TY  - JOUR
A1  - Heieis, Jule
A1  - Böcker, Jonas
A1  - D'Angelo, Olfa
A1  - Mittag, Uwe
A1  - Albracht, Kirsten
A1  - Schönau, Eckhard
A1  - Meyer, Andreas
A1  - Voigtmann, Thomas
A1  - Rittweger, Jörn
T1  - Curvature of gastrocnemius muscle fascicles as function of muscle–tendon complex length and contraction in humans
JF  - Physiological Reports
N2  - It has been shown that muscle fascicle curvature increases with increasing contraction level and decreasing muscle–tendon complex length. The analyses were done with limited examination windows concerning contraction level, muscle–tendon complex length, and/or intramuscular position of ultrasound imaging. With this study we aimed to investigate the correlation between fascicle arching and contraction, muscle–tendon complex length and their associated architectural parameters in gastrocnemius muscles to develop hypotheses concerning the fundamental mechanism of fascicle curving. Twelve participants were tested in five different positions (90°/105°*, 90°/90°*, 135°/90°*, 170°/90°*, and 170°/75°*; *knee/ankle angle). They performed isometric contractions at four different contraction levels (5%, 25%, 50%, and 75% of maximum voluntary contraction) in each position. Panoramic ultrasound images of gastrocnemius muscles were collected at rest and during constant contraction. Aponeuroses and fascicles were tracked in all ultrasound images and the parameters fascicle curvature, muscle–tendon complex strain, contraction level, pennation angle, fascicle length, fascicle strain, intramuscular position, sex and age group were analyzed by linear mixed effect models. Mean fascicle curvature of the medial gastrocnemius increased with contraction level (+5 m−1 from 0% to 100%; p = 0.006). Muscle–tendon complex length had no significant impact on mean fascicle curvature. Mean pennation angle (2.2 m−1 per 10°; p < 0.001), inverse mean fascicle length (20 m−1 per cm−1; p = 0.003), and mean fascicle strain (−0.07 m−1 per +10%; p = 0.004) correlated with mean fascicle curvature. Evidence has also been found for intermuscular, intramuscular, and sex-specific intramuscular differences of fascicle curving. Pennation angle and the inverse fascicle length show the highest predictive capacities for fascicle curving. Due to the strong correlations between pennation angle and fascicle curvature and the intramuscular pattern of curving we suggest for future studies to examine correlations between fascicle curvature and intramuscular fluid pressure.
KW  - biomechanics
KW  - connective tissue
KW  - physiology
KW  - ultrasound
Y1  - 2023
U6  - http://dx.doi.org/10.14814/phy2.15739
SN  - 2051-817X
VL  - 11
IS  - 11
SP  - e15739, Seite 1-11
PB  - Wiley
ER  - 
TY  - JOUR
A1  - Waldvogel, Janice
A1  - Freyler, Kathrin
A1  - Helm, Michael
A1  - Monti, Elena
A1  - Stäudle, Benjamin
A1  - Gollhofer, Albert
A1  - Narici, Marco V.
A1  - Ritzmann, Ramona
A1  - Albracht, Kirsten
T1  - Changes in gravity affect neuromuscular control, biomechanics, and muscle-tendon mechanics in energy storage and dissipation tasks
JF  - Journal of Applied Physiology
N2  - This study evaluates neuromechanical control and muscle-tendon interaction during energy storage and dissipation tasks in hypergravity. During parabolic flights, while 17 subjects performed drop jumps (DJs) and drop landings (DLs), electromyography (EMG) of the lower limb muscles was combined with in vivo fascicle dynamics of the gastrocnemius medialis, two-dimensional (2D) kinematics, and kinetics to measure and analyze changes in energy management. Comparisons were made between movement modalities executed in hypergravity (1.8 G) and gravity on ground (1 G). In 1.8 G, ankle dorsiflexion, knee joint flexion, and vertical center of mass (COM) displacement are lower in DJs than in DLs; within each movement modality, joint flexion amplitudes and COM displacement demonstrate higher values in 1.8 G than in 1 G. Concomitantly, negative peak ankle joint power, vertical ground reaction forces, and leg stiffness are similar between both movement modalities (1.8 G). In DJs, EMG activity in 1.8 G is lower during the COM deceleration phase than in 1 G, thus impairing quasi-isometric fascicle behavior. In DLs, EMG activity before and during the COM deceleration phase is higher, and fascicles are stretched less in 1.8 G than in 1 G. Compared with the situation in 1 G, highly task-specific neuromuscular activity is diminished in 1.8 G, resulting in fascicle lengthening in both movement modalities. Specifically, in DJs, a high magnitude of neuromuscular activity is impaired, resulting in altered energy storage. In contrast, in DLs, linear stiffening of the system due to higher neuromuscular activity combined with lower fascicle stretch enhances the buffering function of the tendon, and thus the capacity to safely dissipate energy.
KW  - electromyography
KW  - locomotion
KW  - overload
KW  - stretch-shortening cycle
KW  - ultrasound
Y1  - 2023
U6  - http://dx.doi.org/10.1152/japplphysiol.00279.2022
SN  - 1522-1601 (Onlineausgabe)
SN  - 8750-7587 (Druckausgabe)
VL  - 134
IS  - 1
SP  - 190
EP  - 202
PB  - American Physiological Society
CY  - Bethesda, Md.
ER  -