Increasing plantarflexion angle during landing reduces vertical ground reaction forces, loading rates and the hip's contribution to support moment within participants

Establishing Phase Definitions for Jump and Drop Landings and an Exploratory Assessment of Performance-Related Metrics to Monitor During Testing

ABSTRACT

Harry, JR, Simms, A, and Hite, M. Establishing phase definitions for jump and drop landings and an exploratory assessment of performance-related metrics to monitor during testing. J Strength Cond Res 38(2): e62-e71, 2024-Landing is a common task performed in research, physical training, and competitive sporting scenarios. However, few have attempted to explore landing mechanics beyond its hypothesized link to injury potential, which ignores the key performance qualities that contribute to performance, or how quickly a landing can be completed. This is because a lack of (a) established landing phases from which important performance and injury risk metrics can be extracted and (b) metrics known to have a correlation with performance. As such, this article had 2 purposes. The first purpose was to use force platform data to identify easily extractable and understandable landing phases that contain metrics linked to both task performance and overuse injury potential. The second purpose was to explore performance-related metrics to monitor during testing. Both purposes were pursued using force platform data for the landing portion of 270 jump-landing trials performed by a sample of 14 NCAA Division 1 men's basketball players (1.98 ± 0.07 m; 94.73 ± 8.01 kg). The proposed phases can separate both jump-landing and drop-landing tasks into loading, attenuation, and control phases that consider the way vertical ground reaction force (GRF) is purposefully manipulated by the athlete, which current phase definitions fail to consider. For the second purpose, Pearson's correlation coefficients, the corresponding statistical probabilities ( α = 0.05), and a standardized strength interpretation scale for correlation coefficients (0 < trivial ≤ 0.1 < small ≤ 0.3 < moderate ≤ 0.5 < large ≤ 0.7 < very large) were used for both the group average (i.e., all individual averages pooled together) and individual data (i.e., each individual's trials pooled together). Results revealed that landing time, attenuation phase time, average vertical GRF during landing, average vertical GRF during the attenuation phase, average vertical GRF during the control phase, vertical GRF attenuation rate, and the amortization GRF (i.e., GRF at zero velocity) significantly correlated with landing performance, defined as the ratio of landing height and landing time ( R ≥ ± 0.58; p < 0.05), such that favorable changes in those metrics were associated with better performance. This work provides practitioners with 2 abilities. First, practitioners currently assess jump capacity using jump-landing tests (e.g., countermovement jump) with an analysis strategy that makes use of landing data. Second, this work provides preliminary data to guide others when initially exploring landing test results before identifying metrics chosen for their own analysis.

Effects of Kinesio taping on lower limb biomechanical characteristics during unexpected jumping in patients with chronic ankle instability

PURPOSE

The current biomechanical research on the application of Kinesio taping (KT) to patients with chronic ankle instability (CAI) has focused on testing the expected movements. However, unexpected movements are more common in actual sports. Therefore, the present study aimed to investigate the effects of KT on the biomechanical characteristics of the knee and ankle joints during unexpected jumping movements.

METHODS

Twenty-one patients with unilateral CAI were recruited to capture the biomechanical parameters during unexpected jumping movements under different interventions: no taping (NT), placebo taping (PT), and KT. A one-way repeated measures analysis of variance was used to compare the differences in knee and ankle biomechanical characteristics among patients with CAI between the three intervention conditions.

RESULTS

At initial contact, the KT group demonstrated a significant decrease in ankle plantarflexion and knee flexion angles compared to the NT group (p < 0.05). At the early landing phase, the KT group had a significant increase in peak ankle dorsiflexion angle, peak ankle eversion angle, peak ankle dorsiflexion moment, and peak ankle eversion moment compared to the NT and PT groups (p < 0.05). Furthermore, the KT group had a significantly reduced peak knee flexion angle, peak knee eversion angle, and peak vertical ground reaction force (p < 0.05) compared to the NT and PT groups.

CONCLUSION

KT significantly improves the sprain-prone touchdown posture of patients with CAI. And reducing the risk of ankle sprains during the early landing phase by promoting ankle dorsiflexion and eversion angles and moments.

Case study: The influence of Achilles tendon rupture on knee joint stress during counter-movement jump - Combining musculoskeletal modeling and finite element analysis

BACKGROUND

Presently, the current research concerning Achilles tendon rupture repair (ATR) is predominantly centered on the ankle joint, with a paucity of evidence regarding its impact on the knee joint. ATR has the potential to significantly impede athletic performance and increase tibiofemoral contact forces in athletes. The purpose of this study was to prognosticate the distribution of stress within the knee joint during a countermovement jump through the use of a simulation method that amalgamated a musculoskeletal model of a patient who underwent Achilles tendon rupture repair with a finite element model of the knee joint.

METHODS

A male elite badminton player who had suffered an acute Achilles tendon rupture in his right leg one year prior was selected as our study subject. In order to analyze his biomechanical data, we employed both the OpenSim musculoskeletal model and finite element model to compute various parameters such as joint angles, joint moments, joint contact forces, and the distribution of knee joint stress.

RESULTS

During the jumping phase, a significantly lower knee extension angle (p < 0.001), ankle dorsiflexion angle (p = 0.002), peak vertical ground reaction force (p < 0.001), and peak tibiofemoral contact force (p = 0.009) were observed on the injured side than on the uninjured side. During the landing phase, the ankle range of motion (ROM) was significantly lower on the injured side than on the uninjured side (p = 0.009), and higher peak vertical ground reaction forces were observed (p = 0.012). Additionally, it is logical that an injured person will put higher load on the uninjured limb, but the finite element analysis indicated that the stresses on the injured side of medial meniscus and medial cartilage were significantly greater than the uninjured side.

CONCLUSIONS

An Achilles tendon rupture can limit ankle range of motion and lead to greater joint stress on the affected area during countermovement jumps, especially during the landing phase. This increased joint stress may also transfer more stress to the soft tissues of the medial knee, thereby increasing the risk of knee injury. It is worth noting that this study only involves the average knee flexion angle and load after ATR in one athlete. Caution should be exercised when applying the conclusions, and in the future, more participants should be recruited to establish personalized knee finite element models to validate the results.

Less impact absorption at the ankle joint is related to the single-leg landing stability deficit in patients with chronic ankle instability

Single-leg landing (SLL) stability deficits are common dysfunctions after lateral ankle sprain (LAS), and are associated with reinjury and needs to be addressed. SLL stability deficits could be associated with impact absorption ability. Thus, we evaluated these relationships. We recruited 46 patients with chronic ankle instability (CAI) and 64 control patients and measured their kinematics, SLL stability, and impact absorption ability. The SLL stability was evaluated by calculating the anterior-posterior stability index (APSI) and medial-lateral stability index (MLSI). The impact absorption ability was evaluated by calculating the energy absorption (EA). The large negative value of the EA indicated the absorption of a large amount of energy. The Japanese version of identification of functional ankle instability (IdFAI-J) score (P < 0.001), MLSI value (P = 0.004), and sagittal plane ankle EA value (less EA at ankle joint) (P < 0.001) were significantly high in CAI, and sagittal plane knee EA value (more EA at knee joint) (P < 0.041) was significantly low in CAI than in the control group. Multiple regression analysis showed that the APSI was associated with sagittal plane ankle EA (β = 0.275, P = 0.004). The MLSI was associated with sagittal plane ankle EA (β = 0.204, P = 0.034) and the idFAI score (β = 0.234, P = 0.015). The SLL stability impairment after LAS was related to decreased impact absorption ability at the ankle joint.

Sex difference in effect of ankle landing biomechanics in sagittal plane on knee valgus moment during single-leg landing

Ankle landing strategies affects the biomechanical characteristics of the knee joint, especially knee frontal plane loading. However, no studies have investigated whether the association between ankle landing biomechanics in sagittal plane and the knee frontal plane loading differs between sexes. The purpose of this study was to examine whether there is a sex difference in the effect of ankle plantar flexion at the contact angle, ankle range of motion (ROM), and ankle plantar flexion moment on knee valgus loading during single-leg landing. Twenty-five females and twenty-four males performed a single-leg landing. Joint kinematics and kinetics of the lower extremities were measured. The relationship between ankle biomechanics in the sagittal plane (ankle plantar flexion angle at contact, ROM, and peak ankle plantar flexion moment) and peak knee valgus moment were analyzed. In males, the larger ankle plantarflexion angle at contact and ROM were significantly associated with lower peak knee valgus moment. In addition, in males only, a greater peak ankle plantar flexion moment was significantly associated with a lower peak knee valgus moment and greater peak ankle inversion moment. Altering ankle landing strategies in the sagittal plane during single-leg landing may reduce the knee valgus moment, which is one of risk factors for anterior cruciate ligament injury, in males only.

Movement Variability and Loading Characteristics in Athletes With Athletic Groin Pain: Changes After Successful Return to Play and Compared With Uninjured Athletes

Background:

Athletic groin pain (AGP) can lead to altered movement patterns during rapid deceleration and acceleration. However, the effect of AGP on movement variability and loading patterns during such actions remains less clear.

Purpose:

To investigate, using a continuous lateral hurdle hop task, how movement variability and magnitude measures of 3-dimensional (3D) kinematic, kinetic, and vertical ground-reaction force (vGRF) variables are (1) affected by AGP (AGP vs uninjured controls [CON]) and (2) changed after successful rehabilitation (AGP prerehabilitation vs AGP postrehabilitation vs CON).

Study Design:

Controlled laboratory study.

Methods:

A total of 36 athletes diagnosed with AGP and 36 uninjured CON athletes matched on age (18-35 years), level (subelite), and type of sports played (multidirectional field sport) performed a continuous lateral hurdle hop test that involved 10 side-to-side hops over a 15-cm hurdle. The 3D joint kinematic, kinetic, and vGRF variables (total, eccentric, and concentric; ground contact time, peak force, and impulse; and eccentric rate of force development) were examined. The AGP and CON groups were tested at baseline, and the AGP group was retested after participants successfully completed a standardized, exercise-based rehabilitation program targeting intersegmental control.

Results:

There were no differences in baseline characteristics between the AGP (mean ± SD: age, 27.5 ± 4.8 years; height, 179.8 ± 6.3 cm; mass, 80.3 ± 7.1 kg) and CON (mean ± SD: age, 24.1 ± 4.5 years; height, 181.0 ± 5.8 cm; mass, 80.4 ± 8.2 kg) groups. At baseline, athletes with AGP demonstrated altered loading patterns in the vGRF (longer ground contact times, reduced peak force, and reduced rate of force development) compared with CON athletes, while no significant difference in any movement variability variables was evident. After rehabilitation, the athletes with AGP demonstrated significant changes in transverse and coronal plane hip and trunk kinematics, with no significant differences in vGRF variables compared with the CON group.

Conclusion:

The differences in baseline vGRF measures between the AGP and CON groups were no longer evident after athletes with AGP underwent rehabilitation. No differences in movement variability were evident between the AGP and CON groups, either before or after rehabilitation.

Clinical Relevance:

Rehabilitation programs should consider targeting intersegmental hip and trunk movement patterns to positively influence loading patterns in athletes with AGP.

Association of Ankle Dorsiflexion and Landing Forces in Jumping Athletes

BACKGROUND

Dorsiflexion range of motion restriction has been associated with patellar tendinopathy, but the mechanisms of how dorsiflexion restriction could contribute to knee overload remain unknown.

HYPOTHESIS

Peak ankle dorsiflexion and ankle dorsiflexion excursion are negatively associated with peak vertical ground-reaction force (vGRF) and loading rate, and with peak patellar tendon force and loading rate, and positively associated with peak ankle plantar flexor moment.

STUDY DESIGN

Cross-sectional study.

LEVEL OF EVIDENCE

Level 4.

METHODS

Kinematic and kinetic data of 26 healthy recreational jumping athletes were measured during a single-leg drop vertical jump. Pearson's correlation coefficients were calculated to establish the association between peak ankle dorsiflexion and ankle dorsiflexion excursion with peak vGRF and vGRF loading rate, with peak patellar tendon force and patellar tendon force loading rate, and with peak ankle plantar flexor moment.

RESULTS

Ankle dorsiflexion excursion negatively correlated with peak vGRF loading rate (r = -0.49; P = 0.011) and positively correlated with peak ankle flexor plantar moment (r = 0.52; P = 0.006). In addition, there was a positive correlation between peak ankle dorsiflexion and peak vGRF (r = 0.39; P = 0.05).

CONCLUSION

Ankle kinematics are associated with vGRF loading rate, ankle flexor plantar moment and peak vGRF influencing knee loads, but no association was observed between ankle kinematics and patellar tendon loads.

CLINICAL RELEVANCE

These results suggest that increasing ankle dorsiflexion excursion may be an important strategy to reduce lower limb loads during landings but should not be viewed as the main factor for reducing patellar tendon force.

Biomechanical characterization of the foot-ground interaction among Service members with unilateral transtibial limb loss performing unconstrained drop-landings: Effects of drop height and added mass

There exist limited data to guide the development of methodologies for evaluating impact resilience of prosthetic ankle-foot systems, particularly regarding human-device interaction in ecologically valid scenarios. The purpose of this study was to biomechanically characterize foot-ground interactions during drop-landings among Service members with and without unilateral transtibial limb loss. Seven males with, and seven males without, unilateral transtibial limb loss completed six drop-landing conditions consisting of all combinations of three heights (20 cm, 40 cm, 60 cm) and two loads (with and without a 22.2 kg weighted vest). Peak ground reaction forces (GRF), vertical GRF loading rate and impulse, as well as ankle-foot, knee, and hip joint negative (absorption) powers and work were compared across groups (i.e., contralateral side and prosthetic side vs. uninjured controls) by height and load conditions. Loading occurred primarily in the vertical direction, and increased with increasing drop height and/or with added load. Vertical GRFs were overall ~ 15% smaller on the prosthetic side (vs. controls) with similar loading rates across limbs/groups. From the most challenging condition (i.e., 60 cm with 22 kg load), ankle-foot absorption energies on the prosthetic side were 64.6 (7.2) J; corresponding values were 187.4 (8.9) J for the contralateral limb and 161.2 (6.7) J among uninjured controls. Better understanding biomechanical responses to drop-landings in ecological scenarios will help inform future iterations of mechanical testing methodologies for evaluating impact resilience of prosthetic ankle-foot systems (enhancing prescription criteria and return-to-activity considerations) as well as identifying and mitigating risk factors for long-term secondary complications within the contralateral limb (e.g., joint degeneration).

Estimation of vertical ground reaction force parameters during athletic tasks using 2D video

BACKGROUND

Given that elevated vertical ground reaction forces (vGRF) have been reported to contribute to various lower-extremity injuries, there is a need for a practical method to characterize movement behavior that is representative of elevated impact forces.

RESEARCH QUESTION

Can images obtained from 2D video be used to predict vGRF parameters during athletic tasks? Specifically, we sought to determine whether the 2D thigh angle obtained at peak knee flexion could be used to predict the peak vGRF and vGRF impulse during single limb and double limb landings and movements that involve a change of direction.

METHODS

2D sagittal plane video and vGRFs were obtained simultaneously from 39 participants (15 males and 24 females) during 5 athletic tasks (drop jump, lateral shuffle, deceleration, triple hop, side-step-cut). Linear regression analysis was performed to determine if the 2D thigh angle at peak knee flexion predicted the first peak of the vGRF and vGRF impulse during the deceleration phase of each task.

RESULTS

The 2D thigh angle predicted the peak vGRF for all tasks except cutting (R² = 0.17 to 0.47, all p < 0.01). However, the 2D thigh angle predicted the vGRF impulse for all 5 tasks (R² = 0.13 to 0.39, all p < 0.025).

SIGNIFICANCE

An increased 2D thigh angle (which is representative of increased hip and knee flexion) was able to predict lower peak vGRFs and vGRF impulse during athletic tasks. The 2D thigh angle is a potential clinical method to characterize movement behavior that may expose individuals to high impact forces.

The Influence of Kinesio Tape and an Ankle Brace on the Lower Extremity Joint Motion in Fatigued, Unstable Ankles during a Lateral Drop Landing

BACKGROUND

An unstable ankle along with plantar flexor muscle fatigue may exacerbate landing performance. External support may be an option to control the ankle motion and protect joints from injuries. Research goal: To investigate the immediate changes in the joint motion of a lower extremity under ankle plantar flexors fatigue conditions in athletes with unstable ankles using different external supports.

METHODS

A total of 44 participants were allocated to a control (Cn) group, an ankle brace (AB) group, and a kinesio tape (KT) group, and were asked to perform a lateral drop landing before and after a fatigue protocol. The outcome measures were fatigue-induced changes in the maximal joint angle and changes in the angle ranges of the hip, knee, and ankle.

RESULTS

Smaller changes in the maximal hip abduction were found in the AB group (p = 0.025), and the KT group exhibited smaller changes in the maximal ankle dorsiflexion (p = 0.009). The AB group landed with a smaller change in the range of hip flexion and knee flexion (p = 0.008 and 0.006). The Cn group had greater fatigue-induced changes in the COM range than AB and KT group (p = 0.002 and 0.028).

SIGNIFICANCE

Despite the beneficial effect in the postural control in the frontal plane, the use of AB might constrain the distal joint motion which might lead to an extended knee landing posture resulting in secondary injuries to the knee joint. Therefore, the use of AB in conjunction with an additional training of landing strategy might be recommended from the injury prevention perspective.

Restrictions in Ankle Dorsiflexion Range of Motion Alter Landing Kinematics But Not Movement Strategy When Fatigued

CONTEXT

Ankle dorsiflexion range of motion (DF ROM) has been associated with a number of kinematic and kinetic variables associated with landing performance that increase injury risk. However, whether exercise-induced fatigue exacerbates compensatory strategies has not yet been established.

OBJECTIVES

(1) Explore differences in landing performance between individuals with restricted and normal ankle DF ROM and (2) identify the effect of fatigue on compensations in landing strategies for individuals with restricted and normal ankle DF ROM.

DESIGN

Cross-sectional.

SETTING

University research laboratory.

PATIENTS OR OTHER PARTICIPANTS

Twelve recreational athletes with restricted ankle DF ROM (restricted group) and 12 recreational athletes with normal ankle DF ROM (normal group).

MAIN OUTCOME MEASURE(S)

The participants performed 5 bilateral drop-landings, before and following a fatiguing protocol. Normalized peak vertical ground reaction force, time to peak vertical ground reaction force, and loading rate were calculated, alongside sagittal plane initial contact angles, peak angles, and joint displacement for the ankle, knee, and hip. Frontal plane projection angles were also calculated.

RESULTS

At the baseline, the restricted group landed with significantly less knee flexion (P = .005, effect size [ES] = 1.27) at initial contact and reduced peak ankle dorsiflexion (P < .001, ES = 1.67), knee flexion (P < .001, ES = 2.18), and hip-flexion (P = .033, ES = 0.93) angles. Sagittal plane joint displacement was also significantly less for the restricted group for the ankle (P < .001, ES = 1.78), knee (P < .001, ES = 1.78), and hip (P = .028, ES = 0.96) joints.

CONCLUSIONS

These findings suggest that individuals with restricted ankle DF ROM should adopt different landing strategies than those with normal ankle DF ROM. This is exacerbated when fatigued, although the functional consequences of fatigue on landing mechanics in individuals with ankle DF ROM restriction are unclear.

Association between ankle angle at initial contact and biomechanical ACL injury risk factors in male during self-selected single-leg landing

BACKGROUND

Increasing the ankle plantar-flexion angle at initial contact (IC) during landing reduces the impact features associated with landing, such as the vertical ground reaction force and loading rate, potentially affecting the risk of anterior cruciate ligament (ACL) injury. However, the relationships between the ankle plantar-flexion angle at IC and the previously identified biomechanical factors related to noncontact ACL injury have not been studied.

RESEARCH QUESTION

Thus, the purpose of this study was to determine whether significant relationships exist between the ankle plantar-flexion angle at IC and the biomechanical factors related to noncontact ACL injury.

METHODS

The peak anterior tibial shear force, peak external knee valgus moment, peak knee valgus angle, and combined peak external knee valgus plus tibial internal rotation moments were measured in 26 individuals while performing self-selected, single-leg landing. Pearson correlation analyses were performed to assess the relationships between the ankle plantar-flexion angle at IC and the biomechanical factors mentioned above.

RESULTS

The greater ankle plantar-flexion angle at IC was related to smaller the peak knee valgus moment (r = -0.5, p = 0.009) and the combined peak knee valgus plus internal rotation moments (r = -0.58, p = 0.001).

SIGNIFICANCE

These results suggest that large ankle plantar-flexion angle at IC might be associated with lesser loading of the knee frontal plane and altering the self-selective ankle angle may result in biomechanical changes associated with ACL injury risk.

Improved Ankle Mobility After a 4-Week Training Program Affects Landing Mechanics: A Randomized Controlled Trial

Howe, LP, Bampouras, TM, North, JS, and Waldron, M. Improved ankle mobility after a 4-week training program affects landing mechanics: a randomized controlled trial. J Strength Cond Res XX(X): 000-000, 2020-This study examined the effects of a 4-week ankle mobility intervention on landing mechanics. Twenty subjects with restricted ankle dorsiflexion range of motion (DF ROM) were allocated to either a strength training only (n = 9) or a strength training and ankle mobility program (n = 11). Subjects performed a weight-bearing lunge test and bilateral drop-landings before and after the intervention. Normalized peak vertical ground reaction force (vGRF), time to peak vGRF, and loading rate were calculated, alongside sagittal-plane initial contact angles, peak angles, and sagittal-plane joint displacement for the ankle, knee, and hip. Frontal-plane projection angles were also calculated. After the intervention, only the strength and mobility group improved ankle DF ROM (mean difference = 4.1°, effect size [ES] = 1.00, p = 0.002). A one-way analysis of covariance found group effects for ankle joint angle at initial contact (p = 0.045), ankle (p < 0.001) and hip joint angle at peak flexion (p = 0.041), and sagittal-plane ankle (p < 0.001) and hip joint displacement (p = 0.024) during bilateral drop-landings. Post hoc analysis revealed that the strength and mobility group landed with greater ankle plantarflexion at initial contact (mean difference = 1.4 ± 2.0°, ES = 0.46) and ankle dorsiflexion at peak flexion (mean difference = 6.3 ± 2.9°, ES = 0.74) after the intervention, resulting in a greater ankle joint displacement (mean difference = 7.7 ± 4.0°, ES = 1.00). However, the strength training only group landed with increased peak hip flexion (mean difference = 14.4 ± 11.0°, ES = 0.70) and hip joint displacement (mean difference = 8.0 ± 6.6°, ES = 0.44) during post-testing. The findings suggest that changes in landing strategies following the performance of a strength training program are specific to whether restrictions in ankle mobility are considered as part of the intervention.

Effects of Different Ankle Supports on the Single-Leg Lateral Drop Landing Following Muscle Fatigue in Athletes with Functional Ankle Instability

Background: Ankle support has been utilized for athletes with functional ankle instability (FAI), however, its effect on the landing performance during muscle fatigue is not well understood. This study aimed to examine the effects of ankle supports (ankle brace vs. Kinesio tape) on athletes with FAI following fatigued single-leg landing. Methods: Thirty-three young FAI athletes (CAIT scores < 24) were randomly allocated to control (Cn), ankle brace (AB) and Kinesio tape (KT) groups. All athletes performed single-leg lateral drop landings following ankle fatigue protocol. The fatigue-induced changes in kinetic parameters were measured among three groups. Results: A significant increase in peak vertical ground reaction force (vGRF) was found in the AB group (0.12% body weight (BW)) compared to that of the KT (0.02% BW) and Cn (median = 0.01% BW) groups. Significant decrease in both COP medial-lateral (ML) and anterior-posterior (AP) ranges were also found in the KT group (median = −0.15% foot width (FW) & median = −0.28% foot length (FL)) than those of the Cn group (median = 0.67% FW& median = 0.88% FL). Conclusions: Ankle braces might hamper the ability to absorb the impact force during landing. On the other hand, Kinesio tape might be beneficial for the postural control during landing.

Mechanisms to Attenuate Load in the Intact Limb of Transtibial Amputees When Performing a Unilateral Drop Landing

Individuals with unilateral transtibial amputations experience greater work demand and loading on the intact limb compared with the prosthetic limb, placing this limb at a greater risk of knee joint degenerative conditions. It is possible that increased loading on the intact side may occur due to strength deficits and joint absorption mechanics. This study investigated the intact limb mechanics utilized to attenuate load, independent of prosthetic limb contributions and requirements for forward progression, which could provide an indication of deficiencies in the intact limb. Amputee and healthy control participants completed 3 unilateral drop landings from a 30-cm drop height. Joint angles at touchdown; range of motion; coupling angles; peak powers; and negative work of the ankle, knee, and hip were extracted together with isometric quadriceps strength measures. No significant differences were found in the load or movement mechanics (P ≥ .31, g ≤ 0.42), despite deficits in isometric maximum (20%) and explosive (25%) strength (P ≤ .13, g ≥ 0.61) in the intact limb. These results demonstrate that, when the influence from the prosthetic limb and task demand are absent, and despite deficits in strength, the intact limb adopts joint mechanics similar to able-bodied controls to attenuate limb loading.

Reliability of two-dimensional measures associated with bilateral drop-landing performance

The aim of this study was to establish the within-session reliability for two-dimensional (2D) video analysis of sagittal- and frontal-plane measures during bilateral drop-landing tasks. Thirty-nine recreational athletes (22 men, 17 women, age = 22 ± 4 years, height = 1.74 ± 0.15 m, body mass 70.2 ± 15.1 kg) performed five bilateral drop-landings from 50, 100 and 150% of maximum countermovement jump height, twice on the same day. Measures of reliability for initial contact angle, peak flexion angle and joint displacement for the hip, knee, and ankle joints, frontal-plane projection angles (FPPA), as well as inter-limb asymmetries in joint displacement were assessed. No systematic bias was present between trials (P>0.05). All kinematic measurements showed relative reliability ranging from large to near perfect (ICC = 0.52–0.96). Absolute reliability ranged between measures, with CV% between 1.0–1.6% for initial contact angles, 1.9–7.9% for peak flexion angles, 5.3–22.4% for joint displacement, and 1.6–2.3% for FPPA. Absolute reliability for inter-limb asymmetries in joint displacement were highly variable, with minimal detectable change values ranging from 6.0–13.2°. Therefore, 2D video analysis is a reliable tool for numerous measures related to the performance of bilateral drop-landings.

Focus of attention effects on lower extremity biomechanics during vertical jump landings

This study examined biomechanical differences between external and internal foci of attention during vertical jump landings in males and females. Twenty-four healthy adults performed eight vertical jump landings using both internal and external foci while three-dimensional kinematic and ground reaction force (GRF) data were obtained. Two (focus) by two (sex) analyses of variance (α = 0.05) and Cohen's d effect sizes (ES) were used to compare differences in vertical GRF, joint angular positions and displacements, and lower limb joint angular work between foci and between sexes. Significantly greater knee contributions to total angular work occurred during external versus internal focus landings regardless of sex (p = .013; ES = 0.30). Significantly smaller plantarflexion angles (p = .019; ES = 0.53) and significantly greater knee flexion angles were observed at ground contact (p < .001; ES = 1.11) in males during external focus landings. Females exhibited significantly smaller knee flexion angles at both ground contact during external versus internal focus landings (p = .031; ES = 0.20) and compared to males during external focus landings (p < .001; ES = 1.76). Both peak vertical GRF (p = .003; ES = 1.54) and the ankle contributions to total angular work during loading (p = .026; ES = 1.07) were greater in females versus males regardless of foci, whereas the knee contributions to total angular work during loading were smaller in women (p = .026; ES = 1.07). Males and females might consider adopting an external focus during vertical jump landings to increase knee joint contributions to lower limb energy absorption. Females, in particular, might consider external focus use to decrease peak vertical GRF and increase the knee joint's contribution to total energy absorption to magnitudes similar to those exhibited by males.

Altered Movement Biomechanics in Chronic Ankle Instability, Coper, and Control Groups: Energy Absorption and Distribution Implications

CONTEXT

Patients with chronic ankle instability (CAI) exhibit deficits in neuromuscular control, resulting in altered movement strategies. However, no researchers have examined neuromuscular adaptations to dynamic movement strategies during multiplanar landing and cutting among patients with CAI, individuals who are ankle-sprain copers, and control participants.

OBJECTIVE

To investigate lower extremity joint power, stiffness, and ground reaction force (GRF) during a jump-landing and cutting task among CAI, coper, and control groups.

DESIGN

Cross-sectional study.

SETTING

Laboratory.

PATIENTS OR OTHER PARTICIPANTS

A total of 22 patients with CAI (age = 22.7 ± 2.0 years, height = 174.6 ± 10.4 cm, mass = 73.4 ± 12.1 kg), 22 ankle-sprain copers (age = 22.1 ± 2.1 years, height = 173.8 ± 8.2 cm, mass = 72.6 ± 12.3 kg), and 22 healthy control participants (age = 22.5 ± 3.3 years, height = 172.4 ± 13.3 cm, mass = 72.6 ± 18.7 kg).

INTERVENTION(S)

Participants performed 5 successful trials of a jump-landing and cutting task.

MAIN OUTCOME MEASURE(S)

Using motion-capture cameras and a force plate, we collected lower extremity ankle-, knee-, and hip-joint power and stiffness and GRFs during the jump-landing and cutting task. Functional analyses of variance were used to evaluate between-groups differences in these dependent variables throughout the contact phase of the task.

RESULTS

Compared with the coper and control groups, the CAI group displayed (1) up to 7% of body weight more posterior and 52% of body weight more vertical GRF during initial landing followed by decreased GRF during the remaining stance and 22% of body weight less medial GRF across most of stance; (2) 8.8 W/kg less eccentric and 3.2 W/kg less concentric ankle power, 6.4 W/kg more eccentric knee and 4.8 W/kg more eccentric hip power during initial landing, and 5.0 W/kg less eccentric knee and 3.9 W/kg less eccentric hip power; and (3) less ankle- and knee-joint stiffness during the landing phase. Concentric power patterns were similar to eccentric power patterns.

CONCLUSIONS

The CAI group demonstrated altered neuromechanics, redistributing energy absorption from the distal (ankle) to the proximal (knee and hip) joints, which coincided with decreased ankle and knee stiffness during landing. Our data suggested that although the coper and control groups showed similar landing and cutting strategies, the CAI group used altered strategies to modulate impact forces during the task.

Ankle dorsiflexion range of motion is associated with kinematic but not kinetic variables related to bilateral drop-landing performance at various drop heights

Limited evidence is available concerning ankle dorsiflexion range of motion (DF ROM) and its relationship with landing performance from varying drop heights. The aim of this investigation was to determine the relationship between ankle DF ROM and both kinetic and kinematic variables measured during bilateral drop-landings from 50%, 100% and 150% of countermovement jump height. Thirty-nine participants were measured for their ankle DF ROM using the weight-bearing lunge test, after which five bilateral drop-landings were performed from 50%, 100% and 150% of maximal countermovement jump height. Normalized peak vertical ground reaction force (vGRF), time to peak vGRF and loading rate was calculated for analysis, alongside sagittal-plane initial contact angles, peak angles and joint displacement for the hip, knee and ankle. Frontal-plane projection angles were also calculated. Ankle DF ROM was not related to normalized peak vGRF, time to peak vGRF or loading rate (P > 0.05), regardless of the drop height. However, at drop heights of 100% and 150% of countermovement jump height, there were numerous significant (P < 0.05) moderate to large correlations between ankle DF ROM and initial contact angles (r = -0.34 to -0.40) and peak angles (r = -0.42 to -0.52) for the knee and ankle joint. Knee joint displacement (r = 0.39-0.47) and frontal-plane projection angle (r = 0.37-0.40) had a positive relationship with ankle DF ROM, which was consistent across all drop heights. Ankle DF ROM influences coordination strategies that allow for the management of vGRF during bilateral drop-landings, with alterations in alignment for the knee and ankle joints at both initial contact and peak angles.

Evaluating Performance During Maximum Effort Vertical Jump Landings

The ability to rapidly complete a jump landing has received little attention in the literature despite the need for rapid performance in a number of sports. As such, our purpose was to investigate differences between groups of individuals who land quickly (FAST) and slowly (SLOW) relative to peak vertical ground reaction forces (vGRFs), loading rates, rates of vGRF attenuation, contributions to lower extremity mechanical energy absorption at the involved joints, and the onsets of preparatory joint flexion/dorsiflexion. Twenty-four healthy adults (26.1 [3.3] y, 75.7 [18.9] kg, 1.7 [0.1] m) were stratified into FAST and SLOW groups based on landing time across 8 jump-landing trials. Independent t tests (α = .05) and effect sizes (ESs; large ≥ 0.8) compared differences between groups. A greater rate of vGRF attenuation (P = .02; ES = 0.95) was detected in the FAST group. The FAST group also exhibited greater contributions to lower extremity energy absorption at the ankle (P = .03; ES = 0.98) and knee (P = .03; ES = 0.99) during loading and attenuation, respectively. The SLOW group exhibited greater contributions to energy absorption at the hip during loading (P = .02; ES = 1.10). Results suggest that individuals who land quickly utilize different energy absorption strategies than individuals who land slowly. Ultimately, the FAST group’s strategy resulted in superior landing performance (more rapid landing time).

Performance Differences Among Skilled Soccer Players of Different Playing Positions During Vertical Jumping and Landing

Harry, JR, Barker, LA, James, CR, and Dufek, JS. Performance differences among skilled soccer players of different playing positions during vertical jumping and landing. J Strength Cond Res 32(2): 304-312, 2018-Both jumping and landing performance of skilled soccer players is diminished when task demands are increased. However, it is unclear if performance changes are specific to players of certain playing positions. Therefore, we assessed jumping and landing performance among skilled soccer players of different playing positions. Twenty-five National Collegiate Athletic Association (NCAA) Division 1 male soccer players (179.5 ± 7.8 cm, 75.5 ± 7.1 kg, 19.7 ± 1.2 years) performed maximum effort vertical jump landings (VJLs), whereas vertical ground reaction force (vGRF) data were obtained. Participants were stratified into goalkeeping (GK), defensive (DEF), midfield (MID), and attacking (ATT) group according to their primary playing position. One-way analyses of variance (α = 0.05) and effect sizes (ESs; large ≥ 0.80) were used to compare differences among groups. The jumping phase variables evaluated were jump height, unloading and amortization vGRF magnitudes, eccentric rate of force development, and the reactive strength index. Landing phase variables included the peak vGRF magnitude, vGRF loading rate, vGRF attenuation rate, and landing time. No statistically significant differences were detected for any jumping or landing variable (p ≥ 0.05). However, a number of large magnitude differences were detected during landing after ES calculations. Specifically, greater peak vGRF magnitudes were detected in DEF vs. both MID (ES = 1.08) and ATT (ES = 0.93), a greater vGRF loading rate occurred in DEF vs. MID (ES = 0.93), and a greater vGRF attenuation rate occurred in DEF vs. both MID (ES = 1.00) and AT (ES = 0.80). It is concluded that highly skilled soccer players possess position-specific abilities with respect to the landing phase of VJL. Skilled soccer players might experience enhanced training outcomes after VJL training regimens tailored to the specific demands of their primary playing position.