Emilie Simoneau

Training-induced changes in structural and mechanical properties of the patellar tendon are related to muscle hypertrophy but not to strength gains

To obtain a better understanding of the adaptations of human tendon to chronic overloading, we examined the relationships between these adaptations and the changes in muscle structure and function. Fifteen healthy male subjects (20+/-2 yr) underwent 9 wk of knee extension resistance training. Patellar tendon stiffness and modulus were assessed with ultrasonography, and cross-sectional area (CSA) was determined along the entire length of the tendon by using magnetic resonance imaging. In the quadriceps muscles, architecture and volume measurements were combined to obtain physiological CSA (PCSA), and maximal isometric force was recorded. Following training, muscle force and PCSA increased by 31% (P<0.0001) and 7% (P<0.01), respectively. Tendon CSA increased regionally at 20-30%, 60%, and 90-100% of tendon length (5-6%; P<0.05), and tendon stiffness and modulus increased by 24% (P<0.001) and 20% (P<0.01), respectively. Although none of the tendon adaptations were related to strength gains, we observed a positive correlation between the increase in quadriceps PCSA and the increases in tendon stiffness (r=0.68; P<0.01) and modulus (r=0.75; P<0.01). Unexpectedly, the increase in muscle PCSA was inversely related to the distal and the mean increases in tendon CSA (in both cases, r=-0.64; P<0.05). These data suggest that, following short-term resistance training, changes in tendon mechanical and material properties are more closely related to the overall loading history and that tendon hypertrophy is driven by other mechanisms than those eliciting tendon stiffening.

Antagonist mechanical contribution to resultant maximal torque at the ankle joint in young and older men

A recorded muscular torque at one joint is a resultant torque corresponding to the participation of both agonist and antagonist muscles. This study aimed to examine the effect of aging on the mechanical contributions of both plantar- and dorsi-flexors to the resultant maximal voluntary contraction (MVC) torques exerted at the ankle joint, in dorsi-flexion (DF) and plantar-flexion (PF). The estimation of isometric agonist and antagonist torques by means of an EMG biofeedback technique was made with nine young (mean age 24 years) and nine older (mean age 80 years) men. While there was a non-significant age-related decline in the measured resultant DF MVC torque (-15%; p=0.06), there was a clear decrease in the estimated agonist MVC torque exerted by the dorsi-flexors (-39%; p=0.001). The DF-to-PF resultant MVC torque ratio was significantly lower in young than in older men (0.25 vs. 0.31; p=0.006), whereas the DF-to-PF agonist MVC torque ratio was no longer different between the two populations (0.38 vs. 0.35; p>0.05). Thus, agonist MVC torques in PF and DF would be similarly affected by aging, which could not be deduced when only resultant torques were examined.

Human muscle fascicle behavior in agonist and antagonist isometric contractions

Introduction: The aim of this study was to compare, at a given level of electromyographic (EMG) activity, the behavior of dorsiflexor and plantarflexor muscles as assessed via their architecture (pennation angle and fiber length) during agonist or antagonist isometric contractions. Methods: Real‐time ultrasonography and EMG activity of gastrocnemius medialis (GM) and tibialis anterior (TA) muscles were obtained while young males performed ramp isometric contractions in dorsi‐ and plantarflexion. Results: For both muscles, at a similar level of EMG activity, fiber length was longer, and pennation angle was smaller, during antagonist than during agonist contractions. Conclusions: These results indicate that, at similar levels of EMG activity, GM and TA muscles elicit a higher mechanical output while acting as an antagonist. These findings have important implications for muscle function testing. They show that estimation of antagonistic force using the common method based on the EMG/net torque relationship yields underestimated values. Muscle Nerve 45: 92–99, 2012

Difficult memory task during postural tasks of various difficulties in young and older people: a pilot study.

OBJECTIVE This study examined the effects of a difficult and individually tailored additional cognitive task on postural stability and electromyographic (EMG) activities of the ankle dorsi- and plantar-flexors, in young and older individuals performing postural tasks of varying difficulties. METHODS Eight young (mean age=24 years) and eight older (74 years) men took part in the investigation. Centre of pressure velocity and surface EMG of ankle joint muscles were both examined during various postural conditions. RESULTS The main findings suggested that high levels of muscle activity were a characteristic of age-related declines in postural stability. Moreover, during the complex posture, the postural instability, as well as the EMG activity of the ankle joint muscles, was decreased in older adults when the difficult memory task was added. Regarding young participants, the performance in the cognitive task was significantly improved during the complex posture compared to the easy one. CONCLUSIONS These findings showed that the execution of a second task would make it possible to improve the performance in the original task. SIGNIFICANCE This pilot study seemed to show that, depending on age, the task of highest priority would be the cognitive one for young adults and the postural one for older people.

Trunk's Natural Inclination Influences Stance Limb Kinetics, but Not Body Kinematics, during Gait Initiation in Able Men

The imposing mass of the trunk in relation to the whole body has an important impact on human motion. The objective of this study is to determine the influence of trunks natural inclination - forward (FW) or backward (BW) with respect to the vertical - on body kinematics and stance limb kinetics during gait initiation. Twenty-five healthy males were divided based on their natural trunk inclination (FW or BW) during gait initiation. Instantaneous speed was calculated at the center of mass at the first heel strike. The antero-posterior impulse was calculated by integrating the antero-posterior ground reaction force in time. Ankle, knee, hip and thoraco-lumbar (L5) moments were calculated using inverse dynamics and only peaks of the joint moments were analyzed. Among all the investigated parameters, only joint moments present significant differences between the two groups. The knee extensor moment is 1.4 times higher (P<0.001) for the BW group, before the heel contact. At the hip, although the BW group displays a flexor moment 2.4 times higher (P<0.001) before the swing limbs heel-off, the FW group displays an extensor moment 3.1 times higher (P<0.01) during the swing phase. The three L5 extensor peaks after the toe-off are respectively 1.7 (P<0.001), 1.4 (P<0.001) and 1.7 (P<0.01) times higher for the FW group. The main results support the idea that the patterns described during steady-state gait are already observable during gait initiation. This study also provides reference data to further investigate stance limb kinetics in specific or pathologic populations during gait initiation. It will be of particular interest for elderly people, knowing that this population displays atypical trunk postures and present a high risk of falling during this forward stepping.

How the ankle joint angle alters the antagonist and agonist torques during maximal efforts in dorsi- and plantar flexion.

The aim of this study was to assess, via an EMG bio‐feedback method, the ankle joint angle effect on the agonist and antagonist torques in plantar‐ (PF) and dorsi‐flexion (DF). The isometric PF and DF maximal voluntary contractions (MVCs) torques were measured simultaneously with surface EMG activity of triceps surae (TS) and tibialis anterior (TA) muscles in 12 young adults (mean age 27) at five different ankle joint angles. Our results showed that: (i) The coactivation level does not properly reflect the mechanical effect of the antagonist muscle, (ii) TS antagonist torque significantly altered the DF MVC–angle relationship, whereas TA antagonist torque did not influence this MVC–angle relationship in PF. The alteration of the MVC with angular position was due, in part, to the coactivation phenomenon in DF, but not in PF. Thenceforth, when investigating the torque at the ankle joint, it is necessary to take into account both agonist and antagonist torque modifications with ankle joint angle.

Chronic low back pain sufferers exhibit freezing-like behaviors when asked to move their trunk as fast as possible

BACKGROUND CONTEXT The effect of chronic low back pain (CLBP) on the kinematic parameters of trunk motion has received much more interest in this last decade. However, there are no descriptions of the motor strategies that occur when patients perform trunk movements in the three anatomical planes at different pace conditions. PURPOSE To investigate motor strategies used by CLBP patients and asymptomatic people while performing different go and back trunk movements in an upright standing position. STUDY DESIGN A comparative study. PATIENT SAMPLE The control group (CG, n=33) included 14 men and 19 women with no history of low back pain, and the chronic low back pain group (CLBPG, n=49) included 21 men and 28 women. OUTCOME MEASURES Kinematic data were analyzed during six trunk movements: flexion, extension, left and right lateral bendings, and rotations under two pace conditions (preferred and fast paces). METHODS A three-dimensional optoelectronic motion analysis system was used to assess static (trunk inclinations and base of support) and dynamic (range of motion [ROM] and mean angular velocity of the trunk) parameters during the go and back phases of trunk movements. RESULTS In the initial position, CLBPG showed a more forward-tilted trunk inclination (2.1°±1.1°, p=.013) compared with CG. The base of support was significantly higher in CG (+22.7 cm2, p=.009) during the fast pace when compared with the preferred pace. Regardless of the pace condition, ROM and mean angular velocity of the trunk were significantly lower in CLBPG for all examined movements and the pace condition did not significantly alter ROM. At the preferred pace, both groups displayed the same motor strategy: they all went faster during the second phase of movement than during the first phase. However, at the fast pace, while CG was going faster during the first phase than during the second, CLBPG maintained the same motor strategy as at the preferred pace. CONCLUSIONS Contrary to CG who changed its motor behavior from a preferred pace to a fast pace, CLBPG exhibited freezing-like behaviors. This original result highlights the importance of studying the velocity. The use of this parameter may improve the diagnosis of CLBP patients and could be a key indicator for treatment progress and long-term monitoring.

When motor simulation of disequilibrium increases postural stability

L.P. Heurley*, E.M. Simoneau, S. Leteneur and D. Brouillet LAMIH UMR CNRS 8201 ‘Laboratory of Industrial and Human Automation, Mechanics and Computer Science’, Université Nord de France, Université de Valenciennes et du Hainaut-Cambrésis, Le Mont Houy, 59313 Valenciennes Cedex 9, France; Laboratory EPSYLON EA 4556 ‘Dynamics of Human Abilities and Health Behaviors’, Université Montpellier III, Paul Valéry, Route de Mende, 34199 Montpellier Cedex 5, France

Modeling and Control of Rehabilitation Robotic Device: motoBOTTE

The motoBOTTE is a robot designed for assistive rehabilitation. The identification of a mathematical model for the system is shown; then we design and implement a nonlinear control law for tracking a reference signal. The nonlinear controller design is achieved by combining an exact convex representation with the direct method of Lyapunov. Results are given in terms of linear matrix inequalities (LMI); simulation and real-time results are shown as well.

Does bilateral index differ between countermovement jump, drop jump and squat jump?

In the literature, it has already been reported that in a twolegged vertical jump humans achieve less than twice the jump height they are able to reach in a one-legged jump (van Soest et al. 1985; Challis 1998; Bobbert et al. 2006). This phenomenon is related to the bilateral deficit, which would result from decreased agonist activity, increased antagonist activity or a combination of both (see Jakobi and Chilibeck 2001 for review). Presence of a bilateral deficit during two-legged jumps can mean that the individual would have a potential to jump even higher. This neuromuscular alteration may be reduced or removed with specific training. Indeed, it has already been shown that for people who are experts in sports in which bilateral movements are predominant, the bilateral deficit occurs less frequently in contralateral muscle pairs that have undergone bilateral resistance training (Howard and Enoka 1991). Bilateral deficit has already been highlighted during different types of jumps, such as the squat jump (SJ; Bobbert et al. 2006) and the countermovement jump (CMJ; van Soest et al. 1985). Furthermore, another type of jump, the drop jump (DJ), is often used and examined in sports sciences. Since these three different vertical jumps (CMJ, DJ and SJ) display various complexity in their achievement, one can assume that the different neuromuscular requirements to perform these jumps would lead to different amounts of bilateral deficit. In such a case, specific training could be designed to reduce highlighted bilateral deficit. The purpose of this study was then to determine the amount of bilateral deficit in the three various vertical jumps and to examine whether this amount is linked to the complexity of the jumping task.