RESUMEN
This study aimed to investigate the motor unit firing property immediately after concentric or eccentric contraction exercise. Eighteen healthy men performed repetitive maximal isokinetic knee extension exercises with only concentric or eccentric contraction until they exerted less than 80% of the baseline strength. Before and after the fatiguing exercise, high-density surface electromyography of the vastus lateralis was recorded during submaximal ramp-up isometric contraction and individual motor units were identified. Only motor units that could be tracked before and after exercise were analyzed. Muscle cross-sectional area of the vastus lateralis was measured using ultrasound, and electrically evoked torque was recorded before and after the exercise. Sixty-five and fifty-three motor units were analyzed before and after the concentric and eccentric contractions, respectively. The results showed that motor units with moderate to high recruitment thresholds significantly decreased recruitment thresholds under both conditions, and the motor unit discharge rates significantly increased after concentric contraction compared to eccentric contraction. A greater muscle cross-sectional area was observed with concentric contraction. The evoked torque was significantly decreased under both conditions, but no difference between the conditions. These results suggest that fatiguing exercise with concentric contraction contributes to greater neural input to muscles and metabolic responses than eccentric contraction.
Asunto(s)
Contracción Isométrica , Músculo Esquelético , Masculino , Humanos , Músculo Esquelético/fisiología , Contracción Isométrica/fisiología , Electromiografía/métodos , Rodilla/fisiología , Torque , Fatiga , Contracción Muscular/fisiologíaRESUMEN
Measuring the quality of movement is a need and a challenge for clinicians. Jerk, defined as the quantity of acceleration variation, is a kinematic parameter used to assess the smoothness of movement. We aimed to assess and compare jerk metrics in asymptomatic participants for 3 important movement characteristics that are considered by clinicians during shoulder examination: dominant and non-dominant side, concentric and eccentric contraction mode, and arm elevation plane. In this pilot study, we measured jerk metrics by using Xsens® inertial measurement units strapped to the wrists for 11 different active arm movements (ascending and lowering phases): 3 bilateral maximal arm elevations in sagittal, scapular and frontal plane; 2 unilateral functional movements (hair combing and low back washing); and 2 unilateral maximal arm elevations in sagittal and scapular plane, performed with both arms alternately, right arm first. Each arm movement was repeated 3 times successively and the whole procedure was performed 3 times on different days. The recorded time series was segmented with semi-supervised algorithms. Comparisons involved the Wilcoxon signed rank test (p < 0.05) with Bonferroni correction. We included 30 right-handed asymptomatic individuals [17 men, mean (SD) age 31.9 (11.4) years]. Right jerk was significantly less than left jerk for bilateral arm elevations in all planes (all p < 0.05) and for functional movement (p < 0.05). Jerk was significantly reduced during the concentric (ascending) phase than eccentric (lowering) phase for bilateral and unilateral right and left arm elevations in all planes (all p < 0.05). Jerk during bilateral arm elevation was significantly reduced in the sagittal and scapular planes versus the frontal plane (both p < 0.01) and in the sagittal versus scapular plane (p < 0.05). Jerk during unilateral left arm elevation was significantly reduced in the sagittal versus scapular plane (p < 0.05). Jerk metrics did not differ between sagittal and scapular unilateral right arm elevation. Using inertial measurement units, jerk metrics can well describe differences between the dominant and non-dominant arm, concentric and eccentric modes and planes in arm elevation. Jerk metrics were reduced during arm movements performed with the dominant right arm during the concentric phase and in the sagittal plane. Using IMUs, jerk metrics are a promising method to assess the quality of basic shoulder movement.
RESUMEN
This study compared changes in brachial-ankle pulse wave velocity (baPWV) after concentric (CON) versus eccentric (ECC) cycling. It was hypothesized that baPWV would increase after the first ECC bout (ECC1) because of muscle damage, but not after the second ECC bout (ECC2), and would decrease after CON. Fifteen young (aged 20-30 years) men performed 2 bouts of 30-min ECC (ECC1 and ECC2) at 60% of maximal CON power output and 2 bouts of 30-min CON at the same intensity as that of ECC (CON1), and at the same oxygen consumption as that of ECC (CON2) every 2 weeks. Oxygen uptake during the cycling was recorded, and baPWV was measured before and at 0.5, 1, 24, and 48 h after each cycling bout. Maximal voluntary contraction (MVC) torque and muscle soreness of the knee extensors were assessed before and at 24 and 48 h after each cycling bout. Changes in these variables over time were compared among the 4 cycling bouts by 2-way repeated-measured ANOVA. baPWV decreased (P < 0.05) 8% from the baseline (1119 ± 116 cm/s) at 0.5 h after CON1 (1028 ± 126 cm/s), but no significant changes were evident after ECC1, ECC2, and CON2. MVC torque decreased 10% from the baseline at 24 h after ECC1, but no significant changes were evident after CON1, CON2, and ECC2. These results did not support the hypothesis, and suggest that minor muscle damage induced by eccentric cycling does not affect arterial stiffness.
Asunto(s)
Ciclismo/fisiología , Rigidez Vascular , Adulto , Índice Tobillo Braquial , Prueba de Esfuerzo , Humanos , Rodilla/fisiología , Masculino , Contracción Muscular , Músculo Esquelético/fisiología , Mialgia , Consumo de Oxígeno , Análisis de la Onda del Pulso , Torque , Adulto JovenRESUMEN
Previous studies have reported that different modes of muscle contraction (i.e., eccentric or concentric contraction) with similar contraction times can affect muscle proteolytic responses. However, the effect of different contraction modes on muscle proteolytic response under the same force-time integral (FTI: contraction force × time) has not been investigated. The purpose of this study was to investigate the effect of different contraction modes, with the same FTI, on acute proteolytic signaling responses. Eleven-week-old male Sprague-Dawley rats were randomly assigned to eccentric (EC), concentric (CC), or isometric contraction (IC) groups. Different modes of muscle contraction were performed on the right gastrocnemius muscle using electrical stimulation, with the left muscle acting as a control. In order to apply an equivalent FTI, the number of stimulation sets was modified between the groups. Muscle samples were taken immediately and three hours after exercise. Phosphorylation of FoxO3a at Ser253 was significantly increased immediately after exercise compared to controls irrespective of contraction mode. The mRNA levels of the ubiquitin ligases, MuRF1, and MAFbx mRNA were unchanged by contraction mode or time. Phosphorylation of ULK1 at Ser317 (positive regulatory site) and Ser757 (negative regulatory site) was significantly increased compared to controls, immediately or 3 h after exercise, in all contraction modes. The autophagy markers (LC3B-II/I ratio and p62 expression) were unchanged, regardless of contraction mode. These data suggest that differences in contraction mode during resistance exercise with a constant FTI, are not factors in regulating proteolytic signaling in the early phase of skeletal muscle contraction.
Asunto(s)
Contracción Muscular , Músculo Esquelético/metabolismo , Proteolisis , Transducción de Señal , Animales , Homólogo de la Proteína 1 Relacionada con la Autofagia/genética , Homólogo de la Proteína 1 Relacionada con la Autofagia/metabolismo , Proteína Forkhead Box O3/genética , Proteína Forkhead Box O3/metabolismo , Masculino , Proteínas Asociadas a Microtúbulos/genética , Proteínas Asociadas a Microtúbulos/metabolismo , Proteínas Musculares/genética , Proteínas Musculares/metabolismo , Músculo Esquelético/fisiología , Condicionamiento Físico Animal/fisiología , Ratas , Ratas Sprague-Dawley , Proteínas Ligasas SKP Cullina F-box/genética , Proteínas Ligasas SKP Cullina F-box/metabolismo , Proteínas de Motivos Tripartitos/genética , Proteínas de Motivos Tripartitos/metabolismo , Ubiquitina-Proteína Ligasas/genética , Ubiquitina-Proteína Ligasas/metabolismoRESUMEN
Resistance training with eccentric contraction has been shown to augment muscle hypertrophy more than other contraction modes do (i.e., concentric and isometric contraction). However, the molecular mechanisms involved remain unclear. The purpose of this study was to investigate the effect of muscle contraction mode on mammalian target of rapamycin complex 1 (mTORC1) signaling using a standardized force-time integral (load (weight) × contraction time). Male Sprague-Dawley rats were randomly assigned to three groups: eccentric contraction, concentric contraction, and isometric contraction. The right gastrocnemius muscle was exercised via percutaneous electrical stimulation-induced maximal contraction. In experiment 1, different modes of muscle contraction were exerted using the same number of reps in all groups, while in experiment 2, muscle contractions were exerted using a standardized force-time integral. Muscle samples were obtained immediately and 3 h after exercise. Phosphorylation of molecules associated with mTORC1 activity was assessed using western blot analysis. In experiment 1, the force-time integral was significantly different among contraction modes with a higher force-time integral for eccentric contraction compared to that for other contraction modes (P < 0.05). In addition, the force-time integral was higher for concentric contraction compared to that for isometric contraction (P < 0.05). Similarly, p70S6K phosphorylation level was higher for eccentric contraction than for other modes of contraction (P < 0.05), and concentric contraction was higher than isometric contraction (P < 0.05) 3 h after exercise. In experiment 2, under the same force-time integral, p70S6K (Thr389) and 4E-BP1 phosphorylation levels were similar among contraction modes 3 h after exercise. Our results suggest that mTORC1 activity is not determined by differences in muscle contraction mode itself. Instead, mTORC1 activity is determined by differences in the force-time integral during muscle contraction.