What Happens in Your Body When You Exercise?
por Lara López
translated by Zachary Romansky
The wind, ocean air, and waves have shaped her character and physical fitness. Sports nourished her for more than 30 years. And, currently, both motherhood and research energize her every day. Lucía (Rosarito) Martínez Colón, not only won silver and bronze medals for Puerto Rico in windsurfing and Hobie Cat, but she also participated in the Barcelona (1992) and Atlanta (1996) Olympics while she was working on her master’s in Sports Sciences and her doctorate in Exercise Physiology. She is a professor in the Department of Physical Education and Recreation, coordinator of the Graduate Program in Exercise Sciences, as well as director of the UPR-RP Physical Aptitude and Sports Performance Center.
Martínez Colón’s research focuses on how girls and women’s bodies draw on energy substrates, substances on which enzymes act to produce energy, while exercising. In other words, she studies how women make use of some nutrients—such as carbohydrates and fat—to generate energy and be able to carry out everyday physical activities and other more intense activities such as exercise and sports. The professor has included young girls in her study because they are participating in physical activities starting at earlier and earlier ages in high-performance sports training. There even have been cases of girls as young as six years old participating in full marathons (26 miles) and intensely training for competitive sports such as gymnastics and swimming.
“Normally, people think of little boys and girls as miniature replicas of adults, but research shows that that is not the case. There are physiological and psychological differences between these populations,” explains Martínez Colón.
Very little research has focused on women, and even less has studied girls. But Martínez Colón has been researching female metabolic responses to exercise for more than a decade. She demonstrated in her doctoral dissertation that prepubescent girls expend more energy than adult women while exercising. One possible explanation is the relative contribution of carbohydrates and fats in the form of substrates. Compared with adult women, girls use more fats during moderate exercise. This is a positive result, says Martínez Colón, because the body has large fat reserves, while carbohydrate reserves are limited.
In addition to studying prepubescent and adult female population, Martínez Colón was funded by the Office of the Dean of Graduate Studies and Research to include pubescent female metabolic responses in her research. She and her work team—made up of professor Farah Ramírez; students Enrique Pérez and Ivonne Ramírez; and medical technicians Barbara Segarra and Ruth Rosario from the UPR Medical Sciences Campus—investigate whether there are any differences in energy substrate use and hormonal responses among females in different stages of sexual maturity during moderate exercise sessions. Three groups of ten healthy and physically active prepubescent, pubescent, and adult females were selected and participated in the study.
During two exercise sessions, the researchers collected and analyzed each participant’s exhaled gases while exercising to determine their aerobic capacity and somatotype, or body type. For the third, experimental session, they asked participants to consume a mixed diet and to refrain from any atypical physical activity for three days before the test. To keep sexual hormones from affecting the results, the researchers tested the pubescent and adult females during the follicular phase of their menstrual cycle.
After fasting for 12 hours before the day of the experimental test, participants reported to the UPR-RP Exercise Physiology Lab. There they rested for 45 minutes in a reclining chair, while their basal metabolic rates (oxygen consumption), respiratory exchange ratios (an indicator of carbohydrate and fat contribution), and heart rates were determined. Then they went on to the experimental intervention consisting of 40 minutes of running on the treadmill at 60 percent of their aerobic capacity.
Heart rate, oxygen consumption, and respiratory exchange ratio were continuously measured while the participants exercised. The medical technicians took blood samples from the participants before, during, and after exercise and sent them to the Clendo Reference Laboratory where they were analyzed for energy substrate content (glucose, lactate, and free fatty acids) and for hormone content (insulin, growth hormone, epinephrine, norepinephrine, and total catecholamine). Hemoglobin and hematocrit contents were also evaluated to verify changes in cell volume.
Martínez Colón’s studies offer a view of what affects athletic performance in women of different ages. They might shed light on what nutrients should be consumed by female athletes and which exercises should be prescribed to them to improve physical aptitude and fitness at various stages of sexual maturity.
“The amount of physical activity in girls translates to health, which will affect a woman’s later development. I’m interested in continuing research on the characteristics of these differences to be able to make recommendations to parents and coaches as to what should be consumed during certain stages of maturity and what exercises are safe for women. Our goal is to promote physical activity and sports among women, while at the same time ensuring their well-being and safety,” she says.
The study’s preliminary results indicate changes in hormonal responses and metabolic differences during exercise in females at distinct stages of maturity. These results were presented at the Annual Meeting of the American College of Sports Medicine in Seattle in May 2009.