No abstract

The goal of this study was to investigate the movement coordination among the hip, knee, and ankle joints during solo performance of the Tai Chi (TC) basic movements in order to understand its dynamic postural control. Nine male community-dwelling adults with experienced TC pushing hands participated in this cross-sectional study. The Eagle®motion analysis system with eight cameras was used to collect the trajectories of all reflective markers at sampling rate 100 Hz while the subject performed the ward-off, rollback, press, and push movements. Motion among the hip, knee, and ankle joints was highly coupled. Coupled joint motion, hip flexion-knee flexion-ankle dorsiflexion or reverse, existed in ward-off, rollback, and press phases for the front leg. However, in the push phase, the hip joint angle was kept almost constant with coupled knee and ankle motions. For the rear leg, coupled motion existed between the hip and the knee joints only. The ankle joint motion differed between the front and the rear legs during the basic movements of TC (p < 0.05). Basic characteristics were documented such as the forward knee never extending further than forward toe and both legs maintaining flexion during the full exercise cycle with hip and knee of front and rear legs having synchronized movements in opposite directions. The forward and backward shifts of TC basic movements have considerable contributions to the posture control in terms of the fine coordination of three lower extremity joints. This information could improve training protocol design for TC Chuan teaching and help beginners make an efficient and less damaging movement.

Optical tracking systems have been used in previous studies to capture the motion of the nude breast and breasts in bras, under the assumption that no breast-bra relative movement occurred within the bra. This study compared breast and bra movement through electromagnetic tracking and optical tracking systems to determine the relative breast movement occurring with different breast support and exercise-induced breast discomfort. Total of 30 female participants (mean age: 21.5 ± 2.3 years; cup sizes: A-F) were recruited and their movement at four different levels of breast support was recorded in two motion capture systems for further analysis and comparison. Significant differences between bra and breast vertical displacement were found at all support levels during periods of intense movement (r = 0.556; p < 0.05). Because the greatest bra displacement was observed when participants wore an everyday bra and the greatest breast displacement was observed when participants wore a crop-top bra, there was evident inconsistency in bra and breast motion and a high-impact sports bra was the most effective to reduce breast movement and discomfort among the four types of bras. An electromagnetic tracking system provided direct observation of the actual movement of the breasts, and an optical tracking system enabled us to monitor bra displacement. Significant differences were observed in bra and breast displacement during the intense movements included in this study. The results bring into question the assumption made in previous studies that no relative movement occurs within a breast support garment.

No abstract

The goal of this study was to investigate the differences in ground reaction force during a Tai Chi Chuan (TCC) pushing movement between those with and without TCC experience through a detailed 3D dynamic analysis of the lower extremities. Seven TCC practitioners who had practiced the TCC push-hands movement for 6.0 ± 4.8 years and eight males without any TCC experience were recruited in this study. An eight-camera Expert Vision Eagle motion analysis system and two Kistler force plates were used to collect kinematic data (100 Hz) and the ground reaction force (1000 Hz). About 34 retro-reflective markers were placed on anatomical significant locations that determine embedded axes for segments. Results showed that the angular motions of the knee joint were different between the two groups, both in pattern and magnitude. Compared with the TCC group, the non-TCC group had significantly smaller peak abduction angles at the ankle joint (p < 0.05). The magnitude of the vertical force of the TCC group was greater, whereas the medial and posterior shear forces were smaller. The significant difference in vertical force (p < 0.05) and fraction opponent force of vertical force were found significantly different (p < 0.05) between the two groups. The patterns of the anteroposterior component of the ground reaction force during pushing were different, but those for the other two components were similar. Different lower-limb kinematics and kinetics were found between those with and those without TCC experience during TCC pushing movement and it was also found that the TCC practitioners could generate more effective force transfer than the group with no prior TCC experience. It was further concluded that vertical force plays an important role in a pushing movement, and posterior force exerted from the opponent was absorbed and transformed into anterior force to help the TCC practitioners remain stable.

The present study investigated the adequacy of the interaction between the center of mass (COM) and the center of pressure (COP) for maintaining dynamic stability during Tai Chi Chuan (TCC) Push Hands movements in a fixed stance. The COM of the whole body and COP were calculated. Four TCC experts, with 10.3 ± 1.7 years' experience in the Push Hands technique, and 4 TCC beginners, with 2.5 ± 1.3 years' Push Hands experience, were recruited. An Expert Vision Eagle motion analysis system collected kinematic data and 4 Kistler force plates collected the ground reaction force data. The expert group of TCC practitioners showed a significantly more vertical (P = 0.001) direction in the neutralizing circle, and significantly larger values for anterior–posterior (A–P) (P = 0.006) and vertical (P = 0.0004) displacement in the enticing circle, than the beginner group. Compared with the beginner group, the expert group demonstrated significantly greater velocity A–P (P = 0.001) and vertical (P = 0.001) COM displacements in the enticing circle. A significant extent main effect (P = 0.0028) was observed for the COPA–P excursion between the expert and beginner groups during Push Hands movements. The greater A–P force generated by both groups during the initiation of the Push Hands cycle probably reflects the more rapid and forward-oriented nature of this movement. The TCC beginners might have difficulties with movement transfers because of disruptions in the temporal sequencing of the forces. Overall, results indicated that the initial experience-related differences in COM transfers are reflected in the Push Hands movement cycle.