Search results for "Concentric"
showing 10 items of 147 documents
Changes in isokinetic torque and muscular activity of elbow flexors muscles with age
2001
This study examined the influence of aging on torque-angular velocity relationships for elbow flexion and the corresponding muscular activity levels in order to target the mechanisms involved in the eccentric muscle action in older adults. Maximal constant angular torque (CAT) at 90 degrees was measured at different angular velocities for concentric (CON; 60, 120, 180, 240 degrees s(-1)), isometric (ISO) and eccentric (ECC; -60, -120 degrees s(-1)) elbow flexor muscle actions in older (OG; 6 females and 4 males, 64-82 years) and young adult subjects (YG; 6 females, 6 males, 19-24 years) on an isokinetic dynamometer. Myoelectrical activity was quantified on biceps and triceps muscles, using …
Electromechanical behaviour of human muscles in vertical jumps
1982
The relationships of muscle structure to the potentiation of myoelectrical activity and to the use of prestretching in five lower limb muscles were studied in different vertical jumping conditions. The subjects for the study were six male students, divided according to the muscle fiber distribution in m. vastus lateralis into “fast” and “slow” groups. The subjects performed vertical jumps (1) from a static squatting position (SJ), (2) with a preliminary counter movement (CMJ) and (3) after dropping (DJ) from five different heights. Myoelectrical (EMG) activity was recorded from mm. gluteus maximus, vastus lateralis, vastus medialis, rectus femoris and gastrocnemius in each jumping condition…
Electromechanical delay in human skeletal muscle under concentric and eccentric contractions.
1979
In contraction of skeletal muscle a delay exists between the onset of electrical activity and measurable tension. This delay in electromechanical coupling has been stated to be between 30 and 100 ms. Thus, in rapid movements it may be possible for electromyographic (EMG) activity to have terminated before force can be detected. This study was designed to determine the dependence of the EMG-tension delay upon selected initial conditions at the time of muscle activation. The right forearms of 14 subjects were passively oscillated by a motor-driven dynamometer through flexion-extension cycles of 135 deg at an angular velocity of approximately equal to 0.5 rad/s. Upon presentation of a visual s…
Contribution of the tendinous tissue to force enhancement during stretch–shortening cycle exercise depends on the prestretch and concentric phase int…
2005
When the prestretch intensity and concentric work are increased in stretch-shortening cycle (SSC) exercises, the utilization of the elastic energy can increase during the concentric phase. In order to further understand this process during SSC exercises, the interaction between fascicle-tendinous tissues (TT) of the vastus lateralis (VL) muscle was examined under different prestretch and rebound intensity drop jumps. Ten male subjects participated in the study. Direct VL fascicle lengths (N = 10) and in vivo patellar tendon force (N = 1) were measured together with the electromyographic (EMG) activity of VL during the trials. With increasing drop height but the same rebound height condition…
Neomuscular fatigue to power loading using a weight-stack device fitted with or without additional rubber band resistance
2014
The addition of a rubber band (RB) to traditional weight-based resistance may be beneficial regarding the deceleration phase common during explosive power actions with light weights. This would lead to greater force and muscle activity during the latter part of the movement, but this may influence the distribution of neuromuscular fatigue. Fifteen men performed 2 knee extension power loadings (5 × 5 × 40% of 1 repetition maximum [1RM]) using a typical weight-stack device without (WS) and with the addition of a RB (WS + RB) in a crossover design. Concentric contractions were performed as fast as possible, and analyzed for torque, velocity, power, and vastus lateralis and medialis surface ele…
Kinetic and electromyographic analysis of single repetition constant and variable resistance leg press actions
2010
During a multi-joint leg press action, maximal force capabilities increase with increasing knee angle. In typical resistance exercises, constant resistance is used, which does not stress the neuromuscular system at large knee angles. The purpose of this study was to compare constant and variable resistance settings using a range of contraction loads and velocities. Nine healthy, untrained males performed single contractions using four different resistance settings (constant resistance, two settings that increased resistance at large knee angles and one setting that reduced resistance at large knee angles). Single contractions using 40%, 60%, and 80% of one repetition maximum with both stead…
Prestretch potentiation of human skeletal muscle during ballistic movement
1981
The conditions associated prior to and during the transition from prestretch to shortening may have considerable influence on the final performance of muscle. In the present study male subjects of good physical condition performed vertical jumps on the force-platform with and without preliminary counter movement. In the counter movement jump (CMJ) the amplitude of the knee bending, velocity of the prestretch and the force attained at end of prestretch were the primary parameters of interest. In addition the coupling time indicating the transition from the eccentric (prestretch) phase to the concentric phase was recorded from the angular displacement and reaction force curves. In the final c…
Alterations of mechanical characteristics of human skeletal muscle during strength training
1983
To investigate the influence of strength training on the mechanical characteristics of human skeletal muscle, 14 male subjects went through training of combined heavy concentric and eccentric contractions three times a week for 16 weeks. The strength training program consisted mainly of dynamic exercises for leg extensors with loads of 80 to 120% of one maximum repetition. The force-time curves produced during various vertical jumps were the basis for calculation of various mechanical parameters. In addition to a great increase (p less than 0.001) in maximal isometric force, heavy resistance strength training also caused significant (p less than 0.05-0.01) increases in heights and in variou…
Force and EMG power spectrum during eccentric and concentric actions
2000
This study was designed to examine the force and activation levels of elbow flexor muscles during preactivated eccentric, concentric and isometric actions.Force, average EMG (aEMG), and the EMG power spectrum were investigated at different constant movement velocities (1 rad x s(-1), 2 rad x s(-1), 3 rad x s(-1), and 4 rad x s(-1)) at different joint angles.Average force at a 110 degree elbow angle was lower and aEMG was higher in concentric actions as compared with eccentric and isometric actions. At a 55 degree elbow angle, there was no difference in aEMG, or it was slightly higher in eccentric actions. MF was higher in the concentric as compared with eccentric actions at the three fastes…
Effects of long-term training specificity on maximal strength and power of the upper and lower extremities in athletes from different sports
2002
Maximal concentric one repetition maximum half-squat (1RM(HS)), bench-press (1RM(BP)), power-load curves during concentric actions with loads ranging from 30% to 100% of 1RM(HS) and 1RM(BP)were examined in 70 male subjects divided into five groups: weightlifters (WL, n=11), handball players (HP, n=19), amateur road cyclists (RC, n=18), middle-distance runners (MDR, n=10) and age-matched control subjects (C, n=12). The 1RM(HS)values in WL, HP and RC were 50%, 29% and 28% greater, respectively, ( P<0.001-0.01) than those recorded for MDR and C. The half-squat average power outputs at all loads examined (from 30% to 100%) in WL and HP ( P<0.001 at 45% and 60% with HP) were higher ( P<0.05-0.00…