Gjv. Schenau et al., DOES ELASTIC ENERGY ENHANCE WORK AND EFFICIENCY IN THE STRETCH-SHORTENING CYCLE, Journal of applied biomechanics, 13(4), 1997, pp. 389-415
This target article addresses the role of storage end reutilization of
elastic energy in stretch-shortening cycles. It is argued that for di
screte movements such as the vertical jump, elastic energy does not ex
plain the work enhancement due to the prestretch. This enhancement see
ms to occur because the prestretch allows muscles to develop a high le
vel of active state and force before starting to shorten. For cyclic m
ovements in which stretch-shortening cycles occur repetitively, some a
uthors have claimed that elastic energy enhances mechanical efficiency
. In the current article it is demonstrated that this claim is often b
ased on disputable concepts such as the efficiency of positive work or
absolute work, and it is argued that elastic energy cannot affect mec
hanical efficiency simply because this energy is not related to the co
nversion of metabolic energy into mechanical energy. A comparison of w
ork and efficiency measures obtained at different levels of organizati
on reveals that there is in fact no decisive evidence to either suppor
t or reject the claim that the stretch-shortening cycle enhances muscl
e efficiency. These explorations lead to the conclusion that the body
of knowledge about the mechanics and energetics of the stretch-shorten
ing cycle is in fact quite lean. A major challenge is to bridge the ga
p between knowledge obtained at different levels of organization, with
the ultimate purpose of understanding how the intrinsic properties of
muscles manifest themselves under in-vivo-like conditions and how the
y are exploited in whole-body activities such as running. To achieve t
his purpose, a close cooperation is required between muscle physiologi
sts and human movement scientists performing inverse and forward dynam
ic simulation studies of whole-body exercises.