Relationships between force and muscle oxygenation kinetics during sustained static gripping using a progressive workload.

This study aimed to examine the relationships between force and subjective muscle-fatigue sensation (SMS), and muscle oxygenation kinetics during sustained static gripping using a progressive workload. Subjects consisted of 10 males (height 173.2+/-7.1 cm, body weight 70.3+/-15.1 kg, and age 21.1+/-1.5 years). They performed sustained static gripping with 7 gradually increasing relative demand values of 20% to 80% maximal voluntary contraction (MVC). The staging of the progressive workload was 10 s for 20% MVC, 20 s each for 30, 40, 50, 60, and 70% MVC, and 10 s for 80% MVC. Borg's SMS was used to measure the fatigue sensation of the antebrachial region in a pre-test and every 10 s during the test. The time to reach minimum Oxy-Hb/Mb appeared at about 50 s (52.6+/-25.2 s) after the onset of sustained static gripping, and the time to reach maximum Deoxy-Hb/Mb occurred later at 90 s. Significant and high correlations (r=0.632-0.721) were found between the time to reach maximum Deoxy-Hb/Mb, and Peak Force Time and Average Force. Even though the demand values caused a workload increase and reached 50% MVC, the change of Total Hb/Mb and Oxy-Hb/Mb kinetics was relatively small. Therefore, the effect caused by an obstruction of blood volume may not occur during the progressive workload. It was determined that the contraction time after the peak of SMS is relatively short and an individual difference in force value expands in the phase where SMS reaches its peak.