ELECTROMECHANICAL DELAY AND ITS MECHANISMS ARE NOT IMPAIRED FOLLOWING ECCENTRIC EXERCISE

The aim of the present study was to assess the effect of exercise-induced muscle damage on both electrochemical and mechanical components involved in the electromechanical delay in the gastrocnemius medialis muscle. 15 healthy participants completed 10 sets of 30 maximal eccentric contractions of the plantar flexor muscles at a constant angular velocity of 45°.s-1. Delayed onset muscular soreness, maximal isometric torque, and electromechanical delay were measured before, 1h, and 48h following eccentric exercise. The present study revealed that the time required for both electrochemical and mechanical process involved in electromechanical delay are not impaired by exercise induced muscle damage. This study suggests that the long lasting reduction in force after eccentric exercise cannot be associated to an alteration of the force transmission efficiency

Early detection of exercise-induced muscle damage using elastography

Purpose This study aimed to determine whether an increase in muscle shear modulus measured 30 min after eccentric exercise (30 min) reflects the magnitude of force deficit measured 48-h post-exercise (48 H)

Mechanical and neural parameters during maximal eccentric contractions in Human : Influence on muscle damage

Les contractions excentriques induisent des perturbations structurelles des fibres musculaires mobilisées, définissant le phénomène des dommages musculaires. Pourtant décrits pour le modèle in vitro, les mécanismes à l’origine de l’apparition des dommages musculaires restent relativement méconnus sur le modèle in vivo. L’objectif de cette thèse était donc d’explorer (i) les caractéristiques mécaniques et nerveuses du système neuromusculaire au cours de contractions excentriques maximales chez l’Homme et (ii) l’impact de ces caractéristiques mécaniques et nerveuses sur la sévérité des dommages musculaires. Six études ont contribué à ce travail de thèse. Dans ces études, des paramètres mécaniques, tels que le niveau de force articulaire généré et la longueur des faisceaux musculaires ; et nerveux, telles que la capacité volontaire à activer un muscle de manière maximale et l’excitabilité cortico-spinale, au cours de contractions excentriques maximales ont été mesurés. Ces paramètres mécaniques et nerveux ont également été mis en relation à des symptômes fonctionnels des dommages musculaires (i.e., perte de force et douleurs musculaires). Les résultats ont montré que les dommages musculaires sont déterminés par les caractéristiques mécaniques et nerveuses propres à l’exécution de la contraction excentrique. Cependant, l’augmentation des processus d’inhibition nerveuse à de grandes longueurs musculaires et la contribution des tissus tendineux dans l’allongement total du système musculo-tendineux au cours des contractions excentriques maximales constituent des stratégies permettant de limiter la sévérité des dommages musculaires in vivo.Eccentric contractions induce structural disruptions of exercised muscle fibers, which refer to as muscle damage phenomenon. Although described for in vitro model, underpinning mechanisms of muscle damage remain unclear for in vivo model. This thesis aimed at investigate (i) mechanical and neural behaviors of the neuromuscular system during maximal eccentric contractions in Human and (ii) the effect of these mechanical and neural behaviors on the magnitude of muscle damage. This thesis was divided into six studies, in which mechanical parameters, such as the level of generated joint force and the length of muscle fascicles; and neural parameters, such as the ability to fully activate a muscle voluntarily and corticospinal excitability, during maximal eccentric contractions were measured. These mechanical and neural parameters were also related to muscle damage functional symptoms (i.e., force loss and muscle soreness). The findings showed that muscle damage is related to a compound influence of mechanical and neural factors involved during eccentric contractions. However, neural inhibitory processes at long muscle lengths, and the contribution of tendinous tissues in total muscle-tendon unit lengthening during maximal eccentric contractions allow to reduce the magnitude of muscle damage

Reliability of H-reflex in vastus lateralis and vastus medialis muscles during passive and active isometric conditions

International audiencePurpose: This study aimed to evaluate the modulation and reliability of the vastus medialis (VM) and vastus lateralis (VL) H-reflexes in both passive and active conditions.Methods: Recruitment curves of VM and VL H-reflexes and M-waves at rest and during muscle contraction (30% of maximal voluntary contraction) were performed for 12 healthy males and were then repeated after 1 h, 1 day and 1 week. The maximal H-reflexes of each muscle were normalized to their respective maximal M-waves (H/M ratio) and absolute (CV) and relative (ICC) reliability were calculated.Results: The H-reflex was potentiated in active compared to passive condition and a higher H-reflex occurrence (12 vs. 10 subjects) and amplitude (≈+150%) was found for the VM compared to the VL in active condition. The intra- (ICChour = 0.97) and inter-day (ICCday = 0.92; ICCweek = 0.92) reliability was poor for the passive VM H/M ratio due to high within-subject variations (CVhour = 52.2%; CVday = 69.8%; CVweek = 60.9%) whereas for the active condition the reliability, especially intra-day, was good (ICChour = 0.93 and CVhour = 12%; ICCday = 0.86 and CVday = 14.5%; ICCweek = 0.79 and CVweek = 19.7%).Conclusions: This study showed differential modulation of the H-reflex between vasti muscles of the quadriceps and a higher occurrence and reliability for the active VM H-reflex. One can therefore conclude that it seems more appropriate to evoke quadriceps VM H-reflex (rather than VL) during an isometric muscle contraction

Specific joint angle dependency of voluntary activation during eccentric knee extensions

International audienceIntroduction: This study compared voluntary activation during isometric, concentric, and eccentric maximal knee extensions at different joint angles.Methods: Fifteen participants performed isometric, concentric, and eccentric protocols (9 contractions each). For each protocol, the central activation ratio (CAR) was randomly measured at 50°, 75°, or 100° of knee joint angle (0° = full knee extension) using superimposed supramaximal paired nerve stimulations during contractions.Results: CAR increased between 50° and 100° during isometric (93.6 ± 3.1 vs. 98.5 ± 1.4%), concentric (92.4 ± 5.4 vs. 99.2 ± 1.2%), and eccentric (93.0 ± 3.5 vs. 96.6 ± 3.8%) contractions. CAR was lower during eccentric than both isometric and concentric contractions at 75° and 100°, but similar between contraction types at 50°.Conclusions: The ability to activate muscle maximally is impaired during eccentric contractions compared with other contraction types at 75° and 100°, but not at 50°. Muscle Nerve 56: 750-758, 2017

Countermovement, Hurdle, and Box Jumps: Data-Driven Exercise Selection

Apart from squat jumps, countermovement jumps (CMJ), and drop jumps, differences among other jump variations are not as well researched, making data-driven exercise selection difficult. To address this gap, this study compared selected concentric and eccentric jump parameters of maximal effort CMJ, hurdle jumps over 50 cm hurdle (HJ), and box jumps onto a 50 cm box (BJ). Twenty recreationally trained men (25.2 ± 3.5 years) performed 3 repetitions of CMJs, HJs, and BJs, each on separate days. The data were collected using force platforms and a linear position transducer. The mean of 3 trials of each jump variation was analyzed using repeated measures ANOVA and Cohen’s d. Countermovement depth was significantly greater (p ≤ 0.05) and peak horizontal force significantly lower during CMJ compared to HJ and BJ. However, there were no differences in peak velocity, peak vertical and resultant force, and total impulsion time. Finally, BJ significantly decreased peak impact force by ~51% compared to CMJ and HJ. Therefore, the propulsive parameters of HJ and BJ seem to be similar to CMJ, despite CMJ having a greater countermovement depth. Furthermore, overall training load can be decreased dramatically by using BJ, which reduced peak impact force by approximately half

Muscle length effect on corticospinal excitability during maximal concentric, isometric and eccentric contractions of the knee extensors

Neural control of eccentric contractions differs from that of concentric and isometric contractions, but no previous study has compared responses to motor cortex stimulations at long muscle lengths during such contraction types. In this study, we compared the effect of muscle length on corticospinal excitability between maximal concentric, isometric and eccentric contractions of the knee extensors. Twelve men performed 12 maximal concentric, isometric and eccentric voluntary contractions (36 contractions in total), separated by a 5 min rest between contraction types. The 12 contractions for the same contraction type were performed every 10 s, and transcranial magnetic stimulations (first eight contractions) and electrical femoral nerve stimulations (last four contractions) were superimposed alternately at 75 and 100 deg of knee flexion. Average motor evoked potential amplitude, normalized to the maximal M wave amplitude (MEP/M) and cortical silent period duration were calculated for each angle and compared among the contraction types. The MEP/M was lower (−23 and −28%, respectively) during eccentric than both concentric and isometric contractions at 75 deg, but similar between contraction types at 100 deg (P \u3c 0.05). The cortical silent period duration was shorter (−12 and −10%, respectively) during eccentric than both concentric and isometric contractions at 75 deg, but longer (+11 and +9%, respectively) during eccentric contractions at 100 deg (P \u3c 0.05). These results show that corticospinal excitability during eccentric contractions is angle dependent such that cortical inhibitory processes are greater with no alteration of corticospinal excitability at 100 deg, whereas this control is reversed at 75 deg