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Medicine & Science in Sports & Exercise:
APPLIED SCIENCES: Physical Fitness and Performance

Spine Bone Mineral Density Increases in Experienced but not Novice Collegiate Female Rowers

LARIVIERE, JANE A.; ROBINSON, TRACEY L.; SNOW, CHRISTINE M.

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Abstract

LARIVIERE, J. A., T. L. ROBINSON, and C. M. SNOW. Spine Bone Mineral Density Increases in Experienced but not Novice Collegiate Female Rowers. Med. Sci. Sports Exerc., Vol. 35, No. 10, pp. 1740–1744, 2003.

Purpose: There is evidence that rowing exercise targets the spine, but the dose of exercise required to build bone is poorly understood. To further explore this topic, we studied the bone response at the spine in novice and experienced female collegiate rowers over their 6-month competitive season. We hypothesized that, with rowing strokes similar between groups during training, experienced rowers would produce greater force at the spine than novices and thus, gain more bone mineral density (BMD).

Methods: Subjects included 16 experienced rowers (21.2 ± 1.2 yr) who had been rowing 26 ± 10 months and 19 novice rowers (19.5 ± 0.8 yr) who had been rowing three months and 14 controls (19.2 ± 1.6 yr). BMD was assessed by DXA at baseline and after the 6-month competitive season. During the season, all rowers participated in the same training program and took approximately the same number of strokes per training session (1000–1200 repetitions). On the 2000- and 6000-m rowing ergometer tests experienced rowers had faster times, indicating that their power output, and thus force production, was greater than novices.

Results: In ANCOVA, adjusting for body mass index, age, and initial BMD, the experienced rowers demonstrated a 2.5% increase at the spine that was significantly different than that of the novice rowers, but BMD change scores in the rowing groups were not different than controls.

Conclusion: Because the number of strokes (repetitions) was similar between rowing groups during training, the higher power output in experienced rowers produced higher forces at the spine over the 6-month period that resulted in gains in spine BMD. These results support the theory that force magnitude is a key variable in osteogenesis.

Osteoporosis is a disease characterized by low bone mass, bone fragility, and an increased risk of fracture. Vertebral fractures are the most common of all the osteoporosis-related fractures, with 750,000 cases reported each year (15). Because higher bone density is protective against vertebral fractures, strategies to build spine bone mineral density (BMD) may reduce fracture incidence (3). Exercise is one nonpharmaceutical strategy to increase spine bone density, but the type of exercise that targets the spine is yet to be identified (4).

Clinical reports suggest that load magnitude (force) is more osteogenic than load repetitions (8,11,13,14). For example, our previous data demonstrated that, in gymnasts, where load magnitudes are 10–18 body weights at the ground, BMD at the hip and spine is higher than in runners, where load magnitudes are 2–5 body weights (8). Furthermore, the skeletons of gymnasts respond to high loads imposed over a training season by increasing BMD and respond to “unloading” during summer months by decreasing BMD (11). BMD gains over the training season occur despite values that are more than 15% higher than the mean for young normal women. Although these reports support the notion that load magnitude is a potent osteogenic stimulus, in order to appropriately study the magnitude versus repetition issue, the exercise must target the site measured and the repetitions (cycles) and intensity (load magnitude) should be controlled. Rowing is highly specific to the spine, and the vertebral column is thought to incur the greatest loads (6). In fact, in cross-sectional reports, young women who participate in rowing training have higher spine BMD than nonrowers (6,17). And, in limited longitudinal studies, adolescent girls and college-aged men have shown spine BMD increases as a result of rowing training (2,5).

Our aim was to examine the potentially different bone response at the spine in novice and experienced crew athletes after 6 months of rowing training. All women were members of the Oregon State University women’s rowing team. For comparison, spine BMD of the rowers was compared with that of a normally active control group measured over a similar time period. Specific to this design, we asked the following research question: Is the bone response at the spine after a 6-month competitive season different in experienced versus novice rowers? We expected the experienced rowers to generate higher loads at the spine during the observational period and, thus, hypothesized that experienced rowers would have significantly greater changes in BMD at the spine than the novice rowers.

©2003The American College of Sports Medicine

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