Changes In Vertical Stiffness Research Articles

Thoracic-Worn Accelerometers Detect Fatigue-Related Changes in Vertical Stiffness During Sprinting.

Horsley, BJ, Tofari, PJ, Halson, SL, Kemp, JG, Johnston, RD, and Cormack, SJ. Thoracic-worn accelerometers detect fatigue-related changes in vertical stiffness during sprinting. J Strength Cond Res 38(2): 283-289, 2024-Thoracic-mounted accelerometers are valid and reliable for analyzing gait characteristics and may provide the opportunity to assess running-related neuromuscular fatigue (NMF) during training and competition without the need for additional tests, such as a countermovement jump (CMJ). However, their sensitivity for detecting fatigue-related changes in gait across different speeds is unclear. We, therefore, assessed the changes in accelerometer-derived gait characteristics, including vertical stiffness (K vert ), following a repeated sprint protocol (RSP). Sixteen recreationally active subjects performed single and repeated CMJs on a force plate and 40 m run throughs overground at 3-4, 5-6, and 7-8 m·s -1 pre-post a 12 × 40 m RSP. Gait characteristics (contact time, step frequency, step length, K vert , etc.) were derived from an accelerometer contained within a global navigation satellite system unit on the thoracic spine using a validated algorithm. Changes in running gait and CMJ performance were assessed using a linear mixed-effects model (95% confidence interval [95% CI]; effect size [ES]). Significance was set at p < 0.05. A significant reduction in K vert occurred at 7-8 m·s -1 following the RSP (-8.51 kN·m -1 [-13.9, -3.11]; p = 0.007; ES [95% CI] = -0.39 [-0.62, -0.15]) which coincided with a decreased jump height (-0.03 m [-0.04, -0.01]; p = 0.002; ES [95% CI] = -0.87 [-1.41, -0.30]). However, all other gait characteristics were not significantly different irrespective of speed. Thoracic-worn accelerometers can detect changes in K vert at 7-8 m·s -1 which may be useful for monitoring NMF during sprinting. However, a RSP does not result in altered gait mechanics in subsequent running at lower speeds.

Track‐Bridge Interaction: Influence of Transition Zone on the Stability of Continuous Welded Rail

AbstractRealization of high‐speed rail track demands continuous welded rail (CWR) to be laid on bridges without providing special expansion joints. In India, the existing rail bridges must be evaluated for their suitability for upgradation to CWR. CWR Inherently develops axial stress on account of the surrounding temperature changes. CWR in track‐bridge transition zone is subjected to additional stress and displacements as a result of track‐bridge interaction (TBI). Longitudinal thermal loading is a major source of rail stress and substructure forces due to TBI. Also, TBI results in accumulation of large compressive stress in transition zone. Further, the tamping effect in the transition zone by passing vehicles due to sudden change in vertical stiffness weakens the transition zone ballast. CWR is a slender steel element prone to buckling under large compressive stress. A numerical model is developed for track bridge interaction phenomenon in SAP2000 considering the aspect of CWR track buckling. In this study, the developed model is utilized to perform nonlinear buckling analysis to assess the influence of change in ballast stiffness on CWR stability in transition zone. Also, the influence of missing ballast contact raising from ballast subsidence locally in the transition zone was investigated. A single span simply supported steel bridge is considered. Longitudinal thermal loading is considered in this study. CWR supported on the ballasted track is considered. Material Nonlinearity associated with ballast is considered. Maintenance of CWR track is found to play a key role in track stability as the loose ballast or missing of ballast underneath the rail sleeper is to introduce discontinuity in CWR track support and reduces the critical buckling temperatures of the track considerably. Overall, this study contributes to the understanding of track‐bridge interaction and the stability of CWR in the transition zone.

Kinetics and Vertical Stiffness of Female Volleyball Players: Effect of Low-intensity Plyometric Training

ABSTRACT Purpose: The purpose of this study was threefold: 1) to assess kinematic/kinetic variables and vertical stiffness of recreational young female volleyball players during a vertical jump, 2) to identify the changes in those variables that occurred after low-intensity plyometric training, 3) to determine the relationship between stiffness and performance. Method: Twenty-eight female volleyball players aged 14–18 years were randomly allocated to plyometric group and control group. All participants performed a countermovement jump (CMJ) 3 days prior to and 3 days after the 7-week plyometric training and kinematic and kinetic variables, along with vertical stiffness, were measured. Results: Jump height, average force, average power, peak power and absolute vertical stiffness significantly increased in plyometric group (p < .01). Propulsion impulse and normalized vertical stiffness also increased (p < .05). Maximum displacement of the center of mass significantly decreased in plyometric group (p < .01). Changes in vertical stiffness after the plyometric training showed very strong significant correlations with changes in average force (r = 0.818, p < .01), average power (r = 0.784, p < .01), maximum displacement of the center of mass (r = −0.850, p < .01) and propulsion duration (r = −0.781, p < .01). Conclusion: The 7-week low-intensity plyometric training produced changes in most kinematic and kinetic variables improving CMJ performance. The increase in vertical stiffness after plyometric training may not directly enhance jump performance but it makes the jump quicker increasing the probability of success in volleyball games.

Hydrolyzed Collagen Supplementation on Lower Body Stiffness in Recreational Triathletes

Background: Myotendinous stiffness is related to the collagen content of the muscle and tendon, and can be estimated during running by changes in vertical stiffness (kvert) and the resulting modifications of the spatiotemporal parameters (on-off ground asymmetry and landing-takeoff asymmetry). Supplementation with amino acids found in collagen, such as proline, glycine, and hydroxyl proline, combined with ascorbic acid, improve collagen synthesis and potentially result in improved mechanical strength and stiffness. Objectives: To determine if hydrolyzed collagen (HC) supplementation increases kvert and improves the spatiotemporal parameters during running in recreational triathletes. Methods: Nine active males (weight; 68.4 ± 5.7 kg, height; 171.8 ± 5.4 cm, age; 32.5 ± 4.1 years; Vo2max; 53.15 ± 2.19 mL/kg/min) were randomly distributed into a collagen group (CollG, n = 5) and a control group (CG, n = 4). Participants were supplemented for 4 weeks with 15g HC (CollG) or 15g placebo (CG; maltodextrin), 3 times per week. One hour after supplementation, the participants of both groups were asked to perform four repetitions of short sprints to further stimulate collagen synthesis. The ground reaction forces were recorded during running at 4.44 m s-1, 5.55 m.s-1, and 6.66 m.s-1 for assessment of kvert and the spatiotemporal step parameters. Results: Both groups increased kvert with speed (4.44 - 6.66 m s-1) from 24.8 ± 2.7 to 53.7 ± 16.5 N/m and from 25.1 to 49.8 N/m in the CollG and CG, respectively (P &lt; 0.0001); however, there were no differences between groups before and after the supplementation period. As a consequence, the spatiotemporal parameters of running were also similar between groups. Conclusions: Four weeks of HC supplementation does not improve the bouncing mechanism of running in recreational triathletes.

Parameter Influences on Rail Corrugation of Metro Tangential Track

Rail corrugation can reduce riding comfort by vibration and noise, and even cause running accident. In this paper, the vehicle–track coupled dynamic model was developed for a metro’s tangential track considering the wear in rail materials. The influences of different track structure parameters and vehicle speed on the generation and development of rail corrugation of the tangential track were analyzed using the developed model by the control variable method. The results show that for different parameters, the friction power in wheel–rail contact patch fluctuates with time, but the overall fluctuation range is relatively uniform. Meantime, an analysis of one-third octave curves of the friction power reveals that the characteristic frequencies of friction power are mainly concentrated in the middle and low frequency bands. At the dominant characteristic frequency, the longitudinal stiffness and damping of fasteners, and lateral and vertical damping of fasteners have less influence on rail corrugation, while the lateral and vertical stiffnesses of fasteners, spacing of fasteners, wheel–rail friction coefficient and vehicle speed have greater effect on rail corrugation. The changes in vertical stiffness and spacing of fasteners will cause the characteristic frequency of friction power to be offset, resulting in a shift from 80[Formula: see text]Hz to 100[Formula: see text]Hz, which will further lead to rail corrugation of the corresponding wavelength. Thus, it can be concluded that the vertical stiffness and spacing of fasteners have an important impact on the generation and development of rail corrugation at the specific frequency. Besides, the variations of the other variables bring little change to the characteristic frequencies of friction power as well as on rail corrugation. The mechanism of parameters unveiled here provides some guides for the parameter optimization problem on restraining the generation or development of rail corrugation on the tangential track.

The effect of low-Dye taping on hopping performance in handball players

Low-Dye taping is a useful technique for preventing foot injuries. However, the use of inextensible tape may lead to a decline in movement performance as a result of limited foot joint mobility and a change in vertical stiffness due to the passive stiffening of the tarsus and metatarsus. Therefore, the aim of the present study was to determine the effect of low-Dye taping on sport movement performance observed during a hopping task. The study was carried out on a group of 11 male handball players. The Myotest accelerometer was used to evaluate the effect of low-Dye taping on jumping height, ground contact time and vertical stiffness during the hopping test. Each study participant performed four series of 5 hops (hopping test): two series before low-Dye taping and two after. No statistically significant differences were found between the values recorded before and after low-Dye taping for the variables that describe the hopping task: mean jump height, mean ground contact time and mean vertical stiffness. Low-Dye taping can be successfully used in handball players since it has a preventive effect that reduces the risk of injury to the foot and does not influence vertical stiffness or jump height to a significant extent.

The effect of water-based plyometric training on vertical stiffness and athletic performance.

Since higher vertical stiffness is related to superior athletic performance, training has traditionally been aimed at augmenting this variable to enhance neuromuscular output. However, research has linked elevated stiffness with increased injury risk, therefore, this study examined the effect of a novel training intervention on vertical stiffness and athletic performance. Vertical stiffness, jump performance and athletic performance were assessed in two randomly allocated groups, prior to, and following, an eight-week period. One group was exposed to a training intervention involving aqua-based plyometrics (n = 11) over the 8 weeks while the other acted as a control group (n = 9). The training intervention involved hopping, jumping and bounding in water at a depth of 1.2m whilst control participants performed their normal training. There were no significant changes in vertical stiffness in either group. Countermovement jump height and peak power significantly increased within the aqua plyometric group (p < 0.05). Athletic performance markers improved in the aqua plyometric group as measured using an agility and a 5-bound test exhibiting superior values at the post-test (p < 0.05). The results suggest that an aqua plyometric training program can enhance athletic performance without elevating stiffness. The increase in athletic performance is likely due to a reduction in ground reaction forces created by the buoyancy of the water, causing a shorter amortization phase and a more rapid application of concentric force. The findings from this study can inform exercise professionals and medical staff regarding the ability to enhance neuromuscular performance without elevating vertical stiffness. This has implications for improving athletic performance while concurrently minimising injury risk.

Effects of upper and lower body wearable resistance on spatio-temporal and kinetic parameters during running

ABSTRACT Wearable resistance training involves added load attached directly to the body during sporting movements. The effects of load position during running are not yet fully established. Therefore, the purpose of this research was to determine spatio-temporal and kinetic characteristics during submaximal running using upper, lower and whole-body wearable resistance (1–10% body mass (BM)). Twelve trained male runners completed eight 2-min treadmill running bouts at 3.9 m/s with and without wearable resistance. The first and last bouts were unloaded, while the middle 6 were randomised wearable resistance conditions: upper body (UB) 5% BM, lower body (LB) 1%, 3%, 5% BM and whole body (WB) 5%, 10% BM. Wearable resistance of 1–10% BM resulted in a significant increase in heart rate (5.40–8.84%), but minimal impact on spatio-temporal variables. Loads of 5% BM and greater caused changes in vertical stiffness, vertical and horizontal force, and impulse. Functional and effective propulsive force (2.95%, 2.88%) and impulse (3.40%, 3.38%) were significantly (p < 0.05) greater with LB5% than UB5%. Wearable resistance may be used to increase muscular kinetics during running without negatively impacting spatio-temporal variables. The application of these findings will vary depending on athlete goals. Future longitudinal studies are required to validate training contentions.

A simple finite element for nonlinear wheel/rail contact and separation simulations

To simulate the contact and separation of wheels and rails accurately, the stiffness between them should be correct. This paper developed a nonlinear moving wheel element based on a simple point contact scheme to simulate moving train problems, where the element stiffness is set to a power function directly fitted from the finite-element result of the wheel and rail contact analysis. The finite-element result of the wheel/rail contact analysis indicates that the changes in vertical stiffness with changing contact forces can be accurately fitted by using the proposed power function, and the horizontal stiffness can be simply regressed using a constant. The validated example in this paper shows that the nonlinear moving wheel element can simulate the complicated contact and separation problem correctly, both in the displacement and contact force fields, and the major advantage is that a fine mesh is not necessary in the moving train contact analysis.

Seismic response of structures with coupled vertical stiffness–strength irregularities

AbstractSeveral seismic design codes around the world restrict the use of theit Equivalent Lateral Force analysis method to structures satisfying structural regularity limits. These regularity limits are based on engineering judgement and lack quantitative justification. One common irregularity is that of a change in vertical stiffness over the building height. This stiffness irregularity is almost always associated with a change in vertical strength over the building height. For this reason, the effect of various realistic combinations of stiffness–strength irregularity in shear‐type buildings is evaluated to quantify regularity limits.Structures analysed had 3, 5, 9 and 15 storeys, and the floor mass at all the levels were kept the same. Both regular and irregular structures were designed in accordance with the Equivalent Lateral Force procedure to produce the same engineering demand parameter. Structural ductility factors of 1, 2, 3, 4 and 6, and target (design) interstorey drift ratios ranging between 0.5 and 3%, were used in this study. The irregular structures were created by modifying specific storey lateral stiffnesses from that of the regular structure. Strengths at these storeys were also modified to ensure realistic relationships between stiffness and strength. The modified structures were then redesigned until the target interstorey drift ratio was achieved at the critical storey. Inelastic dynamic time‐history analysis was conducted to compare the maximum interstorey drift ratio demands of the regular and irregular structures. Simple equations were developed to estimate possible variations in demand due to vertical stiffness–strength irregularity applied at critical locations in structures. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Changes in spring-mass model characteristics during repeated running sprints

This study investigated fatigue-induced changes in spring-mass model characteristics during repeated running sprints. Sixteen active subjects performed 12×40m sprints interspersed with 30s of passive recovery. Vertical and anterior-posterior ground reaction forces were measured at 5-10m and 30-35m and used to determine spring-mass model characteristics. Contact (P<0.001), flight (P<0.05) and swing times (P<0.001) together with braking, push-off and total stride durations (P<0.001) lengthened across repetitions. Stride frequency (P<0.001) and push-off forces (P<0.05) decreased with fatigue, whereas stride length (P=0.06), braking (P=0.08) and peak vertical forces (P=0.17) changes approached significance. Center of mass vertical displacement (P<0.001) but not leg compression (P>0.05) increased with time. As a result, vertical stiffness decreased (P<0.001) from the first to the last repetition, whereas leg stiffness changes across sprint trials were not significant (P>0.05). Changes in vertical stiffness were correlated (r>0.7; P<0.001) with changes in stride frequency. When compared to 5-10m, most of ground reaction force-related parameters were higher (P<0.05) at 30-35m, whereas contact time, stride frequency, vertical and leg stiffness were lower (P<0.05). Vertical stiffness deteriorates when 40m run-based sprints are repeated, which alters impact parameters. Maintaining faster stride frequencies through retaining higher vertical stiffness is a prerequisite to improve performance during repeated sprinting.