ABSTRACT
This work aims to investigate cardiac autonomic nervous system modulation during short term isometric skeletal muscle contraction. The study was done on thirty male nonsmoker volunteers, aged 19-23 years [mean=20.46 +/- 1.27], body mass index [BMI] ranged 15.7-29.05 [mean=22.84 +/- 3.84], with history of no medical problems, normal physical examination and laboratory tests, including complete blood count, blood chemistry, chest X-ray and electrocardiography, were selected from among the medical students of King Abdul-Aziz University [KAAU] in Saudi Arabia Kingdom. The standardization of conditions including the temperature the laboratory and the food and beverages containing caffeine intake must be avoided after 8:00 PM the day preceding the test. After a 30-min rest in the sifting position in an air-conditioned room [temperature range, 23°C to 24°C], the test was performed between 10:00 AM and 12:30 PM. At rest, blood pressure was measured by digital sphygmomanometer and parameters of heart rate variability [time and frequency domains] were recorded by Power Lab instrument. A two-minutes sustained isometric contraction was done by both hands simultaneously lifting 2 fire extinguishers [each weighing about 7 kg], and then the previous parameters were also recorded. Results revealed increased sympathetic activity and decreased vagal activity during short-term sustained isometric skeletal muscle contraction