Intermittent neck flexion induces greater sternocleidomastoid deoxygenation than inspiratory threshold loading

Area of Science:

• Respiratory Physiology
• Exercise Physiology
• Muscle Metabolism

Background:

• Inspiratory muscle training is crucial for respiratory rehabilitation.
• Understanding the metabolic demands of different inspiratory exercises is essential for optimizing training protocols.
• The sternocleidomastoid, scalenes, and diaphragm/intercostals are key inspiratory muscles.

Purpose of the Study:

• To compare the deoxygenation patterns of the sternocleidomastoid, scalenes, and diaphragm/intercostals during submaximal intermittent neck flexion (INF) versus submaximal inspiratory threshold loading (ITL) in healthy adults.
• To assess the metabolic activity and perceived exertion associated with these two inspiratory loading methods.

Main Methods:

• A randomized, cross-over design was employed with 14 healthy participants.
• Participants performed submaximal INF and ITL, each targeting 50% of maximal voluntary contraction or inspiratory pressure, until task failure.
• Near-infrared spectroscopy (NIRS) measured muscle deoxygenation (ΔHHb) and oxygenation (ΔO2Hb) in key inspiratory muscles.

Main Results:

• The sternocleidomastoid showed greater initial deoxygenation during INF compared to ITL.
• At isotime, sternocleidomastoid blood volume (ΔtHb) and oxygenation (ΔO2Hb) were higher during INF.
• Lower perceived exertion (Borg scores) was reported at task failure during INF compared to ITL.

Conclusions:

• Intermittent neck flexion (INF) elicits significant metabolic activity in the sternocleidomastoid muscle.
• INF results in a lower perception of effort compared to inspiratory threshold loading (ITL).
• INF may serve as an alternative inspiratory muscle training method, particularly for mechanically ventilated individuals.