Table 2.

Omnibus tests (Friedman) of within-subject effects.

Variable	Q (df)	P value
IBIa	7.625 (2)	.02
HRb	7.429 (2)	.02
SDNNc	25.125 (2)	<.001
RMSSDd	24.0 (2)	<.001
pNN50e	10.889 (2)	.004
HF-HRVf	15.5 (2)	<.001
LF-HRVg	19.5 (2)	<.001
VLF-HRVh	2.0 (2)	.37
LF/HF ratioi	14.0 (2)	<.001
BPMj	21.709 (2)	<.001
ARAk	1.175 (2)	.56

^aIBI: interbeat interval (milliseconds).

^bHR: heart rate (beats per minute).

^cSDNN: standard deviation of normal R-R intervals (milliseconds).

^dRMSSD: root mean square of successive differences between adjacent heartbeats.

^epNN50: percentage of normal R-R intervals that are greater than 50 milliseconds away from their adjacent intervals.

^fHF-HRV: high-frequency heart rate variability (0.15-0.4 Hz).

^gLF-HRV: low-frequency heart rate variability (0.04-0.15 Hz).

^hVLF-HRV: very-low-frequency heart rate variability (0.0033-0.04 Hz).

ⁱLF/HF ratio: low- to high-frequency ratio of heart rate variability.

^jBPM: respiration cycles per minute.

^kARA: abdominal respiration amplitude (volts).