Muscle-fiber pennation angles are greater in hypertrophied than in normal muscles

Kawakami, Yasuo; Abe, Takashi; Fukunaga, Tetsuo

doi:10.1152/jappl.1993.74.6.2740

Cited by 438 publications

(420 citation statements)

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“…Pennation, a key-parameter of muscle architecture, is a natural strategy to pack more contractile elements in to a given muscle volume. A decrease in pennation angle (θ), due to muscle atrophy, is commonly interpreted as a decrease in the number of fascicles in parallel (Kawakami et al, 1993). Reductions in θ seen after only short durations of ULLS or bed rest (~8-13% in the vastus lateralis muscle after 23 to 35 days, (de Boer et al 2007(de Boer et al & 2008 indicate that substantial muscle remodelling occurs with few days of muscle unloading.…”

Section: Introductionmentioning

confidence: 99%

Skeletal muscle adaptations to physical inactivity and subsequent retraining in young men

et al. 2013

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Narici, M. V. (2013). Skeletal muscle adaptations to physical inactivity and subsequent retraining in young men. Biogerontology (Dordrecht), 14,(247)(248)(249)(250)(251)(252)(253)(254)(255)(256)(257)(258)(259) Dette er siste tekst-versjon av artikkelen, og den kan inneholde små forskjeller fra forlagets pdf-versjon. Forlagets pdf-versjon finner du på link.springer.com: http://dx.doi.org/10. 1007/s10522-013-9427-6 This is the final text version of the article, and it may contain minor differences from the journal's pdf version. The original publication is available at link.springer.com: http://dx.doi.org/10.1007/s10522-013-9427-6 AbstractSkeletal muscle structure and function are markedly affected by chronic disuse. With unloading, muscle mass is lost at rate of about 0.4%/day but little is known about the recovery of muscle mass and strength following disuse. Here we report an extensive data set describing in detail skeletal muscle adaptations in structure and function in response to both disuse and retraining. Eight young men (23±2.2 yrs) underwent 3 weeks of unilateral lower limb suspension (ULLS) followed by a 3-week resistance training recovery program. Knee extensor (KE) isometric torque, voluntary activation (VA), quadriceps femoris (QF) muscle volume (QF vol ), fascicle length (Lf) and pennation angle (θ), physiological cross-sectional area (PCSA) of all four heads of the QF muscle, were measured before, after ULLS, and post-ULLS-resistance training. Needle biopsies were taken from the vastus lateralis muscle of a subgroup (n=6) of the same subjects and cross sectional area of individual muscle s and myosin content of muscle samples were determined. Following 3 weeks of ULLS, isometric torque decreased by 26%, PCSA by 3%, QF vol by 10%. Lf and θ of all four heads of QF significantly decreased (P≤0.05). Following the 3-week retraining period, isometric torque, PCSA, QF vol , Lf and θ of all four heads of QF were all fully restored to pre ULLS values. CSA of individual muscle fibres and myosin content of muscle samples decreased by 26% and 35% respectively (post-ULLS) and recovered to almost pre-ULLS values following retraining. There were no significant changes in voluntary activation of the quadriceps muscles in response to either ULLS or subsequent retraining. These results indicate that, 1) the loss of muscle force with 3-week unloading in humans is mostly explained by muscle atrophy and by a decrease in myosin content and, 2) all the neuromuscular changes induced by this model of disuse can be fully restored after a resistance training intervention of equal duration. KeywordsDisuse, Skeletal muscle, atrophy, recovery, resistance training 2 Introduction Deficits in skeletal muscle mass and function are primary outcomes of chronic unloading, with antigravity muscles such as the knee extensors (KE) being particularly affected (Narici and De Boer 2011). An extensive knowledge of these adverse conditions is paramount, for they are inevitably linked to clinical situations such as prolonged best rest or ...

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Section: Introductionmentioning

confidence: 99%

Skeletal muscle adaptations to physical inactivity and subsequent retraining in young men

et al. 2013

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“…Recently, it was shown that the problem of electrode alignment can be overcome with principal component analysis (PCA), which was applied on multiple monopolar EMG channels and is thus unbiased with respect to the muscle fiber direction (Staudenmann et al, 2006). So far, PCA-processed monopolar multi-channel EMG has been applied on the triceps brachii, and triceps surae (Staudenmann et al, 2006(Staudenmann et al, , 2009a, both mainly pennate and architecturally complex muscles (Chow et al, 2000;Kawakami et al, 1993). A substantial improvement in muscle activation estimates was achieved with PCA as compared to multiple bipolar EMG using the same electrodes (Staudenmann et al, 2006(Staudenmann et al, , 2009a, suggesting that the misalignment of (multiple) bipolar EMG is a cause of errors in the estimation.…”

Section: Introductionmentioning

confidence: 99%

Redundancy or heterogeneity in the electric activity of the biceps brachii muscle? Added value of PCA-processed multi-channel EMG muscle activation estimates in a parallel-fibered muscle

Staudenmann

Stegeman

Dieën

2013

Journal of Electromyography and Kinesiology

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Conventional bipolar EMG provides imprecise muscle activation estimates due to possibly heterogeneous activity within muscles and due to improper alignment of the electrodes with the muscle fibers. Principal component analysis (PCA), applied on multi-channel monopolar EMG yielded substantial improvements in muscle activation estimates in pennate muscles. We investigated the degree of heterogeneity in muscle activity and the contribution of PCA to muscle activation estimates in biceps brachii (BB), which has a relatively simply parallel-fibered architecture. EMG-based muscle activation estimates were assessed by comparison to elbow flexion forces in isometric, two-state isotonic contractions in eleven healthy male subjects. Monopolar EMG was collected over the entire surface of the BB with about 63 electrodes. Estimation quality of different combinations of EMG channels showed that heterogeneous activation was found mainly in medio-lateral direction, whereas adding channels in the longitudinal direction added largely redundant information. Multi-channel bipolar EMG amplitude improved muscle activation estimates by 5-14% as compared to a single bipolar. PCA-processed monopolar EMG amplitude yielded a further improvement of (12-22%). Thus multi-channel EMG, processed with PCA, substantially improves the quality of muscle activation estimates compared conventional bipolar EMG in BB.

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“…In healthy individuals, improved muscle function during strengthening exercise is due to improved neuromuscular adaptation (21), increased cross-sectional muscle fiber area (22,23), changes in fiber type composition (24), and metabolic changes (25)(26)(27). Healthy sedentary individuals usually respond to any type of exercise (28,29) and can attain a 40% increased muscle strength in 4 weeks, whereas longer periods of exercise are necessary to obtain the same effects in more trained individuals (23).…”

Section: Introductionmentioning

confidence: 99%

Benefits of intensive resistance training in patients with chronic polymyositis or dermatomyositis

Alexanderson¹,

Dastmalchi²,

Esbjörnsson-Liljedahl³

et al. 2007

Arthritis & Rheumatism

128

115

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Objective. To investigate the benefits and safety of an intensive muscular training program in patients with chronic polymyositis (PM) and dermatomyositis (DM).Methods. Nine patients with chronic PM or DM (median age 53 years, range 44 -61) were included. Assessments of impairment (10 -15 voluntary repetition maximum [VRM], the Functional Index 2 [FI-2], the Grippit, and pain rated on the Borg CR-10 scale), activity limitation (Myositis Activities Profile), and participation restriction (patients' disease impact on well-being) were performed 4 weeks prior to baseline, at baseline, and after 7 weeks of exercise. A 6-item core set of disease activity measures was administered and muscle biopsy samples of vastus lateralis were obtained at baseline and after 7 weeks of exercise. Response criteria at an individual level were set for disability and disease activity. The patients exercised 3 days per week for 7 weeks on loads allowing 10 VRM. Results. On a group level there were no significant differences between assessments at 4 weeks before baseline compared with baseline. The group improved significantly regarding 10 -15 VRM and FI-2 at 7 weeks compared with baseline (P < 0.05). All patients were responders with respect to impairment and 2 were activity limitation responders whereas participation restriction remained unchanged in all. Two patients were responders with reduced disease activity and no patient had signs of increased muscle inflammation in the muscle biopsy sample after 7 weeks of exercise. Conclusion. Patients with chronic, stable PM and DM can perform this intensive resistive exercise program with beneficial effects on impairment and activity limitation without increased muscle inflammation.

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Muscle-fiber pennation angles are greater in hypertrophied than in normal muscles

Cited by 438 publications

References 11 publications

Skeletal muscle adaptations to physical inactivity and subsequent retraining in young men

Skeletal muscle adaptations to physical inactivity and subsequent retraining in young men

Redundancy or heterogeneity in the electric activity of the biceps brachii muscle? Added value of PCA-processed multi-channel EMG muscle activation estimates in a parallel-fibered muscle

Benefits of intensive resistance training in patients with chronic polymyositis or dermatomyositis

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