During daily life activities, muscles and tendons interact to satisfy the mechanical demands imposed by the task. While skeletal muscles power movements, tendons stretch and store elastic strain energy when force is applied to them, and recoil to release energy when force decays. Although this elastic action is simple, it serves a diverse set of functions, including metabolic energy conservation, amplification and attenuation of muscle power input, affecting the mechanical and metabolic demands of the entire muscle-tendon unit. In recent years, our understanding of the mechanisms and importance of the interaction between muscles and tendons in healthy, trained, and pathological populations has advanced significantly, highlighting potential mechanisms that could explain the loss of function in different conditions. In this symposium, an international perspective will be presented by researchers from Italy (Dr Monte), Germany (Dr Bohm), and Belgium (Dr Vanwanseele) with the aims of (1) providing a clear introduction to the biomechanics and energetics of human locomotion; (2) revealing how muscles and tendons interact during human movements (e.g., walking and running); (3) describing the contribution of muscles and tendons in determining the metabolic and mechanical demands of human locomotion; and (4) examining their effects on perturbated tasks (e.g., loss of balance) and special situations (e.g., pathological populations).
ECSS Paris 2023: IS-BM01
Over the last decades, human walking has been considered an inverted pendulum where the potential and kinetic energies of the body center of mass are out of phase and continuously exchange, reducing the total mechanical energy oscillations over a stride. On the other side, from an energetic point of view, the metabolic energy expended to cover one-unit distance as a function of speed was empirically described by a quadratic (U-shape) function that shows a minimum at a speed of about 4-5 km.h-1, often called the “optimal walking speed”. Thanks to this whole-body approach, it was possible to describe the salient characteristics of human walking in healthy and pathological situations. Therefore, the first aim of this study is to provide a comprehensive description of human walking at the whole-body level. Along this line of reasoning, within the last years, several researchers have tried to explain the changes in metabolic and mechanical demands of walking from muscle and tendon perspectives in order to discover new training strategies and therapies to counteract the loss of function imposed by several conditions. In this regard, using a combination of ultrasound, EMG, kinematic and dynamometric measurements, we observed that changes in muscle fascicle behaviour imposed by an increase in walking speed could partially explain the changes in the metabolic cost as well as the transition between walking and running; while this was not the case for the behaviour of the elastic tissues. Hence, the second aim of this presentation is to report the influences of muscle and tendon behaviour in determining the energetics and mechanics of walking as a function of speed, in order to understand how their modification could affect the biomechanics of walking in pathological situations. Finally, I will report new data from experimental studies, in which the behaviour of plantar flexor muscle fascicles and the Achilles tendon have been investigated during walking at different speeds in people with type 2 diabetes, pre and post ten weeks of stretching training program. Our preliminary data showed that the increases in energy cost of walking, typically observed in people with type 2 diabetes, could be partially counteracted by using a simple stretching training protocol. In this regard, stretching was able to modify the stiffness of the Achilles tendon, leading the muscle fascicles to operate in a more favourable portion of the F-L and F-V curves, finally reducing the energy cost of walking. In the last part of this talk, final remarks and future directions will be provided and discussed.
Read CV Andrea MonteECSS Paris 2023: IS-BM01
Over the last decades it has become more and more recognized that running has played a major role in human evolution. Compared to other (quadrupedal) animals, humans are very average sprinters, but we perform surprisingly well at endurance running. Nowadays running is among the most popular physical activities worldwide, primarily because its accessibility and association with health benefits. Watching runners passing by, there are substantial differences in how individuals run. Despite the large body of running research, research into the underlying mechanisms explaining the variability in running patterns is very limited. A commonly used and widely accepted hypothesis to explain why humans move the way they do is that we optimize performance (e.g. minimize certain neuromuscular cost function while performing the movement). There is scientific evidence that humans seem to be able to self-optimize their running pattern, as they adopt a specific running gait, e.g. stride frequency, stride width, foot strike pattern, associated with minimal energy consumption. Hence, energy minimization is often assumed to be one of the major neuromuscular mechanisms underlying the preferred running pattern. However, why a certain running pattern requires less energy, and is thus more optimal, than another for a specific runner is still an open question. Skeletal muscles are the tissues consuming the majority of energy during running. Hence, explaining the metabolic cost of running from a muscular perspective is an important next step to enhance our insights on the metabolic cost of running. However, the metabolic cost of the muscles during running cannot be measured directly. We therefore need to use a combination of experimental and simulation approaches combining motion capture, EMG, ultrasound with musculoskeletal modelling and muscle metabolic cost models. I will first explain how we modified existing musculoskeletal models to represent better experimental measures. Then, I will present the results from several studies using this approach to investigate how triceps surae muscle-tendon interactions affect whole-body and muscle metabolic rate during preferred and adjusted running patterns. I will present data on the effect of changes of speed, stride frequency and foot strike pattern on triceps surae fascicle length, length changes and simulated metabolic energy. Increasing the running speed increased triceps surae metabolic cost through an increase in muscle forces and changes in muscle-tendon interaction. While changing foot strike pattern had the opposite effect on the muscle forces and muscle fascicle length changes, resulting in no differences in muscle metabolic energy and whole-body metabolic energy. Lastly, I will present the results on how stride frequency influences muscle fascicle behavior and how changes in whole-body metabolic energy consumption can be explained by a combination of muscle fascicle behavior and muscle activation.
Read CV Benedicte VanwanseeleECSS Paris 2023: IS-BM01
Human locomotion covers a broad range of speeds and is driven by the generated forces of the lower limb muscles. To sustain submaximal running for a longer period of time, economical muscle force generation and efficient muscle work production may optimize the metabolic cost. However, when increasing speed to the maximum, high mechanical power production is needed at the expense of metabolic energy cost. Moreover, real-world environments rarely allow for stable and constant locomotion. Most often, the locomotor behavior faces unsteadiness and external environmental perturbations that challenge the neuromuscular system to generate compensatory muscle forces for the maintenance of the stability of the body. A muscle’s mechanical output is dictated by its operating contractile conditions, particularly the fascicle length and velocity during the movement with respect to the intrinsic force-length, force-velocity, power-velocity and efficiency-velocity relationships. The decoupling of the muscle fascicle length changes from the muscle-tendon unit due to the compliance of the attached tendon and the fascicle rotation (changes in pennation angle) provides regulatory mechanisms of the operating muscle length and velocity. Furthermore, previous in vitro and in situ evidence suggest that the force-length relationship depends on the activation level, i.e. optimal length for force generation shifts towards longer length at decreasing activation levels. This activation dependence reasonably influences the force generation during movements with variable activation pattern. The talk will present current experimental findings on the contractile conditions and activation of the soleus, as the main muscle for propulsion, during steady and perturbed locomotion. We found that during submaximal running, the soleus fascicles shorten close to optimal length and at a velocity close to the efficiency-maximum, two contractile conditions for economical work production. At high and maximum running speeds, the fascicles still operate near optimum length, yet the fascicle shortening velocity increase and shift towards the optimum for mechanical power production with a simultaneous increase in muscle activation, indicating three cumulative mechanisms to enhance mechanical power production. Furthermore, our preliminary results show how the contractile conditions and activation of the soleus muscle contribute to compensatory muscle force generation in response to a walking perturbation induced by an unpredictable drop in surface height. Particular attention will be given to the regulatory effect of the fascicle decoupling by tendon compliance and fascicle rotation as well as to the influence of the activation dependence of optimal length on the soleus muscle contractile conditions during the different running speeds and stability recovery response.
Read CV Sebastian BohmECSS Paris 2023: IS-BM01