Fast myosin binding protein C knockout in skeletal muscle alters length-dependent activation and myofilament structure.

In striated muscle, the sarcomeric protein myosin-binding protein-C (MyBP-C) is bound to the myosin thick filament and is predicted to stabilize myosin heads in a docked position against the thick filament, which limits crossbridge formation. Here, we use the homozygous Mybpc2 knockout (C2) mouse line to remove the fast-isoform MyBP-C from fast skeletal muscle and then conduct mechanical functional studies in parallel with small-angle X-ray diffraction to evaluate the myofilament structure. We report that C2 fibers present deficits in force production and calcium sensitivity.

Fast myosin binding protein C knockout in skeletal muscle alters length-dependent activation and myofilament structure.

In striated muscle, some sarcomere proteins regulate crossbridge cycling by varying the propensity of myosin heads to interact with actin. Myosin-binding protein C (MyBP-C) is bound to the myosin thick filament and is predicted to interact and stabilize myosin heads in a docked position against the thick filament and limit crossbridge formation, the so-called OFF state. Via an unknown mechanism, MyBP-C is thought to release heads into the so-called ON state, where they are more likely to form crossbridges.

The history-dependent features of muscle force production: A challenge to the cross-bridge theory and their functional implications.

The cross-bridge theory predicts that muscle force is determined by muscle length and the velocity of active muscle length changes. However, before the formulation of the cross-bridge theory, it had been observed that the isometric force at a given muscle length is enhanced or depressed depending on active muscle length changes before that given length is reached. These enhanced and depressed force states are termed residual force enhancement (rFE) and residual force depression (rFD), respectively, and together they are known as the history-dependent features of muscle force production.

Characterizing residual and passive force enhancements in cardiac myofibrils.

Residual force enhancement (RFE), an increase in isometric force after active stretching of a muscle compared with the purely isometric force at the corresponding length, has been consistently observed throughout the structural hierarchy of skeletal muscle. Similar to RFE, passive force enhancement (PFE) is also observable in skeletal muscle and is defined as an increase in passive force when a muscle is deactivated after it has been actively stretched compared with the passive force following deactivation of a purely isometric contraction. These history-dependent properties have been investigated abundantly in skeletal muscle, but their presence in cardiac muscle remains unresolved and controversial.

The Nonintuitive Contributions of Individual Quadriceps Muscles to Patellar Tracking.

The purpose of this study was to quantify the contribution of the individual quadriceps muscles to patellar tracking. The individual and/or combined quadriceps muscles were activated in rabbits (n = 6) during computer-controlled flexion/extension of the knee. Three-dimensional patellar tracking was measured for the vastus lateralis, vastus medialis, and rectus femoris when activated alone and when activated simultaneously at different frequencies, producing a range of knee extensor torques.

Gender disparities in fear of failure among 15-year-old students: The role of gender inequality, the organisation of schooling and economic conditions.

Introduction: Prior research indicates that female students express higher fear of failure than male students and that fear of failure is associated with lower social and emotional well-being and higher levels of stress, anxiety, burnout and depression. Fear of failure also leads individuals to limit their choices and take fewer risks than would be warranted given their ability and context to minimise the possibility of failing.

Methods: We examined cross-country differences in gender gaps in fear of failure as well as factors that explain gender gaps and variations of gender gaps across countries using multilevel modelling techniques.

Effect of Vastus Medialis Loss on Rabbit Patellofemoral Joint Contact Pressure Distribution.

Vastus medialis (VM) weakness is thought to alter patellar tracking, thereby changing the loading of the patellofemoral joint (PFJ), resulting in patellofemoral pain. However, it is challenging to measure VM force and weakness in human studies, nor is it possible to measure the associated mechanical changes in the PFJ. To obtain fundamental insight into VM weakness and its effects on PFJ mechanics, the authors determined PFJ loading in the presence of experimentally simulated VM weakness.

Residual and passive force enhancement in skinned cardiac fibre bundles.

In skeletal muscle, steady-state force is consistently greater following active stretch than during a purely isometric contraction at the same length (residual force enhancement; RFE). Similarly, when deactivated, the force remains higher following active stretch than following an isometric condition (passive force enhancement; PFE). RFE and PFE have been associated with the sarcomere protein titin, but skeletal and cardiac titin have different structures, and results regarding RFE in cardiac muscle have been inconsistent and contradictory.

Why do muscles lose torque potential when activated within their agonistic group?

Agonistic muscles lose approximately 20% of their individual torque-generating capacity when activated with their agonistic muscles compared with when stimulated in isolation. In this study, we (1) tested if this loss in torque was accompanied by a corresponding loss in force, thereby testing the potential role of changes in moment arms between conditions; (2) removed all inter-muscular connections between the quadriceps muscles, thus determining the potential role of inter-muscular force transmission; and (3) systematically changed the inter-muscular pressure by performing experiments at different activation/force levels, thereby exploring the possible role of inter-muscular pressure in the loss of torque capacity with simultaneous muscle activation. Experiments were performed in a New Zealand white rabbit quadriceps model (=5).

Contribution of individual quadriceps muscles to knee joint mechanics.

Many attempts have been made to determine the contribution of individual muscles in an agonistic group to the mechanics of joints. However, previous approaches had the limitations that muscles often could not be controlled in a precise manner, that individual muscles in an agonistic group could not be activated individually, and that individual muscle contributions could not be measured in an actively contracting agonistic group. Here, we introduce a surgical approach that allows for controlled activation of individual muscles of an agonistic group.

The mechanics of agonistic muscles.

Introduction: In this study, we tested two assumptions that have been made in experimental studies on muscle mechanics: (i) that the torque-angle properties are similar among agonistic muscles crossing a joint, and (ii) that the sum of the torque capacity of individual muscles adds up to the torque capacity of the agonist group.

Methods: Maximum isometric torque measurements were made using a specifically designed animal knee extension dynamometer for the intact rabbit quadriceps muscles (n = 10) for knee angles between 60 and 120°. The nerve branches of the vastus lateralis (VL), vastus medialis (VM) and rectus femoris (RF) muscles were carefully dissected, and a custom made nerve cuff electrode was implanted on each branch.

Asynchronous Alterations of Muscle Force and Tendon Stiffness Following 8 Weeks of Resistance Exercise with Whole-Body Vibration in Older Women.

This study aimed to examine whether muscle force and tendon stiffness in a muscle-tendon complex alter synchronously following 8-week whole-body vibration (WBV) training in older people. Forty older women aged 65 years and older were randomly assigned into control (CON, n = 15) and whole-body vibration (WBV) training groups (exposure time, n = 13; vibration intensity, n = 12). For the training groups, a 4-week detraining period was completed following the training period.

Predictors of quality of life in ulcerative colitis: the importance of symptoms and illness representations.

Background: Establishing predictors of quality of life (QoL) in individuals with inflammatory bowel disease could help to identify those patients who are most likely to experience poor QoL and to target therapeutic interventions appropriately. We aimed to investigate how disease-specific QoL depends on demographic, diseaserelated, and physiological markers of disease activity, cognitive representations of illness, and perceived general health status.

Methods: A total of 111 individuals completed the Inflammatory Bowel Disease Questionnaire (IBDQ), the Medical Outcomes Study 36-Item Short-Form Health Survey (SF-36), and the Illness Perception Questionnaire (IPQ).