Variation of the maximum maintenance time of an isometric contraction in the presence of a second contraction

During maintenance of an isometric, contraction, an increase in perfusion of the contracting muscle would cause a prolongation in the maximum maintenance time (limit-time). This improvement in blood perfusion to an upper limb muscle can easily be obtained if the subject is asked to perform simultaneously a second isometric contraction of another muscle group at a slightly higher relative force than the first; it happens involuntarily through the involvement of different muscle groups (fixator muscles of the body trunk, limbs, neck and head) at the same time as the muscle under study. Seventeen subjects (nine women and eight men) carried out simultaneously sustained isometric contractions until exhaustion of the right (RA) and left elbow flexors (LA). The relative forces were 40% of the maximum voluntary contraction (MVC) for RA and 50% of MVC for LA. Contraction of LA occurred after a relative time interval (RTI) corresponding to 0, 25, 50, 75, and 100% of the limit-time of RA alone which was predetermine...