Table 2. Correlations among the time (6:00 to 9:00), level of activity, sleepiness, and fatigue.

		Sleepiness	Sense of fatigue	LF/HF	HR	Level of activity
Time (6:00 to 9:00)	Nap	r=0.049 n.s.	r=0.157 n.s	r=–0.565**	r=–0.759***	r=–0.696***
	No nap	r=0.112 n.s.	r=0.129 n.s.	r=0.007 n.s.	r=0.537**	r=–0.209 n.s.
Level of activity	Nap	r=–0.155 n.s	r=–0.039 n.s.	r=0.589***	r=0.594**	–
	No nap	r=–0.063 n.s.	r=0.069 n.s.	r=–0.560***	r=0.315 n.s.	–

*: p<0.05, **: p<0.01, ***: p<0.001. n.s.: not significant, r: correlation coefficient.