Anabolic hormones exert a biological effect on many tissues in the human body [1
]. For example, they are important for the growth and maintenance of skeletal muscle, enzymatic proteins, bone, and red blood cells as well as helping to enhance neural function [1
]. Testosterone is a key steroid-based anabolic hormone that induces many of these biological effects in both men and women [1
]. It is also a hormone that plays a role in the adaptive process to exercise training [1
]. The exercise role and response of testosterone is well known in men but to a much lesser degree in women [3
]. Because testosterone is associated with the muscle hypertrophy response to exercise, many exercise studies have examined its response to resistance, strength-based activities. Research on the effects of prolonged endurance exercise on hormones, such as testosterone, are less frequently studied in both men and women, even though the evidence clearly points to the necessity of testosterone in the physiological adaptations of endurance-based activities [4
The worldwide involvement of women in endurance sporting activities, such as competitive marathons and triathlons, has grown exponentially over the last few decades [6
]. This expanded involvement has led to calls for more research on women athletes [7
]. This seems especially warranted in competitive sporting-like scenarios that place great demands and stress on athletes [6
]. This last point is an important consideration, since intensive competitive exercise provokes differing endocrine responses than non-competitive exercise situations [8
]. Therefore, the purpose of this study was to examine and describe the response of testosterone in women to an intensive, prolonged endurance exercise bout to exhaustion which mimicked a competitive event.
Exhaustion occurred at a mean time of 75.1 ± 7.0 min (±SE) at a mean running speed of 12.0 ± 0.2 km/h. At the end of exercise HR = 177.3 ± 3.5 bpm, RPE = 15.8 ± 0.6 Borg units, VO2 = 2.36 ± 0.08 L/min which represented 98.8 ± 2.4 % of their VT.
presents the hormonal and binding protein changes before and in response to the exhaustive exercise into recovery. At the end of the exercise, total, free, and bioavailable testosterone were significantly increased from resting, pre-exercise values (p
< 0.05). Sex hormone-binding globulin and albumin displayed similar responses (p
After these significant increases immediately post-exercise, all measurements gradually decreased, returning to pre-exercise levels by 90 min post-exhaustion. At the 24 h post-exercise time, total, free, and bioavailable testosterone reached significantly lower levels than their resting, pre-exercise values (p < 0.05). In contrast, SHBG and albumin were elevated at 24 h post-exercise (p < 0.10 > 0.05), albeit these differences were not statistically significant.
The ES for all these changes are also reported in Table 2
. This analysis demonstrates that for the significant changes in our measures, the ES ranged from medium to large in magnitude.
Our purpose was to examine and describe the response of testosterone to intensive, prolonged endurance exercise in women that mimicked a competitive sporting event. Women have traditionally been an understudied population in exercise research [6
]. This occurrence is despite the exponential growth in the involvement of girls and women in physical activity and sports over the last several decades [7
]. The testosterone response of men to nearly all forms of exercise is well defined, but not so in women, even though testosterone has physiological effects in women just as in men [1
]. Thus, our research group wondered if the behavior of testosterone was similar in women as that in men when performing strenuous exercise, specifically endurance activities. The latter was of interest as testosterone responses to endurance activities are studied less often compared to resistance-based exercise.
The present hormonal findings for testosterone are remarkably comparable in nature relative to similar male-based research. The published findings of Anderson et al. [14
], Keizer et al. [15
], and Hloogeveen et al. [16
] all show alike steroid hormonal changes in men as we observed in our female subjects. That is, prolonged endurance exercise produces a biphasic response in testosterone in which, initially, there are increases from the exercise followed by reductions in recovery. Although, it is important to recognize that the magnitude of some of the absolute hormonal concentration changes observed in these studies vary from those of the present data due to the fact of sex-related differences [1
]. Furthermore, the ES magnitude of our hormonal responses (i.e., of the significant testosterone responses) ranged from medium to very large for the observed responses in our subjects [13
]. Since ES is independent of sample size, the magnitudes of the ES values suggest our findings are more robust than what the significance testing (p
levels) implies [13
Perhaps the most interesting finding within our results was the tendency for testosterone to be reduced 24 h into the recovery from the exercise. It is unclear if the observed reduction is a feedback regulatory suppression following the acute substantial hormonal increases in response to the exercise [17
], the consequence of a delayed increase in the metabolic clearance of the hormone, or perhaps a stress reactivity response (e.g., due to the fact of a cortisol-induced inhibition) and, as such, a dysfunctional response [4
]. Conversely, Kraemer et al. [18
] has proposed these type changes are reflective of the homeostatic mechanisms involved in the repair and recovery process. Our finding of this biphasic hormonal responses, leading to the reduction in testosterone during recovery, needs to be addressed in future research in women so the underlying rationale and mechanism can be identified.
We recognize our study was limited due to the presence of several factors: (1) its small sample size, (2) its relatively narrow range of biomarkers assessed, and (3) the fact that we only examined women in the follicular phase of their menstrual cycle. Further research is recommended to expand upon our work and overcome these limitations.
In conclusion, we found in exercise-trained women, testosterone remained elevated in the early recovery period following exhaustive endurance exercise but was reduced by 24 h afterward. These outcomes are comparable to similar types of exercise responses seen in men when sex-related concentration differences are taken into account.