Active Voice: Amenorrhea Not Only Negatively Impacts Bones It Can Also Decrease Exercise Performance
By Gretchen A. Casazza, Ph.D.
Viewpoints presented in SMB commentaries reflect opinions of the authors and do not necessarily reflect positions or policies of ACSM.
Gretchen A. Casazza, Ph.D., is an ACSM member and assistant adjunct professor in the College of Biological Sciences and research director for the sports medicine program at the University of California, Davis. Her research interests relate to cardiovascular and metabolic adaptations to exercise, as well as the effects of ovarian hormones on exercise performance and bone health. This commentary presents Dr. Casazza’s views associated with the research article she and her colleagues published in the Jan. 2011 Medicine & Science in Sports & Exercise®.
Female endurance athletes often come to our clinic for training advice to optimize performance. Many of these women strive to be as lean as possible, as their coaches have emphasized leanness as a factor to successful performance. These women also typically have very high volumes of training and little understanding of sports nutrition and the importance of energy balance. As a result, there is high prevalence of female athletes with chronically low energy availability due to high rates of energy expenditure, insufficient food intake or both. As it is one of the most expensive metabolic processes, reproductive function is sensitive to overall energy status. The activity of the hypothalamus – a portion of the brain that links the nervous system to the hormonal system – is suppressed in response to caloric deprivation, resulting in the reduction of many hormones including reproductive and metabolic hormones. While some of these women still have menstrual cycles, their cycles are often prolonged and may not result in ovulation. Often, these athletes end up losing their menstrual cycle altogether, a condition called “amenorrhea.”
While the negative impact of chronically low estrogen levels on reproduction and bone health is well known (see ACSM’s position stand on The Female Athlete Triad), very few athletes recognize the effects of chronically low energy availability on the rest of the hormonal systems. Studies have shown women with amenorrhea have low cortisol, insulin and thyroid hormone levels as well as low blood glucose. In addition, studies have found a decreased resting metabolic rate. Together, these changes point to a catabolic, energy-conserving physiological state, supporting the notion that low energy availability results in profound hormonal and metabolic changes in order to preserve fuel stores.
Knowledge of the consequences of caloric deficiency in amenorrheic athletes raises concern about its potential impact on exercise metabolism and athletic performance. Indeed, as intense and prolonged exercise presents a challenge to glucose balance, an appropriate sympathetic and glucocorticoid response is important in order to maintain normal blood glucose levels. In extreme states of fatigue or glycogen depletion, the counter-regulatory response to exercise may be impaired, forcing the individual to quit exercising or reduce workload to protect vital fuel stores. This has been documented in glycogen-depleted and chronically over-trained athletes who exhibit a suppressed neuroendocrine response to intense exercise and a concomitant drop in performance. A recent study from our laboratory is one of the first to find decreased catecholamine responses to high intensity exercise in female athletes with amenorrhea. Our amenorrheic athletes (runners and triathletes running an average of 38 miles per week) showed significantly lower peak catecholamine and lactate values compared to age and training matched athletes with normal menstrual cycles.
An impaired catecholamine response to maximal and sub-maximal exercise in athletes with amenorrhea not only impacts their ability to maintain normal blood glucose levels but also probably impairs performance at peak intensities of exercise, when catecholamine responses assist in blood pressure regulation and mobilization of muscle glycogen. Athletes diagnosed with amenorrhea should be thoroughly educated on the cause and adverse health and performance consequences of low energy availability. While athletes may not pay as much attention to health consequences, they will pay attention to decreases in performance.