Androgenicity of the progestin in oral contraceptives does not affect maximal leg strength

Abstract

Purpose

This study was conducted to examine androgenicity of the progestin in oral contraceptive pills and its effect on maximal leg strength in females.

Methods

Twelve participants who were using a monophasic pill containing 30 μg ethinylestradiol plus either 150 μg levonorgestrel (LEV) or 250 μg norgestimate (NOR) for at least the last 6 months were recruited (mean±SEM; LEV: age, 19.8±0.3 years; stature, 1.67±0.17 m; mass, 65.9±1.9 kg; NOR: age, 20.6±0.2 years; stature, 1.65±0.17 m; mass, 64.6±2.4 kg). Three maximal isokinetic extension and flexion tests were performed on three occasions (Days 3–6, 11–14 and 18–21 of the pill cycle) to assess peak extension and peak flexion torque (in Newton meters).

Results

No significant (p>.05) differences were found in the LEV and NOR groups in peak extension torque (F=0.719; p=.416) or peak flexion torque (F=0.291, p=.601) throughout the pill cycle and between groups.

Conclusion

In this small study, the androgenicity of the progestin in the contraceptive pill had no significant association with maximal strength in these female athletes.

Introduction

Many females taking part in sports take some form of oral contraceptive pill (OCP), with reports estimating that OCP use in female athletes is similar to the prevalence of OCP use in the general community [1]. The androgenic potency of an OCP is determined by the type and dose of both the estrogen and progestin within the OCP [2]. An estimate of the estrogenic and androgenic potency of an OCP may be obtained by measuring the major carrier protein for testosterone and estradiol synthesized in the liver, namely, sex hormone binding globulin (SHBG) [3]. Because most synthetic progestins in the OCP decrease SHBG levels with respect to those seen with estrogen alone, it has been suggested that they impart a degree of androgenicity to combination OCPs [3]. Progestogens with greater androgenicity should have a greater impact on responses to exercise than progestins with a lower androgenicity [3]. Thus, the type of progestin within the OCP is important to consider as it may directly affect the actions of estradiol and, thus, athletic performance [4].

There is a growing body of evidence suggesting that the high synthetic steroid hormone concentrations provided by OCP could impair various physiological capacities and, thus, athletic performance [5]. However, the information pertaining to the effect of OCP on strength is minimal [6]. Sarwar et al. [7] found that the maximal force of the quadriceps and hand muscles did not change in monophasic OCP users over two pill cycles, whereas non-OCP users had an 11% increase in quadriceps strength. Phillips et al. [4] found no significant change in maximal voluntary force of the adductor pollicis in women taking OCPs, and Elliot et al. [8] reported no significant differences in strength between OCP users and eumenorrheic participants or between OCP withdrawal and eumenorrheic participants, despite significant differences in the concentration of progestin and estrogen between the groups. However, many studies had limitations as they typically used a variety of OCPs without specifying the type and/or level of exogenous hormones within the pills. In addition, research has focused predominantly on the estrogen component of the pill because it has been linked with the undesirable side effects of weight gain, bloating, tender breasts and nausea [9]. Little information pertaining to the effect of the type of progestin present in the OCP and its effect on performance has been gained [10]. No study has examined the effects of the type of progestin within OCPs on strength performance. This type of data is required to test the association between androgenicity of the progestin and muscle strength because muscle strength is a vital biomotor ability in many athletic events. To better understand the relationship between progestin androgenicity and maximal strength, we enrolled a group of monophasic OCPs users in this study. The OCPs were chosen to ensure a known and consistent amount and type of estrogen but two different types of progestin, levonorgestrel (LEV) and norgestimate (NOR), and two levels of androgenicity. Thus, one could observe and compare the effects of the progestin amount and type on maximal leg strength performance. The hypothesis for this study was that the NOR OCP group would have maximal strength values that were significantly different from the LEV OCP group due to LEV having greater androgenicity than NOR, thus opposing the actions of the estrogen to a greater degree.