Scientific Programme
Biomechanics & Motor control
IS-BM01 - Muscle-tendon interactions: Performance and injury
Date: 08.07.2026, Time: 15:00 - 16:15, Session Room: SG 1138 (EPFL)
Description
Human movement results from a complex chain of events triggered by supraspinal signals that generate muscle forces exerted on bones, producing segment rotations. Ultrafast ultrasound imaging has made movements of the muscle-tendon machinery that produce and transmit forces an observable phenomenon. Its use has revealed that tendinous tissues uncouple muscle and whole muscle-tendon unit length changes during various locomotor tasks and muscle contractions. This differentiated behavior modulates the strain sustained by contractile versus passive tissues, influencing mechanical output and functional consequences of various motor tasks on muscle and tendon. Extensive research has explored how muscle-tendon interactions influence athletic performance, showing that muscle and tendon properties are highly sensitive to fatigue, training, aging and pathologies, raising the question of what extent muscle-tendon interactions adapt to such contexts and interventions. This symposium presents the latest data (i) muscle-tendon interactions during various motor tasks from signal-joint contractions to complex movements and how muscle-tendon properties influence athletic performance; (ii) the role of muscle fascicles and tendinous tissues in muscle damage amplitude and injury exposure risk in vivo; and (iii) how interventions such as thermal stress may alter muscle-tendon adaptations for recovery and health purposes.
Chair(s)
Gael Guilhem
French Institute of Sport (INSEP), Laboratory Sport, Expertise and Performance
France
Speaker A
Anthony Blazevich
Edith Cowan University, School of Exercise and Health Sciences
Australia
Read CVECSS Lausanne 2026: IS-BM01 [7403]
How muscles and tendons behave, and why it matters for physical function and injury risk
Muscles are the motors that power our daily movements, including in exercise and sporting arenas. However, muscles have unique architectural designs that influence their function during contraction, and determine whether they change length (i.e., do work) substantially. Generally, muscles located proximally in the body have relatively large volumes and long fibers, sometimes with significant fiber angulation (pennation). When they operate, the fibers both shorten and rotate, ensuring the muscle produces a force over a relatively large movement range. The work done is used to give energy to our limbs and whole body to propel us. Alternatively, negative work can be done during lengthening (eccentric contractions), with energy absorbed and ultimately dissipated. Because muscles must operate under a wide range of force, velocity, and movement range conditions, individual muscles may vary in the relative degree of fiber length change versus rotation: when either the initial pennation angles or degree of fiber rotation are greater, muscle length change and velocity exceed fiber length change and velocity, and the muscle works at a gear ratio (muscle-to-fiber length change ratio) greater than 1.0. Importantly, gear can change as contraction conditions change – muscles ‘change gear’ – influencing muscle function and thus movement performance, at least when muscles function well. A first aim of this presentation is to describe the process of muscle gearing and then discuss what we do and do not know about the muscle design factors influencing it, and the effects of muscle fatigue, aging and disability. Muscles located distally in the limbs tend to have relatively smaller volumes (and thus mass) and shorter fibers. Their work capacity is therefore lower than in proximal muscles, although exceptions exist (e.g. soleus), and they tend to operate in series with long compliant tendons (e.g. Achilles or finger-wrist flexor or extensor tendons). The ability for tendons to stretch to store energy and subsequently recoil to release it improves both muscle power and economy, and is thus a critical factor influencing physical performance. Nonetheless, the often long connective border between the muscle fibers and tendon, or the tendon’s long aponeurotic inscription into the muscle, provides a surface at which muscle-tendon injury risk is typically high. How muscles and tendons cooperate to function optimally while resisting injury is currently an area of great research interest. The second aim of this presentation is to describe how muscles and tendons work synchronously during movement tasks and how their behaviors might influence both physical performance and injury risk, before briefly looking at future research opportunities in the area.
Speaker B
Gael Guilhem
French Institute of Sport (INSEP), Research Department, Laboratory Sport, Expertise and Performance (EA 7370)
France
Read CVECSS Lausanne 2026: IS-BM01 [8853]
Muscle-tendon interactions may mitigate injury risk
The muscle-tendon complex plays a major role in producing and transmitting forces required to initiate, perform and adjust movement. As the cornerstone of movement mechanics, muscle and tendon tissues withstand substantial load when muscle fascicles produce force and when passive elements release this force to bone lever arms. This mechanical stress may increase when muscle contraction aims to resist an external force exceeding force-generating capacity during eccentric contractions involved in braking actions. Several experimental and ecological models have revealed that such constraints may lead to functional impairments including exercise-induced muscle damage, or non-physiological alterations such as injury. Such failure occurs when mechanical stress exceeds muscle force and strain capacity by application of a singular high-magnitude stress or repeated loading. It is well known that muscle damage is associated with functional impairments such as force loss, delayed inflammation, oedema and soreness, yet understanding of the mechanical processes involved in eccentric contractions that govern muscle damage is limited in vivo. Recent research using high-frame rate ultrasound imaging suggests that the strain applied to human muscle fibers during eccentric contractions influences the muscle damage magnitude induced by single-joint or multi-joint (pedaling, backward walking) tasks. An unresolved question is whether these functional alterations following eccentric contractions might lower the threshold of muscle-tendon unit resilience to injury risk. While functional capacities such as muscle force or joint flexibility have been associated with injury risk, these global indices do not fully reflect the force transmission capacities of muscle-tendon tissues and thus may conceal localized properties and lead to suboptimal preventive training programs. Recent studies have reported that biceps femoris long head muscle and proximal aponeurosis geometry, particularly exposed to injury, may alter the strain experienced in muscle adjacent to the musculotendinous junction during active lengthening. These findings suggest a putative role of muscle geometry and mechanical properties of elastic tissues in injury risk exposure. A follow-up question relates to the functional consequences of initial injury, which are well-identified as primary determinants of re-injury risk. While significant reductions in hip joint flexibility have been reported in previously injured athletes, muscle stiffness inferred from shear wave elastography measurements does not differ between injured and uninjured muscles of elite athletes. These findings highlight the need for more localized measurements of mechanical properties of elastic tissues to inform the design of preventive and rehabilitation interventions aiming to adjust these properties and reduce injury risk exposure.
Speaker C
Adèle MORNAS
National Institute of Health and Medical Research (INSERM, France), Laboratory Sport, Expertise and Performance
France
Read CVECSS Lausanne 2026: IS-BM01 [31805]
Thermal stress as a modulator of muscle-tendon interactions, recovery and health
Muscle-tendon unit interactions may be modulated to improve recovery or health. Heat appears as an emerging tool to modulate muscle-tendon properties. In the current context of global warming, its effects on muscle-tendon interaction should not be neglected, as highlighted by a growing body of research on muscle function in response to thermal stress. It is therefore important to study changes in muscle-tendon unit properties and interactions elicited by acute or chronic heat stress, to provide a better understanding of muscle mechanics, and thus motor performance under heat stress. Using ultrafast ultrasound imaging, it is possible to investigate muscle fascicle behavior in vivo during dynamic contractions in situ (i.e., running), thereby providing relevant mechanistic information on muscle-tendon responses to heat stress. Recent findings can be summarized into two key messages. First, acute passive heat exposure improves explosive force production in its early phase, which may be attributed to accelerated neuromuscular activation, while soft tissue stiffness is reduced. These findings evidence the decoupled effects of heat on muscle-tendon unit contractile and passive properties. Secondly, active heat exposure, whether acute (during running exercise) or chronic (during cycling-induced heat acclimation), does not tend to alter muscle-tendon unit properties or tissue behaviors. The lack of influence of ambient temperature on muscle properties allows provision of novel practical information to athletes who exercise in hot environments or use heat acclimation to prepare for competitions in the heat. From a recovery and health perspective, localized passive heating is emerging as a potential strategy to improve muscle healing in humans. Indeed, it was recently reported that repeated hot water immersion after simulated musculoskeletal injury in humans improved muscle regeneration by reducing chronic perceived pain and blood-based markers of muscle damage. Localized heat therapy, used during immobilization and rehabilitation may reduce muscle atrophy and maintain plantar flexor strength in healthy individuals. This suggests that heat can be used as a therapeutic tool to minimize muscle deconditioning in immobilized athletes. Collectively, heat may not alter muscle-tendon interactions when exercising in the heat, however it may provide benefits for recovery and health through improved muscle regeneration and reduced muscle atrophy, respectively. In the current context, although we have no choice but to confront heat, we should use it to our advantage: to protect our muscles!