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
