Biomedical subjects

B Morlon

Publications and source records attributed to B Morlon.

14 recordsLinked to original sources

PubMed1997

Joined effects of pennation angle and tendon compliance on fibre length in isometric contractions: a simulation study.

The main purpose of this study was to investigate the joined behaviours of tendon and pennation angle during maximal isometric contractions. A musculotendon model of the human soleus muscle was simulated as a function of ankle joint position, which determines the soleus length. Analysis of the respective values of tendon length and pennation angle for various musculotendon lengths showed that the primary effects of tendon elasticity and pennation angle variation were to reduce the fibre length variations by absorption of the musculotendon lengthening. The efficiency of this reduction process was the highest at short soleus lengths and principally related to tendon length variations. Finally, it was suggested that the optimal solution for musculotendon actuators acting in high lengthening ranges were long tendon units and great pennation angles. The heuristic model used in this study highlighted the existence of some dynamic phenomena inside the actuator. However, it did not pretend to represent the overall complexity of the mechanical interactions between the different elements composing the soleus architecture.

Ankle Joint↗

PubMed1997

Effects of the type of recovery training on the concentric strength of the knee extensors.

The aim of this study was to examine the effects of specific concentric and eccentric training on concentric muscular strength following an initial standardized period of excessive training that combined concentric and eccentric actions. For a period of 12 weeks, 37 young elite female basketball players performed standardized training, which included concentric and eccentric actions at 70% and 110% of one-repetition maximum (1-RM), respectively. They were then divided into three groups that followed 12 week programmes which included concentric (C-E/C, n = 13), eccentric (C-E/E, n = 13) or a combination of both concentric and eccentric (C-E/-E, n = 11) exercises. The standardized and specific training programmes consisted of 16 and 8 sets of eight repetitions respectively, performed four times a week. Eleven players who did not participate in either the standardized or specific training programmes served as controls (n = 11). Following the initial 12 weeks of standardized training, the concentric strength of the knee extensors was evaluated isokinetically and using leg-press and squat-jump tests. Significant (P < 0.05) reductions in isokinetic torque, and leg-press and squat-jump performance, were seen. The C-E/C group showed significant (P < 0.05) increases in isokinetic torque, and leg-press and squat-jump performance, after 24 weeks of training when compared with pre-training values. Conversely, no significant differences were noted for the C-E/E and C-E/C-E groups. These findings confirm the mode specificity principle, as only the concentric specific training programme improved the concentric strength of the knee extensors.

Adolescent↗

PubMed1997

Concentric and/or eccentric training-induced alterations in shoulder flexor and extensor strength.

To examine the effect of specific concentric and eccentric training on muscular strength following an initial standardized period of excessive training, shoulder extensors and flexors were tested. The shoulder is a joint particularly susceptible to injury and requires a specific strength training program. For a period of 12 weeks, subjects performed training, including concentric and eccentric actions. Thereafter, they were divided into three groups that performed specific 12-week programs, including either concentric (C-E/C), eccentric (C-E/E), or a combination of both concentric and eccentric exercises (C-E/C-E). Following the initial period of training, significant increases (p < 0.05) in performance were observed for all experimental groups. The C-E/C group showed significant increases (p < 0.05) in performance after 24 weeks of training, especially at high concentric angular velocities. However, the C-E/E group showed significant increases (p < 0.05) only in their eccentric moments. No significant differences were noted for the C-E/C-E group. These findings seem to partly confirm the mode-specificity principle, as only the concentric-specific training program improved concentric and eccentric strength. Moreover, the velocity-specificity principle was strongly supported.

Adolescent↗

PubMed1996

Co-activation and tension-regulating phenomena during isokinetic knee extension in sedentary and highly skilled humans.

The aim of this study was to examine isokinetic torque produced by highly skilled (HS) and sedentary (S) human subjects, during knee extension, during maximal voluntary and superimposed electrical activation. To verify the level of activation of agonist (vastus lateralis, VL, and vastus medialis, VM) and antagonist muscles (semi-tendineous, ST), during maximal voluntary activation, their myo-electrical activities were detected and quantified as root mean square (rms) amplitude. Ten HS and ten S subjects performed voluntary and superimposed isometric actions and isokinetic knee extensions at 14 angular velocities (from -120 to 300 degrees*s(-1)). The rms amplitude of each muscle was normalized with respect to its rms amplitude when acting as agonist at 15 degrees*s(-1). Whatever the angular velocity considered, peak torque and constant angular torque at 65 degrees of HS were significantly higher (P <0.05) than those of S. Eccentric superimposed torque of S, but not HS, was significantly higher (P <0.05) than voluntary torque at -120, -90, - 60 and - 30 degrees*s(-1) angular velocities. For a given velocity, the rms amplitude of VL and VM were significantly lower (P <0.05), during eccentric than during concentric actions, in S, but not in HS. However, whatever the angular velocity, ST co-activation in HS was significantly lower (P < 0.05) than in S. We concluded that co-activation phenomenon could partly explain differences in isokinetic performances. Differences between voluntary and superimposed eccentric torques as well as lower agonist rms amplitude during eccentric action in S, support the possibility of the presence of a tension-regulating mechanism in sedentary subjects.

Adult↗

PubMed1996

Viscosity of the elbow flexor muscles during maximal eccentric and concentric actions.

The aim of the present study was to estimate the damping coefficient (B factor) of the elbow flexor muscles during both eccentric and concentric muscle actions. We used a muscle model consisting of a viscous damper associated in parallel with a contractile component, both in series with an elastic component. The viscous damper allowed the concentric loss and the eccentric gain of force to be modelled. Eight volunteer subjects performed maximal eccentric and concentric elbow movements on an isokinetic dynamometer at angular velocities of 0.52, 1.04 and 2.09 rad*s(-1). Torques at an elbow joint angle of 90 degrees were recorded. Electromyogram (EMG) signals from the belly of the right elbow flexor and from the long head of the triceps brachia muscles were recorded using two pairs of bipolar surface electrodes. The root mean square (rms) of the EMG was determined. Eccentric and concentric rms were not significantly different (P >0.05). The B factor was higher in the concentric than in the eccentric conditions (P <0.05), and, whatever the muscle action type it decreased as the velocity increased. These results indicated that the concentric loss and the eccentric gain of force were attributable to the behaviour of the contractile machinery. Furthermore, whatever the exact cause of loss and gain of tension, our study showed that the total effect can be modelled by the viscous damper of a three-component muscle model.

Adult↗

PubMed1996

Simulation of in situ soleus isometric force output as a function of neural excitation.

The purpose of this study was to investigate the behaviour of the human soleus muscle during isometric contraction. A model taking into account the musculoskeletal geometry, the musculotendon architecture and the neural excitation input has been developed. The neural excitation input was simulated using a recruitment and firing rate organisation model. The musculotendon actuator was modelled as a tendon inserted in series with fibres defined by a contractile component in parallel with an elastic component. At maximal neural excitation, the model highlighted the functional significance of tendon stiffness and pennation angle. These architectural parameters tended to increase the operative ankle joint angle range of the soleus actuator, either to the maximal plantarflexion positions for the pennation angle or to the maximal dorsiflexion positions for tendon elasticity. When the model was simulated under various neural excitation levels, it predicted a displacement of the soleus fibre optimal length towards the soleus long length (maximal dorsiflexion position) with increasing neural excitation. The study concluded that the effect of muscular architecture should be taken into account to analyse the effect of neural excitation level on isometric force output.

Ankle Joint↗

PubMed1996

[Recruitment of the bi-articular gastrocnemius muscles during maximal isometric contractions in humans].

The main purpose of this study was to investigate the maximal isometric plantarflexion moment as a function of the triceps surae's length. As the gastrocnemius are bi-articular actuators, their respective lengths were modified by variations of the ankle and knee joints angles. The mechanical results agreed ones previously published in the literature. The maximal and minimal isometric moments were attained at maximal lengthening and shortening of the gastrocnemius respectively. The gastrocnemius electromyographic (EMG) activities showed paradoxal results. Their EMG activities decreased with their lengthening when this was induced by ankle joint angle variations. Inversely, their EMG activities increased with their lengthening when this was induced by knee joint angle variations. These results allowed the authors to hypothesize the existence of specific recruitment of neuro-muscular compartments of the gastrocnemius with knee extension.

Ankle Joint↗

PubMed1995

Changes induced by eccentric training on force-velocity relationships of the elbow flexor muscles.

The aim of this study was to examine the effects of a short term eccentric training period on force-velocity relationships of the elbow flexor muscles. From a muscle model, the maximal shortening velocity Vo(x) and the af parameter which varies according to the curvature of the force-velocity relationship of the muscle were determined. Sixteen volunteer subjects divided into 2 groups participated in this study (Group Eccentric GE, n = 8; Group Control GC, n = 8). The subjects performed, on an isokinetic ergometer, 2 maximal concentric elbow flexions at different angular velocities (60, 120, 180, 240, 300, 360 degrees s-1) and held maximal and submaximal isometric actions at an elbow flexion angle of 90 degrees. Under isometric conditions, myoelectrical activity (EMG) of the biceps was recorded and quantified as a RMS value. All tests were performed before and after training sessions. Training was conducted 3 times a week for 4 weeks by the GE, and included 6 x 5 eccentric actions with a load of 100% of 1 RM. After training and for the GE, the af parameter and Vo(x) increased significantly (p < 0.05). These changes were accompanied by a significant increase (p < 0.05) of the RMS value of the maximal isometric action. This evolution towards faster characteristics for the elbow flexor muscles after training could be partly due to nervous adaptation.

Elbow↗

PubMed1995

[Activation of agonist and antagonist muscles during plantar flexion of the ankle].

The aim of this study was to examine isokinetic moment produced by well-trained and sedentary subjects, during plantar flexion, at 13 angular velocities (from -120 to 300 degrees.s-1), under maximal voluntary and superimposed electrical conditions. In order to verify the level of activation of agonist (Soleus (SOL) and Gastrocnemius Medialis (GM)) and antagonist muscles (Tibialis Anterior (TA), their myoelectrical activities were detected and quantified as Root Mean Square (RMS). Whatever the angular velocity considered, the moments developed at 90 degrees by well-trained subjects were significantly (p < 0.05) higher than those developed by sedentary subjects, except at -10 degrees.s-1. Eccentric superimposed moments of sedentary subjects were significantly (p < 0.05) higher than those developed by the same subjects under maximal voluntary conditions. For a given velocity, the RMS's of S and GM muscles were significantly (p < 0.05) lower, during eccentric than during concentric actions, in sedentary, but not in well-trained subjects. The TA co-activation in well-trained subjects was significantly (p < 0.05) lower than in sedentary subjects, whatever the angular velocity considered. We concluded that a co-activation phenomenon could partly explain differences in isokinetic performances. Differences between voluntary and superimposed eccentric moment as well as lower agonists' RMS during eccentric action, support the presence of a tension-regulating mechanism in sedentary subjects.

Ankle↗

PubMed1994

Theoretical and experimental behaviour of the muscle viscosity coefficient during maximal concentric actions.

The aim of this study was to calculate the theoretical variation of the nonlinear damping factor (B) as a function of the muscle shortening velocity, and then to compare the theoretical values with the experimental data obtained on both the elbow flexor and the ankle extensor muscles. The theoretical variation of the B factor was determined from a muscle model consisting of a contractile component in parallel with a viscous damper both in series with an elastic component, and by using, the characteristic equation of the force velocity curve. In this muscle model, the viscous element modelled the inability of the muscle to generate as big a contracting force (while shortening) as possible under isometric conditions. Eight volunteer subjects performed maximal concentric elbow flexions and ankle extensions on an isokinetic ergometer at angular velocities of 60, 120, 180, 240, 300 and 360 degrees.s-1, and held two maximal isometric actions at an elbow angle of 90 degrees (0 degrees corresponds to the full extension) and at an ankle angle of 0 degree (0 degree corresponds to the foot flexion of 90 degrees relative to the leg axis). From these measurements, the force and the shortening velocity values of each muscle were determined by using a musculo-skeletal model of the joint. The results showed that the theoretical behaviour of the B factor would seem to be dependent on the shortening velocity and on the parameter which varies according to the muscle fibre type composition and affects the curvature of the force-velocity curve (af).(ABSTRACT TRUNCATED AT 250 WORDS)

Humans↗

PubMed1994

The influence of electrostimulation on mechanical and morphological characteristics of the triceps surae.

The present study assessed the effects of training using electrostimulation of muscle (EMS) on the torque-angular velocity and torque-angle relationships, and the cross-sectional area (CSA) of the triceps surae. Twelve physical education students, divided into two groups (6 controls, 6 experimental), participated in the experiment. The EMS sessions were undertaken using a 'Complex-type' stimulator. Flexible elastomer electrodes were used. The current used discharged pulses lasting for 200 microseconds at a frequency of 70 Hz. The durations of contraction and rest were 5 and 15 s, respectively. The session lasted for 10 min for each muscle. The training regimen was three sessions per week for 4 weeks. Biomechanical tests were performed with the Biodex (Biodex Corporation, Shirley, NY, USA) isokinetic ergometer. Plantar flexions of the ankle over a concentric range of voluntary contractions were performed at different angular velocities (1.05, 2.10, 3.14, 4.20, 5.23 and 6.28 rad s-1) and maximum voluntary isometric contractions were held for 5 s at several ankle flexion angles (-30 degrees, -15 degrees, 0 degree and 15 degrees; 0 degree corresponds to foot flexion of 90 degrees relative to the leg axis). The peak value of the torque was recorded. Morphological tests consisted of measuring the CSA of the triceps surae on the right leg, 15 cm below the tibial protuberance, by a computerized tomography technique. The torque-velocity relationship was seen to shift significantly upwards after EMS training. The increase in the isometric torque observed after EMS training was greater in dorsiflexion than in plantarflexion.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1994

[Effects of different types of training on torque/angular velocity relationship. Experimental study by isokinetic ergometry in high-level basketball players].

The purpose of this study was to examine the alterations of the Torque/Angular Velocity relationship in knee extensor and flexor muscles due to a long-term training programme. Thirty five young elite basketball players were tested before, after 12 weeks of a common weight-lifting programme (including concentric and eccentric actions) and after 24 weeks including only concentric (C-E/C group) or concentric and eccentric actions (C-E/C-E group). After 12 weeks, significant decrease in torque of knee extensor muscles was observed. In contrast, significant increases in torque of knee flexor and shoulder flexor and extensor muscles were noted. After 24 weeks, significant increases were noted in torque of all muscular groups, for the C-E/C group but not for the C-E/C-E group. It is concluded that training including concentric and eccentric actions have not the same effect on agonist and antagonist muscular groups. The alternation of the contraction mode influences straingthly the strength restoration.

Adolescent↗

PubMed1994

[Modelling of viscosity equivalent factor in the human muscle during muscular shortening].

The aim of this study was to calculate the theoretical variation of the non linear damping factor (B) as a function of the muscle shortening velocity. The theoretical variation of the B factor was determined from a muscle model which consists of a contractile component in parallel with a viscous damper both in series with an elastic component, and by using the characteristic equation of the force-velocity curve. In this muscle model, the viscous element modeled the inability of the muscle to generate as a big contracting force (while shortening) as possible under isometric conditions. The results show that the theoretical behaviour of the B factor was dependent on the shortening velocity and on the af parameter which varies according to the muscle fibre type composition and affects the curvature of the force-velocity curve.

Humans↗

PubMed1993

Effect of electrical stimulation training on the contractile characteristics of the triceps surae muscle.

This study aimed to assess the effects of training using electrical stimulation (ES) on the contractile characteristics of the triceps surae muscle. A selection of 12 subjects was divided into two groups (6 control, 6 experimental). The ES sessions were carried out using a stimulator. Flexible elastomer electrodes were used. The current used discharged pulses lasting 200 microseconds at 70 Hz. Contraction time was 5 s and rest time 15 s. The session lasted 10 min for each muscle. Training sessions were three times a week for 4 weeks. Biomechanical tests were performed using an isokinetic ergometer. Subjects performed plantar flexions of the ankle over a concentric range of movement at different angular velocities (60, 120, 180, 240, 300, 360 degrees.s-1) and held isometric contractions for 5 s at several ankle flexion angles (-30/-15/0/15 degrees-0 corresponded to foot flexion of 90 degrees relative to the leg axis). The force-velocity relationship was seen to shift evenly upwards under the influence of ES (P < 0.05). The increased force during the "after" test was greater (P < 0.05) for ankle angle positions of 15 degrees and -30 degrees, which demonstrated a link between the training angle and the gain in strength. No change was noted in the cross-sectional area of the muscle. The results showed that ES allowed the contractile qualities of muscle to be developed in isometric and dynamic conditions. Nervous mechanisms can account for most of these adaptations.

Adult↗