In this study a practical guarding work is carried out for 180 minutes as
the same as the actual guarding work that is done by nine students of the
department of security services in K University in order to investigate changes
in circadian rhythms during long hour guarding in bodyguards at practical
sites. In the results of the tests of the heart rate variation and autonomic
nervous system with the interval of 30 minutes using HRV (Heart rate
variability), there are no significant differences in HRV and SDNN and that
leads to maintain it stably during the guarding work for 180 minutes. In the
case of TP which reflects the overall activity level in the autonomic nervous
system, it shows a high significant difference (p<.05) at 90 and 120 minutes
compared to that of normal states. Also, it shows a significant decrease in
the level after a lapse of 120 minutes and that shows a decrease in the activity
of the autonomic nervous system for the guarding work more than 120
minutes. Although differences in VLF, LF, and HF are not significant levels,
these are influenced on the change in TP. The LH/HF ratio that represents
the balance between the sympathetic nerve and the parasympathetic nerve
shows a significant high level (p<.05) after a lapse of 30 minutes. Thus, it
is considered that the concentration of the guarding work after a lapse of 120
minutes is decreased and there are some tensions and excitations after a lapse
of 30 minutes since the beginning of the guarding work.