Vertical Ground Reaction Force Data Research Articles

The Modified Reactive Strength Index Is a Valid Measure of Lower-Body Explosiveness in Male and Female High School Athletes.

Witte, BC, Schouten, TC, Westphal, JA, VanZile, AW, Jones, DD, Widenhoefer, TL, Dobbs, WC, Jagim, AR, Luedke, JA, and Almonroeder, TG. The modified reactive strength index is a valid measure of lower-body explosiveness in male and female high school athletes. J Strength Cond Res XX(X): 000-000, 2024-The modified reactive strength index (mRSI) is a commonly used metric to quantify lower-body explosiveness during countermovement jump (CMJ) performance. However, few studies have attempted to examine its validity as a measure of explosiveness, particularly among high school athletes. The purpose of this study was to examine the validity of the mRSI as a measure of lower-body explosiveness among a relatively large sample of male and female high school athletes from various sports. As part of this study, male (n = 132) and female (n = 43) high school athletes performed CMJs, while ground reaction forces were recorded using a force platform. The vertical ground reaction force data collected during the CMJs were used to derive the following variables: peak force (PF), peak power, time to PF, time to take-off, peak rate of force development, and the mRSI. Principal component analysis was applied and reduced these variables into 2 components related to "force" and "speed." The mRSI loaded on both the force (loading = 0.82) and speed (loading = -0.46) components, indicating that it incorporates elements of both force and speed, although it loaded more strongly on the force component than the speed component. The observed pattern of cross-loading suggests that the mRSI is generally a valid measure of lower-body explosiveness for male and female high school athletes.

Interlimb kinetic asymmetries during the tuck jump assessment are more exposed following kinetic stabilization

ObjectiveTo analyse interlimb kinetics and asymmetries during the tuck jump assessment (TJA), before and after kinetic stabilization, to identify injury risk in healthy female athletes. DesignCross-sectional study. SettingLaboratory. ParticipantsTwenty-five healthy females (age 21.0 ± 1.83 yrs; height 1.68 ± 0.06 m; body mass 69.4 ± 10.7 kg). Main outcome measuresKinetics were measured during 10-s trials of the TJA and absolute asymmetries compared, before and after kinetic stabilization using paired sample t-tests. Statistical parametric mapping (SPM) compared vertical ground reaction force (VGRF) data for each limb during the jumping cycles before and after stabilization. ResultsSmall to moderate increases in interlimb asymmetries were observed after stabilization for VGRF, relative vertical leg stiffness, average loading rate, total and propulsive impulse, peak braking and propulsive force (p < 0.05). SPM revealed significant interlimb differences between 77-98% and 83–99% of ground contact for the jumping cycles pre- and post-stabilization respectively. ConclusionsLarger asymmetries were evident after kinetic stabilization, with increased VGRF in the non-dominant limb. We speculate that participants sacrificed interlimb landing symmetry to achieve kinetic stability, which may reflect a primal landing strategy that forgoes movement quality. Assessing lower limb biomechanics using the TJA should involve examining kinetic stability and interlimb kinetic asymmetries.

Relationship Between Kinetic and Kinematic Measures of the Countermovement Jump and National Weightlifting Performance

Abstract Purpose The association between vertical jump and weightlifting performance have been well established often using discrete performance measures such as jump height or peak power which provides little insight into temporal strategies. The purpose of this investigation was to identify currently unassessed temporal countermovement jump metrics and their reliability and relationship to national weightlifting performance. Methods A total of 42 national weightlifting athletes (n = 30 females and 12 males), were recruited for this study. Countermovement jump was measured using a force plate following a national and international competition. Vertical ground reaction force and time data were analyzed using a custom script where temporal metrics relating to specific phases of the jump were extracted. Snatch, Clean and Jerk and Total weightlifting performance was obtained following each competition. Reliability of jump metrics were determined using coefficient of variation and interclass correlation coefficient. A Spearman’s Rho, non-parametric bivariate correlation was used to determine the relationship between the jump metrics and weightlifting performance. Results From a total of 15 metrics, 13 were deemed reliable, with propulsive impulse showing the greatest level of reliability. Correlational analysis showed strong to very strong (r = 0.676–0.817) relationships between all absolute measures of weightlifting performance and propulsive impulse for both women and men. Conclusion This novel finding suggests that practitioners may wish to use propulsive impulse as it may provide more insight into changes of force capabilities following training. Additionally, it may also be used as a talent identification tool given its strong relationship to performance.

Using load sensing insoles to identify knee kinetic asymmetries during landing in patients with an Anterior Cruciate Ligament reconstruction

BackgroundKnee extension moment asymmetry is a known second anterior cruciate ligament injury risk factor in patients who have had an anterior cruciate ligament reconstruction. Traditionally, assessing asymmetries requires motion capture and force platforms which are expensive and occupy a large space. Wireless force sensing insoles could be a feasible surrogate. MethodsTwenty-nine patients following anterior cruciate ligament reconstruction performed ten bilateral stop jumps while insole forces, ground reaction forces, and lower extremity kinematics were collected. Peak knee extension moment symmetry was computed using the kinematic and kinetic data, and peak impact force symmetry and impulse symmetry were computed using both the insole force data and vertical ground reaction force data. The relationship between outcomes was analyzed using Pearson correlation coefficients. Patients were classified as symmetric or asymmetric for each outcome based on an 85% symmetry cutoff. The resulting classifications were qualitatively compared across outcome measures. FindingsPeak knee extension moment symmetry had a strong association with the force plate symmetry outcomes (r = 0.72–0.96, p < 0.001) and a moderate to strong association with insole symmetry outcomes (r = 0.67–0.77, p < 0.001). There was strong agreement between insole and force plate symmetry outcomes (r = 0.69–0.90, p < 0.001). Four patients were identified as symmetric when using the peak knee extension moment symmetry, five when using force plate data, and eight when using insole data. InterpretationForce sensing insoles could be used as a surrogate for knee extension moment asymmetry in patients who have had an anterior cruciate ligament reconstruction.

Evaluation of Different Pressure-Based Foot Contact Event Detection Algorithms across Different Slopes and Speeds.

If validated, in-shoe pressure measuring technology allows for the field-based quantification of running gait, including kinematic and kinetic measures. Different algorithmic methods have been proposed to determine foot contact events from in-shoe pressure insole systems, however, these methods have not been evaluated for accuracy, reliability against a gold standard using running data across different slopes, and speeds. Using data from a plantar pressure measurement system, seven different foot contact event detection algorithms based on pressure signals (pressure sum) were compared to vertical ground reaction force data collected from a force instrumented treadmill. Subjects ran on level ground at 2.6, 3.0, 3.4, and 3.8 m/s, six degrees (10.5%) inclined at 2.6, 2.8, and 3.0 m/s, and six degrees declined at 2.6, 2.8, 3.0, and 3.4 m/s. The best performing foot contact event detection algorithm showed maximal mean absolute errors of only 1.0 ms and 5.2 ms for foot contact and foot off, respectively, on level grade, when compared to a 40 N ascending and descending force threshold from the force treadmill data. Additionally, this algorithm was unaffected by grade and had similar levels of errors across all grades.

The reliability of lower limb 3D gait analysis variables during a change of direction to 90- and 135-degree manoeuvres in recreational soccer players.

Several biomechanical outcomes are being used to monitor the risk of injuries; therefore, their reliability and measurement errors need to be known. To measure the reliability and measurement error in lower limb 3D gait analysis outcomes during a 90∘ and 135∘ change of direction (COD) manoeuvre. A test re-test reliability study for ten healthy recreational players was conducted at seven-day intervals. Kinematics (Hip flexion, adduction, internal rotation angles and knee flexion abduction angles) and kinetics (Knee abduction moment and vertical ground reaction force) data during cutting 90∘ and 135∘ were collected using 3D gait analysis and force platform. Five trials for each task and leg were collected. Standard error of measurement (SEM) and the intraclass correlation coefficient (ICC) were calculated from the randomised leg. The ICC values of the kinematics, kinetics, and vertical ground reaction force (VGRF) outcomes (90∘ and 135∘) ranged from 0.85 to 0.95, showing good to excellent reliability. The SEM for joint angles was less than 1.69∘. The VGRV showed a higher ICC value than the other outcomes. The current study results support the use of kinematics, kinetics, and VGRF outcomes for the assessment of knee ACL risk in clinic or research. However, the hip internal rotation angle should be treated with caution since the standard measurement error exceeded 10% compared to the mean value. The measurement errors provided in the current study are valuable for future studies.

Analysis of plantar impact characteristics of walking in patients with flatfoot according to basic mechanical features and continuous wavelet transform

Flatfoot is a common foot deformity, and the collapse of the arch structure affects the foot cushioning during walking. A growing number of scholars have found that the analysis of the impact force should be combined with both the magnitude and the frequency of the impact force. Therefore, the aim of this study is to investigate the plantar impact characteristics of flatfoot patients and normal foot people at different load-bearing buffer stage from the time and frequency domains. Sixteen males with flatfoot and sixteen males with normal foot were recruited to walk on the plantar pressure test system at the same step speed, and the vertical ground reaction force data were collected from the heel contact stage and the arch support stage. The differences in the frequency domain of the ground reaction force between the flatfoot and the normal foot in the two stages were analyzed according to the basic mechanical characteristics and the continuous wavelet transform. Independent sample t-test was used to compare the baseline data of subjects, and the differences in foot impact force characteristics at different stages of foot type and weight-bearing cushion phase were compared by two-factor repeated measures Analysis of Variance. 1) In terms of basic mechanical characteristics, In both groups for flatfoot patients and normal foot people, the peak ground reaction force was higher in the arch support stage compared to the heel contact stage (Pflatfoot&amp;lt;0.001, Pnormal foot&amp;lt;0.001), and the load rate of force change was smaller in this stage (Pflatfoot&amp;lt;0.001, Pnormal foot&amp;lt;0.001). However, no differences in peak ground reaction force and time of occurrence were found between flatfoot and normal foot in the two stages (p &amp;gt; 0.05), in the arch support stage, the force change load rate of patients with flatfoot was lower than that of normal foot people (p = 0.021). 2) The results of time and frequency domain characteristics showed that during the heel contact and the arch support stage, no significant differences in the maximum signal power as well as the corresponding time and the frequency of the main impact force between the normal foot and the flatfoot were found. In both flatfoot and normal foot types, compared with the foot heel contact stage, the maximum signal power in the arch support stage was higher (Pflatfoot &amp;lt; 0.001, Pnormal foot&amp;lt;0.001), and the corresponding impact frequency was smaller (Pflatfoot = 0.002, Pnormal foot = 0.004). Once the step speed was controlled, the flatfoot patients only showed a smaller impact force load rate in the arch support stage, which may be related to their lower arch rigidity. The characteristics of the impact force in different stages of walking support period were different in time and frequency domain, suggesting that there may be differences in the function of various parts of the foot.

Visualising knee loading patterns during kneeling and the development of a laboratory-based adaptation of the Aberdeen Weight-Bearing Test (Knee)

BackgroundInformation regarding the loading of key anatomical structures of the knee during kneeling would enhance existing functional tests, yet current visualisation methods are limited and require further development. Aims(1) Develop a knee loading visualisation technique to investigate loading patterns of the knee during kneeling; and (2) determine the utility of the technique in combination with vertical ground reaction forces and centre of pressure data in the lab-based Aberdeen Weight-Bearing Test (Knee) by assessing their reliability. MethodsFourteen healthy participants conducted kneeling tasks with and without knee pads across two testing sessions. Eight force-sensitive resistors were affixed to the right knee throughout different kneeling tasks: upright kneeling, and reaching forward, back, left, and right. A photo of the force-sensitive resistor configuration was used to generate participant-specific heat maps of knee loading. Two in-ground force platforms were used to measure vertical ground reaction forces and centre of pressure. ResultsThe inferior patella tendon showed the highest proportion of activation during both bare and knee pad kneeling for all kneeling tasks. Knee pads reduced the repeatability of knee loading patterns. Force-sensitive resistor activation and vertical ground reaction force components of the lab-based Aberdeen Weight-Bearing Test (Knee) were shown to be reliable, whereas the centre of pressure data was unreliable. ConclusionWe have developed a lab-based technique for visualising knee loading using force-sensitive resistors. The combination of force-sensitive resistor activation and vertical ground reaction force data provides valuable insights into both the magnitude and locations of applied loads throughout kneeling.

Ground reaction force and plantar pressure distribution data Korean young adults during barefoot walking

Gait analysis has been used to evaluate disease progression and efficiency of rehabilitation. This study aimed to establish the population database of the vertical ground reaction force and plantar pressure time-series data during walking. Plantar pressure and ground reaction force data were collected from 171 asymptomatic young Korean adults, and the normality of the data were tested. The normative data of the spatiotemperal gait parameters, time-series vertical ground reaction force curves, and butterfly diagrams (center of pressure trajectory) were established. The data collected in the current study would serve as the reference gait data of young Korean population and help healthcare professionals assess the existence or severity of abnormal gait patterns of patients.

Jump landing among chronic ankle instability individuals who did or did not attend rehabilitation at the time of injury

ObjectivesThe purpose was to compare vertical ground reaction forces and sagittal-plane energy dissipation patterns of the lower extremity during a single-limb jump-stabilization task between individuals with chronic ankle instability who did or did not attend rehabilitation after their initial ankle sprain. DesignCross-sectional. SettingResearch laboratory. ParticipantsEight participants with chronic ankle instability who did and 12 participants who did not attend rehabilitation were enrolled. Main outcome measuresNormalized vertical ground reaction force data were used to calculate the average loading rate, time to peak force, and the peak force. Sagittal plane kinematics and joint moments at the ankle, knee, and hip, were used to calculate each joint's relative energy dissipation at 50, 100, 150, and 200 ms post-landing. ResultsParticipants who attended rehabilitation had a slower average loading rate (P = 0.025) and smaller peak vertical ground reaction force (P = 0.025). The average relative energy dissipation at the knee was higher in those who attended rehabilitation at the 100 ms (P = 0.041), 150 ms (P = 0.046), and 200 ms (P = 0.042) time intervals. ConclusionsAttending rehabilitation after an ankle sprain may have a beneficial effect on jump-stabilization outcomes among individuals with chronic ankle instability.

Shoe Bending Stiffness Influence on Lower Extremity Energetics in Consecutive Jump Take-Off.

Objective This study examined the influence of shoe bending stiffness on lower extremity energetics in the take-off phase of consecutive jump. Methods Fifteen basketball and volleyball players wearing control shoes and stiff shoes performed consecutive jumps. Joint angle, angular velocity, moments, power, jump height, take-off velocity, take-off time, and peak vertical ground reaction force data were simultaneously captured by motion capture system and force platform. Paired t-tests were performed on data for the two shoe conditions that fit the normal distribution assumptions, otherwise Wilcoxon signed-rank tests. Results There are significant differences (P < 0.05) in take-off velocity and take-off time between stiff and control shoe conditions; the stiff shoes had faster take-off velocity and shorter take-off time than control shoes. There was no significant difference between two conditions in jump height (P = 0.512) and peak vertical ground reaction force (P = 0.589). The stiff shoes had significantly lower MTP dorsiflexion angle and greater joint work than the control shoes (P < 0.05). The MTP range of motion and maximum angular velocity in stiff shoe condition were significantly lower than those in control shoe condition (P < 0.01). However, there are no significant differences between two conditions in kinetics and kinematics of the ankle, knee, and hip joint. Conclusions The findings suggest that wearing stiff shoes can reduce the effect of participation of the MTP joint at work and optimize the energy structure of lower-limb movement during consecutive jumps.

Novel machine learning-based hybrid strategy for severity assessment of Parkinson's disorders.

Parkinson's disease (PD) severity assessment in clinical settings largely depends on expertise level of clinicians which have inherent limitations and non-uniformity. Instrumented gait analysis plays a significant role in disease diagnosis and management. However, these are agonized from data dispersion due to demography, anthropometry, and self-selected walking speed of an individual. This research work aims to develop computationally efficient hybrid strategy using normalized features for PD severity evaluation. The relevance of each considered gait feature in demonstrating the outcomes is explained through feature importance and partial dependence plot (PDP) to build substantial insight for clinical needs. Gait, a biomarker, is used to access human mobility by utilizing vertical ground reaction force (VGRF) data of 72 healthy and 93 Parkinson's individuals. A multi-variate normalization approach identifies gait differences between PD and non-PD. The proposed hybrid model used is able to detect PD with accuracy of 99.39% and 99.9%, and its severity assessment based on MDS-UPDRS-III shows coefficient of determination (R2) as 97% and 98.7% using leave-one-out cross-validation (CV) and tenfold CV respectively. The significant features suitable for clinical implications are reported. Moreover, normalized gait parameters supplement capability to compare individuals with diverse physical properties, resulting in assistive system for evaluation of PD severity.

Analysis of the stance phase of the gait cycle in Parkinson’s disease and its potency for Parkinson’s disease discrimination

In this study, using vertical ground reaction force (VGRF) data and focusing on the stance phase of the gait cycle, the effect of Parkinson’s disease (PD) on gait was investigated. The used dataset consisted of 93 PD and 72 healthy individuals. Multiple comparisons correction ANOVA test and student t-test were used for statistical analyses. Results showed that a longer stance duration with a larger VGRF peak value (p < 0.05) was observed for PD patients during the stance phase. In addition, the VGRF peak value was delayed and blunted in PD cases compared with healthy individuals. These results indicated more time and effort for PD patients for posture stabilization during the stance phase. The time delay for different locations of the foot sole to contact the ground during the stance phase indicated that PD patients might use a different strategy for maintaining their body stability compared with healthy individuals. Although the VGRF time-domain pattern during the stance phase in PD was similar to healthy conditions, its local characteristics like duration and peak value differed significantly. The classification analysis based on the VGRF time-domain extracted features during the stance phase obtained PD recognition with accuracy, sensitivity and specificity of 90.82%, 88.63% and 82.56%, respectively.

Age-gender specific prediction model for Parkinson’s severity assessment using gait biomarkers

Parkinson’s disease (PD) causes gait impairments resulting in tremor, balance instabilities, increased fall risk, and disability. The current clinical diagnosis success rate is around 80%. Thus, automated classification of these impairments in gait with machine learning techniques can serve as an assessment tool for identification of PD. The primary focus of the study is to investigate anthropometric parameter-based models for classification of non-PD and PD subjects together with their severity. The proposed work performs the computation of clinically relevant features using Vertical Ground Reaction Force (VGRF) data from a total of 165 individuals’ database consisting 93 Parkinson’s and 72 healthy controls. All extracted features are tested for significance and redundancy among other gait characteristics. The optimal combination of features is selected using Recursive Feature Elimination technique with 10-fold cross validation for classification. In this study, wide range of machine learning techniques from different domains are used and their performance is evaluated based on accuracy, specificity, recall, precision and F1-score. Both gender and age-gender specific models outperformed the generalized model for PD as well as PD severity assessment. The highest prediction accuracy reported for age-gender specific models is 98.50% (non-PD and PD) using Support Vector Machine (SVM) classifier and 97.76% (non-PD and PD with severity scales) using k-Nearest Neighbor (kNN) and SVM. This study demonstrates integration of gait data with machine learning techniques as a potential biomarker for assessment of PD severity.

Effects of medial longitudinal arch flexibility on propulsion kinetics during drop vertical jumps

This study examined the effects of medial longitudinal arch (MLA) flexibility on kinetics during the eccentric and concentric subphases of a drop vertical jump (DVJ). Physically active adults with flexible (n = 16) and stiff (n = 16) MLA completed DVJs onto a force platform from a height of 30 cm. Eccentric and concentric subphases of the DVJ were identified from the vertical ground reaction force (GRF) data. Jump height, ground contact time, reactive strength index (RSI), vertical center-of-mass depth, vertical stiffness and time of the eccentric and concentric subphases were evaluated. Amortization force, peak vertical GRF and vertical impulse were also obtained for the eccentric and concentric subphases of the DVJ. Dependent variables were compared between groups using independent samples t-tests (p < 0.05). Significantly greater vertical stiffness (p = 0.048; ES = 0.63) was found in the stiff arch group (−173.91 ± 99.73 N/kg/m) compared to the flexible arch group (−122.95 ± 63.42 N/kg/m). A moderate-magnitude difference (ES = 0.58) was observed for RSI between flexible (0.89 ± 0.39) and stiff arch (1.20 ± 0.70) groups, but was not significant (p = 0.063). The active and passive structures supporting the MLA may be used differently to achieve similar vertical jump height during a DVJ. Additional research is warranted to further understand the contributions of MLA flexibility to jumping performance.

Kinematic and kinetic analyses of the gait of horses wearing novel legwear for variably limiting extension of the metacarpophalangeal joint.

To investigate the effects of novel legwear designed to limit metacarpophalangeal joint (MCPJ) extension and redirect loading forces from the flexor apparatus through analyses of 2-D kinematic and kinetic data. 6 adult horses without musculoskeletal disease. Horses were subjected to 4 treatments: control (no legwear), inactive legwear (unlimited legwear extension), and active legwear with mild (30°) and moderate (20°) legwear extension limitation. Two-dimensional kinematic data were collected for the right forelimb (FL) during walk and trot and from leading and trailing FLs during canter on a treadmill. Ground reaction force (GRF) data were collected from FLs during overground walk and trot. Peak MCPJ angle and angular velocity were calculated from kinematic data, and peak force and average loading rate were calculated from vertical GRF data during the stance phase of the gait. Interactions between gait and treatment were determined via ANOVA. Interactions between gait and treatment for peak MCPJ angle were significant. Significant reductions in MCPJ angle were noted between the control treatment and legwear with moderate extension limitation for trot and canter (leading and trailing FL) and between inactive legwear and legwear with moderate extension limitation for trot and leading FL during canter. Interactions among peak MCPJ angular velocity, peak vertical GRF, and average loading rate of the vertical GRF showed nonsignificance. Significant reductions in MCPJ extension without significant alterations to peak vertical GRF suggested the legwear's ability to redistribute internal forces. Findings suggested that the legwear may be beneficial for horses rehabilitating from flexor apparatus injuries.

Parkinson's Disease Diagnosis and Severity Assessment Using Ground Reaction Forces and Neural Networks.

Gait analysis plays a key role in the diagnosis of Parkinson’s Disease (PD), as patients generally exhibit abnormal gait patterns compared to healthy controls. Current diagnosis and severity assessment procedures entail manual visual examinations of motor tasks, speech, and handwriting, among numerous other tests, which can vary between clinicians based on their expertise and visual observation of gait tasks. Automating gait differentiation procedure can serve as a useful tool in early diagnosis and severity assessment of PD and limits the data collection to solely walking gait. In this research, a holistic, non-intrusive method is proposed to diagnose and assess PD severity in its early and moderate stages by using only Vertical Ground Reaction Force (VGRF). From the VGRF data, gait features are extracted and selected to use as training features for the Artificial Neural Network (ANN) model to diagnose PD using cross validation. If the diagnosis is positive, another ANN model will predict their Hoehn and Yahr (H&Y) score to assess their PD severity using the same VGRF data. PD Diagnosis is achieved with a high accuracy of 97.4% using simple network architecture. Additionally, the results indicate a better performance compared to other complex machine learning models that have been researched previously. Severity Assessment is also performed on the H&Y scale with 87.1% accuracy. The results of this study show that it is plausible to use only VGRF data in diagnosing and assessing early stage Parkinson’s Disease, helping patients manage the symptoms earlier and giving them a better quality of life.

Dynamic Core Flexion Strength is Important for Using Arm-Swing to Improve Countermovement Jump Height

Background: Specificity of core strength training to sports events is crucial for performance improvement. The purpose of this study was to examine the specific relationship between core strength and countermovement jump (CMJ) performance. Methods: Twenty active college students (7 male, 13 female) participated in the project. CMJ heights with (HAS) and without arm-swing (HNAS) were estimated from vertical ground reaction force data collected using a force platform. Twelve dynamic and static core strength measurements of flexion and extension were tested using a dynamometer. The shared variance between CMJ height and core strength measurements was estimated using the square of Pearson correlation coefficients (R2). Linear regression analyses were conducted to determine which independent variables in core strength measurements were major predictors of CMJ height. Results: Significant correlations (p &lt; 0.05) were observed between all 12 core strength measurements and CMJ height with/without arm-swing. Normalized (normalized with individuals’ body mass) peak torque during dynamic flexion at 180°per second (NPDF180) and normalized peak torque during static flexion at 120° (NPSF120) shared 72.0% variance with HAS, and NPSF120 shared 57.0% variance with HNAS. Conclusion: Dynamic core flexion strength is vital for using arm-swing to improve CMJ height. The structure of kinematic and kinetic core training could be considered to improve CMJ performance for coaches as well as professional and recreational athletes.

Digital bathroom scales with open source software provide valid dynamic ground reaction force data for assessment and biofeedback

BackgroundMeasuring dynamic vertical ground reaction force allows for assessment of important clinical and physical capacity factors such as weight bearing asymmetry, force distribution, and rate of force development. However, current technologies for accurately assessing ground reaction force are typically expensive. Research QuestionThe aim of this study was to examine the validity and reliability of obtaining static and dynamic ground reaction force data from low-cost modified digital bathroom scales. MethodsFour modified bathroom scales, two units each of two different brands, were examined. Repeated mechanical loading trials were performed with known loads ranging from 0.01 to 65 kg, with acquired data compared against the known loading to calculate accuracy, hysteresis, and non-linearity. Dynamic trials consisting of 5 times sit-to-stand and weight-shifting were performed by 32 adults. Absolute and relative agreement intraclass correlation coefficient, and Pearson’s and Spearman’s correlations were performed to determine validity and reliability for the mechanical tests. Bland-Altmann plots were created for each comparison. Mean absolute error (MAE) and unbiased cross-correlation were performed on the dynamic data, comparing the calibrated data to the known values from a Bertec force platform. ResultsHysteresis and non-linearity were excellent (<0.2 % full-scale), and mechanical test results showed excellent reliability and validity. Cross-correlation results for the dynamic data were excellent, however MAE for the more rapid sit-to-stand task was higher than the slower weight-shifting test. This may have been due to the low default sampling rate for the lowest noise setting of the HX711 amplifier (10 Hz). SignificanceIn summary, our results suggest that digital bathroom scales can be easily and inexpensively modified to obtain accurate vertical ground reaction force data, with sensitivity to detect changes of as little as 0.01 kg.

Biofeedback augmenting lower limb loading alters the underlying temporal structure of gait following anterior cruciate ligament reconstruction.

Biofeedback has recently been explored to target deviant lower extremity loading mechanics following anterior cruciate ligament reconstruction (ACLR) to mitigate the development of post traumatic osteoarthritis. The impact this feedback has on the structure of the stride interval dynamics-a barometer of gait system health-however, have yet to be examined. This study was designed to assess how feedback, used to alter lower-extremity loading during gait, affects the structure of stride interval variability by examining long-range stride-to-stride correlations during gait in those with unilateral ACLR. Twelve participants walked under three separate loading conditions: (1) control (i.e., no cue) (2) high loading, and (3) low loading. Baseline vertical ground reaction force (vGRF) data was used to calculate a target 5% change in vGRF for the appropriate loading condition (i.e., high loading was +5% vGRF, low loading was -5% vGRF). The target for the load condition was displayed on a screen along with real-time vGRF values, prescribing changes in stride-to-stride peak vertical ground reaction forces of each limb. From time-series of stride intervals (i.e., duration), we analyzed the mean and standard deviation of stride-to-stride variability and, via detrended fluctuation analysis (i.e., DFA α), temporal persistence for each feedback condition. Both the high and low loading conditions exhibited a change toward more temporally persistent stride intervals (high loading: α =0.92, low loading: α=0.98) than walking under the control condition (α=0.78; high vs. control: p=.026, low vs. control: p=.001). Overall, these results indicate that altering lower extremity load changes the temporal persistence of the stride internal dynamics in ACLR individuals, demonstrating the implications of the design of gait training interventions and the influence feedback has on movement strategies.