Quadriceps muscle function and fatigue in women with Addison's disease

In nine patients with Addison's disease (mean +/- SE: 51 +/- 2 years) recei ving conventional steroid treatment, and nine age-matched healthy controls (56 +/- 2 years), we investigated maximum voluntary quadriceps force (MVC) and contractile properties evoked with stimulation and central activation b oth at rest and during a submaximal intermittent fatigue task. The MVC was similar (-3%), but twitch tension (-27%) and central activation were signif icantly less (-7%), and tetanic half-retaxation time was similar to 40% slo wer in the patients. Twitch amplitudes were potentiated by 6% in the patien ts, but unchanged in the control group. The patients self-terminated a subm aximal intermittent fatigue protocol (0.6 duty cycle) at similar to5 +/- 1 min, whereas the controls stopped when they lost 50% of MVC force (similar to 10 +/- 1 min). Force loss was similar between groups over the first 5 mi n of the fatigue task. In the patient group, maximal and submaximal relativ e integrated electromyogram (IEMG) increased significantly in the first min ute of fatigue and remained elevated, whereas the controls exhibited a grad ual increase in submaximal IEMG with little change in maximal IEMG. These r esults indicate that conventionally treated Addison's patients have similar MVC strength, but altered contractile properties and decreased endurance c ompared with controls. (C) 2001 John Wiley & Sons, Inc.