PubMed · 5233393
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O Grosfeld. 1967. [Contribution to the discussion on function regulators].. https://pubmed.ncbi.nlm.nih.gov/5233393/
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This article reviews, without mathematics, the important principles governing the acquisition and use of normative data in electrodiagnostic medicine. Common flaws in neurophysiological normative data include vague clinical criteria for establishing freedom from disease, samples that are too small and inadequately stratified, and application of Gaussian statistics to non-Gaussian variables. Other problematic issues concern the trade-off between permissible false-positivity and false-negativity in defining the limits of normative from sample data, test-retest variability, and the use of multiple independent test measurements in each electrodiagnostic examination. The following standards for normative data are proposed: (1) standardized objective determination of freedom from disease; (2) appropriately large sample of normal subjects; (3) proportional statification of normal subjects for known relevant variables; (4) test of Gaussian fit for application of Gaussian statistics; and (5) data presentation by percentiles when Gaussian fit is in doubt. Many existing normative studies in clinical neurophysiology do not meet these standards. High-quality normative data, readily accessible, is essential for the accurate electrodiagnosis of neuromuscular diseases.
A 47-year-old female with paramyotonia congenita was studied with electromyography and showed minimal myotonic discharges but prominent repetitive discharges in hand muscles at room temperature. With cooling the hand, the repetitive discharges ceased as the myotonic potentials became prominent. With exercise and further cooling, the myotonic discharges increased and the strength of the muscle and recruitment pattern decreased. With warming, the myotonic discharges decreased as the repetitive discharges reappeared. This is the first report of repetitive discharges occurring in a patient with temperature-sensitive sodium channel myotonia. It is postulated that the repetitive discharges as well as the myotonic discharges are the manifestation of muscle membrane hyperexcitability secondary to the abnormal, noninactivating sodium channels.
The hypothesis was tested that the magnitude of cross education is greater following training with muscle lengthening than shortening. Changes in contralateral concentric, eccentric, and isometric strength and vastus lateralis and biceps femoris surface electromyographic (EMG) activity were analyzed in groups of young men who exercised the ipsilateral quadriceps with either eccentric (N = 7) or concentric (N = 8) contractions for 36 sessions over 12 wk. Control subjects (N = 6) did not train. Concentric training increased concentric strength 30% and isometric strength 22%, and eccentric training increased eccentric strength 77% and isometric strength 39% (all P < 0.05). Eccentric training improved eccentric strength three times more than the concentric training improved concentric strength (P < 0.05), and eccentric compared with concentric training improved isometric strength about 2 times more (P < 0.05). The eccentric group improved significantly from pre- to mid-training in eccentric and isometric strength (P < 0.05). The control group showed no significant changes (P < 0.05). Surface EMG activity of the vastus lateralis increased 2.2 times (pre- to mid-training), 2.8 (mid- to post-training) and 2.6 more (pre- to post-training) (P < 0.05) in the eccentric than concentric group. No significant changes in EMG activity occurred in the control group (P > 0.05). It was concluded that the greater cross education following training with muscle lengthening is most likely being mediated by both afferent and efferent mechanisms that allow previously sedentary subjects to achieve a greater activation of the untrained limb musculature.