Amelie Werkhausen

• Werkhausen, Amelie; Lund-Hansen, Magne; Wiedenbruch, Lucas; Peikenkamp, Klaus & Rice, Hannah (2024). Technologically advanced running shoes reduce oxygen cost and cumulative tibial loading per kilometer in recreational female and male runners. Scientific Reports. ISSN 2045-2322. 14(1). doi: 10.1038/s41598-024-62263-0.
• Rice, Hannah; Seynnes, Olivier R. & Werkhausen, Amelie (2023). Effect of increased running speed and weight carriage on peak and cumulative tibial loading. Scandinavian Journal of Medicine & Science in Sports. ISSN 0905-7188. doi: 10.1111/sms.14476. Vis sammendrag

  Introduction: Tibial stress injuries are a burdensome injury among military recruits. Military activities include running and the carriage of additional weight, and this may be related to the high risk of bone stress injuries. The aim of this study was to quantify tibial loading when running at two different speeds, with and without additional weight, and to quantify their combined influence. Methods: Fourteen male distance runners who ran at least 40 km per week ran barefoot on a force-instrumented treadmill in four conditions representing preferred running speed (mean (SD) 3.1 (0.3) m/s) and 20% increased running speed (3.8 (0.4) m/s), with and without 20% of body weight carried in a weight vest. Kinematics and kinetics were synchronously collected. Bending moments were estimated about the medial-lateral axis of the tibial centroid located 1/3rd of the length from distal to proximal. Static equilibrium was ensured at each 1% of stance. Peak bending moments were obtained in addition to cumulative-weighted loading, where weighted loading accounted for the relative importance of the magnitude of the bending moment and the quantity of loading using a bone-dependent weighting factor. Results: There were no interaction effects for running speed and weight carriage on peak or cumulative tibial loading. Running at a 20% faster speed increased peak and cumulative loading per kilometer by 8.0% (p < 0.001) and 4.8% (p < 0.001), respectively. Carriage of an additional 20% of body weight increased peak and cumulative loading per kilometer by 6.6% (p < 0.001) and 8.5% (p < 0.001), respectively. Interpretation: Increasing the physical demand of running by increasing speed or weight carriage increased peak tibial loading and cumulative tibial loading per kilometer, and this may increase the risk of tibial stress injury. Running speed and weight carriage independently influenced tibial loading.

• Werkhausen, Amelie; Lundervold, Anders & Gløersen, Øyvind (2023). Muscle function during cross-country skiing at different speed and incline conditions. Journal of Experimental Biology. ISSN 0022-0949. 226(12), s. 1–8. doi: 10.1242/jeb.245474. Fulltekst i vitenarkiv
• Werkhausen, Amelie; Gløersen, Øyvind; Nordez, Antoine; Paulsen, Gøran; Bojsen-Møller, Jens & Seynnes, Olivier R. (2023). Linking muscle architecture and function in vivo: conceptual or methodological limitations? PeerJ. ISSN 2167-8359. 11. doi: 10.7717/peerj.15194. Fulltekst i vitenarkiv Vis sammendrag

  Background Despite the clear theoretical link between sarcomere arrangement and force production, the relationship between muscle architecture and function remain ambiguous in vivo. Methods: We used two frequently used ultrasound-based approaches to assess the relationships between vastus lateralis architecture parameters obtained in three common conditions of muscle lengths and contractile states, and the mechanical output of the muscle in twenty-one healthy subjects. The relationship between outcomes obtained in different conditions were also examined. Muscle architecture was analysed in panoramic ultrasound scans at rest with the knee fully extended and in regular scans at an angle close to maximum force (60°), at rest and under maximum contraction. Isokinetic and isometric strength tests were used to estimate muscle force production at various fascicle velocities. Results: Measurements of fascicle length, pennation angle and thickness obtained under different experimental conditions correlated moderately with each other (r = 0.40−.74). Fascicle length measured at 60° at rest correlated with force during high-velocity knee extension (r = 0.46 at 400° s−1) and joint work during isokinetic knee extension (r = 0.44 at 200° s−1 and r = 0.57 at 100° s−1). Muscle thickness was related to maximum force for all measurement methods (r = 0.44–0.73). However, we found no significant correlations between fascicle length or pennation angle and any measures of muscle force or work. Most correlations between architecture and force were stronger when architecture was measured at rest close to optimal length. Conclusion: These findings reflect methodological limitations of current approaches to measure fascicle length and pennation angle in vivo. They also highlight the limited value of static architecture measurements when reported in isolation or without direct experimental context.

• Werkhausen, Amelie; Gløersen, Øyvind Nøstdahl; Nordez, Antoine; Paulsen, Gøran; Bojsen-Møller, Jens & Seynnes, Olivier R. (2022). Rate of force development relationships to muscle architecture and contractile behavior in the human vastus lateralis. Scientific Reports. ISSN 2045-2322. 12(1). doi: 10.1038/s41598-022-26379-5. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Werkhausen, Amelie; Solberg, Christian E.; Paulsen, Gøran; Bojsen-Møller, Jens & Seynnes, Olivier R. (2021). Adaptations to explosive resistance training with partial range of motion are not inferior to full range of motion. Scandinavian Journal of Medicine & Science in Sports. ISSN 0905-7188. 31(5), s. 1026–1035. doi: 10.1111/sms.13921. Vis sammendrag

  We tested whether explosive resistance training with partial range of motion (ROM) would be as effective as full ROM training using a noninferiority trial design. Fifteen subjects with strength training experience took part in an explosive—concentric only—leg press training program, three times per week for 10 weeks. One leg was randomly assigned to exercise with partial ROM (ie, 9º) and the other leg to full ROM. Before and after training, we assessed leg press performance, isokinetic concentric and isometric knee extension torque, and vastus lateralis muscle architecture. Overall, both training modalities increased maximal strength and rate of force development. Training with partial ROM yielded noninferior results compared to full ROM for leg press peak power (+69 ± 47% vs. +61 ± 64%), isokinetic strength (4-6 ± 6%-12% vs. 1-6 ± 6%-10% at 30, 60, and 180˚s-1), and explosive torque after 100 (47 ± 24 vs. 35 ± 22) and 150 ms (57 ± 22% vs. 42 ± 25%). The comparison was inconclusive for other functional parameters (ie, isokinetic peak torque (300˚s−1), joint angle at isokinetic peak torque, explosive torque after 50 ms, and electrically evoked torque) and for muscle fascicle length and thickness, although noninferiority was established for pennation angle. However, partial ROM was not found statistically inferior to full ROM for any measured variable. Under the present conditions, the effects of explosive heavy resistance training were independent of joint ROM. Instead, these data suggest that the distinct timing of muscle work in explosive contractions confers more influence to the starting joint angle than ROM on adaptations to this type of training.

• Mausehund, Lasse; Werkhausen, Amelie; Bartsch, Julia & Krosshaug, Tron (2021). Understanding Bench Press Biomechanics-The Necessity of Measuring Lateral Barbell Forces. Journal of Strength and Conditioning Research. ISSN 1064-8011. 36(10), s. 2685–2695. doi: 10.1519/JSC.0000000000003948. Vis sammendrag

  The purpose of this study was to advance the expertise of the bench press exercise by complementing electromyographic (EMG) with net joint moment (NJM) and strength normalized NJM (nNJM) measurements, thus establishing the magnitude of the elbow and shoulder muscular loads and efforts. Normalized NJMs were determined as the ratio of the bench press NJMs to the maximum NJMs produced during maximum voluntary isokinetic contractions. Furthermore, we wanted to assess how changes in grip width and elbow positioning affected elbow and shoulder NJMs and nNJMs, and muscle activity of the primary movers. Thirty-five strength-trained adults performed a 6–8 repetition maximum set of each bench press variation, while elbow and shoulder NJMs and EMG activity of 7 upper extremity muscles were recorded. The results show that all bench press variations achieved high elbow and shoulder muscular efforts. A decrease in grip width induced larger elbow NJMs, and larger EMG activity of the lateral head of the triceps brachii, anterior deltoid, and clavicular head of the pectoralis major (p ≤ 0.05). An increase in grip width elicited larger shoulder NJMs and nNJMs, and larger EMG activity of the abdominal head of the pectoralis major (p ≤ 0.05). In conclusion, all bench press variations may stimulate strength gains and hypertrophy of the elbow extensors and shoulder flexors and horizontal adductors. However, greater adaptations of the elbow extensors and shoulder flexors may be expected when selecting narrower grip widths, whereas wider grip widths may induce greater adaptations of the shoulder horizontal adductors.

• Werkhausen, Amelie; Willwacher, Steffen & Albracht, Kirsten (2021). Medial gastrocnemius muscle fascicles shorten throughout stance during sprint acceleration. Scandinavian Journal of Medicine & Science in Sports. ISSN 0905-7188. 31(7), s. 1471–1480. doi: 10.1111/sms.13956. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Kirkebø, Jan Egil; Werkhausen, Amelie; Seynnes, Olivier R. & Austeng, Andreas (2020). Automated Characterization of Muscle Architectural Variation in Ultrasound Images. Proceedings - IEEE Ultrasonics Symposium. ISSN 1948-5719. doi: 10.1109/IUS46767.2020.9251536. Fulltekst i vitenarkiv Vis sammendrag

  Fascicle (fiber bundle) orientation and length are useful parameters to infer the force potential of skeletal muscles. Ultrasound imaging is commonly used to determine fascicle characteristics. In most of the literature, automated methods simplify analysis by assimilating fascicles and aponeuroses (connective tissue on which fascicles are anchored) to straight lines that are homogeneously arranged along the muscle length. In practice, manual adjustments are often needed to the realizations of the proposed automated methods due to the low signal-to-noise ratio of the images. We propose a fully automated and robust method that determines non-linear aponeuroses and fascicles over entire panoramic images, reflecting the real structure of the muscle and its fibers.

• Werkhausen, Amelie Corinna; Cronin, Neil J; Albracht, Kirsten; Paulsen, Gøran; Larsen, Askild V. & Bojsen-Møller, Jens [Vis alle 7 forfattere av denne artikkelen] (2019). Training-induced increase in Achilles tendon stiffness affects tendon strain pattern during running. PeerJ. ISSN 2167-8359. 2019(4). doi: 10.7717/peerj.6764. Fulltekst i vitenarkiv Vis sammendrag

  Background: During the stance phase of running, the elasticity of the Achilles tendon enables the utilisation of elastic energy and allows beneficial contractile conditions for the triceps surae muscles. However, the effect of changes in tendon mechanical properties induced by chronic loading is still poorly understood. We tested the hypothesis that a training-induced increase in Achilles tendon stiffness would result in reduced tendon strain during the stance phase of running, which would reduce fascicle strains in the triceps surae muscles, particularly in the mono-articular soleus. Methods: Eleven subjects were assigned to a training group performing isometric single-leg plantarflexion contractions three times per week for ten weeks, and another ten subjects formed a control group. Before and after the training period, Achilles tendon stiffness was estimated, and muscle-tendon mechanics were assessed during running at preferred speed using ultrasonography, kinematics and kinetics. Results: Achilles tendon stiffness increased by 18% (P < 0.01) in the training group, but the associated reduction in strain seen during isometric contractions was not statistically significant. Tendon elongation during the stance phase of running was similar after training, but tendon recoil was reduced by 30% (P < 0.01), while estimated tendon force remained unchanged. Neither gastrocnemius medialis nor soleus fascicle shortening during stance was affected by training. Discussion: These results show that a training-induced increase in Achilles tendon stiffness altered tendon behaviour during running. Despite training-induced changes in tendon mechanical properties and recoil behaviour, the data suggest that fascicle shortening patterns were preserved for the running speed that we examined. The asymmetrical changes in tendon strain patterns supports the notion that simple in-series models do not fully explain the mechanical output of the muscle-tendon unit during a complex task like running.

• Werkhausen, Amelie Corinna; Cronin, Neil J; Albracht, Kirsten; Bojsen-Møller, Jens & Seynnes, Olivier R. (2019). Distinct muscle-tendon interaction during running at different speeds and in different loading conditions. Journal of applied physiology. ISSN 8750-7587. 127(1), s. 246–253. doi: 10.1152/japplphysiol.00710.2018. Fulltekst i vitenarkiv
• Werkhausen, Amelie Corinna; Albracht, Kirsten; Cronin, Neil J; Paulsen, Gøran; Bojsen-Møller, Jens & Seynnes, Olivier R. (2018). Effect of training-induced changes in Achilles tendon stiffness on muscle-tendon behavior during landing. Frontiers in Physiology. ISSN 1664-042X. 9. doi: 10.3389/fphys.2018.00794. Vis sammendrag

  During rapid deceleration of the body, tendons buffer part of the elongation of the muscle–tendon unit (MTU), enabling safe energy dissipation via eccentric muscle contraction. Yet, the influence of changes in tendon stiffness within the physiological range upon these lengthening contractions is unknown. This study aimed to examine the effect of training-induced stiffening of the Achilles tendon on triceps surae muscle–tendon behavior during a landing task. Twenty-one male subjects were assigned to either a 10-week resistance-training program consisting of single-leg isometric plantarflexion (n = 11) or to a non-training control group (n = 10). Before and after the training period, plantarflexion force, peak Achilles tendon strain and stiffness were measured during isometric contractions, using a combination of dynamometry, ultrasound and kinematics data. Additionally, testing included a step-landing task, during which joint mechanics and lengths of gastrocnemius and soleus fascicles, Achilles tendon, and MTU were determined using synchronized ultrasound, kinematics and kinetics data collection. After training, plantarflexion strength and Achilles tendon stiffness increased (15 and 18%, respectively), and tendon strain during landing remained similar. Likewise, lengthening and negative work produced by the gastrocnemius MTU did not change detectably. However, in the training group, gastrocnemius fascicle length was offset (8%) to a longer length at touch down and, surprisingly, fascicle lengthening and velocity were reduced by 27 and 21%, respectively. These changes were not observed for soleus fascicles when accounting for variation in task execution between tests. These results indicate that a training-induced increase in tendon stiffness does not noticeably affect the buffering action of the tendon when the MTU is rapidly stretched. Reductions in gastrocnemius fascicle lengthening and lengthening velocity during landing occurred independently from tendon strain. Future studies are required to provide insight into the mechanisms underpinning these observations and their influence on energy dissipation.

• Werkhausen, Amelie Corinna; Albracht, Kirsten; Cronin, N.J.; Meier, Rahel; Bojsen-Møller, Jens & Seynnes, Olivier R. (2017). Modulation of muscle-tendon interaction in the human triceps surae during an energy dissipation task. Journal of Experimental Biology. ISSN 0022-0949. 220(22), s. 4141–4149. doi: 10.1242/jeb.164111. Vis sammendrag

  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 3D 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, while plantarflexor muscles were activated. Combined elastic elements lengthened until peak ankle moment and recoiled thereafter, whilst 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.

• Ritzmann, Ramona; Freyler, Kathrin; Werkhausen, Amelie Corinna & Gollhofer, Albert (2016). Changes in Balance Strategy and Neuromuscular Control during a Fatiguing Balance Task — A Study in Perturbed Unilateral Stance. Frontiers in Human Neuroscience. ISSN 1662-5161. 10. doi: 10.3389/fnhum.2016.00289. Vis sammendrag

  Fatigue impairs sensorimotor performance, reduces spinal reflexes and affects the interaction of antagonistic muscles in complex motor tasks. Although there is literature dealing with the interference of fatigue and postural control, the interpretation is confounded by the variety of paradigms used to study it. This study aimed to evaluate the effects of postural fatigue on balance control and strategy, as well as on neuromuscular modulation, in response to postural perturbation (PERT) during a fatiguing balance task. A fatigue protocol consisting of continuous exposure to perturbations until exhaustion was executed in 24 subjects. Number of failed attempts, paths of center of pressure displacement (COP), ankle, knee, and hip joint kinematics, electromyographic activity of the soleus (SOL), tibialis anterior (TA), rectus femoris (RF), vastus lateralis (VL), biceps femoris (BF), and gluteus maximus muscles (GM) and spinal excitability of SOL at the peak of the short-latency responses (SLR) were recorded after posterior PERT. The co-contraction index (CCI) was calculated for TA_SOL, VL_BF and RF_GM. (1) The number of failed attempts significantly increased while COP amplitude and velocity, as well as angular excursion at the ankle, knee and hip joints, decreased with fatigue (P < 0.05). (2) Concomitantly, CCI of SOL_TA, VL_BF and RF_GM increased and spinal excitability in SOL declined. (3) Adaptations progressively augmented with progressing exhaustion and occurred in the distal prior to proximal segment. Distinctly deteriorated balance ability was accompanied by a modified neuromuscular control—the increase in co-contraction reflected by simultaneously activated antagonists is accompanied by smaller knee and hip joint excursions, indicating an elevated level of articular stiffness. These changes may be associated with an exaggerated postural rigidity and could have caused the delayed and reduced postural reactions that are reflected in the changes in COP displacement when compensating for sudden PERT. The reduction in spinal excitability may either be caused by fatigue itself or by an increase in reciprocal inhibition due to augmented TA activity.

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• Werkhausen, Amelie; Lundervold, Anders & Gløersen, Øyvind (2023). Gastrocnemius Muscle Fascicle Behaviour during Diagonal Stride Skiing.

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