Muscle Activation Assessed with Electromyography is Suboptimal During Physical Therapy in Mechanically Ventilated Patients

Abstract

Physical therapy (PT) is a standard component of care for mechanically ventilated (MV) patients. Recent studies have raised concerns, however, that this treatment may be relatively ineffective. The purpose of the present study was to objectively analyze the effect of PT on leg strength in MV patients. Studies were performed on 22 MV patients receiving PT for 2 weeks. To assess PT intensity, we measured: (a) exercise duration, (b) PT types (range of motion, transfers, exercise machine usage, walking, resistance training), and (c) the intensity of muscle activation using wireless electromyogram (EMG) recordings of four leg muscles. To assess the response to PT, we measured quadriceps force generation evoked by magnetic femoral nerve stimulation. We found that response to PT was poor, and leg strength before and following PT (8.6 ± 3.4 and 7.6 ± 2.8 N) was not significantly different. EMG recordings indicated that patient effort during exercises was also poor. In particular, integrated normalized EMG activity fell substantially over time during training sessions in the majority of patients (the EMG index had a median of 30.3 (25–75% CI of 16.7–46.1) for the initial exercise and decreased to 18.1 (25–75% CI of 2.6–24.4) for the final exercise, p=0.039). There was dramatic patient‐to‐patient variation in the effort made during specific types of PT, resulting in substantial time spent performing ineffective exercises. We also found that, in many cases, the weakest patients received far less PT than patients with normal strength. These data provide a potential explanation why PT in MV patients is largely ineffective. We speculate that use of novel techniques to direct exercises (EMG targeting) and to accurately measure the response to PT (magnetic twitch assessment of strength) may dramatically improve responses of MV patients to PT.Support or Funding InformationR01HL113494, 5I01BX002132, R01HL112085