This study newly characterizes the physical demands of 7 standing yoga poses in a sample of older adults who had been trained for 32 weeks. We quantified the JMOFs associated with the performance of these yoga poses (10 including Leading and Trailing limbs). A significant main effect for pose was found across all of the JMOFs examined, suggesting significantly different musculoskeletal demands among the top 4–5 ranked poses.
Frontal plane JMOFs
The Tree pose generated the greatest hip and knee abductor JMOFs; whereas, Warrior II generated the greatest hip and knee adductor JMOFs. The frontal JMOFs during Warrior II were also greater than the peak JMOFs generated during self-selected walking. Several studies have quantified the relations among hip abductor performance, osteoarthritis progression , balance, and fall risk [24–26]. Thus, the Tree, and to a lesser extent the One-Legged Balance pose, would appear to be good selections for improving balance and reducing fall risk. Gluteus medius EMG findings also support that these poses target the hip abductors. To our knowledge, associations among hip adductor performance, balance capabilities, and fall risk, have not been examined.
Our findings regarding the frontal-plane JMOFs about the knee may have exceptionally important implications for instructors and clinicians designing programs for individuals with knee pain and/or pathology. Load demands in the frontal plane of the knee joint are primarily supported by passive structures (i.e. ligaments and the joint capsule), and not by muscle. Moreover, high frontal-plane JMOFs at the knee are associated with high compressional forces on the opposite side of the joint [4, 27] and these high compressional forces, in turn, can exacerbate existing OA, accelerate articular cartilage degeneration, and increase pain [5, 23, 28, 29]. While Tree and Warrior II poses were the best candidates for improving hip abductor and adductor performance, respectively, they also generated the greatest torque about the medial and lateral knee joint. For example, the average knee adductor JMOF produced by Warrior II was 267% greater than the peak knee JMOF produced during self-selected walking—suggesting that for long-term yoga practice, this pose may need to be modified or substituted for seniors with knee pain or pathology.
Across all poses, the JMOFs at the ankle were smaller than the average peak JMOF produced during self-selected walking. Only Crescent Trailing and Warrior II Trailing poses generated ankle abductor JMOFs. Large ankle adductor JMOFs were observed with One-legged Balance and Tree. Both ankle invertor and evertor strength are important for balance and safe ambulation, and they are related to performance in the timed up-and go test and Berg Balance Scale . Practicing the aforementioned poses will likely target the ankle invertors and evertors and potentially improve balance associated with various daily living activities.
When exercise is prescribed, biomechanical assessment may be used to quantify the magnitude of the musculoskeletal demands associated with exercise activities [15, 31], in order to appropriately “dose” the participants. In the present investigation, we calculated the JMOFs associated with the performance of 7 specific yoga poses in order to quantify their musculoskeletal demands in a sample of seniors, whose strength and flexibility capacities are undoubtedly less than those of average young-to-middle aged yoga practitioners. The JMOF profiles of these 7 asanas may ultimately be used to guide yoga instructors in the choice of poses that are well-balanced, target a variety of functionally important muscle groups and avoid overloading musculoskeletal structures.
Although net JMOFs have been used to quantify the musculoskeletal demands associated with a variety of exercise activities [32, 33] this kinetic approach has inherent limitations. In calculating the JMOFs we used an inverse dynamics approach and thus do not account for co-activation of antagonistic muscle groups. Consequently, the actual internal (muscular) joint moments are likely to be underestimated. EMG analysis can be used to support the JMOF findings and in general the EMG results of the present study were in agreement with the kinetic data – muscle activities were low in those poses that had small JMOFs and high in poses generating higher JMOFs. In addition, poses with EMG activations lower than those generated during self-selected walking also generated JMOFs which were less than the average peak JMOFs produced during the walking trials.
When comparing the JMOFs generated during the yoga poses with the average peak JMOF generated during walking, it is important to consider that walking is a cyclic activity in which the JMOFs increase and decrease during a gait cycle. Thus, we calculated and recorded the peak JMOFs, across the hip, knee, and ankle, which were produced during the walking trials. In contrast, during both the yoga classes and the laboratory sessions, the participants held their poses static “for a full breath” before returning to a starting position, and we calculated the average JMOFs engendered during the middle 3-seconds of each pose. Thus, a fair comparison between the JMOFs engendered during yoga and walking should take into consideration the fact that peak JMOFs reported during walking only occur for an instant in time, whereas the average JMOFs produced during each yoga pose persist for more than 3 seconds. Consequently, although the peak JMOFs produced during dynamic activities such as walking may be greater than the average JMOFs generated during the yoga poses, the overall muscular stimulation (i.e. activation and loading) afforded during yoga posing may be greater than that produced during walking or other dynamic activities (e.g. resistance exercise). Additionally, it is important to note that because we limited our analysis to the static phase of the poses, we cannot directly extrapolate our findings to other vinyasa-based or “flowing” yoga styles that may use similar postures.