Higher Vertical Ground Reaction Force Research Articles

Collegiate Dancers With Chronic Ankle Instability Possess Altered Strength and saut de chat Leap Landing Mechanics.

Ankle sprains are among the most common injuries in dancers. Following one or more severe sprains, some individuals will experience residual mechanical and functional deficits, otherwise known as chronic ankle instability (CAI). Dancers who suffer from CAI may have weaker musculature surrounding the ankle and altered landing mechanics. The purpose of this study was to compare ankle strength and saut de chat landing mechanics between dancers with and without CAI. Dancers with and without CAI, defined by the Identification of Functional Ankle Instability (IdFAI), participated in the study (CAI n = 8; IdFAI = 18.75 ± 5.50 points; age = 20 ± 1.5 years; training = 15.5 ± 3.5 years) (Control n = 8; IdFAI = 7.13 ± 3.40 points; age = 19 ± 0.6 years; training = 15.9 ± 2.5 years). Strength and leap landing mechanics were measured on the affected ankle for the CAI group and on the preferred landing leg of a leap for the control group. Concentric and eccentric ankle plantar flexion, and subtalar inversion and eversion strength were determined with dynamometry set at an angular velocity of 60°•s-1. Force plates and motion capture cameras were used to calculate lower extremity kinematic and kinetic data as participants performed 3 saut de chat leaps. Independent t-tests were calculated to determine differences between groups. Compared to dancers without CAI, dancers with CAI had lower eccentric plantar flexor strength, landed with higher vertical ground reaction forces, and absorbed greater power at the knee-joint during landing. Whether dancers who are weaker are more prone to injury or ankle-joint injury leads to muscular weakness is unknown. Dancers with CAI appear to lack control during leap landing while concomitantly shifting loads proximally away from the ankle-joint. We encourage dancers with and without CAI to engage in additional training that enhances ankle strength.

A Feasibility Study of Piecewise Phase Variable Based on Variable Toe-Off for the Powered Prosthesis Control: A Case Study

To achieve stable walking and provide proper assistance, it is crucial to have synchronized control of the prosthesis, treating the user and the prosthesis as a coupled system. Additionally, speed adaptability is important for controlling the prosthesis at different walking speeds. One approach to achieving this is by using a phase variable to estimate the user's gait phase and control the prosthesis in synchrony with the user. However, the current phase variable (i.e., PV) cannot reflect variable toe-off timing at different speeds, although individuals have different toe-off timings per walking speed. To address this issue, we propose a piecewise phase variable (i.e., PW-PV) that can be adjusted for different toe-off timings while estimating the user's gait phase at various walking speeds. As a case study, we conducted a treadmill walking experiment with two participants (i.e., one healthy and one amputee) using a custom-built powered prosthesis. We collected and analyzed joint kinematics, kinetics, and ground reaction force data to validate the feasibility of the PW-PV. The use of the PW-PV resulted in both participants experiencing faster load transfer and a more natural rollover while walking. This allowed healthy and amputee participants to walk with longer push-off durations of 10.6% and 15.2%, respectively, and greater ankle push-off work of 7.3% and 16.9%. Furthermore, with the PW-PV, the amputee participant demonstrated higher vertical ground reaction forces of 5.4% and 4.7% on her prosthesis side leg during load acceptance and push-off periods, potentially suggesting increased confidence in using the prosthesis. We anticipate that by using the proposed phase variable, we will be able to provide more appropriate and timely assistance to individuals at variable walking speeds.

Athletes with high knee abduction moments show increased vertical center of mass excursions and knee valgus angles across sport-specific fake-and-cut tasks of different complexities.

Young female handball players represent a high-risk population for anterior cruciate ligament (ACL) injuries. While the external knee abduction moment (KAM) is known to be a risk factor, it is unclear how cutting technique affects KAMs in sport-specific cutting maneuvers. Further, the effect of added game specificity (e.g., catching a ball or faking defenders) on KAMs and cutting technique remains unknown. Therefore, this study aimed: (i) to test if athletes grouped into different clusters of peak KAMs produced during three sport-specific fake-and-cut tasks of different complexities differ in cutting technique, and (ii) to test whether technique variables change with task complexity. Fifty-one female handball players (67.0 ± 7.7 kg, 1.70 ± 0.06 m, 19.2 ± 3.4 years) were recruited. Athletes performed at least five successful handball-specific sidestep cuts of three different complexities ranging from simple pre-planned fake-and-cut maneuvers to catching a ball and performing an unanticipated fake-and-cut maneuver with dynamic defenders. A k-means cluster algorithm with squared Euclidean distance metric was applied to the KAMs of all three tasks. The optimal cluster number of koptimal = 2 was calculated using the average silhouette width. Statistical differences in technique variables between the two clusters and the tasks were analyzed using repeated-measures ANOVAs (task complexity) with nested groupings (clusters). KAMs differed by 64.5%, on average, between clusters. When pooling all tasks, athletes with high KAMs showed 3.4° more knee valgus, 16.9% higher downward and 8.4% higher resultant velocity at initial ground contact, and 20.5% higher vertical ground reaction forces at peak KAM. Unlike most other variables, knee valgus angle was not affected by task complexity, likely due to it being part of inherent movement strategies and partly determined by anatomy. Since the high KAM cluster showed higher vertical center of mass excursions and knee valgus angles in all tasks, it is likely that this is part of an automated motor program developed over the players' careers. Based on these results, reducing knee valgus and downward velocity bears the potential to mitigate knee joint loading and therefore ACL injury risk.

Atypical Lower Limb Mechanics During Weight Acceptance of Stair Descent at Different Time Frames After Anterior Cruciate Ligament Reconstruction

Background: An anterior cruciate ligament (ACL) rupture may result in poor sensorimotor knee control and, consequentially, adapted movement strategies to help maintain knee stability. Whether patients display atypical lower limb mechanics during weight acceptance of stair descent at different time frames after ACL reconstruction (ACLR) is unknown. Purpose: To compare the presence of atypical lower limb mechanics during the weight acceptance phase of stair descent among athletes at early, middle, and late time frames after unilateral ACLR. Study Design: Controlled laboratory study. Methods: A total of 49 athletes with ACLR were classified into 3 groups according to time after ACLR—early (<6 months; n = 17), middle (6-18 months; n = 16), and late (>18 months; n = 16)—and compared with asymptomatic athletes (control; n = 18). Sagittal plane hip, knee, and ankle angles; angular velocities; moments; and powers were compared between the ACLR groups’ injured and noninjured legs and the control group as well as between legs within groups using functional data analysis methods. Results: All 3 ACLR groups showed greater knee flexion angles and moments than the control group for injured and noninjured legs. For the other outcomes, the early group had, compared with the control group, less hip power absorption, more knee power absorption, lower ankle plantarflexion angle, lower ankle dorsiflexion moment, and less ankle power absorption for the injured leg and more knee power absorption and higher vertical ground reaction force for the noninjured leg. In addition, the late group showed differences from the control group for the injured leg revealing more knee power absorption and lower ankle plantarflexion angle. Only the early group took a longer time than the control group to complete weight acceptance and demonstrated asymmetry for multiple outcomes. Conclusion: Athletes with different time frames after ACLR revealed atypically large knee angles and moments during weight acceptance of stair descent for both the injured and the noninjured legs. These findings may express a chronically adapted strategy to increase knee control. In contrast, atypical hip and ankle mechanics seem restricted to an early time frame after ACLR. Clinical Relevance: Rehabilitation after ACLR should include early training in controlling weight acceptance. Including a control group is essential when evaluating movement patterns after ACLR because both legs may be affected.

What differentiates rearfoot strike runners with low and high vertical load rates?

BackgroundRunners with a rearfoot strike pattern typically show high vertical ground reaction force loading rates (LRs), that are associated with injuries, compared with forefoot strikers. However, some runners with a rearfoot strike pattern run in a way that reduces LRs. Our purpose was to identify differences in running mechanics between rearfoot strike runners with high and low vertical LRs. Methods42 healthy runners, 21 with high (≥ 80.5 BW/s) and 21 with low (≤ 46.3 BW/s) LRs, were included in the current study. Lower extremity kinematic and kinetic data were then collected while participants ran along a 30 m runway. Running mechanics were calculated, including sagittal plane knee stiffness during early stance, the components of knee stiffness (Δ knee flexion and flexion moment), sagittal joint angles at initial contact, as well as cadence. The two LR groups were compared for differences in outcome variables using independent t-tests or Mann Whitney U tests. FindingsKnee stiffness was significantly lower in the low LR group (p < 0.01, d = 0.87), due to higher knee flexion excursion (p < 0.01, d = 1.38). At initial contact, the low LR group showed lower hip and knee flexion, but greater ankle and foot dorsiflexion (p = 0.01–0.04, d = 0.64–0.93). No differences were found in cadence. InterpretationThese results provide potential targets, related to gait kinematics and kinetics, for gait retraining aimed at reducing LRs in rearfoot strike runners.

Effect Of Hip Strength On Backwards Single-Legged Jump-Landing Vertical Ground Reaction Force

Commonly proposed risk factors for lower-extremity injury include high vertical peak ground reaction force (vGRF) and rate of force development (vRFD) during a backward single-legged jump-landing (SLJL), deficient hip external rotation (ER) and abduction (ABD) strength, and fatigue. PURPOSE: The purpose of this study was to evaluate the effect of ER and ABD on vGRF and vRFD following SLJL. It was hypothesized low ER and ABD coupled with fatigue would be associated with high vGRF and vRFD. METHODS: Twenty-seven healthy males (n = 10) and females (n = 17) (24.0 ± 2.8 y, 1.73 ± .08 m, 75.0 ± 14.0 kg) participated in this repeated measure study which included rest (R) and fatigue (F) protocols. ER and ABD isometric torque (Nm·kg-1) on the dominate leg were measured using a handheld dynamometer. For R, participants performed SLJL (PRE), rested for 5 minutes, and then reperformed SLJL (POST). For F, participants performed SLJL (PRE), a 7 minute fatigue protocol, and then reperformed SLJL (POST). R and F were performed in a random order. SLJL was performed by jumping backward off the test leg over a .15 m hurdle, landing on the test leg on a force plate, and stabilizing quickly. vGRF (N·kg-1) and vRFD (N·kg-1·s-1) were calculated. Participants were stratified into high-strength (HS) and low-strength (LS) groups using ER and ABD and a k-means cluster analysis. Linear mixed-models were used to assess the effect of group and protocol on vGRF and vRFD with Bonferroni corrected post-hoc tests. Significance was initially set to p < .05. RESULTS: 16 participants were stratified into HS (ER = 4.3 ± .9, ABD = 8.3 ± 1.0) and 11 into LS (ER = 3.3 ± 1.0, ABD = 5.8 ± .9). There was no effect of group on vGRF (HS = 2.98 ± .59, LS = 3.03 ± .59, p = .627) or vRFD (HS = 35.8 ± 19.8, LS = 37.1 ± 18.9, p = .735). HS and LS did not responded differently to R and F for vGRF (p = .694) or vRFD (p = .899). Further, with all subjects pooled, they did not respond differently to R and F for vGRF (p = .081), but they did for vRFD (p < .001). vRFD POST F (41.2 ± 22.3) was higher than PRE F (34.9 ± 22.3, p < .001) and POST R (32.9 ± 22.3, p < .001). CONCLUSION: There is no effect of ER and ABD on vGRF and vRFD and vGRF does not increase with fatigue, but vRFD does increase with fatigue. This may suggest a reduction in the ability to quickly attenuate forces when fatigued and may potentially increase the risk for injury.

Noncontact Knee Ligament Injury Prevention Screening in Netball: A Clinical Commentary with Clinical Practice Suggestions for Community-Level Players.

Netball is a predominantly female team court-sport which is played worldwide. Netball is becoming more popular in the United States following its countrywide introduction to schools and community centers. A unique characteristic of netball is the footwork rule which restricts players to a one-step landing after catching the ball. Most netball landings are single-leg landings resulting in high vertical ground reaction forces and high skeletal tissue forces. Thus, high-risk landing events that have the biomechanical potential for injury occur frequently. Noncontact knee ligament injuries are common following a knee abduction collapse when landing. Because the consequences of noncontact knee ligament injury are profound, strategies are needed to mitigate the burden of such injury for players, teams, and society.The purpose of this clinical commentary is to demonstrate how theoretical principles, different types of research, and different levels of evidence underpin a rational clinical reasoning process for developing noncontact knee ligament injury prevention screening procedures in netball. The theoretical principles that are discussed in this commentary include injury control, the sequence of prevention, principles of screening in injury prevention, the multifactorial model of injury etiology, complex systems theory, and systems science. The different types of research that are reviewed include descriptive and analytic-observational studies. The different levels of evidence that are discussed include prospective studies, cross-sectional studies, and clinicians’ own kinesiological modelling. Subsequently, an integrated approach to the evidence-informed development of noncontact knee ligament injury prevention screening procedures is presented. Clinical practice suggestions include a selection of evidence-informed screening tests that are quickly and easily implemented with netball players in local communities. The need for repeated screening at strategic timepoints across a season/year is explained. Sports physical therapists will find this commentary useful as an example for how to undertake clinical reasoning processes that justify the content of screening procedures contributing to noncontact knee ligament injury prevention in community-level netball.Level of Evidence5

Asymmetrical Loading Patterns in Military Personnel With a History of Self-Reported Low Back Pain.

Servicemembers are required to operate at high levels despite experiencing common injuries such as chronic low back pain. Continuing high levels of activity while compensating for pain may increase the risk of musculoskeletal injuries. As such, the purpose of this project was to determine if servicemembers with chronic low back pain have reduced lower extremity performance, and if they use alternate strategies to complete a functional performance task as compared to healthy servicemembers. Of a total of 46 male United States Marine Corps Forces Special Operations Command (MARSOC) personnel, 23 individuals who suffered from chronic low back pain (age = 28.6 ± 4.4 years, weight = 84.2 ± 6.8 kg) and 23 healthy controls (age = 27.9 ± 3.8 years, weight = 83.8 ± 7.7 kg) completed a stop jump task. In this task, three-dimensional biomechanics were measured, and lower extremity and trunk strength were assessed. The low back pain group exhibited higher vertical ground reaction force impulse on the dominant limb (0.26% body weight [BW]/s), compared to the nondominant limb (0.25% BW/s, p = .036). The control group demonstrated relationships between jump height and strength in both limbs (dominant: r = 0.436, p = .043; nondominant: r = 0.571, p = .006), whereas the low back pain group demonstrated relationships between jump height and dominant limb knee work (r = 0.470, p = .027) and ankle work (r = 0.447, p = .037). This study demonstrates that active-duty MARSOC personnel with a history of low back pain reach similar levels of jump height during a counter movement jump, as compared to those without a history of low back pain. However, the asymmetries displayed by the low back pain group suggest an alternate strategy to reaching similar jump heights as compared to healthy individuals.

The Effect of Divided Attention with Bounce Drop Jump on Dynamic Postural Stability.

This study determined the effect of divided attention on controlling postural stability during a drop vertical jump task. In total, 30 participants were tested for drop vertical jumps from a 30-cm high platform and landing on a single leg with or without divided attention tasks. Three-dimensional marker trajectories and ground reaction forces were collected simultaneously. Vertical ground reaction force, loading rate, and dynamic postural stability index were analyzed with or without divided attention tasks. The paired sample t test indicated a significantly low knee flexion angle, high vertical ground reaction force, and increased loading rate in the divided attention task. Moreover, participants showed an increased vertical stability index and dynamic postural stability index in the divided attention task than in the nondivided attention task. Thus, results demonstrated that the divided attention task could affect posture control, leading to poor dynamic posture stability and possibly increasing lower extremity injury risk. The influence of the divided attention task on movement quality likely indicates that an athlete can no longer focus his attention on the bounce drop jump maneuver. Therefore, the bounce drop jump combined with dynamic postural stability index could be used in posture stability screening.

A biomechanical comparison of conventional classifications of bowling action-types in junior fast bowlers

ABSTRACT Fast bowling is categorised into four action types: side-on, front-on, semi-open and mixed; however, little biomechanical comparison exists between action types in junior fast bowlers. This study investigated whether there are significant differences between action-type mechanics in junior fast bowlers. Three-dimensional kinematic and kinetic analyses were completed on 60 junior male fast bowlers bowling a five-over spell. Mixed-design factorial analyses of variance were used to test for differences between action-type groups across the phases of the bowling action. One kinetic difference was observed between groups, with a higher vertical ground reaction force loading rate during the front-foot contact phase in mixed and front-on compared to semi-open bowlers; no other significant group differences in joint loading occurred. Significant kinematic differences were observed between the front-on, semi-open and mixed action types during the front-foot contact phase for the elbow and trunk. Significant kinematic differences were also present for the ankle, T12-L1, elbow, trunk and pelvis during the back-foot phase. Overall, most differences in action types for junior fast bowlers occurred during the back-foot contact phase, particularly trunk rotation and T12-L1 joint angles/ranges of motion, where after similar movement patterns were utilized across groups during the front-foot contact phase.

Effect of antioxidants, mitochondrial cofactors and omega-3 fatty acids on telomere length and kinematic joint mobility in young and old shepherd dogs – A randomized, blinded and placebo-controlled study

In dogs, decreasing telomere length is a biomarker for cellular aging. On a systemic level, aging affects the locomotor system in particular, leading to restricted joint mobility. As aging is thought to be related to oxidative stress, it may be counteracted by a diet enriched with antioxidants, mitochondrial cofactors and omega-3 fatty acids. This randomized, blinded and placebo-controlled study examined the influence of an accordingly enriched diet compared to a control diet on 36 young and 38 old shepherd dogs. At the outset, after 3 and after 6 months, mean and minimum telomere lengths were measured. Furthermore, minimum and maximum joint angles and range of motion of the shoulder, elbow, carpal, hip, stifle and tarsal joints were measured by computer-assisted gait analysis. A positive influence of the enriched diet on old dogs could be verified for minimum telomere length and all three parameters of the shoulder joint on the side with the higher vertical ground reaction force after 6 months. In the other joints there were less significant differences; in some cases they indicated a contrary influence of the enriched diet on young dogs, probably due to its reduced protein content. The greater effect of the enriched diet on minimum than on mean telomere length may be due to the higher preference of telomerase for short telomeres. The greater effect on shoulder joint mobility is explained by the greater influence of musculature and connective tissue in this joint. For elderly dogs it is advisable to feed these nutritional supplements.

Lower Extremity Stiffness Predicts Ground Reaction Force Loading Rate in Heel Strike Runners.

High vertical ground reaction force (vGRF) loading rates are thought to contribute to lower extremity injuries in runners. Given that elevated lower extremity stiffness has been reported to be associated with increased GRFs, the purpose of the current study was to determine if overall lower extremity stiffness, individual joint angular excursions and/or torsional stiffness are predictive of the average vGRF loading rate during running. Forty heel strike runners (20 men and 20 women) ran overground at a speed of 3.4 m·s. Average vGRF loading rate, lower extremity stiffness, and hip, knee, and ankle joint excursions and torsional stiffness from initial contact to the first peak of the vGRF were quantified. Stepwise multiple linear regression was performed to determine the best predictor(s) of average vGRF loading rate. Lower extremity stiffness was found to the best predictor of average vGRF loading rate (R = 0.68, P < 0.001). The second variable that entered the stepwise regression model of average vGRF loading rate was knee joint excursion (ΔR = 0.03, P = 0.023). Increased lower extremity stiffness immediately after initial contact may expose heel strike runners to higher vGRF loading rates.

Females Decrease Vertical Ground Reaction Forces Following 4-Week Jump-Landing Feedback Intervention Without Negative Affect on Vertical Jump Performance

High vertical ground reaction force (vGRF) when initiating ground contact during jump landing is one biomechanical factor that may increase risk of anterior cruciate ligament injury. Intervention programs have been developed to decrease vGRF to reduce injury risk, yet generating high forces is still critical for performing dynamic activities such as a vertical jump task. To evaluate if a jump-landing feedback intervention, cueing a decrease in vGRF, would impair vertical jump performance in a separate task (Vertmax). Randomized controlled trial. Patients (or Other Participants): Forty-eight recreationally active females (feedback: n = 31; 19.63 [1.54]y, 1.6 [0.08]cm, 58.13 [7.84]kg and control: n = 15; 19.6 [1.68]y, 1.64 [0.05]cm, 60.11 [8.36]kg) participated in this study. Peak vGRF during a jump landing and Vertmax were recorded at baseline and 4 weeks post. The feedback group participated in 12 sessions over the 4-week period consisting of feedback provided for 6 sets of 6 jumps off a 30-cm box. The control group was instructed to return to the lab 28 days following the baseline measurements. Change scores (postbaseline) were calculated for peak vGRF and Vertmax. Group differences were evaluated for peak vGRF and Vertmax using a Mann-Whitney U test (P < .05). There were no significant differences between groups at baseline (P > .05). The feedback group (-0.5 [0.3]N/kg) demonstrated a greater decrease in vGRF compared with the control group (0.01 [0.3]N/kg) (t(46) = -5.52, P < .001). There were no significant differences in change in Vertmax between groups (feedback = 0.9 [2.2]cm, control = 0.06 [2.1]cm; t(46) = 0.46, P = .64). While the feedback intervention was effective in decreasing vGRF when landing from a jump, these participants did not demonstrate changes in vertical jump performance when assessed during a different task. Practitioners should consider implementing feedback intervention programs to reduce peak vGRF, without worry of diminished vertical jump performance.

Kinematics of Usain Bolt’s maximal sprint velocity

This study investigated the maximal sprint velocity kinematics of the fastest 100 m sprinter, Usain Bolt. Two high-speed video cameras recorded kinematics from 60 to 90 m during the men 100 m final at the IAAF World Challenge Zagreb 2011, Croatia. Despite a relatively slow reaction time (194 ms), Bolt won in 9.85 s (mean velocity: 10.15 m/s). His fastest 20-m section velocity was 12.14 m/s, reached between 70 and 90 m, by 2.70-m long strides and 4.36 strides/s frequency. At the maximal velocity, his contact and flight times were 86 and 145 ms, respectively, and vertical ground reaction force generated equalled 4.2 times his body weight (3932 N). The braking and propulsion phase represented 37% and 63% of ground contact, respectively, with his centre of mass (CoM) exhibiting minor reductions in horizontal velocity (2.7%) and minimal vertical displacement (4.9 cm). Emerged Bolt’s maximal sprint velocity and international predominance from coordinated motor abilities, power generation capacities, and effective technique. This study confirms that his maximal velocity was achieved by means of relatively long strides, minimal braking phase, high vertical ground reaction force, and minimal vertical displacement of CoM. This study is the first in-depth biomechanical analysis of Bolt’s maximal sprinting velocity with the segmental reconstruction.

Sagittal Plane Hip, Knee, and Ankle Biomechanics and the Risk of Anterior Cruciate Ligament Injury: A Prospective Study.

Background:Stiff landings with less knee flexion and high vertical ground-reaction forces have been shown to be associated with an increased risk of anterior cruciate ligament (ACL) injury. The literature on the association between other sagittal plane measures and the risk of ACL injuries with a prospective study design is lacking.Purpose:To investigate the relationship between selected sagittal plane hip, knee, and ankle biomechanics and the risk of ACL injury in young female team-sport athletes.Study Design:Case-control study; Level of evidence, 3.Methods:A total of 171 female basketball and floorball athletes (age range, 12-21 years) participated in a vertical drop jump test using 3-dimensional motion analysis. All new ACL injuries, as well as match and training exposure data, were recorded for 1 to 3 years. Biomechanical variables, including hip and ankle flexion at initial contact (IC), hip and ankle ranges of motion (ROMs), and peak external knee and hip flexion moments, were selected for analysis. Cox regression models were used to calculate hazard ratios (HRs) with 95% CIs. The combined sensitivity and specificity of significant test variables were assessed using a receiver operating characteristic (ROC) curve analysis.Results:A total of 15 noncontact ACL injuries were recorded during follow-up (0.2 injuries/1000 player-hours). Of the variables investigated, landing with less hip flexion ROM (HR for each 10° increase in hip ROM, 0.61 [95% CI, 0.38-0.99]; P < .05) and a greater knee flexion moment (HR for each 10-N·m increase in knee moment, 1.21 [95% CI, 1.04-1.40]; P = .01) was significantly associated with an increased risk of ACL injury. Hip flexion at IC, ankle flexion at IC, ankle flexion ROM, and peak external hip flexion moment were not significantly associated with the risk of ACL injury. ROC curve analysis for significant variables showed an area under the curve of 0.6, indicating a poor combined sensitivity and specificity of the test.Conclusion:Landing with less hip flexion ROM and a greater peak external knee flexion moment was associated with an increased risk of ACL injury in young female team-sport players. Studies with larger populations are needed to confirm these findings and to determine the role of ankle flexion ROM as a risk factor for ACL injury. Increasing knee and hip flexion ROMs to produce soft landings might reduce knee loading and risk of ACL injury in young female athletes.

Achilles Tendon Load is Progressively Increased with Reductions in Walking Speed.

Achilles tendon rehabilitation protocols commonly recommend a gradual increase in walking speed to progressively intensify tendon loading. This study used transmission-mode ultrasound to evaluate the influence of walking speed on loading of the human Achilles tendon in vivo. Axial transmission speed of ultrasound was measured in the right Achilles tendon of 33 adults (mean ± SD: age, 29 ± 3 yr; height, 1.725 ± 0.069 m; weight, 71.4 ± 19.9 kg) during unshod, steady-state treadmill walking at three speeds (slow, 0.85 ± 0.12 ms; preferred, 1.10 ± 0.13 m·s; fast, 1.35 ± 0.20 m·s). Ankle kinematics, spatiotemporal gait parameters and vertical ground reaction force were simultaneously recorded. Statistical comparisons were made using repeated-measures ANOVA models. Increasing walking speed was associated with higher cadence, longer step length, shorter stance duration, greater ankle plantarflexion, higher vertical ground reaction force peaks, and a greater loading rate (P < 0.05). Maximum (F1,38 = 7.38, P < 0.05) and minimum (F1,46 = 8.95, P < 0.05) ultrasound transmission velocities in the Achilles tendon were significantly lower (16-23 m·s) during the stance but not swing phase of gait, with each increase in walking speed. Despite higher vertical ground reaction forces and greater ankle plantarflexion, increasing walking speed resulted in a reduction in the axial transmission velocity of ultrasound in the Achilles tendon; indicating a speed-dependent reduction in tensile load within the triceps surae muscle-tendon unit during walking. These findings question the rationale for current progressive loading protocols involving the Achilles tendon, in which reduced walking speeds are advocated early in the course of treatment to lower Achilles tendon loads.

Physiological and Biomechanical Mechanisms of Distance Specific Human Running Performance.

Running events range from 60-m sprints to ultra-marathons covering 100 miles or more, which presents an interesting diversity in terms of the parameters for successful performance. Here, we review the physiological and biomechanical variations underlying elite human running performance in sprint to ultramarathon distances. Maximal running speeds observed in sprint disciplines are achieved by high vertical ground reaction forces applied over short contact times. To create this high force output, sprint events rely heavily on anaerobic metabolism, as well as a high number and large cross-sectional area of type II fibers in the leg muscles. Middle distance running performance is characterized by intermediates of biomechanical and physiological parameters, with the possibility of unique combinations of each leading to high-level performance. The relatively fast velocities in mid-distance events require a high mechanical power output, though ground reaction forces are less than in sprinting. Elite mid-distance runners exhibit local muscle adaptations that, along with a large anaerobic capacity, provide the ability to generate a high power output. Aerobic capacity starts to become an important aspect of performance in middle distance events, especially as distance increases. In distance running events, V˙O2max is an important determinant of performance, but is relatively homogeneous in elite runners. V˙O2 and velocity at lactate threshold have been shown to be superior predictors of elite distance running performance. Ultramarathons are relatively new running events, as such, less is known about physiological and biomechanical parameters that underlie ultra-marathon performance. However, it is clear that performance in these events is related to aerobic capacity, fuel utilization, and fatigue resistance.

LANDING WITH LESS HIP FLEXION IS ASSOCIATED WITH INCREASED RISK OF ACL INJURIES IN YOUNG FEMALE TEAM SPORTS PLAYERS

BackgroundStiff landings with less knee flexion and high vertical ground reaction force have shown to be associated with increased risk of ACL injuries (Leppänen et al. 2016). The association between...

Ground reaction force and required friction during stair ascent and descent

AbstractA stair climbing experiment was performed using a four‐stair instrumented stairway. A force platform was mounted in the first stair. Four floor surfaces, including the original force platform surface and three additional floor coverings on the platform, were tested. Human subjects wore the same type of lab shoes and ascended and descended the stairway. Their ground reaction forces were collected. The results showed that when descending, the double‐stair condition resulted in significant (p &lt; .0001) higher vertical ground reaction force at foot landing as compared to the single‐stair condition. The vertical ground reaction force at foot push‐off for stair ascent were significantly (p &lt; .0001) higher than those for stair descent. The mean required coefficient of friction ranged from 0.086 to 0.245 and from 0.051 to 0.246 for foot landing and foot push‐off spots, respectively. Stair descent required significant (p &lt; .001) higher friction than stair ascent both at foot landing and push‐off. Double‐stair stepping required higher friction than single‐stair stepping. Stair descent should be of primary concern in assessing the risk of slip‐ and fall‐related incidents on stairway, and double‐stair descent should be avoided.

Landing from different heights: Biomechanical and neuromuscular strategies in trained gymnasts and untrained prepubescent girls

The purpose of this study was to examine the biomechanics of the lower limb, during landing in female prepubertal gymnasts and prepubertal untrained girls, aged 9–12years. Ten healthy participants were included in each group and performed five landings from 20, 40, and 60cm. Kinematics, ground reaction forces (GRF) and electromyogram (EMG) from the lateral gastrocnemius, tibialis anterior, and vastus lateralis are presented. Gymnasts had higher vertical GRF and shorter braking phase during landing. Compared to untrained girls, gymnasts exhibited for all examined drop heights more knee flexion before and at ground contact, but less knee flexion at maximum knee flexion position. Especially when increasing drop heights the gymnasts activated their examined muscles earlier, and generally they had higher pre- and post landing EMG amplitudes normalized to the peak EMG at 60cm drop height. Furthermore, gymnasts had lower antagonist EMG for the tibialis anterior compared to untrained girls, especially when landing from higher heights. It is concluded that the landing strategy preferred by gymnasts is influenced by long-term and specialized training and induces a stiffer landing pattern. This could have implications in injury prevention, which requires further investigation.