Influence of fascicle strain and corticospinal excitability during eccentric contractions on force loss.

New Findings: What is the central question of this study? Do neural and/or mechanical factors determine the extent of muscle damage induced by eccentric contractions? What is the main finding and its importance? The extent of muscle damage induced by eccentric contractions is related to both mechanical strain and corticospinal excitability measured at long muscle lengths during eccentric contractions.

Abstract: In this study, we investigated whether the mechanical and neural characteristics of maximal voluntary eccentric contractions would determine the extent of change in postexercise maximal voluntary isometric contraction (MVC) torque and muscle soreness. Eleven men performed 10 sets of 15 isokinetic (45 deg s ) maximal voluntary eccentric knee extensions.

Changes in Motor Coordination Induced by Local Fatigue during a Sprint Cycling Task.

Purpose: This study investigated how muscle coordination is adjusted in response to a decrease in the force-generating capacity of one muscle group during a sprint cycling task.

Methods: Fifteen participants were tested during a sprint before and after a fatigue electromyostimulation protocol was conducted on the quadriceps of one leg. Motor coordination was assessed by measuring myoelectrical activity, pedal force, and joint power.

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

What is the central question of this study? Does sensory input from peripheral mechanoreceptors determine the specific neural control of eccentric contractions? How corticospinal excitability (i.e. muscle responses to motor cortex stimulation) is affected by muscle length has never been investigated during eccentric contractions.

Comparison of two methodological approaches for the mechanical analysis of single-joint isoinertial movement using a customised isokinetic dynamometer.

Compared to isokinetic and isometric tests, isoinertial movements have been poorly used to assess single-joint performance. Two calculation procedures were developed to estimate mechanical performance during single-joint isoinertial movements performed on a customised isokinetic dynamometer. The results were also compared to appreciate the effects of measurement systems and calculation procedures.

Effects of Duchenne muscular dystrophy on muscle stiffness and response to electrically-induced muscle contraction: A 12-month follow-up.

The present study aimed to assess the ability of muscle stiffness (shear modulus) and response to electrically-induced muscle contraction to detect changes in muscle properties over a 12-month period in children with Duchenne muscular dystrophy (DMD). Ten children with DMD and nine age-matched healthy male controls participated in two experimental sessions (T and T) separated by 12.4 ± 0.

Specific joint angle dependency of voluntary activation during eccentric knee extensions.

Introduction: 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.

Motor adaptations to local muscle pain during a bilateral cyclic task.

The aim of this study was to determine how unilateral pain, induced in two knee extensor muscles, affects muscle coordination during a bilateral pedaling task. Fifteen participants performed a 4-min pedaling task at 130 W in two conditions (Baseline and Pain). Pain was induced by injection of hypertonic saline into the vastus medialis (VM) and vastus lateralis (VL) muscles of one leg.

Neuromuscular Changes and Damage after Isoload versus Isokinetic Eccentric Exercise.

Purpose: This study compared the effects of isoload (IL) and isokinetic (IK) knee extensor eccentric exercises on changes in muscle damage and neuromuscular parameters to test the hypothesis that the changes would be different after IL and IK exercises.

Methods: Twenty-two young men were paired based on their strength and placed in the IL (N = 11) or the IK (N = 11) group. The IL group performed 15 sets of 10 eccentric contractions with a 150% of predetermined one-repetition maximum load.

Time-Course of Neuromuscular Changes during and after Maximal Eccentric Contractions.

This study tested the relationship between the magnitude of muscle damage and both central and peripheral modulations during and after eccentric contractions of plantar flexors. Eleven participants performed 10 sets of 30 maximal eccentric contractions of the plantar flexors at 45°·s(-1). Maximal voluntary torque, evoked torque (peripheral component) and voluntary activation (central component) were assessed before, during, immediately after (POST) and 48 h after (48 h) the eccentric exercise.

Salivary Hormones Response to Preparation and Pre-competitive Training of World-class Level Athletes.

This study aimed to compare the response of salivary hormones of track and field athletes induced by preparation and pre-competitive training periods in an attempt to comment on the physiological effects consistent with the responses of each of the proteins measured. Salivary testosterone, cortisol, alpha-amylase, immunoglobulin A (IgA), chromogranin A, blood creatine kinase activity, and profile of mood state were assessed at rest in 24 world-class level athletes during preparation (3 times in 3 months) and pre-competitive (5 times in 5 weeks) training periods. Total mood disturbance and fatigue perception were reduced, while IgA (+61%) and creatine kinase activity (+43%) increased, and chromogranin A decreased (-27%) during pre-competitive compared to preparation period.

Time-course of performance changes and underlying mechanisms during and after repetitive moderately weight-loaded knee extensions.

The purpose of this study was to investigate the mechanisms of fatigue development induced by isoload (IL) fatiguing knee extensions. Nine physically active males (age=23±2years, height=179±7cm, mass=76±7kg) performed repetitive ballistic knee extensions at 30% of the isometric maximal voluntary peak torque. Fatigue development was assessed throughout the fatiguing exercise by quantifying changes in peak torque, agonist and antagonist electromyographic activity (EMG) and torque- and EMG-angle relationships.

Non-invasive assessment of muscle stiffness in patients with Duchenne muscular dystrophy.

Introduction: Assessment of muscle mechanical properties may provide clinically valuable information for follow-up of patients with Duchenne muscular dystrophy (DMD) through the course of their disease. In this study we aimed to assess the effect of DMD on stiffness of relaxed muscles using elastography (supersonic shear imaging).

Methods: Fourteen DMD patients and 13 control subjects were studied.

New insights on contraction efficiency in patients with Duchenne muscular dystrophy.

The decrease in muscle strength in patients with Duchenne muscular dystrophy (DMD) is mainly explained by a decrease in the number of active contractile elements. Nevertheless, it is possible that other electrochemical and force transmission processes may contribute. The present study aimed to quantify the effect of DMD on the relative contribution of electrochemical and force transmission components of the electromechanical delay (i.

Impact of forearm fatigue on the postural response to an externally initiated, predictable perturbation.

Purpose: The objective was to examine the impact of non-postural muscle fatigue on anticipatory postural control, during postural perturbations induced by platform translations. The experimental setup investigated the central changes caused by fatigue without the potential confounding influence of peripheral fatigue within the postural muscles.

Methods: Fatigue induced in forearm muscles by a maximal handgrip contraction has been previously shown to influence forearm force production for 10 min, reduce ankle plantarflexion force for 1 min and create measureable central fatigue for 30 s.

Impact of ankle muscle fatigue and recovery on the anticipatory postural adjustments to externally initiated perturbations in dynamic postural control.

The aim of this study was to determine whether and how young participants modulate their postural response to compensate for postural muscle fatigue during predictable but externally initiated continuous and oscillatory perturbations. Twelve participants performed ten postural trials before and after an ankle muscle fatigue protocol. Each postural trial was 1 min long and consisted of continuous backward and forward oscillations of the platform.

Shear elastic modulus can be used to estimate an index of individual muscle force during a submaximal isometric fatiguing contraction.

The present study was designed to determine whether fatigue alters the ability to estimate an index of individual muscle force from shear elastic modulus measurements (experiment I), and to test the ability of this technique to highlight changes in load sharing within a redundant muscle group during an isometric fatiguing task (experiment II). Twelve subjects participated in experiment I, which consisted of smooth linear torque ramps from 0 to 80% of maximal voluntary contraction (MVC) performed before and after an isometric fatigue protocol, beginning at 40% of MVC and stopped when the force production dropped below 30% of MVC. Although the relationships between modulus and torque were very similar for pre- and postfatigue [root mean square deviation (RMS(deviation)) = 3.

Neuromuscular adaptations to isoload versus isokinetic eccentric resistance training.

Purpose: The purpose of this study was to compare neuromuscular adaptations induced by work-matched isoload (IL) versus isokinetic (IK) eccentric resistance training.

Methods: A total of 31 healthy subjects completed a 9-wk IL (n = 11) or IK (n = 10) training program for the knee extensors or did not train (control group; n = 10). The IL and IK programs consisted of 20 training sessions, which entailed three to five sets of eight repetitions in the respective modalities.

Fatiguing handgrip exercise alters maximal force-generating capacity of plantar-flexors.

Exercise-induced fatigue causes changes within the central nervous system that decrease force production capacity in fatigued muscles. The impact on unrelated, non-exercised muscle performance is still unclear. The primary aim of this study was to examine the impact of a bilateral forearm muscle contraction on the motor function of the distal and unrelated ankle plantar-flexor muscles.

Prediction of time-to-exhaustion in the first dorsal interosseous muscle from early changes in surface electromyography parameters.

Introduction: In this study we evaluated the precision of the time-to-exhaustion (T(lim)) prediction from the early changes in surface electromyography (sEMG) of the first dorsal interosseous muscle.

Methods: Thirty subjects performed an index finger isometric abduction at 35% of maximal voluntary contraction (MVC) until exhaustion. Ten participants performed the same exercise at 50% MVC 1 week later.

A methodologic approach for normalizing angular work and velocity during isotonic and isokinetic eccentric training.

Context: Resistance exercise training commonly is performed against a constant external load (isotonic) or at a constant velocity (isokinetic). Researchers comparing the effectiveness of isotonic and isokinetic resistance-training protocols need to equalize the mechanical stimulus (work and velocity) applied.

Objective: To examine whether the standardization protocol could be adjusted and applied to an eccentric training program.

Fatigue-related adaptations in muscle coordination during a cyclic exercise in humans.

Muscle fatigue is an exercise-induced reduction in the capability of a muscle to generate force. A possible strategy to counteract the effects of fatigue is to modify muscle coordination. We designed this study to quantify the effect of fatigue on muscle coordination during a cyclic exercise involving numerous muscles.

No evidence of expertise-related changes in muscle synergies during rowing.

The purpose of the present study was to determine whether expertise in rowing is driven by a specific structure in muscular coordination. We compared seven experienced rowers and eight untrained (i.e.

Effect of power output on muscle coordination during rowing.

The present study was designed to quantify the effect of power output on muscle coordination during rowing. Surface electromyographic (EMG) activity of 23 muscles and mechanical variables were recorded in eight untrained subjects and seven experienced rowers. Each subject was asked to perform three 2-min constant-load exercises performed at 60, 90 and 120% of the mean power output over a maximal 2,000-m event (denoted as P60, P90, and P120, respectively).