The relationship between single muscle fibre and voluntary rate of force development in young and old males.

Purpose: It is suggested that the early phase (< 50 ms) of force development during a muscle contraction is associated with intrinsic contractile properties, while the late phase (> 50 ms) is associated with maximal force. There are no direct investigations of single muscle fibre rate of force development (RFD) as related to joint-level RFD METHODS: Sixteen healthy, young (n = 8; 26.4 ± 1.

Titin force in muscle cells alters lattice order, thick and thin filament protein formation.

Skeletal muscle force production is increased at longer compared to shorter muscle lengths because of length-dependent priming of thick filament proteins in the contractile unit before contraction. Using small-angle X-ray diffraction in combination with a mouse model that specifically cleaves the stretch-sensitive titin protein, we found that titin cleavage diminished the length-dependent priming of the thick filament. Strikingly, a titin-sensitive, length-dependent priming was also present in thin filaments, which seems only possible via bridge proteins between thick and thin filaments in resting muscle, potentially myosin-binding protein C.

COVID-19 Pandemic and Exercise (COPE) trial: a multigroup pragmatic randomised controlled trial examining effects of app-based at-home exercise programs on depressive symptoms.

Background: The number of adults across the globe with significant depressive symptoms has grown substantially during the COVID-19 pandemic. The extant literature supports exercise as a potent behaviour that can significantly reduce depressive symptoms in clinical and non-clinical populations.

Objective: Using a suite of mobile applications, at-home exercise, including high intensity interval training (HIIT) and/or yoga, was completed to reduce depressive symptoms in the general population in the early months of the pandemic.

The torque-frequency relationship is impaired similarly following two bouts of eccentric exercise: No evidence of a protective repeated bout effect.

High-intensity eccentric exercise can lead to muscle damage and weakness. The 'repeated bout effect' (RBE) can attenuate these impairments when performing a subsequent bout. The influence of eccentric exercise-induced muscle damage on low-frequency force production is well-characterized; however, it is unclear how eccentric exercise and the RBE affect torque production across a range of stimulation frequencies (i.

Rate of force development is Ca-dependent and influenced by Ca-sensitivity in human single muscle fibres from older adults.

Natural adult aging is associated with declines in skeletal muscle performance, including impaired Ca sensitivity and a slowing of rapid force production (rate of force redevelopment; k). The purpose of this study was to investigate the relationship between impaired Ca sensitivity and k of single muscle fibres from young and older adults. Participants included 8 young (22-35 yrs) and 8 older (60-81 yrs) males who were living independently.

Power loss is attenuated following a second bout of high-intensity eccentric contractions due to the repeated bout effect's protection of rate of torque and velocity development.

High-intensity unaccustomed eccentric contractions result in weakness and power loss because of fatigue and muscle damage. Through the repeated bout effect (RBE), adaptations occur, then damage and weakness are attenuated following a subsequent bout. However, it is unclear whether the RBE protects peak power output.

Fiber Type and Size as Sources of Variation in Human Single Muscle Fiber Passive Elasticity.

Studies on single muscle fiber passive material properties often report relatively large variation in elastic modulus (or normalized stiffness), and it is not clear where this variation arises. This study was designed to determine if the stiffness, normalized to both fiber cross-sectional area and length, is inherently different between types 1 and 2 muscle fibers. Vastus lateralis fibers (n = 93), from ten young men, were mechanically tested using a cumulative stretch-relaxation protocol.

Residual force enhancement and force depression in human single muscle fibres.

Residual force depression (rFD) and residual force enhancement (rFE) are intrinsic contractile properties of muscle. rFD is characterized as a decrease in steady-state isometric force following active shortening compared with a purely isometric contraction at the same muscle length and level of activation. By contrast, isometric force is increased following active lengthening compared to a reference isometric contraction at the same muscle length and level of activation; this is termed rFE.

Prolonged exercise training improves the acute type II muscle fibre satellite cell response in healthy older men.

Key Points: Skeletal muscle stem cells, termed satellite cells, play a crucial role in repair and remodelling of muscle in response to exercise An age-related decline in satellite cell number and/or function has been hypothesized to be a key factor in the development of sarcopenia and/or the blunted muscle fibre adaptive response to prolonged exercise training in older persons We report that performing prolonged exercise training improves the acute type II muscle fibre satellite cell response following a single bout of resistance exercise in older men. The observed improvement in muscle satellite function is associated with an increase in muscle fibre capillarization following exercise training suggesting a possible functional link between capillarization and satellite cell function.

Abstract: Age-related type II muscle fibre atrophy is accompanied by a fibre type-specific decline in satellite cell number and function.

Activation reduction following an eccentric contraction impairs torque steadiness in the isometric steady-state.

Background: The isometric steady-state following active lengthening is associated with greater torque production and lower activation, as measured by electromyographic activity (EMG), in comparison with a purely isometric contraction (ISO) at the same joint angle. This phenomenon is termed residual force enhancement (RFE). While there has been a great deal of research investigating the basic mechanisms of RFE, little work has been performed to understand the everyday relevance of RFE.

Mitigating the bilateral deficit: reducing neural deficits through residual force enhancement and activation reduction.

Purpose: The bilateral deficit (BLD) is characterized by a reduction in maximal voluntary torque during a bilateral contraction relative to the sum of left and right unilateral contractions. The BLD has been attributed to interhemispheric inhibition as a result of unilateral torque differences between limbs. If the BLD is the result of interhemispheric inhibition, lowering activation for a torque matching task, as shown in residual force enhancement (RFE), may help overcome the decrease in neural drive during bilateral contractions.

Ingestion of a Multi-Ingredient Supplement Does Not Alter Exercise-Induced Satellite Cell Responses in Older Men.

Background: Nutritional supplementation can have beneficial effects on body composition, strength, and function in older adults. However, whether the response of satellite cells can be altered by nutritional supplementation in older adults remains unknown.

Objective: We assessed whether a multi-ingredient protein-based supplement taken over a prolonged period of time could alter the muscle satellite cell response after exercise in older men.

Pronounced energy restriction with elevated protein intake results in no change in proteolysis and reductions in skeletal muscle protein synthesis that are mitigated by resistance exercise.

Preservation of lean body mass (LBM) may be important during dietary energy restriction (ER) and requires equal rates of muscle protein synthesis (MPS) and muscle protein breakdown (MPB). Currently, the relative contribution of MPS and MPB to the loss of LBM during ER in humans is unknown. We aimed to determine the impact of dietary protein intake and resistance exercise on MPS and MPB during a controlled short-term energy deficit.

Neither load nor systemic hormones determine resistance training-mediated hypertrophy or strength gains in resistance-trained young men.

We reported, using a unilateral resistance training (RT) model, that training with high or low loads (mass per repetition) resulted in similar muscle hypertrophy and strength improvements in RT-naïve subjects. Here we aimed to determine whether the same was true in men with previous RT experience using a whole-body RT program and whether postexercise systemic hormone concentrations were related to changes in hypertrophy and strength. Forty-nine resistance-trained men (23 ± 1 yr, mean ± SE) performed 12 wk of whole-body RT.