Effect of Shoe and Surface Stiffness on Lower Limb Tendon Strain in Jumping

Differences in Player Performance and Longevity After Achilles Tendon Rupture Between Professional Basketball Players in the NBA and WNBA

Background

Prior studies in the National Basketball Association (NBA) and Women's National Basketball Association (WNBA) reported worse player performance after Achilles tendon rupture (ATR).

Purpose/Hypothesis

The purpose of this study was to compare time to return to play (RTP) and performance after ATR between NBA and WNBA athletes. It was hypothesized that there would be no relative difference between the NBA and WNBA players.

Study Design

Cohort study; Level of evidence, 3.

Methods

ATRs in the NBA between 1987 and 2017 and WNBA between 2006 and 2017 were identified through a rigorous online search of articles. Included athletes had no prior leg injuries and had played ≥3 seasons before and after ATR. Sex, age, position, body mass index, height, years of experience, time to RTP, and player efficiency rating (PER) were recorded. Relative performance was measured by matching injured athletes to uninjured controls in the same league in a 1:2 ratio. Relative differences were compared between leagues, with adjustment for baseline features. Multiple regression analysis was employed to identify variables correlating with RTP and PER.

Results

Included were 102 professional basketball players, of whom 34 sustained ATR (21 male, 13 female). Sex/league correlated with differences in RTP (P < .001). There was a significant difference between the WNBA and NBA in PER when comparing 1 year pre- and 1 year postinjury (1.49 ± 0.25 vs 3.87 ± 0.43, respectively; mean ± SD P < .001). Compared with intraleague controls, the relative difference in PER postinjury was 0.81 ± 0.11 (WNBA) and 3.9 ± 0.89 (NBA) (P < .001). Multiple regression analysis indicated that when controlling for years of experience, player position, and age, NBA players took 126 days longer than WNBA players to RTP (P < .001) and NBA players had 9.96 times increased odds of taking >200 days to RTP compared with WNBA players (P = .006).

Conclusion

Sex/league was a significant predictor of RTP after ATR. When compared with their respective controls, NBA players saw a greater decrease in postinjury performance than WNBA players. NBA players took longer to RTP than WNBA players. ATRs appear to more negatively affect NBA players than WNBA players.

Advanced MRI Approaches for Evaluating Common Lower Extremity Injuries in Basketball Players: Current and Emerging Techniques

Magnetic resonance imaging (MRI) can provide accurate and non-invasive diagnoses of lower extremity injuries in athletes. Sport-related injuries commonly occur in and around the knee and can affect the articular cartilage, patellar tendon, hamstring muscles, and bone. Sports medicine physicians utilize MRI to evaluate and diagnose injury, track recovery, estimate return to sport timelines, and assess the risk of recurrent injury. This article reviews the current literature and describes novel developments of quantitative MRI tools that can further advance our understanding of sports injury diagnosis, prevention, and treatment while minimizing injury risk and rehabilitation time. Innovative approaches for enhancing the early diagnosis and treatment of musculoskeletal injuries in basketball players span a spectrum of techniques. These encompass the utilization of T2, T1ρ, and T2* quantitative MRI, along with dGEMRIC and Na-MRI to assess articular cartilage injuries, 3D-Ultrashort echo time MRI for patellar tendon injuries, diffusion tensor imaging for acute myotendinous injuries, and sagittal short tau inversion recovery and axial long-axis T1-weighted, and 3D Cube sequences for bone stress imaging. Future studies should further refine and validate these MR-based quantitative techniques while exploring the lifelong cumulative impact of basketball on players' knees. LEVEL OF EVIDENCE: 5 TECHNICAL EFFICACY: Stage 2.

Hip and knee kinematics, center of pressure position, and ground reaction force are associated with Achilles tendon force during jump landing

PURPOSE

Jump-landing exercises are often performed during the rehabilitation of Achilles tendon (AT) injuries. However, the factors that affect the AT force (ATF) during landing are unclear. This study aimed to determine the kinematics and ground reaction force (GRF) variables associated with the peak ATF during a drop vertical jump (DVJ).

METHODS

The landing phase of DVJ was evaluated in 101 healthy participants (46 males, age: 21.2 ± 1.4 years old) using a three-dimensional motion analysis system with two force plates. ATF was estimated from the ankle flexion angle and moment. Univariate and multivariate regression analyses were performed with the peak ATF as the dependent variable. The vertical GRF (VGRF), center of pressure (COP), forward trunk leaning, hip/knee/ankle joint angles at peak ATF, and sex were used as independent variables.

RESULTS

In the univariate regression analysis, larger VGRF (β = 0.813), more anterior COP position (β = 0.214), smaller knee flexion (β = -0.251) and adduction (β = -0.252), smaller hip flexion (β = -0.407), smaller forward trunk lean (β = -0.492), and male sex (β = -0.282) were significantly associated with a larger peak ATF. Multivariate analysis revealed that larger VGRF (β = 1.018), more anterior COP position (β = 0.320), a larger knee (β = 0.442), and smaller hip flexion (β = -0.205) were associated with the larger peak ATF.

CONCLUSIONS

The VGRF, COP position, and knee and hip flexion were independently associated with ATF. Modifying these factors may be useful in managing tendon loading during jump-landing exercises.

In Vivo Strain Patterns in the Achilles Tendon During Dynamic Activities: A Comprehensive Survey of the Literature

Achilles' tendon (AT) injuries such as ruptures and tendinopathies have experienced a dramatic rise in the mid- to older-aged population. Given that the AT plays a key role at all stages of locomotion, unsuccessful rehabilitation after injury often leads to long-term, deleterious health consequences. Understanding healthy in vivo strains as well as the complex muscle-tendon unit interactions will improve access to the underlying aetiology of injuries and how their functionality can be effectively restored post-injury. The goals of this survey of the literature with a systematic search were to provide a benchmark of healthy AT strains measured in vivo during functional activities and identify the sources of variability observed in the results. Two databases were searched, and all articles that provided measured in vivo peak strains or the change in strain with respect to time were included. In total, 107 articles that reported subjects over the age of 18 years with no prior AT injury and measured while performing functional activities such as voluntary contractions, walking, running, jumping, or jump landing were included in this review. In general, unclear anatomical definitions of the sub-tendon and aponeurosis structures have led to considerable confusion in the literature. MRI, ultrasound, and motion capture were the predominant approaches, sometimes coupled with modelling. The measured peak strains increased from 4% to over 10% from contractions, to walking, running, and jumping, in that order. Importantly, measured AT strains were heavily dependent on measurement location, measurement method, measurement protocol, individual AT geometry, and mechanical properties, as well as instantaneous kinematics and kinetics of the studied activity. Through a comprehensive review of approaches and results, this survey of the literature therefore converges to a united terminology of the structures and their common underlying characteristics and presents the state-of-knowledge on their functional strain patterns.

Are subject-specific models necessary to predict patellar tendon fatigue life? A finite element modelling study

Patellar tendinopathy is an overuse injury that occurs from repetitive loading of the patellar tendon in a scenario resembling that of mechanical fatigue. As such, fatigue-life estimates provide a quantifiable approach to assess tendinopathy risk and may be tabulated using nominal strain (NS) or finite element (FE) models with varied subject-specificity. We compared patellar tendon fatigue-life estimates from NS and FE models of twenty-nine athletes performing countermovement jumps with subject-specific versus generic geometry and material properties. Subject-specific patellar tendon material properties and geometry were obtained using a data collection protocol of dynamometry, ultrasound, and magnetic resonance imaging. Three FE models were created for each subject, with: subject-specific (hyperelastic) material properties and geometry, subject-specific material properties and generic geometry, and generic material properties and subject-specific geometry. Four NS models were created for each subject, with: subject-specific (linear elastic) material properties and moment arm, generic material properties and subject-specific moment arm, subject-specific material properties and generic moment arm, and generic material properties and moment arm. NS- and FE-modelled fatigue-life estimates with generic material properties were poorly correlated with their subject-specific counterparts (r²≤0.073), while all NS models overestimated fatigue life compared to the subject-specific FE model (r²≤0.223). Furthermore, FE models with generic tendon geometry were unable to accurately represent the heterogeneous strain distributions found in the subject-specific FE models or those with generic material properties. These findings illustrate the importance of incorporating subject-specific material properties and FE-modelled strain distributions into fatigue-life estimations.

Effects of cyclic loading on the mechanical properties and failure of human patellar tendon

Patellar tendinopathy is a common overuse injury in sports such as volleyball, basketball, and long-distance running. Microdamage accumulation, in response to repetitive loading of the tendon, plays an important role in the pathophysiology of patellar tendinopathy. This damage presents mechanically as a reduction in Young's modulus and an increase in residual strain. In this study, 19 human patellar tendon samples underwent cyclic testing in load control until failure, segmented by four ramped tests where digital image correlation (DIC) was used to assess anterior surface strain distributions. Ramped tests were performed prior to cyclic testing and at timepoints corresponding to 10%, 20%, and 30% of cyclic stiffness reduction. Young's modulus significantly decreased and cyclic energy dissipation significantly increased over the course of cyclic testing. The DIC analysis illustrated a heterogeneous strain distribution, with strain concentrations increasing in magnitude and size over the course of cyclic testing. Peak stress and initial peak strain magnitudes significantly correlated with the number of cycles to failure (r² = 0.65 and r² = 0.57, respectively, p < 0.001); however, the rates of peak cyclic strain and modulus loss displayed the highest correlations with the number of cycles to failure (r² = 96% and r² = 86%, respectively, p < 0.001). The high correlation between the rates of peak cyclic strain and modulus loss suggest that non-invasive methods to continuously monitor tendon strain may provide meaningful predictions of overuse injury in the patellar tendon.

Increasing the midsole bending stiffness of shoes alters gastrocnemius medialis muscle function during running

In recent years, increasing the midsole bending stiffness (MBS) of running shoes by embedding carbon fibre plates in the midsole resulted in many world records set during long-distance running competitions. Although several theories were introduced to unravel the mechanisms behind these performance benefits, no definitive explanation was provided so far. This study aimed to investigate how the function of the gastrocnemius medialis (GM) muscle and Achilles tendon is altered when running in shoes with increased MBS. Here, we provide the first direct evidence that the amount and velocity of GM muscle fascicle shortening is reduced when running with increased MBS. Compared to control, running in the stiffest condition at 90% of speed at lactate threshold resulted in less muscle fascicle shortening (p = 0.006, d = 0.87), slower average shortening velocity (p = 0.002, d = 0.93) and greater estimated Achilles tendon energy return (p ≤ 0.001, d = 0.96), without a significant change in GM fascicle work (p = 0.335, d = 0.40) or GM energy cost (p = 0.569, d = 0.30). The findings of this study suggest that running in stiff shoes allows the ankle plantarflexor muscle-tendon unit to continue to operate on a more favourable position of the muscle's force-length-velocity relationship by lowering muscle shortening velocity and increasing tendon energy return.

EFFECTS OF SURFACE ON TRIPLE HOP DISTANCE AND KINEMATICS

Background

The single leg triple hop (SLTH) test is often utilized by rehabilitation practitioners as a functional performance measure in a variety of patient groups. Accuracy and consistency are important when measuring the patient progress and recovery. Administering the SLTH test on different surfaces, consistent with the patient's sport, may affect the hop distances and movement biomechanics.

Purpose

The purpose of this study was to examine the effects of court and turf surfaces on the hop distance, limb symmetry index (LSI), and lower extremity kinematics of a SLTH test.

Methods

Recreationally active female participants (n=11, height 163.8 ± 7.1cm, mass 63.1 ± 7.1kg, age 18.9 ± 0.9yrs), without injury, volunteered to participate in the study. Three maximal effort SLTH test trials on two different surfaces (court, synthetic turf) were collected and analyzed using 3D motion analysis techniques. Outcome variables included SLTH test distances and LSI values and sagittal plane kinematics including trunk, hip, knee and ankle range of motion (ROM) during the last two landings of each SLTH test trial. The second landing involves an absorption phase and propulsion phase in contrast to the final landing which involves absorption and final balance on the single leg. Paired t-tests were used to determine differences between surfaces in hop distance and LSI values. Two-way repeated measures ANOVA were used to determine differences between surfaces in kinematic variables.

Results

The total SLTH test distance was not statistically different between the court (4.11 ± 0.47m) and turf (4.03 ± 0.42m, p=0.47) surfaces. LSI for the court surface was 100.8 ± 3.0% compared to 99.7 ± 3.0% for turf surface, which was not statistically different (p=0.30). Knee flexion ROM was significantly less (p=0.04) on the turf compared to the court surface during the second landing. Ankle flexion range of motion was also significantly less (p=0.03) during the second landing on turf compared to court.

Conclusions

Type of surface influenced landing kinematics but not total SLTH test distance. When evaluating the quality of landings during a SLTH test, it may be warranted to observe each type of landing and the type of surface used during single leg tests.

Level of Evidence

2.

Influence of Artificial Turf Surface Stiffness on Athlete Performance

Properties of conventional playing surfaces have been investigated for many years and the stiffness of the surface has potential to influence athletic performance. However, despite the proliferation of different infilled artificial turfs with varying properties, the effect of surface stiffness of these types of surfaces on athlete performance remains unknown. Therefore, the purpose of this project was to determine the influence of surface stiffness of artificial turf systems on athlete performance. Seventeen male athletes performed four movements (running, 5-10-5 agility, vertical jumping and sprinting) on five surfaces of varying stiffness: Softest (-50%), Softer (-34%), Soft (-16%), Control, Stiff (+17%). Performance metrics (running economy, jump height, sprint/agility time) and kinematic data were recorded during each movement and participants performed a subjective evaluation of the surface. When compared to the Control surface, performance was significantly improved during running (Softer, Soft), the agility drill (Softest) and vertical jumping (Soft). Subjectively, participants could not discern between any of the softer surfaces in terms of surface cushioning, however, the stiffer surface was rated as harder and less comfortable. Overall, changes in surface stiffness altered athletic performance and, to a lesser extent, subjective assessments of performance, with changes in performance being surface and movement specific.

Effects of Surface Properties on Gastrocnemius Medialis and Vastus Lateralis Fascicle Mechanics During Maximal Countermovement Jumping

Interactions between human movement and surfaces have previously been studied to understand the influence of surface properties on the mechanics and energetics of jumping. However, little is known about the muscle-tendon unit (MTU) mechanics associated with muscle activity and leg adjustments induced by different surfaces during this movement. This study aimed to examine the effects of three surfaces with different properties (artificial turf, hybrid turf, and athletic track) on the muscle mechanics and muscle excitation of the gastrocnemius medialis (GM) and vastus lateralis (VL) during maximal countermovement jumping (CMJ). Twelve participants performed maximal CMJs on the three sport surfaces. GM and VL muscle fascicles were simultaneously imaged using two ultrafast ultrasound systems (500 Hz). MTUs lengths were determined based on anthropometric models and two-dimensional joint kinematics. Surface electromyography (EMG) was used to record GM and VL muscle activity. Surface mechanical testing revealed systematic differences in surface mechanical properties (P = 0.006, η²: 0.26–0.32, large). Specifically, the highest force reduction and vertical deformation values have been observed on artificial turf (65 ± 2% and 9.0 ± 0.3 mm, respectively), while athletic track exhibited the lowest force reduction and vertical deformation values (28 ± 1% and 2.1 ± 0.1 mm, respectively) and the highest energy restitution (65 ± 1%). We observed no significant difference in CMJ performance between the three surfaces (∼35–36 cm, P = 0.66). GM and VL fascicle shortening (P = 0.90 and P = 0.94, respectively) and shortening velocity (P = 0.13 and P = 0.65, respectively) were also unaffected by the type of surface. However, when jumping from greater deformable surface, both GM muscle activity (P = 0.022, η² = 0.18, large) and peak shortening velocity of GM MTU (P = 0.042, η² = 0.10, medium) increased during the push-off phase. This resulted in a greater peak plantar flexion velocity late in the jump (P = 0.027, η² = 0.13, medium). Our findings suggest that maximal vertical jumping tasks in humans is not affected by common sport surfaces with different mechanical properties. However, internal regulatory mechanisms exist to compensate for differences in surface properties.

The Effects of Increased Midsole Bending Stiffness of Sport Shoes on Muscle-Tendon Unit Shortening and Shortening Velocity: a Randomised Crossover Trial in Recreational Male Runners

BACKGROUND

Individual compliances of the foot-shoe interface have been suggested to store and release elastic strain energy via ligamentous and tendinous structures or by increased midsole bending stiffness (MBS), compression stiffness, and resilience of running shoes. It is unknown, however, how these compliances interact with each other when the MBS of a running shoe is increased. The purpose of this study was to investigate how structures of the foot-shoe interface are influenced during running by changes to the MBS of sport shoes.

METHODS

A randomised crossover trial was performed, where 13 male, recreational runners ran on an instrumented treadmill at 3.5 m·s-1 while motion capture was used to estimate foot arch, plantar muscle-tendon unit (pMTU), and shank muscle-tendon unit (sMTU) behaviour in two conditions: (1) control shoe and (2) the same shoe with carbon fibre plates inserted to increase the MBS.

RESULTS

Running in a shoe with increased MBS resulted in less deformation of the arch (mean ± SD; stiff, 7.26 ± 1.78°; control, 8.84 ± 2.87°; p ≤ 0.05), reduced pMTU shortening (stiff, 4.39 ± 1.59 mm; control, 6.46 ± 1.42 mm; p ≤ 0.01), and lower shortening velocities of the pMTU (stiff, - 0.21 ± 0.03 m·s-1; control, - 0.30 ± 0.05 m·s-1; p ≤ 0.01) and sMTU (stiff, - 0.35 ± 0.08 m·s-1; control, - 0.45 ± 0.11 m·s-1; p ≤ 0.001) compared to a control condition. The positive and net work performed at the arch and pMTU, and the net work at the sMTU were significantly lower in the stiff compared to the control condition.

CONCLUSION

The findings of this study showed that if a compliance of the foot-shoe interface is altered during running (e.g. by increasing the MBS of a shoe), the mechanics of other structures change as well. This could potentially affect long-distance running performance.