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- Patel, T. J., et al.
(författare)
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Sarcomere strain and heterogeneity correlate with injury to frog skeletal muscle fiber bundles
- 2004
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Ingår i: J Appl Physiol. - : American Physiological Society. - 8750-7587. ; 97:5, s. 1803-13
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Tidskriftsartikel (refereegranskat)abstract
- Sarcomere length and first-order diffraction line width were measured by laser diffraction during elongation of activated frog tibialis anterior muscle fiber bundles (i.e., eccentric contraction) at nominal fiber strains of 10, 25, or 35% (n = 18) for 10 successive contractions. Tetanic tension, measured just before each eccentric contraction, differed significantly among strain groups and changed dramatically during the 10-contraction treatment (P < 0.01). Average maximum tetanic tension for the three groups measured before any treatment was 203.7 +/- 6.8 kN/m2, but after the 10-eccentric contraction sequence decreased to 180.3 +/- 3.8, 125.1 +/- 7.8, and 78.3 +/- 5.1 kN/m2 for the 10, 25, and 35% strain groups, respectively (P < 0.0001). Addition of 10 mM caffeine to the bathing medium decreased the loss of tetanic tension in the 10% strain group but had only a minimal effect on either the 25 or 35% strain groups. Diffraction pattern line width, a measure of sarcomere length heterogeneity, increased significantly with muscle activation and then continued to increase with successive stretches of the activated muscle. Line width increase after each stretch was significantly correlated with the lower yield tension of the successive contractile record. These data demonstrate a direct association and, perhaps, a causal relationship between sarcomere strain and fiber bundle injury. They also demonstrate that muscle injury is accompanied by a progressive increase in sarcomere length heterogeneity, yielding lower yield tension as injury progresses.
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- Gerdle, Björn, 1953-, et al.
(författare)
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The influences of muscle fibre proportions and areas upon EMG during maximal dynamic knee extensions
- 2000
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Ingår i: European Journal of Applied Physiology and Occupational Physiology. - 0301-5548 .- 1432-1025. ; 81:1-2
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Tidskriftsartikel (refereegranskat)abstract
- This study is an investigation of the relationship between muscle morphology and surface electromyographic (EMG) parameters [mean frequency of the power spectrum (MNF), signal amplitude (root mean square, RMS) and the signal amplitude ratio (SAR, i.e. the ratio between the RMS level during the passive part of the contraction cycle and the RMS level during the active part of the contraction cycle)] during 100 maximal dynamic knee extensions at 90░.s-1. Each contraction cycle comprised of 1 s of active knee extension and 1 s of passive knee flexion. The surface EMG was recorded from the vastus lateralis muscle. Twenty clinically healthy subjects participated in the study, and muscle biopsy samples of the vastus lateralis were obtained from 19 of those subjects. The relationships between muscle morphology and EMG were investigated at three stages of the test: initially, during the fatigue phase (initial 40 contractions), and at the endurance level (the final 50 contractions). Major findings on correlations are that SAR and MNF tended to correlate positively with the proportion of type 1 fibres, and RMS correlated positively with the proportion of type 2 muscle fibres. The muscle fibre areas showed little correlation with the EMG variables under investigation. The results of the present study showed that the three EMG variables of a dynamic endurance test that were investigated (RMS, MNF and SAR were clearly correlated with the proportions of the different fibre types, but only to a small extent with fibre areas. These findings contradict some of the theoretical models of the EMG, especially for parameters in the frequency domain.
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- Necking, Lars, et al.
(författare)
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Hand muscle weakness in long-term vibration exposure.
- 2002
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Ingår i: Journal of Hand Surgery (British Volume). - : SAGE Publications. - 0266-7681. ; 27:6, s. 520-525
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Tidskriftsartikel (refereegranskat)abstract
- Hand muscle strength was compared between workers regularly exposed to hand-held vibrating tools ( n = 81) and a non-exposed control group ( n = 45). Maximal voluntary strengths of hand grip, thumb pinch, thumb palmar abduction and index and little finger abduction were measured. The exposed workers had significantly weaker extrinsic (7%, P < 0.01) and intrinsic (19%, P < 0.0001) muscles than the controls. Reduced vibration perception was noted in nine vibration-exposed workers who presented with symptoms of hand muscle weakness ( P < 0.01). Cold intolerance following vibration exposure was found to precede sensorineural and vasospastic symptoms. We therefore postulate that cold intolerance may be a valuable marker for early detection of the adverse effects of vibration. This study emphasizes the need for tests of intrinsic muscle strength in order to evaluate the impairment of hand function observed in vibration-exposed workers.
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