2 training on muscle strength with positive results [14, 15]. Current WBV machines deliver vibrations at a frequency between 15 and 60 Hz. The resonance frequencies of the spine occur between 5 and 15 Hz [16] which are also the fre- quencies considered to be a causative factor in low back pain [17] and circulatory disorders like Raynaud’s phenomenon [18]. However, WBV-related injuries (back pain, muscular discomfort, etc.) can be prevented by limiting the duration to a maximum of 10 minutes and maintaining the posture of the participant in a semisquat stance which involves the leg muscles reducing the transmission of vibrations to the head [19]. Therefore, WBV may be safer to apply and easier to comply with than AEX, particularly in a community setting. However, there is no consensus regarding the beneﬁts, safety, and long-term application of WBV. To our knowledge, there is also no comparison of the eﬀects of WBV and AEX on BMD in elderly. Therefore, the purpose of this paper was to evaluate and compare the eﬀect of AEX and WBV on BMD at various skeletal sites in older population and to explain the possible mechanisms of their action on bone. 2. Methods Papers on AEX and whole-body vibration published in English were searched using PubMed and MedLine (First- Search) databases. Combinations of the following phrases as keywords were used in the search “Aerobic exercise/ whole-body vibration,” “bone mineral density/content,” “older women/female,” “older men/male,” and “running/ walking/jumping” and would have to be present in the title, abstract, or keywords. AEX included treadmill walking, stepping exercise, and jumping. Studies with strength and resistance exercise were not included in this context. After excluding studies with vitamin D and calcium supplemen- tation, or those involving subjects on medications and diﬀerent chronic conditions, 17 studies were selected and are discussed in this paper for the eﬀects of AEX. After excluding studies that examined WBV but focused on bone implants and those in which medications and other special treatment were used, 4 studies were selected and discussed in this paper. A snapshot of the relevant studies and their overall description is shown in Tables 1 and 2. 3. Effect of Aerobic Exercise on Bone in Older Population 3.1. Organized Aerobic Activities. Women entering meno- pause face many challenges regarding their bone health, especially those with a history of or current inactivity [37]. Therefore, engaging the elderly in exercise programs is necessary to maintain BMD and increase the quality of life. Most of resistance exercises have shown a positive eﬀect on increasing or maintaining BMD in postmenopausal women [38, 39]. Whether AEX has the same eﬀect is questionable. Results from a meta-analysis revealed that AEX maintained spine and signiﬁcantly increased femoral neck BMD, suggesting that the femoral neck might be more responsive to high-impact AEX than the lumbar spine Journal of Aging Research [40]. Welsh and Rutherford [33] found that 1-year AEX including high-load step and jumping signiﬁcantly increased femoral neck and trochanter BMD in a group of previously sedentary men and postmenopausal women. In addition, Chien et al. [21] found that a 6-month AEX intervention, including graded treadmill-walking and stepping, signif- icantly increased femoral neck, but not spine BMD in Chinese postmenopausal women. Even in the chronic stroke population, AEX maintained the femoral neck BMD, while a signiﬁcant reduction in BMD was observed in controls [32]. These results suggest that AEX has positive impact on femoral neck BMD. Confounding results still exist as some studies have shown that AEX did not enhance BMD in postmenopausal women [28, 30, 41]. These conﬂicting results were most likely due to insuﬃcient intensity and frequency of exercise, small sample sizes, and the choice of measurement site employed in each study. The most frequently used duration and frequency of AEX were 30–60 minutes per session, 2- 3 times a week. In a community exercise program, it was found that 1 year of AEX combined with strength training did not show an improvement in BMD at several skeletal sites in women aged 60 years and over [28]. Martin and Notelovitz [30] showed that 1 year of moderate AEX did not improve spine or forearm BMD due to inadequate sample sizes to detect small changes in bone. Other limitations were the low intensity of exercise and the lack of the involvement of upper extremities activities. Results from the meta-analysis showed that exercise did not improve femoral neck BMD in postmenopausal women [41] thought resistance training was included in their data analysis. The conﬂicting conclusion may be due to the combination of aerobic and resistance exercise in their data analysis and the diﬀerent choice of measurement such as forearm or spine. If we only consider the eﬀect of AEX on BMD, not including other kinds of exercises, AEX seems to increase femoral BMD in older adults. 3.2. Running and Walking. Some longitudinal studies exam- ined the impact of running on BMD in older individuals. Although Wiswell et al. [34] found that 54 male runners aged 40 to 80 years maintained their hip and spine BMD over a 4- to 5-year running period by self-reporting training hours compared to their baseline measurements, the age range used may be too large to draw meaningful conclusions. A similar study revealed that runners exhibited a lower age-related bone loss compared to controls although both runners and controls had a signiﬁcant decrease in spine BMD after a 5- year followup [31]. A 9-year longitudinal study following the running subjects showed that those who maintained their training volume lost less bone in the spine than those who did not maintain their running regimens [29]. These results demonstrate that running is beneﬁcial to maintain the BMD for elderly. In contrast, Kirk et al. [26] found that postmenopausal runners tended to have lower spine BMD than age- and height-matched controls, indicating that running prevents hip BMD loss, but it may not maintain age- related reduction of spine BMD in older men and women.