Influence of posture and breathing route on neural drive to upper airway dilator muscles during exercise

Our purpose was to determine the influence of posture and breathing route o n electromyographic (EMG) activities of nasal dilator (NDM) and genioglossu s (GG) muscles during exercise. Nasal and oral airflow rates and EMG activi ties of the NDM and GG were recorded in 10 subjects at rest and during upri ght and supine incremental cycling exercise to exhaustion. EMG activities i mmediately before and after the switch from nasal to oronasal breathing wer e also determined for those subjects who demonstrated a clear switch point (n = 7). NDM and GG EMG activities were significantly correlated with incre ases in nasal, oral, and total ventilatory rates during exercise, and these relationships were not altered by posture. In both upright and supine exer cise, NDM activity rose more sharply as a function of nasal inspired ventil ation compared with total or oral inspired ventilation (P < 0.01), but GG a ctivity showed no significant breathing-route dependence. Peak NDM integrat ed EMG activity decreased (P = 0.008), and peak GG integrated EMG activity increased (P = 0.032) coincident with the switch from nasal to oronasal bre athing. In conclusion, 1) neural drive to NDM and GG increases as a functio n of exercise intensity, but the increase is unaltered by posture; 2) NDM a ctivity is breathing-route dependent in steady-state exercise, but GG activ ity is not; and 3) drive to both muscles changes significantly at the switc h point, but the change in GG activity is more variable and is often transi ent. This suggests that factors other than the breathing route dominate dri ve to the GG soon after the initial changes in the configuration of the oro nasal airway are made.