Changes in pennation with joint angle and muscle torque: In vivo measurements in human brachialis muscle

Prince of Wales Medical Research Institute, University of New South Wales, Sydney, Australia.
The Journal of Physiology (Impact Factor: 4.54). 05/1995; 484 ( Pt 2)(Pt 2):523-32. DOI: 10.1113/jphysiol.1995.sp020683
Source: PubMed

ABSTRACT 1. Estimates of pennation in human muscles are usually obtained from cadavers. In this study, pennation of human brachialis was measured in vivo using sonography. Effects of static and dynamic changes in elbow angle and torque were investigated. 2. Pennation was measured in eight subjects using an 80 mm, 5 MHz, linear-array ultrasound transducer to generate sagittal images of the brachialis during maximal and submaximal isometric contractions at various elbow angles. It was shown that estimates of pennation were reproducible, representative of measurements made throughout the belly of the muscle and not distorted by compression of the muscle with the transducer or rotation of the muscle out of the plane of the transducer. 3. Mean resting pennation was 9.0 +/- 2.0 deg (S.D., range 6.5-12.9 deg). When the muscle was relaxed there was no effect of elbow angle on pennation. However, during a maximal isometric contraction (MVC), with the elbow flexed to 90 deg, pennation increased non-linearly with elbow torque to between 22 and 30 deg (mean 24.7 +/- 2.4 deg). The effect of increasing torque was small when the elbow was fully extended. The relationship between elbow angle, elbow torque and brachialis pennation suggests that the relaxed brachialis muscle is slack over much of its physiological range of lengths. 4. There was no hysteresis in the relationship between torque and pennation during slow isometric contractions (0.2 MVC s-1), and the relationship between elbow angle and pennation was similar during slow shortening and lengthening contractions. 5. Two consequences follow from these findings. Firstly, intramuscular mechanics are complex and simple planar models of muscles underestimate the increases in pennation which occur during muscle contraction. Second, spindle afferents from relaxed muscles may not encode joint angle over the full range of movement.

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Available from: Simon C Gandevia, Aug 20, 2015
    • "These two effects might ( partially ) cancel each other out , but can also amplify each other , leading to substantial error on the predicted maximum muscle force . Also other effects that are rarely incorporated in musculoske - letal models such as the non - linear activation - induced changes in pennation angles that were for example reported for the brachialis ( Herbert and Gandevia , 1995 ) ( from 9 . 0° at rest to 24 . "
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    ABSTRACT: Personalisation of model parameters is likely to improve biomechanical model predictions and could allow models to be used for subject- or patient-specific applications. This study evaluates the effect of personalising physiological cross-sectional areas (PCSA) in a large-scale musculoskeletal model of the upper extremity. Muscle volumes obtained from MRI were used to scale PCSAs of five subjects, for whom the maximum forces they could exert in six different directions on a handle held by the hand were also recorded. The effect of PCSA scaling was evaluated by calculating the lowest maximum muscle stress (σmax, a constant for human skeletal muscle) required by the model to reproduce these forces. When the original cadaver-based PCSA-values were used, strongly different between-subject σmax-values were found (σmax=106.1±39.9Ncm(-2)). A relatively simple, uniform scaling routine reduced this variation substantially (σmax=69.4±9.4Ncm(-2)) and led to similar results to when a more detailed, muscle-specific scaling routine was used (σmax=71.2±10.8Ncm(-2)). Using subject-specific PCSA values to simulate an shoulder abduction task changed muscle force predictions for the subscapularis and the pectoralis major on average by 33% and 21%, respectively, but was <10% for all other muscles. The glenohumeral (GH) joint contact force changed less than 1.5% as a result of scaling. We conclude that individualisation of the model's strength can most easily be done by scaling PCSA with a single factor that can be derived from muscle volume data or, alternatively, from maximum force measurements. However, since PCSA scaling only marginally changed muscle and joint contact force predictions for submaximal tasks, the need for PCSA scaling remains debatable. Copyright © 2015 Elsevier Ltd. All rights reserved.
    Journal of Biomechanics 05/2015; DOI:10.1016/j.jbiomech.2015.05.005 · 2.50 Impact Factor
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    • "Since the RMSD obtained with all electrodes over the whole BB was not different from the distal configurations only, we conclude that redundancy is present between proximal and distal parts of BB. However, the brachialis muscle, a synergist of the BB in elbow flexion, arises from a broad origin about midway of the humerus and inserts into the ulna (Herbert and Gandevia, 1995). Due to the fusiform shape of the distal part of BB (e.g. "
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    ABSTRACT: 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.
    Journal of electromyography and kinesiology: official journal of the International Society of Electrophysiological Kinesiology 04/2013; DOI:10.1016/j.jelekin.2013.03.004 · 1.73 Impact Factor
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    • "However, EMG offers a poor spatial resolution and it does not in general provide any information about muscle structure and mechanical aspects. Imaging techniques such as magnetic resonance imaging (MRI) and ultrasound imaging have mainly been used to study the size and architectural parameters of muscles since they have a great impact on the muscle force production and high spatial resolution (Herbert and Gandevia 1995; Fukunaga et al. 1997; Narici 1999; Blazevich et al. 2006; Kawakami et al. 2006). The high temporal resolution makes ultrasound specially suited as a technique when it comes to studying structural movements in real-time (Shi et al. 2008). "
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