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Surface acceleration transmission during drop landings in humans
Abstract
The purpose of this study was to quantify the magnitude and frequency content of surface-measured accelerations at each major human body segment from foot to head during impact landings. Twelve males performed two single leg drop landings from each of 0.15 m, 0.30 m, and 0.45 m. Triaxial accelerometers (2000 Hz) were positioned over the: first metatarsophalangeal joint; distal anteromedial tibia; superior to the medial femoral condyle; L5 vertebra; and C6 vertebra. Analysis of acceleration signal power spectral densities revealed two distinct components , 2-14 Hz and 14-58 Hz, which were assumed to correspond to time domain signal joint rotations and elastic wave tissue deformation, respectively. Between each accelerometer position from the metatarsophalangeal joint to the L5 vertebra, signals exhibited decreased peak acceleration, increased time to peak acceleration, and decreased power spectral density integral of both the 2-14 Hz and 14-58 Hz components, with no further atten-uation beyond the L5 vertebra. This resulted in peak accelerations close to vital organs of less than 10% of those at the foot. Following landings from greater heights, peak accelerations measured distally were greater, as was attenuation prior to the L5 position. Active and passive mechanisms within the lower limb therefore contribute to progressive attenuation of accelerations, preventing excessive accelerations from reaching the torso and head, even when distal accelerations are large.
... In addition, trunk positioning (24,68) and gait cycle features, including cadence, step length, and gait regularity and symmetry (134,159), can affect the magnitude and timing of the postimpact elastic wave (propagation of impact-related energy [i.e., measured accelerations] through body tissues and decreasing of amplitude with distance from the source). Finally, muscle damping by which sites further from impact are also less affected by the amplifying effect of greater GRF (35,129,194) Therefore, the correlations between accelerations or accelerometer-based metrics at different body positions may not be particularly high (80). It should also be considered that acceleration signals comprise various frequencies, not all of which relate directly to the postimpact elastic wave (117,129,174). ...
... Finally, muscle damping by which sites further from impact are also less affected by the amplifying effect of greater GRF (35,129,194) Therefore, the correlations between accelerations or accelerometer-based metrics at different body positions may not be particularly high (80). It should also be considered that acceleration signals comprise various frequencies, not all of which relate directly to the postimpact elastic wave (117,129,174). complex additional processing and lacks direct application. ...
... The specificity of these thresholds to the between-scapulae measurement site should be considered when interpreting studies that have applied the same processes at alternative body sites. For example, single-leg drop landings from a height of 0.45 m have resulted in peak surface-measured accelerations on average of 68 g at the metatarsophalangeal joint but 4 g at the C6 vertebra (129). Peak accelerations at the C6 vertebra level of 2.6 6 0.8 g following 0.15-m single-leg drop landings may not have been sufficient to exceed the abovementioned thresholds in some individuals. ...
Athlete load monitoring using upper back-mounted Global Navigation Satellite System (GNSS) player tracking is common within many team sports. However, accelerometer-based load monitoring may provide information that cannot be achieved with GNSS alone. This review focuses on the accelerometer-based metrics quantifying the accumulation of accelerations as an estimation of athlete training load, appraising the validity and reliability of accelerometer use in upper back-mounted GNSS player tracking systems, the accelerometer-based metrics, and their potential for application within athlete monitoring. Reliability of GNSS-housed accelerometers and accelerometer-based metrics are dependent on the equipment model, signal processing methods, and the activity being monitored. Furthermore, GNSS unit placement on the upper back may be suboptimal for accelerometer-based estimation of mechanical load. As there are currently no feasible gold-standard comparisons for field-based whole-body biomechanical load, the validity of accelerometer-based load metrics has largely been considered in relation to other measures of training load and exercise intensity. In terms of convergent validity, accelerometer-based metrics (e.g., PlayerLoadTM, Dynamic Stress Load, Body LoadTM) have correlated, albeit with varying magnitudes and certainty, with measures of internal physiological load, exercise intensity, total distance, collisions and impacts, fatigue, and injury risk and incidence. Currently, comparisons of these metrics should not be made between athletes due to mass and/or technique differences, or between manufacturers due to processing variations. Notable areas for further study include the associations between accelerometer-based metrics and other parts of biomechanical load-adaptation pathways of interest, such as internal biomechanical loads or methods of manipulating these metrics through effective training design.
... Previous studies have suggested that the mean power spectra of the lower and higher frequency bands respectively indicate the joint voluntary movements and passive tissue creeping effect that occurred during the tasks. 26 Statistical Analysis SPSS 22.0 software (SPSS) was used for statistical analysis in this study. Continuous data were presented as the means and standard deviations, while nominal data were presented as the frequency and median. ...
... 27 Current results indicated a significant increase in power intensity in the lower frequency band during lateral shuffling, which may imply the necessity for enhanced voluntary movement control after experiencing fatigue. 26 Furthermore, this study observed higher mean and median frequencies during drill C. The heightened mean and median frequencies after fatigue, especially during long-distance lateral shuffling, suggest a shift of power toward the higher frequency band and possibly indicate an increase in involuntary contributions such as joint damping and ligament creeping. 37,39 In this study, a decrease in power intensity in the lower frequency band and a concurrent increase in the higher frequency band were observed during drills A and E of the agility-T test, which involved forward and backward running over shorter distances. ...
Background
Badminton is a sport demanding both high aerobic and anaerobic fitness levels, and fatigue can significantly impact game performance. However, relevant studies are limited, and none have employed a wearable inertial measurement unit (IMU) to investigate the effects of fatigue on athletic performance in the field.
Hypothesis
Overall performance and body acceleration in both time and frequency domains during the fundamental badminton skills of vertical jumping and changes of direction will be affected by fatigue.
Study Design
Cross-sectional study.
Level of Evidence
Level 3.
Methods
A total of 38 young badminton players competing at the Division I level participated. Body accelerations while performing vertical jump and agility-T tests before and immediately after undergoing a fatigue protocol were measured by an IMU, positioned at the L4 to L5 level.
Results
Jumping height decreased significantly by 4 cm ( P < 0.01) after fatigue with greater downward acceleration (1.03 m/s ² , P < 0.05) during the squatting subphase. Finishing time increased significantly by 50 ms only during the 10-m side-shuffling of the agility-T test ( P = 0.02) after fatigue with greater peak and mean accelerations (3.83 m/s ² , P = 0.04; 0.43 m/s ² , P < 0.01), and higher median and mean frequency (0.38 Hz, P = 0.04, 0.11 Hz, P = 0.01).
Conclusion
This study using a wearable IMU demonstrates the effects of fatigue on body acceleration in badminton players. The frequency-domain analysis further indicated that fatigue might lead to loss of voluntary control of active muscles and increased impacts on the passive elastic elements.
Clinical Relevance
The findings imply that fatigue can lead to diminished athletic performance and highlight the potential for an increased risk of sports injuries. Consequently, maintaining precision in monitoring fatigue is crucial for elite young badminton players.
... Previous studies have suggested that the average power spectra of the lower and higher frequency 161 bands respectively indicate the joint voluntary movements and passive tissue creeping effect that 162 occurred during the tasks 24 . Continuous data were presented as the mean and standard deviation (SD), while nominal data were 166 11 presented as the frequency and median. ...
... Notably, Mohr and 231 15 Federolf observed decreased pelvis mediolateral movement speed and reduced movement 232 smoothness following fatigue, suggesting that individuals may heighten their neuromuscular 233 awareness to engage greater muscle activation to meet task demands 25 . Current results indicated a 234 significant increase in power intensity in the lower frequency band during lateral shuffling, which 235 may imply the necessity for enhanced voluntary movement control after experiencing fatigue 24 . 236 Furthermore, this study observed higher mean and median frequencies during drill C. The 237 heightened mean and median frequencies after fatigue, especially during long-distance lateral 238 ...
Background: Badminton is a sport demanding both high aerobic and anaerobic fitness levels, and fatigue can significantly impact game performance. However, relevant studies are limited, and none have employed a wearable inertial measurement unit (IMU) to investigate the effects of fatigue on athletic performance in the field.
Hypothesis: Overall performance and body acceleration in both time- and frequency-domains during the fundamental badminton skills of vertical jumping and changes of direction will be affected by fatigue.
Study Design: Cross-sectional study.
Level of Evidence: Level 3.
Methods: Thirty-eight young badminton players competing at the Division One level participated. Body accelerations while performing vertical jump and agility-T tests before and immediately after undergoing a fatigue protocol were measured by an IMU, positioned at the L4-L5 level.
Results: Jumping height significantly decreased by 4 centimeters (p < 0.01) after fatigue with greater downward acceleration (1.03 m/s2, p = 0.049) during the squatting subphase. Finishing time significantly increased by 50 milliseconds only during the 10-meter side-shuffling of the agility-T test (p = 0.02) after fatigue with greater peak and mean accelerations (3.83 m/s2, p = 0.04; 0.43 m/s2, p < 0.01), and higher median and mean frequency (0.38 Hz, p = 0.04, 0.11 Hz, p = 0.01).
Conclusion: This is the first study using a wearable IMU to demonstrate the effects of fatigue on body acceleration in badminton players. The results of frequency-domain analysis further indicated that fatigue might lead to the potential loss of voluntary control of active muscles and increased impacts on the passive elastic elements.
Clinical Relevance: The findings imply that fatigue can lead to diminished athletic performance and highlight the potential for an increased risk of sports injuries. Consequently, maintaining precision in monitoring fatigue is crucial for elite young badminton players.
... It was concluded that an unrestricted model is appropriate for simulating kinematic performance, but compliance is required elsewhere in the link system (e.g., within joint structures) to accurately calculate internal forces. This may also improve the timing of modeled elastic wave transmission [60], which is typically instantaneous in rigid systems, but not in vivo [142]. ...
... Although this method enables soft tissue displacement, future advancements may facilitate more realistic displacement magnitudes and damping periods [60,70,71]. Additionally, the inclusion of compliance within joint structures [61,62] may facilitate more accurate predictions of ground reaction forces, internal forces, and elastic wave transmission in sporting movements with great impact forces [60,142]. ...
The identification of optimum technique for maximal effort sporting tasks is one of the greatest challenges within sports biomechanics. A theoretical approach using forward-dynamics simulation allows individual parameters to be systematically perturbed independently of potentially confounding variables. Each study typically follows a four-stage process of model construction, parameter determination, model evaluation, and model optimization. This review critically evaluates forward-dynamics simulation models of maximal effort sporting movements using a dynamical systems theory framework. Organismic, environmental, and task constraints applied within such models are critically evaluated, and recommendations are made regarding future directions and best practices. The incorporation of self-organizational processes representing movement variability and "intrinsic dynamics" remains limited. In the future, forward-dynamics simulation models predicting individual-specific optimal techniques of sporting movements may be used as indicative rather than prescriptive tools within a coaching framework to aid applied practice and understanding, although researchers and practitioners should continue to consider concerns resulting from dynamical systems theory regarding the complexity of models and particularly regarding self-organization processes.
... As the trunk is the heaviest body segment and is positioned proximally on the body, these accelerations have been proposed to represent whole-body mass centre accelerations and, therefore, relate to the ground reaction forces or impact magnitudes experienced by the athlete (i.e., external biomechanical training load). However, this neglects the influence of other body segment accelerations, considerable post-impact shockwave attenuation inferior to the sensor [60], and the contribution of various frequency components to the overall acceleration signal [58,61]. Even an entirely accurate measure of ground reaction force or mass centre acceleration may not correlate with the internal forces experienced by specific tissues if muscle forces are not accounted for [62]. ...
E-textiles have emerged as a fast-growing area in wearable technology for sports and fitness due to the soft and comfortable nature of textile materials and the capability for smart functionality to be integrated into familiar sports clothing. This review paper presents the roles of wearable technologies in sport and fitness in monitoring movement and biosignals used to assess performance, reduce injury risk, and motivate training/exercise. The drivers of research in e-textiles are discussed after reviewing existing non-textile and textile-based commercial wearable products. Different sensing components/materials (e.g., inertial measurement units, electrodes for biosignals, piezoresistive sensors), manufacturing processes, and their applications in sports and fitness published in the literature were reviewed and discussed. Finally, the paper presents the current challenges of e-textiles to achieve practical applications at scale and future perspectives in e-textiles research and development.
... The design of the lower limb prosthesis is focused on patients who have a transfemoral amputation, either due to some disease such as diabetes. Therefore, the design will feature EMG muscle sensors in the biceps femoris part as seen in Fig. 2. On the other hand, the triaxial accelerometer will be located on the knee so that the movement can be simulated, as shown in Fig. 3. Location of the triaxial accelerometers [14]. Fig. 4 shows the design of the parallel robot in which the electric actuators with linear travel rods were used, having as reference a 30w /24v linear actuator [15]. ...
... Additionally, the PSD difference from the distal to the proximal tibia and shock attenuation characteristics in this study supported that quantifying the shock attenuation at the tibia is critical for understanding acceleration and impact absorption differences among footwear conditions in the time and frequency domains [19,37] because impact loading maintains a similar magnitude from the knee [38]. ...
Tibial shock attenuation is part of the mechanism that maintains human body stabilization during running. It is crucial to understand how shock characteristics transfer from the distal to proximal joint in the lower limb. This study aims to investigate the shock acceleration and attenuation among maximalist shoes (MAXs), minimalist shoes (MINs), and conventional running shoes (CONs) in time and frequency domains. Time-domain parameters included time to peak acceleration and peak resultant acceleration, and frequency-domain parameters contained lower (3–8 Hz) and higher (9–20 Hz) frequency power spectral density (PSD) and shock attenuation. Compared with CON and MAX conditions, MINs significantly increased the peak impact acceleration of the distal tibia (p = 0.01 and p < 0.01). Shock attenuation in the lower frequency depicted no difference but was greater in the MAXs in the higher frequency compared with the MIN condition (p < 0.01). MINs did not affect the tibial shock in both time and frequency domains at the proximal tibia. These findings may provide tibial shock information for choosing running shoes and preventing tibial stress injuries.
The aim of this research was to quantify the magnitude and timing of surface measured accelerations during the fast-bowling action. Eleven males performed 6 maximum velocity deliveries with accelerometers positioned over: both ankles; knees; hips; L5; L1; and the C7 vertebrae. Accelerometer signals exhibited decreased peak and increased time to peak acceleration from the ankle to the C7 sensor. Even when distal accelerations were largest at front foot contact, the body was still able to dissipate more than 90% of the acceleration. Active and passive mechanisms such as joint compliance and spinal compression within the body therefore likely contribute to the progressive attenuation of accelerations. The effects of such compliance on investigations of the intersegmental forces and moments during cricket fast-bowling via inverse dynamics warrants further investigation.
Editorial - free online access at https://doi.org/10.1080/14763141.2020.1782555
The use of multi-body optimisation (MBO) to estimate joint kinematics from stereophotogrammetric data while compensating for soft tissue artefact is still open to debate. Presently used joint models embedded in MBO, such as mechanical linkages, constitute a considerable simplification of joint function, preventing a detailed understanding of it. The present study proposes a knee joint model where femur and tibia are represented as rigid bodies connected through an elastic element the behaviour of which is described by a single stiffness matrix. The deformation energy, computed from the stiffness matrix and joint angles and displacements, is minimised within the MBO. Implemented as a “soft” constraint using a penalty-based method, this elastic joint description challenges the strictness of “hard” constraints. In this study, estimates of knee kinematics obtained using MBO embedding four different knee joint models (i.e., no constraints, spherical joint, parallel mechanism, and elastic joint) were compared against reference kinematics measured using bi-planar fluoroscopy on two healthy subjects ascending stairs. Bland-Altman analysis and sensitivity analysis investigating the influence of variations in the stiffness matrix terms on the estimated kinematics substantiate the conclusions. The difference between the reference knee joint angles and displacements and the corresponding estimates obtained using MBO embedding the stiffness matrix showed an average bias and standard deviation for kinematics of 0.9±3.2° and 1.6±2.3 mm. These values were lower than when no joint constraints (1.1±3.8°, 2.4±4.1 mm) or a parallel mechanism (7.7±3.6°, 1.6±1.7 mm) were used and were comparable to the values obtained with a spherical joint (1.0±3.2°, 1.3±1.9 mm). The study demonstrated the feasibility of substituting an elastic joint for more classic joint constraints in MBO.
The aim of this paper is to provide a Bayesian formulation of the so-called magnitude-based inference approach to quantifying and interpreting effects, and in a case study example provide accurate probabilistic statements that correspond to the intended magnitude-based inferences. The model is described in the context of a published small-scale athlete study which employed a magnitude-based inference approach to compare the effect of two altitude training regimens (live high-train low (LHTL), and intermittent hypoxic exposure (IHE)) on running performance and blood measurements of elite triathletes. The posterior distributions, and corresponding point and interval estimates, for the parameters and associated effects and comparisons of interest, were estimated using Markov chain Monte Carlo simulations. The Bayesian analysis was shown to provide more direct probabilistic comparisons of treatments and able to identify small effects of interest. The approach avoided asymptotic assumptions and overcame issues such as multiple testing. Bayesian analysis of unscaled effects showed a probability of 0.96 that LHTL yields a substantially greater increase in hemoglobin mass than IHE, a 0.93 probability of a substantially greater improvement in running economy and a greater than 0.96 probability that both IHE and LHTL yield a substantially greater improvement in maximum blood lactate concentration compared to a Placebo. The conclusions are consistent with those obtained using a 'magnitude-based inference' approach that has been promoted in the field. The paper demonstrates that a fully Bayesian analysis is a simple and effective way of analysing small effects, providing a rich set of results that are straightforward to interpret in terms of probabilistic statements.
Harold Jeffreys pioneered the development of default Bayes factor hypothesis tests for standard statistical problems. Using Jeffreys's Bayes factor hypothesis tests, researchers can grade the decisiveness of the evidence that the data provide for a point null hypothesis H0 versus a composite alternative hypothesis H1. Consequently, Jeffreys's tests are of considerable theoretical and practical relevance for empirical researchers in general and for experimental psychologists in particular. To highlight this relevance and to facilitate the interpretation and use of Jeffreys's Bayes factor tests we focus on two common inferential scenarios: testing the nullity of a normal mean (i.e.,the Bayesian equivalent of the t-test) and testing the nullity of a correlation. For both Bayes factor tests, we explain their development, we extend them to one-sided problems, and we apply them to concrete examples from experimental psychology.
The principle aim of the study was to assess the acute alterations in tri-axial accelerometry (PlayerLoad™; PLVM) and its individual axial-planes (anterior-posterior-PlayerLoad™ [PLAP], medial-lateral-PlayerLoad™ [PLML] and vertical-PlayerLoadTM [PLV]) during a standardised 90-min soccer match-play simulation (SAFT90). Secondary aims of the study were to assess the test-retest reliability and anatomical location of the devices.
Semi-professional (n=5) and University (n=15) soccer players completed 3 trials (1 familiarisation, 2 experimental) of SAFT90. PlayerLoad™ and its individual planes were measured continuously using micromechanical-electrical systems (MEMS) positioned at the scapulae (SCAP) and near the centre of mass (COM).
There were no between-half differences in PLVM, however, within-half increases were recorded at the COM, but only during the 1st half at the SCAP. Greater contributions to PLVM were provided by PLV and PLML when derived from the SCAP and COM, respectively. PLVM (COM: 1451 ± 168; SCAP: 1029 ± 113), PLAP (COM: 503 ± 99; SCAP: 345 ± 61), PLML (COM: 712 ± 124; SCAP: 348 ± 61) and PLV (COM: 797 ± 184; SCAP: 688 ± 124) were significantly greater at the COM compared to the SCAP. Moderate and high test-retest reliability was observed for PlayerLoad™ and its individual planars at both locations (ICC: 0.80-0.99).
PlayerLoad™ and its individual planes are reliable measures during SAFT90 and detected within-match changes in movement strategy when the unit was placed at the COM, which may have implications for fatigue management. Inferring alterations in lower-limb movement strategies from MEMS units positioned at the SCAP should be undertaken with caution.
Whole-body vibration (WBV) training has become popular in recent years. However, WBV may be harmful to the human body. The goal of this study was to determine the acceleration magnitudes at different body segments for different frequencies of WBV. Additionally, vibration sensation ratings by subjects served to create perception vibration magnitude and discomfort maps of the human body. In the first of two experiments, 65 young adults mean (± SD) age range of 23 (± 3.0) years, participated in WBV severity perception ratings, based on a Borg scale. Measurements were performed at 12 different frequencies, two intensities (3 and 5 mm amplitudes) of rotational mode WBV. On a separate day, a second experiment (n = 40) included vertical accelerometry of the head, hip and lower leg with the same WBV settings. The highest lower limb vibration magnitude perception based on the Borg scale was extremely intense for the frequencies between 21 and 25 Hz; somewhat hard for the trunk region (11-25 Hz) and fairly light for the head (13-25 Hz). The highest vertical accelerations were found at a frequency of 23 Hz at the tibia, 9 Hz at the hip and 13 Hz at the head. At 5 mm amplitude, 61.5% of the subjects reported discomfort in the foot region (21-25 Hz), 46.2% for the lower back (17, 19 and 21 Hz) and 23% for the abdominal region (9-13 Hz). The range of 3-7 Hz represents the safest frequency range with magnitudes less than 1 g(*)sec for all studied regions.
Copyright © 2015 IPEM. Published by Elsevier Ltd. All rights reserved.
It is well established nowadays the benefits that physical activity can have on the health of individuals. Walking is considered a fundamental method of movement and using a backpack is a common and economical manner of carrying load weight. Nevertheless, the shock wave produced by the impact forces when carrying a backpack can have detrimental effects on health status. Therefore, the aim of this study was to investigate differences in the accelerations placed on males and females whilst carrying different loads when walking. Twenty nine sports science students (16 males and 13 females) participated in the study under 3 different conditions: no weight, 10% and 20% body weight (BW) added in a backpack. Accelerometers were attached to the right shank and the centre of the forehead. Results showed that males have lower accelerations than females both in the head (2.62 ± 0.43G compared to 2.83 + 0.47G) and shank (1.37 ± 0.14G compared to 1.52 ± 0.15G; p<0.01). Accelerations for males and females were consistent throughout each backpack condition (p>0.05). The body acts as a natural shock absorber, reducing the amount of force that transmits through the body between the foot (impact point) and head. Anthropometric and body mass distribution differences between males and females may result in women receiving greater impact acceleration compared to men when the same load is carried.
Human locomotion has been modeled as a force-driven harmonic oscillator (FDHO). The minimum forcing function in locomotion has been shown to occur at the resonant frequency of the FDHO and results in the suggestion that oxygen cost may be considered an optimality criterion for locomotion. The purposes of this study were twofold: first, to determine the relationship between stride frequency and shock attenuation, and second, to determine whether shock attenuation may also be considered an optimality criterion. Ten healthy young adult males served as subjects in this study. Each subject's preferred running speed and preferred stride frequency (PSF) were determined. In addition to the PSF, they ran at stride frequencies corresponding to −20%, −10%, +10%, and +20% of the PSF at the preferred running speed. Metabolic data as well as leg and head acceleration data were collected during a steady state run at each of the stride frequency conditions. The metabolic data produced a U-shaped curve hypothesized by the FDHO model. Spectral analysis on the leg and head acceleration data were used to develop transfer functions for each of the stride frequency conditions. Analysis of the transfer function indicated that there was a gain at the low frequencies and an attenuation at the higher frequencies. The transfer function at the higher frequencies indicated that the impact shock signal was attenuated as it passed through the body. However, the transfer functions appeared to vary according to the amount of shock input to the system with the result that the head accelerations remained constant. It would appear that impact (high frequency) shock attenuation increases with stride frequency and thus does not fit the FDHO model as an optimization criterion. At all stride frequencies, regardless of the impact shock, head accelerations were maintained at a constant level.
This experiment, which extends a previous investigation (Pozzo et al. 1990), was undertaken to examine how head position is controlled during natural locomotor tasks in both normal subjects (N) and patients with bilateral vestibular deficits (V). 10 normals and 7 patients were asked to perform 4 locomotor tasks: free walking (W), walking in place (WIP), running in place (R) and hopping (H). Head and body movements were recorded with a video system which allowed a computed 3 dimensional reconstruction of selected points in the sagittal plane. In order to determine the respective contribution of visual and vestibular cues in the control of head angular position, the 2 groups of subjects were tested in the light and in darkness. In darkness, the amplitude and velocity of head rotation decreased for N subjects; these parameters increased for V subjects, especially during R and H. In darkness, compared to the light condition, the mean position of a line placed on the Frankfort plane (about 20-30 degrees below the horizontal semi-circular canal plane) was tilted downward in all conditions of movement, except during H, for N subjects. In contrast, this flexion of the head was not systematic in V subjects: the Frankfort plane could be located above or below earth horizontal. In V subjects, head rotation was not found to be compensatory for head translation and the power spectrum analysis shows that head angular displacements in the sagittal plane contain mainly low frequencies (about 0.3-0.8 Hz). The respective contribution of visual and vestibular cues in the control of the orientation and the stabilization of the head in space is discussed.
A method to measure the capability of the human shock absorber system to attenuate input dynamic loading during the gait is presented. The experiments were carried out with two groups: healthy subjects and subjects with various pathological conditions. The results of the experiments show a considerable difference in the capability of each group's shock absorbers to attenuate force transmitted through the locomotor system. Comparison shows that healthy subjects definitely possess a more efficient shock-absorbing capacity than do those subjects with joint disorders. Presented results show that degenerative changes in joints reduce their shock absorbing capacity, which leads to overloading of the next shock absorber in the locomotor system. So, the development of osteoarthritis may be expected to result from overloading of a shock absorber's functional capacity.
Mechanical analysis at the whole human body level typically assumes limbs are rigid bodies with fixed inertial parameters, however, as the human body consists mainly of deformable soft tissue, this is not the case. The aim of this study was to investigate changes in the inertial parameters of the lower limb during landing and stamping tasks using high frequency three-dimensional motion analysis. Seven males performed active and passive drop landings from 30 and 45 cm and a stamp onto a force plate. A sixteen-camera 750 Hz Vicon system recorded markers for standard rigid body analysis using inverse kinematics in Visual 3D and 7 × 8 and 7 × 9 marker arrays on the shank and thigh. Frame by frame segment volumes from marker arrays were calculated as a collection of tetrahedra using the Delaunay triangulation method in 3D and further inertial parameters were calculated using the method of Tonon (2004). Distance between the centres of mass (COM) of the rigid and soft tissues changed during impact in a structured manner indicative of a damped oscillation. Group mean amplitudes for COM motion of the soft tissues relative to the rigid body of up to 1.4 cm, and changes of up to 17% in moment of inertia of the soft tissue about the rigid body COM were found. This study has shown that meaningful changes in inertial parameters can be observed and quantified during even moderate impacts. Further examination of the effects these could have on movement dynamics and energetics seems pertinent.
Context:
Contemporary developments in GPS technology present a means of quantifying mechanical loading in a clinical environment with high ecological validity. However, applications to date have typically focussed on performance rather than rehabilitation.
Objective:
To examine the efficacy of GPS micro-technology in quantifying the progression of loading during functional rehabilitation from ankle sprain injury, given the prevalence of re-injury and need for quantifiable monitoring. Furthermore, to examine the influence of unit placement on the clinical interpretation of loading during specific functional rehabilitation drills.
Design:
Repeated measures.
Setting:
University athletic facilities.
Participants:
22 female intermittent team sports players.
Intervention:
All players completed a battery of 5 drills (anterior hop, inversion hop, eversion hop, diagonal hop, diagonal hurdle hop) designed to reflect the mechanism of ankle sprain injury, and progress functional challenge and loading.
Main outcome measures:
GPS-mounted accelerometers quantified uni-axial PlayerLoad for each drill, with units placed at C7 and the tibia. Main effects for drill type and GPS location were investigated.
Results:
There was a significant main effect for drill type (P<0.001) in the medio-lateral (ɳ2=0.436), anterio-posterior (ɳ2=0.480), and vertical planes (ɳ2=0.516). The diagonal hurdle hop elicited significantly greater load than all other drills, highlighting a non-linear progression of load. Only medio-lateral load showed evidence of progressive increase in loading. PlayerLoad was significantly greater at the tibia than at C7 for all drills, and in all planes (P<0.001, ɳ2≥0.662). Furthermore, the tibia placement was more sensitive to between-drill changes in medio-lateral load than the C7 placement.
Conclusions:
The placement of the GPS unit is imperative to clinical interpretation, with both magnitude and sensitivity influenced by the unit location. GPS does provide efficacy in quantifying multi-planar loading during (p)rehabilitation, in a field or clinical setting, with potential in extending GPS analyses (beyond performance metrics) to functional injury rehabilitation and prevention.
Purpose:
A statistical method called "magnitude-based inference" (MBI) has gained a following in the sports science literature, despite concerns voiced by statisticians. Its proponents have claimed that MBI exhibits superior type I and type II error rates compared with standard null hypothesis testing for most cases. I have performed a reanalysis to evaluate this claim.
Methods:
Using simulation code provided by MBI's proponents, I estimated type I and type II error rates for clinical and nonclinical MBI for a range of effect sizes, sample sizes, and smallest important effects. I plotted these results in a way that makes transparent the empirical behavior of MBI. I also reran the simulations after correcting mistakes in the definitions of type I and type II error provided by MBI's proponents. Finally, I confirmed the findings mathematically; and I provide general equations for calculating MBI's error rates without the need for simulation.
Results:
Contrary to what MBI's proponents have claimed, MBI does not exhibit "superior" type I and type II error rates to standard null hypothesis testing. As expected, there is a tradeoff between type I and type II error. At precisely the small-to-moderate sample sizes that MBI's proponents deem "optimal," MBI reduces the type II error rate at the cost of greatly inflating the type I error rate-to two to six times that of standard hypothesis testing.
Conclusions:
Magnitude-based inference exhibits worrisome empirical behavior. In contrast to standard null hypothesis testing, which has predictable type I error rates, the type I error rates for MBI vary widely depending on the sample size and choice of smallest important effect, and are often unacceptably high. Magnitude-based inference should not be used.
Estimation of muscle forces through musculoskeletal simulation is important in understanding human movement and injury. Unmatched filter frequencies used to low-pass filter marker and force platform data can create artifacts during inverse dynamics analysis, but their effects on muscle force calculations are unknown. The objective of this study was to determine the effects of filter cutoff frequency on simulation parameters and magnitudes of lower extremity muscle and resultant joint contact forces during a high-impact maneuver. Eight participants performed a single leg jump-landing. Kinematics were captured with a 3D motion capture system and ground reaction forces were recorded with a force platform. The marker and force platform data were filtered using two matched filter frequencies (10-10Hz, 15-15Hz) and two unmatched frequencies (10-50Hz, 15-50Hz). Musculoskeletal simulations using Computed Muscle Control were performed in OpenSim. The results revealed significantly higher peak quadriceps (13%), hamstrings (48%), and gastrocnemius forces (69%) in the unmatched (10-50Hz, 15-50Hz) conditions than in the matched (10-10Hz, 15-15Hz) conditions (p<0.05). Resultant joint contact forces and reserve (non-physiologic) moments were similarly larger in the unmatched filter categories (p<0.05). This study demonstrated that artifacts created from filtering with unmatched filter cutoffs result in altered muscle forces and dynamics which are not physiologic.
Kinematic models of lower limb joints have several potential applications in musculoskeletal modelling of the locomotion apparatus, including the reproduction of the natural joint motion. These models have recently revealed their value also for in vivo motion analysis experiments, where the soft-tissue artefact is a critical known problem. This arises at the interface between the skin markers and the underlying bone, and can be reduced by defining multibody kinematic models of the lower limb and by running optimization processes aimed at obtaining estimates of position and orientation of relevant bones. With respect to standard methods based on the separate optimization of each single body segment, this technique makes it also possible to respect joint kinematic constraints. Whereas the hip joint is traditionally assumed as a 3 degrees of freedom ball and socket articulation, many previous studies have proposed a number of different kinematic models for the knee and ankle joints. Some of these are rigid, while others have compliant elements. Some models have clear anatomical correspondences and include real joint constraints; other models are more kinematically oriented, these being mainly aimed at reproducing joint kinematics. This paper provides a critical review of the kinematic models reported in literature for the major lower limb joints and used for the reduction of soft-tissue artefact. Advantages and disadvantages of these models are discussed, considering their anatomical significance, accuracy of predictions, computational costs, feasibility of personalization, and other features. Their use in the optimization process is also addressed, both in normal and pathological subjects.
This article explains the foundational concepts of Bayesian data analysis using virtually no mathematical notation. Bayesian ideas already match your intuitions from everyday reasoning and from traditional data analysis. Simple examples of Bayesian data analysis are presented that illustrate how the information delivered by a Bayesian analysis can be directly interpreted. Bayesian approaches to null-value assessment are discussed. The article clarifies misconceptions about Bayesian methods that newcomers might have acquired elsewhere. We discuss prior distributions and explain how they are not a liability but an important asset. We discuss the relation of Bayesian data analysis to Bayesian models of mind, and we briefly discuss what methodological problems Bayesian data analysis is not meant to solve. After you have read this article, you should have a clear sense of how Bayesian data analysis works and the sort of information it delivers, and why that information is so intuitive and useful for drawing conclusions from data.
The purpose of this study was to determine the effects of increasing impact shock levels on the spectral characteristics of impact shock and impact shock wave attenuation in the body during treadmill running. Twelve male subjects ran at 2.0, 3.0, 4.0, and 5.0 m s ⁻¹ on a treadmill. Axial accelerations of the shank and head were measured using low-mass accelerometers. The typical shank acceleration power spectrum contained two major components which corresponded to the active (5–8 Hz) and impact (12–20 Hz) phases of the time-domain ground reaction force. Both the amplitude and frequency of leg shock transients increased with increasing running speed. Greatest attenuation of the shock transmitted to the head occurred in the 15–50 Hz range. Attenuation increased with increasing running speed. Thus transmission of the impact shock wave to the head was limited, despite large increases in impact shock at the lower extremity.
Bayes/frequentist correspondences between the p-value and the posterior probability of the null hypothesis have been studied in univariate hypothesis testing situations. This paper extends these comparisons to multiple testing and in particular to the Bonferroni multiple testing method, in which p-values are adjusted by multiplying by k, the number of tests considered. In the Bayesian setting, prior assessments may need to be adjusted to account for multiple hypotheses, resulting in corresponding adjustments to the posterior probabilities. Conditions are given for which the adjusted posterior probabilities roughly correspond to Bonferroni adjusted p-values.
The effect of the soft tissue between bone and a preloaded skin surface accelerometer was studied in vivo by comparing its output with the output of an accelerometer connected directly to the bone by a needle through the soft tissue. A 34-g skin surface accelerometer gave an output with little resemblance to the bone motions, appearing to oscillate at its resonant frequency on the soft tissue. A 1. 5-g skin surface accelerometer showed nearly identical output to the bone acceleration.
The influence of the posture of the legs and the vibration magnitude on the dynamic response of the standing human body exposed to vertical whole-body vibration has been investigated. Motions were measured on the body surface at the first and eighth thoracic and fourth lumbar vertebrae (T1, T8 and L4), at the right and left iliac crests and at the knee. Twelve subjects took part in the experiment with three leg postures (normal, legs bent and one leg), and five magnitudes of random vibration (0·125–2·0 ms−2r.m.s.) in the frequency range from 0[msde]5–30 Hz. The main resonance frequencies of the apparent masses at 1·0 ms−2r.m.s. differed between postures: 5·5 Hz in the normal posture, 2·75 Hz in the legs bent posture and 3·75 Hz in the one leg posture. In the normal posture, the transmissibilities to L4 and the iliac crests showed a similar trend to the apparent mass at low frequencies. With the legs straight, no resonance was observed in the legs at frequencies below 15 Hz. In the legs bent posture, a bending motion of the legs at the knee and a pitching or bending motion of the upper-body appeared to contribute to the resonance of the whole body as observed in the apparent mass, with attenuation of vibration transmission to the upper body at high frequencies. In the one leg posture, coupled rotational motion of the whole upper-body about the hip joint may have contributed to the resonance observed in the apparent mass at low frequencies and the attenuation of vertical vibration transmission at high frequencies. The resonance frequency of the apparent mass in the normal posture decreased from 6·75–5·25 Hz with increasing vibration magnitude from 0·125 to 2·0 ms−2r.m.s. This “softening” effect was also found in the transmissibilities to many parts of the body that showed resonances.
The head motions of standing subjects have been measured while they were exposed to floor vibration occurring in each of the three translational axes: fore-and-aft, lateral and vertical. While exposed to fore-and-aft floor vibration, the 12 male subjects were instructed to stand in two postures: holding a handrail in front of them lightly; and holding the handrail rigidly. During exposure to lateral floor vibration subjects stood in three postures: feet together, feet 30 cm apart and feet 60 cm apart. The postures investigated during exposure to vertical floor vibration were: straight legs (i.e., locked), legs very slightly bent (i.e., unlocked) and legs bent. Variability within and between subjects (i.e., intra- and inter-subject variability) was investigated for all axes of excitation and all postures. Transmissibilities between the floor and the head were calculated for all conditions. During exposure to fore-and-aft floor vibration, the head motion occurred mostly in the mid-sagittal plane; a rigid grip on the handrail resulted in higher transmissibilities than a light grip. During exposure to lateral floor vibration, the head motion occurred mainly below 3 Hz and in the lateral axis; the 60 cm foot separation resulted in more head motion below 3 Hz than the other postures. During exposure to vertical floor vibration, head motion occurred principally in the mid-sagittal plane. For frequencies below about 5 Hz, a legs bent posture resulted in the highest transmissibilities, while a legs locked posture showed the lowest motion; this order was reversed at higher frequencies. Differences in transmissibility as large as 20:1 occurred between subjects for some conditions.
Background:
Knee joint osteoarthritis is painful and with an overweight of female incidence. The cardinal symptom is pain, which causes compensatory gait changes, and gender differences in pain sensitivity exist. Impact loadings at heel strike during walking are suspected as a co-factor in development of knee osteoarthritis. Thus the purpose of this study was to investigate the influence of experimental muscle pain and gender on generation and attenuation of impact loading during walking.
Methods:
Ten healthy males and 10 healthy females were recruited. Impact loadings during walking were measured using force platforms and accelerometers attached to the tibia and sacrum. Impact ground reaction force peaks and loading rates, and peak accelerations were used to quantify impact loadings. Attenuation was quantified by means of a transfer function between the tibial and sacral accelerometer signals, and the relative peak acceleration reduction. Knee joint kinematics were collected using a three-dimensional movement analysis system. The study was a cross-over study and data were collected before, during, and after experimental vastus medialis pain and a control situation.
Findings:
Experimental muscle pain did not affect generation or attenuation of impact loading in either gender. While the impact loading magnitude was similar across genders, lower loading rates and more efficient attenuation were observed in females.
Interpretation:
It is concluded that generation and attenuation of impact loadings during walking are independent of quadriceps pain in both genders. The present study does not provide any evidence of the tested variables to address the gender differences in loading rates and attenuation.
The effects of body postures in standing position on the transmission of whole-body vibration to body segments have been investigated. The magnitude acceleration in theZ-axis direction of six body segments: the metatarsus, ankle, knee, hip, shoulder and head has been measured during exposure to random vibration. Ten male subjects exposed to floor vibration stood in ten postures described as: relaxed standing, legs stiffened, legs bent, standing on the toes, standing on one leg with or without support of the other foot and standing in steps. The transmissibility of random vibration from the floor to the body points was calculated at frequencies ranging from 4–250 Hz in 1/3 octave bands. The body postures of the subjects modified both the width of the resonant bands and the transmissibility values. The squared multiple correlation coefficient (R2) between the transmissibility and the 16 variables (10 postures, 6 body segments) was not very high at resonance frequencies in the range 4–12·5 Hz but above 25 Hz, 50% of the variability in the transmissibility was due to the postures and the body segments.
Simulation models of human movement comprising pin-linked segments have a potential weakness for reproducing accurate ground reaction forces during high impact activities. While the human body contains many compliant structures such a model only has compliance in wobbling masses and in the foot-ground interface. In order to determine whether accurate GRFs can be produced by allowing additional compliance in the foot-ground interface, a subject-specific angle-driven computer simulation model of triple jumping with 13 pin-linked segments was developed, with wobbling masses included within the shank, thigh, and trunk segments. The foot-ground interface was represented by spring-dampers at three points on each foot: the toe, ball, and heel. The parameters of the spring-dampers were varied by a genetic algorithm in order to minimise the differences between simulated GRFs, and those measured from the three phases of a triple jump in three conditions: (a) foot spring compression limited to 20 mm; (b) this compression limited to 40 mm; (c) no restrictions. Differences of 47.9%, 15.7%, and 12.4% between simulation and recorded forces were obtained for the 20 mm, 40 mm, and unrestricted conditions, respectively. In the unrestricted condition maximum compressions of between 43 mm and 56 mm were obtained in the three phases and the mass centre position was within 4mm of the actual position at these times. It is concluded that the unrestricted model is appropriate for simulating performance whereas the accurate calculation of internal forces would require a model that incorporates compliance elsewhere in the link system.
Understanding the biomechanics of the medial longitudinal arch (MLA) may provide insights into injury risk and prevention, as well as function of the arch-supporting structures. Our understanding of MLA deformation is currently limited to sit-to-stand, walking, and running.
Three-dimensional deformation of the MLA of the right foot was characterized in 17 healthy participants during several simulated activities of daily living. MLA deformation was quantified by both changes in arch length and navicular displacement during the stance phase of three motions: walking, stair ascent, and stair descent. Three levels of load were also evaluated: no load, a front load (13.6 kg), and a backpack load (13.6 kg). Force platforms and an eight-camera motion capture system were used to collect relevant lower extremity kinetic and kinematic data.
Motion type had a significant (p < 0.05) effect on navicular displacement and arch length elongation with navicular displacement being greatest during stair descent, while the walking and stair descent conditions showed the greatest increase in arch length. External load did not significantly affect either of these two measures (p > 0.05).
Differences in the MLA deformation variables resulting from varied dynamic activities of daily living can be greater than those during walking and should be considered.
Detailing the mechanics of the MLA may aid in further understanding injuries associated with the MLA, and the results of the current study indicate that these mechanics change based on activity.
This article was published in the serial, Journal of Applied Biomechanics [© Human Kinetics]. The definitive version is available at: http://journals.humankinetics.com/JAB The aims of this study were to quantify intra-segmental motion using an array of 28 surface mounted markers to examine frequency and amplitude measurements of the intra-segmental motion to calculate forces and energy transfer; and to show that the underlying muscles are a major contributor to the skin marker motion. One subject performed 27 trials under three conditions in which his forearm was struck against a solid object fixed to a force plate while the locations of the markers were recorded at 240 Hz. For impacts with equal peak forces the muscle tension significantly affected the amount of intra-segmental motion. Tensing the arm reduced the intra-segmental motion by 50 %. The quadrilateral sectors defined by the markers changed in area by 11% with approximately equal motion in the vertical and horizontal direction. The maximum linear marker motion was 1.7 cm. The intra-segmental motion had distinct frequency components around 14 and 20 Hz. Soft tissue deformation could account for 70 % of the energy lost from the forearm during these impacts. The study has demonstrated the important role that intra-segment soft tissue motion can have on the kinetics of an impact. Accepted for publication
This article was accepted for publication in the Journal of Biomechanics [© Elsevier]. It is also available at: www.elsevier.com/locate/jbiomech The aim of this study was to test the hypothesis that by accounting for soft tissue motion of the lower leg during the impacts associated with in vivo testing, that the differences between in vivo and in vitro estimates of heel pad properties can be explained. To examine this a two-dimensional model of the shank and heel pad was developed using DADS. The model contained a heel pad element and a rigid skeleton to which was connected soft tissue which could move relative to the bone. Simulations permitted estimation of heel pad properties directly from heel pad deformations, and from the kinematics of an impacting pendulum. These two approaches paralleled those used in vitro and in vivo respectively. Measurements from the pendulum indicated that heel pad properties changed from those found in vitro to those found in vivo as relative motion of the bone and soft tissue was allowed. This would indicate that pendulum measures of the in vivo heel pad properties are also measuring the properties of the whole lower leg. The ability of the wobbling mass of the shank to dissipate energy during an impact was found to be significant. These results demonstrate the important role of both the heel pad and soft tissue of the shank to the dissipation of mechanical energy during impacts. These results provide a further clarification of the paradox between the measurements of heel pad properties made in vivo and in vitro. Accepted for publication
This study aimed to determine whether the landing phase of a drop landing (DL) differed with respect to a complete jumping and landing task, a spike jump (SJ), and whether fatigue altered the landing of these movements. Fourteen male volleyball players performed five DL and SJ in a counterbalanced order under two experimental conditions: non-fatigued and fatigued. Fatigue, induced by repetitive jumping sets, was confirmed by decrements in vertical jump height >25% and increased blood lactate >6 mmol/L. Each landing task was characterized by the resultant ground reaction forces (GRF), sagittal plane kinematics and muscle recruitment patterns of six lower extremity muscles. Two-way repeated analysis of variance results indicated a main effect of movement on many of the GRF, kinematic and electromyographic variables characterizing landing, indicating that the two tasks required substantially different lower limb biomechanics during landing. Although fatigue did not alter the GRF in either task, there were significant movement x fatigue condition interactions. The significant between-task differences in the biomechanical variables characterizing landing and the differential effects of fatigue on each landing task, question the validity of using a DL as an experimental task to investigate lower limb landing mechanics of whole jumping and landing movements.
Statistical guidelines and expert statements are now available to assist in the analysis and reporting of studies in some biomedical disciplines. We present here a more progressive resource for sample-based studies, meta-analyses, and case studies in sports medicine and exercise science. We offer forthright advice on the following controversial or novel issues: using precision of estimation for inferences about population effects in preference to null-hypothesis testing, which is inadequate for assessing clinical or practical importance; justifying sample size via acceptable precision or confidence for clinical decisions rather than via adequate power for statistical significance; showing SD rather than SEM, to better communicate the magnitude of differences in means and nonuniformity of error; avoiding purely nonparametric analyses, which cannot provide inferences about magnitude and are unnecessary; using regression statistics in validity studies, in preference to the impractical and biased limits of agreement; making greater use of qualitative methods to enrich sample-based quantitative projects; and seeking ethics approval for public access to the depersonalized raw data of a study, to address the need for more scrutiny of research and better meta-analyses. Advice on less contentious issues includes the following: using covariates in linear models to adjust for confounders, to account for individual differences, and to identify potential mechanisms of an effect; using log transformation to deal with nonuniformity of effects and error; identifying and deleting outliers; presenting descriptive, effect, and inferential statistics in appropriate formats; and contending with bias arising from problems with sampling, assignment, blinding, measurement error, and researchers' prejudices. This article should advance the field by stimulating debate, promoting innovative approaches, and serving as a useful checklist for authors, reviewers, and editors.
Results of mechanical analyses of running may be helpful in the search for the etiology of running injuries. In this study a mechanical analysis was made of the landing phase of three trained heel-toe runners, running at their preferred speed and style. The body was modeled as a system of seven linked rigid segments, and the positions of markers defining these segments were monitored using 200 Hz video analysis. Information about the ground reaction force vector was collected using a force plate. Segment kinematics were combined with ground reaction force data for calculation of the net intersegmental forces and moments.
The transmission of heel-strike vibration using skin-mounted accelerometers was measured in normal subjects and subjects with ankylosing spondylitis. In normal subjects transmissibility was enhanced between 5 and 13 Hz and attenuated at frequencies above 15 Hz. In ankylosing spondylitis transmissibility was enhanced at 4 Hz but less so between 5 and 13 Hz and little attenuation was observed at the higher frequencies. This difference is expected in view of the pathological changes occurring in the spinal column in ankylosing spondylitis. The results support the hypothesis that the normal spinal column has to bend in order to absorb vibrations with a frequency greater than 15 Hz.
A biomechanical study has been carried out on 20 cadaveric knees to investigate their load-absorbing mechanism. The impact load was applied using a weight falling onto the transected proximal femur and the force transmitted through the knee was measured at the transected distal tibia using a load transducer. The peak force transmitted increased as, sequentially, meniscus, articular cartilage and subchondral bone were damaged or removed. The most striking result was found in an implanted knee replacement where the transmitted force reached 180% of that in the intact knee. The results show that the joint has an impact-absorbing property in each segment and that in the osteoarthritic knee there is less absorption of shock than in the normal knee. The high impact force in an implanted knee suggests that microfractures of the cancellous bone might be expected and may produce loosening.
Simultaneous measurements during normal walking of the transient acceleration on heel strike in the tibia and skull show peaks of ∼ 5 g and 0.5 g respectively when hard heels were worn. Resilient heels halved the amplitudes, while rebound could be avoided by a construction including a viscoelastic polymer insert. The transient is propagated as travelling waves up (and outwards from) the skeleton, its inconspicuous appearance in force plate studies being due to the non-uniform and non-synchronous acceleration of various parts of the body.Implications of these findings are noted, including the potential contribution of heel strike transients to osteoarthritic degeneration. Aggravation of symptoms in sufferers from back troubles may well be due to shear induced by them in para-osteal tissue. Possible physiological roles for the transients, which may account for their existence, are also mentioned.
In this second of three papers, the principles of a non-invasive in vivo method to quantitatively evaluate the shock absorbing capacity of the human musculoskeletal system and the correlation of this shock absorbing capacity with low back pain (LPB) symptoms are presented. The experiments involved patients suffering from low back pain (as well as other degenerative joint diseases) and healthy patients. The obtained results reveal that low back pain correlates with the reduced capacity of the human musculoskeletal system between the femoral condyle and the forehead to attenuate incoming shock waves. Examination of the absolute values of the amplitude of the propagated waves leads to the conclusion that the human locomotor system, which possesses reduced attenuation capacity, tries to prevent overloading of the head from insufficiently attenuated shock waves. Results of the present investigation support the idea that the repetitive loading resulting from gait generates intermittent waves that propagate through the entire human musculoskeletal system from the heel up to the head. These waves are gradually attenuated along this course by the natural shock absorbers (bone and soft tissues). Contemporary methods for examination of the human musculoskeletal system may by improved by using the proposed non-invasive in vivo technique for quantitative characterization of the locomotor system's shock absorbing capacity.
The principles of a noninvasive measurement of the shock absorbing capacity of the knee are presented. Accelerometry, which has been proven to be a useful tool for noninvasive measurements in biomechanical investigation, was employed for quantitative evaluation of the knee's shock absorbing capacity by registration of bone vibrations resulting from the gait. Results of the experiments show that both patients with painful knee and patients after meniscectomy suffer from insufficient shock absorbing capacity of the knee. It was found that the shock absorbing capacity of a normal knee is about 20% higher than that of a pathological one. The results indicate that while meniscectomy may reduce pain, instability, swelling, etc. in an injured knee, it cannot improve its reduced shock absorbing capacity, which eventually will lead to development of degenerative osteoarthritis. It seems that the pain syndrome is a biological reaction to severe repetitive overloading of the knee. Noninvasive in vivo determination of the knee's shock absorbing properties may be useful as an additional clinical technique to reveal a knee's pathology. It may lead to early discovery of knee insufficiency, so that preventive steps can be taken to delay or reverse the process of degeneration.
The attenuation of shock waves invading the human locomotion system during gait has been studied. The purpose of this work is to evaluate attenuational capacity of the healthy locomotion system by using an original system which consists of accelerometers attached to specified points of the legs, body and head and to recording devices.The experiments were performed on clinically healthy subjects who, on the basis of obtained data, were divided into two groups: those truly healthy and those with a high risk for development of degenerative changes in their joints.The shock absorbing capacity of the truly healthy subjects' locomotor systems has been estimated.The methodology presented may serve as a simple diagnostic tool for early revealing of the deficiency of the subject's locomotion system. This may allow some preventive action to be taken to delay or cancel the process of joint degeneration.
The influence of the mechanical characteristics of certain insole materials in the generation and transmission of heel strike impacts while walking was studied. Three insole materials were selected according to their mechanical characteristics under heel strike impacts. The selection of materials has made it possible to distinguish the effect of rigidity and loss tangent in the transmission of heel strike impacts. A lower rigidity and a high loss tangent have been shown to reduce the transmission of impacts to the tibia. A low rigidity was seen to significantly increase the transmission of impacts from tibia to forehead.
The shocks imparted to the foot during locomotion may lead to joint-degenerative diseases and jeopardize the visual-vestibular functions. The body relies upon several mechanisms and structures that have unique viscoelastic properties for shock attenuation. The purpose of the present study was to determine whether impact severity and initial knee angle (IKA) could alter the shock transmission characteristics of the body. Impacts were administered to the right foot of 38 subjects with a human pendulum device. Combinations of velocities (0.9, 1.05 and 1.2 m s-1) and surfaces (soft and hard foams) served to manipulate impact severity in the first experiment. Three IKA (0, 20 and 40 degrees) were examined in the second experiment. Transmission between shank and head was characterized by measuring the shock at these sites with miniature accelerometers. Velocity and surface had no effect on the frequency profile of shock transmission suggesting a consistent response of the body to impact severity. Shank shock power spectrum features accounted for the lower shock ratio (head/shank) measured under the hard surface condition. IKA flexion caused considerable reduction in effective axial stiffness of the body (EASB), 28.7-7.9 kNm-1, which improved shock attenuation. The high correlation (r = 0.97) between EASB and shock ratio underscored the importance of EASB to shock attenuation. The present findings provide valuable information for the development of strategies aimed at protecting the joints, articular cartilage, spine and head against locomotor shock.
A three-dimensional model of the lower limb containing 47 muscles was developed to study the differences between a two- and three-dimensional approach for determining internal loads, the role of the dynamic joint representation, and the behavior of different load-bearing criteria in walking and running. The problem of redundancy of the musculo-skeletal system was resolved by applying inverse dynamics and static optimization methods. Different hypothetical load-bearing capabilities of hinge, spherical and intermediate joint types for the knee and the ankle joints were tested. It was found that even almost planar movements such as walking and running are associated with significant three-dimensional intersegment moments, especially in the frontal plane. Thus, a two-dimensional approach may underestimate internal loads up to 60%. It is shown that pure hinge joints are inappropriate for modeling the dynamical joint function of the knee and ankle joints. A more flexible joint representation in combination with a squared muscle stress minimization criterion predicted a lot of synergistic as well as antagonistic muscle activation which was also found in the EMG patterns. The results indicate the importance of muscular joint stabilization in natural human movements. Compared to in vivo measurements it is speculated that the predicted force magnitudes are considerably overestimated due to error propagation and still insufficient anatomical models. Thus, increased efforts to improve further the reliability of internal load calculations should be made in the future.
The foot-ground impact experienced during running produces a shock wave that is transmitted through the human skeletal system. This shock wave is attenuated by deformation of the ground/shoe as well as deformation of biological tissues in the body. The goal of this study was to investigate the locus of energy absorption during the impact phase of the running cycle.
Running speed (3.83 m x s[-1]) was kept constant across five stride length conditions: preferred stride length (PSL), +10% of PSL, -10% of PSL, +20% of PSL, and -20% of PSL. Transfer functions were generated from accelerometers attached to the leg and head of ten male runners. A rigid body model was used to estimate the net energy absorbed at the hip, knee, and ankle joints.
There was an increasing degree of shock attenuation as stride length increased. The energy absorbed during the impact portion of the running cycle also increased with stride length. Muscles that cross the knee joint showed the greatest adjustment in response to increased shock.
It was postulated that the increased perpendicular distance from the line of action of the resultant ground reaction force to the knee joint center played a role in this increased energy absorption.
The purpose of the study was to investigate changes in lower extremity joint energy absorption for different landing heights and landing techniques.
Nine healthy, active male subjects volunteered to perform step-off landings from three different heights (0.32 m, 2.5 m(-s); 0.62 m, 3.5 m(-s); and 1.03 m, 4.5 m(-s)) using three different landing techniques (soft, SFL; normal, NML; and stiff landing, STL). Each subject initially performed five NML trials at 0.62 m to serve as a baseline condition and subsequently executed five trials in each of the nine test conditions (3 heights x 3 techniques).
The results demonstrated general increases in peak ground reaction forces, peak joint moments, and powers with increases in landing height and stiffness. The mean eccentric work was 0.52, 0.74, and 0.87 J x kg(-1) by the ankle muscles, and 0.94, 1.31, and 2.15 J x kg(-1) by the hip extensors, at 0.32, 0.62, and 1.03 m, respectively. The average eccentric work performed by the knee extensors was 1.21, 1.63, and 2.26 J x kg(-1) for the same three heights.
The knee joint extensors were consistent contributors to energy dissipation. The ankle plantarflexors contributed more in the STL landings, whereas the hip extensors were greater contributors during the SFL landings. Also a shift from ankle to hip strategy was observed as landing height increased.
Surface myoelectric signals often appear to carry more information than what is resolved in root mean square analysis of the progress curves or in its power spectrum. Time-frequency analysis of myoelectric signals has not yet led to satisfactory results in respect of separating simultaneous events in time and frequency. In this study a time-frequency analysis of the intensities in time series was developed. This intensity analysis uses a filter bank of non-linearly scaled wavelets with specified time-resolution to extract time-frequency aspects of the signal. Special procedures were developed to calculate intensity in such a way as to approximate the power of the signal in time. Applied to an EMG signal the intensity analysis was called a functional EMG analysis. The method resolves events within the EMG signal. The time when the events occur and their intensity and frequency distribution are well resolved in the intensity patterns extracted from the EMG signal. Averaging intensity patterns from multiple experiments resolve repeatable functional aspects of muscle activation. Various properties of the functional EMG analysis were shown and discussed using model EMG data and real EMG data.
Vibration characteristics were recorded for the soft tissues of the triceps surae, tibialis anterior, and quadriceps muscles. The frequency and damping of free vibrations in these tissues were measured while isometric and isotonic contractions of the leg were performed. Soft tissue vibration frequency and damping increased with both the force produced by and the shortening velocity of the underlying muscle. Both frequency and damping were greater in a direction normal to the skin surface than in a direction parallel to the major axis of each leg segment. Vibration characteristics further changed with the muscle length and between the individuals tested. The range of the measured vibration frequencies coincided with typical frequencies of impact forces during running. However, observations suggest that soft tissue vibrations are minimal during running. These results support the strategy that increases in muscular activity may be used by some individuals to move the frequency and damping characteristics of the soft tissues away from those of the impact force and thus minimize vibrations during walking and running.
This study tested the hypotheses that when the excitation frequency of mechanical stimuli to the foot was close to the natural frequency of the soft tissues of the lower extremity, the muscle activity increases 1) the natural frequency and 2) the damping to minimize resonance. Soft tissue vibrations were measured with triaxial accelerometers, and muscle activity was measured by using surface electromyography from the quadriceps, hamstrings, tibialis anterior, and triceps surae groups from 20 subjects. Subjects were presented vibrations while standing on a vibrating platform. Both continuous vibrations and pulsed bursts of vibrations were presented, across the frequency range of 10-65 Hz. Elevated muscle activity and increased damping of vibration power occurred when the frequency of the input was close to the natural frequency of each soft tissue. However, the natural frequency of the soft tissues did not change in a manner that correlated with the frequency of the input. It is suggested that soft tissue damping may be the mechanism by which resonance is minimized at heel strike during running.
In clinical research, parameters required for sample size calculation are usually unknown. A typical approach is to use estimates from some pilot studies as the true parameters in the calculation. This approach, however, does not take into consideration sampling error. Thus, the resulting sample size could be misleading if the sampling error is substantial. As an alternative, we suggest a Bayesian approach with noninformative prior to reflect the uncertainty of the parameters induced by the sampling error. Based on the informative prior and data from pilot samples, the Bayesian estimators based on appropriate loss functions can be obtained. Then, the traditional sample size calculation procedure can be carried out using the Bayesian estimates instead of the frequentist estimates. The results indicate that the sample size obtained using the Bayesian approach differs from the traditional sample size obtained by a constant inflation factor, which is purely determined by the size of the pilot study. An example is given for illustration purposes.
The principle of specificity suggests that it may be beneficial to undertake plyometric drop-jump training when fatigued. However, this may increase peak-impact accelerations and therefore increase the risk of injury. The aims of the study were to determine if whole-body fatigue (i) increased peak-impact acceleration on the proximal tibia during plyometric drop jumps and (ii) produced associated changes in knee-joint kinematics during landing.
Fifteen physically active male subjects performed drop jumps (30 and 50 cm) when nonfatigued and when fatigued. Whole-body fatigue was induced using a treadmill running protocol that incrementally increased effort. Peak-impact acceleration was measured with an accelerometer attached to the proximal tibia. Knee-joint kinematics were assessed during the eccentric phase: angle at initial touch down, maximum angle of flexion, range of motion, and peak angular velocity.
Fatigue caused a significant increase in tibial impact acceleration and peak angular velocity in drop jumps from 30 cm (154.9 +/- 93.8 vs 192.6 +/- 103.9 m x s(-2): 24%; 675.3 +/- 60.7 vs 811.4 +/- 68.9 degrees x s(-1): 20%), but not from 50 cm (222.4 +/- 74.9 vs 234.1 +/- 83.9 m x s(-2): 5%; 962.0 +/- 189.0 vs 984.4 +/- 189.3 degrees x s(-1): 2.6%), with no associated change in the knee-joint angles assessed. It was argued, however, that rather than the neuromuscular system being selectively affected by fatigue at 30 cm and not 50 cm, drop jumps from 50 cm resulted in larger-impact accelerations with the neuromuscular system having only a limited ability to attenuate them per se, whether fatigued or nonfatigued.
Care should be taken when performing drop jumps from a height of 30 cm in a fatigued state because of the reduced capacity to attenuate impact accelerations at the tibia, which may be associated with an increased risk of injury.
The purposes of this study were to measure the relative linear and angular displacements of each pair of adjacent cervical vertebrae and to compute changes in distance between two adjacent facet joint landmarks during low posterior-anterior (+Gx) acceleration without significant hyperextension of the head. A total of twentysix low speed rear-end impacts were conducted using six postmortem human specimens. Each cadaver was instrumented with two to three neck targets embedded in each cervical vertebra and nine accelerometers on the head. Sequential x-ray images were collected and analyzed. Two seatback orientations were studied. In the global coordinate system, the head, the cervical vertebrae, and the first or second thoracic vertebra (T1 or T2) were in extension during rear-end impacts. The head showed less extension in comparison with the cervical spine. Relative motion for each cervical motion segment went from flexion at the upper cervical levels to extension at the lower cervical levels, with a transition region at the mid-cervical levels. This rotational pattern formed an "S" shape in the cervical spine during the initial phase of low-speed rear impacts. A pair of facet joint landmarks on each cervical motion segment was used to measure the distance across the joint space. Uni-axial facet capsular strains were calculated by dividing changes in this distance over the original distance in seven tests using three specimens. In 20-degree seatback tests, the average strain was 32+/-11% for the C2/C3 facet joint (17%-43% range), and 59+/-26% for the C3/C4 facet joint (41%-97% range). The C4/C5 and C5/C6 facet joints exhibited peak tensile or compressive strains in different specimens. In 0-degree seatback tests, the average strain was 28+/-11% for the C2/C3 facet joint (21%-41% range), 30+/-9% for the C3/C4 facet joint (21%-39% range), 22+/-4% for the C4/C5 facet joint (19%-25% range), and 60+/-13% for the C5/C6 facet joint (51%-69% range). In 20-degree seatback tests, there was less initial cervical lordosis, more upward ramping of the thoracic spine, and more relative rotation of each cervical motion segment in comparison with the 0-degree seatback tests. Relative to T1, the head went from flexion to extension for 20-degree seatback tests while stayed in extension for 0-degree seatback tests.
According to experimental studies, low-amplitude high-frequency vibration is anabolic to bone tissue, whereas in clinical trials, the bone effects have varied. Given the potential of whole body vibration in bone training, this study aimed at exploring the transmission of vertical sinusoidal vibration to the human body over a wide range of applicable amplitudes (from 0.05 to 3 mm) and frequencies (from 10 to 90 Hz). Vibration-induced accelerations were assessed with skin-mounted triaxial accelerometers at the ankle, knee, hip, and lumbar spine in four males standing on a high-performance vibration platform. Peak vertical accelerations of the platform covered a range from 0.04 to 19 in units of G (Earth's gravitational constant). Substantial amplification of peak acceleration could occur between 10 and 40 Hz for the ankle, 10 and 25 Hz for the knee, 10 and 20 Hz for the hip, and at 10 Hz for the spine. Beyond these frequencies, the transmitted vibration power declined to 1/10th-1/1000 th of the power delivered by the platform. Transmission of vibration to the body is a complicated phenomenon because of nonlinearities in the human musculoskeletal system. These results may assist in estimating how the transmission of vibration-induced accelerations to body segments is modified by amplitude and frequency and how well the sinusoidal waveform is maintained. Although the attenuation of vertical vibration at higher frequencies is fortunate from the aspect of safety, amplitudes >0.5 mm may result in greater peak accelerations than imposed at the platform and thus pose a potential hazard for the fragile musculoskeletal system.