Since I consult with a number of college and professional teams I sometimes come across an interesting dual X-ray absorptiometry (DXA) case(s). This is one of those interesting cases that involved a female athlete, who had just undergone a dual X-ray absorptiometry (DXA) scan as part of her pre-season testing program. The athlete’s weight at the pre-season scan was 228.25 lbs. In looking at this particular athlete’s end of the previous season DXA scan, her weight was 220.98 lb. It is not unusual for athletes to gain some weight in the off-season.  Many athletes start a heavy strength training program in an effort to gain additional lean muscle mass. So in reviewing pre-season DXA scans I like to compare the last DXA scan with the current pre-season scan.  When I did that for this particular athlete I found something very surprising. As I mentioned the athlete had gained some weight over the off-season, however in comparing the two scans (Table 1) you see that the total lean muscle mass was almost identical between the end of the season (149.09 lb) and the pre-season (149.18 lb).  What had changed was the total fat mass. The end-of-season DXA scan indicated she had 65.22 lb of fat mass, while her current pre-season DXA scan measured her fat mass at 72.35 lb, which represented a 2.2% increase in fat mass. The athlete and the coach were both confused by the results and asked if I would look at the results and help them understand them.

In talking with the strength coach for the team I learned that each athlete had been given an off-season workout program.  The strength coach assured me that this athlete had attended the off-season workout sessions and had followed the program to the letter. I thought there might be something else besides training that could possibly account for the results. I thought the best route might be to talk with the athlete so I scheduled a phone conversation where I asked the athlete about her diet and whether she made any changes to the amount of calories she was consuming or the composition of her diet. She told me that she was eating a similar diet as before and was following what the team dietitian had prescribed. Then I asked her if she had made any other changes. Maybe added some new diet supplement or medication? She mentioned she had been having very heavy menstrual flows and, at the suggestion of the team physician, had gone on birth control to help with this issue. I asked if she knew the name of birth control and she said it was a birth control implant called Nexplanon.

Nexplanon Implant
I decided to look into the research regarding Nexplanon to see if anything had been reported about this medication and body composition. If you are not familiar with Nexplanon, it is a newer version of the birth control implant called Implanon. The implant itself is a plastic rod about the size of a matchstick. The small implant contains a form of the hormone progesterone called etonogestrel that, once the implant is placed under the skin, releases small amounts of etonogestrel.  Although more expensive than the typical oral birth control pills the birth control implant has the advantage that an individual does not have to remember to take a daily pill. Additionally, the Nexplanon implant can function for up to 3 years before it needs replacement. The literature on the Nexplanon implant indicated that it was successful in reducing painful periods and heavy menstrual flow. However, upon examining the research on Nexplanon or Implanon, previous studies (Dal’Ava et al., 2012; Modesto et al., 2015) had reported an increase in body weight as well as fat mass as a result of its use. Therefore, it was possible that the increase in body mass and fat mass that the athlete experienced was a result of the Nexplanon implant. I relayed the information to both the athlete and her coach.  

Nexplanon Implant’s possible effect on regional body composition
Taking a closer look at the athlete’s data I observed an interesting issue involving the regional body composition measures. If you look at Table 2 below, you will see the body composition data for the right and left arm. In the right arm, you will see that there is a 0.5 lb increase in arm mass.  Approximately 0.3 lb of the increase was fat mass while the lean muscle mass increased by approximately 0.2 lb. Bone mass remained relatively constant. The left arm showed a much different picture. While there was only a 0.02 lb increased in total mass, lean muscle mass fell from 7.63 lb to 7.39 lb, which was a loss of 0.24 lb. Fat mass on the other hand increased from 3.76 lb to 4.01 lb, which was an increase of 0.25 lb. When I asked the athlete which arm the Nexplanon implant had been placed in she told me the left arm. Although regional measures of body composition involving the Nexplanon implant have not been reported, my theory was there was a regional effect of the implant.

I, then, decided to look at the regional body composition for the legs as well (Table 3).  One would suspect that the two legs would be similar since the implant was not localized to either leg. What I found was a similar pattern of body composition. The left leg had a 0.74 lb increase in total mass (41.62 vs. 42.36 lb). This increase could be attributed to a 1.28 lb increase in fat mass (13.43 vs. 14.71 lb) and a 0.56 lb loss in lean muscle mass (26.72 vs. 26.16 lb.). The right leg had a 1.36 lb increase in total mass (41.49 vs. 42.85 lb).  However, in the right leg lean muscle mass increased by 0.17 lb (27.04 vs 27.21 lb), while fat mass increased by 1.19 lb (12.92 vs. 14.11 lb).  While not quite as different as the two arms, the two legs did show a similar pattern of body composition change for the two sides of the body.

So what does this case study mean? First, note that birth control implants may have an effect on body composition. The result can be an increase in total body mass as well as total fat mass. Does that mean that female athletes should not take birth control? The decision to take birth control should be up to the athlete and the medical staff. However, it is important for coaches, trainers, and athletes to be aware of the possible changes in body composition that these medications may have.   


Dal’Ava N, Bahamondes L, Bahamondes MV, De Oliveira Santos A, Monteiro I. Body weight and composition in users of levonorgestrel-releasing intrauterine system. Contraception. 2012; 86:350–3. 

Modesto W, Dal Ava N, Monteiro I, Bahamondes L. Body composition and bone mineral density in users of the etonogestrel-releasing contraceptive implant. Arch Gynecol Obstet. 2015; 292:1387–91. 

About the Author
Donald Dengel, Ph.D., is a Professor in the School of Kinesiology at the University of Minnesota and is a co-founder of Dexalytics. He serves as the Director of the Laboratory of Integrative Human Physiology, which provides clinical vascular, metabolic, exercise and body composition testing for researchers across the University of Minnesota.

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