PubMed · 7108111
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A K Whitney, D R Green. 1982. Pseudoequinus.. https://doi.org/10.7547/87507315-72-7-365
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When the nervous system produces a multi-joint movement it must select a unique set of motor patterns for movement production from a variety of appropriate motor pattern solutions: this is the so-called degrees-of-freedom problem. One strategy which the nervous system could use to simplify the selection of a unique set of motor patterns (i.e. net muscle moments) for movement production would be to constrain the relationships between the net muscle moments of the various joints. Therefore, we addressed the following question: Do the inter-joint relationships of muscle moments and powers become more phase-locked during the acquisition of a novel multi-joint movement. Subjects performed 16 blocks (16 trials per block) of a discrete kicking movement, which involved motion of the hip, knee, and ankle--a weight (1.674 kg) attached to the subject's foot increased movement novelty. Subjects attempted to perform all movements as close as possible to a goal movement time of 400 ms, while maintaining spatial accuracy. An optoelectric imaging system was used to record movement kinematics for the hip, knee, ankle, and toe of the kicking leg, and inverse dynamics were then used to obtain net-muscle-moment profiles. Following learning, inter-joint moments became more closely phase-locked, with hip-flexor and knee-extensor moments being produced simultaneously, as were hip-extensor and knee-flexor moments. This increased phase-locking of inter-joint moment relationships with learning resulted in increased phase-locking of inter-joint power relationships.(ABSTRACT TRUNCATED AT 250 WORDS)
The influence of muscle activation, position and velocities of body segments at touchdown and surface properties on impact forces during heel-toe running was investigated using a direct dynamics simulation technique. The runner was represented by a two-dimensional four- (rigid body) segment musculo-skeletal model. Incorporated into the muscle model were activation dynamics, force-length and force-velocity characteristics of seven major muscle groups of the lower extremities: mm. glutei, hamstrings, m. rectus femoris, mm. vasti, m. gastrocnemius, m. soleus and m. tibialis anterior. The vertical force-deformation characteristics of heel, shoe and ground were modeled by a non-linear visco-elastic element. The maximum of a typical simulated impact force was 1.6 times body weight. The influence of muscle activation was examined by generating muscle stimulation combinations which produce the same (experimentally determined) resultant joint moments at heelstrike. Simulated impact peak forces with these different combinations of muscle stimulation levels varied less than 10%. Without this restriction on initial joint moments, muscle activation had potentially a much larger effect on impact force. Impact peak force was to a great extent influenced by plantar flexion (85 N per degree of change in foot angle) and vertical velocity of the heel (212 N per 0.1 m s-1 change in velocity) at touchdown. Initial knee flexion (68 N per degree of change in leg angle) also played a role in the absorption of impact. Increased surface stiffness resulted in higher impact peak forces (60 N mm-1 decrease in deformation).(ABSTRACT TRUNCATED AT 250 WORDS)
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