This paper aims to investigate changes in biomechanical and neuromuscular variables that are responsible for controlling different submaximal intensities of the CMJ. 8 healthy and uninjured volleyball players from the first league of the Republic of Serbia, average age 21.9 ± 1.9 years, average body height 191.6 ± 9.2 cm, average body weight 83.1 ± 7.1 kg were included in the study. Subjects performed CMJ at three different jump heights (approximately 65%, 80%, and 95% of the maximal height). For the analysis of electromyographic data, the value of root mean square analysis was used separately for the amortization phase and the jump phase, for the following muscles: m. gluteus maximus (GlutM), m. rectus femoris (RF), m. biceps femoris (BF), m. vastus lateralis (VL), m. tibialis anterior (TA) and m. gastrocnemius medialis(GastM).Kinematic and kinetic variableswere monitored: vertical center of mass displacement in the amortization phase [m], the center of mass height at take-off point [m], jump height [m], jump speed [m/s], angular displacement in the ankle, knee and hip joint [rad], maximal vertical ground reaction force [N/ kg], vertical stiffness [kN/m/kg], the torque of the ankle, knee and hip joint [Nm/kg]. The change in jump height (65, 80 and 95%) did not have a significant effect on the change in activation for most muscles (p≥0.05), except for GastM where a tendency towards increase was observed (p=0.066). During jump phase, the activation of VL, BF, GlutM, TA muscles significantly increased compared to the amortization phase (p≤0.05). The torque in the hip joint increased significantly with increasing jump height (65&lt;80=95%) (p=0.028). During amortization phase, the values of vertical center of mass displacement increased significantl y between each jump height (65&lt;80&lt;95%) (p≤0.05), while the values of vertical stiffness decreased with increasing jump height, where significant differences were observed between 80% and 95% of maximal jump height (65=80&lt;95%) (p=0.012). Angular displacements in the knee and hip joint increased significantly with increasing jump height (65&lt;80&lt;95%) (p≤0.05) while no changes in angular displacement in the ankle joint were observed (p≥0.05). The results of the research show that the increase in the jump height is related to an increase in the amortization phase, due to an increase in angular displacements in the knee and hip joint, as well as an increase in torque of the hip joint.

Influence of lower limb dominance on mechanical asymmetries during high-speed treadmill running

ABSTRACT We determine whether mechanical asymmetries differ between dominant and non-dominant legs at fast treadmill speed. Stride temporal variables, derived from high-speed camera recordings, allowed to estimate leg and vertical stiffness through the sine-wave method in 31 uninjured males during treadmill running at 6.67 m.s−1. Lower limb dominance was determined by the triple-jump test. The asymmetry was expressed as dominant—non-dominant and indexed by the absolute asymmetry index (ASI). The lowest and highest mean ASI values were detected for contact time (1.69%) and flight time (5.66%), respectively; ASI values for spring-mass characteristics (2.6% ≤ leg and vertical stiffness, peak vertical force, change in vertical leg length and centre of mass vertical displacement ≤ 4.7%) were within this range. Inter-subject variability in ASI varied substantially among the seven analysed variables with larger and smaller range of variability in ASI found for flight time (0–16.56%) and contact time (0–3.47%), respectively. Because the magnitude of group mean ASI appears inconsistent among stride temporal and spring-mass characteristics, different biomechanical variables should not be used interchangeably to assess laterality effects at fast treadmill speed. The widespread ASI range also indicates that using a ‘fixed cut-off’ threshold is an arbitrary approach.

용무도 앞굴러치기 동작의 운동역학적 분석

The purpose of this study is to kinetic analysis of the apgulleochigi motion of Yongmoodo. And the kinematic variables such as the duration time, COM(center of mass) displacement and velocity, the maximum impact force at landing were analyzed. And the following conclusions were drawn. First, the duration time of the apgulleochigi motion of Yongmoodo was 0.42±0.06 s in P1, 0.48±0.06 s in P2, 0.24±0.10 s in P3, and the total time was 1.14±0.16 s. In addition, the time required for each section during apgulleochigi motion of Yongmoodo showed a long duration time in the order of P2, P1, and P3. Second, the left and right displacements of COM of apgulleochigi motion of Yongmoodo were 0.40±0.05 m for E1, 0.39±0.03 m for E2, 0.39±0.08 m for E3, and 0.37±0.07 m for E4. The displacement before and after COM was 0.52±0.28 m for E1, 0.86±0.22 m for E2, 1.44±0.12 m for E3, and 1.86±0.13 m for E4. COM vertical displacement was 0.99±0.03 m for E1, 0.68±0.04 m for E2, 0.55±0.12 m for E3, and 0.31±0.01 m for E4. Third, the COM left and right velocity of apgulleochigi motion of Yongmoodo are -0.03±0.07 m/s for E1, 0.00±0.07 m/s for E2, -0.02±0.18 m/s for E3, and -0.13±0.33 m/s for E4. The velocity before and after COM was 0.69±0.22 m/s for E1, 0.86±0.18 m/s for E2, 1.56±0.52 m/s for E3, and 2.03±0.15 m/s for E4. The COM vertical speed was -0.36±0.15 m/s for E1, -0.89±0.17 m/s for E2, -1.19±0.44 m/s for E3, and -0.03±0.34 m/s for E4. Fourth, in the apgulleochigi motion of Yongmoodo, the maximum impact force generated by the hand closing to the ground was 1.76±0.25 BW. In summary, in the apgulleochigi motion of Yongmoodo, it would be advantageous to increase the duration of P1 and increase the impact speed upon landing in order to minimize the impact. In addition, it is judged that the impact force is reduced as the right arm is closer to the ground before the upper body is lowered and the vertical velocity of the COM is slowed down during an impact.

Evaluation of an inertial measurement unit-based approach for determining centre-of-mass movement during non-seated cycling

Instantaneous crank power does not equal total joint power if a rider’s centre of mass (CoM) gains and loses mechanical energy. Thus, estimating CoM motion and the associated energy changes can provide valuable information about the mechanics of cycling. To date, an accurate and precise method for tracking CoM motion during outdoor cycling has not been validated. PurposeTo assess the suitability of using data from a single inertial measurement unit (IMU) secured to the lower back of the rider for estimating CoM motion during non-seated cycling by comparing vertical displacement derived from the IMU to that of an attached marker cluster and to a full-body kinematic estimate of vertical CoM displacement. MethodsIMU and motion capture data were collected synchronously for 10 s while participants (n = 7) cycled on an ergometer in a non-seated posture at six combinations of power output and cadence. A limits-of-agreement analysis, corrected for repeated measures, was performed on the range of vertical displacement between the IMU and the two other measures. A total of 303 crank cycles were analysed. ResultsThere was excellent agreement between the vertical displacement derived from the IMU and the attached marker cluster (accuracy = 1.6 mm, precision = 3.5 mm). Vertical displacement derived from the IMU systematically overestimated the kinematic estimate of whole-body CoM—with errors increasing linearly with displacement. ConclusionWe interpret these findings as evidence that a single IMU secured to the lower back can provide a suitable approach for deriving a cyclist’s CoM displacement when they ride out of the saddle, but only if the linearly increasing overestimation is accounted for.

Muscle Function and Kinematics during Submaximal Equine Jumping: What Can Objective Outcomes Tell Us about Athletic Performance Indicators?

Simple SummaryJumping represents the most popular equestrian discipline. However, traditional selection and training strategies for jumping horses have not been validated using instrumented performance analyses to scientifically inform the optimization of athlete selection, training and competitive performance. We aimed to quantify the role of muscle function during the equine jump, its relationship to athletic performance indicators, and how this objective information can inform equestrian selection and training practices. We used three-dimensional kinematic and surface electromyography data to quantify movement and muscle activation, respectively, from horses executing a submaximal jump. Horses were grouped based on their ability to raise the center of mass during the jump suspension—a fundamental, objective measure of jumping performance. Kinematic data were used to objectively measure equestrian-derived preferences for movement traits related to impulsion, engagement and joint articulation. Horses that raised the center of mass highest during jumping displayed muscle activation and movement strategies that indicate a greater ability to rapidly generate hindlimb muscular force during jump take-off. These findings provide objective support for equestrian preferences related to the generation of engagement, impulsion and hindlimb muscle power when selecting and training jumping horses and justify their prioritization as objective performance indicators for the sport of equine jumping.Selection and training practices for jumping horses have not yet been validated using objective performance analyses. This study aimed to quantify the differences and relationships between movement and muscle activation strategies in horses with varying jump technique to identify objective jumping performance indicators. Surface electromyography (sEMG) and three-dimensional kinematic data were collected from horses executing a submaximal jump. Kinematic variables were calculated based on equestrian-derived performance indicators relating to impulsion, engagement and joint articulation. Horses were grouped using an objective performance indicator—center of mass (CM) elevation during jump suspension (ZCM). Between-group differences in kinematic variables and muscle activation timings, calculated from sEMG data, were analyzed using one-way ANOVA. Statistical parametric mapping (SPM) evaluated between-group differences in time and amplitude-normalized sEMG waveforms. Relationships between movement and muscle activation were evaluated using Pearson correlation coefficients. Horses with the greatest ZCM displayed significantly (p < 0.05) shorter gluteal contractions at take-off, which were significantly correlated (p < 0.05) with a faster approach and more rapid hindlimb shortening and CM vertical displacement and velocity, as well as shorter hindlimb stance duration at take-off. Findings provide objective support for prioritizing equestrian-derived performance indicators related to the generation of engagement, impulsion and hindlimb muscle power when selecting or training jumping horses.

Smartphone Monitoring of Gait and Balance During Irregular Surface Walking and Obstacle Crossing.

As gait adaptation is vital for successful locomotion, the development of field-based tools to quantify gait in challenging real-world environments are crucial. The aims of this study were to assess the reliability and validity of a smartphone-based gait and balance assessment while walking on unobstructed and obstructed terrains using two phone placements. Furthermore, age-related differences in smartphone-derived gait strategies when navigating different walking conditions and environments were evaluated. By providing a method for evaluating gait in the simulated free-living environment, results of this study can elucidate the strategies young and older adults utilize to navigate obstructed and unobstructed walking paths. A total of 24 young and older adults ambulated indoors and outdoors under three conditions: level walking, irregular surface walking, and obstacle crossing. Android smartphones placed on the body and in a bag computed spatiotemporal gait (i.e., velocity, step time, step length, and cadence) and balance (i.e., center of mass (COM) displacement), with motion capture and video used to validate parameters in the laboratory and free-living environments, respectively. Reliability was evaluated using the intraclass correlation coefficient and validity was evaluated using Pearson's correlation and Bland-Altman analysis. A three-way ANOVA was used to assess outcome measures across group, condition, and environment. Results showed that smartphones were reliable and valid for measuring gait across all conditions, phone placements, and environments (ICC2,1: 0.606–0.965; Pearson's r: 0.72–1.00). Although body and bag placement demonstrated similar results for spatiotemporal parameters, accurate vertical COM displacement could only be obtained from the body placement. Older adults demonstrated a longer step time and lower cadence only during obstacle crossing, when compared to young adults. Furthermore, environmental differences in walking strategy were observed only during irregular surface walking. In particular, participants utilized a faster gait speed and a longer step length in the free-living environment, compared to the laboratory environment. In conclusion, smartphones demonstrate the potential for remote patient monitoring and home health care. Along with being easy-to-use, inexpensive, and portable, smartphones can accurately evaluate gait during both unobstructed and obstructed walking, indoors and outdoors.

골볼 터닝 드로우 동작의 운동역학적 분석

The purpose of this study is to analyze the kinematics of the goal ball turning throwing motion, and the conclusions are as follows. First, the total time for goal ball turning and throwing motion was 1.82 s, 76.95 % in P1 and 23.02 % in P2. Second, it was found that the COM (center of mass) left and right displacement of the goalball turning throwing motion moved leftward from P1 (E1~E2) and moved to the right from P2 (E2~E3). COM forward and backwark displacement Moved to the forward according to the progress of the event. COM vertical displacement moved downward according to the progress of the event. Third, the COM left and right velocities of the goal ball turning throwing motion showed the fastest velocity from E3 to the right, and the COM forward and backward velocities showed the fastest speed from E2 to the forward. COM vertical velocity showed the fastest downward velocity at E2. Fourth, when the goal ball turning throwing motion was released, the velocity of the ball was 12.00±0.88 ㎧, and the stride width was 1.09±0.12 m. Fifth, the body segment’s angular momentum at the time of release of the goal ball turning throwing motion was found to be the largest in the trunk. And the upper arm, forearm, and hand segment of the upper limb all showed greater angular momentum than the left. In the case of the lower extremities, the right thigh and foot segments showed greater angular momentum than the left, but the left shank segment showed greater angular momentum than the right. Sixth, when the goal ball turning throwing motion was released, the ground reaction force of the forefoot showed the force in the right direction, the rear direction, and the vertical upward direction, and at this time, the large force was in the order of Fz, Fy, and Fx.

Effect of Approach Distance and Change of Direction Angles Upon Step and Joint Kinematics, Peak Muscle Activation, and Change of Direction Performance.

The aim of the study was to compare the step kinematics, joint angles, and muscle activations between change of direction (COD) maneuvers with different angles and approach distances, suggested to require different strength and velocity demands. Twenty-three male soccer players completed eight COD tests consisting of both 4 and 20-m sprint approaches with one directional change which varied between each COD test (45, 90, 135, and 180°). Peak muscle activity, step and joint kinematics of the lower limbs of the plant, and re-acceleration step were measured. Compared to 4-m CODs, the 20-m COD approach distances increased vertical center of mass displacement (p < 0.001), number of deceleration steps (p < 0.001), revealing no statistical differences upon joint angles (p > 0.05). Greater COD angles resulted in increased ankle dorsiflexion, hip abduction and flexion, greater displacement of the center of mass and tibia angle, longer contact times, and more deceleration steps (p < 0.034). The CODs categorized as velocity-dominant revealed higher peak muscle activity in the adductor longus, semitendinosus, biceps femoris, and gastrocnemius. It was concluded that velocity-dominant CODs revealed higher muscle activity due to a higher eccentric loading, implicating task-specific training considerations for enhancing COD performance.

Spring-like leg dynamics and neuromuscular strategies for hopping on a mini-trampoline in adults and children.

Improved balance control is an often-cited potential benefit for trampoline interventions. However, it is unknown whether the soft, elastic surface of a trampoline elicits different motion and neuromuscular strategies between adults and children. Therefore, the purpose of the study was to evaluate the center-of-mass (COM) dynamics and neuromuscular strategies for hopping on a mini-trampoline in adults and children. Fourteen children aged 7-12years and 15 adults aged 18-35years hopped on a stiff surface and a mini-trampoline. We evaluated the vertical displacement of COM and leg length, as well as the horizontal displacements between hops. We also assessed muscle activation from tibialis anterior, lateral gastrocnemius, biceps femoris, and vastus lateralis during time periods surround landing and estimated fatigue across the hopping cycles. Our results indicated both groups used spring-like leg dynamics to regulate the COM movement while hopping on a mini-trampoline. Children increased horizontal displacements between hops on the mini-trampoline, requiring greater muscle activation during time-periods associated with proprioceptive input. Moreover, children might not have developed the adult-like ability to appropriately adjust muscle pre-activation for feedforward control. Hopping on a mini-trampoline might increase proprioceptive information and postural demand compared to a stiff surface while reducing neuromuscular fatigue.

Determinants Of Metabolic Cost During Four Styles Of 30-second Sprint Rope Skipping

Rope jumping has been a major training tool for many sports. However, no study has been conducted as yet to determine energy expenditure with incremental skipping rate per jump (difficulty) from single under to quad under. PURPOSE: To determine and compare 30-seconds all-out effort energy expenditure between four incremental rope skipping difficulties. METHOD: Ten skilled rope-jumpers (height=169.3±4.7cm, body mass=65.5±9.2kg, age=23.2±2.1yrs, years of training=3.8±1.3yrs) volunteered to participate this study. Participants conducted rope skipping as many repetitions as possible at 1 skip.jump-1 (single under, SU), 2 skips.jump-1 (double under, DU), 3 skips.jump-1 (triple under, TU) and 4 skips.jump-1 (quad under, QU) during 30-second test with 24 hours between trials. Kinematic and kinetic data were collected to calculate flight time (FT) and vertical center of mass displacement (vCOM). Each style was assessed in three trials and then averaged. Net energy expenditure (Wtot) was calculated from VO2 during exercise, the fast component of the EPOC above resting and net blood lactate production. RESULT: SU exhibited significantly lower VO2peak (28.01±4.62 ml.kg-1.min-1, p<0.05) compared to TU (34.96±3.45) and QU (36.12±6.38). Wtot (J.jump-1) in QU (7975.1±3265.66 J.jump-1) was significantly higher than these values of the other three styles (SU 474.9±108.80, DU 1086.4±183.17, TU 1769.3±540.46, p<0.05). FT (ms) and vCOM (cm) increased significantly with increase in difficulty (SU: 125.0±19.6 and 1.95±0.66, DU: 276.6±36.1 and 9.53±2.24, TU: 473.6±32.1 and 27.64±3.76, QU: 544.4±60.5 and 36.76±8.15, p<0.01). 30s skip repetitions in QU (46.0±19.34) was significantly lower than the other styles (SU 105.2±12.08, DU 128.2±15.12, TU 126.9±20.39, p<0.01). Standard Wtot (J.kg-1.jump-1) was exponentially related to skipping difficulty from 1 skip.jump-1 to 4 skips.jump-1 (R2=0.89, p<0.001). CONCLUSION: Skipping difficulty (skip per jump) is one of the main determinants of metabolic cost, whereas skip repetition does not significantly contribute to metabolic cost during 30 seconds all-out rope skipping.

Associations Between 24-Hour Dietary Intake And Biomechanical Changes During A Long Run: An Exploratory Study

Both nutrition and biomechanics play important roles for running and athletic performance. However, to date they have usually been studied separately and there is minimal literature evaluating effects of nutritional status or interventions on biomechanical outcomes. PURPOSE: This exploratory study evaluated relationships between nutritional status prior to a long hilly run and changes in running mechanics following the run. METHODS: Eight trail runners (5 M/3 F; weekly mileage: 27.6 ± 8.5 miles) ran a 10-mile hilly run which matched the elevation profile of a popular local trail run. 3D kinematics and ground reaction forces were collected during five-minute level ground running sections prior to and following the run. Changes in spatial temporal parameters, ground reaction forces, and leg stiffness variables from pre to post run were computed for each participant's left leg using Visual3D. Pre-run 24-hour dietary recalls were analyzed for total caloric intake (Tkcal) and percent calories from carbohydrate (%CHO), protein (%PRO), and fat (%FAT). Pearson's correlations were used to asses associations between each nutritional variable and changes in biomechanical variables. RESULTS: There were significant associations between %PRO and changes in peak ground reaction force and changes in contact time such that runners with higher %PRO displayed smaller changes in biomechanics (Figure 1). Similar associations were observed between Tkcal and %FAT and changes in vertical center of mass displacement. CONCLUSIONS: This preliminary study suggests nutritional status prior to a long run may affect the changes in biomechanics a runner experiences during the run. These biomechanical effects have implications for both performance and injury, and highlight the importance of protein for long distance runners. Additional research is required to evaluate whether manipulating nutrition can be used to manage biomechanical changes associated with long duration running.

Riders Use Their Body Mass to Amplify Crank Power during Nonseated Ergometer Cycling

To date, neither the CoM movement strategies during nonseated cycling nor the limb mechanics that allow this phenomenon to occur have been quantified. Here we estimate how much power can be contributed by a rider's CoM at each instant during the crank cycle by combining a kinematic and kinetic approach to measure CoM movement and joint powers of 15 participants riding in a nonseated posture at three individualized power outputs (10%, 30%, and 50% of peak maximal power) and two different cadences (70 and 120 rpm). The peak-to-peak amplitude of vertical CoM displacement increased significantly with power output and with decreasing cadence. Accordingly, the greatest peak-to-peak amplitude of CoM displacement (0.06 ± 0.01 m) and change in total mechanical energy (0.54 ± 0.12 J·kg) occurred under the combination of high-power output and low cadence. At the same combination of high-power output and low cadence, we found that the peak rate of CoM energy loss (3.87 ± 0.93 W·kg) was equal to 18% of the peak crank power. Consequently, it appears that for a given power output, changes in CoM energy contribute to peak instantaneous power output at the crank, thus reducing the required muscular contribution. These findings suggest that the rise and fall of a rider's CoM acts as a mechanical amplifier during nonseated cycling, which has important implications for both rider and bicycle performance.

Changes in Gait Kinematic Parameters after Severe Traumatic Brain Injury during Post-Acute Rehabilitation

Changes in gait after traumatic brain injury (TBI) are very important for evaluation, clinical reasoning and forintervention programs. Most studies analyze gait during acute phase, but there is lack of information during post-acute period. The aim of the research was to determine gait biomechanical joint angles and centre of mass displacement changes during post-acute TBI rehabilitation. Participant was a 21-year-old male, after severe TBI, 2 years after trauma. Biomechanical joints angles and centre of mass displacement changes were observed during 3D gait analysis. The subject was asked to walk straight 6 meters, 18 times at his preferred comfortable pace. During walking 1–2 minute breaks were made. Intensive 5 week program was composed of physiotherapy (3 times per week) and yoga (2 times per week). Physiotherapy included stretching, coordination, balance and weight-bearing exercises. Yoga was performed to built core stability, train flexibility and diminish muscle tone. After 5 week rehabilitation statistically significant changes were observed in the centre of mass displacement and in lower extremities and lumbar biomechanics (p &lt; 0.05). After procedures trunk flexion and trunk lateral flexion, lateral pelvic tilt increased, while anterior pelvic tilt decreased (p &lt; 0.05). Hip extension at terminal stance increased, as well while hip adduction in stance phase decreased (p &lt; 0.05). Statistically significant reduction was observed in knee flexion at initial contact, mid-stance and midswing phase (p &lt; 0.05). Prevalent knee flexion at initial contact, observed before rehabilitation, decreased after it (p &lt; 0.05). After the procedure lateral centre of mass displacement decreased and vertical centre of mass displacement increased (p &lt; 0.05). Five weeks of rehabilitation composed of traditional physiotherapy and yoga is effective for gait quality treatment. However, further research is necessary to determine gait biomechanical joint angles and dynamic balance improvements during severe post-acute TBI.Keywords: head injury, walking, balance.

Acute changes in sagittal plane kinematics while wearing a novel belt device during treadmill running

ABSTRACT Somatosensory feedback is used in walking retraining; however, its utility in running is less feasible due to the greater associated speeds. The purpose of this study was to examine the acute effects of wearing a novel running belt device on sagittal plane running kinematics. Ten healthy runners ran on a treadmill with and without the use of a running belt device within a repeated measures study design. Temporal-spatial characteristics and sagittal plane knee and ankle kinematics were recorded with three-dimensional motion analysis. Wilcoxon Signed-Rank Tests revealed significant decreases in centre of mass vertical displacement (z = −2.083, p = 0.003), tibial inclination at initial contact (z = −2.803, p = 0.003), and stance phase knee joint excursion (z = −2.701, p = 0.003), and greater knee flexion at initial contact (z = −2.803, p = 0.003) when the belt was donned. No differences were observed in step rate (z = −0.351, p = 0.363), foot inclination angle at initial contact (z = −2.090, p = 0.018), or peak knee flexion during stance (z = −1.172, p = 0.121). Findings suggest that donning a running belt can minimise specific high-risk biomechanical characteristics in runners with particular kinematic profiles.

Lower-Limb Stiffness and Maximal Sprint Speed in 11–16-Year-Old Boys

Meyers, RW, Moeskops, S, Oliver, JL, Hughes, MG, Cronin, JB, and Lloyd, RS. Lower-limb stiffness and maximal sprint speed in 11-16-year-old boys. J Strength Cond Res 33(7): 1987-1995, 2019-The purpose of the study was to examine the relationship between vertical stiffness, leg stiffness, and maximal sprint speed in a large cohort of 11-16-year-old boys. Three-hundred thirty-six boys undertook a 30-m sprint test using a floor-level optical measurement system, positioned in the final 15-m section. Measures of speed, step length, step frequency, contact time, and flight time were directly measured while force, displacement, vertical stiffness, and leg stiffness, were modeled from contact and flight times, from the 2 fastest consecutive steps for each participant over 2 trials. All force, displacement, and stiffness variables were significantly correlated with maximal sprint speed (p ≤ 0.05). Relative vertical stiffness had a very large (r > 0.7) relationship with sprint speed, whereas vertical center of mass displacement, absolute vertical stiffness, relative peak force, and maximal leg spring displacement had large (r > 0.5) relationships. Relative vertical stiffness and relative peak force did not significantly change with advancing age (p > 0.05), but together with maximal leg spring displacement accounted for 96% of the variance in maximal speed. It seems that relative vertical stiffness and relative peak force are important determinants of sprint speed in boys aged 11-16 years, but are qualities that may need to be trained because of no apparent increases from natural development. Practitioners may wish to use training modalities such as plyometrics and resistance training to enable adaptation to these qualities because of their importance as predictors of speed in youth.