Table 4. Chronological changes in MDF of target muscles during PImax measurement under no load.

	PImax (n=14)
	Trapezius	Sternocleidomastoid	Pectoralis major	Diaphragm	Rectus abdominis	External oblique	Internal oblique
Pre-load	56.4 ± 13.6	78.7 ± 11.4	68.0 ± 12.5	70.7 ± 13.1	76.5 ± 18.7	57.4 ± 10.3	89.0 ± 30.6
2 min	60.9 ± 15.7	74.9 ± 9.6	78.6 ± 18.0	75.3 ± 14.6	78.6 ± 25.0	58.2 ± 9.1	86.2 ± 33.6
4 min	61.0 ± 15.4	72.1 ± 9.5	76.7 ± 11.7	69.8 ± 15.6	84.7 ± 21.4	54.7 ± 9.5	86.4 ± 35.4
6 min	61.1 ± 11.5	74.0 ± 7.0	76.6 ± 19.0	78.2 ± 18.7	85.4 ± 23.1	58.2 ± 12.5	93.9 ± 25.8
8 min	60.1 ± 15.3	78.7 ± 11.4	76.7 ± 19.6	71.5 ± 16.1	82.1 ± 23.1	57.0 ± 10.5	91.6 ± 34.3
10 min	61.5 ± 13.0	75.5 ± 10.5	79.7 ± 18.3	74.1 ± 16.6	80.5 ± 22.5	53.4 ± 11.4	107.9 ± 42.2
12 min	59.6 ± 14.8	78.5 ± 10.4	78.2 ± 17.0	71.3 ± 13.3	82.9 ± 22.2	55.7 ± 10.7	99.4 ± 37.2
14 min	65.8 ± 19.8	79.5 ± 11.9	71.3 ± 14.3	71.0 ± 15.0	78.5 ± 22.7	54.5 ± 10.2	96.7 ± 33.6
16 min	62.4 ± 18.2	84.1 ± 17.7	69.7 ± 9.1	75.3 ± 15.1	79.9 ± 25.0	57.1 ± 12.0	95.4 ± 27.2
18 min	60.7 ± 14.0	78.9 ± 16.6	72.1 ± 14.4	78.6 ± 16.4	83.5 ± 25.6	58.1 ± 10.3	94.7 ± 31.9
20 min	66.1 ± 17.5	77.2 ± 9.0	71.4 ± 10.4	75.1 ± 16.1	78.8 ± 19.5	58.0 ± 15.3	94.6 ± 32.9
5 min rest	64.6 ± 16.2	79.2 ± 8.4	73.2 ± 10.8	70.4 ± 13.5	82.3 ± 20.4	56.4 ± 10.1	94.7 ± 34.7
10 min rest	63.4 ± 18.1	78.5 ± 16.1	77.3 ± 15.4	71.6 ± 13.5	82.4 ± 24.8	53.3 ± 10.3	90.1 ± 35.7
15 min rest	58.2 ± 20.1	78.2 ± 12.2	72.9 ± 12.2	74.0 ± 14.8	77.0 ± 21.9	60.0 ± 12.2	84.8 ± 24.6
20 min rest	61.8 ± 14.3	77.3 ± 11.7	71.6 ± 13.3	73.8 ± 12.3	80.0 ± 21.9	54.9 ± 10.3	102.4 ± 37.1
25 min rest	60.3 ± 17.5	77.7 ± 11.7	71.5 ± 17.1	76.4 ± 17.5	83.6 ± 21.5	58.4 ± 6.6	94.6 ± 31.0
30 min rest	61.2 ± 15.8	81.0 ± 14.1	70.0 ± 16.8	71.9 ± 12.0	77.7 ± 17.2	60.0 ± 10.4	86.5 ± 29.9

Unit: Hz (mean ± standard deviation), *p<0.05 (Comparison with pre-load), †p<0.05 (Comparison with +20  min load and rest), n=14.

MDF: median power frequency; PImax: maximal inspiratory mouth pressure.