Isometric training with maximal co-contraction instruction does not increase co-activation during exercises against external resistances.

The present investigation verified that strength is improved by a training programme consisting of repetitions of maximal isometric voluntary co-contractions without increasing co-activations during contractions against external resistances. Ten participants performed 12 training sessions (four sets of 6 × 4 second maximal isometric co-contraction of the elbow flexor and extensors, 3 days a week for 4 weeks). Surface electromyograms of triceps and biceps brachii were collected during maximal voluntary isometric elbow flexion and extension against a force transducer.

Muscle activation of the elbow flexor and extensor muscles during self-resistance exercises: comparison of unilateral maximal cocontraction and bilateral self-resistance.

Muscle activation during self-resistance exercises was studied in 18 subjects performing (a) maximal unilateral isometric cocontractions of flexor and extensor muscles of the right elbow (UNI); (b) bilateral exercises consisting of maximal isometric extensions of the right elbow against the left elbow flexors (BiExt) and maximal isometric flexion of the right elbow against the left elbow extensors (BiFlex). Force production by the biceps brachii (BB), brachioradialis (BR), and triceps brachii (TB) during UNI, BiFlex, and BiExt were estimated by comparing the integrated surface electromyograms (iEMG) of BB, BR, and TB during UNI, BiExt, and BiFlex with the individual iEMG-force relationship determined from isometric contractions at 30, 60, and 100% maximal voluntary contraction during elbow flexion (MVCflex) or extension (MVCext) against a force transducer. During BiFlex for BB or BR and BiExt for TB, the values (mean ± SE) of BB-iEMG, BR-iEMG, and TB-iEMG were 74.

Effect of aging on the coordination between equilibrium and movement: what changes?

This investigation studies the effect of aging on the coordination between equilibrium and trunk movement. Eight young adults and seven adults at the end of middle age bent their trunk forward and stabilized their position. The center of mass shift was studied as an indicator of equilibrium control as was the electromyographic pattern of the main muscles involved in the movement.

Balance control and adaptation of kinematic synergy in aging adults during forward trunk bending.

The present study focuses on the organization of kinematic synergy and its adaptation to an unstable support surface during upper trunk movements in aging adults. Seven healthy aging adults (49-66 years old) were instructed to bend the trunk forward (the head and the trunk together) by about 40 degrees and to stabilize their final position, in the standard condition (both feet on the ground), and on a seesaw swinging in the sagittal plane. Kinematic synergy was quantified by performing a principal components analysis on the hip, knee and ankle angle changes during the movement.

Kinematic synergy adaptation to an unstable support surface and equilibrium maintenance during forward trunk movement.

The aim of this investigation was to study the adaptation to an unstable support surface of kinematic synergy responsible for equilibrium control during upper trunk movements. Eight adult subjects were asked to bend their upper trunk forward to an angle of 35 degrees and then to hold the final position for 3 s, first in a standard condition, with two feet on the ground and the second, on a rocking platform swinging in the sagittal plane. The movement characteristics (duration, amplitude, and mean angular velocity of the trunk), the time course of the antero-posterior center of mass (CM) shift during the movement, and the EMG pattern of the main muscles involved in the movement were studied under the two experimental conditions.