Horizontal Ground Reaction Forces Research Articles

Activation of the Gluteus Maximus During Performance of the Back Squat, Split Squat, and Barbell Hip Thrust and the Relationship With Maximal Sprinting.

Williams, MJ, Gibson, N, Sorbie, GG, Ugbolue, UC, Brouner, J, and Easton, C. Activation of the gluteus maximus during performance of the back squat, split squat, and barbell hip thrust and the relationship with maximal sprinting. J Strength Cond Res 35(1): 16-24, 2021-The purpose of this research was to compare muscle activation of the gluteus maximus and ground reaction force between the barbell hip thrust, back squat, and split squat and to determine the relationship between these outcomes and vertical and horizontal forces during maximal sprinting. Twelve, male, team sport athletes (age, 25.0 ± 4.0 years; stature, 184.1 ± 6.0 cm; body mass, 82.2 ± 7.9 kg) performed separate movements of the 3 strength exercises at a load equivalent to their individual 3 repetition maximum. The ground reaction force was measured using force plates and the electromyography (EMG) activity of the upper and lower gluteus maximus and was recorded in each leg and expressed as percentage of the maximum voluntary isometric contraction (MVIC). Subjects then completed a single sprint on a nonmotorized treadmill for the assessment of maximal velocity and horizontal and vertical forces. Although ground reaction force was lower, peak EMG activity in the gluteus maximus was higher in the hip thrust than in the back squat (p = 0.024; 95% confidence interval [CI] = 4-56% MVIC) and split squat (p = 0.016; 95% CI = 6-58% MVIC). Peak sprint velocity correlated with both anterior-posterior horizontal force (r = 0.72) and peak ground reaction force during the barbell hip thrust (r = 0.69) but no other variables. The increased activation of gluteus maximus during the barbell hip thrust and the relationship with maximal running speed suggests that this movement may be optimal for training this muscle group in comparison to the back squat and split squat.

Determining the best combination of ground reaction force parameters for maximising power during the power snatch

ABSTRACTThe purpose of this study was to determine the best combination of ground reaction force (GRF) parameters for maximising power during the power snatch. Ten skilled weightlifters (five males and five females) completed a total of five power snatch trials with 60% of one repetition maximum. Vertical GRF (VGRF), horizontal GRF (HGRF), rate of vertical force development (VFD), rate of horizontal force development (HFD) and horizontal centre-of-pressure (HCOP) were extracted through a three-dimensional motion analyses and used as the GRF parameters. Multiple-regression (stepwise) analyses were conducted to evaluate the prediction of power with the GRF parameters being independent variables and determine the above-mentioned best combination. VGRF, VFD and HCOP were identified as significant predictors of power during the power snatch with up to 72% of the variance in power explained (VGRF and VFD: p < 0.01; HCOP: p < 0.05). Specifically, increased VGRF and decreased VFD and HCOP would increase power during the power snatch. In conclusion, a horizontal movement is inevitable as a counter movement before second pull during the power snatch. However, it needs to be minimised as increased VFD and HCOP would have negative impacts on power.

Foot orthoses alter lower limb biomechanics but not jump performance in basketball players with and without flat feet

BackgroundFlat-footed individuals are believed to have poorer jump performance compared to normal-arched individuals. Foot orthoses are commonly used to support the deformed foot arch, and improve normal foot function. However, it is unclear if foot orthoses use affects jump performance in athletes. Our study aims to investigate if foot type and/or foot orthosis influence countermovement jump (CMJ) and standing broad jump (SBJ) performance and lower limb biomechanics.MethodsTwenty-six male basketball players were classified into normal-arched (n = 15) or flat-footed (n = 11) groups using the Chippaux-Smirak index, navicular drop test, and the resting calcaneal angle measurement. They performed jumps with and without prefabricated foot orthoses. We measured jump height and distance for CMJ and SBJ, respectively. Hip, knee and ankle joint angles, angular velocities, moments and powers during take-off were also measured.ResultsFor CMJ, the flat-footed group exhibited less ankle plantarflexion (F1,24 = 8.407, p = 0.008, ηp2 = 0.259 large effect) and less hip joint power (F1,24 = 7.416, p = 0.012, ηp2 = 0.244 large effect) than the normal-arched group. Foot orthoses reduced ankle eversion in both groups (F1,24 = 6.702, p = 0.016, ηp2 = 0.218 large effect). For SBJ, the flat-footed group produced lower peak hip angular velocity (F1,24 = 7.115, p = 0.013, ηp2 = 0.229 large effect) and generated lower horizontal GRF (F1,24 = 5.594, p = 0.026, ηp2 = 0.189 large effect) than the normal-arched group. Wearing foot orthoses reduced ankle eversion (F1,24 = 5.453, p = 0.028, ηp2 = 0.185 large effect), peak horizontal GRF (F1,24 = 13.672, p = 0.001, ηp2 = 0.363 large effect) and frontal plane ankle moment (F1,24 = 4.932, p = 0.036, ηp2 = 0.170 large effect).ConclusionFoot type and the use of foot orthoses influence take-off biomechanics, but not actual CMJ and SBJ performances in basketball players. Compared to the normal-arched individuals, flat-footed athletes generated smaller propulsion GRF and lower hip flexion velocity and power, which suggests possible compensatory movement strategies to maximise jump performance. Future studies may investigate whether these altered biomechanics, taking into consideration their respective magnitude and effect sizes, may have implications on lower limb injuries. The use of foot orthoses resulted in biomechanical changes in both the normal-arched and flat-footed groups but does not enhance jumping performance.

Spring-loaded inverted pendulum goes through two contraction-extension cycles during the single-support phase of walking.

ABSTRACTDespite the overall complexity of legged locomotion, the motion of the center of mass (COM) itself is relatively simple, and can be qualitatively described by simple mechanical models. In particular, walking can be qualitatively modeled by a simple model in which each leg is described by a spring-loaded inverted pendulum (SLIP). However, SLIP has many limitations and is unlikely to serve as a quantitative model. As a first step to obtaining a quantitative model for walking, we explored the ability of SLIP to model the single-support phase of walking, and found that SLIP has two limitations. First, it predicts larger horizontal ground reaction forces (GRFs) than empirically observed. A new model – angular and radial spring-loaded inverted pendulum (ARSLIP) – can overcome this deficit. Second, although the leg spring (surprisingly) goes through contraction-extension-contraction-extensions (CECEs) during the single-support phase of walking and can produce the characteristic M-shaped vertical GRFs, modeling the single-support phase requires active elements. Despite these limitations, SLIP as a model provides important insights. It shows that the CECE cycling lengthens the stance duration allowing the COM to travel passively for longer, and decreases the velocity redirection between the beginning and end of a step.

Generation of Stealth Walking Gait on Frictionless Descending Stairs Utilizing Upper Body and Reaction Wheel

Towards adaptation to slippery ground surface for underactuated locomotion robots, the authors proposed the method of stealth walking, which avoids energy loss at landing of swing foot. Moreover, they proposed angular momentum constraint control (AMCC), which constraints the horizontal ground reaction force to zero, to make the robots walk on the frictionless road surface stably. In this paper, we investigate a more severe situation, i.e., stable walking on frictionless descending stairs. First, we introduce a mathematical model of an underactuated rimless wheel with an upper body and a reaction wheel for analysis, and develop the control law for achieving trajectory tracking control of the stance-leg angle and AMCC simultaneously. Second, we investigate the validity of the proposed method and discuss the nonlinearity of zero dynamics through numerical simulations.

Lower-limb joint mechanics during maximum acceleration sprinting.

We explored how humans adjust the stance phase mechanical function of their major lower-limb joints (hip, knee, ankle) during maximum acceleration sprinting. Experimental data [motion capture and ground reaction force (GRF)] were recorded from eight participants as they performed overground sprinting trials. Six alternative starting locations were used to obtain a dataset that incorporated the majority of the acceleration phase. Experimental data were combined with an inverse-dynamics-based analysis to calculate lower-limb joint mechanical variables. As forward acceleration magnitude decreased, the vertical GRF impulse remained nearly unchanged whereas the net horizontal GRF impulse became smaller as a result of less propulsion and more braking. Mechanical function was adjusted at all three joints, although more dramatic changes were observed at the hip and ankle. The impulse from the ankle plantar-flexor moment was almost always larger than those from the hip and knee extensor moments. Forward acceleration magnitude was linearly related to the impulses from the hip extensor moment (R2=0.45) and the ankle plantar-flexor moment (R2=0.47). Forward acceleration magnitude was also linearly related to the net work done at all three joints, with the ankle displaying the strongest relationship (R2=0.64). The ankle produced the largest amount of positive work (1.55±0.17 J kg-1) of all the joints, and provided a significantly greater proportion of the summed amount of lower-limb positive work as running speed increased and forward acceleration magnitude decreased. We conclude that the hip and especially the ankle represent key sources of positive work during the stance phase of maximum acceleration sprinting.

Understanding the impact loading characteristics of a badminton lunge among badminton players.

BackgroundThe rapid and repetitive badminton lunges would produce strenuous impact loading on the lower extremities of players and these loading are thought to be the contributing factors of chronic knee injuries. This study examined the impact loading characteristics in various groups of badminton athletes performing extreme lunges.MethodsFifty-two participants classified into male skilled, female skilled, male unskilled, and female unskilled groups performed badminton lunge with their maximum-effort. Shoe-ground kinematics, ground reaction forces, and knee moments were measured by using synchronised force platform and motion analysis system. A 2 (gender) x 2 (skill-level) factorial ANOVA was performed to determine the effects of different gender and different playing levels, as well as the interaction of two factors on all variables.ResultsMale athletes had faster approaching speed (male 3.87 and female 1.08 m/s), longer maximum lunge distance (male 1.47 and female 1.16 m), larger maximum (male 215.7 and female 121.65 BW/s) and mean loading rate (male 178.43 and female 81.77 BW/s) and larger peak knee flexion moment (male 0.75 and female 0.69) compared with female athletes (P < 0.001). Unskilled athletes exhibited smaller footstrike angle (skilled 45.78 and unskilled 32.35°), longer contact time (skilled 0.69 and unskilled 0.75 s), larger peak horizontal GRF (skilled 1.61 and unskilled 2.40 BW), smaller mean loading rate (skilled 150.15 and unskilled 110.05 BW/s) and larger peak knee flexion moment (P < .05; skilled 0.69 and unskilled 0.75 Nm/BW) than the skilled athletes. In addition, the interaction indicated greater peak GRF impact in female unskilled athletes compared with female skilled athletes (P < 0.001; female skilled 2.01 and female unskilled 2.95 BW), while there was no difference between male participants (P > 0.05; male skilled 2.19 and male unskilled 2.49 BW).ConclusionsThese data suggested that male athletes and/or unskilled athletes experience greater impact loading rates and peak knee flexion moment during lunge compared with female and skilled athletes, respectively. This may expose them to higher risk of overuse injuries. Furthermore, female unskilled athletes seemed to be more vulnerable to lower extremity injuries.

Combined three-dimensional gait and plantar pressure analyses detecting significant functional deficits in children with juvenile idiopathic arthritis

BackgroundChildren suffering from juvenile idiopathic arthritis (JIA), a heterogeneous group of chronic inflammatory joint diseases, adapt to individual gait patterns to avoid loading of inflamed, swollen and painful joints. As the interpretability of previous studies is limited, this study aims to assess the functional capacity, loads and plantar pressure distribution in the gait of a homogeneous JIA group. Research questionDoes a symmetrical lower limb joint involvement influence the gait dynamics in JIA patients, and how are the results of three-dimensional gait analysis (3DGA) and pedobarography related? MethodsFifty JIA patients with symmetrical hip, knee and ankle joint arthritis and 27 healthy controls performed 3DGA and pedobarography at self-selected walking speeds. Kinematics and kinetics of lower limb joints were retrospectively compared in range of motion and in time-normalized waveforms. Plantar load was evaluated by measuring peak pressure, pressure-time integral and maximum force of the whole foot and ten selected foot regions. 1D-SPM analysis, parametric and non-parametric statistical significance tests and correlation coefficients were used for statistical analysis. ResultsJIA patients had a significantly slower walking speed with an anteriorly tilted pelvis and a reduced extension motion of all joints of the lower limb. The horizontal ground reaction forces and generated hip and ankle power during propulsion phase were small. Patients experienced reduced loading at toe regions, which correlated with limited ankle plantarflexion motion in the push-off phase. The total peak pressure was significantly increased and loads at lateral midfoot and metatarsal regions were higher in patients. SignificanceSymmetrical lower limb arthritis is linked to crouch-like gait and restricted gait dynamics with increased total peak pressure. The results confirm earlier results of 3DGA and provide new insights regarding waveform analysis and plantar loading in JIA patients. The used methods help to design individualized functional treatment of JIA patients.

Do forelimb shape and peak forces co‐vary in strepsirrhines?

In this study, we explore whether ground reaction forces recorded during horizontal walking co-vary with the shape of the long bones of the forelimb in strepsirrhines. To do so, we quantify (1) the shape of the shaft and articular surfaces of each long bone of the forelimb, (2) the peak vertical, mediolateral, and horizontal ground reaction forces applied by the forelimb during arboreal locomotion, and (3) the relationship between the shape of the forelimb and peak forces. Geometric morphometric approaches were used to quantify the shape of the bones. Kinetic data were collected during horizontal arboreal walking in eight species of strepsirrhines that show variation in habitual substrate use and morphology of the forelimb. These data were then used to explore the links between locomotor behavior, morphology, and mechanics using co-variation analyses in a phylogenetic framework. Our results show significant differences between slow quadrupedal climbers (lorises), vertical clinger and leapers (sifaka), and active arboreal quadrupeds (ring-tailed lemur, ruffed lemur) in both ground reaction forces and the shape of the long bones of the forelimb, with the propulsive and medially directed peak forces having the highest impact on the shape of the humerus. Co-variation between long bone shape and ground reaction forces was detected in both the humerus and ulna even when accounting for differences in body mass. These results demonstrate the importance of considering limb-loading beyond just peak vertical force, or substrate reaction force. A re-evaluation of osseous morphology and functional interpretations is necessary in light of these findings.

Average of trial peaks versus peak of average profile: impact on change of direction biomechanics

ABSTRACT The aims of this study were twofold: firstly, to compare lower limb kinematic and kinetic variables during a sprint and 90° cutting task between two averaging methods of obtaining discrete data (peak of average profile vs. average of individual trial peaks); secondly, to determine the effect of averaging methods on participant ranking of each variable within a group. Twenty-two participants, from multiple sports, performed a 90° cut, whereby lower limb kinematics and kinetics were assessed via 3D motion and ground reaction force (GRF) analysis. Six of the eight dependent variables (vertical and horizontal GRF; hip flexor, knee flexor, and knee abduction moments, and knee abduction angle) were significantly greater (p ≤ 0.001, g = 0.10–0.37, 2.74–10.40%) when expressed as an average of trial peaks compared to peak of average profiles. Trivial (g ≤ 0.04) and minimal differences (≤ 0.94%) were observed in peak hip and knee flexion angle between averaging methods. Very strong correlations (ρ ≥ 0.901, p < 0.001) were observed for rankings of participants between averaging methods for all variables. Practitioners and researchers should obtain discrete data based on the average of trial peaks because it is not influenced by misalignments and variations in trial peak locations, in contrast to the peak from average profile.

Kinematic and kinetic benefits of implantable peroneal nerve stimulation in people with post-stroke drop foot using an ankle-foot orthosis.

Contralesional 'drop foot' after stroke is usually treated with an ankle-foot orthosis (AFO). However, AFOs may hamper ankle motion during stance. Peroneal functional electrical stimulation (FES) is an alternative treatment that provides active dorsiflexion and allows normal ankle motion. Despite this theoretical advantage of FES, the kinematic and kinetic differences between AFO and FES have been scarcely investigated. To test whether walking with implanted FES leads to improvements in stance stability, propulsion, and swing initiation compared to AFO. A 4-channel peroneal nerve stimulator (ActiGait®) was implanted in 22 chronic patients after stroke. Instrumented gait analyses were performed during comfortable walking up to 26 weeks (n = 10) or 52 weeks (n = 12) after FES-system activation. Kinematics of knee and ankle (stance and swing phase) and kinetics (stance phase) of gait were determined, besides spatiotemporal parameters. Finally, we determined whether differences between devices regarding late stance kine(ma)tics correlated with those regarding the swing phase. In mid-stance, knee stability improved as the peak knee extension velocity was lower with FES (β = 18.1°/s, p = 0.007), while peak ankle plantarflexion velocity (β = -29.2°/s, p = 0.006) and peak ankle plantarflexion power (β = -0.2 W/kg, p = 0.018) were higher with FES compared to AFO. With FES, the ground reaction force (GRF) vector at peak ankle power (i.e., 'propulsion') was oriented more anteriorly (β = -1.1°, p = 0.001). Similarly, the horizontal GRF (β = -0.8% body mass, p = 0.003) and gait speed (β = 0.03 m/s, p = 0.015) were higher. An increase in peak ankle plantarflexion velocity and a more forward oriented GRF angle during late stance were moderately associated with an increase in hip flexion velocity during initial swing (rs = 0.502, p = 0.029 and rs = 0.504, p = 0.028, respectively). This study substantiates the evidence that implantable peroneal FES as a treatment for post-stroke drop foot may be superior over AFO in terms of knee stability, ankle plantarflexion power, and propulsion.

Stretch Could Reduce Hamstring Injury Risk During Sprinting by Right Shifting the Length-Torque Curve.

Ruan, M, Li, L, Chen, C, and Wu, X. Stretch could reduce hamstring injury risk during sprinting by right shifting the length-torque curve. J Strength Cond Res 32(8): 2190–2198, 2018—It was hypothesized that static stretch would shift the length-torque curve to the right, which may reduce the risk of muscle strain injuries. The purpose of this study was to evaluate the acute effects of static stretching of hamstring (SSH) on the risk of hamstring injury during sprinting indicated by the shift of the length–torque relationship. Twelve female college athletes (age: 20.8 ± 0.7 years; height: 1.61 ± 0.05 m; body mass: 54.25 ± 4.22 kg) participated in this study. Subjects performed overground sprinting under 2 conditions: after warm-up with 4 × 30 seconds SSH or after warm-up without SSH. Three-dimensional kinematic and kinetic data and electromyography of biceps femoris long head (BFlh), rectus femoris, and vastus medialis were collected during testing. The maximum length of BFlh during late swing phase increased after SSH with large effect size and close to statistically significant (p = 0.05, d = 1.22), but the knee flexion torque at the peak length did not change significantly. Static stretching of hamstring significantly reduced peak values of both horizontal (d = 1.46) and vertical (d = 1.79) ground reaction forces, and BFlh's activation level during the preactivation (late swing) phase (p = 0.05, d = 2.16). The results indicated that the length of BFlh–knee torque relationship and the length of BFlh–hip torque relationships during the late swing phase and initial stance phase were shifted to the right after SSH, which may reduce risk of hamstring strain injuries. We suggest that preactivity static stretching should not be simply removed and participators should give priority to stretch muscles that are vulnerable to strain injuries.

Muscle-tendon unit length changes differ between young and adult sprinters in the first stance phase of sprint running.

The aim of this study was to compare young and adult sprinters on several biomechanical parameters that were previously highlighted as performance-related and to determine the behaviour of several muscle–tendon units (MTU) in the first stance phase following a block start in sprint running. The ground reaction force (GRF) and kinematic data were collected from 16 adult and 21 young well-trained sprinters. No difference between the groups was found in some of the previously highlighted performance-related parameters (ankle joint stiffness, the range of dorsiflexion and plantar flexor moment). Interestingly, the young sprinters showed a greater maximal and mean ratio of horizontal to total GRF, which was mainly attributed to a greater horizontal GRF relative to body mass and resulted in a greater change in horizontal centre of mass (COM) velocity during the stance phase in the young compared with the adult sprinters. Results from the MTU length analyses showed that adult sprinters had more MTU shortening and higher maximal MTU shortening velocities in all plantar flexors and the rectus femoris. Although previously highlighted performance-related parameters could not explain the greater 100 m sprinting times in the adult sprinters, differences were found in the behaviour of the MTU of the plantar flexors and rectus femoris during the first stance phase. The pattern of length changes in these MTUs provides ideal conditions for the use of elastic energy storage and release for power enhancement.

Differences in Ground Reaction Forces When Collegiate Quarterbacks Throw Using Different Drop Patterns

While there is limited research examining the kinematics of the quarterback passing throw, to date there have not been any studies reporting on ground reaction forces (GRF) during this type of throwing motion. Additionally, there have been no studies reporting how foot positions or drop patterns used by quarterbacks might change GRF parameters. This information would useful to both coaches and sports medicine professionals as it provides both performance and injury related insights. PURPOSE: Compare GRF parameters between three commonly used quarterback drop patterns: a one step (1S), a three step (3S), and a three plus one step (3P1) when performed with the rearfoot angled 90° relative to the throwing direction and 45° relative to the throwing direction. METHODS: Three NCAA Division I quarterbacks participated in this study. Participants performed three throws using each type of drop and each foot position. Two force plates were used to record GRF data at 1000 Hz. Trials were considered valid if both the front (FF) and rear (RF) feet landed on their respective force plates, with the RF foot in the appropriate orientation. For both the RF and FF, peak horizontal and vertical forces, and horizontal and vertical impulses were calculated. Differences between foot positions and drop patterns were evaluated using a 2x3 repeated measures ANOVA. RESULTS: There were no differences in any force metrics for the FF. For the RF, peak horizontal GRFs showed a main effect of drop (F2,4=43.9, p=.002), with peak forces being lower in the 3P1 (210.7 ± 13.5 N) than the 3S (476.7 ± 50.5 N) or 1S(378.7 ± 2.6 N) conditions. Peak vertical forces in the RF also showed a main effect of drop (F2,4=20.3, p=.008), with peak forces being lower in the 3P1 (1201.7 ± 39.8 N) than the 3S (1359.9 ± 105.8 N). Lastly, there was a main effect of drop for RF horizontal impulse (F2,4=55.7, p=.001), with impulses being lower in the 3P1 (58.2 ± 9.12 Ns) than the 3S(150.7 ± 4.5 Ns) or 1S (150.8 ± 5.1 Ns) conditions. CONCLUSION: A 3P1 drop pattern makes use of horizontal momentum, thus requiring the athlete to generate less force and smaller impulses with the RF during the throw. As such, coaches should emphasize pushing with the RF when using a 1S or 3S drop pattern. Changing foot positions does not appear to influence force parameters.

The contribution analysis of knee compression bandage and arm swing control on maximum horizontal distance in standing long jump.

The aim of the study was to analyze the effect of knee compression bandage and arm swing control on the maximum horizontal distance and ground reaction force variables in standing long jump. Adult male (n=8; mean age, 22.75±1.98 years; mean heights, 1.77±0.03 m; mean weights, 71.82±12.87 kg) participated in the experiment. The results obtained from variables of ground reaction force (GRF) in medial lateral, anterior posterior (AP), vertical (V) direction, resultant GRF (RGRF), decay rate (%), and maximum horizontal distance (MHD) were as follows; MHD, AP GRF, VGRF, RGRF (AP-V), and ratio of load reduction (%) showed more effective result under both wearing of knee compression bandage and arm swing. In analysis of main effects, MHD, AP GRF, VGRF, and RGRF showed more increased value in case of wearing of knee compression bandage than as was not. While arm swing during standing long jump (SLJ) works as important factor to MHD, showed more effective factor in exercise rehabilitation, injury prevention and swell treatment etc. in wearing of worn knee compression bandage. Therefore it was assumed that arm swing and wearing of knee compression bandage may improve the performance of SLJ. Also, the characteristics of knee compression bandage suggest that it can be a great help for those participating in exercise rehabilitation.

Using inertial measurement units to identify medio-lateral ground reaction forces due to walking and swaying

Horizontal ground reaction forces (GRFs) due to human walking and swaying have been investigated (respectively) through direct measurements using a treadmill and a set of force plates. These GRFs have also been measured (or estimated) indirectly using acceleration data provided by inertial measurement units (IMUs).One motivation for this research has been the lack of published data on these two forms of loading that are generated by movements of the human body in the medio-lateral plane perpendicular to the direction of walking or the direction faced during swaying. The other motivation, following from successful developments in applying IMUs to in-situ vertical GRF measurements, has been to identify best practice for estimating medio-lateral GRFs outside the constraints of a laboratory.Examination of 852 treadmill measurements shows that medio-lateral GRFs at the first sub-harmonic of pacing rate can exceed 10% of body weight. Using a smaller and more recent set of measurements including motion capture, it has been shown that IMUs can be used to reconstruct these GRFs using a linear combination of body accelerations at each of the lower back and sternum positions. There are a number of potential applications for this capability yet to be explored, in particular relating to footbridge performance.A separate set of measurements using force plates has shown that harmonic components of medio-lateral dynamic load factors due to on the spot swaying can approach 50% of body weight. Such forces provide a capability to excite horizontal vibration modes of large civil structures with frequencies below 2 Hz that are problematic for mechanical excitation. As with walking, the ability to use IMUs to estimate medio-lateral swaying GRFs outside laboratory constraints has been demonstrated. As for walking a pair of IMUs is needed, but the best linear combination varies strongly between individuals, according to swaying style. In-situ application of indirect measurement has been successfully demonstrated through a very challenging application of system identification of a multi-storey building, including estimation of modal mass.

Biomechanical insights into the determinants of speed in the fencing lunge

For fencing, speed of the lunge is considered critical to success. The aim of this study is to investigate determinants of lunge speed based on biomechanics. Ground reaction force (GRF) and three-dimensional kinematic data were collected from 7 elite fencers and 12 intermediate-level fencers performing maximum-effort lunges. The results showed that elite fencers acquired a higher horizontal peak velocity of the centre of gravity (HPV) and concomitantly a higher horizontal peak GRF exerted by rear leg (PGRF) than intermediate-level fencers (P < .01). Studying the affecting factors, elite fencers obtained higher joint peak power, joint peak moment, and range of motion of rear knee than intermediate-level fencers (P < .05) during the lunge, and these parameters were significantly correlated with both HPV and PGRF (P < .05). Both elite and intermediate-level fencers had joint flexion before the extension in forward knee; however, the latter showed greater flexion, higher peak angular velocity and less time for extension compared to the former (P ≤ .05). Our findings suggest that training aimed at enhancing strength and power of rear knee extensors is important for fencers to improve speed of the lunge. Also, increasing the extension of rear knee during the lunge, at the same time decreasing the flexion of the forward knee before extension are positive for lunge performance.

Do rotational shear-cushioning shoes influence horizontal ground reaction forces and perceived comfort during basketball cutting maneuvers?

BackgroundCourt shoe designs predominantly focus on reducing excessive vertical ground reaction force, but shear force cushioning has received little attention in the basketball population. We aimed to examine the effect of a novel shoe-cushioning design on both resultant horizontal ground reaction forces and comfort perception during two basketball-specific cutting movements.MethodsFifteen university team basketball players performed lateral shuffling and 45-degree sidestep cutting at maximum effort in basketball shoes with and without the shear-cushioning system (SCS). Paired t-tests were used to examine the differences in kinetics and comfort perception between two shoes.ResultsSCS shoe allowed for larger rotational material deformation compared with control shoes, but no significant shoe differences were found in braking phase kinetics during both cutting movements (P = 0.35). Interestingly, a greater horizontal propulsion impulse was found with the SCS during 45-degree cutting (P < 0.05), when compared with the control. In addition, players wearing SCS shoes perceived better forefoot comfort (P = 0.012). During lateral shuffling, there were no significant differences in horizontal GRF and comfort perception between shoe conditions (P > 0.05).DiscussionThe application of a rotational shear-cushioning structure allowed for better forefoot comfort and enhanced propulsion performance in cutting, but did not influence the shear impact. Understanding horizontal ground reaction force information may be useful in designing footwear to prevent shear-related injuries in sport populations.

Neuromuscular adaptations in older males and females with knee osteoarthritis during weight-bearing force control

BackgroundFemales exhibit significantly greater incidence, prevalence, and severity of osteoarthritis (OA) compared to males. Despite known biological, morphological, and functional differences between males and females, there has been little sex-related investigation into sex-specific biomechanical and neuromuscular responses to OA. ObjectiveTo identify sex-related differences in OA-affected adults and within-sex differences between healthy and OA-affected adults' muscular activation patterns during lower limb loading. MethodsThirty adults with OA and 36 controls completed a standing ground reaction force (GRF) matching protocol requiring participants to expose equal body weight to each leg and modulate horizontal GRFs while maintaining constant joint positions. Electromyography was plotted as a function of GRF direction to depict muscle activation patterns. Muscles were classified as a general joint stabilizer, specific joint stabilizer or moment actuator by quantifying activation patterns with a test of asymmetry, specificity index and mean direction of activity. Lower limb kinematics and kinetics were also recorded. ResultsIn general, muscle roles as it relates to joint stability did not differ between groups. Compared to controls, both males and females with OA demonstrated greater rectus femoris activity and reduced knee rotation moments. Females with OA had significantly greater biceps femoris and gastrocnemius activity during respective lateral, and anterior–medial loading directions compared to males with OA. ConclusionsWe identified fundamental differences in muscular stabilization strategies in older adults with OA as well as sex-related changes in neuromuscular function that may influence joint loading conditions and provide insight into the greater incidence of knee OA in females.

Prediction of ground reaction forces for Parkinson's disease patients using a kinect-driven musculoskeletal gait analysis model

Kinetic gait abnormalities result in reduced mobility among individuals with Parkinson's disease (PD). Currently, the assessment of gait kinetics can only be achieved using costly force plates, which makes it difficult to implement in most clinical settings. The Microsoft Kinect v2 has been shown to be a feasible clinic-based alternative to more sophisticated three-dimensional motion analysis systems in producing acceptable spatiotemporal and kinematic gait parameters. In this study, we aimed to validate a Kinect-driven musculoskeletal model using the AnyBody modeling system to predict three-dimensional ground reaction forces (GRFs) during gait in patients with PD. Nine patients with PD performed over-ground walking trials as their kinematics and ground reaction forces were measured using a Kinect v2 and force plates, respectively. Kinect v2 model-based and force-plate measured peak vertical and horizontal ground reaction forces and impulses produced during the braking and propulsive phases of the gait cycle were compared. Additionally, comparison of ensemble curves and associated 90% confidence intervals (CI90) of the three-dimensional GRFs were constructed to investigate if the Kinect sensor could provide consistent and accurate GRF predictions throughout the gait cycle. Results showed that the Kinect v2 sensor has the potential to be an effective clinical assessment tool for predicting GRFs produced during gait for patients with PD. However, the observed findings should be replicated and model reliability established prior to integration into the clinical setting.