Biomedical subjects

A Veicsteinas

Publications and source records attributed to A Veicsteinas.

At least 19 recordsLinked to original sources

PubMed2005

Nutritional status and dietary patterns in disabled people.

BACKGROUND AND AIM: Obesity, cardiovascular diseases, diabetes and osteoporosis are the most frequent pathologies among people with a severe reduction of physical activity. The impairment in nutritional status, consequent to quantitative and qualitative inadequacy of diet, could be one of the first steps in the development of co-morbidities in disabled subjects. In order to evaluate this hypothesis we investigated the nutritional status and the food intake in patients with physical or mental disabilities. METHODS AND RESULTS: Thirty-seven disabled subjects (24 with exclusively physical inactivity and 13 with mental retardation and physical inactivity) mean age 33.5+/-9.2 years and 25 healthy subjects (mean age 31.0+/-9.3 years) were enrolled. Anthropometric measurements, indirect calorimetry, dual-energy X-ray absorptiometry, dietary intake and biochemical parameters were collected for each subject. Forty percent of disabled were overweight and 14% were obese. Fat free mass (FFM) and bone mineral content (BMC) was lower and fat mass (FM) was higher than able-bodied control. Absolute resting energy expenditure (REE) was lower in disabled subjects, but this difference disappeared when REE was normalized to FFM. Dietary intake resulted unbalanced (16%, 31%, 50% of total daily energy intake derived from protein, lipid and carbohydrate respectively) with a distribution of dietary fatty acid quite far from the recommended ratio [3.1(SFA):4.1(MUFA):1.0(PUFA)] and an excessive consumption of simple carbohydrates (mean intake 17.5+/-4.9%). Insufficient intake of fibre, iron, calcium, potassium and zinc was also found. Finally, alterations in the cholesterol profile were evident in more than one third of the disabled subjects, whereas fasting glucose intolerance was evident in one fourth. CONCLUSION: This study shows a consistent nutritional status impairment in disabled patients resulting in an reduction of FFM and BMC, in an over-representation of FM and in a number of biochemical risk factors for cardiovascular disease. The altered nutritional status is counterparted by a widespread inadequacy of dietary patterns. This nutritional and dietary impairment occurs both in subjects with mental and physical diseases.

Absorptiometry, Photon↗

PubMed2005

Effects of short term cast wearing on respiratory and cardiac responses to submaximal and maximal exercise in adolescents with idiopathic scoliosis.

AIM: Bracing is widely used to treat adolescent scoliosis. However, bracing may also affect respiratory and cardiovascular function. In this thirteen-weeks longitudinal study we evaluated the effect of brace wearing on maximal and submaximal cardiorespiratory capacity in adolescents with moderate idiopathic scoliosis. METHODS: Eight boys and 8 girls (12-18 years) with scoliosis of the thoracic spine (Cobb angle range 32 degrees - 42 degrees in boys and 32 degrees - 60 degrees in girls) were enrolled. Respiratory basal function (forced vital capacity, FVC, and forced expired volume in 1 s, FEV(1)) and cardiorespiratory adjustments to submaximal and maximal cycle ergometer exercise (heart rate, HR, pulmonary ventilation, VE, and oxygen consumption, VO(2)) were measured a week before fitting a brace, after 1 and 12 weeks of brace wearing, and a week after brace removal. RESULTS: With respect to pretreatment values: a) after 1 week of brace wearing FVC and FEV(1) were significantly reduced in both genders; b) after 12 weeks of bracing the amount of oxygen consumed per heart beat was reduced during maximal and submaximal exercises in females only; c) ventilatory efficiency was unchanged in both genders in each condition; d) oxygen uptake during maximal exercise was decreased (by about 10-20%) in females only; e) after brace removal all variables tended to regress to pretreatment values. CONCLUSIONS: Although data are preliminary and need to be confirmed on larger samples of patients, the brace appears to limit maximal exercise performance especially in girls, where it affects the cardiopulmonary efficiency. Thus, moderate physical exercise during brace wearing is advised to counteract respiratory, cardiovascular and muscle inefficiency due to ribcage movement limitations.

Adolescent↗

PubMed2003

Body composition assessment in spinal cord injury subjects.

Total and segmental body composition (fat mass, FM; fat-free mass, FFM; bone mineral density, BMD) were evaluated in 13 sedentary spinal cord injury (SCI) subjects and in 13 able-bodied healthy males (control, C) using dual X-ray absorptiometry (DXA) and skinfold methods. In the SCI group, total FM was significantly higher (31.1+/-8.2 vs. 20.8+/-6.9%) and total FFM was significantly lower (62.2+/-8.9 vs. 73.5+/-6.4%) than in C subjects. Total BMD did not differ between the SCI and C groups (1.20+/-0.11 vs. 1.30+/-0.11 g/cm(2)). In the SCI group, segmental FM was higher in the legs and trunk, whereas BMD was lower in legs only. The skinfold method significantly underestimated FM in the SCI group. Body composition is severely modified in paralyzed segments. The predictive equations developed for healthy populations appear to be inapplicable to SCI subjects.

Absorptiometry, Photon↗

PubMed2003

Energy consumption of locomotion with orthosis versus Parastep-assisted gait: a single case study.

STUDY DESIGN: Single case study. OBJECTIVES: To evaluate the energy expenditure during ambulation with the Advanced Reciprocating Gait Orthosis (ARGO), with and without functional electrical stimulation (FES), and with the Parastep system in a single subject, in order to avoid the effect of inter-subject variability. SETTING: The Centre of Sport Medicine and Bioengineering Centre 'Don C Gnocchi' Foundation ONLUS IRCCS, Milano, Italy. METHODS: A single patient (lesion level T5-T6) was trained specifically for each walking system and was evaluated after each training period. The effects of FES on muscle conditioning, spasticity and bone density were also evaluated. The HR/VO2 relationship and the energy cost of locomotion were measured during wheelchair (WHCH) use, during locomotion with ARGO (with and without FES) and Parastep system at different speeds. RESULTS: The following was observed at the end of the whole training: (a) circumferences of both lower limbs and quadriceps forces were increased, whereas fatigue index was slightly decreased, spasticity and bone density were unchanged; (b) compared to WHCH locomotion, the slope of HR/VO2 curves with ARGO was higher (slope difference=51.1 b 1O2(-1)), with ARGO+FES was similar (slope difference=-5.3 b 1O2(-1)) and with Parastep was smaller (slope difference=-55.6 b 1O2(-1)); (c) HR increased linearly with all locomotion systems, but did not rise above 125 bpm with Parastep; (d) the cost of locomotion was higher with Parastep than with ARGO (with and without FES), tested at each velocity; (e) Parastep appears to be easier to use for the subject. CONCLUSIONS: (a) FES can improve ambulation with orthosis, but the cost of locomotion remains very high; (b) the Parastep assisted gait elicits a higher energy expenditure than other orthoses, probably due to the lower speed of locomotion and to the high isometric effort of the stimulated muscles. SPONSORSHIP: This work has been partially supported by the Italian Minister of Public Health (Ricerca Finalizzata IRCCS no ICS030.7/RF97.25).

Adaptation, Physiological↗

PubMed2001

Cardio-respiratory adjustments and cost of locomotion in school children during backpack walking (the Italian Backpack Study).

The use of a school backpack is one of the possible causes of back pain in children. Oxygen consumption (VO2), pulmonary ventilation, and heart rate (fc) were measured in 35 pre-pubertal subjects [17 girls and 18 boys, mean (SD) age 11.3 (0.6) years]. They took part in a four-step experiment: (1) standing for 5 min, (2) walking at 3 km.h(-1) for 7 min, (3) walking at 3 km.h(-1) for 7 min carrying a school backpack weighing 8 kg, and (4) walking at 7 km.h(-1) for 5 min with no load. The occurrence of back pain in the last 2-3 years and during the last 15 days was assessed for the subjects by means of a questionnaire. Mean (SD) standing VO2, was 215 (45) ml.min(-1) during walking at 3 km.h(-1), 503 (101) ml.min(-1) during walking without a load, and increased to 541 (98) ml.min(-1) during walking with a load (P<0.01). Carrying a backpack increased fc only minimally. The energy cost of walking at 3 km.h(-1) without the backpack was 10.0 (2.0) ml O2.m(-1), and with the backpack was 10.8 (1.9) ml O2.m(-1) (P< 0.01). The net energy cost of locomotion was 0.129 (0.032) ml.kg body mass(-1).m(-1) for the unloaded condition and slightly lower, at 0.123 (0.025) ml.kg body mass(-1).m(-1) during loaded walking (P < 0.05). Ventilation did not change significantly between unloaded and loaded conditions. When the data were assessed according to the occurrence of back pain, the fc/VO2 slope was significantly lower in children without back pain, even though the net energy cost of locomotion was similar. Overall, these data suggest that the cardiovascular effortrequired for locomotion while carrying a backpack is minimal. However, fatigability and back pain are more likely to take place in less physical performing subjects. Thus, the occurrence of back pain in schoolchildren during locomotion while carrying a backpack may improve with an improvement in their level of fitness.

Back↗

PubMed2001

Sinusoidal 50 Hz magnetic fields do not affect structural morphology and proliferation of human cells in vitro.

The effects of electromagnetic fields on several processes related to cell physiology and proliferation are currently being investigated. Although the results are still not conclusive and even conflicting, there seems to be a fairly good agreement on the early effects of electromagnetic fields on the generation of free radicals and on Ca++-intracellular concentration and transport. To evaluate the long-lasting consequences of these precocious events, we examined the effects of short- and long-term magnetic field exposure on structural organization (cytokeratin or actin detection), proliferation (bromodeoxyuridine incorporation and propidium iodide staining), colony forming ability and viability (trypan blue exclusion test) of highly proliferating MCF-7 cells (from human breast carcinoma) and on slowly proliferating normal human fibroblasts (from healthy donors). Cells were exposed to either 20 or 500 microT sinusoidally oscillating (50Hz) magnetic fields for different lengths of time (1 to 4 days). Short (1 day)- and long (4 days)-time exposure to the two intensities did not affect MCF-7 growth and viability, colony number and size, or cellular distribution along the cell cycle; neither were the cell morphology and the intracellular distribution and amount of cytokeratin modified. Similarly, no modifications in the actin distribution and proliferative potential were observed in normal human fibroblasts. These findings suggest that under our experimental conditions, continuous exposure to magnetic fields does not result in any appreciable effect in both normal and tumor cells in vitro.

Actins↗

PubMed2000

Metabolic and cardiorespiratory responses to maximal intermittent knee isokinetic exercise in young healthy humans.

There have been many studies on the effects of isokinetic exercise on muscle performance in training and rehabilitative programmes. On the other hand, the cardiovascular and metabolic responses elicited by this type of exercise have been poorly investigated. This study was specifically designed to describe the relationships, if any, between metabolic and cardiorespiratory responses and power output during maximal intermittent knee isokinetic exercise when a steady state is reached. A group of 18 healthy subjects (10 men and 8 women, age range 25-30 years) were requested to perform at maximal concentric isokinetic knee extensions/flexions 60 degrees. s(-1) and 180 degrees. s(-1) for 5 min, with a 5-s pause interposed between consecutive repetitions. The power output (W) was calculated; before and during the tasks heart rate (f(c)) and arterial blood pressure (AP(a)) were continuously monitored. Pulmonary ventilation (V(E)) and oxygen uptake (VO(2)) were measured at the 4th and at the 5th min of exercise and blood lactate concentration at rest and at the 3rd min of recovery. From the 4th to the 5th min only a slight decrease in W was observed, both at 60 degrees. s(-1) and 180 degrees. s(-1). The VO(2), V(E), f(c) and AP(a) showed similar values in the last 2 min of exercise, suggesting that a steady state had been reached. The VO(2) increased linearly as a function of +W, showing a significantly steeper slope at 60 degrees. s(-1) than at 180 degrees. s(-1). The f(c), in spite of a large interindividual variation, was linearly related to metabolic demand, and was not affected by angular velocity. Systolic and diastolic AP(a) were not related either to VO(2) or to angular velocity. In conclusion it would appear that the metabolic response to maximal intermittent knee isokinetic exercise resembles that of dynamic exercise. Conversely, the cardiocirculatory responses would seem to reflect a relevant role of the isometric postural component, the importance of which should be carefully evaluated in each subject.

Adult↗

PubMed2000

Heart rate variability during dynamic exercise in elderly males and females.

It has been proposed that cardiac control is altered in the elderly. Power spectral analysis of heart rate variability (HRV) was performed on 12 male and 11 female elderly subjects (mean age 74 years) while at rest in supine and sitting positions, and at steady states during 5 min of exercise (35-95% peak oxygen consumption, VO2peak). There were no differences in power, measured as a percentage of the total of the high frequency peak (HF, centred at about 0.25 Hz; 13% in males vs 12% in females), low frequency peak (LF, centred at 0.09 Hz; 25% in males and 22% in females), and very low frequency component (VLF, at 0.03 Hz; 66% in males and 69% in females) between body positions at rest. There was no difference in spectral power between male and female subjects. Total power decreased as a function of oxygen consumption during exercise, LF% did not change up to about 14 ml x kg(-1) x min(-1) (40% and 80% VO2peak in males and females, respectively), then decreased towards minimal values in both genders. HF% power and central frequency increased linearly with metabolic demand, reaching higher values in male subjects than in female subjects at VO2peak, while VLF% remained unchanged. Thus, the power spectra components of HRV did not reflect the changes in autonomic activity that occur at increasing exercise intensities, confirming previous findings in young subjects, and indicated similar responses in both genders.

Aged↗

PubMed2000

Force and surface mechanomyogram frequency responses in cat gastrocnemius.

Muscle surface displacement is a mechanical event taking place simultaneously with the tension generation at the tendon. The two phenomena can be studied by the surface mechanomyogram signal (MMG) (produced by a laser distance sensor) and the force signal (from a load cell). The aim of this paper was to provide data on the reliability of the laser detected MMG in muscle mechanics research. To this purpose it was verified if the laser detected MMG was suitable to estimate a frequency response in the cat medial gastrocnemius and its frequency response was compared with the one retrieved by the force signal at the tendon level. The force and MMG from the exposed medial gastrocnemius of four cats were analysed. The frequency response was investigated by sinusoidally changing the number of orderly recruited motor units, in different trials, in the 0.4-6 Hz range. It resulted that it was possible to model the force and MMG frequency response by a critically damped second-order system with two real double poles and a pure time delay. On the average, the poles were at 1.83 Hz (with 22.6 ms delay) and at 2.75 Hz (with 38 ms delay) for force and MMG, respectively. It can be concluded that MMG appears to be a reliable tool to investigate the muscle frequency response during stimulated isometric contraction. Even though not statistically significant. the differences in the second-order system parameters suggest that different components of the muscle mechanical model may specifically affect the force or MMG.

Animals↗

PubMed2000

Paraplegic adaptation to assisted-walking: energy expenditure during wheelchair versus orthosis use.

STUDY DESIGN: To study the energy cost of locomotion during ambulation with different orthoses (HIP Guidance Orthosis Orlau Parawalker (PW), n=4; Reciprocating Gait Orthosis (RGO), n=6; RGO + FNS, n=4). OBJECTIVES: Since high energy costs of locomotion have been proposed as a major reason for early rejection of orthotic use, our aims were (a) to evaluate the impact of functional neuromuscular stimulation (FNS) on energy expenditure during orthosis-assisted ambulation; (b) to study whether energy expenditure data can predict the poor long-term patients' compliance and (c) to assess selection criteria for the assignment of the different types of orthosis. SETTING: The study was completed at the Center of Sports Medicine and Center of Bioengineering, don C. Gnocchi Foundation, IRCCS, Milan, Italy. METHODS: The HR/VO2 relationship and the energy cost of locomotion (C) were studied in 14 patients (lesion level C7-T11) during wheelchair (WHCH) use at various speeds and during locomotion with different orthotic devices. Patients' short- and long-term compliance were assessed by questionnaires evaluating duration of and problems related to orthotic use. RESULTS: (a) In patients using RGO + FNS the slope difference of HR/VO2 curves (deltaslHR/VO2) between WHCH and orthosis was significantly lower than in other groups (-3 beats l(-1) in RGO + FNS vs 43 and 52 beats l(-1) in RGO and PW, respectively); (b) neither C, nor VO2 peak, or deltaslHR/VO2 correlated with orthosis duration of use; (c) in the RGO + FNS group, C was lower at maximal walking speed, which linearly correlated with maximal WHCH speed. CONCLUSION: (a) Electrical stimulation seems to improve locomotion, as a consequence of hemodynamic effects, but does not decrease energy expenditure, which remains high; (b) the poor long-term compliance to orthosis use cannot be predicted by the energy expenditure parameters; (c) the subjects who can reach high speeds by WHCH seem to be the most appropriate for RGO + FNS locomotion.

Adaptation, Physiological↗

PubMed1999

Surface mechanomyogram reflects the changes in the mechanical properties of muscle at fatigue.

The contractile properties of muscle are usually investigated by analysing the force signal recorded during electrically elicited contractions. The electrically stimulated muscle shows surface oscillations that can be detected by an accelerometer; the acceleration signal is termed the surface mechanomyogram (MMG). In the study described here we compared, in the human tibialis anterior muscle, changes in the MMG and force signal characteristics before, and immediately after fatigue, as well as during 6 min of recovery, when changes in the contractile properties of muscle occur. Fatigue was induced by sustained electrical stimulation. The final aim was to evaluate the reliability of the MMG as a tool to follow the changes in the mechanical properties of muscle caused by fatigue. Because of fatigue, the parameters of the force peak, the peak rate of force production and the peak of the acceleration of force production (d2F/dt2) decreased, while the contraction time and the half-relaxation time (1/2-RT) increased. The MMG peak-to-peak (p-p) also decreased. The attenuation rate of the force oscillation amplitude and MMG p-p at increasing stimulation frequency was greater after fatigue. With the exception of 1/2-RT, all of the force and MMG parameters were restored within 2 min of recovery. A high correlation was found between MMG and d2F/dt2 in un-fatigued muscle and during recovery. In conclusion, the MMG reflects specific aspects of muscle mechanics and can be used to follow the changes in the contractile properties of muscle caused by localised muscle fatigue.

Adult↗

PubMed1999

Force and surface mechanomyogram relationship in cat gastrocnemius.

The aim of this study was to compare the force (F) and the muscle transverse diameter changes during electrical stimulation of the motor nerve. In four cats the exposed motor nerves of the medial gastrocnemius were stimulated as follows: (a) eight separate trials at fixed firing rates (FR) from 5 to 50 Hz (9 s duration, supramaximal amplitude); (b) 5 to 50 Hz linear sweep in 2.5, 5, 7.5 and 10 s (supramaximal amplitude, separate trials); (c) four separate trials at 40 Hz, the motor units (MUs) being orderly recruited in 2.5, 5, 7.5 and 10 s. The muscle surface displacement was detected by a laser distance sensor pointed at the muscle surface. The resulting electrical signal was termed surface mechanomyogram (MMG). In stimulation patterns (a) and (b) the average F and MMG increased with FR. With respect to their values at 50 Hz the amplitude of the unfused signal oscillations at 5 Hz was much larger in MMG than in force. The signal rising phase was always earlier in MMG than in F. In (c) trials, F increased less in the first than in the second half of the recruiting time. MMG had an opposite behaviour. The results indicate that the force and the lateral displacement are not linearly related. The different behaviour of F and MMG, from low to high level of the MUs' pool activation, suggests that the force generation and the muscle dimensional change processes are influenced by different components of the muscle mechanical model.

Animals↗

PubMed1999

Influence of low and high dietary fat on physical performance in untrained males.

PURPOSE: Dietary manipulations have been used in athletes to enhance aerobic performance. We intended to verify whether the quality of energy substrate provided by food (percentage of total calories from fat and carbohydrates) per se has the ability to affect aerobic performance in sedentary humans. METHOD: Fourteen healthy sedentary males were sequentially submitted to 4-wk eucaloric diets (spontaneous diet: 30% of total calories from fat; low-fat, 15% fat; high-fat, 55% fat; and spontaneous, 30% fat). After each diet period, individual body mass, percentage body fat (plicometry), VO2max (incremental bicycle-ergometry) and endurance (pedaling time to exhaustion at 75%VO2max) were measured. VO2, VCO2, VE, R, and heart rate (HR) were measured at rest and during exercise tests. Body composition and performance data (VO2max and endurance) were compared for significant differences by repeated measures ANOVA. RESULTS: Subjects' body weight, percentage body fat, and fitness status (indicated by intercept and slope of the HR/VO2 linear relationship) did not change significantly during the study, thus ruling out the influence of these potential confounders. For a given workload, VO2, VE, and R were unaffected by diet composition. VO2max and endurance time were not significantly modified by the different diets. CONCLUSIONS: Our study showed no impact, positive or negative, of diet's macronutrient composition on physical performance. It appears that the quality of energy substrate provided by food does not have the ability to affect either maximal or submaximal aerobic performance in untrained individuals.

Adult↗

PubMed1998

Heart rate variability in exercising humans: effect of water immersion.

Power spectrum analysis of heart-rate variability was made in seven men [mean age 22 (SEM 1) years] in head-out water immersion (W) and in air (A, control) at rest and during steady-state cycling to maximal intensity (maximum oxygen uptake, VO2max). At rest W resulted in a trebled increase in the total power (P < 0.05), coupled with minimal changes in the power (as a percentage of the total) of the high frequency peak (HF, centred at 0.26 Hz; 18% vs 28%) and of the low frequency peak (LF, 0.1 Hz; 24% vs 32%). A third peak at about 0.03 Hz (very low frequency, VLF) represented the remaining power both in W and A. These changes as a whole indicated that immersion caused a vagal dominance in cardiac autonomic interaction, due to the central pooling of blood and/or the pressure of water on the trunk. Exercise caused a decrease in the total power in W and A. The LF% did not change up to about 50% V02max, thereafter decreasing towards nil in both conditions. The HF% decreased in similar ways in W and A to about half at 55%-60% VO2max and then increased to reach 1.5 times the resting values at VO2max. The central frequency of HF increased linearly with oxygen uptake, showing a tendency to be higher in W than in A at medium to high intensities. The VLF% remained unchanged. The lack of differences in the LF peak between W and A during exercise would suggest that blood distribution had no effect on the readjustments in control mechanisms of arterial pressure. On the other hand, the findings of similar HF powers and the very similar values for ventilation in W and A confirmed the direct effect of the respiratory activity in heart rate modulation during exercise.

Adult↗

PubMed1998

Electromyogram and mechanomyogram changes in fresh and fatigued muscle during sustained contraction in men.

In surface electromyogram (EMG) and mechanomyogram (MMG) the electrical and mechanical activities of recruited motor units (MU) are summated. Muscle fatigue influences the electrical and mechanical properties of the active MU. The aim of this study was to evaluate fatigue-induced changes in the electrical and mechanical properties of MU after a short recovery period, using an analysis of force, surface EMG and MMG. In seven subjects the EMG and MMG were recorded from the biceps brachii muscle during sustained isometric effort at 80% of the maximal voluntary contraction (MVC), before (test 1) and 10 min after (test 2) a fatiguing exercise. From the time and frequency domain analysis of the signals, the root mean square (rms) and the mean frequency (f) of the power spectrum were calculated. The results were that the mean MVC was 412 (SEM 90) N and 304 (SEM 85) N in fresh and fatigued muscle, respectively; during tests 1 and 2 the mean EMG rms increased from 0.403 (SEM 0.07) mV to 0.566 (SEM 0.09) mV and from 0.476 (SEM 0.07) mV to 0.63 (SEM 0.09) mV, respectively; during test 1 the mean MMG rms decreased from 9.4 (SEM 0.8) mV to 5.7 (SEM 0.9) mV; in contrast, during test 2 constantly lower values were observed throughout contraction; during tests 1 and 2 the EMG f declined from 122 (SEM 7) Hz to 74 (SEM 7) Hz and from 106 (SEM 8) Hz to 60 (SEM 7) Hz, respectively; during test 1 the MMG f increased in the first 6 s from 19.3 (SEM 1.4) Hz to 23.9 (SEM 2.9) Hz, falling to 13.9 (SEM 1.3) Hz at the end of contraction; in contrast, during test 2 the MMG f declined continuously from 18.7 (SEM 1) Hz to 12.4 (SEM 0.8) Hz. The lower MVC after the fatiguing exercise and the changes in the EMG parameters confirmed that 10 min after the fatiguing exercise, the mechanical and electrical activities of MU were altered. In addition, the MMG results suggested that after a 10-min recovery, some highly fatigable MU might not be recruitable.

Adult↗

PubMed1997

Electrically-elicited surface mechanomyogram in myotonic dystrophy.

The surface oscillation of the muscle during electrical stimulation is detectable by an accelerometer as a surface mechanomyogram (MMG). The aim of this study was to evaluate whether MMG properties reflect the mechanical muscle changes induced by myotonic dystrophy (MyD). To this end, the tibialis anterior of seven MyD patients and seven age- and sex-matched controls (C) was supramaximally stimulated at 1 (single twitches), 5, 10, 15, 20 Hz for 3 s at the most proximal motor point. RESULTS SINGLE TWITCHES: The MMG amplitude was 67% less, the duration 37% longer, the electromechanical delay 64% longer, and the spectrum mean frequency, 44% lower in the MyD patients than in controls. REPETITIVE STIMULATION: At each stimulation frequency, the average MMG peak-to-peak was less in the MyD patients than in C. CONCLUSION: The differences between the MMGs of MyD patients and C support the hypothesis that, together with the well-known changes in sarcolemmal excitability, an alteration in electromechanical coupling and a failure in contractile machinery may coexist in MyD.

Biomechanical Phenomena↗

PubMed1996

Development of chicken embryos exposed to an intermittent horizontal sinusoidal 50 Hz magnetic field.

The effects of intermittent exposure (2 h on/22 h off) to a 200 microT horizontal, sinusoidally oscillating (50 Hz) magnetic field were studied in 210 fertilized chicken eggs. Two hundred ten control eggs (sham-exposed) were incubated in the same chamber as the experimental eggs. Chick embryos were examined for developmental anomalies and maturity stage after 48 h of incubation. Immunohistochemical analysis of extracellular membrane components (laminin, fibronectin, and type IV collagen) were conducted on day 7 and histological examinations for malformations of brain, liver, and heart, on days 7, 12, and 18 of incubation. Furthermore, egg fertility and egg weights were evaluated on days 2, 7, 12, and 18. The investigation also measured the body weight of chickens for 90 days from hatching and included histological analysis of body organs. Each variable was investigated blind. Statistical comparison between exposed and sham-exposed values did not show significant differences in any of the variables investigated. Thus, it appears that the exposure of embryos to an intermittent 200 microT magnetic field at 50 Hz does not cause developmental anomalies, changes in maturity stage, alterations in distribution of extracellular membrane components, or malformations in the brain, liver, or heart. Moreover, there were no differences in body weight, morphology, or histology of central nervous system, liver, heart, or testis in 90-day-old chickens hatched from exposed in comparison to sham-exposed eggs.

Animals↗

PubMed1996

Time and frequency domain analysis of electromyogram and sound myogram in the elderly.

The aim of this work was to evaluate the influence of the ageing process on the time and frequency domain properties of the surface electrical and mechanical activity of muscle. In 20 healthy elderly subjects (10 men and 10 women, age range 65-78 years) and in 20 young controls, during isometric contractions of the elbow flexors in the 20%-100% range of the maximal voluntary contraction (MVC), estimations were made of the root mean square (rms) and the mean frequency (MF) of the power density spectrum distribution, from the surface electromyogram (EMG) and sound myogram (SMG) signals, detected at the belly of the biceps brachii muscle. Compared to the young controls, the MVC was lower in the elderly subjects (P < 0.05); at the same %MVC the rms and the MF of EMG and SMG were lower (P < 0.05) in elderly subjects; the rms and MF of the two signals increased as a function of the effort level in all groups. Only in the 80%-100% MVC range did the EMG-MF level off and the SMG-rms decrease; in contrast the young controls, at 80% MVC the high frequency peak in the SMG power spectrum density distribution was not present in the elderly subjects. The results for MVC and %MVC can be related to the reduction in the numbers of muscle fibres in aged subjects. In particular, the lack of fast twitch fibre motor units (MU), attaining high firing rates, might also explain the result at 80% MVC. In 80%-100% MVC range the two signals rms and MF behaviour may have been related to the end of the recruitment of larger MU with high conduction velocity, and to the further increment of MU firing rate in the biceps brachii muscle beyond 80% MVC, respectively. Thus, the coupled analysis of the EMG and SMG with force suggests that in the elderly subjects the reduction of the number of muscle fibres may have co-existed with a MU activation pattern similar to that of the young subjects.

Adult↗