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ABSTRACT: The aims of this study were to examine if surface EMG signals can be detected from the quadriceps femoris muscle of severely obese patients and to investigate if differences exist in quadriceps force and myoelectric manifestations of fatigue between obese patients and lean controls. Fourteen severely obese patients (body mass index, BMI, mean±SD: 44.9±6.3kg/m(2)) and fourteen healthy controls (BMI: 23.7±2.5kg/m(2)) were studied. The vastus medialis and lateralis of the dominant thigh were concurrently investigated during voluntary isometric contractions (10-s long at submaximal and maximal intensities and intermittent submaximal contractions until exhaustion) and sustained (120-s long) electrically elicited contractions. We found that the detection of surface EMG signals from the quadriceps is feasible also in severely obese subjects presenting increased thickness of the subcutaneous fat tissue. In addition, we confirmed and extended previous findings showing that the volume conductor properties determine the amplitude and spectral features of the detected surface EMG signals: the lower the subcutaneous tissue thickness, the higher the amplitude and mean frequency estimates. Further, we found no differences in the mechanical and myoelectric manifestations of fatigue during intermittent voluntary and sustained electrically elicited contractions between obese patients and lean controls.
Journal of electromyography and kinesiology: official journal of the International Society of Electrophysiological Kinesiology 10/2012; · 2.00 Impact Factor
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ABSTRACT: Electrical stimulation of innervated muscles has been investigated for many decades with alternations of high and low clinical interest in the fields of rehabilitation medicine and sports sciences. Early work demonstrated that afferent fibers have lower thresholds and are usually activated first (therefore eliciting an H-reflex). In the case of nerve trunk stimulation, the order of recruitment is mostly conditioned by the axonal dimension and excitability threshold. In the case of muscle motor point stimulation, the spatial distribution of nerve branches plays a predominant role. Sustained stimulation produces a progressive increase of force that is often maintained in subsequent voluntary activation by stroke patients. This observation suggested a facilitation mechanism at the spinal and/or supraspinal level. Such facilitation has been observed in healthy subjects as well, and may explain the generation of cramps elicited during stimulation and sustained for dozens of seconds after the stimulation has been interrupted. The most recent interpretations of facilitation resulting from peripheral stimulation focused on presynaptic (potentiation of neurotransmitter release from afferent fibers) or postsynaptic (generation of "persistent inward currents" in spinal motor neurons or interneurons) mechanisms. The renewed attention to these phenomena is once more increasing the interest toward electrical stimulation of the neuromuscular system. This is an opportunity for a structured investigation of the field aimed to resolving elements of confusion and controversy that still plague this area of electrophysiology.
Artificial Organs 03/2011; 35(3):221-5. · 2.00 Impact Factor
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ABSTRACT: Glucocorticoids are known to decrease protein synthesis and impair membrane excitability of muscle fibers. However, their short-term effects on muscle structure and function of healthy subjects remain poorly understood.
Our objective was to investigate whether steroid administration could decrease the circulating levels of muscle proteins and modify myoelectric indexes of sarcolemmal excitability and fatigability.
We conducted a single-blind, placebo-controlled study in 20 men randomized to receive dexamethasone (8 mg/d) or placebo for 1 wk. Blood sampling, force measurements for knee extensors and elbow flexors, and electrophysiological tests for biceps brachii, vastus lateralis and medialis, and tibialis anterior muscles were performed before and after the intervention.
Dexamethasone administration improved force by 6.0 +/- 6.0% (P = 0.01) for elbow flexors and by 8.5 +/- 5.5% (P < 0.01) for knee extensors, decreased levels of creatine kinase by 50.5 +/- 30.0% (P < 0.01) and myoglobin by 41.8 +/- 17.5% (P < 0.01), and impaired sarcolemmal excitability, as shown by the decline of muscle fiber conduction velocity for the four muscles (range from -6 to -10.5%, P < 0.05). Moreover, significant reductions of the myoelectric manifestations of fatigue were observed for the four muscles; the decrease in the rate of change of the mean frequency of the electromyographic power spectrum ranged from -22.6 to -43.9% (P < 0.05). In contrast, no significant changes were observed in muscle excitability and fatigability in subjects who received the placebo.
The demonstration that glucocorticoid-induced muscle impairments can be unraveled by means of blood sampling and noninvasive electrophysiological tests has clinical implications for the early identification of subclinical or preclinical forms of myopathy in treated patients.
The Journal of clinical endocrinology and metabolism 02/2010; 95(4):1663-71. · 6.50 Impact Factor
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ABSTRACT: This article is the second part of a larger review work that has been structured in three parts. The three parts concern a) advances in surface EMG detection and processing techniques, b) recent progress in surface EMG clinical research applications, and c) myoelectric control in neurorehabilitation. This second part concerns state of the art applications of surface EMG techniques to a) the external anal sphincter in relation to episiotomy and incontinence; b) the assessment of postural control mechanisms; c) exercise physiology, electrical stimulation and muscle cramps; and d) ergonomics and work-related neuromuscular disorders. The material is presented with an effort to fill gaps left by previous reviews and identify areas open for future research.
Critical Reviews in Biomedical Engineering 01/2010; 38(4):347-79.
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ABSTRACT: Hormones, motoneurons, and skeletal muscle fibers represent the main actors in regulating the motor performance during acute
physical exercise. Moreover, muscle growth in response to exercise conditioning is related to direct actions of hormones and
autocrine/paracrine factors on skeletal muscle fibers. The aim of this chapter is to illustrate the main interactions that
take place between the neuro-endocrine and neuro-muscular systems in response to acute exercise and to review the main hormonal
mechanisms that underlie the structural growth and remodeling of skeletal muscle fibers in response to chronic exercise training.
01/1970: pages 43-49;
