Biomedical subjects

E B Simonsen

Publications and source records attributed to E B Simonsen.

46 records · Page 3Linked to original sources

PubMed1994

Moment and power generation during maximal knee extensions performed at low and high speeds.

In the present study a method was developed to determine knee joint moment and power generated at low to very high velocities of knee extension. A group of 21 male subjects performed maximal knee extensions at four levels of external loading provided by a flywheel system. Knee extension was performed with no restrictions on joint angular velocity and acceleration. An interpolation procedure was employed to obtain moment and power at standard velocities. During each single knee extension peak velocity, peak moment, peak power and moment and power at 50 degrees knee flexion were determined (0 degree = full extension). While maximal recorded angular velocity averaged 693 degrees.s-1 (range 479-1030), maximal recorded moment and power were 226 N.m (157-278) and 1140 W (573-1688), respectively, which were generated at velocities of 55 degrees.s-1 (12-148) and 523 degrees.s-1 (327-846). Isokinetic moment and power were obtained for comparison. The velocity range applied was larger using the flywheel method (21-1030 degrees.s-1 individual range) than that achieved isokinetically (30-240 degrees.s-1). Significant differences were observed between flywheel and isokinetic measurements. These discrepancies may be ascribed to differences in the time course of muscle length change and contractile force generation imposed by the two measuring methods. However, by the nonisokinetic measuring method presently employed, knee extension moment and power could be determined from low to very high angular extension velocity, at loading and contraction conditions comparable to those encountered during sport and exercise.

Adult↗

PubMed1994

Effects of different strength training regimes on moment and power generation during dynamic knee extensions.

This study examined the effect of different training regimes on moment and power generation during maximal knee extensions at low to very high extension velocities (0-1000 degrees.s-1 individual range). A group of 24 soccer players performed 12 weeks of progressively adjusted strength training of the knee extensors at either high resistance (HR, n = 7), low resistance (LR, n = 6), loaded kicking movements (FU, n = 6), while one group served as controls (n = 5). Moment and power generation of the knee extensors were determined before and after the training period with a nonisokinetic measuring method recently described. Following HR training, knee extension moment increased 9%-10% at knee angular velocities 0 (isometric) and 30 degrees.s-1 (P < 0.05), peak moment increased 20% at 240-300 degrees.s-1 (P < 0.05), while power generation increased 5%-29% at 240-480 degrees.s-1 (P < 0.01). In addition, in the HR group maximal recorded power increased 45% (P < 0.01). After FU training a 7%-13% increase in moment and power was observed at 30-180 degrees.s-1 (P < 0.05). Following LR training, peak moment increased 9% at 120 degrees.s-1 (P < 0.05). Improvements in knee extension moment and power were generally related to the angular velocities employed during training. However, as evaluated using the present measuring method, moment and power increased not only at very low but also at high knee angular velocities following the high-resistance strength training.

Adult↗

PubMed1993

Motor unit recruitment during prolonged isometric contractions.

Motor unit recruitment patterns were studied during prolonged isometric contraction using fine wire electrodes. Single motor unit potentials were recorded from the brachial biceps muscle of eight male subjects, during isometric endurance experiments conducted at relative workloads corresponding to 10% and 40% of maximal voluntary contraction (MVC), respectively. The recordings from the 10% MVC experiment demonstrated a characteristic time-dependent recruitment. As the contraction progressed both the mean number of motor unit spikes counted and the mean amplitude of the spikes increased significantly (P < 0.01). This progressive increase in spike activity was the result of a discontinuous process with periods of increasing and decreasing activity. The phenomenon in which newly recruited motor units replace previously active units is termed "motor unit rotation" and appeared to be an important characteristic of motor control during a prolonged low level contraction. In contrast to the 10% MVC experiment, there was no indication of de novo recruitment in the 40% MVC experiment. Near the point of exhaustion a marked change in action potential shape and duration dominated the recordings. These findings demonstrate a conspicuous difference in the patterns of motor unit recruitment during a 10% and a 40% MVC sustained contraction. It is suggested that there is a close relationship between intrinsic muscle properties and central nervous system recruitment strategies which is entirely different in fatiguing high and low level isometric contractions.

Action Potentials↗

PubMed1993

Shoulder muscle load and muscle fatigue among industrial sewing-machine operators.

Physiological responses to physical work were assessed for 29 female industrial sewing-machine operators during an 8-h working day under ordinary working conditions. During sewing-machine work, the average (left and right) static load in the trapezius muscle was 9% of the maximal electromyogram (EMG) amplitude (% EMGmax), while the average mean load was 15% EMGmax, and the average peak load was 23% EMGmax. The static load level was unrelated to the muscle strength of the sewing-machine operators, which for the group as a whole was within the normal range. The load levels remained unchanged during the working day, while changes in the EMG mean power frequency and zero crossing frequency rate occurred, both indicating the development of muscle fatigue in left and right trapezius muscle during the working day. In line with this, the rating of perceived exertion in the shoulder and neck region increased during the working day. Dividing the group of sewing-machine operators into two groups, those with the highest frequency and those with the lowest frequency of shoulder/neck troubles showed that the former group had significantly lower muscle strength, despite the fact that no differences in the surface EMG during sewing were found between the two groups. It was concluded that industrial sewing-machine work involves a pattern of shoulder muscle activity which induces fatiguing processes in the shoulder and neck regions. Furthermore, since the static shoulder muscle load was independent of muscle strength, factors other than working posture may be of significance for the static shoulder muscle load.

Adult↗

PubMed1991

Dynamic control of muscle stiffness and H reflex modulation during hopping and jumping in man.

1. The objective of the study was to evaluate the functional effects of reflexes on muscle mechanics during natural voluntary movements. The excitability of the H (Hoffmann) reflex was used as a measure of the excitability of the central component of the stretch reflex. 2. We recorded EMG, ground reaction forces and the H reflex in the soleus muscle in humans while landing from a downward jump, during drop jumping and during hopping. The movements were also recorded by high-speed cinematography. 3. The EMG pattern was adapted to the motor task. When landing the EMG in the soleus muscle and in the anterior tibial muscle showed preinnervation and alternating activity after touch down. When hopping there was little preinnervation in the soleus muscle, and the activity was initiated about 45 ms after touch down by a peak and continued unbroken until lift off. In the drop jumps the EMG pattern depended on the jumping style used by the subject. 4. The H reflex in the soleus muscle was strongly modulated in a manner appropriate to the requirements of the motor task. During landing from a downward jump the H reflex was low at touch down whereas while hopping it was high at touch down. During drop jumping it was variable and influenced by the jumping technique. 5. Muscle stiffness in the ankle joint was negative after touch down when landing, but always positive when hopping. 6. It is suggested that during landing the alternating EMG pattern after touch down was programmed and little influenced by reflexes. During hopping reflexes could contribute to the initial peak and the EMG during lift off. 7. The programmed EMG activity and the suppression of the H reflex while landing probably contribute to the development of the negative stiffness and change the muscles from a spring to a damping unit.

Adult↗

PubMed1985

Activity of mono- and biarticular leg muscles during sprint running.

A cinematographic recording of the movements of the lower limbs together with simultaneous emg tracings from nine lower limb muscles were obtained from two male track sprinters during three phases of a 100 m sprint run. The extensor muscles of the hip joint were found to be the primary movers by acceleration of the body's center of gravity (C.G.) during the ground phase of the running cycle. The extensors of the knee joint were also important in this, but to a minor extent, while the plantar flexors of the ankle joint showed the least contribution. The biarticular muscles functioned in a way different from the monoarticular muscles in the sense that they perform eccentric work during the flight and recovery phases and concentric work during the whole ground phase (support), whereas the monoarticular muscles are restricted first to eccentric work and then to concentric work during the ground phase. Furthermore, the biarticular muscles show variation (and rate of variation) in muscle length to a larger extent than the monoarticular muscles. Paradoxical muscle actions appear to take place around the knee joint, where the hamstring muscles, m. gastrocnemius, m. vastus laterialis and m. vastus medialis act as synergists by extending the knee joint during the last part of the ground phase.

Ankle↗

PubMedDate not supplied

Evaluation of the walking pattern in clubfoot patients who received early intensive treatment.

The walking pattern in a group of nine adult male subjects who had received early intensive treatment for congenital clubfoot was evaluated and compared to the walking pattern in a control group of 15 adult healthy male subjects. All subjects were filmed with a five-camera video system as they walked across two force plates. A three-dimensional inverse dynamics approach was used to calculate average joint angles, moments, power, and work. The results showed that there were no differences in the joint angles between the two groups. The overall patterns of the joint moments were very similar in the two groups. However, analysis revealed a smaller ankle joint moment and larger knee and hip joint moments in those with clubfoot. It was concluded that the larger knee and hip joint moments served as compensation for the smaller ankle moment. The reduced ankle moment and work developed about the ankle joint in the clubfeet could possibly be owing to weaker plantar flexors. In conclusion, gait analysis can be an important tool when evaluating treatment for clubfoot. However, further investigation is needed to determine whether the higher hip and knee joint moments observed in subjects with clubfoot may lead to the development of knee or hip joint pathologies.

Adolescent↗

PubMedDate not supplied

Biomechanical responses to repeated stretches in human hamstring muscle in vivo.

To examine stiffness, energy, and passive torque in the dynamic and static phases of a stretch maneuver in the human hamstring muscle in vivo we used a test-retest protocol and a repeated stretches protocol. Resistance to stretch was defined as passive torque (in newton-meters) offered by the hamstring muscle group during passive knee extension as measured using an isokinetic dynamometer with a modified thigh pad. In 13 uninjured subjects, the knee was passively extended to a predetermined final position (0.0875 rad/ sec, dynamic phase) where it remained stationary for 90 seconds (static phase). The test-retest protocol included two tests administered 1 hour apart. On a separate occasion, five consecutive static stretches were administered separated by 30 seconds and followed by a sixth stretch 1 hour later. For the test-retest phase, stiffness and energy in the dynamic phase and passive torque in the static phase did not differ and yielded correlations of r = 0.91 to 0.99. During the static phase, passive torque declined in both tests (P < 0.0001). For the repeated stretches, decreases were observed for energy (P < 0.01) and stiffness (P < 0.05) in the dynamic phase and for passive torque (P < 0.0001) in the static phase. However, the decline in the variables returned to baseline within 1 hour. The data show that the method employed is a useful tool for measuring biomechanical variables during a stretch maneuver. This may provide a more detailed method to examine skeletal muscle flexibility.

Adult↗

PubMedDate not supplied

The effect of strength and flexibility training on skeletal muscle electromyographic activity, stiffness, and viscoelastic stress relaxation response.

The present study examined whether isometric strength training alone or isometric strength training combined with flexibility training of the hamstring muscles altered the viscoelastic response during stretch. Twelve male subjects performed isometric training (strength) on one side and isometric and flexibility training (strength and flexibility) on the other side for 13 weeks; 10 other subjects served as controls. Passive torque offered by the hamstring muscle group was measure during passive knee extension using a dynamometer. The knee was passively extended to a predetermined final position at 0.0875 rad/sec (dynamic phase), where it remained stationary for 90 seconds (static phase). The slope of the line (stiffness) and the area under the curve (energy) in the dynamic phase, and the decline in passive torque (viscoelastic stress relaxation) in the static phase were analyzed. Isometric strength was determined with a dynamometer. A strength test and a stretch maneuver were administered before and after the training period. All variables were unchanged in the control group. Isometric strength increased similarly on both training sides by 43%. The stretch maneuver showed that energy, stiffness, and passive torque increased on both training sides while low-level electromyographic recordings remained constant. Furthermore, the viscoelastic stress relaxation response (31% to 33%) was unaffected by the training. The addition of flexibility exercise had no significant effect on these strength training responses. These data suggest that an increase in isometric strength is accompanied by changes in the material properties of the muscle that are unaffected by flexibility exercises.

Adult↗

PubMedDate not supplied

A new concept for isokinetic hamstring: quadriceps muscle strength ratio.

Conventionally, the hamstring:quadriceps strength ratio is calculated by dividing the maximal knee flexor (hamstring) moment by the maximal knee extensor (quadriceps) moment measured at identical angular velocity and contraction mode. The agonist-antagonist strength relationship for knee extension and flexion may, however, be better described by the more functional ratios of eccentric hamstring to concentric quadriceps moments (extension), and concentric hamstring to eccentric quadriceps moments (flexion). We compared functional and conventional isokinetic hamstring: quadriceps strength ratios and examined their relation to knee joint angle and joint angular velocity. Peak and angle-specific (50 degrees, 40 degrees, and 30 degrees of knee flexion) moments were determined during maximal concentric and eccentric muscle contractions (10 degrees to 90 degrees of motion; 30 and 240 deg/sec). Across movement speeds and contraction modes the functional ratios for different moments varied between 0.3 and 1.0 (peak and 50 degrees), 0.4 and 1.1 (40 degrees), and 0.4 and 1.4 (30 degrees). In contrast, conventional hamstring:quadriceps ratios were 0.5 to 0.6 based on peak and 50 degrees moments, 0.6 to 0.7 based on 40 degrees moment, and 0.6 to 0.8 based on 30 degrees moment. The functional hamstring:quadriceps ratio for fast knee extension yielded a 1:1 relationship, which increased with extended knee joint position, indicating a significant capacity of the hamstring muscles to provide dynamic knee joint stability in these conditions. The evaluation of knee joint function by use of isokinetic dynamometry should comprise data on functional and conventional hamstring:quadriceps ratios as well as data on absolute muscle strength.

Analysis of Variance↗