RESUMEN
Gigantopyramidal neurons, referred to as Betz cells in primates, are characterized by large somata and extensive basilar dendrites. Although there have been morphological descriptions and drawings of gigantopyramidal neurons in a limited number of species, quantitative investigations have typically been limited to measures of soma size. The current study thus employed two separate analytical approaches: a morphological investigation using the Golgi technique to provide qualitative and quantitative somatodendritic measures of gigantopyramidal neurons across 19 mammalian species from 7 orders; and unbiased stereology to compare the soma volume of layer V pyramidal and gigantopyramidal neurons in primary motor cortex between 11 carnivore and 9 primate species. Of the 617 neurons traced in the morphological analysis, 181 were gigantopyramidal neurons, with deep (primarily layer V) pyramidal (n = 203) and superficial (primarily layer III) pyramidal (n = 233) neurons quantified for comparative purposes. Qualitatively, dendritic morphology varied considerably across species, with some (sub)orders (e.g., artiodactyls, perissodactyls, feliforms) exhibiting bifurcating, V-shaped apical dendrites. Basilar dendrites exhibited idiosyncratic geometry across and within taxonomic groups. Quantitatively, most dendritic measures were significantly greater in gigantopyramidal neurons than in superficial and deep pyramidal neurons. Cluster analyses revealed that most taxonomic groups could be discriminated based on somatodendritic morphology for both superficial and gigantopyramidal neurons. Finally, in agreement with Brodmann, gigantopyramidal neurons in both the morphological and stereological analyses were larger in feliforms (especially in the Panthera species) than in other (sub)orders, possibly due to specializations in muscle fiber composition and musculoskeletal systems.
Asunto(s)
Evolución Biológica , Corteza Motora/citología , Células Piramidales/ultraestructura , Animales , Recuento de Células , Dendritas/ultraestructura , Femenino , Humanos , Masculino , Mamíferos/anatomía & histología , Células Piramidales/clasificación , Células Piramidales/citología , Tinción con Nitrato de Plata , Especificidad de la EspecieRESUMEN
Consumption of energy drinks by both recreational and competitive athletes has increased dramatically in recent years. The primary ingredients in many energy drinks include caffeine (CAF) in various forms and taurine. The purpose of this randomized, double-blind, crossover study was to examine the effect of sugar-free (SF) Red Bull (RB) containing CAF and taurine to a CAF only drink and a SF CAF-free placebo (PL) on 1 repetition maximum (1RM) bench press (BP) and the volume load (VL; repetitions × kg at 70% 1RM) during one BP set to failure in experienced lifters. Seventeen college-age men randomly received the following: (A) 500 mL of SF-RB containing CAF (160 mg) and taurine (2000 mg); (B) 500 mL of a SF drink containing CAF only (160 mg); or (C) a SF CAF-free 500 mL PL drink 60 minutes before testing on 3 separate occasions. After a standard warm-up, the 1RM was determined for each subject and, after 5 minutes rest, they completed repetitions to failure at 70% of their 1RM to assess VL. Differences between trials for 1RM BP and the VL were identified using repeated measures analysis of variance (p < 0.05). The results indicated that neither SF-RB nor the CAF drink had any effect on 1RM BP (115.13 ± 16.19 kg and 114.87 ± 16.16 kg, respectively) or VL (1173.08 ± 170.66 kg and 1164.14 ± 147.03 kg, respectively) compared with PL (1RM = 114.07 ± 16.09 kg; VL = 1141.46 ± 193.41 kg). Although the CAF content in the energy drinks used in the present study was low (â¼2.0 mg/kg), the finding of no effect of the CAF containing energy drinks for 1RM BP are in agreement with previous studies using intakes up to 6.0 mg/kg. These findings suggest that SF-RB has no effect on upper body 1RM strength or VL in resistance trained men.
Asunto(s)
Bebidas Energéticas , Fatiga Muscular/efectos de los fármacos , Fuerza Muscular/efectos de los fármacos , Resistencia Física/efectos de los fármacos , Adulto , Cafeína/farmacología , Estudios Cruzados , Método Doble Ciego , Prueba de Esfuerzo , Humanos , Masculino , Entrenamiento de Fuerza , Taurina/farmacología , Adulto JovenRESUMEN
The purpose of this study was to compare critical velocity (CV) estimates from five mathematical models, and to examine the oxygen uptake (VO(2)) and heart rate (HR) responses during treadmill runs at the five estimates of CV. Ten subjects (six males and four females) performed one incremental test to determine maximal oxygen consumption (VO(2max)) and four or five randomly ordered constant-velocity trials on a treadmill for the estimation of CV. Five mathematical models were used to estimate CV for each subject including two linear, two nonlinear, and an exponential model. Up to five randomly ordered runs to exhaustion were performed by each subject at treadmill velocities that corresponded to the five CV estimates, and VO(2) and HR responses were monitored throughout each trial. The 3-parameter, nonlinear (Non-3) model produced CV estimates that were significantly (P < 0.05) less than the other four models. During runs at CV estimates, five subjects did not complete 60 min at the their estimate from the Non-3 model, nine did not complete 60 min at their estimate from the Non-2 model, and no subjects completed 60 min at any estimate from the other three models. The mean HR value (179 +/- 18 beats min(-1), HR(peak)) at the end of runs at CV using the Non-3 model was significantly less than the maximal HR (195 +/- 7 beats min(-1), HR(max)) achieved during the incremental trial to exhaustion. However, mean HR(peak) values from runs at all other CV estimates were not significantly different from HR(max). Furthermore, data indicated that mean HR(peak) values increased during runs at CV estimates from the third minute to the end of exercise for all models, and that these increases in VO(2) (range = 367-458 ml min(-1)) were significantly greater than that typically associated with O(2) drift ( approximately 200 ml min(-1)) for all but the exponential model, indicating a VO(2) slow component associated with CV estimates from four of the five models. However, the mean VO(2) values at the end of exercise during the runs at CV estimates for all five mathematical models were significantly less than the mean VO(2max) value. These results suggest that, in most cases, CV estimated from the five models does not represent a fatigueless task. In addition, the mean CV estimates from the five models varied by 18%, and four of the five mean CV estimates were within the heavy exercise domain. Therefore, CV would not represent the demarcation point between heavy and severe exercise domains.
Asunto(s)
Frecuencia Cardíaca/fisiología , Modelos Biológicos , Modelos Teóricos , Consumo de Oxígeno/fisiología , Carrera/fisiología , Adulto , Ejercicio Físico/fisiología , Prueba de Esfuerzo , Femenino , Humanos , Masculino , Resistencia Física/fisiología , Distribución Aleatoria , Factores de TiempoRESUMEN
The purpose of this investigation was to determine the accuracy of near-infrared interactance (NIR) instruments and population-specific NIR equations for estimating percent body fat (% fat) in young wrestlers. Forty-four white male youth wrestlers (mean age +/- SD = 11.0 +/- 2.1 years) volunteered for this study. Thirteen NIR % fat estimates were cross-validated against the criterion % fat from underwater weighing. The results of this study indicated that the total error (TE) values associated with the NIR instrument generated % fat estimates as well as % fat estimates from population-specific NIR equations developed for high school wrestlers or adult men were too large (TE = 5.7-27.3% fat) to be used with young wrestlers. Based on the present findings, it is recommended that new NIR equations be developed and validated specifically for use in young male athletes.
Asunto(s)
Composición Corporal , Espectroscopía Infrarroja Corta/instrumentación , Medicina Deportiva/instrumentación , Lucha , Adolescente , Tamaño Corporal , Niño , Humanos , Masculino , Valor Predictivo de las PruebasRESUMEN
The purpose of this study was to examine the responses of peak torque (PT), mean power output (MP), mechanomyographic (MMG) and electromyographic (EMG) amplitude and mean power frequency (MPF) of the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) in males and females during maximal, concentric isokinetic muscle actions. Subjects performed maximal leg extensions at 60 degrees s(-1), 120 degrees s(-1), 180 degrees s(-1), 240 degrees s(-1), 300 degrees s(-1), 360 degrees s(-1), 420 degrees s(-1), and 480 degrees s(-1). No gender differences were observed, but there were muscle-specific differences for the patterns of MMG MPF, EMG amplitude, and EMG MPF. The MP and MMG amplitude increased to 180-240 degrees s(-1), plateaued, and then decreased to 480 degrees s(-1). MMG MPF for the VL and VM remained unchanged to 300 degrees s(-1), but then increased to 480 degrees s(-1). The EMG amplitude for the RF and EMG MPF for the VL decreased across velocity. Overall, these findings indicated that there were muscle-specific, velocity-related differences in the associations among motor control strategies (EMG amplitude and MPF) and the mechanical aspects of isokinetic muscular activity (MMG amplitude and MPF).
Asunto(s)
Contracción Isométrica/fisiología , Músculo Esquelético/fisiología , Muslo/fisiología , Adulto , Fenómenos Biomecánicos , Impedancia Eléctrica , Electromiografía , Femenino , Humanos , Masculino , Factores Sexuales , Procesamiento de Señales Asistido por Computador , TorqueRESUMEN
PURPOSE: The purpose of this study was to examine the patterns of the mechanomyographic (MMG) and electromyographic (EMG) amplitude responses of the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) during 25 maximal, eccentric, isokinetic muscle actions. METHODS: Seven healthy adult females (22.1 +/- 2.4 yr) completed 25 maximal, eccentric muscle actions on a calibrated Cybex 6000 isokinetic dynamometer. EMG and MMG signals were obtained from the VL, RF, and VM during this test, and polynomial regression models were used to examine the relationships for normalized torque, EMG amplitude, and MMG amplitude versus repetition number. RESULTS: There was a cubic relationship (P < 0.05) between torque and repetition number. EMG amplitude demonstrated a positive linear relationship (P < 0.05) for the VL, a quadratic relationship (P < 0.05) for the RF, and no relationship (P > 0.05) for the VM over the 25 repetitions. MMG amplitude demonstrated a negative linear relationship (P < 0.05) for both the VL and VM, and a cubic relationship (P < 0.05) for the RF over the 25 repetitions. CONCLUSION: The results of the present study demonstrated differences between the VL, RF, and VM muscles for the patterns of EMG and MMG responses across the 25 maximal, eccentric muscle actions. These findings suggested that there are muscle-specific motor control strategies during repeated eccentric, isokinetic muscle actions.
Asunto(s)
Pierna/fisiología , Contracción Muscular/fisiología , Músculo Esquelético/fisiología , Adulto , Fenómenos Biomecánicos , Electromiografía , Femenino , Humanos , Cinética , Periodicidad , TorqueRESUMEN
The purpose of this study was to determine mechanomyographic (MMG) and electromyographic (EMG) responses of the superficial quadriceps muscles during repeated isokinetic contractions in order to provide information about motor control strategies during such activity, and to assess uniformity in mechanical activity (MMG) between the investigated muscles. Ten adults performed 50 maximal concentric muscle contractions at three randomly selected contraction velocities (60, 180, and 300 degrees.s(-1)) on different days. Surface electrodes and an MMG sensor were placed on the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM). EMG and MMG amplitude and peak torque (PT) were calculated for each contraction, normalized, and averaged across all subjects. The results demonstrated that MMG amplitude more closely tracked the fatigue-induced decline in torque production at each velocity than did EMG amplitude. This indicates that MMG amplitude may be useful for estimating force production during fatiguing dynamic contractions when a direct measure is not available, such as during certain rehabilitative exercises. MMG amplitude responses of the VL, RF, and VM were not uniform for each velocity or across velocities, indicating that it may be possible to detect the individual contribution of each muscle to force production during repeated dynamic contractions. Therefore, MMG amplitude may be clinically useful for detecting abnormal force contributions of individual muscles during dynamic contractions, and determining whether various treatments are successful at correcting such abnormalities.
Asunto(s)
Contracción Muscular/fisiología , Fatiga Muscular/fisiología , Músculo Esquelético/fisiología , Adulto , Electromiografía , Femenino , Humanos , Articulación de la Rodilla/fisiología , Masculino , TorqueRESUMEN
The purpose of this study was to examine the responses of peak torque (PT), mean power output (MP), mechanomyographic (MMG) and electromyographic (EMG) amplitudes, and mean power frequencies (MPFs) of the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) in men and women during dynamic muscle actions. Twelve women (mean +/- SD age = 22 +/- 3 years) and 11 men (22 +/- 3 years) performed maximal, concentric, isokinetic leg extensions at velocities of 60, 120, 180, 240, and 300 degrees x s(-1) on a Cybex 6000 dynamometer. Piezoelectric MMG-recording sensors and bipolar surface EMG electrodes were placed over the VL, RF, and VM muscles. No sex-related differences were found among the velocity-related patterns for PT, MP, MMG amplitude, MMG MPF, or EMG MPF. There were, however, sex-related differences in the patterns of EMG amplitude across velocity. The results indicated similar velocity-related patterns of increase of MP and MMG amplitude for all 3 muscles and of EMG amplitude for the VL and VM in the women. Velocity-related decreases (p
Asunto(s)
Ejercicio Físico/fisiología , Músculo Esquelético/fisiología , Caracteres Sexuales , Adulto , Electromiografía , Femenino , Humanos , Pierna , Masculino , Contracción Muscular/fisiología , Procesamiento de Señales Asistido por ComputadorRESUMEN
The purpose of this investigation was to examine the effects of unilateral, isometric training of the forearm flexors on strength and the mechanomyographic (MMG) and electromyographic (EMG) responses of the biceps brachii in the trained and untrained limb at three joint angles. Seventeen adult females (mean age +/- SD = 21 +/- 2 years) were randomly assigned to a control (CTL; N=7) or a training (TRN; N=10) group. The TRN group performed isometric training of the non-dominant forearm flexors on a Cybex II Dynamometer at a joint angle such that the Cybex lever arm was positioned 60 degrees above the horizontal plane. The training consisted of 3 to 5 sets of 8, 6-second repetitions at 80% of maximal voluntary contraction 3 times per week for 8 weeks. The results indicated a significant increase in flexed arm circumference as well as isometric strength in the trained limb at all three joint angles. There were, however, no changes in MMG or EMG amplitude in the trained or untrained limb and no cross-training effect for strength or flexed arm circumference. These findings suggested that the increased strength may have been due to factors associated with hypertrophy, independent of neural adaptations in the biceps brachii. Furthermore, hypertrophy may have had counteractive effects on the MMG signal that could be responsible for the lack of a training-induced change in the MMG amplitude.
Asunto(s)
Brazo/fisiología , Ejercicio Físico/fisiología , Contracción Isométrica/fisiología , Músculo Esquelético/fisiología , Educación y Entrenamiento Físico/métodos , Adulto , Antropometría , Electromiografía/métodos , Femenino , Humanos , Postura/fisiología , Valores de Referencia , TorqueRESUMEN
The purpose of the present investigation was to examine the velocity-related patterns of peak torque (PT), mean power output (MP), mechanomyographic (MMG) amplitude, and electromyographic (EMG) amplitude of the vastus lateralis (VL) muscle in men and women during maximal, eccentric isokinetic muscle actions of the leg extensors. Eight women [mean (SD)] [aged 23 (3) years] and seven men [aged 23 (2) years] volunteered for this investigation. Their PT was measured on a calibrated dynamometer at randomly ordered velocities of 30, 90, and 150 degrees x s(-1). A piezoelectric MMG recording sensor was placed between bipolar surface EMG electrodes (Ag-AgCl) over the VL muscle. Their MP was determined using the dynamometer software. The results indicated no sex-related differences (P > 0.05) for the patterns of PT, MP, MMG amplitude, or EMG amplitude across velocity. The normalized values for MP and MMG amplitude increased (P<0.05) from 30 to 150 degrees x s(-1) (30 degrees x s(-1) <90 degrees x s(-1) < 150 degrees x s(-1)), while PT and EMG amplitudes remained unchanged across velocity. The results indicated close associations between the velocity-related patterns of MP and MMG amplitudes as well as PT and EMG amplitudes. Thus, MMG amplitude reflected the velocity-related changes in muscle power output, but not torque production, while EMG amplitude reflected torque production, but not muscle power output. During maximal, eccentric isokinetic muscle actions, EMG and MMG signals provided unique information regarding the electrical and mechanical aspects of muscle strength and power.