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Florian Fath, Anthony J. Blazevich, Charlie M. Waugh, Stuart C. Miller and Thomas Korff

The muscle-tendon moment arm is an important input parameter for musculoskeletal models. Moment arms change as a function of joint angle and contraction state and depend on the method being employed. The overall purpose was to gain insights into the interactive effects of joint angle, contraction state and method on the Achilles tendon moment arm using the center of rotation (COR) and the tendon excursion method (TE). Achilles tendon moment arms were obtained at rest (TErest, CORrest) and during a maximum voluntary contraction (CORMVC) at four angles. We found strong correlations between TErest and CORMVC for all angles (.72 ≤ r ≤ .93) with Achilles tendon moment arms using CORMVC being 33–36% greater than those obtained from TErest. The relationship between Achilles tendon moment arms and angle was similar across both methods and both levels of muscular contraction. Finally, Achilles tendon moment arms for CORMVC were 1–8% greater than for CORrest.

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Sharon J. Dixon and David G. Kerwin

This study investigated the influence of heel lift interventions on the loading of the Achilles tendon for heel-toe runners. It was hypothesized that the peak Achilles tendon force and peak rate of loading would be reduced by the increase in heel lift, and that the peak Achilles tendon force would occur significantly later in stance. Achilles tendon forces were determined by calculating sagittal-plane ankle joint moments using inverse-dynamics techniques and dividing these moments by Achilles tendon moment arm lengths. Methods for estimating Achilles tendon moment arm length using skin markers were justified via MRI data for one participant. Seven participants underwent running trials under three heel lift conditions: zero, 7.5-mm, and 15-mm heel lift. Average magnitude and occurrence time of peak Achilles tendon force and peak rate of loading were determined for each condition over the 7 participants. Despite group reductions in peak Achilles tendon force and peak rate of loading for the increased heel lift conditions, statistical analysis (ANOVA) revealed no significant differences for these variables, p > 0.05. Individual participant observations highlighted varied responses to heel lift; both increases and decreases in peak Achilles tendon force were observed. For the group data, the time of peak impact force occurred significantly later in the 15-mm heel lift condition than in the zero heel lift, p < 0.05. It is suggested that the success of increased heel lift in treating Achilles tendon injury may be due to a later occurrence of peak Achilles tendon force in response to this intervention, reducing Achilles tendon average rate of loading. In addition, the individuality of Achilles tendon peak force changes with heel lift intervention highlights the need for individual participant analysis.

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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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Michelle A. Sandrey

Objective:

To present the basic concepts of normal composition and structure of tendons and indicate how they are affected by acute and chronic tendon-injury pathomechanics.

Data Sources:

MEDLINE (1970-1999) and SPORTDiscus (1970-1999) were searched using the key words pathoanatomic, tendinitis, tendinosis, biomechanics, pathomechanics, histology, chronic, and mechanical behavior.

Data Synthesis:

Acute loading modes to tendons are based on the response of tendons to tensile and compressive stress. Chronic loading modes are based on frictional forces and repetitive movement.

Conclusions and Recommendations:

With an appreciation of the pathologic changes in acute tendon injuries, the clinician can better understand injury mechanics and the healing process. Until we know more about what is happening in and around the tendon, principally in the early and late phases of chronic injury we will not be able to adequately address injury classification of structures and, hence, the pathomechanics of chronic injury

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Michelle A. Sandrey

Objective:

Tendons have biomechanical properties based on collaborative remodeling of all their cells through normal lysis and synthesis. This review assesses factors that affect the healing response and presents solutions for rehabilitating acute and chronic tendon injuries.

Data Sources:

MEDLINE (1970–2002) and SPORTDiscus (1970–2002). Key words searched were tendon, tendinitis, tendinosis, tendinopathy, rehabilitation, ultrasound, NSAIDs, exercise, mobilization, aging, immobilization, and healing.

Data Synthesis:

The biomechanical roles tendons play change throughout one’s lifetime and are influenced by maturation and aging, injury and healing, immobilization, exercise, medications, and therapeutic modalities. Suggestions from animal, case, and clinical studies are varied but provide solutions in the treatment of acute and chronic tendon injuries.

Conclusions and Recommendations:

All factors that affect the tendon structure should be considered in a rehabilitation program. Therapeutic exercise, medications, or therapeutic modalities should never be used as a stand-alone therapy.

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Melissa R. Lachowitzer, Anne Ranes and Gary T. Yamaguchi

In order to create a flexible model of the foot for dynamic musculoskeletal models, anthropometric data combined with geometric information describing the intrinsic musculature are needed. In this study, the left feet of two male and two female cadavers were dissected to expose the intrinsic musculotendon pathways. Three-dimensional coordinates of bony landmarks, tendon origins, insertions, and via points were digitized to submillimeter accuracy. Muscle architectural parameters were also measured, including volume, weight, and pennation angle and sarcomere, fascicle, and free tendon lengths. Optimal muscle fascicle lengths, pennation angles at optimal length, physiological cross-sectional areas (PCSA), and tendon slack lengths were calculated from the directly measured values. Fascicle length and pennation angle varied greatly within each subject. Average fascicle lengths normalized by optimal fascicle length varied between 0.73 and 1.25, with 75% of the formalin-preserved muscles being found in a shortened state. The muscle volume and PCSA also had a large variability within subjects but less variation between subjects. The ratio of tendon slack length to optimal fascicle length was found to vary between 1.05 and 9.56. Using this data, a deformable model of the foot can now be created. It is envisioned that deformable feet will significantly improve

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Kristinn I. Heinrichs and Catherine R. Haney

The efficacy of the nonoperative and operative approaches to Achilles tendon rapture has been debated in the literature. In addition, there is little consensus regarding postoperative immobilization with regard to immobilization type, casting position, cast time, and weight-bearing progression. The rehabilitation of the surgically repaired Achilles tendon has not been well described in the literature. The epidemiology and biomechanics of Achilles tendon rupture as well as splint fabrication and rehabilitation protocol for the surgically repaired Achilles tendon in two patients will be presented.

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Sharon J. Dixon and David G. Kerwin

In this study, a modeling method was developed to estimate Achilles tendon forces in running. Owing to the common use of heel lift devices in the treatment of Achilles tendon injury, we investigated the influence of increased heel lift on Achilles tendon loading. The hypothesis was that heel lift manipulation can influence maximum Achilles tendon force. Responses to heel lift variation were found to differ among 3 elite runners demonstrating distinct running styles. A rearfoot and a midfoot striker demonstrated significant increases in maximum Achilles tendon force with increased heel lift, whereas a forefoot striker demonstrated no changes in maximum Achilles tendon force values with heel lift manipulation (p < .05). Analysis of the factors contributing to the observed changes in maximum Achilles tendon force highlighted the influence of the moment arm of ground reaction force and the moment arm of the Achilles tendon about the ankle joint center. The finding that increased heel lift may increase maximum Achilles tendon force suggests that caution is advised in the routine use of this intervention. The different responses to heel lift increase between subjects highlight the importance of classifying subjects based on running style.

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Federico Morelli, Andrea Ferretti, Fabio Conteduca, Francesca Nanni, Lucilla Monteleone and Marco Valente

The purpose of this study was to develop a new device, which represents a modification of the Cryo-Jaw described by Riemersa and Schamhardt and modified by Hamner et al., for in vitro biomechanical testing of tendons which allows the lower clamp to move in every direction and thus simulate a pathological dislocation of the knee. Tendons are fixed to the device by freezing the clamped part with dry ice. After fixation of their free ends, the lower clamp was rotated 45°, translated 1 cm, and angled 40° to simulate a knee sprain. Various configurations of bundles were tested: parallel, twisted, and braided. Tests were performed on 10 paired bovine bifurcated digital extensor tendons and 6 paired human hamstring tendons. Grafts were then tested to failure subjected to impulsive load, using a servohydraulic machine. The highest ultimate load recorded for parallel bundles was 4662 ± 565.71 N for bovine bifurcated digital extensor tendons, and 3057 ± 475.44 N for human hamstring tendons. In any case, the tendons ruptured midway, well clear of the frozen part; in no case was slippage of the tendons observed. Thus the device proposed allows one to test what happens to the graft of an ACL reconstructed knee during physiological and pathological movements because it can be easily displaced in every direction.

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Derek N. Pamukoff and J. Troy Blackburn

Greater lower extremity joint stiffness may be related to the development of tibial stress fractures in runners. Musculotendinous stiffness is the largest contributor to joint stiffness, but it is unclear what factors contribute to musculotendinous stiffness. The purpose of this study was to compare plantar flexor musculotendinous stiffness, architecture, geometry, and Achilles tendon stiffness between male runners with and without a history of tibial stress fracture. Nineteen healthy runners (age = 21 ± 2.7 years; mass = 68.2 ± 9.3 kg; height = 177.3 ± 6.0 cm) and 19 runners with a history of tibial stress fracture (age = 21 ± 2.9 years; mass = 65.3 ± 6.0 kg; height = 177.2 ± 5.2 cm) were recruited from community running groups and the university’s varsity and club cross-country teams. Plantar flexor musculotendinous stiffness was estimated from the damped frequency of oscillatory motion about the ankle follow perturbation. Ultrasound imaging was used to measure architecture and geometry of the medial gastrocnemius. Dependent variables were compared between groups via one-way ANOVAs. Previously injured runners had greater plantar flexor musculotendinous stiffness (P < .001), greater Achilles tendon stiffness (P = .004), and lesser Achilles tendon elongation (P = .003) during maximal isometric contraction compared with healthy runners. No differences were found in muscle thickness, pennation angle, or fascicle length.