In vivo force-velocity relation of human muscle: a modelling from sinusoidal oscillation behaviour

Maximal fascicle shortening velocity measurements in human medial gastrocnemius muscle in vivo

This study evaluated the maximal fascicle shortening velocity under near-no-load conditions. In addition, we determined whether the rate of torque development during ballistic contraction was related to maximal fascicle shortening velocity. Under passive and active conditions, the medial gastrocnemius muscle fascicle shortening velocity was measured using ultrasonography at 300, 400, 500, 600, 700, 800, 900, and 1000 ° s-1 . The maximal fascicle shortening velocity was defined as the fascicle shortening velocity under the lowest angular velocity that satisfied the following two conditions; (1) the difference in torque values between passive and active conditions was below 2.4 Nm and (2) the difference in fascicle shortening velocities between passive and active conditions was below 10 mm s-1 . The rate of torque development was analyzed during the periods of 32, 48, 96, 152, and 200 ms after the onset of contraction during ballistic contraction. At the angular velocity (678.6 ± 147.7 ° s-1 ) that satisfied the two previously mentioned conditions, the exerted torque and the maximal fascicle shortening velocity were 1.4 ± 1.3 Nm and 251.0 ± 40.5 mm s-1 . No significant correlations were found between the maximal fascicle shortening velocity and the rate of torque development at each time point. In conclusion, the maximal fascicle shortening velocity was quantified when the angular velocity satisfied the two conditions. Furthermore, the rate of torque development, often used as an indicator of muscle velocity, did not represent the maximal fascicle shortening velocity.

In vivo maximal fascicle-shortening velocity during plantar flexion in humans

Interindividual variability in performance of fast movements is commonly explained by a difference in maximal muscle-shortening velocity due to differences in the proportion of fast-twitch fibers. To provide a better understanding of the capacity to generate fast motion, this study aimed to 1) measure for the first time in vivo the maximal fascicle-shortening velocity of human muscle; 2) evaluate the relationship between angular velocity and fascicle-shortening velocity from low to maximal angular velocities; and 3) investigate the influence of musculo-articular features (moment arm, tendinous tissues stiffness, and muscle architecture) on maximal angular velocity. Ultrafast ultrasound images of the gastrocnemius medialis were obtained from 31 participants during maximal isokinetic and light-loaded plantar flexions. A strong linear relationship between fascicle-shortening velocity and angular velocity was reported for all subjects (mean R2 = 0.97). The maximal shortening velocity (VFmax) obtained during the no-load condition (NLc) ranged between 18.8 and 43.3 cm/s. VFmax values were very close to those of the maximal shortening velocity (Vmax), which was extrapolated from the F-V curve (the Hill model). Angular velocity reached during the NLc was significantly correlated with this VFmax ( r = 0.57; P < 0.001). This finding was in agreement with assumptions about the role of muscle fiber type, whereas interindividual comparisons clearly support the fact that other parameters may also contribute to performance during fast movements. Nevertheless, none of the biomechanical features considered in the present study were found to be directly related to the highest angular velocity, highlighting the complexity of the upstream mechanics that lead to maximal-velocity muscle contraction.

Changes in contractile and elastic properties of the triceps surae muscle induced by neuromuscular electrical stimulation training

PURPOSE

Neuromuscular electrical stimulation (NMES) training is known to induce improvement in force production capacities and fibre-type transition. The aim of this study was to determine whether NMES training also leads to changes in the mechanical properties of the human triceps surae (TS) muscle.

METHODS

Fifteen young male subjects performed a training protocol (4 weeks, 18 sessions, 4-5 sessions per week) based on a high-frequency isometric NMES programme of TS muscle. Quick-release test was used to evaluate Musculo-Tendinous (MT) stiffness index (SIMT) as the slope of the linear MT stiffness-torque relationships under submaximal contraction. Sinusoidal perturbations allowed the assessment of musculo-articular stiffness index (SIMA) as well as the calculation of the maximal angular velocity ([Formula: see text]) of TS muscle using an adaptation of Hill's equation.

RESULTS

After NMES training, Maximal Voluntary Contraction under isometric conditions and [Formula: see text] increased significantly by 17.5 and 20.6 %, respectively, while SIMT and SIMA decreased significantly (-12.7 and -9.3 %, respectively).

CONCLUSIONS

These changes in contractile and elastic properties may lead to functional changes of particular interest in sport-related activities as well as in the elderly.

ESTIMATION OF MUSCLE FORCE DERIVED FROM IN VIVO MR ELASTOGRAPHY TESTS: A PRELIMINARY STUDY

The objective is to estimate the vastus medialis (VM) muscle force from multifrequency magnetic resonance elastography (MMRE) tests and two different rheological models (Voigt and springpot). Healthy participants (N = 13) underwent multifrequency (70, 90 and 110 Hz) magnetic resonance elastography MMRE tests. Thus, in vivo experimental elastic (μ) properties of the VM in passive and active (20% MVC) conditions were characterized. Moreover, the muscle viscosity (η) was determined with Voigt and springpot rheological models, in both muscle states. Subsequently, the VM muscle forces were calculated with a generic musculoskeletal model (OpenSIM) where the active and passive shear moduli (μ) were implemented. The viscosity measured with the two rheological models increased when the muscle is contracted. During the stance and the swing phases, the VM tensile forces decrease and the VM force was lower with the springpot model. It can be noted that during the swing phase, the muscle forces estimated from springpot model showed a higher standard deviation compared to the Voigt model. This last result may indicate a strong sensitivity of the muscle force to the change of active and passive contractile components in the swing phase of gait. This study provides for the first time an estimation of the muscle tensile forces for lower limb, during human motion, from in vivo experimental muscle mechanical properties. The assessment of individualized muscle forces during motion is valuable for finite element models, increasing the patient specific parameters. This novel muscle database will be of use for the clinician to better elucidate the muscle pathophysiology and to better monitor the effects of the muscle disease.

Smart Rehabilitation Devices: Part II - Adaptive Motion Control

This article presents a study of adaptive motion control of smart versatile rehabilitation devices using MR fluids. The device provides both isometric and isokinetic strength training and is reconfigurable for several human joints. Adaptive controls are developed to regulate resistance force based on the prescription of the therapist. Special consideration has been given to the human-machine interaction in the adaptive control that can modify the behavior of the device to account for strength gains or muscle fatigue of the human subject.

Shortening velocity of human triceps surae muscle measured with the slack test in vivo

Unloaded shortening velocity (V(0)) of human triceps surae muscle was measured in vivo by applying the 'slack test', originally developed for determining V(0) of single muscle fibres, to voluntary contractions at varied activation levels (ALs). V(0) was measured from 10 subjects at five different ALs defined as a fraction (5, 10, 20, 40 and 60%) of the maximum voluntary contraction (MVC) torque. Although individual variability was apparent, V(0) tended to increase with AL (R(2) = 0.089; P = 0.035) up to 60%MVC (8.6 +/- 2.6 rad s(-1)). This value of V(0) at 60%MVC was comparable to the maximum shortening velocity of plantar flexors reported in the previous studies. Electromyographic analysis showed that the activities of soleus, medial gastrocnemius and lateral gastrocnemius muscles increased with AL during isometric contraction and after the application of quick release in a similar manner. Also, it showed that the activity of an antagonist, tibialis anterior muscle, was negligible, even though a slight increase took place after the quick release of agonist. Correlation analysis showed that there were no significant correlations between V(0) and MVC torque normalized with respect to body mass, although the correlation coefficient was relatively high at low ALs. The results suggest that in human muscle, V(0) represents the unloaded velocity of the fastest muscle fibres recruited, and increases with AL possibly because of progressive recruitment of faster fibres. Individual variability may be explained, at least partially, by the difference in fibre-type composition.

A prototype rehabilitation device with variable resistance and joint motion control

Resistance exercise has been widely reported to have positive rehabilitation effects for patients with neuromuscular and orthopaedic conditions. This paper presents the design of a versatile rehabilitation device in the form of a rotating joint arm mounted on the adjustable seat that provides passive resistance during strength training for muscles. The resistance is supplied by a magnetorheological damper. Intelligent controls are developed to produce resistance force based on the prescription of the therapist. The device provides both isometric and isokinetic strength training and is reconfigurable for several human joints. Special consideration has been given to the human-machine interaction in the adaptive control algorithms that can modify the behavior of the device to account for strength gains or muscle fatigue.

Effects of eccentric training on torque-angular velocity-power characteristics of elbow flexor muscles in older women

The purpose of this study was to investigate the potential of eccentric training to improve elbow flexor muscle power in elderly subjects. Fourteen older female volunteers (age range 60-78 years) were randomly assigned into either a training group (TG) or a control group (CG). For the TG, the 21-session 7-week eccentric training program consisted of 5x6 eccentric muscle actions at 60-100% of concentric three maximal repetitions. Before and after training, maximal elbow flexions were performed against increasing inertia. Maximal isokinetic elbow flexions at four angular velocities (eccentric actions, -60 degrees s(-1), -30 degrees rads(-1); concentric actions, 30, 60 degrees s(-1)) and maximal isometric actions were also performed. Maximal power (Pmax) and an index of maximal shortening velocity (VImax)were determined. For all action conditions, the myoelectric activities of the biceps and the triceps brachii muscles were recorded and quantified as a root mean square (RMS) value. In the TG, maximal torque developed under isometric, isokinetic and inertial conditions increased significantly after training (ranging from 11 to 19%). Pmax and VImax also increased significantly (31.3 and 25.9%, respectively). These parameters remained unchanged in the CG. The RMS activity of the biceps and triceps muscles was not affected by eccentric training for all action conditions excepting the eccentric condition at -30 degrees s(-1) where the RMS activity of the biceps increased significantly. The gains in maximal torque, Pmax and VImax observed after training would result more from intramuscular modifications than from changes in muscular activity, except for eccentric condition at -30 degrees s(-1) where the torque gains could also be partly explained by a reduction in inhibition of the motor unit pool.

Behavior of human muscle fascicles during shortening and lengthening contractions in vivo

The aim of the present study was to investigate the behavior of human muscle fascicles during dynamic contractions. Eight subjects performed maximal isometric dorsiflexion contractions at six ankle joint angles and maximal isokinetic concentric and eccentric contractions at five angular velocities. Tibialis anterior muscle architecture was measured in vivo by use of B-mode ultrasonography. During maximal isometric contraction, fascicle length was shorter and pennation angle larger compared with values at rest (P < 0.01). During isokinetic concentric contractions from 0 to 4.36 rad/s, fascicle length measured at a constant ankle joint angle increased curvilinearly from 49.5 to 69.7 mm (41%; P < 0.01), whereas pennation angle decreased curvilinearly from 14.8 to 9.8 degrees (34%; P < 0.01). During eccentric muscle actions, fascicles contracted quasi-isometrically, independent of angular velocity. The behavior of muscle fascicles during shortening contractions was believed to reflect the degree of stretch applied to the series elastic component, which decreases with increasing contraction velocity. The quasi-isometric behavior of fascicles during eccentric muscle actions suggests that the series elastic component acts as a mechanical buffer during active lengthening.