Article

Adapted strategies in rising from a chair occur with muscle weakness. To assess
whether muscle weakness caused the strategy change, an experimental simulation
was performed that allowed to investigate separately effects of reduced muscle
capacity and of strategy change on movement dynamics.
It was hypothesized that a
sit-to-stand (STS) strategy change spares muscles that become overloaded when
muscle weakness develops. Ten healthy females participated; seven of them
completed all tests. Muscle weakness causes an increased load-over-capacity
ratio. In the present study, this ratio was increased by providing participants
with a waist-coat containing 45% of their body mass. Participants performed
sit-to-stand manoeuvres with and without added mass; moreover they were
instructed to perform two different strategies, the moment-transfer-strategy and
the stabilization-strategy. During these STS-tasks sagital 2D-video analysis were
made and ground reaction forces (GRF) were measured. Joint moments and powers for
ankle, knee and hip joint were calculated. The preferred strategy under the
normal condition was the moment-transfer strategy. Increasing the load without
adapting the strategy resulted in significantly higher (13%) knee-joint extension
moments. Allowing a strategy shift in the loaded condition spared the knee-joint
extensors (-6%) and transferred effort to hip-joint extensors (57%) and plantar
flexor (67%) muscles. These results suggest that the capacity of knee-joint
extensors limits the STS-performance when muscle weakness occurs.

Langue : ANGLAIS