The activity in the primary motor cortex (M1) reflects the direction of movements, but little is known about physiological changes in the M1 during generation of bilateral isometric forces in different directions. Here, we used transcranial magnetic stimulation to examine motor evoked potentials (MEPs), short-interval intracortical inhibition (SICI), and interhemispheric inhibition (IHI) in the...

We developed a model to investigate the influence of the muscle force twitch on the simulated firing behavior of motoneurons and muscle force production during voluntary isometric contractions. The input consists of an excitatory signal common to all the motor units in the pool of a muscle, consistent with the "common drive" property. Motor units respond with a hierarchically structured firing ...

PURPOSE Studies have both supported and refuted the concept that it is the intent to perform ballistic contractions that determines velocity-specific gains in resistance training. The purpose of this investigation was to determine whether ballistic intent is as effective as ballistic movement in improving muscle activation, force, movement time, and reaction time. METHODS Subjects completed 8...

The primary objective of this study was to determine the effectiveness of isometric exercise (IE) as a countermeasure to hindlimb unloading (HU)-induced atrophy of the slow (soleus) and fast (plantaris and gastrocnemius) muscles. Rats were assigned to either weight-bearing control, 7-day HU (H7), H7 plus IE (I7), 14-day HU (H14), or H14 plus IE (I14) groups. IE consisted of ten 5-s maximal isom...

Long-latency (40-80 ms) electromyographic (e.m.g.) responses of the contracting flexor pollicis longus to stretches applied at the thumb-tip, were studied in normal human subjects. Stretches were applied during four classes of contraction: (i) isometric 'hold', in which the subject held a steady isometric contraction; (ii) isometric tracking, in which the subject tracked a steadily rising force...

A conventional five-step chemo-mechanical cycle of the myosin-actin ATPase reaction, which implies myosin detachment from actin upon release of hydrolysis products (ADP and phosphate, Pi) and binding of a new ATP molecule, is able to fit the [Pi] dependence of the force and number of myosin motors during isometric contraction of skeletal muscle. However, this scheme is not able to explain why t...

Using transcranial magnetic stimulation (TMS), differences in the excitability changes of motor evoked potentials (MEPs) between isometric (force task) and isotonic (movement task) muscle contractions in a distal (first dorsal interosseous; FDI) and a proximal (middle deltoid; MD) muscle were studied. In the FDI muscle, the active threshold of MEP recruitment was significantly lower in the isot...