College Age Dancers Have Great Bone Mass than Runners and Controls, Despite Low Energy Availability

Hawley C. Almstedt & Zakkoyya H. Lewis-PowellLoyola Marymount University, Los Angeles, CA

Department of Health & Human SciencesHuman Performance Laboratory

Conclusion

Introduction

Abstract

Methods

• EA and BMD were not significantly correlated at any bone site• There was no significant difference in EA between groups, and

all groups exhibit low EA compared to previous work (2)• Dancers had significantly higher BMD than the runners and

dancers at the AP spine despite low energy availability• The energy expenditure of runners was significantly greater

than the dancers and controls

References

• NCAA cross-country runners (n=13) and students actively pursing a degree in dance (n=11) were recruited from campus

• Women of similar age (n=15) who were physically active less than 3 hours a week, served as controls

• Dual energy x-ray absorptiometry (DXA, Hologic Explorer, Waltham, MA) was used to measure bone mineral density (BMD) at the spine, hip, and whole body

• Dietary intake was assessed using the Block 2005 Food Frequency Questionnaire (Nutrition Quest, Berkeley, CA)

• Energy expenditure was recorded for an average of four days using an accelerometer worn at the hip (Philips Actical, Bend, OR)

Results

Dietary intake and physical activity are important lifestyle behaviors which influence bone mineral density (BMD). The Female Athlete Triad is a syndrome comprised of poor energy availability (EA), menstrual dysfunction, and suboptimal bone health (1). The components of the Triad are exhibited at clinical levels with amenorrhea, eating disorders, and osteoporosis, but in practice they are commonly observed to a lesser degree. Previous research has found that low energy availability can alter menstrual function and bone metabolism, suggesting that after time BMD may be altered negatively, increasing risk for fracture and osteoporosis (2). Physical activity, especially modes incorporating high impact activity, is beneficial for bone health. However, when calorie intake does not match energy expended through activity, bone metabolism and menstrual function are altered (2, 3). Athletes at risk for the Female Athlete Triad are often involved in aesthetic or endurance sports which emphasize leanness (3). Athletes in this at-risk population may be restricting dietary intake in order to maintain a lean physique which fits the body image of their sport. High energy demands in combination with low dietary intake leads to low EA increasing risk for poor bone health. At the current time, there is insufficient research investigating whether EA can predict BMD. This research aims to explore relationships between EA and BMD.

AcknowledgementsCoach Scott Guerrero and LMU Cross Country Team; Professor Judy Scalin and the LMU Dance Majors; Student Research Assistants: Becky Yen, Maria

Frye, Gianna Ligouri; LMU Seaver College of Science and Engineering

1. Nattiv, A., Loucks, A.B., Manore, M. & et al. (2007). ACSM position stand. The female athlete triad. Med Sci Sports Exerc, 39(10), 1867-92.

2. Ihle, R., & Loucks, A. B. (2004). Dose-response relationships between energy availability and bone turnover in young exercising women. J Bone Miner Res, 19(8), 1231-1240.

3. Nichols, D. L., Sanborn, C. F., & Essery, E. V. (2007). Bone density and young athletic women. Sports Med, 37(11), 1001-1014.

4. McKay, H., Tsang, G., Heinonen, A. & et al. (2005). Ground reaction forces associated with an effective elementary school based jumping intervention. Br J Sports Med, 39(1), 10-14.

The Female Athlete Triad is a syndrome comprised of three inter-related conditions: menstrual dysfunction, suboptimal bone health, and poor energy availability (EA). EA is calculated as kilocalorie intake minus energy expended through activity. PURPOSE: The goal of this research was to evaluate the relationship between EA and bone mineral density (BMD) in runners, dancers, and controls. METHODS: Runners (n=12), dancers (n=11), and controls (n=14) between the ages of 18-22 (mean=19.8±1.1 years) underwent BMD testing at the hip, spine, and whole body using dual-energy x-ray absorptiometry (DXA, Hologic Explorer, Waltham, MA). Dietary intake was assessed using the Block 2005 Food Frequency Questionnaire (Nutrition Quest, Berkeley, CA). Average daily energy expenditure was measured via an accelerometer (Philips Respironics Actical, Bend, OR) worn by participants at the right hip for an average of four days. RESULTS: Groups were similar in age, height, weight, lean mass, protein and calcium intake. EA did not correlate significantly with BMD at any site. Dancers showed a moderate, nonsignificant, negative relationship between EA and BMD at the femoral neck (r= -0.65, p>0.05). When controlling for lean mass (LM), there were no significant differences in EA between groups: dancers=29.9±17.0 kcals/kg LM, runners=24.2±8.0 kcals/kg LM, and controls=31.9±13.7 kcals/kg LM. An ANCOVA (controlling for BMI) revealed that dancers have significantly greater mean BMD at the anterior-posterior spine (1.06±0.10 g/cm2) than runners (0.94±0.07 g/cm2) and controls (0.97±0.09 g/cm2). Dancers also had significantly greater mean femoral neck BMD (0.97±0.13 g/cm2) than controls (0.85±0.10 g/cm2, p<0.01) but not runners (0.88±0.06 g/cm2). Groups were similar in BMD at the whole body. CONCLUSION: Our research shows that despite similarly low EA, dancers exhibit greater BMD at the spine than runners and controls. This implies that perhaps the loading nature of dancing has a greater positive impact on bone than running.

We found no significant relationship between EA and BMD in this population of college-age runners, dancers, and controls. This implies that there are other factors influencing bone health, such as mechanical loading and the adequate intake of bone nutrients. Furthermore, the EA of each group was below the optimal 45 kcals/kg of lean mass (LM) as proposed by previous research (2). According to others, EA below 45 kcal/kg of lean mass impairs bone metabolism; however we found that BMD can be normal despite low EA (2). Perhaps the threshold of 45 kcals/kg of lean mass is not appropriate for the population examined here or this methodology of assessing EA. Regardless of whether 45 kcals/kg of lean mass is appropriate for this population, the athletes in this study are below the EA of the controls, however not significantly. The low EA measured in these dancers does not seem to inhibit bone health. As a matter of fact, their BMD significantly surpasses the BMD of both runners and controls at the AP spine and of controls at the femoral neck. In a review by Nichols et al., researchers noted that sports with specific types of mechanical loading tend to produce a greater osteogenic response (2). Jumping activities that are incorporated in dance have a greater ground reaction force than running or walking which may contribute to their greater BMD (4). Running is also a loading sport that initiates bone remodeling, however it places less strain on the bone than jumping (4). Based on the loading activities, one would expect the BMD of the runners to be significantly greater than controls, however we did not find this to be the case. Runners in our study expended significantly more energy, though they were not significantly different in the energy availability. This indicates that runners are eating slightly more calories while expending more during running, resulting in a similar EA to dancers. In combination with the lower impact activity, this makes probable cause as to why their BMD is lower. One weakness of this study is that dietary intake was self reported and it is possible that participants underestimated calories in order to fit social pressures. More research needs to be done to pin point factors related to BMD and the Female Athlete Triad.

*p <0.05† p <0.01

Significantly different from dancers

1 LMU Drive, Los Angeles, CA 90045Hawley.Almstedt@lmu.edu (310) 338-1925

†

ParticipantsVariables Runners (n=12) Dancers (n=11) Controls (n=14)Age (years) 19.9+1.4 19.5+0.9 19.9+1.1Height (cm) 166.3+4.3 159.6+5.8 166.4+6.7Weight (kg) 54.1+3.4 15.5+4.8 59.3+6.5Body Mass Index (kg/m2) 19.6+0.8† 22.3+2.5 21.4+2.2Lean Mass (kg) 39.5+2.1 37.6+2.3 39.4+3.8Percent Body Fat 22.0+2.7† 28.4+5.6 28.5+3.4Energy Expended due to Activity (kcals) 931.0+196.1† 624.2+129.5 519.3+287.6

Energy Availability (kcals) 955.5+318.2 1095.6+570.9 1229.9+463.0Kcals/kg of Lean Mass 24.2+8.0 29.9+17.0 31.9+13.4Energy Intake (kcals/d) 1886.4+340.9 1719.8+342.2 1749.2+370.1Calcium (mg/d) 1219.2+372.4 844.7+397.5 850.5+222.8Protein (g/kg/d) 2.2+0.5 1.6+0.6 1.9+0.5

mean+SD †p<0.01, runners significantly different than dancers and controls