FATIGABILITY OF TRUNK MUSCLES WHEN SIMULATING PUSHING MOVEMENT DURING TREADMILL WALKING Yi-Ling Peng1, Yang-Hua Lin1, Hen-Yu Lien1 and Wen-Ke Chiou2 1 Graduate Institute of Rehabilitation Science, Chang Gung University, Taoyuan, Taiwan 2 Graduate Institute of Industrial Design, Chang Gung University, Taoyuan, Taiwan email:
[email protected] INTRODUCTION
In order to provide a clinical guideline of endurance test and fatigability in trunk muscles during pushing movement, the purpose of the present study was to demonstrate the effect of continuous pushing movement on trunk mus c l e s ’a c t i vi t ya ndf a t igability. METHODS Thirty healthy young adults would be expected in this program to perform treadmill walking with simulating pushing and without simulating pushing movement. Volunteers first perform walking with simulating pushing until reaching subjective assessment of trunk muscle fatigue by Borg CR-10 Scale, and at least a week later, return to carry out walking without pushing movement. In the walking with simulating pushing condition, volunteers are asked to pushing with their maximum pushing force, and visual and verbal feedback are provided to maintain the hand force. The electromyography signal of erector spinea (ES), multifidus (MF), rectus abdominis (RA) and external oblique (EO) muscles at both sides are collected by surface electrodes. Median frequency (MDF) and root-mean-square (RMS) are calculated in the initial, middle and final
(-)decease Hz (+)increase
15.00 ESr
10.00
ESl
5.00
MFr
0.00
MFl
-5.00
RAr
-10.00
RAl
-15.00
EOr
-20.00
EOl without pushing
with pushing
Figure 1: Median frequency (MDF) change in with pushing and without pushing conditions during treadmill walking. RMSratio change: final - initial
RMS ratio (-)decrease (+)increase
Pushing is a common movement in moving objects, and it also related to about 9% to 20% low back injuries occurrence [1]. During pushing, not only different pushing handle heights and pushing weights would influence the trunk muscle activity and lumbar spine compression force [2] [3], but also poor muscle endurance is a possible cause of low back pain.
MDFchange: final - initial
1.0 0.8 0.6 0.4 0.2 0.0 -0.2 -0.4 -0.6
ESr ESl MFr MFl RAr RAl EOr without pushing
with pushing
EOl
Figure 2: Root-mean-square (RMS) change in with pushing and without pushing conditions during treadmill walking. periods of both walking with and without simulating pushing conditions. Pushing force of both dominate and non-dominate hands are recorded by load cells, and Borg’ s scale are also noted in every thirty seconds. Two-way repeated measure ANOVA is used to compare the differences of MDF and RMS between the two conditions in three periods. The
difference of pushing force between initial and final periods is calculated by paired-t test. RESULTS AND DISCUSSION At present, MDF of ES, MF and RA decrease in both walking with and without simulating pushing conditions (figure 1). Time is a main factor of MDF in back extensors. MDF of ES (p=0.039) and MF (p=0.006) decrease with exercise time. However, condition is a main factor of MDF in trunk flexors. MDF of RA (p=0.004) and EO (p=0.047) is higher in walking without pushing than with pushing condition (table 1). RMS of ES, MF and RA increase only in simulating pushing condition (figure 2). There is no interaction or main effect of time and condition in all trunk muscles, rectus abdominus and external oblique (p>0.05) (table 2). MDF of trunk extensors decreased with time demonstrated muscle fatigue. RMS increased in trunk flexors in walking with simulating pushing condition indicated more muscle activities involved at the final period.
CONCLUSIONS MDF and RMS changes showed different trends in walking with and without pushing conditions. Besides, there were different factors to affect MDF on trunk flexors and extensors. Time is a main factor of MDF in back extensors and condition is a main factor of MDF in trunk flexors. REFERENCES 1.Hoozemans MJ, et al. Pushing and pulling in relation to musculoskeletal disorders: a review of risk factors. Ergonomics 41, 757-81, 1998. 2.Hoozemans MJ, et al. Mechanical loading of the low back and shoulders during pushing and pulling activities. Ergonomics 47, 1-18, 2004. 3.Lee PJ and Granata KP. Interface stability influences torso muscle recruitment and spinal load during pushing tasks. Ergonomics 49, 235-48, 2006. ACKNOWLEDGEMENTS This work was supported by National Science Council (NSC96-2314-B-182-024)
Table 1: Mean and SD of MDF in tree periods of walking with pushing and without pushing conditions. Condition with pushing MDF (Hz) Initial Middle Final Trunk extensors ES 134.56±15.06 131.72±13.81 129.78±16.11 MF 134.42±23.18 132.45±19.78 125.73±15.92 Trunk flexors RA 140.22±17.52 134.30±17.97 128.48±21.91 EO 109.80±11.82 107.20±8.82 108.08±6.94
Condition without pushing MDF (Hz) Initial Middle Final
Main effect Condition Time p p
139.62±6.04 145.15±20.73
132.18±4.07 139.65±13.75
129.01±11.12 130.36±17.40
p=0.685 p=0.192
p=0.039 p=0.006
158.01±14.92 113.91±10.48
146.86±36.47 117.88±9.88
151.42±23.56 121.02±6.28
p=0.004 p=0.047
p=0.230 p=0.063
Table 2: Mean and SD of RMS in tree periods of walking with pushing and without pushing conditions. Condition with pushing RMS Initial Middle Final Trunk extensors ES 1.481±1.178 1.577± 1.443 2.046± 2.210 MF 1.581±1.196 1.666±1.231 1.846±1.689 Trunk flexors RA 0.410±0.373 0.648±0.495 0.563±0.246 EO 0.820±0.670 0.769±0.240 0.557±0.164
Condition without pushing RMS Initial Middle Final
Main effect Condition Time p p
1.352±0.841 1.556±1.099
1.295±0.804 1.441±0.732
1.130±0.865 1.338±0.911
p=0.301 p=0.528
p=0.681 p=0.975
0.121±0.058 0.518±0.189
0.339±0.472 0.463±0.228
0.180±0.148 0.379±0.159
p=0.075 p=0.09
p=0.077 p=0.117
