Recruitment of Abdominal and Neck Muscles During Four Different Exercises in Healthy Adults

Background and Purpose: Prolonged mechanical ventilation can greatly increase morbidity and mortality. Diaphragm weakness has been identified as a major contributor for 50% of patients; however, other muscles besides the diaphragm contribute to efficient ventilatory function. The purpose of this study was to compare the change in deoxyhemoglobin (ΔHHb) and muscle oxygen saturation (ΔSmO 2 ) (markers of muscle recruitment) of 3 extra-diaphragmatic muscles across 4 different bed exercises. Methods: Using a pretest–posttest design, healthy participants (n = 18) performed 3 minutes of 30 repetitions of 4 exercises: resisted trunk flexion (TF), resisted neck flexion (NF), expiratory threshold loading (ETL), and neuromuscular electrical stimulation (NMES) of the rectus abdominis and external obliques. Near infrared spectroscopy was used to measure ΔHHb, and ΔSmO 2 in the sternocleidomastoid, rectus abdominis, and external obliques during these exercises. Results: Increases of ΔHHb were highest for the sternocleidomastoid during NF and for rectus abdominis and external obliques during TF ( P < .010). The opposite pattern was shown for ΔSmO 2; decreases of ΔSmO 2 were largest for the sternocleidomastoid during NF and for rectus abdominis and external obliques during TF ( P < .005). No significant differences were observed in ΔHHb and ΔSmO 2 for rectus abdominis and external obliques during ETL versus NF or NMES nor were there differences when comparing NF versus NMES for these 2 muscles. Conclusion: TF and NF are most effective for recruiting abdominal muscles and sternocleidomastoid, respectively, whereas ETL showed a variable response. Stimulation parameters of NMES and its tolerance can limit outcomes.