The relationship of static muscle function to use of oral contraceptives

Abstract

The handgrip endurance time (ET) and the total force output (FO) at 50% maximum voluntary contraception (MVC) of 26 females aged 18-33 were measured during the follicular phase (day 8 +or- 2) and luteal phase (day 21 +or- 3) of 1 menstrual cycle. 3 groups were utilized: 1) normals (nonusers of oral contraceptives [OCs] 2) users of OCs only (not of vitamin B6) and 3) users of OCs and vitamin B6. Vitamin B6 status was assessed by measurement of 24 hour urine xanthurenic acid (XA) excretion following a 2 g loading dose of L-tryptophan. Recent vitamin B6 intake was assessed by measurement of 24 hour urine 4-pyridoxic acid (4-PA) excretion. There were no significant among-group differences in MVC however. MVC during the follicular phase was signficantly (P<0.05) greater than during the luteal phase. The ET and FO of normal subjects was signficantly (P<0.05) greater than that of the combined group of users of OCs only and users of OCs and vitamin B6. There was no significant difference between users of OCs only and users of OCs and vitamin B6 in either ET or FO nor between the follicular and luteal phases of the menstrual cycle. Levels of 4-PA confirmed that the subjects who reported being users of OCs and vitamin B6 had substantially larger intakes of vitamin B6 than did the other subjects. Levels of XA indicated that only 2 subjects both OC users only were vitamin B6 deficient. Compared to other users of OCs only the mean MVC of the vitamin B6 deficient subjects was lower the mean ET higher and the mean FO approximately equal. Therefore we have concluded that OC users appear to exhibit lower static muscle endurance than normal subjects and their vitamin B6 status was not a mediating factor. (authors)