Simulation of the influence of sports surfaces on vertical ground reaction forces during landing

Plantar Loads of Habitual Forefoot Strikers during Running on Different Overground Surfaces

The objective of this study is to investigate plantar loads characteristics of habitual forefoot strike runners while running on different surfaces. Twenty-six runners (age: 28.2 ± 6.8 y, height: 172.9 ± 4.1 cm, weight: 67.7 ± 9.6 kg, BMI (body mass index): 22.6 ± 2.8 kg/m2, running age: 5.0 ± 4.2 y, running distance per week: 14.6 ± 11.7 km) with habitual forefoot strike participated in the study. Runners were instructed to run at 3.3 ± 0.2 m/s on three surfaces: grass, synthetic rubber and concrete. An in-shoe pressure measurement system was used to collect and analyze plantar loads data. Running on the synthetic rubber surface produced a lower plantar pressure in the lateral forefoot (256.73 kPa vs. 281.35 kPa, p = 0.006) than running on concrete. Compared with the concrete surface, lower pressure–time integrals were shown at the central forefoot (46.71 kPa⋅s vs. 50.73 kPa⋅s, p = 0.001) and lateral forefoot (36.13 kPa⋅s vs. 39.36 kPa⋅s, p = 0.004) when running on the synthetic rubber surface. The different surfaces influence plantar loads of habitual forefoot strikers and runners should choose appropriate overground surface to reduce the risk of lower extremity musculoskeletal injuries.

Surface properties affect the interplay between fascicles and tendinous tissues during landing

PURPOSE

Muscle-tendon units are forcefully stretched during rapid deceleration events such as landing. Consequently, tendons act as shock absorbers by buffering the negative work produced by muscle fascicles likely to prevent muscle damage. Landing surface properties can also modulate the amount of energy dissipated by the body, potentially effecting injury risk. This study aimed to evaluate the influence of three different surfaces on the muscle-tendon interactions of gastrocnemius medialis (GM), and vastus lateralis (VL) during single- and double-leg landings from 50 cm.

METHODS

Ultrasound images, muscle activity and joint kinematics were collected for 12 participants. Surface testing was also performed, revealing large differences in mechanical behavior.

RESULTS

During single-leg landing, stiffer surfaces increased VL fascicle lengthening and velocity, and muscle activity independent of joint kinematics while GM length changes showed no difference between surfaces. Double-leg landing resulted in similar fascicle and tendon behavior despite greater knee flexion angles on stiffer surfaces.

CONCLUSION

This demonstrates that VL fascicle lengthening is greater when the surface stiffness increases, when performing single-leg landing. This is due to the combination of limited knee joint flexion and lower surface absorption ability which resulted in greater mechanical demand mainly withstood by fascicles. GM muscle-tendon interactions remain similar between landing surfaces and types. Together, this suggests that surface damping properties primarily affect the VL muscle-tendon unit with a potentially higher risk of injury as a result of increased surface stiffness when performing single-leg landing tasks.

Effects of weight-bearing exercise on a mini-trampoline on foot mobility, plantar pressure and sensation of diabetic neuropathic feet; a preliminary study

Objective: Foot and ankle exercise has been advocated as a preventative approach in reducing the risk of foot ulceration. However, knowledge about the appropriate types and intensity of exercise program for diabetic foot ulcer prevention is still limited. The current study aimed to examine the effects of an eight-week mini-trampoline exercise on improving foot mobility, plantar pressure and sensation of diabetic neuropathic feet.

Methods: Twenty-one people with diabetic peripheral neuropathy who had impaired sensation perception were divided into two groups. The exercise group received a foot-care education program plus an eight-week home exercise program using the mini-trampoline (n = 11); whereas a control group received a foot-care education only (n = 10). Measurements were undertaken at the beginning, at the completion of the eight-week program and at a 20-week follow-up.

Results: Both groups were similar prior to the study. Subjects in the exercise group significantly increased the range of the first metatarsophalangeal joint in flexion (left: p = 0.040, right: p = 0.012) and extension (left: p = 0.013) of both feet more than controlled subjects. There was a trend for peak plantar pressure at the medial forefoot to decrease in the exercise group (p = 0.016), but not in the control group. At week 20, the number of subjects in the exercise group who improved their vibration perception in their feet notably increased when compared to the control group (left: p = 0.043; right: p = 0.004).

Conclusions: This is a preliminary study to document the improvements in foot mobility, plantar pressure and sensation following weight-bearing exercise on a flexible surface in people with diabetic neuropathic feet. Mini-trampoline exercise may be used as an adjunct to other interventions to reduce risk of foot ulceration. A larger sample size is needed to verify these findings. This trial is registered with COA No. 097.2/55.

Management of a delayed-union sesamoid fracture in a dancer

BACKGROUND

Misdiagnosed o sesamoid bone pathology in dancers may result in prolonged pain, disability, and career limitation. A thorough understanding of sesamoid disorders and appropriate treatment facilitates timely recovery. The potential loss of hallux plantar flexion strength consequent to sesamoidectomy is a major consideration for dancers.

CASE DESCRIPTION

An 18-year-old dance student sustained a delayed-union fracture of her lateral (fibular) sesamoid. Treatment included an inductive coupling external bone stimulator with pulsed electromagnetic field, activity, and weight-bearing restrictions, protective padding, strengthening, functional retraining, and progressive return to dance.

OUTCOME

Following use of an external bone stimulator for 12 months, the dancer successfully returned to her previous level of dancing. Repeated SF-36 and Dance Functional Outcome System scores confirmed this improvement.

DISCUSSION

Loss of hallux plantar flexion strength with sesamoid resection can be devastating to a dancer who requires push-off strength for multiple turns and jumps. Treatment with bone stimulation was therefore selected over more invasive measures. The dancer was compliant with systematic functional progression. Improvement, as seen on radiographs and outcome scores, accompanied her full functional recovery.

Site-specific response of bone to exercise in premenopausal women

We studied the response of bone at specific skeletal sites to either lower body exercise alone or complemented with upper body exercise in premenopausal women. Thirty-five exercisers and 24 age-matched controls completed the 12-month study. Exercising women (N = 35) were randomly assigned to either lower body resistance plus jump exercise (LOWER) (N = 19) or to lower and upper body resistance plus jump exercise (UPPER + LOWER) (N = 16). Exercisers trained three times per week completing 100 jumps and 100 repetitions of lower body resistance with or without 100 repetitions of upper body resistance exercise at each session. Intensity for lower body exercise was increased using weighted vests for jump and resistance exercises, respectively. Intensity for upper body exercise was increased using greater levels of tautness in elastic bands. Bone mineral density (BMD) at the total hip, greater trochanter, femoral neck, lumbar spine and whole body were measured by dual energy X-ray absorptiometry (Hologic QDR-1000/W) at baseline, 6 and 12 months. Data were analyzed first including all enrolled participants who completed follow-up testing and secondly including only those women whose average attendance was > or =60% of prescribed sessions. Group differences in 12-month %change scores for BMD variables were analyzed by univariate ANCOVA adjusted for baseline differences in age. Post hoc tests were performed to determine which groups differed from one another. Initial analysis showed significant differences in greater trochanter BMD between each exercise group and controls, but not between exercise groups (2.7%+/-2.5% and 2.2%+/-2.8% vs. 0.7%+/-1.7%, for LOWER and UPPER + LOWER vs. controls, respectively; p < 0.02) and near significant group differences at the spine (p = 0.06). Excluding exercisers with low compliance, group differences at the greater trochanter remained, while spine BMD in UPPER + LOWER was significantly different from LOWER and controls, who were not significantly different from one another (1.4%+/-3.9% vs. -0.9%+/-1.7% and -0.6%+/-1.8%, for UPPER + LOWER vs. LOWER and controls, respectively; p < 0.05). No significant differences among groups were found for femoral neck, total hip or whole body BMD. Our data support the site-specific response of spine and hip bone density to upper and lower body exercise training, respectively. These data could contribute to a site-specific exercise prescription for bone health.

Modeling a Viscoelastic Gymnastics Landing Mat during Impact

Landing mats that can undergo a large amount of area deformation are now essential for the safe completion of landings in gymnastics. The objective of this study was to develop an analytical model of a landing mat that reproduces the key characteristics of the mat-ground force during impact with minimal simulation run time. A force plate and two high-speed video cameras were used to record the mat deformation during vertical drop testing of a 24-kg impactor. Four increasingly complex point mass spring-damper models, from a single mass spring-damper system, Model 1, to a 3-layer mass spring-damper system, Model 4, were constructed using Matlab to model the mat's behavior during impact. A fifth model composed of a 3-layer mass spring-damper system was developed using visual Nastran 4D. The results showed that Models 4 and 5 were able to match the loading phase of the impact with simulation times of less than 1 second for Model 4 and 28 seconds for Model 5. Both Models 4 and 5 successfully reproduced the key force-time characteristics of the mat-ground interface, such as peak forces, time of peak forces, interpeak minima and initial rates of loading, and could be incorporated into a gymnast-mat model.

Video Analysis of the Deformation and Effective Mass of Gymnastics Landing Mats

INTRODUCTION

Landing mats that undergo large area deformation are now essential for the safe completion of landings in gymnastics. The aim of this study was to determine the effective mass, shock transmission time, and deformation characteristics of a mat during impacts using high-speed video and to improve the accuracy of measuring foot-mat contact forces during landing. For validation, the same variables need to be accurately assessed using accelerometer and force plate data.

METHODS

A 24-kg impactor with an attached accelerometer was dropped onto the sample mat from various heights. The surface deformation of the mat was recorded using high-speed video, and force data were obtained from a force plate beneath the mat.

RESULTS

The maximum vertical deformations were between 0.088 and 0.118 m, with corresponding volume deformation estimates ranging from 0.030 to 0.044 m3. The delay between accelerometer and force plate readings at initial contact was approximately 7 ms. The delay between peak acceleration and peak force was 3 ms. The peak acceleration calculated from the video data was within 2.5% of that recorded via the accelerometer. The effective mass of the mat being accelerated corresponded to forces that ranged from 481 to 930 N, up to 12% of the peak force.

CONCLUSIONS

The acceleration estimates obtained from high-speed video were combined with the effective mass estimates from the volume calculation to give peak calculated forces at the bottom of the mat to within -1.1 to +3.7% of the force recorded via the force plate. The use of high-speed video can be used to give data of sufficient accuracy for measuring foot/mat contact forces in gymnastics landings.