Journal of Rehabilitation Medicine 51-4inkOmslag | Page 75

Spastic co-contraction and active motor impairment
Table II. Co-contraction index, net elbow extension torque during maximal voluntary contraction and clinical characteristics
Participants
Control group (n  = 10)
Median (IQR)
Brain-injured group
1
2
3
4
5
6
7
8
9
10
Median (IQR)
Co-contraction index
during sub-maximal elbow Net elbow extension torque (Nm)
extension (%)
during maximal voluntary contraction
Limitation of active elbow
extension (degree) Elbow flexors spasticity
(Tardieu scale, 0–4)
1.7 (0.9) 27.4 (18.9) – –
4.5
2.3
2.7
6.9
3.9
4.7
2.9
1.8
48.3
13.1
4.2 (2.7)* 16.8
18.2
20.3
17.2
51.9
21.6
23.6
6.8
4.2
32.7
19.3 (6.8)* 0
0
0
20
0
0
0
0
45
30
0 (20) 1
2
2
1
0
2
2
3
2
0
2 (1)
*Indicates a significant difference between HEMI and CONTROL groups (p  < 0.05).
IQR: interquartile range.
Data processing
Net torque was low-pass filtered at 100  Hz with a 6th-order
zero-lag Butterworth filter. EMG data were 10–400-Hz band-
pass filtered (4th-order zero-lag Butterworth filter), full-wave
rectified, and smoothed at 9 Hz to obtain the linear envelopes.
The co-contraction index was determined as the ratio (expres-
sed in percentage) between the root mean square value of the
elbow flexors EMG envelopes during the sub-maximal elbow
extensions and the root mean square of the same muscle during
the highest maximal voluntary elbow flexion contraction (9).
Statistical analysis
Non-parametric analysis using Wilcoxon rank-sum test was per-
formed to compare the co-contraction index and the maximal net
elbow extension torque between HEMI and CONTROL groups.
Non-parametric Spearman’s correlations (r s ) were performed
to investigate the relationship between co-contraction index,
elbow-flexor spasticity, maximal net elbow extension torque
with: (i) limitation to active elbow extension, (ii) elbow-flexor
spasticity, (iii) Fugl-Meyer Assessment score for the upper
limb, and (iiii) Action Research Arm Test. It is notable that that
there was a significant difference in age between the HEMI and
CONTROL groups (Table I). However, preliminary analysis of
the data showed a lack of any correlation with age (p > 0.05),
enabling the results to be interpreted independently of age.
RESULTS
A higher co-contraction index occurred in the HEMI
group compared with the CONTROL group (w 19  = 3.4,
p < 0.01), with a mean difference (SD) of 7.6±12.9%.
Lower net elbow extension torque during maximal vol-
untary contraction was found in the HEMI compared
with the CONTROL group (w 19  = –2.34, p<0.05), with
a mean difference (SD) of 17.6 ± 17 Nm. Results of the
Spearman’s correlations are shown in Table III.
DISCUSSION
This pilot study aimed to elucidate the consequences of
spasticity and spastic co-contraction of elbow flexors
on limitation of active elbow extension in adults with
brain injury. A strong association was found between
the co-contraction index and (i) the limitation of ac-
tive elbow extension, (ii) the Fugl-Meyer Assessment
score, and (iii) the score on Action Research Arm Test.
Conversely, no significant correlation was found bet-
ween spasticity and any of the variables cited above.
These results are thus the first to show that spastic
co-contraction primarily contributes to a deficit in
active elbow extension in adults with brain injury,
which occurs even in the absence of spasticity (see, for
example, Table II, HEMI participants 5 and 10). These
findings confirm the absence of an association between
spasticity and spastic co-contraction, supporting the
idea that they refer to different forms of overactivity
with different underlying physiological mechanisms
Table III. Spearman correlations (95% confidence interval) for HEMI participants between co-contraction index, net elbow extension
torque during maximal voluntary contraction and clinical variables
Limitation of active elbow
extension
309
Co-contraction index during the sub-maximal
elbow extension
Elbow flexors spasticity
Net elbow extension torque during maximal
voluntary contraction
0.88** [0.59, 0.97]
–0.23 [–0.72, 0.42]
–0.26 [–0.74, 0.40]
Elbow flexors
spasticity
0.01 [–0.59, 0.60]
–
–0.49 [–0.92, –0.08]
Fugl-Meyer Assessment
score (upper limb) Action Research Arm
Test
–0.86** [–0.96, –0.53]
0.10 [–0.53, 0.66] –0.66* [–0.90, –0.09]
0.06 [–0.63, 0.56]
0.44 [–0.21, 0.82]
0.41 [–0.19, 0.80]
*Indicates a significant correlation at p  < 0.05. **Indicates a significant correlation at p  < 0.01.
J Rehabil Med 51, 2019