Relationships between force-time parameters and muscle oxygenation kinetics during maximal sustained isometric grip and maximal repeated rhythmic grip with different contraction frequencies.

The purposes of this study were to examine the relationships between various force-time parameters and muscle oxygenation kinetics during maximal sustained isometric grip (SIG) and maximal repeated rhythmic grips (RRG) with different grip intervals (interval times: 5, 4, 3, and 2 s). Subjects were 10 healthy young males, aged 20-26 years (height 173.9+/-7.3 cm, body mass 71.5+/-11.2 kg). After measuring maximal grip force, each subject performed the SIG and RRG tests with a target frequency of 12, 15, 20, and 30 grips.min(-1) (interval times: 5, 4, 3, and 2 s, respectively) for 6 min. The decreasing time until 80% MVC showed significant and high correlations with final force values in RRGs with over 3 s intervals (r=0.866-0.941), but not in the SIG and RRG with a 2 s interval. The time at the lowest Oxy-Hb/Mb value showed a significant and high correlation with the time at the highest Deoxy-Hb/Mb value only in the SIG and RRG with a 2 s interval (r=0.825-0.916). Oxy-Hb/Mb decreases markedly and deoxy-Hb/Mb increases after the onset of SIG due to the obstruction of blood flow caused by the increase in intramuscular pressure. A similar physiological response to that of SIG occurs also in RRG with a 2 s interval, but RRGs with intervals over 3 s achieve more resumption of blood flow in the muscular relaxation phase. Hence, in spite of the same RRGs, it was determined that RRGs with intervals over 3 s differ significantly in a changing pattern of grip force and muscle oxygen kinetics from RRGs with a 2 s interval.