Vertical Ground Reaction Force Research Articles

Effects of prosthetic stiffness and added mass on metabolic power and asymmetry in female runners with a leg amputation.

Similar to nonamputees, female athletes with unilateral transtibial amputation (TTA) using running-specific leg prostheses (RSPs) may have worse running economy and higher rates of running-related injury than male athletes. Optimizing RSP configuration for female athletes could improve running economy and minimize biomechanical asymmetry, which has been associated with running-related injury. Nine females with a TTA ran at 2.5 m/s while we measured metabolic rates and ground reaction forces. Subjects used an RSP with a manufacturer-recommended stiffness category, one category less stiff and two categories less stiff than recommended. Use of an RSP two categories less stiff resulted in 3.0% lower net metabolic power (P = 0.04), 7.8% lower affected leg stiffness (P = 6.01 × 10-4), increased contact time asymmetry (P = 0.04), and decreased stance average vertical ground reaction force asymmetry (P = 0.04) compared with a recommended stiffness category RSP. Lower RSP stiffness (kN/m) values were associated with lower net metabolic power (P = 0.02), lower affected leg stiffness (P = 1.36 × 10-4), longer affected leg contact time (P = 1.46 × 10-4), and similar affected leg peak and stance-average vertical ground reaction force compared with higher RSP stiffness values. Subjects then used the RSP stiffness category that elicited the lowest net metabolic power with 100 g, 200 g, and 300 g added distally. We found no significant effects of added mass on net metabolic power, biomechanics, or asymmetry. These results suggest that female runners with a TTA could decrease metabolic power during running while minimizing biomechanical asymmetries, which have been associated with running-related injury, by using an RSP two categories less stiff than manufacturer recommended.NEW & NOTEWORTHY Females with unilateral transtibial amputation can improve running performance through reductions in net metabolic power by using a running-specific prosthesis (RSP) that is less stiff than manufacturer-recommended. Lower RSP stiffness values are associated with greater leg stiffness and contact time asymmetry, and lower stance-average vertical ground reaction force asymmetry. However, we found that adding mass to the RSP did not affect net metabolic power and stance-phase biomechanical asymmetries during running.

The impact of landing forces on repeated jumping performance.

High-velocity concentric actions can be negatively impacted by cumulative fatigue during plyometric training. Reducing vertical ground reaction forces (GRF) upon landing could decrease eccentric demands, potentially minimizing fatigue, maintaining concentric performance, and benefiting concentric training adaptations. Therefore, this study examined the effect of intentionally higher and lower landing vertical GRF on the ability to sustain concentric jumping performance. Twenty men (25.2±3.5 years) performed 30 maximal effort jumps over a 50 cm hurdle (high-landing GRF) and onto a 50 cm box (low-landing GRF), on two separate occasions in a counter-balanced order. Jumps were measured using two force platforms (one for takeoff and one for landing) and a linear position transducer. The 30 jumps were divided into 5 groups of 6 repetitions, and the mean value for each group was analyzed. There was no significant condition × repetition group interaction for any parameters, indicating that the greater landing GRF during hurdle jumps did not negatively affect concentric jump performance throughout the 30 jumps. Concentric velocities and jump height were significantly greater during box jumps compared to hurdle jumps. Thirty maximal-effort jumps did not cause fatigue-related decrease of performance, independent of jump type (i.e., the magnitude of landing GRF). Although, reduced vertical GRF upon landing appears to have a neutral-to-positive effect on concentric jumping performance. Therefore, reducing landing GRF, such as by using BJs, could acutely augment jumping performance and help to reduce cumulative training load.

Effects of Fatigue on Lower Limb Biomechanics and Kinetic Stabilization During the Tuck-Jump Assessment.

General and local muscular fatigue is postulated to negatively alter lower limb biomechanics; however, few prospective studies have been done to examine the effect of fatigue on tuck-jump performance. The tuck-jump assessment (TJA) is a criteria-based visual screening tool designed to identify neuromuscular deficits associated with anterior cruciate ligament (ACL) injury. Use of kinetics during the TJA after an intense sport-specific fatigue protocol may identify fatigue-induced neuromuscular deficits associated with ACL injury risk. To examine the effects of a sport-specific fatigue protocol on visually evidenced (2-dimensional) technical performance of repeated tuck jumps and lower limb kinetic stabilization. Cross-sectional study. Laboratory. Twelve female netball athletes (age = 20.8 ± 2.6 years, height = 170.0 ± 0.04 cm, mass = 67.5 ± 7.4 kg). Participants performed 1 set of a TJA before and after a sport-specific fatigue protocol. Paired t tests and effect sizes were used to evaluate differences and the magnitude of differences in TJA scoring criterion, kinetics, and kinetic stabilization prefatigue to postfatigue. A small increase was observed for vertical relative lower extremity stiffness postfatigue (P = .005; Hedges g = 0.45). Peak center-of-mass displacement, time of jump cycle, ground contact time, flight time, jump height, and vertical net impulse decreased with small to moderate effect sizes (P < .01; Hedges g range, 0.41-0.74). No differences were observed for TJA composite scores, peak vertical ground reaction force, and stabilization indices of kinetic variables after the fatigue protocol (P > .05). Kinetic analysis of repeated tuck jumps after a fatigue protocol identified an altered jumping strategy, which was not identifiable via visual 2-dimensional assessment. However, based on kinetic measures, fatigue induces a stiffer jumping strategy, and practitioners should consider assessing load attenuation strategies that may not be visually evident when evaluating ACL-injury risk factors in athletes who are fatigued.

Effect of different resistance increments during warm-up on the snatch performance of male weightlifters

This study investigated the effect of different resistance increments during warm-up on snatch performance of male weightlifters. Nine male college weightlifters were recruited. The 3 warm-up protocols were performed every 7 days with a randomized order: 1. Power snatch exercise with 10 % resistance increment (50 %, 60 %, 70 %, and 80 % of one-repetition maximum); 2. Power snatch exercise with 15 % resistance increment (50 %, 65 %, and 80 % of one-repetition maximum); 3. Self-selected resistance increment. Participants were tested based on 85 % maximum weight snatch after warm-up. Snatch performance was measured using peak vertical ground reaction force. Postural stability was measured using center-of-pressure displacement. Activation of seven shoulder, back, and leg muscles was measured using electromyography on the dominant side. In snatch performance, the 10 % increment protocol had a significantly higher peak vertical ground reaction force during the second-pull phase than the 15 % increment (d = 0.92, p < 0.05) and self-selected (d = 1.32, p < 0.05) protocols. In postural stability, no significant differences in center-of-pressure displacement among the three protocols were observed. For muscle activation, the 10 % increment protocol resulted in significantly higher activation of shoulder (d = 1.2–2.2, p < 0.05) during the second-pull phase than the other two protocols and higher activation of hip muscles (d = 1.73, p < 0.05) than self-selected protocol. To conclude, a warm-up protocol combining slow progression is preferable in improving power output during snatch in male weightlifters, probably through facilitating the activation of proximal limb muscles. It can enhance training quality while potentially reducing the risk of sports injuries.

Response of Knee Joint Biomechanics to Landing Under Internal and External Focus of Attention in Female Volleyball Players.

The aim of this study was to examine the effect of attentional focus instructions on the biomechanical variables associated with the risk of anterior cruciate ligament injury of the knee joint during a drop landing task using a time series analysis. Ten female volleyball players (age: 20.4 ± 0.8years, height: 169.7 ± 7.1cm, mass: 57.6 ± 3.1kg, experience: 6.3 ± 0.8years) performed landings from a 50cm height under three different attentional focus conditions: (1) external focus (focus on landing as soft as possible), (2) internal focus (focus on bending your knees when you land), and (3) control (no-focus instruction). Statistical parameter mapping in the sagittal plane during the crucial first 30% of landing time showed a significant effect of attentional focus instructions. Despite the similarity in landing performance across foci instructions, adopting an external focus instruction promoted reduced vertical ground reaction force and lower sagittal flexion moment during the first 30% of execution time compared to internal focus, suggesting reduced knee loading. Therefore, adopting an external focus of attention was suggested to reduce most biomechanical risk variables in the sagittal plane associated with anterior cruciate ligament injuries, compared to internal focus and control condition. No significant differences were found in the frontal and horizontal planes between the conditions during this crucial interval.

Relationship of Ball Speed with Kinematic and Kinetic Patterns during Pitching

PURPOSE This study aimed to analyze the differences in ground reaction forces (GRF) and pelvis and trunk kinematic patterns between groups based on ball speed during pitching.METHODS Twenty-nine males were recruited for this study. Participants were categorized based on ball speed into high (HG), medium (MG), and low (LG) ball speed groups. Statistical analysis was performed using one-dimensional statistical parametric mapping (SPM1D) one-way analysis of variance to compare GRF and pelvis and trunk kinematic patterns, followed by Bonferroni post-hoc tests.RESULTS Drive leg anterior and resultant GRF were greater in the HG than in the LG (&lt;i&gt;p&lt;/i&gt;&lt;0.001). The posterior GRF of the stride leg in the HG was greater than in the LG (&lt;i&gt;p&lt;/i&gt;&lt;0.008). Additionally, the vertical GRF of the stride leg was greater in the HG than in the LG (&lt;i&gt;p&lt;/i&gt;&lt;0.003), as was the resultant GRF of the stride leg (&lt;i&gt;p&lt;/i&gt;&lt;0.003).CONCLUSIONS The GRF of the drive and stride legs was significantly related to ball speed, indicating that a pitching strategy to maximize the GRF of the drive and stride legs is required.

Ankle mechanics during jump landings across different foot positions in professional ballet dancers

ABSTRACT This study aimed to investigate the effect foot position on ankle joint mechanics and vertical ground reaction forces (vGRF) across jump landings in professional ballet dancers. Twenty-seven professional ballet dancers (men: 14; women: 13) attended one data collection session, completing five maximal countermovement jumps in parallel, first, second, fourth, and fifth positions. Three-dimensional ankle mechanics, landing vGRF variables, and jump height were recorded via a seven-camera motion capture system and one force platform. A repeated measures multivariate analysis of variance was used to assess the main effects foot position across all target variables. A linear discriminate analysis was conducted to investigate target variables across foot positions. Frontal and transverse plane ankle mechanics had the largest impact when discriminating between foot positions. Ankle power in the transverse plane during jump landing in fourth was double that of all other positions. Our findings suggest that ankle range of motion should be restored before returning to jumps in fourth and fifth positions following distal lower extremity injury. The multiplanar energy transfer observed indicates a need for specific exercises to develop multiplanar force and rate of force development of local structures around the ankle.

Total ankle arthroplasty improves discrete and continuous stance phase gait symmetry

BackgroundTotal ankle arthroplasty (TAA) is used to treat symptomatic end-stage ankle arthritis (AA). However, little is known about TAA's effects on gait symmetry. Research questionDetermine if symmetry changes from before surgery through two years following TAA utilizing the normalized symmetry index (NSI) and statistical parametric mapping (SPM). Methods141 patients with end-stage unilateral AA were evaluated from a previously collected prospective database, where each participant was tested within two weeks of surgery (Pre-Op), one year and two years following TAA. Walking speed, hip extension angle and moment, hip flexion angle, ankle plantarflexion angle and moment, ankle dorsiflexion angle, weight acceptance (GRF1), and propulsive (GRF2) vertical ground reaction forces were calculated for each limb. Gait symmetry was assessed using the NSI. A linear mixed effects model with a single response for each gait symmetry variable was used to examine the fixed effect of follow-up time (Pre-Op, Post-1 yr, Post-2 yr) and the random effect of participant with gait speed as a covariate in the model. A one-dimensional repeated measures analysis of variance (ANOVA) statistical parameter mapping (SPM) was completed to examine differences in the time-series NSI to determine regions of significant differences between follow-up times. ResultsRelative to Pre-Op values, GRF1, and GRF2 showed increased symmetry for discrete metrics and the time-series NSI across sessions. Hip extension moment had the largest symmetry improvement. Ankle plantarflexion angle was different between Pre-Op and Post-2 yr (p=0.010); and plantarflexion moment was different between Pre- Op and each post-operative session (p<0.001). The time-series Ankle Angle NSI was greater during the early stance phase in the Pre-Op session compared to Post-2 yr. SignificanceSymmetry across most of the stance phase improved following TAA indicating that TAA successfully improves gait symmetry and future work should determine if these improvements restore symmetry to levels equivalent with health age-match controls.

Immediate Effects of Wearing an Ankle Bandage on Fine Coordination, Proprioception, Balance and Gait in the Subacute Phase of Ankle Sprains.

Ankle sprains are the most frequently occurring musculoskeletal injuries among recreational athletes. Ankle support through bandages following the initial orthotic treatment might be beneficial for rehabilitation purposes. However, the literature is sparse regarding the use of an ankle support directly after the acute phase of an ankle sprain. Therefore, this study investigates the hypothesis that wearing an ankle bandage immediately after an acute ankle sprain improves motor performance, stability and reduces pain. In total, 70 subjects with acute unilateral supination trauma were tested. Subjects were tested five weeks post-injury to assess immediate effects of the ankle bandage. On the testing day, subjects completed rating questionnaires and underwent comprehensive biomechanical assessments. Biomechanical investigations included fine coordination and proprioception tests, single leg stances, the Y-Balance test, and gait analysis. All biomechanical investigations were conducted for the subject's injured leg with and without a bandage (MalleoTrain® Bauerfeind AG, Zeulenroda-Triebes, Germany) and the healthy leg. Results indicated moderate to strong improvements in ankle stability and pain relief while wearing the bandage. Wearing the bandage significantly normalized single leg stance performance (p < 0.001), stance phase duration (p < 0.001), and vertical ground reaction forces during walking (p < 0.05). However, the bandage did not have a clear effect on fine coordination and proprioception. The findings of our study suggest that ankle bandages may play a crucial role in early-stage rehabilitation by enhancing motor performance and reducing pain.

Biomechanical variations in patients with flatfoot deformity: Impact of gender, age, and BMI on foot kinetics and kinematics

BackgroundFlatfoot is considered by the collapse of the foot arch, altered biomechanics and impacting functional abilities. The biomechanical gait alteration of foot kinematics and kinetics in individuals with flatfoot, based on gender, age and Body mass index (BMI) in each cohort is unclear. This study explores how gender, age, and body mass index (BMI) impact distinct foot biomechanical characteristics, including ankle joint angle (Jc°), Ground force reaction angle (GFR°), Achilles tendon force (T), Ankle joint force (Jc) and vertical ground reaction force (VGRF) during the gait stance phase, in flatfoot versus normal-foot individuals on Indian Population. MethodA foot pressure test and sagittal plane motion analysis were performed on 142 individuals with normal-foot arches and 102 with flatfoot, stratified by gender, age, and BMI. Calculations of the magnitude and direction of forces in ankle joint equilibrants relied on inverse dynamic analysis, vertical ground force reaction and mapping motion data of the gait stance phases. ResultIn the midstance phase, females with high BMI (HBMI) in the middle and older age group (p = 0.029 and p = 0.014), and males with HBMI in the older age group (p = 0.039) demonstrate significantly higher VGRF. Females and males with HBMI in middle and older age groups, along with males with normal BMI in the older age cohort, show positive and negative ranges of GFR°, indicating gait instability. In the push-off phase, females with HBMI in a middle-aged group exhibit significantly lower TandJc (p = 0.023 and p = 0.026) respectively. ConclusionThe biomechanical issues in individuals with flatfoot, while accounting for the influence of gender, age and BMI, are crucial for tailored interventions and precise solutions to biomechanical issues, thereby enhancing foot function and reducing discomfort.

Classification of Parkinson's disease severity using gait stance signals in a spatiotemporal deep learning classifier.

Parkinson's disease (PD) is a degenerative nervous system disorder involving motor disturbances. Motor alterations affect the gait according to the progression of PD and can be used by experts in movement disorders to rate the severity of the disease. However, this rating depends on the expertise of the clinical specialist. Therefore, the diagnosis may be inaccurate, particularly in the early stages of PD where abnormal gait patterns can result from normal aging or other medical conditions. Consequently, several classification systems have been developed to enhance PD diagnosis. In this paper, a PD gait severity classification algorithm was developed using vertical ground reaction force (VGRF) signals. The VGRF records used are from a public database that includes 93 PD patients and 72 healthy controls adults. The work presented here focuses on modeling each foot's gait stance phase signals using a modified convolutional long deep neural network (CLDNN) architecture. Subsequently, the results of each model are combined to predict PD severity. The classifier performance was evaluated using ten-fold cross-validation. The best-weighted accuracies obtained were 99.296(0.128)% and 99.343(0.182)%, with the Hoehn-Yahr and UPDRS scales, respectively, outperforming previous results presented in the literature. The classifier proposed here can effectively differentiate gait patterns of different PD severity levels based on gait signals of the stance phase.

Jump Roping High-Intensity Interval Training Enhances Vascular Function in Adults with Overweight/Obesity

A few studies have shown that body-weight- and laboratory-based high-intensity interval training (HIIT) effectively improves endothelial function. However, the effect of HIIT in the form of jump roping that significantly increases vertical ground reaction force on endothelial function remains unknown. Thus, the objective of this study was to determine the effects of a 12-week jump roping exercise programme on vascular function in adults with overweight/obesity. Twenty young adults with overweight/obesity were randomly assigned to the exercise or control group. The exercise group performed 12 intervals jump roping HIIT – 1 minute at 85%–95% maximal heart rate (HRmax) and 1 minute at 50%–70% HRmax – for 12 weeks (five sessions per week). The control group was asked to maintain the usual lifestyle pattern throughout the study period. The outcome measures were per cent flow-mediated dilation (%FMD), baseline artery diameter (FMDbase), peak artery diameter (FMDpeak), mean blood flow velocity (MBFV) and per cent body fat (%BF). Results revealed that there was a significant group × time interaction for %FMD, FMDpeak and MBFV after the intervention (all P &lt;0.05). There was no significant group × time interaction for the other variables. There were no significant changes in the outcome variables between pre- and post-intervention and between the groups (all P &gt;0.05), except for %FMD. In conclusion, jump roping HIIT increased %FMD, FMDpeak and MBFV, indicating the cardiovascular-protective effects of this approach in adults with overweight/obesity.

Using inertial measurement units to estimate ground reaction force and knee angular velocity during decelerations

Despite undergoing anterior cruciate ligament (ACL) reconstruction, athletes continue to present altered ground reaction force (GRF) and knee angular velocities (AV) for 6-24 months as they return to highly demanding tasks such as rapid decelerations (Schmitt et al., 2015, Med Sci Sports Ex, 47, 1426). In-field identification of GRF and knee AV during such deceleration tasks is challenging due to the laboratory restrictions of force platforms and 3D motion capture. Therefore, the use of inertial measurement units (IMU) has been suggested as an appropriate alternative to estimate such variables in the field (Pratt &amp; Sigward, 2018. Sensors, 3460). The study aimed to establish whether IMU-derived measures can be used to estimate GRF and knee AV that are indicative of ACL injury risk during decelerations. Following ethical approval from the Cardiff Metropolitan Ethics Committee, ten male team-sport athletes performed five maximal decelerations at three approach speeds (100, 85, and 70% relative to maximal attainable speed), for a total of fifteen trials per athlete. GRF and kinematics were measured using four Kistler force platforms and Theia3D markerless motion capture. Pearson’s correlation coefficient was used to determine the relationship between IMeasureU Blue Trident IMUs mounted at the thigh or shank and vertical GRF, horizontal GRF, and knee AV during the first step of deceleration. A measure was considered field-viable if a very large significant correlation (r ≥ 0.7; P ≤ 0.05) was observed. At approach speeds of 85 and 70%, shank AV had a very large significant correlation (r = 0.79, 0.76; P = 0.001, 0.01, respectively) to vertical GRF, a moderate to large significant correlation to horizontal GRF (r = 0.46, 0.51; P = 0.04, 0.02, respectively), and a moderate significant correlation to knee AV (r =0.46, 0.40; P = 0.004, 0.02, respectively). At 100% approach speeds, shank AV had no significant correlation to GRF (r &lt;0.3; P&gt;0.05) and a moderate correlation to knee AV (r = 0.40; P = 0.02). This study was the first to find a strong association between shank AV and vertical GRF for whole-body decelerations at 85 and 70% approach speeds. This supports the use of IMUs in sport-specific settings (e.g., football pitches) to better quantify vertical GRF deficits during decelerations. This can further enhance in-field monitoring of GRF deficits and better assess athletes' readiness to return to sport following ACL reconstruction. However, alternative methods are required to accurately estimate horizontal GRFs and knee AV in the field.

Definition of an insole comfort equation using biomechanics data from a real-world data collection method

Comfort is among the priorities of wearers, this creates a requirement to understand and measure footwear comfort within the real-world where footwear is being used. Comfort is subjective however associations have been drawn to biomechanical parameters. Prediction of real-world footwear or insole comfort based upon biomechanical parameters is appealing due to the reduction of potential participant biases. This study aims to develop an equation to predict insole comfort from real-world biomechanics data. Five conditions were evaluated, a control (participant shoe only) and four commercially available insole conditions (Insole A, B, C, D). The RunScribe IMU was worn for one day per condition for the participants normal daily activity, measuring previously validated variables: vertical ground reaction force (GRF), vertical GRF loading rate (GRFr), impact shock (IS), braking shock, total shock, pronation excursion (PE), and maximum pronation velocity (PV). Comfort was measured using a 100 mm visual analogue scale (VAS). A mixed model with fixed effects was used to develop the comfort equation, pseudo r 2 statistics were assessed to identify the best equation. All combinations of conditions were tested from single conditions to all 5 together. The following equation was defined using data from insole A and insole B: Comfort = 96.557 + (−0.456*GRFr) + (−11.757*IS) + (−2.869*PE) + (0.142*PV). Marginal pseudo r 2 = 0.175 and conditional pseudo r 2 = 0.675, meaning that 17.5% of the variance in comfort was explained by the biomechanics variables. Previous footwear comfort equations focused on different biomechanics variables including EMG, plantar pressure, loading rates and lower limb kinematics and reported larger explained variance (34.9%–71.4%). Additional variables would be required to improve the current equation; however, it provides insight into how comfort could be improved for usage within product development, as well as measuring comfort during testing.

Balance, Landing Biomechanics, and Functional Movement Screen Characteristics With and Without Knee Exoskeleton in Military Soldiers.

A light-weight pneumatic-powered knee exoskeleton could augment mobility and lifting capabilities for a variety of occupational settings. However, added weight/bulkiness and artificially produced knee extension torque could compromise sensorimotor characteristics. Ten healthy participants conducted 3 visits within 10 days to the biomechanics laboratory. Participants were asked to complete the following tasks on each visit: single-leg balance, single-leg drop-landing, and select functional movement tasks. Balance characteristics (the ground reaction forces variability and center-of-pressure velocity) were derived from force plates while knee flexion angles during drop-landing and functional movement tasks were captured using a motion capture system. Descriptive statistics as well as paired t-tests or Wilcoxon signed-rank tests were used to compare between conditions. Significance was set at P < .05 a priori. During single-leg balance, the ground reaction force variabilities were significantly increased (P = .013-.019) and the center of pressure velocity was decreased (P = .001-.017) when wearing knee exoskeleton. During single-leg drop-landing, the exoskeleton condition showed lower knee flexion angles at the initial contact (P = .004-.021) and peak (P = .006-.010). Additionally, the peak vertical ground reaction force was higher in the exoskeleton condition (P = .007). During functional movement tasks, the exoskeleton condition showed less knee flexion range-of-motion during the overhead squat (P = .007-.033) and hurdle step-over (P = .004-.005). Participants exhibited stiffer landing technique with the exoskeleton. Given that these compromised sensorimotor characteristics have been associated with musculoskeletal injury risk, modifications to exoskeletons to promote softer landing and greater knee flexion range-of-motion during dynamic activities may be warranted.

Validity of the Hawkin Dynamics Wireless Dual Force Platform System Against a Piezoelectric Laboratory Grade System for Vertical Countermovement Jump Variables.

Dos'Santos, T, Evans, DT, and Read, DB. Validity of the Hawkin dynamics wireless dual force platform system against a piezoelectric laboratory grade system for vertical countermovement jump variables. J Strength Cond Res 38(6): 1144-1148, 2024-The aim of this study was to determine the criterion validity of the Hawkin Dynamics (HD) wireless dual force platform system for assessing vertical countermovement jump (CMJ) variables, compared with those derived from a Kistler piezoelectric laboratory grade force platform system. During a single testing session, HD force platforms were placed directly on top of 2 adjacent Kistler force platforms to simultaneously collect vertical ground reaction forces produced by 2 male recreational soccer players (age: 29.0 ± 2.8 years, height: 1.79 ± 0.01 m, mass: 85.6 ± 4.7 kg) that performed 25 vertical CMJs each. Sixteen vertical CMJ variables pertaining to jump height (JH), flight time (FT), time-to-take off (TTT), countermovement depth, body weight (BW), propulsive and braking mean, and peak powers, forces, and impulses were compared between systems. Fixed bias was observed for 6 of 16 variables (peak and mean braking power, mean propulsion force, TTT, FT, and BW), while proportional bias was present for 10 of 16 variables (peak and mean propulsive and braking force, TTT, FT, peak and mean braking power, mean propulsive power, and BW). For all variables regardless of fixed or proportional bias, percentage differences were ≤3.4% between force platform systems, with near perfect to perfect correlations (r or ρ = 0.977-1.000) observed for 15 of 16 variables. The HD dual wireless force platform system can be considered a valid alternative to a piezoelectric laboratory grade force platform system for the collection of vertical CMJ variables, particularly outcome (i.e., JH, reactive strength index modified) and strategy variables (countermovement depth).

Step type is associated with loading and ankle motion in tap dance.

Tap dance generates forces and joint motions that can lead to injury; however, little is known about the magnitude of load across different tap steps. The purpose of this study was to calculate peak vertical forces, average vertical foot velocities, and maximum/minimum ankle angles produced by tap dancers with different levels of experience performing the toe cannon, heel cannon, flap, and cramp roll. This prospective cross-sectional study included 14 female tap dancers aged ≥18 years with varying tap experience. Participants were recorded by three cameras while performing a choreographed tap combination containing four steps of interest on a force platform. Adjusting for experience and dancer-level clustering, we identified the steps-cramp roll and toe cannon-that had the highest peak vertical ground reaction force, angles, and velocities compared to flap and heel cannon. There was no effect of experience. The results supported our hypothesis and provide new insights into step production. Over time, the larger forces associated with these steps could pose an increased risk of injury to bones and joints when compared to smaller forces, which may suggest the importance of adjusting routines to reduce or avoid injury.

Single Leg Hop Performance After Anterior Cruciate Ligament Reconstruction: Ready for Landing but Cleared for Take-Off?

While the landing phases of the single-leg hop for distance (SLHD) are commonly assessed, limited work reflects how the take-off phase influences hop performance in patients with anterior cruciate ligament reconstruction (ACLR). To compare trunk and lower extremity biomechanics between individuals with ACLR and matched uninjured controls during take-off of the SLHD. Cross-sectional study design. Laboratory setting. 16 individuals with ACLR and 18 uninjured controls. Normalized quadriceps isokinetic torque, hop distance, and respective limb symmetry indices (LSI) were collected for each participant. Sagittal and frontal kinematics and kinetics of the trunk, hip, knee, and ankle, as well as vertical and horizontal ground reaction forces (GRF) were recorded for loading and propulsion of the take-off phase of the SLHD. Those with ACLR had weaker quadriceps peak torque in the involved limb (p=0.001) and greater strength asymmetry (p<0.001) compared to controls. Normalized hop distance was not statistically different between limbs or between groups (p>0.05) and hop distance symmetry was not different between groups (p>0.05). During loading, the involved limb demonstrated lesser knee flexion angles (p=0.030) and knee power (p=0.007) compared to the uninvolved limb, and lesser knee extension moments compared to the uninvolved limb (p=0.001) and controls (p=0.005). During propulsion, the involved limb demonstrated lesser knee extension moment (p=0.027), knee power (p=0.010), knee (p=0.032) and ankle work (p=0.032), anterior- posterior GRF (p=0.047), and greater knee (p=0.016) abduction excursions compared to the uninvolved limb. Between-limb differences in SLHD take-off suggest a knee underloading strategy in the involved limb. These results provide further evidence that distance covered during SLHD assessment can overestimate function and fail to identify compensatory biomechanical strategies.

Lower extremity joint angle, moment, and coordination throughout a double limb drop vertical jump in individuals with anterior cruciate ligament reconstruction

ABSTRACT Individuals with anterior cruciate ligament reconstruction (ACLR) utilise different landing biomechanics between limbs, but previous analyses have not considered the continuous or simultaneous joint motion that occurs during landing and propulsion. The purpose of this study was to compare sagittal plane ankle/knee and knee/hip coordination patterns as well as ankle, knee, and hip angles and moments and vertical ground reaction force (vGRF) between the ACLR and uninjured limbs during landing and propulsion. Fifteen females and thirteen males performed a drop vertical jump from a 30 cm box placed half their height from force platforms. Coordination was compared using a modified vector coding technique and binning analysis. Kinematics and kinetics were time normalised for waveform analyses. Coordination was not different between limbs. The ACLR limb had smaller dorsiflexion angles from 11 to 16% of landing and 24 to 75% of landing and propulsion, knee flexion moments from 5 to 15% of landing, 20 to 31% of landing, and 35 to 91% of landing and propulsion, and vGRF from 92 to 94% of propulsion compared with the uninjured limb. The ACLR limb exhibited smaller dorsiflexion angles to potentially reduce the knee joint moment arm and mitigate the eccentric and concentric demands on the ACLR knee during landing and propulsion, respectively.

Kinematics but not kinetics alterations to single-leg drop jump movements following a subject-tailored fatiguing protocol suggest an increased risk of ACL injury.

Neuromuscular fatigue causes a transient reduction of muscle force, and alters the mechanisms of motor control. Whether these alterations increase the risk of anterior cruciate ligament (ACL) injury is still debated. Here we compare the biomechanics of single-leg drop jumps before and after the execution of a fatiguing exercise, evaluating whether this exercise causes biomechanical alterations typically associated with an increased risk of ACL lesion. The intensity of the fatiguing protocol was tailored to the aerobic capacity of each participant, minimizing potential differential effects due to inter-individual variability in fitness. Twenty-four healthy male volunteers performed single leg drop jumps, before and after a single-set fatiguing session on a cycle ergometer until exhaustion (cadence: 65-70 revolutions per minute). For each participant, the intensity of the fatiguing exercise was set to 110% of the power achieved at their anaerobic threshold, previously identified by means of a cardiopulmonary exercise test. Joint angles and moments, as well as ground reaction forces (GRF) before and after the fatiguing exercise were compared for both the dominant and the non-dominant leg. Following the fatiguing exercise, the hip joint was more extended (landing: Δ=-2.17°, p = 0.005; propulsion: Δ=-1.83°, p = 0.032) and more abducted (landing: Δ=-0.72°, p = 0.01; propulsion: Δ=-1.12°, p = 0.009). Similarly, the knee joint was more extended at landing (non-dominant leg: Δ=-2.67°, p < 0.001; dominant: Δ=-1.4°, p = 0.023), and more abducted at propulsion (both legs: Δ=-0.99°, p < 0.001) and stabilization (both legs: Δ=-1.71°, p < 0.001) hence increasing knee valgus. Fatigue also caused a significant reduction of vertical GRF upon landing (Δ=-0.21 N/kg, p = 0.003), but not during propulsion. Fatigue did not affect joint moments significantly. The increased hip and knee extension, as well as the increased knee abduction we observed after the execution of the fatiguing exercise have been previously identified as risk factors for ACL injury. These results therefore suggest an increased risk of ACL injury after the execution of the participant-tailored fatiguing protocol proposed here. However, the reduced vertical GRF upon landing and the preservation of joint moments are intriguing, as they may suggest the adoption of protective strategies in the fatigued condition to be evaluated in future studied.