Transcript Document

Muscle Activation Patterns During Gait Initiation
Natasha Kyle, MSc and D. Gordon E. Robertson, PhD, FCSB
School of Human Kinetics, University of Ottawa, Ontario, Canada
Introduction
Gait initiation is a temporary movement between upright posture and
steady-state gait. The activation of several postural muscles has been
identified to precede changes observed in vertical reaction force (Winter,
1995). Although previous research has focused on the lower limb, few
studies have examined recruitment patterns of the thigh and trunk
musculature. This study was conducted to determine the phasic patterns of
muscles of the lower limbs and trunk for the duration from quiet stance to
trail-limb toe-off.
Methods
Eleven healthy participants initiated gait with their right legs. Two force
platforms (Kistler) were used to measure vertical ground reaction forces
(GRF), at 1040 Hz, from quiet stance to toe-off of the trail limb. In addition,
electromyographic data (Octopus, Bortec) were collected at 1040 Hz
beginning at quiet stance to the end of the third step. EMG electrodes were
placed bilaterally over the erector spinae (ES), the tensor fasciae latae
(TFL), the adductor magnus (ADD) and the tibialis anterior (TA) muscles.
Participants stood with one foot on each plate, distributing their weight
equally. Each participant walked briskly, after the researcher gave a “go”
command. Ten trials were collected for each subject. Force platform data
were filtered with a zero-lag, second-order, critically damped, low-pass filter
with a cut-off frequency of 20 Hz. To remove low frequency motion
artefacts, the raw electromyographic data were high-pass filtered with a
cut-off frequency of 8 Hz (Robertson & Dowling, 2003). Electromyographic
data were full-wave rectified and filtered by a second-order, critically
damped, low-pass filter with a cut-off frequency of 5 Hz, producing a linear
envelope (Robertson & Dowling, 2003).
An amplitude threshold criterion determined the start and end of
muscle activity. The threshold was based on three times the standard
deviation of the EMG during quiet stance for each muscle, estimated from
the least variable 100 ms period of each EMG. Timings of all eight muscle
onsets and offsets were recorded from time-normalized, ensembleaveraged data for each subject for the period beginning 1.5 s before traillimb toe- off.
Biomechanics Laboratory
Results
Table 1 holds the muscle onset times for the nine subjects. The earliest muscle
activated was consistently the lead-limb tibialis anterior, followed by the lead-limb
tensor fasciae latae (figure 1). The trail-limb tibialis anterior, trail-limb tensor
fasciae latae and the trail-limb adductor magnus were next to become active,
respectively. The order of muscle activity during the middle of the gait initiation
process varied. Specifically, there were notable inconsistencies between subjects
for the order of the fifth and sixth muscle activations. The last two muscles to
activate were consistently the erector spinae of the trail-limb side followed by the
erector spinae of the lead-limb.
Discussion
Presumably the two tibialis anterior muscles with the simultaneous release
of the gastrocnemius/soleus muscles caused the posterior movement of
the centre of pressure, whereas the lead-limb tensor fasciae latae (figure 2)
contributed to the initial lateral shift toward the lead limb reported by Winter
(1995). The delayed reaction of the erector spinae muscles confirm the
kinetic analysis of gait initiation conducted by Robertson et al. (2005) that
showed a brief period of falling prior to lead-limb heel-contact.
Figure 1: From top to bottom: bilateral raw EMG of lead-limb then trail-limb TA,
ADD, TFL, ES (blue) and vertical GRF data (black) for a single trial.
T a b le 1 : M u scle o n set tim es d u rin g g ait in itiatio n
S u b je c t1
S u b je c t2
S u b je c t3
S u b je c t4
S u b je c t5
S u b je c t6
S u b je c t7
S u b je c t8
S u b je c t9
M ean
St Dev
L -E S
51
43
51
45
41
63
46
41
48
4 7 .7
7 .3 5
T -E S
84
25
75
36
35
40
35
39
32
4 4 .6
2 0 .4
L -T F L
18
20
21
12
20
16
11
15
14
1 6 .3
3 .6 4
T -T F L
22
35
36
18
28
12
16
34
39
2 6 .7
9 .9 4
L -A D D
49
79
50
17
24
18
33
26
21
3 5 .2
2 0 .5
T -A D D
35
24
39
30
34
19
18
28
18
2 7 .2
7 .9 2
L -T A
16
13
17
11
19
32
10
12
17
1 6 .3
6 .6 3
T -T A
19
15
30
20
23
28
15
17
13
2 0 .0
5 .9 4
Note: Muscle onset timings are all expressed as a percentage of total gait
initiation (0-100%). L-ES & T-ES are the lead-limb and trail-limb erector
spinae; L-TFL & T-TFL are the lead-limb and trail-limb tensor fasciae latae; LADD & T-ADD are the lead-limb and trail-limb adductor magnus; L-TA & T-TA
are the lead-limb and trail-limb tibialis anterior.
Figure 2: Ensemble averages (±1 SD) of the eight muscles for one subject.
Time normalized linear envelope EMG throughout gait initiation. EMGs order
from top is lead-limb then trail-limb TA, ADD, TFL and ES.
References
Robertson DGE & Dowling JJ (2003) J Electromyo Kines, 13: 569-573.
Robertson DGE, Smith, O’Dwyer (2005) Proceed ISB XX, p.102.
Winter DA (1995) A.B.C. of Balance during Standing and
Walking. Waterloo: Waterloo Biomechanics.