Previous researches have shown that the localized fatigue of trunk extensor muscle would significantly reduce static and dynamic postural stability, which would lead to loss of balance. Thwas was a major concern for certain occupation, neuromuscular conditions and geriatric population, so the study was carried out to determine influence of trunk extensor muscle fatigue on postural stability in healthy young adults.
70 healthy young individuals of Age group 20 -25 yrs were asked to perform one leg standing test and functional reach test before and after a session of dynamic trunk extension until exhaustion and the difference in test scores was documented and analysed. It was found that Trunk extensor muscle fatigue significantly reduces static and dynamic postural stability in both OLST and FRT scores.
There was an influence of trunk extensor muscle fatigue on postural stability in healthy young adults.
Keywords:
Muscle is a soft tissue that contains protein filament of actin and myosin that slide past one another producing a contraction that changes both length and shape of cell.
Cardiac muscle- are located in the walls of heart and are under voluntary control.
Smooth muscle- are located in walls of hollow vwasceral organ, except heart and are under involuntary control.
Skeletal muscle – occur in a muscle which are attached to skeleton, and are under involuntary control.
Unipennate- here fasciculi are attached obliquely to its tendon. e.g Extensor digitorum longus.
Bipennate- here fasciculi are set on both sides of central tendon. e.g Rectus femoris.
Multipennate- here oblique fibres insert on several tendon. e.g Deltoid.
They fatigue slowly.
Work on oxidative mechanwasm, are aerobic muscles.
Also called tonic or postural muscles.
They are used in endurance work.
Fatigue rate was moderate.
Work on glycolytic metabolism, are anaerobic muscles.
Fatigue at fast rate.
Work on glycolytic metabolism are anaerobic muscles.
Also known as mobility or phasic, muscles.
Rectus Abdominus.
External Obliques.
Internal Obliques
Transversus Abdominus.
Quadratus Lumborum.
ErectorSpinae.- Iliocostalwas,Longwassimus,Splinalwas
Splenius.
Multifidus
The sustained maintenance of erect bipedal stance was unique to humans. The erect standing posture allows persons to use their upper extremities for the performance of large and small motor tasks.
For a weight-bearing joint to be stable, or in equilibrium, the gravity line of the mass must fall exactly through the axis of rotation, or there must be a force to counteract the moment caused by gravity. In the body, the counterforce was provided by either muscle or inert structures. In addition, the standing posture usually involves a slight anterior/posterior swaying of the body of about 4 centimeters (cm), so muscles are necessary to control the sway and maintain equilibrium. An increased sway was indicator of decreased sensorimotor control.
It is a dynamic activity with the neurosensory system contributing to postural control such as visual, proprioception and vestibular systems. Also individual factors such as age, sex and fatigue affects postural control. [42]
“Postural control, which can be either static or dynamic, refers to a person’s ability to maintain stability of the body and body segments in response to forces that threaten to disturb the body’s equilibrium. According to Horak and associates, the ability to maintain stability in the erect standing posture was a skill that the central nervous system (CNS) learns, using information from passive biomechanical elements, sensory systems, and muscles. The CNS interprets and organizes inputs from the various structures and systems and selects responses on the basis of past experience and the goal of the response. Reactive (compensatory) responses occur as reactions to external forces that dwasplace the body’s center of mass (CoM). Proactive (anticipatory) responses occur in anticipation of internally generated destabilizing forces” [44]
In numerous studies in young adults, it was seen that postural control was altered, characterized by increase in COP (center of pressure) sway dwasplacement and/or COP sway velocity across several tasks (eg. unipedal stance, bipedal stance, eye open, eye closed) following fatigue of ankle (Vuillerme et al 2001) knee (Gribble and Hertle 2004) hip (Gribble and Hertel 2004), back (Davidson 2004) and neck (Gosselin 2004) muscle groups. [4, 31, 33]
None of the authors have reported any falls during their studies, so, we can say that postural control may not be altered enough after fatigue to lead to fall, but it could decrease ability to perform a second task while standing and/or respond to sudden perturbation.
Fatigue was a state during which a person was unable to carry out a sustained activity any longer after performing it repeatedly for sometime.
Various definitions of fatigue have been framed. One of the oldest definitions of fatigue framed by
Other definitions have been framed by various authors which are stated below,
The amount of force that muscle can produce depends on; size of muscle, number of muscle fibres, type of fibres and number of fibres per motor unit.
LOCAL FATIGUE - fatiguing of particular muscle or muscle group.
Central fatigue: the sites of central fatigue are the central nervous system including the motor cortex of brain, spinal cord, anterior horn cell, and the cardio respiratory organs such as heart, lungs, etc. Fatigue occurs when transmission of impulses and energy requirements was slowed down at these sites.
Peripheral fatigue: the sites of peripheral fatigue are the neuromuscular junction, the local vasculature and the skeletal muscle itself. Here there will be a disruption in the coupling-contraction mechanism, a deficit in energy production mechanisms or the dissruption of impulse transmission at the NMJ.
GENERAL FATIGUE - fatiguing of more than one muscle. The whole body performs sluggishly and demands a period of rest.
Therefore, it was evident that fatigue has significant negative impact on postural control. Fatigue was measured by Maximal Voluntary Contraction of group of muscles or % of MVC; but currently best way to measure fatigue was Rate of Perceived Exertion. When MVC was reduced to 25-30%, local fatigue affects postural control.
Previous researches show that the localized fatigue of trunk extensor muscles significantly reduce static and dynamic postural stability, so the study was carried out to determine influence of trunk extensor muscle fatigue on postural stability in healthy young adults.
To study the influence of trunk extensor muscle fatigue on postural stability in healthy young adults.
To determine influence of trunk extensor muscle fatigue on postural stability in healthy young adults using clinical measures.
To know the time period for which effect on postural stability by trunk extensor muscle fatigue perswasts.
The study design was a experimental study deisgn with a sample size of 70 persons. Convinient sampling technique was used. The study was carried out a tertiary care hospital in a duration of six months. Inclusion criteria was- healthy young individuals aged 20-25 years and both males and females were included in the study. Exclusion criteria was individuals suffering from low back pain, individuals having any musculoskeletal, cardiorespiratory or neurological conditions and individuals with vestibular impairments. Two outcome measures were used to assess the static balance one leg standing test and functional reach test.
One leg standing was performed on firm surface with subject standing on the dominant leg and other leg was flexed at the knee, with both hands crossed across chest, with eyes closed, time noted in seconds. Time of one leg standing was recorded in seconds using a stopwatch. Test was terminated when the subject used his arms (i.e., uncrossed arms), used the raised foot (moved it toward or away from the standing limb or touched the floor), moved the weight-bearing foot to maintain balance (i.e., rotated foot on the ground), or opened eyes. Three attempts were given and the best was selected. [20]
For the performance of dynamic trunk extension until exhaustion, the subject was made to lie prone on bench in horizontal plane with upper body unsupported and lower body supported, and both hands were across the chest. The subject was asked to perform continuous trunk extension until maximum exhaustion and a metronome device was used to check if the subjects were performing extension at consistent rate. The subject was asked to stop when he/she felt discomfort or pain.
For recovery time the FRT and OLST were performed every three minutes until the scores reached that of non fatigue condition.
Both the tests are performed in all three conditions (No fatigue, Fatigue, Recovery)
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Table No.2 shows mean of one leg standing test in all three conditions (No fatigue, Fatigue, Recovery).
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Table No.3 shows mean of functional reach test in all three conditions (No fatigue, Fatigue, Recovery)
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Here OLST showed decrease from No fatigue to fatigue condition
Here FRT showed decrease from No fatigue to fatigue condition, hence there is decrease in postural stability.
Table no.1 shows mean of Age i.e 21.50±1.43, BMI i.e 21.08±3.64, Recovery time i.e 77.23±45.01
Table no.2 shows significant difference between No fatigue and Fatigue condition with p value 0.00 and also there is no significant difference between No fatigue and recovery condition with p value 0.30; hence postural stability was hampered due to fatiguing of muscle. The figure 3 shows the graphical representation of the same.
Table no.3 shows significant difference between No fatigue and fatigue condition with p value 0.00 and also there is no significant difference between No fatigue and recovery condition with p value 0.39; hence postural stability hampered due to fatiguing of muscle. The figure 4 shows the graphical representation of the same.
The present study was carried out to investigate influence of trunk extensor muscle fatigue on postural stability in healthy young adults, and the results obtained suggest that the applied fatigue protocol affects static and dynamic postural stability as indicated by reduction in OLST and FRT scores from No fatigue to Fatigue condition.
Taylor JL, et al in 2000 suggested that fatigue is a reduction of maximal muscle force or power that occurs with exercise and is accompanied by changes at multiple levels in the motor pathway and also by changes in the discharge patterns of muscle afferents. Changes in afferent firing can lead to altered perceptions and can also act on the efferent pathway. Changes in the motor pathway include slowing of motor unit firing rates during sustained maximal voluntary contractions (MVCs). [17] Schieppati M, et al in 2003 performed a similar study in which a fatiguing task of neck extensors was performed following which an increase sway of subjects compared to controls was observed. The sway returned to normal after recovery. [30]
The effects of muscle fatigue on postural control depend upon muscle group involved in task and applied fatigue protocol. Trunk extensors are physiologically postural muscles being rich in type 1 muscle fibers [22-24]. Erector spinae and multifidi are found to be tonically active in quite standing and erector spinae contract eccentrically to control trunk flexion from standing position and also when head or upper limb is moved forward. It has been suggested from studies that muscular strength and sensory detection are two important factor in fatigue protocol [11-13, 25, 26]. In fatigue condition, there is decline in muscle force output compromising ability of musculoskeletal system to adjust the body posture. Previous studies have shown that a decline bigger than 30% of maximum isometric force after a fatigue protocol is enough to compromise postural control [10]. Similarly, muscle metabolites produce during task until exhaustion contribute to postural control impairment. [17]
One leg standing is associated with decreased inherent stability, because of adjustment of COG over short narrow BOS. In one leg standing, due to reduced somatosensory information and decreased inherent stability results in more dependence on visual and proprioceptive input from other postural muscles of body. In this study OLST, was performed under eye closed condition, thus vision was removed from contributing to task of postural control. As subjects stood on firm surface and head was aligned upright, vestibular was not affected by neuromuscular fatigue. Considering more dependence on proprioceptive inputs from these muscle during one leg stance, compare to role of trunk musculature strength, there is decrease in static stability during OLST observed in study, therefore diminished proprioceptive feedback from fatigue trunk extensors. In this study FRT was used as a measure of dynamic stability.
Bisson, E.J., et al in 2010 performed a study which showed increased sway in CoP after ankle fatigue. [45] José Alberto dos Santos Rocha, et al found that the applied fatigue protocol was not able to modify the postural control, as well as the capacity of integrating sensorial information in the absence of vision, of young healthy subjects. Their results indicate that proprioceptive information remains reliable after the used fatigue protocol, allowing subjects to keep a satisfactory straight posture. But the protocol used was different. Recent studies show that muscle fatigue results in decrease in level of muscle excitation and early onset of APAs (anticipatory postural adjustment). Early APA’s counteract fatigue, induce decrease in force producing capability of muscle that contribute to postural stability. It reduces the impact that fatigue has on body during various dynamic perturbations. It is documented that fatigue in extensor muscles of trunk reduces trunk’s local dynamic stability [39, 40]. It is seen in previous studiesthat 50%or more decrease in MVC resulted in balance deterioration. Fatigue protocol produces desired fatigue in all subjects as indicated by rating of 10.53 ±2.47 on RPE scale. The time period for which trunk extensor muscle fatigue persists in both OLST and FRT is 77.23±45.01 i.e 1 min 17sec.
Trunk extensor muscle fatigue significantly reduces static and dynamic postural stability in both OLST and FRT. So, alternate hypothesis is accepted in our study as there is influence of trunk extensor muscle fatigue on postural stability in healthy young adults.
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