FORCETRANSMITTING TISSUES. FUNCTION DURING IN VIVO LOADING, AND ADAPTATION TO USE/DISUSE

Tendons have previously been regarded inert structures that mainly transmit forces from muscle to bone. However, with technological/methodological gains in recent decades, the ability to examine in vivo tendon function has improved significantly, and moreover, it has become clear that tendinous tissues, like most other tissues, undergo adaptation in consequence of changes in loading. Although mechanical function and load adaptation is not entirely understood, a large body of recent literature has contributed to the comprehension of tendon function. The present paper examines current knowledge on tendon mechanical function during human movement, and tendon response to acute and chronic changes in loading

Genome-wide Purification of Extrachromosomal Circular DNA from Eukaryotic Cells

Extrachromosomal circular DNAs (eccDNAs) are common genetic elements in Saccharomyces cerevisiae and are reported in other eukaryotes as well. EccDNAs contribute to genetic variation among somatic cells in multicellular organisms and to evolution of unicellular eukaryotes. Sensitive methods for detecting eccDNA are needed to clarify how these elements affect genome stability and how environmental and biological factors induce their formation in eukaryotic cells. This video presents a sensitive eccDNA-purification method called Circle-Seq. The method encompasses column purification of circular DNA, removal of remaining linear chromosomal DNA, rolling-circle amplification of eccDNA, deep sequencing, and mapping. Extensive exonuclease treatment was required for sufficient linear chromosomal DNA degradation. The rolling-circle amplification step by φ29 polymerase enriched for circular DNA over linear DNA. Validation of the Circle-Seq method on three S. cerevisiae CEN.PK populations of 1010 cells detected hundreds of eccDNA profiles in sizes larger than 1 kilobase. Repeated findings of ASP3-1, COS111, CUP1, RSC30, HXT6, HXT7 genes on circular DNA in both S288c and CEN.PK suggests that DNA circularization is conserved between strains at these loci. In sum, the Circle-Seq method has broad applicability for genome-scale screening for eccDNA in eukaryotes as well as for detecting specific eccDNA types

Rate of force development relationships to muscle architecture and contractile behavior in the human vastus lateralis

In this study, we tested the hypotheses that (i) rate of force development (RFD) is correlated to muscle architecture and dynamics and that (ii) force–length–velocity properties limit knee extensor RFD. Twenty-one healthy participants were tested using ultrasonography and dynamometry. Vastus lateralis optimal fascicle length, fascicle velocity, change in pennation angle, change in muscle length, architectural gear ratio, and force were measured during rapid fixed-end contractions at 60° knee angle to determine RFD. Isokinetic and isometric tests were used to estimate individual force–length–velocity properties, to evaluate force production relative to maximal potential. Correlation analyses were performed between force and muscle parameters for the first three 50 ms intervals. RFD was not related to optimal fascicle length for any measured time interval, but RFD was positively correlated to fascicle shortening velocity during all intervals (r = 0.49–0.69). Except for the first interval, RFD was also related to trigonometry-based changes in muscle length and pennation angle (r = 0.45–0.63) but not to architectural gear ratio. Participants reached their individual vastus lateralis force–length–velocity potential (i.e. their theoretical maximal force at a given length and shortening velocity) after 62 ± 24 ms. Our results confirm the theoretical importance of fascicle shortening velocity and force–length–velocity properties for rapid force production and suggest a role of fascicle rotation.publishedVersio

Measurements of Kinematic Properties of the Cervical Spine Using Magnetic Resonance Imaging

This paper presents kinematic data on the cervical and upper thoracic spine, based on measurements made on 20 Scandinavian healthy, female volunteers, aged 22-58 years (mean age 40.4). The aim was to provide anatomical in vivo data, primarily intended as data for biomechanical modelling of the upper spine. Together with the measurements of standard anthropometric body dimensions, magnetic resonance imaging (MRI) was used to capture the inner anatomy for each subject. A rigid linkage system is described for the vertebrae C1 –Tvi, with one link per vertebra. Measurements include link lengths, link rotations, and antero-posterior endpoints of the spinous process. Furthermore, correlation coefficients are calculated between link lengths and anthropometric measurements. Also presented are regression equations for each link length, with stature as a predictor. Using additional images of lower accuracy, a sub-study (N=15) investigated possible differences in link length and link rotation between non-flexion and maximum-flexion of the neck. The differences in link lengths were significant (p>0.05) for only 1 of 16 measured links (Cii-Tx). Regarding link rotation, differences were significant for 4 links (Cv–T1). Finally, the precision of the results was evaluated using two methods: by using a phantom for determining the geometrical uncertainties caused by the scanner; and by comparing results between two repeated measurement rounds. The phantom test revealed that the pixel resolution and magnetic field inhomogenities had only a minor influence on the results. The comparisons of repeated measurements revealed a significant difference for the links Ci and Cii, indicating that the landmarks for determining the occipital and Ci/Cii joints were the most difficult to identify on the images

Modulation of muscle–tendon interaction in the human triceps surae during an energy dissipation task

The compliance of elastic elements allows muscles to dissipate energy safely during eccentric contractions. This buffering function is well documented in animal models but our understanding of its mechanism in humans is confined to non-specific tasks, requiring a subsequent acceleration of the body. The present study aimed to examine the behaviour of the human triceps surae muscle–tendon unit (MTU) during a pure energy dissipation task, under two loading conditions. Thirty-nine subjects performed a single-leg landing task, with and without added mass. Ultrasound measurements were combined with three-dimensional kinematics and kinetics to determine instantaneous length changes of MTUs, muscle fascicles, Achilles tendon and combined elastic elements. Gastrocnemius and soleus MTUs lengthened during landing. After a small concentric action, fascicles contracted eccentrically during most of the task, whereas plantar flexor muscles were activated. Combined elastic elements lengthened until peak ankle moment and recoiled thereafter, whereas no recoil was observed for the Achilles tendon. Adding mass resulted in greater negative work and MTU lengthening, which were accompanied by a greater stretch of tendon and elastic elements and a greater recruitment of the soleus muscle, without any further fascicle strain. Hence, the buffering action of elastic elements delimits the maximal strain and lengthening velocity of active muscle fascicles and is commensurate with loading constraints. In the present task, energy dissipation was modulated via greater MTU excursion and more forceful eccentric contractions. The distinct strain pattern of the Achilles tendon supports the notion that different elastic elements may not systematically fulfil the same function