Changes of forearm muscle activities in fast wrist movements during sustained
hand griping force
1
1
1
2
3
1
Masuo Muro , Chigaya Tadano , Kiyotaka Kamibayasi , Masae Yona , Hiroyuki Seki , Kazuyuki Oka
1
Toho University School of Medicine, Japan
2
Tokyo College of Pharmacy, Japan
3
Niigata Management , Japan
Introduction
The co-activation of the extensor and flexor muscles of the wrist movements requires a precise tuning of the central
and peripheral inputs which control the motoneurones of synergist and antagonist muscles. In ball’s sports, the fast
wrist movements require a sustained level of hand prehensile force to reduce the possibilities for injuries such as
epicondylitis. The effects of the co-contraction of forearm muscles have been investigated so far in terms of the short
latency component of the stretch reflex, but the long latency reflex is not analyzed in the co-activation with the wrist
movements during co-activation of antagonist extensor and flexor muscles (hand clenching). The purpose of this
study was to examine how EMG activities of the antagonist muscle change when the fast wrist movement was
performed during the sustained hand griping contractions.
Methods
Experiments were performed on dominant arm of eight healthy male aged 22 – 52 years. Each subject was instructed
to grasp the gripping device as similar tennis racket grip size. The subjects were asked to perform the wrist flexion
and extension movements during various sustained hand griping contractions (20% - 100% MV C), that to perform
three trials as fast as possible. Each movement was performed to before- and after muscle fatigue that was
performed intermittent contractions (50%MVC) for 10 minutes. EMG activity was recorded from electrode (φ2) placed
on the skin over the extensor carpi radialis (ECR) and the flex-or carpi ulnaris (FCU) by mono-polar lead technique.
The baseline for muscle activity was the average EMG activity in the 15msec interval. We measured, in particular, the
peak amplitude and latency of averaged EMG in synergist and antagonist muscles (M2 & M3 components) for each
trial.
Relative latency after fatigue (% of control)
Relative amplitude after fatigue (% of control)
Results
at lexion
at extension
at flexion
at extension
The sustained hand griping force at the fast wrist
350 M1
350 M1
ECR
FCU
ECR
FCU
300
300
movement increases rapidly in the flexion more than the
250
250
extension. After fatigue of the forearm muscles, the
200
200
150
force decreased clearly at the fast wrist flexion. The
150
100
100
antagonist EMG activities (M1, M2, M3) enhance in the
50
50
ECR more than the FCU when the antagonist was
0
0
extended at these wrist movements. The EMG activities
250
250
M2
M2
200
200
of both the ECR and FCU increased gradually with
150
150
increase of the sustained hand griping contractions.
100
100
The latency of the EMG activities was prolonged also in
50
50
0
0
the ECR more than the FCU.
250
250
After fatigue, the antagonist EMG activities (M1, M2,
M3
M3
200
200
M3) decreased in ECR at 20%MVC (hand clenching),
150
150
but that increased in FCU at 20-40%MVC. The latency
100
100
50
50
of EMG activities (M1, M2, M3) was prolonged in both
0
0
ECR and FCU at 20-40%MVC. In particular, the latency
20%MVC 40%MVC
20%MVC 40%MVC 20%MVC 40%MVC
20%MVC 40%MVC
of FCU extended markedly in the stretch reflex (M1) at
Fig. 1. The relationships of the short latency stretch
20-40%MVC.
reflex (M1) and the long latency responses (M2 & M3)
The relationship between the onset of co-activation of
to the fast wrist movements during hand clenching
antagonist extensor and flexor EMG activities for the
(20% & 40%MVC).
sustained hand griping contraction levels (20-60%MVC)
was correlated significantly in the fast wrist flexion
(r=0.692), but that was not correlated in the fast wrist extension. After fatigue of forearm muscle, these relation was
correlated both the flexion and extension (r=0.662 and r=0.555).
Discussion/Conclusion
The agonist EMG activity was similar both the FCU and ECR, but the antagonist activity was difference between the
FCU and ECR at the fast wrist movements. This result will be estimated that the co-activation of the extensor and
flexor muscles at the fast wrist movements changes a precise tuning of the central and peripheral inputs which
control the motoneurones of synergist and antagonist muscles. We inferred from these changes that the antagonist
EMG activity increases clearly in ECR because the sustained hand griping force increases rapidly during the fast
wrist flexion, that the latency is prolonged also in ECR because of similar condition. Therefore, these results suggest
that strong hand clenching force during the wrist movements produce the possible injuries such as epicondylitis.
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