67 research outputs found
Costamere remodeling with muscle loading and unloading in healthy young men
No full textCostameres are mechano-sensory sites of focal adhesion in the sarcolemma that provide a structural anchor for
myofibrils. Their turnover is regulated by integrin-associated focal adhesion kinase (FAK). We hypothesized that\ud
changes in content of costamere components (beta 1 integrin, FAK, meta-vinculin, gamma-vinculin) with
increased and reduced loading of human anti-gravity muscle would: (i) relate to changes in muscle size and
molecular parameters of muscle size regulation [p70S6K, myosin heavy chain (MHC)1 and MHCIIA];
(ii) correspond to adjustments in activity and expression of FAK, and its negative regulator, FRNK; and
(iii) reflect the temporal response to reduced and increased loading. Unloading induced a progressive decline in
thickness of human vastus lateralis muscle after 8 and 34 days of bedrest (-4% and -14%, respectively; n = 9),
contrasting the increase in muscle thickness after 10 and 27 days of resistance training (+5% and +13%; n = 6).
Changes in muscle thickness were correlated with changes in cross-sectional area of type I muscle fibers
(r = 0.66) and beta 1 integrin content (r = 0.76) at the mid-point of altered loading. Changes in meta-vinculin
and FAK-pY397 content were correlated (r = 0.85) and differed, together with the changes of beta 1 integrin,
MHCI, MHCII and p70S6K, between the mid- and end-point of resistance training. By contrast, costamere
protein level changes did not differ between time points of bedrest. The findings emphasize the role of FAKregulated
costamere turnover in the load-dependent addition and removal of myofibrils, and argue for two
phases of muscle remodeling with resistance training, which do not manifest at the macroscopic level
On muscle, tendon and high heels
No full textWearing high heels (HH) places the calf muscle-tendon unit (MTU) in a shortened position. As muscles and tendons are highly malleable tissues, chronic use of HH might induce structural and functional changes in the calf MTU. To test this hypothesis, 11 women regularly wearing HH and a control group of 9 women were recruited. Gastrocnemius medialis (GM) fascicle length, pennation angle and physiological cross-sectional area (PCSA), the Achilles' tendon (AT) length, cross-sectional area (CSA) and mechanical properties, and the plantarflexion torque-angle and torque-velocity relationships were assessed in both groups. Shorter GM fascicle lengths were observed in the HH group (49.6±5.7mm vs 56.0±7.7mm), resulting in greater tendon-to-fascicle length ratios. Also, because of greater AT CSA, AT stiffness was higher in the HH group (136.2±26.5Nmm-1 vs 111.3±20.2 N mm-1). However, no differences in the GM PCSA to AT CSA ratio, torque-angle and torque-velocity relationships were found. We conclude that long-term use of high-heeled shoes induces shortening of the GM muscle fascicles and increases AT stiffness, reducing the ankle's active range of motion. Functionally, these two phenomena seem to counteract each other since no significant differences in static or dynamic torques were observed. © 2010. Published by The Company of Biologists Ltd
Early skeletal muscle hypertrophy and architectural changes in response to high-intensity resistance training
No full textThe onset of whole muscle hypertrophy in response to overloading is poorly documented. The purpose of this study was to assess the early changes in muscle size and architecture during a 35-day high-intensity resistance training (RT) program. Seven young healthy volunteers performed bilateral leg extension three times per week on a gravity-independent flywheel ergometer. Cross-sectional area (CSA) in the central (C) and distal (D) regions of the quadriceps femoris (QF), muscle architecture, maximal voluntary contraction (MVC), and electromyographic (EMG) activity were measured before and after 10, 20, and 35 days of RT. By the end of the training period, MVC and EMG activity increased by 38.9 ± 5.7 and 34.8% ± 4.7%, respectively. Significant increase in QF CSA (3.5 and 5.2% in the C and D regions, respectively) was observed after 20 days of training, along with a 2.4 ± 0.7% increase in fascicle length from the 10th day of training. By the end of the 35-day training period, the total increase in QF CSA for regions C and D was 6.5 ± 1.1 and 7.4 ± 0.8%, respectively, and fascicle length and pennation angle increased by 9.9 ± 1.2 and 7.7 ± 1.3%, respectively. The results show for the first time that changes in muscle size are detectable after only 3 wk of RT and that remodeling of muscle architecture precedes gains in muscle CSA. Muscle hypertrophy seems to contribute to strength gains earlier than previously reported; flywheel training seems particularly effective for inducing these early structural adaptations. Copyright © 2007 the American Physiological Society
Increased H-reflex excitability is not accompanied by changes in neural drive following 24 days of unilateral lower limb suspension
No full textThe purpose of this study was to determine whether the gain in soleus H-reflex excitability induced by unilateral lower limb suspension (ULLS) is associated with changes in neural drive to the plantar flexor muscles. Six male subjects (23 ± 2 years, 187 ± 7 cm, 79 ± 9 kg) underwent 24 days of ULLS of the dominant limb. Plantar flexor maximal voluntary contraction (MVC) torque, activation capacity (twitch interpolation), soleus maximal electromyographic (EMG) activity, Hoffman (H)-reflex, and the first volitional (V) wave normalized to the compound muscle action potential (M-wave) were quantified before and after ULLS. Following ULLS, MVC torque decreased by 15% (P < 0.05). However, neither activation capacity nor EMG activity was significantly altered after the suspension. The V-wave remained unchanged consistently after ULLS, whereas the H-reflex increased significantly (+20%). Furthermore, there was no significant relationship between changes in H-reflex and V-wave over the ULLS period. These findings indicate that 24 days of ULLS can result in a substantial reduction of muscle strength without any apparent change in voluntary activation capacity. H-reflex and V-wave findings suggest that the spinal adaptations that underlie the unloading-induced increase in resting soleus H-reflex excitability did not significantly affect the efferent motor output to the plantar flexor muscles. © 2009 Wiley Periodicals, Inc
Human muscle fascicle behavior in agonist and antagonist isometric contractions
No full textIntroduction: The aim of this study was to compare, at a given level of electromyographic (EMG) activity, the behavior of dorsiflexor and plantarflexor muscles as assessed via their architecture (pennation angle and fiber length) during agonist or antagonist isometric contractions. Methods: Realtime ultrasonography and EMG activity of gastrocnemius medialis (GM) and tibialis anterior (TA) muscles were obtained while young males performed ramp isometric contractions in dorsiand plantarflexion. Results: For both muscles, at a similar level of EMG activity, fiber length was longer, and pennation angle was smaller, during antagonist than during agonist contractions. Conclusions: These results indicate that, at similar levels of EMG activity, GM and TA muscles elicit a higher mechanical output while acting as an antagonist. These findings have important implications for muscle function testing. They show that estimation of antagonistic force using the common method based on the EMG/net torque relationship yields underestimated values
Effect of androgenic-anabolic steroids and heavy strength training on patellar tendon morphological and mechanical properties
No full textCombined androgenic- anabolic steroids (AAS) and overloading affects tendon collagen metabolism and ultrastructure and is often associated with a higher risk of injury. The aim of this prospective study was to investigate whether such effects would be reflected in the patellar tendon properties of individuals with a history of long-term resistance training and AAS abuse (RTS group), compared with trained (RT) and untrained (CTRL) nonsteroids users. Tendon cross-sectional area (CSA), stiffness, Young's modulus, and toe limit strain were measured in vivo, from synchronized ultrasonography and dynamometry data. The patellar tendon of RT and RTS subjects was much stiffer and larger than in the CTRL group. However, stiffness and modulus were higher in the RTS group (26%, P < 0.05 and 30%, P < 0.01, respectively) than in the RT group. Conversely, tendon CSA was 15% (P < 0.05) larger in the RT group than in RTS, although differences disappeared when this variable was normalized to quadriceps maximal isometric torque. Yet maximal tendon stress was higher in RTS than in RT (15%, P < 0.05), without any statistical difference in maximal strain and toe limit strain between groups. The present lack of difference in toe limit strain does not substantiate the hypothesis of changes in collagen crimp pattern associated with AAS abuse. However, these findings indicate that tendon adaptations from years of heavy resistance training are different in AAS users, suggesting differences in collagen remodeling. Some of these adaptations (e.g., higher stress) could be linked to a higher risk of tendon injury. Copyright © 2013 the American Physiological Society
Whole muscle contractile parameters and thickness loss during 35-day bed rest
No full textExtended exposure to microgravity leads to significant musculoskeletal adaptations. Contractile parameters of four skeletal muscles (biceps brachii-BB, vastus medialis-VM, biceps femoris-BF and gastrocnemius medialis-GM) were measured in ten healthy males (aged 22.3 ± 2.2 years) during 35 days of horizontal bed rest by a mechanomyography-based method termed 'tensiomyography' (TMG). Two contractile parameters: contraction time (Tc) and maximal displacement (Dm) were individually measured from electrically evoked maximal single twitch TMG response of all four muscles before and after bed rest. Significant changes in Tc were found after bed rest, as shown by an increase in GM muscle Tc by 18% (p < 0.01). Dm values significantly increased (p < 0.01) after bed rest, by 24, 26 and 30% in the VM, BF and GM muscles, respectively. In the GM, the change in Dm significantly correlated with the decrease in muscle thickness (r = -0.70, p < 0.01). In conclusion, bed rest induced changes in both Dm and Tc of the TMG signal; changes in Dm being inversely related to those of muscle thickness. Amongst the investigated muscles, most affected, in terms of atrophy and mechanical alterations, were those of the lower limbs. The observed increase in Dm may be attributed to a decrease in muscle, as well as tendon stiffness, causing larger muscle fibre and non-contractile tissue oscillations following contraction. © Springer-Verlag 2008
Time course of muscular, neural and tendinous adaptations to 23 day unilateral lower-limb suspension in young men
No full textMuscles and tendons are highly adaptive to changes in chronic loading, though little is known about the adaptative time course. We tested the hypothesis that, in response to unilateral lower limb suspension (ULLS), the magnitude of tendon mechanical adaptations would match or exceed those of skeletal muscle. Seventeen men (1.79 ± 0.05 m, 76.6 ± 10.3 kg, 22.3 ± 3.8 years) underwent ULLS for 23 days (n = 9) or acted as controls (n = 8). Knee extensor (KE) torque, voluntary activation (VA), cross-sectional area (CSA) (by magnetic resonance imaging), vastus lateralis fascicle length (Lf) and pennation angle (θ), patellar tendon stiffness and Young's modulus (by ultrasonography) were measured before, during and at the end of ULLS. After 14 and 23 days (i) KE torque decreased by 14.8 ± 5.5% (P < 0.001) and 21.0 ± 7.1% (P < 0.001), respectively; (ii) VA did not change; (iii) KE CSA decreased by 5.2 ± 0.7% (P < 0.001) and 10.0 ± 2.0% (P < 0.001), respectively; Lf decreased by 5.9% (n.s.) and 7.7% (P < 0.05), respectively, and θ by 3.2% (P < 0.05) and 7.6% (P < 0.01); (iv) tendon stiffness decreased by 9.8 ± 8.2% (P < 0.05) and 29.3 ± 11.5% (P < 0.005), respectively, and Young's modulus by 9.2 ± 8.2% (P < 0.05) and 30.1 ± 11.9% (P < 0.01), respectively, with no changes in the controls. Hence, ULLS induces rapid losses of KE muscle size, architecture and function, but not in neural drive. Significant deterioration in tendon mechanical properties also occurs within 2 weeks, exacerbating in the third week of ULLS. Rehabilitation to limit muscle and tendon deterioration should probably start within 2 weeks of unloading. © 2007 The Authors. Journal compilation © 2007 The Physiological Society
Effect of alpine skiing training on tendon mechanical properties in older men and women
No full textStrain is one of the parameters determining tendon adaptation to mechanical stimuli. The aim of this study was to test whether the patellar tendon strain induced during recreational alpine skiing would affect tendon mechanical properties in older individuals. Twenty-two older males and females (67 ± 2 years) were assigned to a 12-week guided skiing programe (IG) and 20 aged-matched volunteers served as controls (CG). Patellar tendon mechanical properties and cross-sectional area (CSA) were measured before and after training, with combined dynamometry and ultrasonography scanning. None of the variables changed significantly in the CG after training. In the IG, tendon stiffness and Young's modulus were increased (respectively, 14% and 12%, P<0.01), without any significant change in tendon CSA. In addition, changes in tendon stiffness were blunted in women (9%) compared with men (19%). Serum IGF-1 concentration tended to be lower in women (-19%, P=0.07). These results demonstrate that the mechanical stimulus induced by alpine skiing is sufficient to elicit adaptive changes in patellar tendon mechanical and material properties in older subjects. Furthermore, the present sex-specific adaptations are consistent with previous reports of lower collagen metabolic responsiveness in women and may be underpinned by anthropometric and metabolic differences. © 2011 John Wiley & Sons A/S
Skeletal muscle remodeling in response to alpine skiing training in older individuals
No full textThis study investigated whether regular alpine skiing could reverse sarcopenia and muscle weakness in older individuals. Twenty-two older men and women (67 ± 2 yr) underwent 12 weeks of recreational skiing, 2-3 times a week, each session lasting ~3.5 hours. An age-matched, inactive group (n = 20, 67 ± 4 yr) served as control (CTRL). Before and after the training period, knee extensors muscle thickness (Tm),
pennation angle () and fascicle length (Lf) of the vastus lateralis muscle, were measured by ultrasound. Maximum isokinetic knee extensor torque (MIT) at an angular velocity of 60 deg/s was measured by dynamometry. After the training, Tm increased by 7.1% (P<0.001), Lf by 5.4% (P<0.02) and by 3.4% (P<0.05). The increase in Tm was matched by a significant gain in MIT (13.3%, P<0.001). No
significant changes, except for a decrease in (2.1%, P<0.02) were found in the CTRL group. The gain in Tm in the training group significantly correlated with an increase in focal adhesion kinase (FAK) content, pointing to a primary role of this mechano-sensitive protein in sarcomere remodeling with muscle hypertrophy. Overall, the results show that alpine skiing is an effective intervention for combating sarcopenia and weakness in old age
- …
