+15 jaar member
- Lid geworden
- 24 okt 2002
For newcomers to this forum, these P&Ps are Propositions, not facts or dogmatic proclamations. They are intended to stimulate interaction among users working in different fields, to re-examine traditional concepts, foster distance education, question our beliefs and suggest new lines of research or approaches to training. We look forward to responses from anyone who has views or relevant information on the topics.
PP127 Situps and Hip Flexors Paradox
The risks of straight-legged sit-ups may be grossly exaggerated in the healthy individual, especially regarding the action of the hip flexors on the lumbar spine.
Theoretically it might appear to some folk that the small angle subtended in the straight-legged sit-up by psoas in its proximal attachment to the spine will markedly accentuate the lumbar concavity (as seen from behind), this does not appear to have been shown via clinical measurement. If the psoas angle were more perpendicular to the length of the spine, then it would be far more likely for the psoas to exert sufficient force to increase the lumbar concavity, but the major component of force exerted by psoas is along the length of spine, not vertical to the spine.
Paradoxically, the bent-knee (actually flexed-hip) sit-up would seem to place psoas in a position which enables it to pull more vertically on the lumbar spine, so that that flexed hip sit-ups would appear to be less safe than straight-legged sit-ups! As a matter of interest, has anyone come across any MRIs which have examined exactly how much an activated psoas in a healthy person during sit-ups increases the lumbar concavity (not 'lordosis', since this term accurately refers only to pathology)?
What is far too commonly assumed is that psoas definitely DOES increase the lumbar concavity, and in order to do so, it has to produce extremely large force because of its low angle in the supine or straight body. This certainly is correct IF one assumes that psoas always definitely increases the lumbar concavity. This assumption seems to be totally incorrect, because the poor mechanical advantage of psoas in the supine position does not permit it to produce high levels of torque about the hips. One probably could insert microelectrodes directly into psoas to electrically activate it in a supine person and we still would not be able to generate sufficient vertical force to produce enough torque to deform the lumbar spine, at least to an extent which causes spinal pathology.
All too often, it is presumed that large psoas activation necessarily can and will produce enough force to deform the lumbar spine to such an extent that it will lead to vertebral displacements which will cause nerve impingement in the non-pathological spine. Surely, the likelihood that this level of displacement will occur is vastly exaggerated because the healthy spine and its discs are surrounded by very strong connective tissue that minimise the degree of this displacement.
Then, even if the lumbar spine is subjected to large psoas forces, adjacent vertebrae are not going to experience local dislocations which will produce nerve impingement - instead the lumbar spine, according to basic mechanics, is simply going to exhibit a slightly smaller radius of curvature over a length of many vertebrae. It certainly will not experience the type of deformation and discal stress that is imposed when the lumbar spine is subjected to loaded flexion and rotation.
Moreover, it is impossible or virtually impossible for the average person to sit up in such a way as to allow psoas to strongly become activated before the rest of the abdominal musculature has become activated and minimised the possibility of this happening. The very act of raising the head and shoulders during the early stages of sitting up activates the abdominal musculature so strongly and increases the psoas angle to such an extent that the ability of psoas to increase the lumbar concavity is minimal. If this point is doubted, try sitting up by keeping the back of your head and shoulders in touch with the floor while starting a sit-up and attempt to raise your trunk by relying largely on psoas action. First of all, this will not be possible unless your feet are restrained and you are extremely strong, which hardly is the case with the average fitness fan.
Does all of this not suggest that most or all of the well-meaning advice about executing sit-ups or crunches is exaggerated or redundant, especially regarding the risks of psoas activation necessarily imposing pathological levels of stress on the lumbar spine or its components? Does the body not automatically act to minimise the risks of any high levels of stress as soon as the head and shoulders are raised during the early stages of any supine sit-ups or 'crunches'? Comments from anyone?
Dr Mel C Siff
Dit is al een stukje over het feit dat de risico's rond sit-ups met gestrekte benen wel wat overdreven zou kunnen zijn.
verder zou ik jullie willen vragen : wat vinden jullie beter? situps/crunches en waarom? waarom doen jullie die buikspieroefeningen? en is de manier waarop jullie het doen wel in overeenstemming met jullie doel? en wat is volgens jullie het belang van hip flexors in je training? En geloven jullie in de mythe van boven en onderkant buikspieren?