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a Department of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles
b Department of Kinesiology and Nutritional Science, California State University, Los Angeles
Robert A. Wiswell, Department of Biokinesiology and Physical Therapy, University of Southern California, 1540 East Alcazar Street, CHP 155, Los Angeles, CA 90033 E-mail: wiswell{at}hsc.usc.edu.
Accepted November 8, 2001
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Abstract |
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Methods. We examined a group of 54 male master athletes ranging in age from 40 to 80 years longitudinally over a 5- to 7-year intervening period. Physiological parameters included V·O2peak, body composition, bone density, and running performance. Medical histories and training records were obtained via questionnaire.
Results. Over the average 4.6 years between tests one and two, significant increases in body weight and lean body mass were observed. Aerobic fitness declined, as did weekly mileage and 5K and 10K performance times. Bone mineral density was lower in the whole body but not in the hip or the spine. Finally, we report no significant relationship between the change in training volume, change in body weight or lean mass, and change in aerobic capacity with changes in BMD.
Conclusions. Hip and spine BMD are maintained over a 4- to 5-year period in master runners. Furthermore, changes in bone density or content are not sensitive to moderate changes in training volumes. We conclude that bone density can be maintained by running in older active men. These findings suggest that if a minimal threshold of mileage is required, the level is certainly below the average mileage of master runners.
STUDIES investigating the influence of running mileage and/or marathon running on bone mineral density (BMD) in young and middle-aged runners report little differences between runners and age-matched controls (1)(2). MacDougall and colleagues reported that mileage (from 5–70+ miles per week) had little influence on BMD even though the tibia and fibula cross-sectional area, when normalized to body weight, tended to be greater as mileage increased (3). Goodpaster and colleagues reported in a group of men 42–73 years of age that distance runners did not have significantly different hip or spine BMD than individuals who ran short distances or not at all (4). From these and other findings, it has been suggested that weight-bearing exercise (e.g., running) will not lead to increases in BMD or bone mineral content (BMC) but may help to retard the rate of loss in skeletal mass associated with aging. This lack of weight-bearing exercise effect on increasing BMD in runners has been attributed to (i) decreased body mass (5)(6), (ii) inadequate loading (7), and (iii) decreased testosterone and estrogen associated with chronic training (2).
To address the issue of direct effect of running on bone maintenance, one would need to follow subjects over several years and relate changes in bone to changes in training volume and training intensity. It is only by a longitudinal comparison of active subjects that one could determine the extent of the benefit or detriment associated with chronic running. Therefore, to test the hypothesis that BMD is maintained in runners who train at high running intensities or volume, we examined 54 male runners who are participating in a 20-year longitudinal study started in 1986 (5). It was our specific purpose to relate changes in training volume (miles run per week and days per week of exercise) and V·O2peak to changes in whole body, spine, and hip BMD (by dual-energy x-ray absorptiometry) over a 4- to 5-year period.
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Methods |
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Body Composition Assessment
Residual lung volume was assessed utilizing the oxygen dilution technique (12), and body composition was determined via hydrodensitometry utilizing the Brozek equation. Three-compartment body composition was measured by dual energy x-ray absorptiometry (DEXA) simultaneously with the whole body scan using a Hologic QDR 1500 (Hologic, Inc., Bedford, MA).
Fitness Assessment
Oxygen uptake at fatigue (V·O2peak) was determined using a continuous, graded exercise test on a motor-driven treadmill. The test began at 2.5 mph and 0% grade and increased by 0.5 mph and 2%, respectively, every 2 minutes during exercise. Exercise continued until the subject terminated the test at a point of subjective exhaustion. All metabolic parameters were measured using a SensorMedics 2900 metabolic measurement cart (SensorMedics Corp., Yorba Linda, CA) interfaced with a Marquette electronic MAX-1 exercise electrocardiogram (EKG) system (Marquette Electronics, Inc., Milwaukee, WI). The flow meter and gas analyzers were calibrated daily. The EKG was monitored continuously throughout exercise and during 5 minutes of recovery.
Bone Mineral Density Assessment
Bone mineral density and bone mineral content were measured using the Hologic QDR 1500 DEXA (v. 7.1). Normalized values (T- and Z-scores) were generated from a gender-matched, and in the case of hip scores ethnicity-matched, control data set provided as part of the DEXA software. For the purpose of discussion in this article, we will use the World Health Organization (WHO) guidelines in defining clinical osteopenia (T-score < -1.0 and > -2.5) and osteoporosis (T-score < -2.5) (8). We recognize that these values are based upon relative risk of osteoporosis in postmenopausal women; however, we believe that these guidelines can be used for comparative purposes in a constructive way. The sample size of those with whole body scans was only 36 in that several subjects were evaluated in the lab prior to the university's acceptance of the whole body scan as a research tool.
Performance
Subjects self-reported training and performance data via questionnaire. Subjects were asked to report years of training, distance/time trained per week, days trained per week, best performances (5K, 10K, marathon) for each year they had been competing, and best performances within 2 months of the testing date. Subject responses were confirmed by oral interview on the day of testing.
Statistical Methods
All statistics were performed using the SPSS (v. 10.1) statistical software (SPSS Inc., Chicago, IL). Paired sample t tests were utilized to examine mean T1 and T2 differences. Linear regression was used to provide the magnitude and direction of the relationships among variables. When relating bone density to training and performance variables, partial order correlation was used, controlling for change in body weight or lean body mass (p was considered significant at the .05 level).
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Results |
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A summary of the differences in training volume and running performance is presented in Table 2 . The disparity between the actual number of subjects (N = 54) and the change in running performance (n = 39) relates to the fact that several runners actually changed their competitive event over the intervening years. The results indicate that as these male runners get older, they decrease both mileage and the number of days per week they train. In this sample of older athletes, running performance significantly declined with age in the 5K and 10K events. Marathon times did not differ.
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The longitudinal changes in BMD and BMC are presented in Table 3 . No significant change in whole body BMD or BMC was observed in these subjects. A significant increase in spine BMC and BMD and an increase in hip BMC occurred. The adjusted Z-score increased significantly for several sites—total spine (p < .016), total hip (p < .002), femoral neck (p < .006), and trochanter (p < .025). The increase in Z-score indicates that these runners exhibit a slower decline from peak bone mass than expected for individuals of similar age but not necessarily similar activity patterns. As reported, the direction of bone change over time for the hip in these athletes is toward bone maintenance not loss.
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Discussion |
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MacDougall and coworkers (3) reported no differences in trunk, spine, pelvis, or thigh BMD regardless of the running mileage in a group of 53 runners ranging in age from 20 to 45 years old. In fact, the BMD in these sites was not significantly different from a sedentary control group of similar age. Their data on this younger sample of runners are similar to our findings, that is, mileage is not a significant predictor of BMD. The mileage in their study was between 5 and 10 miles per week in the low group to 60–75+ in the high mileage group and was quite similar to our subjects, who ranged from 2 to 90 miles per week. Our findings extend their conclusion that mileage is not a significant predictor of BMD to the contention that changes in mileage over a number of years are not predictive of changes in BMD over time.
Karlsson and colleagues (9), studied 273 sedentary men over a 3-year period and reported, in sedentary men older than 50 years old, a 0.1% year loss in whole body BMD, a 1.5% decrease per year in femoral neck BMD, and a significant 0.45% per year gain in L2–L4 BMD. Unlike their findings, we report a significant greater loss in whole body BMD (0.27% per year) while neither hip nor spine BMD changed significantly. Our active men did increase spine density by 0.06% per year, but the difference was not significant and the real number value is lower than the 0.45% reported by Karlsson's group (9). It is likely that the increased spine density in both studies is not truly a reflection of changes in bone quality but perhaps a result of excessive compression and degeneration of the vertebrae associated with normal aging. The fact that the spine and hip BMD are maintained, while the WB BMD declines, suggests a site-specific influence of distance running.
The relatively high number of runners (37%) who were less than -1.0 standard deviations below peak BMD estimates for the spine versus the lower percentage at the hip (18%) was puzzling. One explanation of this finding is that the chronic impact of running accelerates bone loss at the spine. This was not the case in this study in that spine (L2–L4) BMD actually increased over the 3.6 years of the study. Second is that running does nothing to the prevalence of osteopenia at the spine but reduces it at the hip as a direct effect of specific hip loading during running. A final explanation may be that the prevalence of spine osteopenia is normally higher than at the hip. Kelsey reported fracture prevalence for the hip of 6% and spine of 5% in men, refuting the premise that differences in our hip/spine osteopenia rates are linked to fracture prevalence (10).
It is difficult to suggest any influence of running on fracture incidence until more longitudinal studies have been conducted. In dogs, Puustjarvi and colleagues (11) reported that chronic running led to a decrease in BMD versus sedentary dogs; however, collagen fibrils became reorganized into a more parallel manner in the runners, which the authors suggested accounted for maintenance of strength properties in bone. In other words, the benefit of exercise in this example was to change the architecture, not the bone mineral density or content. If this is true in humans as well, one could postulate that selective remodeling within specific bone sites more than compensates for the lack of distance running effect on BMD. Obviously, this is only conjecture, but several studies on the value of exercise on reduction of fracture risk may give credence to such speculation.
In conclusion, these data are presented as a longitudinal comparison of physiological variables in a group of older master runners. These data suggest that BMD can be maintained as a result of continuous training in male runners. They also suggest that changes in training patterns (either increases or decreases in days per week of training or miles per week of running) have little influence on the ability to maintain skeletal mass. It is obvious that future studies should increase the sample size and should include control subjects who either do not run or run a limited amount (<2–3 miles/week).
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Acknowledgments |
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Received October 29, 2001
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) represents the T2 values. Regression equations are presented only when a significant r value was observed. The relationships between changes in BMD and changes in miles run per week are presented in the right panel graphs. NS = not significant.