ABSTRACT
Among the paraspinal muscles, the psoas major is essential for leg swing during
running. As its sarcomere length indicates a lower force-generating capacity at
a lengthened position, greater hip extension at higher speeds may limit its
force. Meanwhile, the lumbar spine becomes more lordotic and tilts anteriorly as
running speed increases, which may shorten the psoas major. However, lumbar
spine motion has been neglected when estimating psoas major length. We examined
the effect of lumbar spine motion on psoas major length, comparing models with
(MOVING) and without (FIXED) considering lumbar spine motion. Psoas major length
was estimated during treadmill running at four different speeds (4.0–8.5 m/s).
The main effect of the running speed on psoas major length was not significant
in MOVING (length normalised to standing: from 102.1±1.7 to 102.3±2.0%), whereas
it was significant in FIXED (from 102.2±0.8 to 104.2±0.9%). A strong linear
relationship between hip angle and psoas major length was found in FIXED
(r
2 >0.92), but was compromised in MOVING
(r
2 =0.74±0.17). Lumbar spine motion alters psoas major
dynamics and prevents psoas major elongation at higher speeds. This may
facilitate rapid leg swing by preserving the force-generating capacity of the
psoas major.
Keywords
Lumbar lordosis - Hip flexors - Paraspinal muscles - Sprinting - Iliopsoas
