Impact Loading and Nutrition in Cyclists: A Clinical Intervention to Enhance Bone Mass
Regina Hammond1, Margaret M. Harris1, Craig C. Elder1, Nanna L. Meyer, FACSM1, 2 Thesis directed by Assistant Professor Nanna L. Meyer
1University of Colorado at Colorado Springs, CO. 2 United States Olympic Committee, Colorado Springs, CO.
I presented my thesis titled, “Impact Loading and Nutrition in Cyclists: A Clinical Intervention Study to Enhance Bone Mass” during the Energy Balance thematic poster session at the 60th American College of Sports Medicine Annual Meeting, June 1, 2013. The abstract was published in Medicine and Science in Sports and Exercise, Volume 45:5 Supplement.
Impact Loading and Nutrition in Cyclists: A Clinical Intervention Study to Enhance Bone Mass Regina A. Hammond
INTRODUCTION: Areal bone mineral density (aBMD) is low in endurance athletes, especially in cyclists. Recently, it has been shown that cyclists lose bone mass over the course of a season.
PURPOSE: To examine whether a 4-month clinical intervention would prevent a decline in aBMD in elite cyclists. The intervention was comprised of the following areas: 1) impact-loading through a jumping program; 2) nutritional intervention targeting energy availability (EA); and 3) supplementation to remedy nutrient deficiencies affecting bone metabolism.
METHODS: Six experienced male (42±8y; ht: 1.77±0.05m; wt: 71.8±5.7kg; %body fat [BF]: 11.6±3.2; FFM: 63.65±4.02kg) and 4 female (39±10y ht: 1.65±0.06m; wt: 62.75±12.84; %BF: 25.0±9.3; FFM: 46.5±4.29kg) road and mountain bike cyclists with aBMD Z-score of <0 (DXA) were recruited. The remote program consisted of a progressive jumping program with 10 maximal vertical jumps performed 5 days/week for 4 months, custom meal plan recommendations to increase energy availability > 30 kcal⋅kgFFM-1⋅d-1, and recommendations for calcium and vitamin D supplementation. Vertical jump height and aBMD were assessed at baseline and post-intervention. Restrained eating (RE) was assessed once using the Three Factor Eating Questionnaire and EA monthly using standard procedures. Venous blood samples were collected at baseline, 2, and 4 months and analyzed for 25(OH) vitamin D.
RESULTS: Repeated measures ANOVA revealed no significant differences in wt, %BF, FFM, or vertical jump from pre to post-intervention overall and by gender. Overall, aBMD did not change significantly (whole body: -0.5±1.1%; spine: -0.2±2.2%; femur -0.5±1.1%; left femur -0.7±1.5%; right femur -0.3±1.24%) nor were there differences by gender, although females seemed to gain aBMD, while males seemed to lose aBMD. Despite nutritional intervention, average EA remained low (EA; males 21.2±15.97 kcal⋅kgFFM-1⋅d-1; females 26.1±7.7 kcal⋅kgFFM-1⋅d-1) and RE high (males 12±4; females 14±5). No significant differences were detected for serum 25(OH) vitamin D at baseline, 2 and 4 months (pre: 39.1±7.47ng/mL, 2-month: 41.0±5.45 ng/mL; 4-months: 35.6±9.99ng/mL).
CONCLUSIONS: In conclusion, data show that a 4-month clinical intervention using high-impact jumping and nutrition is, for the most part, insufficient to prevent bone loss in cyclists.
DISCUSSION
To our knowledge, this is the first longitudinal study of BMD in competitive male and female cyclists that took three factors into consideration: a) bone loading through a high-impact jumping program, b) positive energy availability, and c) calcium plus vitamin D3 supplementation. This is also the only longitudinal study that used custom meal plans to improve energy availability, as opposed to a set calorie amount (usually in the form of a high calorie beverage such as Ensure) given to each subject. Ten subjects completed both pre and post DXA measurements. Due to this small sample, the study might have been underpowered to detect statistically significant effects of jumping, EA, and/or supplementation on BMD.
The results of the high-impact jumping program on changes in BMD in subjects who completed at least 60% of the jumps, did not show a statistically significant effect on BMD. In fact, the overall average change in BMD was more negative in subjects more compliant (n=6) than non-compliant (n=4). Looking at gender, females (n=4) non-significantly increased BMD in six (whole body, spine, right femur, neck, right and left neck) of eight regions. Even though the lumbar spine is proven to have lower BMD in cyclists than runners (Rector et al., 2008) and controls (Nichols, Palmer, and Levy, 2003; Stewart & Hannan, 2000; Smathers et al., 2009) the third largest increase in BMD was at the lumbar spine 0.004 gm/cm2. With a standard deviation of ± 0.128 gm/cm2, the widest range of changes in BMD from pre to post was also in the spine. The right femoral neck (0.014 gm/cm2) and femoral neck (0.007 gm/cm2) had the two highest change values. Previous research on BMD in cyclists has focused on males since they are the majority of the participants. Barry and Kohrt (2008) found significant decreases in BMD (total hip -1.5±2.1%, neck -0.7± 2.1%, shaft -0.9±2.1%, trochanter -1.0±1.2%) in all participants (cyclists, 27-44 years) from baseline to twelve months. Their subjects were randomized into high (1500 mg/day) versus low (250 mg/day) calcium groups based upon the amount of supplementation they received.
At baseline, cyclists placed in the high calcium group, had an average calcium intake of 828 mg/day and had BMD values (L1-L4, total hip, femoral neck, trochanter, femoral shaft) higher than those in the low calcium group who had an average intake of 740 mg/day before supplementation. Bone mineral density values decreased between baseline and nine months into the competitive cycling season for both categories at total hip, trochanter, femoral neck, and femoral shaft. At nine months the high calcium group showed a decrease in BMD at the lumbar spine (baseline: 1.082; nine months: 1.065 g/cm2); the low calcium group showed a 1.2% increase in BMD at the lumbar spine (baseline: 1.076; nine months: 1.080 g/cm2) but then further decreased to below baseline at 12 months (1.071 g/cm2). No significance was found for change in BMD between the high or low supplementation groups.
Dermal calcium losses estimated to be greater than 137±61 mg were not significantly associated with changes in BMD. Post BMD measurements of the spine in the current study showed a range of non-significant increases in five subjects ranging from 0.002 to 0.052 g/cm2.The current study was the second phase of a previous one (March – September 2011) that implemented a vertical jumping protocol to decrease the loss of BMD in cyclists.
Two of the four females and three of the six males in the current study were each in the control and experimental groups in the previous study. Subjects in the control group of the previous study did not complete any jumps, but the experimental group completed the same vertical jumping for an average of six months, before entering phase two.This study (October 2011 – February 2012) coincided with the off-season and showed a similar trend as Barry and Kohrt (2008) in decreased BMD at the end of the off-season despite a 16-week jumping program (left femur -0.5±1.1%, left neck -0.0±1.4%, lumbar spine -0.3%±2.9%).
There was no direct relationship between subjects, regardless of gender, who were in the control or experimental group with vertical jump height or change in BMD. Three of five subjects who were in the control group increased vertical jump height while all five showed non-significant increases in BMD for at least one body region. Three of five subjects transferred from the experimental group improved vertical jump height while four of the five improved BMD at one body region (Table 15a, 15b).
In total, subjects from the experimental group participated in at least 12 months of a vertical jumping program without any significant change in BMD from six to twelve months (off-season). The failure to recover bone loss during the off-season for most of the male subjects suggests a cumulative effect from years of cycling on bone loss (Barry & Kohrt, 2008). This clearly demonstrates the need for a bone loading program throughout the competitive season to decrease the rate at which bone mass is lost, with a progressive bone loading program in the off-season to try to recover BMD values to baseline (pre-competitive season).
In 2016, the International Olympic Committee updated their Consensus Statement on the Female Athlete Triad. The statement is broader defined as Relative Energy Deficiency in Sport (RED-S) to include negative energy balance in men who participate in sports. The most significant result of my research was that male cyclists exhibited more energy restriction that that of females. This was based on average caloric intake per week compared against total estimated energy expenditure. Caloric intake in males was also compared against the values established by Anne B. Loucks to prevent menstrual disorders in women (10, 20, 30, 45 kcal/kg/FFM).