Whether the aim is to jump higher, sprint faster, or avoid falling, explosive performance is key. Seminal studies have unravelled mechanisms that determine such capacity. However, within this framework, much remains to be discovered. With this Symposium three approaches that can provide new insights into the neuromechanics of explosive performance are presented. The first approach is looking at elite athletes in nature. In the animal kingdom there are high performers, that make outstanding explosive movements not for pride or profession, but for survival. The study of such evolutionary solutions can help us better understand the determinants and limits of improvement of human explosive performance, on and off the field. The second approach includes the powerful effect of increased input from the reticular formation and reticulospinal pathway to enhance explosive force production, alongside with modelling and the study of chronically trained (strength vs. endurance) populations. The third approach regards the integration of space physiology. The effect of different gravities on the coupling of eccentric and concentric muscle actions to produce an explosive rebound will be examined, along with the muscle mechanical and energetic consequences. Enhancing the potential for explosive performance is a fundamental but not easy task. The more lenses are added to our conceptual framework, the greater are the chances to find solutions for improvement.
ECSS Paris 2023: IS-BM02
Explosiveness is the ability to develop the greatest amount of force in the minimum time. This quality is key in the context of sport performance or physical activity, should the aim be to jump higher or sprint faster than competitors, to recover performance after an injury, or to avoid functional loss as consequence of immobilization, muscle disuse, or aging. To understand what makes people accelerate or decelerate faster, the spotlight is often on high-performance athletes, due to their amazing physical capabilities and resiliency. Sometimes however we overlook examples of explosive high-performance in Nature, a parallel world where Humans can learn from. In such cases, it is not about winning a medal, rather about predation and escape. Still, stakes are very high. In this presentation I will unravel the mechanisms of some of the most astonishing explosive performances in Nature, relating them to Humans, and to the lessons that we can learn out of it for the improvement of our rapid force production capacity. First, I will represent where the explosive capabilities of Human athletes stand in relation to other animals. As it can be guessed, we are not the strongest, but neither the weakest. I will then use the case of standing jumps as a model of explosive force from a static starting condition. To jump as high as possible, evolution has developed two main (divergent) mechanisms: the spring- (or latch-) and the muscle-mediated actuation. What if Humans jumped with a spring-actuated mechanism? And what if they did with a muscle-actuated mechanism? What do explosive force and jump height depend on in the two modes of actuation? And what are the drawbacks of using each mode? Such hypotheses and comparisons can shed light on the determinants of human explosive performance. Finally, I will present an example of a more dynamic situation in Nature to show how Biology can directly help sport-related outcomes. This example regards two seemingly different but congruent mechanisms in explosive performance: the predator-prey interaction in the wild and the change of direction in sport. As sport scientists and practitioners, typically we are not biologists. However, both animal- and sport-related movements are based on biological (common) principles. Some animals have exploited these principles to be high performers in their own habitat. Thus, interacting with Biology, while on one side may not provide in the short-term a performance-enhancing winning solution, may provide a framework to better understand the determinants of Human performance.
Read CV Luca RuggieroECSS Paris 2023: IS-BM02
The motor units, comprised of the alpha motoneuron and all the muscle fibres it innervates, are the most basic elements of the neuromuscular system that transduce the summated synaptic inputs into twitches of individual muscle fibres. The key determinants of rate of force development are motor unit recruitment speed and discharge rate of the recruited motor units. The deterministic role of motor unit discharge rate characteristics in rate of force development underscores the importance of the properties of, and the synaptic input received by the motor pool in rapid force production. In the first part of this talk, I will first show computational and experimental evidence supporting the hypothesis that motor pool characteristics are directly implicated in the rate of force development of a given muscle. Specifically, I will demonstrate that the upper limit of motor unit recruitment in a given motor pool is linked to recruitment speed of motor units, and consequently, the rate of force development. In the second part of the talk, I will explore the neural substrate(s) underpinning the fast recruitment speed and high discharge rate of motor units underpinning rapid force production. I will introduce the importance of excitatory ionotropic inputs to motoneurons from the reticular formation in the brainstem, with experimental evidence suggesting the importance of augmenting the excitatory input to motoneurons via reticulospinal pathway to increase rate of force development and strength. Lastly, I will focus on the interaction of motor unit discharge characteristics and motor unit twitch properties when generating maximal rate of force development using a model of chronically resistance-trained and endurance-trained individuals that confer different adaptations to the neural and muscular system.
Read CV Jakob ŠkarabotECSS Paris 2023: IS-BM02
Explosive movements such as sprinting and jumping require a finely tuned coupling of eccentric and concentric muscle actions. It is known that stretch-shortening cycle (SSC) type actions require a well-tuned and pre-activated muscle-tendon unit (MTU), a short eccentric phase, and an immediate coupling of eccentric and concentric phases to develop high forces in a limited amount of time, to enhance reactive jump performance and to maximize energy storage and release. For meeting such criteria a perfectly coordinated interplay between the central nervous system (CNS) and the MTU is mandatory. The CNS regulates the MTU’s stiffness by modulating the muscle activity prior and during ground contact, and such regulation is phase-, task- and stretch load-dependent. Previous experiments have predominantly used biomechanical methods such as electromyographic recordings, kinematics and kinetics to investigate the underlying mechanisms of SSC type actions. Technological advances such as ultrasound technique revealed direct insights into the muscle function and muscle-tendon interaction during dynamics. Furthermore, in many sports, as well as during human locomotion, requirements and environmental conditions are not necessarily constant and may change even rapidly. To functionally understand how the CNS and the MTU interaction are challenged by variable conditions, this presentation provides an overview of past and current studies investigating the effect of variable stretch load on the neuromuscular control and MTU interaction during reactive explosive movements. In such studies, the effect of variable stretch loads are limited to loading and unloading scenarios of +/- 20-30% of body weight. Stretch loads beyond these limits are normally experimentally challenging and associated with confounding effects. In contrast, parabolic flights are a unique paradigm to induce stretch loads ranging from 0.1 to 2g (-90% to +100% body weight), allowing near-natural movement execution. This presentation also provides an overview of existing parabolic flight experiments which aimed to investigate stretch load dependent modulations at the neuromuscular and muscle mechanical level. Furthermore, biomechanical and energetic consequences will be highlighted. Given the implications of overloading and unloading in weight and velocity-based trainings to enhance explosive force production, this presentation is of high scientific interest for sport scientists, coaches, athletes, as well as other practitioners. Findings from parabolic flight campaigns regarding rapid force production in overloading and unloading conditions may also inform other practitioners such as engineers in the interface with sport science.
Read CV Janice WaldvogelECSS Paris 2023: IS-BM02