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1.
Objective. To elucidate the morphological and biomechanical manifestation of the triceps surae muscle-tendon unit during passive extension.

Design. The instantaneous changes within the load-deformation curve of muscle-tendon unit were analyzed by an in vivo rabbit model.

Background. Although muscle strains occur more frequently than complete failures, the failure mechanism of these sub-failure injuries is rarely investigated. Monitoring of the instantaneous changes in the load-deformation curve allows correlation with the morphological changes that occur during passive extension.

Methods. After anesthesia, the triceps surae muscle of rabbit was dissected and then stretched to failure by a MTS Bionix 858 machine. The morphological changes in failure patterns were recorded by photographs.

Results. The morphological and biomechanical manifestations of the triceps surae muscle-tendon unit was divided into five different portions: first, the viscoelastic portion with minimal morphologic change; second, the portion of micro-failure with local ecchymosis; third and fourth, the portions of macrofailure with sequential rupture of the muscle fibers; and fifth, the portion of rupture and separation of muscle parenchyma.

Conclusions. A threshold for stretch-induced injury does exist. The threshold of the initiation of micro-failure in this model was 16.5% of the strain, which corresponded to 16.6% of the maximal sustainable force.  相似文献

2.

Background

Achilles tendon pathologies may alter the coordinative strategies of synergistic calf muscles. We hypothesized that both surface electromyography and positron emission tomography would reveal differences between symptomatic and asymptomatic legs in Achilles tendinopathy patients and between healthy controls.

Methods

Eleven subjects with unilateral chronic Achilles tendon pain (28 years) and eleven matched controls (28 years) were studied for triceps surae and flexor hallucis longus muscle activity in response to repetitive isometric plantarflexion tasks performed at 30% of maximal voluntary contraction using surface electromyography and glucose uptake using positron emission tomography. Additionally, Achilles tendon glucose uptake was quantified.

Findings

Normalized myoelectric activity of soleus was higher (P < 0.05) in the symptomatic leg versus the contralateral and control legs despite lower absolute force level maintained (P < 0.005). Electromyography amplitude of flexor hallucis longus was also greater on the symptomatic side compared to the healthy leg (P < 0.05). Both the symptomatic and asymptomatic legs tended to have higher glucose uptake compared to the control legs (overall effect size: 0.9 and 1.3, respectively). Achilles tendon glucose uptake was greater in both legs of the patient group (P < 0.05) compared to controls. Maximal plantarflexion force was ~ 14% greater in the healthier leg compared to the injured leg in the patient group.

Interpretations

While the electromyography showed greater relative amplitude in the symptomatic leg, the results based on muscle glucose uptake suggested relatively similar behavior of both legs in the patient group. Higher glucose uptake in the symptomatic Achilles tendon suggests a higher metabolic demand.  相似文献
3.

Objectives

To determine the prevalence of latent myofascial trigger points (MTrPs), specific diagnostic criteria and the association between gender and MTrP prevalence in the triceps surae and upper trapezius.

Design

Cross-sectional study.

Setting

University, Faculty of Health and Life Sciences.

Participants

Two hundred and twenty healthy volunteers (132 females and 88 males; mean age 29.7 (SD 11.0).

Interventions

Not applicable.

Main outcome measures

Prevalence of latent MTrPs in the triceps surae and comparative upper trapezius; specific diagnostic criteria and pressure pain threshold (PPT).

Results

Latent MTrPs were prevalent in all triceps surae (range: 13 to 30%), left upper trapezius (23%) and right upper trapezius (20%). No MTrPs (0%) identified in the middle fibres of deltoid. For each specific diagnostic criterion, taut bands were most prevalent in the right gastrocnemius medial head (81%); tender spot in left gastrocnemius medial head (52%) and nodules in the right upper trapezius (35%). Local twitch response (0.5%), the least frequent diagnostic criterion was only found in the left gastocnemius medial head. A significant increase in latent MTrP prevalence for females compared to males in five of the six triceps surae MTrP sites, with no significant association for gender and latent MTrP prevalence in the left or right upper trapezius.

Conclusions

This study established the prevalence of latent MTrPs, specific diagnostic criteria and baseline normative data in the triceps surae. The middle fibres of deltoid were identified as a potential MTrP control site for future clinical research in the upper limb.  相似文献
4.

Background

Although single-legged heel-raise cycles are often performed on an incline in different knee flexion positions to discriminate the relative contribution of the triceps surae muscles, detailed kinematic and kinetic analyses of this procedure are not available. Our study characterizes and compares the biomechanics and clinical outcomes of single-legged heel-raise cycles performed to volitional exhaustion on an incline with the knee straight (0°) and bent (45°), considering the effect of sex and age.

Methods

Fifty-six male and female volunteers, with equal numbers of younger (20 to 40 years of age) and older (40 to 60 years of age) individuals, completed a maximal number of heel-raise cycles on an incline at both nominal knee angles. Kinematic and kinetic data were acquired during testing using a 3D motion capturing system and multi-axial force plate. The impact of fatigue on performance was quantified using changes in maximal voluntary isometric contraction force and biomechanical performance of cycles.

Findings

Overall, participants completed three more cycles and maintained better biomechanical performance with 45° than 0° of knee flexion. More precisely, the decreases in maximal heel-raise heights, plantar-flexion angles at maximal height and ranges of ankle motion per cycle were all smaller with the knee bent. However, several outcomes indicated similar plantar-flexion fatigue at both knee angles. Males demonstrated a more rapid decline in peak ground reaction forces during testing; but otherwise, neither sex nor age significantly impacted outcomes.

Interpretation

It is concluded that the differences discerned here in the biomechanics of single-legged heel-raise cycles performed at 0° and 45° of knee flexion to volitional exhaustion on an incline may be too small to identify in clinical settings or reflect substantial alterations in the relative contribution of the triceps surae muscles.  相似文献
5.

Background

The objective of this study was to investigate changes in active and passive biomechanical properties of the calf muscle–tendon unit induced by controlled ankle stretching in stroke survivors.

Methods

Ten stroke survivors with ankle spasticity/contracture and ten healthy control subjects received intervention of 60-min ankle stretching. Joint biomechanical properties including resistance torque, stiffness and index of hysteresis were evaluated pre- and post-intervention. Achilles tendon length was measured using ultrasonography. The force output of the triceps surae muscles was characterized via the torque–angle relationship, by stimulating the calf muscles at a controlled intensity across different ankle positions.

Findings

Compared to healthy controls, the ankle position corresponding to the peak torque of the stroke survivors was shifted towards plantar flexion (P < 0.001). Stroke survivors showed significantly higher resistance torques and joint stiffness (P < 0.05), and these higher resistances were reduced significantly after the stretching intervention, especially in dorsiflexion (P = 0.013). Stretching significantly improved the force output of the impaired calf muscles in stroke survivors under matched stimulations (P < 0.05). Ankle range of motion was also increased by stretching (P < 0.001).

Interpretation

At the joint level, repeated stretching loosened the ankle joint with increased passive joint range of motion and decreased joint stiffness. At the muscle–tendon level, repeated stretching improved calf muscle force output, which might be associated with decreased muscle fascicle stiffness, increased fascicle length and shortening of the Achilles tendon. The study provided evidence of improvement in muscle tendon properties through stretching intervention.  相似文献
6.

Background

The effects of an acute bout of moderate-duration static stretching on plantar flexor force production, series compliance of the muscle–tendon unit, and levels of neuromuscular activation were examined.

Methods

Eighteen active individuals (9 men and 9 women) performed four 45-s static plantar flexor stretches and a time-matched control of no stretch (where subjects remained seated in the dynamometer for 4 min with no stretch being performed). Measures of peak isometric moment, rate of force development, neuromuscular activation (interpolated twitch technique and electromyography), twitch force characteristics, passive moment during stretch, and tendon elongation during maximal voluntary contractions were taken before and after the stretching.

Findings

Despite a significant stress–relaxation response during stretch (9.3%, P < 0.01) there were no significant differences in peak isometric moment (P = 0.35; effect size 0.13), rate of force development (P = 0.93; effect size 0.01), neuromuscular activation (interpolated twitch: P = 0.86; electromyography: P = 0.09; effect size 0.02), or tendon elongation (P = 0.61; effect size 0.07) after stretching. Twitch characteristics were also unchanged after stretching, although there was a reduction in the rate of twitch torque relaxation (RRt; P < 0.01).

Interpretation

The acute bout of moderate-duration static stretching did not impair the force generating capacity of the plantar flexors or negatively affect muscle–tendon mechanical properties. Static stretching may not always have detrimental consequences for force production. Thus, clinicians may be able to apply moderate-duration stretches to patients without risk of reducing muscular performance.  相似文献
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