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Effects of Combination Oral Contraceptives on Strength Development in Women Athletes

Nichols, Andrew W1; Hetzler, Ronald K2; Villanueva, Richard J2; Stickley, Christopher D2; Kimura, Iris F2

Journal of Strength and Conditioning Research: September 2008 - Volume 22 - Issue 5 - p 1625-1632
doi: 10.1519/JSC.0b013e31817ae1f3
Original Research

Nichols, AW, Hetzler, RK, Villanueva, RJ, Stickley, CD, and Kimura, IF. Effects of combination oral contraceptives on strength development in women athletes. J Strength Cond Res 22(5): 1625-1632, 2008-This study was designed to investigate the effects of combination oral contraceptive agents (OCAs) on strength and torque production in collegiate women softball and water polo athletes who participated in a 12-week strength development program. A double-blind research design was used to mask subjects to the main outcome of interest. Thirty-one women collegiate softball and water polo players were divided into experimental (OCA users, n = 13), and control (non-OCA users, n = 18) groups. All subjects participated in the same supervised 12-week preseason strength development program. One-repetition maximum bench press (1RMBP), 10-repetition maximum leg extension (10RMLE), isokinetic peak torque bench press (IKBP), and isokinetic peak torque leg extension (IKLE) data were collected at weeks 0 (pre-test), 4, 8, and 12 (post-test). Significant increases in strength and torque production over time were identified regardless of group for 1RMBP, 10RMLE, and IKLE. No significant differences in IKBP torque production occurred during the 12-week strength training program. No significant differences in 1RMBP, 10RMLE, IKBP, or IKLE occurred between the OCA users and the non-OCA users groups. It was concluded that, within the limitations of the study, the use of combination OCAs did not provide sufficient androgenic effect to increase strength gains beyond the stimulus of the training protocol.

1Division of Sports Medicine, Department of Family Medicine and Community Health, John A. Burns School of Medicine and 2Department of Kinesiology and Leisure Science, University of Hawaii at Manoa, Honolulu, Hawaii

Address correspondence to Dr. Ronald K. Hetzler, Hetzler@hawaii.edu.

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Introduction

The human sex steroid hormones estrogen, progesterone, and testosterone have similar molecular structures but exhibit markedly distinct effects on gender differentiation. Relatively high testosterone levels account for many of the observed differences in lean body mass and muscular strength in men compared to women. Exogenous administered testosterone and related anabolic steroids may produce further increases in lean body mass and muscle strength in men and women engaged in strength training programs. Although the effects of exogenous estrogen and progesterone on muscular strength are not known, it is possible that combination oral contraceptive agents (OCAs) with high androgenic activity could have positive effects on muscular strength gains (7). Potential mechanisms by which OCAs may enhance athletic performance include increasing growth hormone levels in response to exercise (2,5), attenuating delayed-onset muscle soreness (37), and reducing the incidence of traumatic injuries by reducing premenstrual symptoms (27).

Previous studies suggest that the use of monophasic, combination OCAs does not significantly affect peak torque (13,30) or isometric strength (13). Combination OCAs have been shown to have no effect on maximal force production measured by adductor pollicis longus maximum voluntary contraction (32), knee extension/flexion peak torque (22), and forearm isometric endurance (31). However, combination OCAs were associated with reduced handgrip endurance time and force output (39). Aerobic performance declined in some OCA users (9,22,28) and did not in others (1,6,10,19,22), and OCA use does not appear to affect anaerobic performance (10,22,24).

To our knowledge, no field studies have been conducted that prospectively compared strength gains between OCA users and non-OCA (NOCA) users who participated in a vigorous resistance training program. The purpose of this study was to examine how combination OCAs may affect strength changes in collegiate women athletes when participating in a prescribed preseason strength training program.

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Methods

Experimental Approach to the Problem

The effects of OCA use during strength training remain unclear (7). This study used a double-blind research design to assess strength gain differences observed between individuals taking combination OCAs vs. those not taking exogenous hormones. Subjects were blinded to the main outcome of interest, i.e., strength gain differences between groups, and the data collection team was blinded to the OCA use of subjects until data collection was completed. Subjects were instructed that the purpose of the study was to assess the effectiveness of a preseason resistance training program. Changes in the dependent variable, strength, were assessed before, during, and after a 12-week resistance training program using isokinetic and repetition maximum procedures. Subjects were divided into an experimental group, OCA users, and a control group, NOCA users, which served as the independent variables for all statistical analyses.

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Subjects

Women collegiate student athlete members of the softball (record: 42-10; NCAA Regional qualifier) and water polo (record: 25-10; National Collegiate Select Championship qualifier) teams at an NCAA Division I university volunteered to participate in this study. Subjects who met the study inclusion criteria (detailed below) participated in a standardized 12-week, fall semester preseason resistance training program. It was assumed that based on their athletic participation history, all subjects had previous resistance training experience, although no attempt was made to quantify experience level. All potential subjects completed informed consent forms as approved by the host institution's Committee on Human Studies before participation.

Each subject completed a survey that detailed recent resistance and aerobic exercise and athletic training habits, the use of performance-enhancing supplements, menstrual history, prescription medications taken, use of tobacco and alcohol, and history and type of hormone therapy or OCA. Study inclusion criteria were 1) successful completion of a preparticipation physical evaluation by university team physicians, 2) absence of significant injuries that could interfere with participation in a resistance training program, 3) regular menstrual cycles (menses every 25-35 days), 4) no use of ergogenic aids or supplements (creatine monohydrate, ephedrine, steroids, clenbuterol, androstenedione, dihydroepiandrosterone, β-hydroxy-β-methylbutyrate, tribestan), 5) completion of the 12-week resistance training program, and 6) nonpregnant status as determined by a medically supervised pregnancy test. The OCA user inclusion criteria were regular and consistent combination OCA use for at least 3 months before and throughout the 12-week training period. The NOCA user inclusion criteria were no OCA use for 3 months before or during the training period. Subjects who reported using progesterone-only contraceptive agents or other hormonal methods of birth control were excluded from the study. Ultimately, 31 athletes, 14 water polo and 17 softball players, met the inclusion criteria and completed participation in the study. Subjects from the 2 sports were combined into OCA and NOCA groups, and no attempt was made to differentiate between sports during analysis. Resistance training programs were the same regardless of sport affiliation. Thirteen subjects were classified as OCA users (experimental group) and 18 as NOCA users (control group). Characteristics of the OCA users and NOCA users appear in Table 1. Body composition was not determined. However, mean body mass index for the OCA and NOCA groups were 25.0 and 24.8, respectively, suggesting similar body composition between groups. The specific estrogen and progestin components of the OCA preparations used by OCA users are listed in Table 2.

Table 1

Table 1

Table 2

Table 2

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Resistance Training Protocol

All subjects participated in the same supervised 12-week preseason strength development program. No attempt was made by the researchers to modify the athletes' existing strength training program as designed by the university's strength and conditioning coach. This program consisted of free weight and machine lifting exercises involving the major muscle groups, performed three times per week (Table 3). Resistance levels were based on percentages ranging from 50% to 80% of initial 1 repetition maximum (1RM) tests. Individual training logs were maintained to monitor subjects' numbers of sets, repetitions, resistance levels, and program compliance. All subjects were compliant with and completed the 12-week resistance training protocol under the supervision of a university strength and conditioning coach.

Table 3

Table 3

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Muscular Strength Evaluation

Subjects were asked to refrain from vigorous physical activity for 24 hours before each data collection session. All data were collected by the same individual who was a board of certification certified athletic trainer and certified strength and conditioning specialist. Muscle strength was assessed after each subject received appropriate instruction and warm-up. One repetition maximum and peak torque were measured for bench press, and 10 repetition maximum (10RM) and peak torque were determined for leg extension at 0 (initial), 4, 8, and 12 weeks into the program. Isokinetic and strength assessment methods were chosen to represent the upper and lower body demands of the sports studied. It was postulated that changes in strength in the major muscle groups of the upper and lower extremity as a result of the 12-week resistance training program would be evident using these established isokinetic and strength tests.

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Strength Evaluation

Strength was assessed by the 1RM bench press using a protocol similar to that described by Kraemer and Fry (20) and 10RM leg extensions. Although reliability was not assessed in the present study, intraclass correlation coefficients for the 1RM test have been previously reported to range from 0.92 to 0.98 (4,34). Preceding all 1RM bench press assessments, subjects performed 3 warm-up sets, which included sets of 10, 8, and 6 repetitions at 50%, 65-70%, and 75-80% intensity levels, respectively. After warm-up sets were complete, subjects performed 1RM sets, progressively adding weight in 5 to 10% increments until a 1RM was achieved. Ten repetition maximum leg extension strength was assessed via the Kell leg extension machine (Marion, OH). The subject was positioned such that the femoral condyles were aligned within the axis of the leg extension machine, and the shin pad was placed 2 in. above the lateral malleolus. Before all 10RM leg extension assessments, subjects performed a 10-repetition warm-up with 30-40 lb. After the warm-up set was complete, weight was progressively added to the leg extension machine until a 10-RM was achieved. Three-minute rest periods were required between all warm-up, 1RM, and 10RM sets to ensure ample and consistent rest during data collection. Equipment set-up positions were recorded and used in all subsequent data collection sessions to maintain reliability.

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Isokinetic Torque Evaluation

Isokinetic peak torque production was assessed with the Biodex System 3 dynamometer (Shirley, NY) at 60°·s−1 using modified bench press and knee flexion/extension exercises. Although not assessed in the present study, the Biodex System 3 dynamometer has been previously shown to be a reliable means of assessing isokinetic peak torque in low to moderate velocity (<300°·s−1) movements (12,16,26). A Lift Station platform and bar were designed to collect isokinetic modified bench press data. Strict adherence to the Biodex System 3 dynamometer Operations Manual (1999) guidelines was maintained. The dynamometer was calibrated at the beginning of each day of data collection and after every sixth data collection session. Before data collection, modified bench press and knee flexion/extension familiarization sessions were conducted for all subjects. Standardized instructions were read to each subject before all modified bench press and knee flexion/extension warm-up and data collection sessions. Dynamometer set-up positions were recorded for each subject to ensure consistency and reproducibility in subsequent practice and data collection sessions.

Before obtaining isokinetic modified bench press and knee flexion/extension measurements, subjects performed a warm-up consisting of 4 submaximal (50% effort) repetitions, 1RM (100% effort), a 60-second rest period, and 3 maximal (100% effort) concentric repetitions at 60°·s−1. A 3-minute rest period was required after the warm-up and before each data collection session. Data collection tests consisted of 2 sets of 5RM (100% effort) at 60°·s−1, with a 3-minute rest period between sets. Peak torque data were obtained for subsequent analysis. Peak torque criterion values were determined by selecting the single repetition per condition with the highest torque value.

Isokinetic right knee extension data were collected in the seated position at 115° of hip flexion. Knee extension/flexion ranges of motion limits were 0-90°. The tester's hip and knee goniometric reliability was r = 0.97 and r = 0.98, respectively. Seat depth was adjusted to align the lateral femoral condyle of the right knee with the axis of the dynamometer. The calf pad was placed 2 in. proximal to the lateral malleolus and secured with the padded shin strap. Subjects were further stabilized with thigh, pelvic, and shoulder straps. Shoulder straps were applied diagonally in a crossed fashion over the subjects' arms, which were placed palms down and touching opposite shoulders to minimize excessive upper body movement and muscular substitution. Subjects started each practice, warm-up, and test repetition in 90° of knee flexion. Subjects were instructed to extend and flex (straighten and bend) the knee as hard and as fast as possible through the full range of motion until told to stop.

Isokinetic modified bench press data were collected 15 minutes after completing the isokinetic knee flexion/extension session. The subject assumed the supine position on a standard horizontal padded bench that was placed on a modified Biodex System 3 Lift Station platform. Subjects started each repetition lightly gripping the modified bench press bar with elbows flexed to 90°, shoulders abducted to 80°, knees flexed, and feet placed flat on the floor of each side of the bench. The tester's shoulder abduction and elbow flexion goniometric reliability were both r = 0.98. Subjects were instructed to push the bar away from the chest as hard and as fast as possible until full elbow extension was achieved.

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Statistical Analyses

The data were analyzed using the Statistical Analysis System (SAS) software program. A 2 × 4 analysis of variance with repeated measures was used to compare differences in strength and peak torque gains between subjects taking combination OCAs and those not taking combination OCAs at weeks 0 (initial), 4, 8, and 12. The general linear model was used for all analyses to account for unequal group sizes. Independent variables were the 2 groups and 4 data collection sessions. Dependent variables were the 1RM bench press (1RMBP), 10RM leg extension (10RMLE), isokinetic peak torque bench press (IKBP), and isokinetic peak torque leg extension (IKLE). Statistical significance was established at the p ≤ 0.05 probability level.

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Results

Strength Production Changes

The 1RMBP and 10RM knee extension both increased significantly (p < 0.05) for subjects during the 12-week training session regardless of whether subjects did or did not use OCAs (Figures 1 and 2). Strength gains did not differ significantly between the experimental OCA group and the control NOCA group for bench press or knee extension.

Figure 1

Figure 1

Figure 2

Figure 2

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Isokinetic Torque Production Changes

Isokinetic bench press peak torque production did not increase during the 12-week training session regardless of whether subjects did or did not use OCAs (p = 0.20) (Figure 3). Isokinetic knee extension peak torque production increased significantly (p < 0.05) during the 12-week training session regardless of whether subjects did or did not use OCAs (Figure 4). Isokinetic torque production gains did not differ significantly between the experimental OCA group and the control NOCA group for bench press or knee extension.

Figure 3

Figure 3

Figure 4

Figure 4

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Discussion

The major finding of this study was that no significant differences in strength or isokinetic peak torque gains occurred between those using combination OCAs and those not taking exogenous hormones. A number of factors may have influenced the results. The overall sample size was relatively small, and no attempt was made to differentiate between sport participation within the OCA or non-OCA groups. Compliance with OCA prescriptions by subjects was based on self-reporting and was not verified by other means. Additionally, we did not obtain hormonal assessments or differentiate between monophasic and multiphasic combination OCAs or between different progestin agents. Furthermore, no attempt was made to control for menstrual cycle phase during strength or isokinetic testing, which may have affected strength and torque production in the control group as women may show increases in maximum voluntary force production during the follicular phase (32). However, previous studies using isokinetic testing to assess differences in torque production throughout the menstrual cycle have reported no differences between the luteal and follicular phases (11,23). Finally, it was assumed that the results of isokinetic peak torque, 1RM, and 10RM strength testing were reliable based on previous research (4,12,16,26,34), although reliability was not assessed in the present study. Although the present study has some important limitations, it was concluded that the use of OCAs had no effect on strength gains achieved in a preseason conditioning program as practiced at an NCAA Division I institution. However, since this study did not differentiate between various OCA hormonal preparations, it is possible that certain OCAs may affect the expression of strength or power in response to training under different conditions. For example, levonorgestrol and norethindrone have been shown to have both androgenic and antiandrogenic properties (36). However, Burrows and Peters (7) asserted that the androgenic component of current OCA formulations is not great enough to influence strength gains but suggested further research into this contention was necessary. Results of the present study support their supposition that OCA use does not produce androgenic responses beyond those normally seen due to strength training.

Combination OCAs consist of estrogen and progestin components. These agents prevent ovulation through the inhibition of gonadotropin-releasing hormone release from the hypothalamus and luteinizing hormone (LH) and follicle-stimulating hormone (FSH) release from the pituitary. OCAs maintain serum estrogen and progesterone levels at early follicular phase levels throughout the menstrual cycle. Combination OCAs may affect circulating free testosterone levels by influencing ovarian production of testosterone and sex hormone-binding globulin levels. The estrogen component of OCAs generally reduces free testosterone levels, whereas the progestin component has a balancing antiestrogenic effect. The net effect in average women is to reduce free testosterone levels (15). However, since different progestins have various levels of androgenicity, it is possible that various combination OCA preparations may also have different effects on serum testosterone levels. This was not tested in the present study.

As expected, our results identified significant strength gains as measured by 1RMBP and 10RMLE in all subjects who completed a 12-week free weight strength training program. These results are consistent with a previous study on female athletes that demonstrated significant gains in 1RMBP, shoulder press, and leg press torque production following a similar 12-week strength training program (3). Similar strength gains in female athletes have also been reported in previous training studies (8,21,25). Our results also showed that OCA users and NOCA users developed significant gains in isokinetic knee extension torque but not in isokinetic bench press torque production. Because the 12-week resistance training program in the present study used constant external resistance, increases in isokinetic peak torque may not be expected based on the findings of Pearson and Costill (29) who previously reported that strength gains from isokinetic and constant external resistance exercise training were specific to the training modality.

Although our results do not indicate that OCAs affect torque production in women athletes participating in a resistance training program, OCA use may provide other potential advantages in women athletes. OCAs help maintain stable gonadotropin levels at early follicular phase levels (17). The follicular phase has been associated with improved aerobic performance (23), muscle strength (32), and enhanced growth hormone levels (14). Additionally, increases in strength and muscle cross-sectional area were greater when using menstrual cycle-triggered training, in which subjects train more frequently during the follicular phase and less frequently during the luteal phase, as opposed to regular training throughout the menstrual cycle (33). Finally, OCA use has been shown to attenuate delayed-onset muscle soreness following exercise (37).

Oral contraceptive agents suppress ovulation, the preovulatory LH/FSH level surge, and the relatively increased progesterone levels of the luteal phase. Progesterone has well-known thermogenic effects on the female body. Mean exercise heart rate, metabolic rate, aerobic performance, and perceived effort may all be negatively affected by the resultant higher body core temperature (33). Peak core temperatures occur during the luteal phase when progesterone levels are elevated when compared with the follicular phase (18). Since OCAs stabilize serum estrogen and progesterone levels, they provide some consistency of thermoregulation throughout the menstrual cycle and facilitate the ability to exercise consistently throughout the cycle.

Athletic performance may decline during the menses (38). Oral contraceptive agents help to regulate menses and allow for the control of the timing of menses. Certain practitioners prescribe OCAs continuously for up to 90 days (as opposed to the traditional 21 days on, 7 days off), before breaking for withdrawal menses. This practice could permit a woman athlete to span an entire competitive season without undergoing menstrual flow providing the advantages of minimizing blood loss and reducing premenstrual symptoms (e.g., breast tenderness, peripheral edema, mood disturbances). Further, other benefits of OCAs must be considered, including the antiosteoporotic effect in hypoestrogenic women athletes and the often desired contraceptive effect in sexually active females.

Oral contraceptive agents may adversely affect athletic performance. The use of OCAs has been associated with delayed strength recovery following eccentric exercise (35) and may have negative effects on muscular strength (30) and aerobic exercise performance (9,22,28). Further, the cost and potential risks and side effects of OCAs, including thromboembolic disease, hypertension, nausea, breakthrough menstrual bleeding, edema, and headache, must be considered.

To our knowledge, this is the first study that prospectively examined resistance training-induced strength gains in athletes who are masked to the main outcome of interest, i.e., differences between OCA users and NOCA users. The present study failed to identify any difference in repetition maximum or isokinetic torque production gains between women collegiate athlete OCA users and NOCA users who participated in a 12-week strength development program. It was concluded that, within the limitations of the study, the use of combination OCAs did not provide sufficient androgenic effect to increase strength gains beyond the stimulus of the training protocol.

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Practical Applications

The use of combination oral contraceptives (birth control pills) did not positively or negatively affect strength gains in collegiate women athletes participating in a 12-week preseason supervised strength training program. Therefore, the use of combination OCAs, as used in this study, did not appear to function as anabolic agents. However, it remains possible that certain types of combination oral contraceptive pills or other forms of hormonal contraception may potentially affect strength gains. Oral contraceptives have a number of potential side effects and complications as well as potential benefits that may negatively or positively affect an athlete's performance.

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Keywords:

strength training; hormone therapy; anabolic agents; training; isokinetic testing; 1 repetition maximum; peak torque

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