TY  - JOUR
A1  - Werkhausen, Amelie
A1  - Willwacher, Steffen
A1  - Albracht, Kirsten
T1  - Medial gastrocnemius muscle fascicles shorten throughout stance during sprint acceleration
JF  - Scandinavian Journal of Medicine & Science in Sports
N2  - The compliant nature of distal limb muscle-tendon units is traditionally considered suboptimal in explosive movements when positive joint work is required. However, during accelerative running, ankle joint net mechanical work is positive. Therefore, this study aims to investigate how plantar flexor muscle-tendon behavior is modulated during fast accelerations. Eleven female sprinters performed maximum sprint accelerations from starting blocks, while gastrocnemius muscle fascicle lengths were estimated using ultrasonography. We combined motion analysis and ground reaction force measurements to assess lower limb joint kinematics and kinetics, and to estimate gastrocnemius muscle-tendon unit length during the first two acceleration steps. Outcome variables were resampled to the stance phase and averaged across three to five trials. Relevant scalars were extracted and analyzed using one-sample and two-sample t-tests, and vector trajectories were compared using statistical parametric mapping. We found that an uncoupling of muscle fascicle behavior from muscle-tendon unit behavior is effectively used to produce net positive mechanical work at the joint during maximum sprint acceleration. Muscle fascicles shortened throughout the first and second steps, while shortening occurred earlier during the first step, where negative joint work was lower compared with the second step. Elastic strain energy may be stored during dorsiflexion after touchdown since fascicles did not lengthen at the same time to dissipate energy. Thus, net positive work generation is accommodated by the reuse of elastic strain energy along with positive gastrocnemius fascicle work. Our results show a mechanism of how muscles with high in-series compliance can contribute to net positive joint work.
KW  - locomotion
KW  - muscle mechanics
KW  - running
KW  - sprint start
KW  - ultrasonography
Y1  - 2021
U6  - http://dx.doi.org/10.1111/sms.13956
SN  - 0905-7188 (Druckausgabe)
SN  - 1600-0838 (Onlineausgabe)
VL  - 31
IS  - 7
SP  - 1471
EP  - 1480
PB  - Wiley-Blackwell
CY  - Oxford
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  -