Few randomized trial have evaluated the potential of Tai Chi to impact multiple fracture-related risk factors in osteopenic women. In this short trial with a modest sample size, BMD and balance-related outcomes were not expected to show statistically significant changes in response to TC, but was measured to detect treatment-related trends and to estimate an effect size for a future study. We observed a clinically relevant trend of TC training attenuating bone loss. Trends towards improved BMD, a reduction in bone turnover, and better health related quality of life in the TC vs. Usual Care were not statistically significant for any variable when evaluated with an intent-to-treat analysis. However, secondary analyses comparing per protocol TC participants to Usual Care for BMD of the femoral neck, physical domains related to quality of life, and osteocalcin levels indicated statistically significant positive effects. Additionally, results from our biomotion sub-study suggest clinically and statistically relevant improvements in balance parameters previously shown to be associated with fall risk. Our results affirm the value of a future, more definitive trial of TC for osteopenic women, provide the preliminary required data for determining sample size for appropriate statistical power for such a trial, and contribute to a growing literature evaluating TC for bone health and fall-related fracture risk.
Prior research on the effects of TC on BMD in post-menopausal osteopenic women is limited [14
]. Cross-sectional studies including elderly women suggest long-term TC practitioners have higher BMD than age-matched sedentary controls [37
], and have slower rates of post-menopausal BMD decline [11
]. One RCT in post-menopausal women observed that DXA measures of BMD at the lumbar spine significantly increased (1.81%) following 10 months of TC while sedentary controls decreased (1.83%) [39
]. A second RCT observed that for older women, 12 months of TC training resulted in maintenance of total hip BMD levels when compared to a non-exercise control that lost 2.25% of total hip BMD [40
This study uniquely extends our understanding of the potential impact of TC on women's bone health. Prior studies have included women with BMDs ranging from normal to severely osteoporotic. Because the effects of antiresorptive treatment on bone turnover and changes in BMD may vary with severity of bone loss [41
], our study specifically informs the value of TC to post-menopausal women with a firm diagnosis of osteopenia. Second, we report on an ethnically diverse Western population. Patterns of postmenopausal BMD loss vary with respect to race and ethnicity, and nearly all prior RCTs evaluating TC for BMD have been conducted in Asia. Our results are in concordance with a recently completed U.S. study of osteopenic women that reported 6 months of Tai Chi improved multiple markers of bone health including higher levels of bone-specific alkaline phosphotase (BAP), higher ratios of BAP to tartrate-resistant acid phosphotase, and elevated levels of serum parathyroid levels [42
]. Third, in contrast to previous RCTs that targeted relatively sedentary populations, we included women who were relatively active since exercise is a standard recommendation for osteopenia. Our results suggest that benefits of TC on the skeleton are not limited to sedentary individuals.
The Erlangen Fitness Osteoporosis Prevention Study (EFOPS) [44
] was a RCT comparing a graded multipurpose exercise program to a usual care control group. After 1 year, magnitudes of differences between the exercise vs. control group in the femoral neck (-0.8% vs. -1.8%) and total hip (-0.3% vs. -0.8%) were comparable to the trends we observed after 9 months of TC training; however, improvement in BMD of the total spine were more dramatic in EFOPS (+1.3% vs. -1.2%). After two years, exercise attenuated any further loss at all sites, whereas cumulative bone loss in the non-exercise control was approximately 2.9%, 1.7%, and 2.3% at the femoral neck, total hip and total spine, respectively [45
]. It is plausible that extending the period of TC training from 9 months to two years would result in continued attenuation of bone loss, as observed in the EFOPS trial. Based on both clinical relevance, feasibility, and our preliminary analyses, we believe a future longer-term TC study is warranted, and estimate that a moderate size trial of approximately 200 participants would be adequately powered to detect the differences in BMD observed in the EFOPS trial.
Independent of changes in BMD, TC may be of benefit to women with low bone density because of its positive effect on fall risk and postural control. Numerous randomized trials suggest TC training can directly reduce prevalence of falls [5
]. Other studies suggest TC positively impacts factors associated with falls including multiple sway parameters [46
], clinical balance tests [49
], musculoskeletal strength and flexibility [50
], and fear of falling [48
]. One study including only osteopenic women reported positive effects of 6 months of Tai Chi on one gait stride length, but not on dynamic posturography or clinical measures of balance [55
]. However, this and the majority of other studies have only included older adults with more limited postural control. The results from our biomotion substudy suggest that the balance-related benefits of Tai Chi observed in older populations may also extend to relatively younger and healthier osteopenic women. Confirmation of our results in a larger and longer-term trial would suggest that, in combination with its modest effects of BMD, TC is a potentially valuable intervention for prevention of falls and fall-related fractures in post-menopausal osteopenic women, and goes beyond most fracture interventions that target only the skeleton.
Our intervention was not based on a single fixed training protocol, but rather relied on the diversity of protocols provided naturalistically in pre-screened, long-standing community TC schools [56
]. As such, our use of a pragmatic intervention affords high external validity, applying not just to one specific TC training protocol, but rather to the diversity of protocols encountered in typical community-based programs. However, our use of naturalistic interventions reduces the internal validity of our study. This intervention heterogeneity may necessitate larger samples to increase statistical power [57
Our choice of a usual care control followed the overarching practical goal of our study--to evaluate the potential benefits to osteopenic women of adding TC to usual care. However, this choice limits the conclusion we can draw, particularly regarding the mechanisms underlying the trends we observed in BMD, postural control and QOL. Because we did not control for group psychosocial interactions, time, and expectancy of receiving a therapy, it is possible that we measured only placebo effects. By not comparing TC to other active interventions that might offer comparable doses of weight bearing, or resistance and flexibility training, we cannot ascribe which aspect(s) of TC contributed to its therapeutic effects.
TC is a complex, multi-component intervention, and it is possible that it impacts bone remodeling via multiple processes. Motion analysis studies of TC practitioners have reported that compared to normal gait, lower extremity movements during TC have: longer cycle duration and single-leg stance time; greater ankle, knee, and hip joint motion; larger lateral body shift; distinct plantar pressure distributions; and greater and unique patterns of lower extremity muscle activation [58
]. Compared to normal gait, TC has also been shown to have larger peak shear forces in the ankle, knee and hip joints, and larger peak moments in the knee and hip joints [63
]. Cross-sectional studies of elders have shown that numerous aspects of lower extremity muscle strength and endurance are comparable to joggers [52
], and other randomized studies have reported that TC training can favorably reorganize lower extremity neuromuscular patterns, resulting in reduced excessive hip compensation and more efficient gait [64
A few other limitations of our study are important to acknowledge. First, subjects were not blinded to their intervention group. We attempted to minimize the potential effects of disappointment in the usual care group by offering free TC classes at the end of study. Second, our relatively small sample size does not discount the possibility that the results we observed were due to chance. Third, the 9-month duration of our study is relatively short from both the perspective of providing an adequate dose of TC, as well as the sensitivity of DXA to detect BMD changes. However, this study was conceived as a pilot study. As such, it has provided the data to inform a future more definitive study that will employ a larger sample and longer period of intervention and observation. Finally, while participant retention and compliance with outcomes protocols was high (loss to follow-up was 2%), adherence to TC training was lower than expected. Earlier TC studies have reported higher protocol adherence rates [65
]. The lower rates we observed in this study may be due to our relatively long, 9-month intervention. Only a handful of TC studies to date have evaluated interventions longer than six months, and most have been less than four months. Lower adherence may also result from our use of a pragmatic design. Prior studies with higher adherence typically utilized study-trained instructors, fixed cohorts of participants sharing a common medical condition, and were based in medical settings with participants having regular contact with study stuff. Greater and more structured contact with study participants and Tai Chi school staff will be required to improve adherence in a future trial.