We hypothesized that patients who fail weaning from mechanical ventilation recruit their inspiratory rib-cage muscles sooner than they recruit their expiratory muscles, and that rib-cage muscle recruitment is accompanied by recruitment of sternomastoid muscles. Accordingly, we measured sternomastoid electrical activity and changes in esophageal (Pes) and gastric pressure (Pga) in 11 weaning-failure and 8 weaning-success patients. At the start of trial, failure patients exhibited a higher Pga-to-Pes ratio than did success patients (p=0.05), whereas expiratory rise in Pga was equivalent in the two groups. Between the start and end of the trial, failure patients developed further increases in Pga-to-Pes ratio (p< 0.0014) and the expiratory rise in Pga also increased (p < 0.004). At the start of trial, sternomastoid activity was present in 8 of 11 failure patients contrasted with 1 of 8 success patients. Over the course of the trial, sternomastoid activity increased by 53.0±9.3% in the failure patients (p=0.0005), whereas it did not change in the success patients. Failure patients recruited their respiratory muscles in a sequential manner. The sequence began with activity of diaphragm and greater-than-normal activity of inspiratory rib-cage muscles; recruitment of sternomastoids and rib-cage muscles approached near maximum within four minutes of trial commencement; expiratory muscles were recruited slowest of all. In conclusion, not only is activity of the inspiratory rib-cage muscles increased during a failed weaning trial, but respiratory centers also recruit sternomastoid and expiratory muscles. Extradiaphragmatic muscle recruitment may be a mechanism for offsetting the effects of increased load on a weak diaphragm.