Effect of Induced Muscular Fatigue on Balance and Core Strength in Normal Individuals

Indian Journal of Physiotherapy & Occupational Therapy. July-September 2014, Vol. 8, No. 3

ABSTRACT

Background: Balance is the ability to maintain proper alignment of body segments with respect to each other. Muscular fatigue is a key factor which can influence performance via impaired joint proprioception and postural control. Fatigue alters the force generation capacity of the muscle and ultimately leads to task failure. The relationship between fatigue and balance is poorly understood.

The purpose of the present study was to assess if fatigue had an immediate effect on balance and core strength in healthy individuals, by checking the static and dynamic stability and the core muscle strength for spinal stability.

Aim: To find the effect of Induced muscular fatigue on Balance and Core strength in Normal Individuals.

Methodology: Functional reach tests, Single Leg Stance, Core strength were measured Pre and post Fatigue, which was induced by squats performed till RPE of 10. The data obtained was statistically analyzed using paired 't' test.

Results: A significant reduction was found in the mean single leg stance time from 10.05 seconds pre-fatigue, to 3.01 s post fatigue (p<0.05). The pre fatigue functional reach distance covered by individuals was 36.36 cms which was reduced to 29.48 cms post fatigue (p<0.05). There was also a reduction in the core muscle strength measured pre fatigue from 43.43 mmHg to 43.16 mmHg post fatigue statistically. (p<0.05)

Conclusion: Fatigue definitely has a significant reduction on Static balance, Dynamic balance & also on lumbar core strength as seen in normal individuals.

Keywords: Muscular Fatigue, Static Balance, Dynamic Balance, Core Strength

INTRODUCTION

Balance can be defined as the position of the body relative to the arrangement of the limbs and segments, for a specific activity, or the characteristic that one bears the weight of one’s body. It is the ability to maintain equilibrium in a gravitational field, and to react to destabilizing forces quickly and efficiently to regain stability via postural adjustments before, during, and after voluntary movement and in response to external perturbation. Balance, is maintained by the dynamic integration of internal and external forces and factors involving the environment. Specifically, balance can be classified as either static i.e. maintaining equilibrium with minimal movement, semi-dynamic i.e. attempting equilibrium while the base of support moves, or dynamic i.e. maintaining a stable base of support while completing prescribed movement. When an individual is in erect standing posture the integrity of stance is maintained by shifting body weight in multiple directions relative to corrective contractions of the muscles of the lower extremities and the trunk. Muscle fatigue is a complex phenomenon resulting in an exercise-induced reduction in the force-generating capacity of the muscles regardless of the task performed. The necessity of those con-tractions is expressed via the somatosensory, vestibular, and visual systems.

Impairments of the sensory systems have been associated with various pathological conditions, as well as transient physiological phenomenon, that increase the likelihood of fall or traumatic injury.

Fatigue, can affect the proprioceptive and kinaesthetic properties of joints, increase the threshold of muscle spindle discharge, which in turn disrupts afferent feedback and can alter joint awareness. The detrimental effect of fatigue on static balance has been established, but its effect on dynamic balance is unknown. To examine the ways in which fatigue affects balance, some authors have induced generalized muscle fatigue via strenuous aerobic exercise or selective muscle-fatiguing protocols. 

The relevance of fatigue to joint stability is evidenced by the relationship between postural control and the endurance of the ankle, knee and back muscles. Studies have shown the influence of foot mechanics on proximal structures i.e. core and have been studied extensively. The influence of proximal stability on lower extremity structure is known. One of the studies initially proposed that stabilization of the pelvis and trunk is necessary for all movements of the extremities. Studies have identified trunk muscle activity before the activity of the lower extremities, which authors felt served to stiffen the spine to provide a foundation for functional movements. This tendency for core instability has been suggested to predispose females to lower extremity injury. Stronger core muscles may help keep ground reaction forces (GRFs) within an optimal range. Based on previous literature and current thought, we hypothesized that fatigue would demonstrate effect on balance of the individual and significant difference in core strength. Therefore, the purpose of this study was to find out the relation between muscular fatigue and balance in normal individuals, by evaluating the static and dynamic stability and also to find if there was any change in the core muscle strength for spinal stability post induction of fatigue.

METHOD AND METHODOLOGY

The current study attempted to determine whether level of fatigue had any effect on balance & on core strength in normal individuals. To do so, experimental study design was used for this study and the study was carried out on general population in an urban region. Study approval was obtained by the institutional ethical board and an informed consent was obtained from all the subjects.

Sixty volunteers (30 men and 30 women; age range, 18-25 years; mean age, 20 ± 1.78 years) were included in the study, they were tested twice (pre and post) during same session. Any subject who had suffered a musculoskeletal injury to a lower extremity or a head injury in the 6 months before testing was excluded from the study.

The Functional reach test and single stance were used to measure the static and dynamic balance. Core strength was measured using aneroid sphygmomanometer. Subjects reported for test sessions were familiarised with the study followed by data collection for Functional reach test, single leg stance and the core strength.

Functional reach test is the measurement of difference between arm’s length and maximum forward reach in standing with a fixed base of support. (Figure 1) The subject was asked to reach as far as possible from comfortable standing posture without taking a step, losing balance and lifting the heel.

Excursion of arm from start to finish was measured with the subject standing parallel to the wall with 10 centimeters base of support. Instructions were given to avoid protraction of shoulder, flex arm near to the wall to 90 degrees and contra lateral upper limb in neutral. 1st point at tip of middle finger on wall was marked. Maintain of reach for three seconds and then again measure at tip of the middle finger. (Figure 2)

Distance between 1st and 2nd point was recorded. For the Single Leg Stance, subject was asked to perform single leg stance barefoot with the dominant leg and on the firm surface (dominant leg was found out by the ball kick test). Instructions were given to keep both the knees apart, not to touch hands to the body and to look straight and focus on any object at a distance of 1 meter. (Figure 3) Balance time was recorded until the subject could maintain the above mentioned posture without any movement.

Core Strength was measured by the pressure biofeedback method using an aneroid sphygmomanometer. Subject, in crook lying, the Cuff placed under the lumbar spine area and inflated to 40 mmHg. Subject were asked to activate core muscles (tuck in) and maintain it between 40 to 50 mmHg for 10 seconds (not more than 50 mmHg as rectus abdominis gets activated, and not less than 40 as it indicates arching of the lumbar spine.) If subject was not able to hold for 10 seconds, then rest was given for 3 minutes and asked to hold again at a lower value for 10 seconds.

Then muscular fatigue was induced. Subjects were asked to perform 90 degree squats with upper limbs in 90 degrees flexion and to be continued till rate of perceived exertion reaches 10/10 (Modified Borg Scale) that is extremely strong. The subjects were instructed to squat, as if sitting on a chair in which tibia remains relatively vertical. Subject may experience musculoskeletal or cardio respiratory fatigue. After this immediately single leg stance, functional reach test and core muscle testing was repeated.

Post fatigue measurements were compared with pre fatigue levels in single leg stance, forward reach test and core strength as well. Paired t test was used to measure pre and post performances to find any significant effects on the dependent variables with alpha set at p </=0.05.

The data thus obtained was analysed for further statistical purposes.

RESULTS

DISCUSSION

The purpose of this study was to evaluate whether fatigue affects the balance which was tested by single leg test and functional reach distance for static and dynamic balance respectively. It shows that there is a significant reduction in the single leg stance time which means the ability of the individual to maintain a stable posture is reduced. Single leg stance represents a very important phase in a normal human gait cycle. Stance phase contributes to 40% of the gait cycle. Postural control or balance can be either static or dynamic, and refers to person’s ability to maintain a stable body and body segments in response to forces that threaten to disturb the body’s structural equilibrium. Reduction in the functional reach distance can be due to diminished ability to maintain balance when the Center of Gravity and Line of Gravity shift out of the base of support in a fatigued state. This requires eccentric and isometric muscle activity by both the type 1 and type 2 muscle fibers. The key elements of muscle performance are strength, power and endurance. Studies concluded the effects of fatigue appear to be condition specific, concurring with previously reported findings that showed fatigue had more of an effect with the tandem-foam and tandem-tremor conditions. Studies also concluded that local muscle fatigue is the diminished response of muscle to repeated stimuli and is reflected by a progressive decrement in amplitude of motor unit potentials. This occurs when a muscle repeatedly contracts either statically or dynamically against imposed load. Rate of perceived exertion is an individual’s potential limitation to fatigue and is the ability to quantify the amount of fatigue to which the subjects are subjected. It would be difficult to compare the effect of fatigue on postural stability if the degree of fatigue is varied across the investigations. To rectify this, we have used the Borg RPE scale in an attempt to quantify the amount of fatigue. The RPE scale may be used as a substitute to determine exercise intensity. Using the 15-point Borg RPE scale, study showed 10 to moderate work load.

In the present study, the imposed load was the persons own body weight. Ideal squat requires greater trunk flexion to maintain balance and stronger quads contraction to support the load of the pelvis posterior to the knee axis. In repetitive squatting there is fatigue of all lower limb muscles especially glutei, quadriceps femoris, hamstrings, planter and dorsi flexors. Fatigue of the calf and thigh muscles affect postural sway in standing. Hence, the force capacity of muscles was altered. The effect of moderate fatigue on dynamic balance requires control and additional demands. In later on assessing core strength there was a difference found in the lumbar core muscle strength from 43.43 mmHg to 43.16 mmHg which was statistically significant. Research showed a clear relationship between trunk muscle stability and activity and lower extremity movement. They concluded that Core stability may provide several benefits to the musculoskeletal system, from maintaining low back health to preventing knee ligament injury & also suggested that decreased core stability may predispose to injury and that appropriate training may reduce injury suggested to contribute to the etiology of lower extremity injuries. Studies concluded that Decreased lumbo-pelvic (or core) stability contributes to the etiology of lower extremity injuries. This prospective study compares core stability measures between genders and between athletes who reported an injury during their season versus those who did not. A combination of these strength measures could be used to identify athletes at risk for lower extremity injury.

Fatigue after prolonged exercise leads to reduction in muscle glycogen. This occurs even if sufficient oxygen is available to generate energy by aerobic pathways. Fatigue leads to increase level of blood and muscle lactic acid and increase in H+ concentration in the exercising muscles. All this alters the activity of myofilaments and impairs muscular performance even when the nerve impulses continue to fire. In all when all motor units are maximally activated, fatigue is accompanied by reduction in neural activity. Here as we also see that there is affection of the lumbar core muscles post squatting, thus local fatigue will have an effect at the same site but might also produce an effect at another site in the body. So this, if not considered can be harmful.

In our everyday life, fatigue can significantly affect our balance & stability function making us predisposed to falls & injuries. A reduced muscle support to the body post fatigue will also cause abnormal joint forces and thus markedly increase the frequency of strains, sprains etc. Fatigue at distal/ peripheral area also has an effect on our core stability making us at risk of back problems & spinal damage. Thus our everyday tasks & activities should be planned & organized so as to minimize the effects of fatigue on our musculoskeletal system as with our other systems. The level of fatigue should be considered and the person should not be pushed beyond their capacity as this will increase the chance of injuries and thus reduced performance.

CONCLUSION

Muscular Fatigue causes a significant reduction in Static & Dynamic balance and also has an effect on reduction in core strength as seen in normal individuals. These results highlight the importance of proximal stabilization for lower extremity.

 Shimpi Apurv P, Kharkar Supriya A, Talreja Ankita A

References and Article at:

http://www.indianjournals.com/ijor.aspx?target=ijor:ijpot&volume=8&issue=3&article=036