TY - JOUR
T1 - Use of ultrasound to make noninvasive in vivo measurement of continuous changes in human muscle contractile length
AU - Loram, Ian
AU - Maganaris, CN
AU - Lakie, Martin
PY - 2005/12/22
Y1 - 2005/12/22
N2 - Continuous measurement of contractile length has been traditionally achieved using animal preparations in which the muscle and tendon are exposed. More modern methods, e.g., sonomicroscopy, are still invasive. There is a widely perceived need for a noninvasive, in vivo method of measuring continuous changes of human muscle contractile length. Ultrasonography has been used for several years to measure relatively static, discrete changes in tendon, aponeurosis, and muscle fascicle length. We have recently developed this technique to continuously track changes in muscle contractile length during quiet standing. Here, we present the tracking algorithm and use externally applied perturbations to establish the spatial and temporal resolution of the technique. Subjects maintained a low level of ankle torque while a pneumatic actuator applied rapid, square-pulse ankle rotations of defined magnitude and 0.2-s duration. Tracked changes in gastrocnemius and soleus contractile length follow the temporal profile of the perturbations and scale progressively (5-400 microm) with the size of the ankle rotation (0.03-0.7 degrees ). In a second experiment, we tracked a wire oscillating in water with known peak to peak amplitudes of 1.5 microm to 8 mm. The ultrasound tracking procedure had near 100% accuracy at all amplitudes for frequencies up to 3 Hz and showed attenuation at higher frequencies consistent with an effective sampling frequency of 12 Hz and sampling time of 80 ms. This noninvasive technique is sensitive, without averaging, to changes as small as 1 microm and is suitable for observing neuromotor activity in posture and locomotion.
AB - Continuous measurement of contractile length has been traditionally achieved using animal preparations in which the muscle and tendon are exposed. More modern methods, e.g., sonomicroscopy, are still invasive. There is a widely perceived need for a noninvasive, in vivo method of measuring continuous changes of human muscle contractile length. Ultrasonography has been used for several years to measure relatively static, discrete changes in tendon, aponeurosis, and muscle fascicle length. We have recently developed this technique to continuously track changes in muscle contractile length during quiet standing. Here, we present the tracking algorithm and use externally applied perturbations to establish the spatial and temporal resolution of the technique. Subjects maintained a low level of ankle torque while a pneumatic actuator applied rapid, square-pulse ankle rotations of defined magnitude and 0.2-s duration. Tracked changes in gastrocnemius and soleus contractile length follow the temporal profile of the perturbations and scale progressively (5-400 microm) with the size of the ankle rotation (0.03-0.7 degrees ). In a second experiment, we tracked a wire oscillating in water with known peak to peak amplitudes of 1.5 microm to 8 mm. The ultrasound tracking procedure had near 100% accuracy at all amplitudes for frequencies up to 3 Hz and showed attenuation at higher frequencies consistent with an effective sampling frequency of 12 Hz and sampling time of 80 ms. This noninvasive technique is sensitive, without averaging, to changes as small as 1 microm and is suitable for observing neuromotor activity in posture and locomotion.
KW - muscle
KW - ultrasonography
KW - contractile element
UR - http://www.scopus.com/inward/record.url?scp=33646351745&partnerID=8YFLogxK
U2 - 10.1152/japplphysiol.01229.2005
DO - 10.1152/japplphysiol.01229.2005
M3 - Article
C2 - 16339341
SN - 1522-1601
VL - 100
SP - 1311
EP - 1323
JO - Journal of Applied Physiology
JF - Journal of Applied Physiology
IS - 4
ER -