Work-rest periods: Their effects on normal physiologic response to isometric and dynamic work

Heart rate (HR) and blood pressure (BP) responses to repeated dynamic and combined dynamic and isometric work bouts of 30sec, 2min, and 6min with equal rest periods at 40% and 80% of V̇O₂max was studied in five healthy men and five healthy women. The work duration for each experimental condition was 24min. The treadmill was used for dynamic work. Subjects pushed a bar horizontally while on the treadmill at 20% of their maximal voluntary strength for isometric work. Results showed that work performed at 40% of V̇O₂max in 30sec bouts compared to 6min bouts reduced HR, BP and the double product (BP x HR) by 11%, 4%, and 14%, respectively. Work performed at 80% of V̇o₂max in 30sec bouts of repeated work or rest compared to the 6min bouts resulted in reducing HR, BP, and double products 28%, 15%, and 39%, respectively. Addition of the isometric load did not significantly change the reslts. This study sugests that cardiac patients may be able to perform more work safely if it is carried out in short periods alternating with rest periods of equal duration.