Reliability of using magnetic stimulation to evaluate muscle function in patients with severe to very severe COPD and healthy subjects

Abstract

In addition to voluntary activation strategies, limb muscle function can also be assessed during non-voluntary limb muscle contractions by calculating activation using un-potentiated (Qtw_unpot) and potentiated twitch force (Qtw_pot) from a series of twitches induced by magnetic stimulation. The test-retest reliability of these measurement techniques was investigated in the present study.

Patients with COPD (n=20) (FEV₁ 38 % predicted) and healthy subjects (n=15) completed two testing sessions (> 48h between sessions) to assess quadriceps muscle function using magnetic stimulation. At each occasion, a ramp protocol of non-potentiated stimulations at increasing intensities (40, 50, 60, 70, 80, 85, 90, 95, 100% of stimulator output) was performed. After participants were asked to perform a set of three maximal 5-s voluntary contractions (MVCs). This was followed by potentiated twitches at 100% stimulator output. Qtw_unpot and Qtw_pot are defined as the peak response observed during the ramp protocol and potentiated twitches, respectively. MVC was defined as the peak of the strongest voluntary contraction. Results presented in Table 1.

Magnetic stimulation of the femoral nerve provides a reliable method for assessing muscle function in patients with COPD and healthy subjects, which, in contrast, to a MVC is independent of the subjects' motivation and cooperation.