Biomechanical analysis of the relation between movement time and joint moment development during a sit-to-stand task

Background  

Slowness of movement is a factor that may cause a decrease of quality of daily life. Mobility in the elderly and people with movement impairments may be improved by increasing the quickness of fundamental locomotor tasks. Because it has not been revealed how much muscle strength is required to improve quickness, the purpose of this study was to reveal the relation between movement time and the required muscle strength in a sit to stand (STS) task. Previous research found that the sum of the peak hip and knee joint moments was relatively invariant throughout a range of movement patterns (Yoshioka et al., 2007, Biomedical Engineering Online 6:26). The sum of the peak hip and knee joint moment is an appropriate index to evaluate the muscle strength required for an STS task, since the effect of the movement pattern variation can be reduced, that is, the results can be evaluated purely from the viewpoint of the movement times. Therefore, the sum of the peak hip and knee joint moment was used as the index to indicate the required muscle strength.     

Nonisometric behavior of fascicles during isometric contractions of a human muscle

Fascicle length, pennation angle, and tendonelongation of the human tibialis anterior were measured in vivo byultrasonography. Subjects (n = 9) wererequested to develop isometric dorsiflexion torque gradually up tomaximal at the ankle joint angle of 20° plantarflexion from theanatomic position. Fascicle length shortened from 90 ± 7 to 76 ± 7 (SE) mm, pennation angle increased from 10 ± 1 to 12 ± 1°, and tendon elongation increased up to 15 ± 2 mm with gradedforce development up to maximum. The tendon stiffness increased withincreasing tendon force from 10 N/mm at 0-20 N to 32 N/mm at240-260 N. Young's modulus increased from 157 MPa at 0-20 Nto 530 MPa at 240-260 N. It can be concluded that, in isometriccontractions of a human muscle, mechanical work, some of which isabsorbed by the tendinous tissue, is generated by the shortening ofmuscle fibers and that ultrasonography can be used to determine thestiffness and Young's modulus for human tendons.