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Keitaro Kubo, Takanori Teshima, Norikazu Hirose and Naoya Tsunoda

The purpose of this study was to compare the morphological and mechanical properties of the human patellar tendon among elementary school children (prepubertal), junior high school students (pubertal), and adults. Twenty-one elementary school children, 18 junior high school students, and 22 adults participated in this study. The maximal strain, stiffness, Young’s modulus, hysteresis, and cross-sectional area of the patellar tendon were measured using ultrasonography. No significant difference was observed in the relative length (to thigh length) or cross-sectional area (to body mass2/3) of the patellar tendon among the three groups. Stiffness and Young’s modulus were significantly lower in elementary school children than in the other groups, while no significant differences were observed between junior high school students and adults. No significant differences were observed in maximal strain or hysteresis among the three groups. These results suggest that the material property (Young’s modulus) of the patellar tendons of elementary school children was lower than that of the other groups, whereas that of junior high school students was already similar to that of adults. In addition, no significant differences were observed in the extensibility (maximal strain) or viscosity (hysteresis) of the patellar tendon among the three groups.

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Bareket Falk

Children develop lower levels of muscle force, and at slower rates, than adults. Although strength training in children is expected to reduce this differential, a synchronous adaptation in the tendon must be achieved to ensure forces continue to be transmitted to the skeleton with efficiency while minimizing the risk of strain- related tendon injury. We hypothesized that resistance training (RT) would alter tendon mechanical properties in children concomitantly with changes in force production characteristics. Twenty prepubertal children (age 8.9 ± 0.3 yr) were equally divided into control (nontraining) and experimental (training) groups. The training group completed a l0-week RT intervention consisting of 2–3 sets of 8–15 plantar flexion contractions performed twice weekly on a recumbent calf-raise machine. Achilles tendon properties (cross-sectional area, elongation, stress, strain, stiffness, and Young’s modulus), electromechanical delay (EMD; time between the onset of muscle activity and force), rate of force development (RFD; slope of the force-time curve), and rate of electromyographic (EMG) increase (REI; slope of the EMG time curve) were measured before and after RT. Tendon stiffness and Young’s modulus increased significantly after RT in the experimental group only (~29% and ~25%, respectively); all other tendon properties were not significantly altered, although there were mean decreases in both peak tendon strain and strain at a given force level (14% and 24%, respectively; not significant) which may have implications for tendon injury risk and muscle fiber mechanics. A decrease of ~13% in EMD was found after RT for the experimental group, which paralleled the increase in tendon stiffness (r = −0.59); however, RFD and REI were unchanged. The present data show that the Achilles tendon adapts to RT in prepubertal children and is paralleled by a change in EMD, although the magnitude of this change did not appear to be sufficient to influence RFD. These findings are of importance within the context of the efficiency and execution of movement.

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Thomas D. O’Brien

Children develop lower levels of muscle force, and at slower rates, than adults. While strength training in children is expected to reduce this differential, a synchronous adaptation in the tendon must be achieved to ensure forces continue to be transmitted to the skeleton with efficiency while minimizing the risk of strainrelated tendon injury. We hypothesized that resistance training (RT) would alter tendon mechanical properties in children concomitantly with changes in force production characteristics. Twenty prepubertal children (8.9 ± 0.3 years) were equally divided into control (nontraining) and experimental (training) groups. The training group completed a 10-week RT intervention consisting of 2-3 sets of 8-15 plantar flexion contractions performed twice weekly on a recumbent calf raise machine. Achilles tendon properties (cross-sectional area, elongation, stress, strain, stiffness and Young’s modulus), electromechanical delay (EMD; time between the onset of muscle activity and force), rate of force development (RFD; slope of the force-time curve) and rate of EMG increase (REI; slope of the EMG-time curve) were measured before and after RT. Tendon stiffness and Young’s modulus increased significantly after RT in the experimental group only (~29% and ~25%, respectively); all other tendon properties were not significantly altered, although there were mean decreases in both peak tendon strain and strain at a given force level (14% and 24%, respectively, n.s) which may have implications for tendon injury risk and muscle fiber mechanics. A ~13% decrease in EMD was found after RT for the experimental group which paralleled the increase in tendon stiffness (r = −0.59), however RFD and REI were unchanged. The present data show that the Achilles tendon adapts to RT in prepubertal children and is paralleled by a change in EMD, although the magnitude of this change did not appear to be sufficient to influence RFD. These findings are of potential importance within the context of the efficiency and execution of movement.

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Li-Xin Guo, Zhao-Wen Wang, Yi-Min Zhang, Kim-Kheng Lee, Ee-Chon Teo, He Li and Bang-Chun Wen

The aim of this study is to investigate the effect of material property changes in the spinal components on the resonant frequency characteristics of the human spine. Several investigations have reported the material property sensitivity of human spine under static loading conditions, but less research has been devoted to the material property sensitivity of spinal biomechanical characteristics under a vibration environment. A detailed three-dimensional finite element model of the human spine, T12– pelvis, was built and used to predict the influence of material property variation on the resonant frequencies of the human spine. The simulation results reveal that material properties of spinal components have obvious influences on the dynamic characteristics of the spine. The annulus ground substance is the dominant component affecting the vertical resonant frequencies of the spine. The percentage change of the resonant frequency relative to the basic condition was more than 20% if Young’s modulus of disc annulus is less than 1.5 MPa. The vertical resonant frequency may also decrease if Poisson’s ratio of nucleus pulposus of intervertebral disc decreases.

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Michael F. Joseph, Katherine Histen, Julia Arntsen, Lauren L’Hereux, Carmine Defeo, Derek Lockwood, Todd Scheer and Craig R. Denegar

Context:

Achilles tendons (ATs) adapt to increased loading generated by long-term adoption of a minimalist shoe running style. There may be difference in the chronology and extent of adaptation between the sexes.

Objective:

To learn the chronology of AT adaptations in female and male runners who transitioned to a minimalist running style through a planned, progressive 12-wk transition program.

Design:

Prospective cohort study of well-trained, traditionally shod runners who transitioned to minimalist shoe running.

Setting:

Repeated laboratory assessment at baseline and 3, 12, and 24 wk after initiating transition program.

Participants:

Fifteen women and 7 men (of 29 enrolled) completed the study.

Main Outcome Measures:

The authors used diagnostic ultrasound and isokinetic dynamometry to generate a force elongation curve and its derivatives at each time point.

Results:

Greater adaptations were observed in men than in women, with men generating more force and having greater increases in CSA, stiffness, and Young’s modulus and less elongation after 12 wk of training.

Conclusion:

Men demonstrated changes in AT properties that were consistent with increased loading of the triceps surae during exercise. The women demonstrated far smaller changes. Further investigation is warranted to understand when adaptations may occur in women and the implications of altered AT mechanical properties for performance and injury risk.

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Annika Kruse, Christian Schranz, Martin Svehlik and Markus Tilp

tendon stiffness and Young’s modulus. Methods Participants In total, 28 children with CP volunteered to participate; however, 6 withdrew during the course of the study for different reasons (Figure  1 ). We recruited ambulatory children aged 8–16 without a contracture of the plantar flexors (maximal

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Kentaro Chino and Hideyuki Takahashi

tissue. 11 , 12 The shear modulus assessed by ultrasound shear wave elastography is strongly and linearly related to Young’s modulus measured by traditional material testing. 13 Collectively, these findings suggest that shear wave elastography enables the assessment of localized muscle stiffness