Compensatory adjustments in lower extremity kinematics in response to a reduced cushioning of the impact interface in heel–toe running

Comparison of muscle activity of the lower limbs while running on different treadmill models

Treadmill running is a common method of exercise and to study human locomotion. Research has examined the kinematics and kinetics of overground and treadmill running, but there has been less focus on the levels of muscle activity during treadmill running. We investigated if muscle activity is different while running overground compared to running on a variety of treadmills. A total of 11 healthy individuals ran at 3 speeds (2.6, 3.6, 4.5 m/s) under 4 different running conditions (3 treadmills, overground). The three treadmills included a typical home exercise treadmill, a midsize commercial research treadmill, and a large, instrumented research treadmill. Surface EMG of the tibialis anterior (TA), gastrocnemius medialis (GM), rectus femoris (RF) and biceps femoris (BF) muscles were measured for each running condition. The integrated EMG was computed for each running condition for the stance and swing phase, as well as 100 ms before and after the heel-strike. Friedman analysis revealed significant effects during the stance phase for GM and RF at all speeds, such that muscle activation was lower on the treadmills relative to overground. During the stance phase at faster speeds, the muscle activity was higher for the TA and lower for the BF while running on the different treadmills compared to overground running. Before heel-strike, the TA was significantly less active during treadmill compared to overground running at 2.6 m/s and the RF showed significantly higher activity at 3.6 m/s and 4.5 m/s while running on the different treadmills. Summarizing, differences were mainly observed between the different treadmill conditions relative to overground running. Muscle activation differences between the different treadmill conditions were observed at faster running speeds for RF during the pre-heel-strike phase only. Different types of treadmills with different mechanical properties affects the muscle activity during stance phase as well as in preparation to heel-strike. Additionally, the muscle activity is greater during overground compared to treadmill running during the stance phase for the GM, BF, and RF.

A Re-examination of the Measurement of Foot Strike Mechanics During Running: The Immediate Effect of Footwear Midsole Thickness

Purpose

Midsole cushioning thickness (MT) is a key component of running footwear that may influence the stiffness setting of the joints, performance enhancement, and injury prevention. Most studies that have investigated the influence of manipulating shoe midsole characteristics on foot strike patterns and vertical force loading rates have not considered the dynamic conditions of initial landing and the associated initial lower limb joint stiffness. In this study, we examined the effect of running in shoes with large changes in MT on both the posture and dynamics associated with foot strike.

Methods

12 injury-free runners with habitual rearfoot strike patterns ran at 4.5 m/s along a 40-m runway in shoe conditions with MT of 30, 42, and 54 mm, respectively. Ground reaction force and the right leg kinematic data were collected. One-way repeated measures ANOVA was conducted to statistically analyze the effect of MT on key variables linked to foot strike.

Results

Increased midsole thickness resulted in a slightly flatter foot strike posture (p < 0.05), a decreased shank retraction velocity (p < 0.05), and an increase in forward horizontal foot velocity (p < 0.05), all at initial ground contact. Vertical force loading rates were reduced with increasing MT (p < 0.05), but this was associated with large increases in the initial ankle and knee joint stiffness (p < 0.05).

Conclusion

Adjustments in the initial conditions of contact with the ground during running were seen in both the posture and dynamics of the lower limbs. To help to mitigate the impact severity from foot-ground collision with the thinnest shoe condition, there was an increased shank retraction velocity and decreased forward velocity of the foot at landing. These active impact-moderating adaptations likely served to reduce the changes in impact severity expected due to midsole material properties alone and should be considered in relation to altering the risk of running-related injuries.

Lack of impact moderating movement adaptation when soccer players perform game specific tasks on a third-generation artificial surface without a cushioning underlay

The objective of this study was to investigate how the inclusion of a cushioning underlay in a third-generation artificial turf (3G) affects player biomechanics during soccer-specific tasks. Twelve soccer players (9 males/3 females; 22.6 ± 2.3 y) participated in this study. Mechanical impact testing of each 3G surface; without (3G-NCU) and with cushioning underlay (3G-CU) were conducted. Impact force characteristics, joint kinematics and joint kinetics variables were calculated on each surface condition during a sprint 90° cut (90CUT), a sprint 180° cut (180CUT), a drop jump (DROP) and a sprint with quick deceleration (STOP). For all tasks, greater peak resultant force, peak knee extensor moment and peak ankle dorsi-flexion moment were found in 3G-NCU than 3G-CU (p < 0.05). During 90CUT and STOP, loading rates were higher in 3G-NCU than 3G-CU (p < 0.05). During 180CUT, higher hip, knee and ankle ranges of motion were found in 3G-NCU (p < 0.05). These findings showed that the inclusion of cushioning underlay in 3G reduces impact loading forces and lower limb joint loading in soccer players across game-specific tasks. Overall, players were not attempting to reduce higher lower limb impact loading associated with a lack of surface cushioning underlay.

Kinematic risk factors for lower limb tendinopathy in distance runners: A systematic review and meta-analysis

INTRODUCTION

Abnormal kinematics have been implicated as one of the major risk factors for lower limb tendinopathy (LLT).

OBJECTIVE

To systematically review evidence for kinematic risk factors for LLT in runners.

METHODS

Individual electronic searches in PubMed, EMBASE and Web of Science were conducted. Two reviewers screened studies to identify observational studies reporting kinematic risk factors in runners with LLT compared to healthy controls. The Down and Black appraisal scale was applied to assess quality. A meta-analysis was performed provided that at least two studies with similar methodology reported the same factor.

RESULTS

Twenty-eight studies were included: Achilles tendinopathy (AT) (9), iliotibial band syndrome (ITBS) (17), plantar fasciopathy (PF) (2), patellar tendinopathy (PT) (1), posterior tibial tendon dysfunction (PTTD) (1). Eighteen studies were rated high-quality and ten medium-quality. The meta-analyses revealed strong evidence of higher peak knee internal rotation, moderate evidence of lower peak rearfoot eversion and knee flexion at heel strike and greater peak hip adduction in runners with ITBS. Very limited evidence revealed higher peak ankle eversion in runners with PF and PTTD or higher peak hip adduction in PT.

SIGNIFICANCE

Peak rearfoot eversion was the only factor reported in all included LLTs; it is a significant factor in ITBS, PT and PTTD but not in AT and PF. More prospective studies are needed to accurately evaluate the role of kinematic risk factors as a cause of LLT. Taken together, addressing rearfoot kinematic and kinematic chain movements accompanied by peak eversion should be considered in the prevention and management of LLT.

The effects of artificial surface temperature on mechanical properties and player kinematics during landing and acceleration

BACKGROUND

Artificial turf is considered a feasible global alternative to natural turf by many sports governing bodies. Consequently, its ability to provide a safe and consistent playing surface regardless of climate becomes essential. The aims of this study were to determine the effects of artificial surface temperature on: (1) mechanical properties of the turf and (2) the kinematics of a turf-sport related movement.

METHODS

Two identical artificial turf pitches were tested: one with a cold surface temperature (1.8°C-2.4°C) and one with a warm surface temperature (14.5°C-15.2°C). Mechanical testing was performed to measure the surface properties. Four amateur soccer players performed a hurdle jump to sprint acceleration movement, with data (contact time, step length and hip, knee and ankle kinematics) collected using CODASport (200 Hz).

RESULTS

The temperature difference had a significant influence on the mechanical properties of the artificial turf, including force absorption, energy restitution, rotational resistance, and the height where the head injury criterion was met. Both step length (p = 0.008) and contact time (p = 0.002) of the initial step after the landing were significantly longer on the warm surface. In addition, significant range of motion and joint angular velocity differences were found.

CONCLUSION

These findings highlight different demands placed on players due to the surface temperature and suggest a need for coaches, practitioners, and sports governing bodies to be aware of these differences.

Lower Extremity Biomechanics and Self-Reported Foot-Strike Patterns Among Runners in Traditional and Minimalist Shoes

CONTEXT

The injury incidence rate among runners is approximately 50%. Some individuals have advocated using an anterior-foot-strike pattern to reduce ground reaction forces and injury rates that they attribute to a rear-foot-strike pattern. The proportion of minimalist shoe wearers who adopt an anterior-foot-strike pattern remains unclear.

OBJECTIVE

To evaluate the accuracy of self-reported foot-strike patterns, compare negative ankle- and knee-joint angular work among runners using different foot-strike patterns and wearing traditional or minimalist shoes, and describe average vertical-loading rates.

DESIGN

Descriptive laboratory study.

SETTING

Research laboratory.

PATIENTS OR OTHER PARTICIPANTS

A total of 60 healthy volunteers (37 men, 23 women; age = 34.9 ± 8.9 years, height = 1.74 ± 0.08 m, mass = 70.9 ± 13.4 kg) with more than 6 months of experience wearing traditional or minimalist shoes were instructed to classify their foot-strike patterns.

INTERVENTION(S)

Participants ran in their preferred shoes on an instrumented treadmill with 3-dimensional motion capture.

MAIN OUTCOME MEASURE(S)

Self-reported foot-strike patterns were compared with 2-dimensional video assessments. Runners were classified into 3 groups based on video assessment: traditional-shoe rear-foot strikers (TSR; n = 22), minimalist-shoe anterior-foot strikers (MSA; n = 21), and minimalist-shoe rear-foot strikers (MSR; n = 17). Ankle and knee negative angular work and average vertical-loading rates during stance phase were compared among groups.

RESULTS

Only 41 (68.3%) runners reported foot-strike patterns that agreed with the video assessment (κ = 0.42, P < .001). The TSR runners demonstrated greater ankle-dorsiflexion and knee-extension negative work than MSA and MSR runners (P < .05). The MSA (P < .001) and MSR (P = .01) runners demonstrated greater ankle plantar-flexion negative work than TSR runners. The MSR runners demonstrated a greater average vertical-loading rate than MSA and TSR runners (P < .001).

CONCLUSIONS

Runners often cannot report their foot-strike patterns accurately and may not automatically adopt an anterior-foot-strike pattern after transitioning to minimalist running shoes.

Four biomechanical and anthropometric measures predict tibial stress fracture: a prospective study of 1065 Royal Marines

Background

Tibial stress fractures (TSFs) cause a significant burden to Royal Marines recruits. No prospective running gait analyses have previously been performed in military settings.

Aim

We aimed to identify biomechanical gait factors and anthropometric variables associated with increased risk of TSF.

Methods

1065 Royal Marines recruits were assessed in week 2 of training. Bilateral plantar pressure and three-dimensional lower limb kinematics were obtained for barefoot running at 3.6 m/s, providing dynamic arch index, peak heel pressure and lower limb joint angles. Age, bimalleolar breadth, calf girth, passive hip internal/external range of motion and body mass index (BMI) were also recorded. 10 recruits who sustained a TSF during training were compared with 120 recruits who completed training injury-free using a binary logistic regression model to identify injury risk factors.

Results

4 variables significantly (p<0.05) predicted increased risk of TSF (ORs and 95% CI): smaller bimalleolar width (0.73, 0.58 to 0.93), lower BMI (0.56, 0.33 to 0.95), greater peak heel pressure (1.25, 1.07 to 1.46) and lower range of tibial rotation (0.78, 0.63 to 0.96).

Summary

Reduced impact attenuation and ability to withstand load were implicated in tibial stress fracture risk.

Dance floor mechanical properties and dancer injuries in a touring professional ballet company

OBJECTIVES

The mechanical properties of the floors used by dancers have often been suggested to be associated with injury, yet limited etiological evidence is available to support this hypothesis. The dance floors at three theatres regularly used by a touring professional ballet company were mechanically quantified with the aim of comparing floor properties with injury incidence in dancers.

DESIGN

Cross sectional.

METHODS

Test points on the floors were quantified in accordance with European Sports Surface Standard protocols for force reduction. Injuries and associated variables occurring within the ballet company dancers during activity on the three floors were recorded by the company's medical staff. An injury was recorded if a dancer experienced an incident that restricted the dancer from performing all normal training or performance activities for a 24 h period. Injuries were delimited to those occurring in the lower limbs or lumbar region during non-lifting tasks.

RESULTS

Floor construction varied between venues and a range of floor mechanical properties were observed. None of the floors complied with the range of force reduction values required by the European Sport Surface Standards. The highest injury rate was observed on the floor with the greatest variability of force reduction magnitudes. No difference in injury frequency was observed between the venues with the highest and lowest mean force reduction magnitudes.

CONCLUSIONS

Professional dancers can be required to perform on floors that may be inadequate for safe dance practice. Intra-floor force reduction variability may have a stronger association with injury risk than mean floor force reduction magnitude.

Biomechanical Response to Changes in Natural Turf During Running and Turning

Integrated biomechanical and engineering assessments were used to determine how humans responded to variations in turf during running and turning. Ground reaction force (AMTI, 960 Hz) and kinematic data (Vicon Peak Motus, 120 Hz) were collected from eight participants during running (3.83 m/s) and turning (10 trials per condition) on three natural turf surfaces in the laboratory. Surface hardness (Clegg hammer) and shear strength (cruciform shear vane) were measured before and after participant testing. Peak loading rate during running was significantly higher (p < .05) on the least hard surface (sandy; 101.48 BW/s ± 23.3) compared with clay (84.67 BW/s ± 22.9). There were no significant differences in running kinematics. Compared with the “medium” condition, fifth MTP impact velocities during turning were significantly (RM-ANOVA, p < .05) lower on clay (resultant: 2.30 m/s [± 0.68] compared with 2.64 m/s [± 0.70]), which was significantly (p < .05) harder “after” and had the greatest shear strength both “before” and “after” participant testing. This unique finding suggests that further study of foot impact velocities are important to increase understanding of overuse injury mechanisms.

Biomechanical response to systematic changes in impact interface cushioning properties while performing a tennis-specific movement

It is currently not known whether human responses across typical sports surfaces are dependent on cushioning or frictional properties of the interface. The present study assessed systematic changes in surface cushioning (baseline acrylic, rubber, thin foam, and thick foam) as participants performed tennis running forehand foot plants wearing a basic neutral shoe (plimsolls). It was hypothesized that systematic decreases in peak rates of loading, heel pressures, and perceived hardness would be yielded as surface cushioning increased (impact test device). A common acrylic top surface provided consistent frictional properties across surfaces. Kinetics (AMTI, 960 Hz and Footscan Pressure Insoles, 500 Hz), kinematics (Peak MOTUS, 120 Hz), and cushioning perception were assessed. Peak and mean loading rates of vertical ground reaction force, peak horizontal force, peak heel pressure, and rates of loading demonstrated significant correlations (P < 0.05) with the participants' perceived levels of cushioning and matched mechanical rankings of surface cushioning. In contrast, peak impact force was lowest on the least cushioned surface. Kinematic responses were not significantly different between surfaces. Present evidence supports ''peak rate of loading'' as a more suitable indicator of surface cushioning than peak impact force. Although cautionary, biomechanical support is also provided for mechanical methods of surface cushioning assessment.

Muscle Tuning During Running: Implications of an Un-tuned Landing

Background: The impact force in heel-toe running is an input signal into the body that initiates vibrations of the soft tissue compartments of the leg. These vibrations are heavily damped and the paradigm of muscle tuning suggests the body adapts to different input signals to minimize these vibrations. The objectives of the present study were to investigate the implications of not tuning a muscle properly for a landing with a frequency close to the resonance frequency of a soft tissue compartment and to look at the effect of an unexpected surface change on the subsequent step of running. Method: Thirteen male runners were recruited and performed heel-toe running over two surface conditions. The peak accelerations and biodynamic responses of the soft tissue compartments of the leg along with the EMG activity of related muscles were determined for expected soft, unexpected hard and expected hard landings. Results and Conclusions: For the unexpected hard landing there was a change in the input frequency of the impact force, shifting it closer to the resonance frequency of the soft tissue compartments. For the unexpected landing there was no muscle adaptation, as subjects did not know the running surface was going to change. In support of the muscle-tuning concept an increase in the soft tissue acceleration did occur. This increase was greater when the proximity of the input signal frequency was closer to the resonance frequency of the soft tissue compartment. Following the unexpected change in the input signal a change in pre-contact muscle activity to minimize soft tissue compartment vibrations was not found. This suggests if muscle tuning does occur it is not a continuous feedback response that occurs with every small change in the landing surface properties. In previous studies with significant adaptation periods to new input signals significant correlations between the changes in the input signal frequency and the EMG intensity have been shown, however, changes in soft tissue accelerations have not been found. The results of the present study showed that changes in these soft tissue accelerations can occur in response to a resonance frequency input signal when a muscle reaction has not happened.