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Indian Journal of Physiotherapy and Occupational Therapy

Balance deficits and recovery timeline after different fatigue protocols

Author(s): Pallavi Khanna, Gagan Kapoor, Kalpana Zutshi

Vol. 2, No. 3 (2008-07 - 2008-09)

Pallavi Khanna1, Gagan Kapoor2, Kalpana Zutshi3

1Post Graduate Physical Therapy Student (Sports Medicine), Jamia Hamdard 2Senior Sports Physiotherapist 3Physical Therapy Lecturer (Sports Medicine), Jamia Hamdard

Background and purpose: Balance is affected after fatigue protocol consisting of aerobic and anaerobic exercises and balance recovers within 20 minutes. The purpose of this study is to evaluate what is the effect of various fatigue protocols i.e. aerobic, anaerobic and mixed fatigue protocol on balance and recovery time line for balance.

Method: 30 active, normal subjects participated in the study. Each subject performed aerobic, anaerobic and mixed fatigue protocol on different days. Balance was assessed by balance error scoring system (BESS) for three stances, double leg, single leg and tandem on two surfaces, firm and foam.

Each trial lasted 20 seconds. Using the Borg scale rating of perceived exertion (RPE) was also measured for level of physical exertion. Pretest balance reading was taken then the subject performed the specific fatigue protocol and then balance was assessed immediately after the protocol (Posttest 1), 5 minutes after the protocol (Posttest 2), 10 minutes (Posttest 3), 15 minutes (Posttest 4) and 20 minutes (Posttest 5) after the protocol.

Data analysis: The General Linear Model Repeated Measures Analysis of Variance (ANOVA) was used to examine the conditions separately for balance and perceived exertion. Bonferroni Post hoc analysis was done if there was significant difference. One-way ANOVA was used to compare balance and exertion scores between conditions. Post hoc analysis for between conditions was done for comparison. The significance level set for this study was p<0.05.

Results: The results show that balance is affected after different fatigue protocols as evident in BESS posttest reading 1 which is increased after fatigue in all the protocols and balance recovers in 15 minutes after aerobic fatigue protocol, 10 minutes after anaerobic fatigue protocol and 20 minutes after mixed fatigue protocol. Similarly rating of perceived exertion score is also increased after fatigue and recovers the same way as balance.

Discussion and conclusion: Aerobic, anaerobic and mixed fatigue protocols all had effect on balance and balance recovers from these protocols within 20 minutes of rest. This information can be applied to the athletic population where the coaches can design a training program in such a way that fatigue does not interfere with performance ability and does not increase the chances of injuries.

Keywords: Balance, fatigue, aerobic protocol, anaerobic protocol, mixed protocol, recovery

Introduction

Balance is a complex task that requires intact information from somatosensory, visual and vestibular system and an intact central nervous system to maintain upright stance1,3. Balance can be defined as ability of body to maintain equilibrium and orientation within the base of support7,17,18,21.

First stimuli from visual, vestibular and somatosensory sources are required to contribute information about the body’s position in space. The three sub components of the balance mechanism collect peripheral information to maintain balance. Afferent information collected by these systems is transferred to the central nervous system, where differing anatomical regions of the brain integrate the signals and produce a motor output. The basal ganglia receive the first inputs and begin a motor response based on the current position of limbs. The signal is integrated with the planned actions of the motor cortex in the cerebellum, where motor impulses are coordinated. A final efferent signal is generated and transmitted through the brainstem to alpha motor neurons. These nerves innervate the skeletal muscles that maintain posture and balance24.

Thus coordinated responses to stimuli must be transmitted to the appropriate muscles to produce corrective movements in certain joints to balance a standing position. Proper balancing movements of separate body segments are essential in maintaining upright stance, firstly to stabilize the body segments and secondly to enable the necessary dynamic changes of the body3.

Since the human body is never stable a control system is required to stabilize the body. Here comes the concept of postural control that helps to keep the body close to equilibrium point3. The postural control system involves the complex organization of many senses that are related by central nervous system to many muscles that act on multilinked musculoskeletal system4.

Balance is a static as well as dynamic process. Thus balance / postural control can be static or dynamic depending upon whether the base is static or dynamic5. Postural control helps to keep the body’s center of gravity within borders of base of support. Overall goal of balance control system is stability and function.

In normal circumstances minimal or no active muscle contraction is required to maintain equilibrium. An external disturbance of the body brings into play anticipatory postural reflexes even before the COG shifts. If however these various anticipatory responses are insufficient then a collection of righting reflexes are brought into play to protect balance. Such postural reactions are triggered by muscular, vestibular or visual cues about body imbalance. Finally if anticipatory postural responses and righting reflexes are insufficient to prevent falling, the normal subjects will engage in a series of protective reflexes to prevent damage when falling for example the arms are thrown out to cushion the landing24.

Reactive control occurs in response to external forces (threats, perturbations) displacing the center of gravity or movements of base of support6.

Proactive control (anticipatory) occurs in anticipation of internally generated destabilizing forces imposed on body’s own movements6.

An individual’s prior experiences allow the various elements of postural control system to be pretuned or readied for upcoming movements. Postural stability is needed in most activities of daily living and major contribution to performance in sports such as golf, gymnastics, shooting, basketball, and soccer7.

Balance movements involve a number of joints such as hip, knee, ankle and coordinated movement along kinetic chain. In event of balance disruption body must be able to determine what strategy to utilize in order to maintain balance.

A variety of methods have been developed to assess postural stability both subjectively and objectively including Romberg Test, Functional Reach Test, Get Up and Go Test, Chattecx Balance system22 and more recently Balance error scoring System (BESS)1,2. BESS is a clinical field test that was developed to provide health care professionals with an inexpensive and objective way to assess postural stability outside laboratory1,2,8. BESS measures postural stability through a clinical assessment battery and is scored by counting the number of errors the subject commits during the test.

Advantages of BESS are that it is less expensive than force platform system and requires less training for effective administration. It is a valid and reliable method as has been proven already.

Factors that impact postural stability include muscular weakness, proprioceptive and range of motion deficits. Fatigue also affects balance. If inaccurate information is provided by any of the three sensory systems because of local fatigue and central nervous system is disturbed through central fatigue and compensation is inadequate balance is disturbed1,2.

Thus Postural stability decreases after isolated muscle fatigue and whole body fatigue (central fatigue). Any form of exercise results in fatigue that is caused by combination of physiologic processes that occur at both central and peripheral levels.

Nardone et al17 noted significant increases in sway path in both eyes closed and eyes open condition, and increases in sway area in eyes closed condition after 25 minutes exhausting treadmill run.

Johnston et al 30 found that fatigue affects ability of an individual to maintain balance on an unstable platform device and fatigued individuals are at increased risk of injury.

Lepers et al18 studied the influence of prolonged exercise on postural control as assessed by dynamic posturography. He found that the ability to maintain balance under conflicting sensory conditions was decreased immediately after 25 km run.

Ludin et al32 examined the effects of plantarflexor and dorsiflexor fatigue on postural control. The fatigue protocol resulted in significant increase in mediolateral postural sway amplitude and increase in anteroposterior postural sway. Numerous variables including postural stability, maximum voluntary contraction force, and reaction time have been studied in conjunction with fatigue protocols to understand how fatigue affects body balance and ability of body to function or perform. These studies have measured postural stability using expensive computerized equipments. Now it has been proven that BESS is a clinical field test that can be used to assess balance1,2,8.

Fatigue (central and peripheral) is a complex interaction of physiological, chemical, sensory and psychological feedback9. The factors that contribute to fatigue from voluntary activity are numerous and interact in a complex multifactorial phenomenon.

The lack of singular factor inducing fatigue points to multitude of mechanisms that protect muscles. These factors decrease the muscle force that occurs during exercise.

The decrease in muscle force leads to decrease in working capacity and represents an internal perturbation to motor system. It can therefore produce impairment in motor coordination and possible postural control.

It is known that small differences in postural sway or body balance because of fatigue or physical exercise might have important effects on outcomes of performance9.

Fatigue is one of the most important factors that limits sustained exercise in sports. Fatigue is often associated with increased clumsiness10. Immediate effect of fatigue is reduction in ability to apply muscle force. Reduced ability can impair efficiency of muscle, skill and performance11.

Improved performance is related to reduction or delay in onset of fatigue. Studies have shown relationship between performance under fatigue and increased incidence of injury16.

Rating of Perceived exertion can be used to detect and interpret sensations arising from body during physical exercise. The evaluation of physical effort during exercise is based on two factors: local factor related to feeling of strain in the exercising muscle and/ or joints and central factor related primarily to sensations or feelings from cardiopulmonary system23. 15 Point Borg scale has been recommended for investigations of perceived exertion and for predictions of exercise intensities26.

The concept of specificity can be extended to fatigue, that is, specific exercises lead to specific mechanisms of fatigue. Thus the effect depends upon the type of exercise and intensity and duration of work12.

High intensity short duration exercises are associated with rapid recovery from fatigue whereas long duration exercises have prolonged recovery time from fatigue. So it can be said that different duration, intensity and exertion levels of exercise leads to difference in recovery time for balance deficit.

It has been shown that balance recovers within 20 minutes after fatigue protocol that consisted of both anaerobic and aerobic exercises for 20 minutes duration1,2. But it has not been studied yet what effects specific fatigue protocols such as aerobic, anaerobic have on balance and if balance is affected after how much time it is regained. This information can be useful when applied to the athletic population where the coaches can design a training program in such a way that fatigue does not interfere with performance ability and does not increase the chances of injuries.

The purpose of this study is to evaluate what is the effect of various fatigue protocols i.e. aerobic, anaerobic and mixed fatigue protocol on balance and recovery time line for balance.

Method

30 active normal subjects participated in the study. Each subject participated in each of the three groups of conditions (Condition A, Condition An, Condition M). The names of the group denote type of fatigue protocol (A – Aerobic, An - Anaerobic, M – Mixed) they are subjected to.

Condition A – aerobic fatigue protocol till exhaustion.
Condition An – anaerobic fatigue protocol till exhaustion.
Condition M – mixed anaerobic and aerobic fatigue protocol for 20 minutes.

Inclusion criteria

  1. Active normal individuals not undergoing any kind of physical training.
  2. Age group: 20-25 year
  3. Male subjects.

Exclusion criteria

  1. Any visual, balance or vestibular disorder
  2. Head injury within last 6 months
  3. Musculoskeletal lower extremity injury within last 6 months
  4. Cardiovascular or pulmonary dysfunction.

Method of selection

Subjects were selected based on the inclusion and exclusion criteria. All the subjects were made aware of the purpose and procedure of the study. A signed informed consent was obtained from the prospective candidates before their participation.

Each subject was asked to participate in all the three fatigue conditions (Condition A, Condition An, Condition M).

Design of the study

Design of the study is experimental, same subject design with pre test posttest design where each subject participates in all three fatigue conditions.

Instrumentation and tools for data collection Treadmill in which speed and grade can be varied, Digital stopwatch for noting the time during balance assessment, 12-inch step and Medium density foam block. (46 × 46 × 13 cm).

Independent variables

Mixed Fatigue Protocol

7-station exertion protocol designed by Wilkins et al1 was used. Station 1 was a 5 minute jog at the subject’s self selected pace. Station 2 was sprint up and down the basketball court for 3 minutes. Station 3 was 2 minutes of push-ups. Station 4 was 2 minutes of sit-ups. Station 5 was 3 minutes of 12-inch step-ups. Station 6 was another 3 minutes of sprints. Station 7 was 2 minute run during which subjects were instructed to maintain the fastest pace they could for entire 2 minutes. All subjects were given verbal feedback in an attempt to maintain high level of exertion throughout the entire exertion protocol.

Aerobic Fatigue Protocol

The standard Bruce protocol was used20. The athlete ran on a treadmill to exhaustion. At timed stages during the test the speed (km/hr) and grade of slope (%) of the treadmill were increased as detailed.

The treadmill was set up with the Stage 1 speed (2.74 km/ hr) and grade of slope (10%) and the athlete commenced the test. At the appropriate times during the test the speed and slope of the treadmill were adjusted. So after 3 minutes into the test the speed was adjusted to 4.02 km/hr and the slope to 12%, after 6 minutes into the test the speed was adjusted to 5.47 km/hr and the slope to 14%, and so on.

Stage Time (min) Speed (km/hr) Slope
1 0 2.74 10%
2 3 4.02 12%
3 6 5.47 14%
4 9 6.76 16%
5 12 8.05 18%
6 15 8.85 20%
7 18 9.65 22%
8 21 10.46 24%
9 24 11.26 26%
10 27 12.07 28%

The test continued until the patient got exhausted, that is he was not able to continue further.

Anaerobic fatigue protocol

The athlete undertook a warm-up on the treadmill for 5 minutes at self-selected moderate pace29. A few short practice starts getting onto the treadmill at the test speed were also performed. Then the treadmill was set at 8.0 miles/hr (13 km/hr) speed and incline of 20%. Then the athlete started running unsupported. The test continued until exhaustion, meaning the athlete was not able to maintain the speed required and was not able to continue further.

Dependent variables
Balance assessment

Balance Error Scoring System (BESS) was used to assess balance under 3 testing stances (double leg, single leg, and tandem) on 2 surfaces, firm and foam.1,2 In the double leg stance the participants stood with their feet together. In the single leg stance, participants stood on the non dominant leg (dominance determined by which leg they would prefer to kick a ball), with the contra lateral leg positioned in approximately 30 degree of hip flexion and 90 degree of knee flexion and foot held approximately 6 inches off the ground. In the tandem stance, participants stood with the dominant foot in heel toe fashion. Each stance was performed on firm surface and medium density foam block. The firm surface was the floor of the gym.

One 20 second trial of each test condition was performed and the order of BESS testing was counterbalanced across conditions for each subject so that the effects of fatigue would not be greater for one condition than another. The same order of testing was used for each subject pretest and posttests. Before testing all subjects were given a practice session for each condition to familiarize them with the actual test. The subjects were asked to keep their eyes closed and their hands on the iliac crest while maintaining the appropriate stance. The subjects were instructed that if any time they fell out of position, they were to return to the test position as quickly as possible, keeping their eyes open until they regained balance. As the subjects performed each 20-second trial, number of errors the subject made were recorded. During the testing the scorer stood 8 to 10 ft away from the subject so that the subjects eyes, hand and feet could all be observed.

One BESS error was scored if the subject engaged in any of the following:

  • Lifting the hands off the iliac crest
  • Opening the eyes
  • Stepping, stumbling or falling out of position
  • Moving the hip into more than 30 degree of flexion or abduction
  • Lifting the forefoot or heel
  • Remaining out of test position for more than 5 seconds

Rating of Perceived Exertion

Borg 15 point scale was used to measure each subjects Rating of Perceived Exertion (RPE) 19 in an attempt to quantify the amount of exertion displayed by each subject. The rating scale was in full view of the subject during the entire test. For all subjects RPE scores were monitored immediately before the intervention and then after the intervention according to different posttests. Validity and reliability of this scale has been proved through various studies.

Before noting the RPE scores the subjects were familiarized with the scale. They were told how to use the scale and what each number in the scale denotes. It was only after the subjects understand the proper use of the scale and how to rate their perceived exertion that the scale was used.

Borg’s 15-point scale can be described as

6 no exertion at all
7 very, very light
8
9 very light
10
11 fairly light
12
13 somewhat hard (feels tired but can continue)
14
15 hard (heavy)
16
17 very hard (very strenuous)
18
19 very, very hard (cannot continue further)
20 maximum exertion

Procedure

The subjects were selected according to the inclusion criteria. Each subject was explained about the purpose and significance of the study and only those who gave voluntary consent participated in this study.

All subjects were familiarized with the equipments, methods and different scales used in the study. They were given instructions about what they were supposed to do in each protocol and test and when to terminate the protocol. Each subject participated in all three test group protocols. There was two days rest interval between each test protocol. Randomization of protocols was done.

All subjects performed one practice session with BESS and familiarized themselves with RPE scores. They were then asked to self stretch as needed before testing to prevent injuries during balance testing and exertion protocol. They were then tested for balance using Balance Error Scoring System (BESS) and perceived exertion noted through Borg’s 15-point scale of Rating of Perceived Exertion (RPE).

The subjects in each of the test group were tested once before the exertion protocol (Pretest) and then the specific fatigue protocol was given depending upon the group in which they are on that particular day. The Condition A group performed Aerobic exercise protocol, Condition An group performed Anaerobic exercise protocol while Condition M group performed Mixed exertion Protocol.

The subjects in the aerobic and anaerobic test group were monitored for their exertion level and told to continue the test until they feel exhausted and cannot continue further and felt that their RPE score is around 19. At that time they stopped the test.

After completion of test protocol each test group was tested immediately for balance and perceived exertion (Posttest 1). Then again after 5, 10, 15 and 20 minutes each test group was tested for balance and perceived exertion (Posttest 2, 3, 4, 5).

All the subjects were tested three times on three different days and average of the readings was taken.

Data was collected in the gym and basketball court, under similar conditions for each of the subjects by the same investigator.

Data analysis

Using SPSS 11.5 software the General Linear Model Repeated Measures Analysis of Variance (ANOVA) was used to examine all the conditions together. Bonferroni Post hoc analysis was done for time if there was significant difference. The General Linear Model of repeated measures ANOVA was used to examine all the conditions separately for balance and perceived exertion. Bonferroni Post hoc analysis was done if there was significant difference. One-way ANOVA was used to compare balance and exertion scores between conditions. Post hoc analysis for between conditions was done for comparison.

The significance level set for this study was p<0.05.

Results

(Table 1.1,1.2,1.3,1.4)
Analysis of BESS scores for all the conditions taken together revealed significant time (F = 5620.06, p< 0.05), condition (F= 26.790, p<0.05) and time × condition effect (F=176.615, p<0.05).

Post hoc analysis of time for all conditions taken together revealed significant differences between pretest and posttest (p<0.05)

Analysis of RPE scores for all the conditions taken together revealed significant time (F= 16341.34, p<0.05), condition (F=445.18, p<0.05) and time × condition effect (F=337.29, p<0.05)

Post hoc analysis of time for all conditions taken together revealed significant differences between pretest and posttest (p<0.05)

Since the analysis for all the conditions taken together revealed differences for time and conditions the conditions were examined separately.

Table 1.1: Subject Characteristics

;Age (Mean ± S.D), years 22.27 ± 1.79
Height (Mean ± S.D), cm 172.07 ± 7.45
Weight (Mean ± S.D), kg 69.23 ± 7.27
Body Mass Index (Mean ± S.D), kg/m2 23.3 ± 0.95

Table 1.2: Condition A- Total BESS and RPE scores (Mean ± S.D), Figure 1.1, 1.4

  Pretest Posttest 1 Posttest 2 Posttest 3 Posttest 4 Posttest 5
BESS 16.31 ± 1.44 27.07 ± 0.97 23.84 ± 0.99 20.07 ± 0.99 15.81 ± 1.36 15.44 ± 1.39
RPE 6.34 ± 0.37 18.12 ± 0.39 14.31 ± 0.37 10.20 ± 0.41 6.34 ± 0.32 6.18 ± 0.15

Table 1.3: Condition An- Total BESS and RPE scores (Mean ± S.D), Figure 1.2, 1.5

  Pretest Posttest 1 Posttest 2 Posttest 3 Posttest 4 Posttest 5
BESS 16.36 ± 1.41 30.08 ± 0.99 23.02 ± 1.54 15.93 ± 1.34 15.72 ± 1.32 15.31 ± 1.32
RPE 6.66 ± 0.32 18.39 ± 0.46 12.87 ± 0.86 6.50 ± 0.20 6.36 ± 0.32 6.24 ± 0.25

Table 1.4: Condition M- Total BESS and RPE scores (Mean ± S.D), Figure 1.3, 1.6

  Pretest Posttest 1 Posttest 2 Posttest 3 Posttest 4 Posttest 5
BESS 16.38 ± 1.37 28.69 ± 1.13 25.23 ± 0.99 22.52 ± 0.99 19.26 ± 0.84 15.75 ± 1.33
RPE 6.49 ± 0.37 18.09 ± 0.25 14.81 ± 0.23 11.76 ± 0.51 9.22 ± 0.34 6.29 ± 0.31

Condition A

Analysis of BESS score within the condition revealed significant differences (F=1846.75, p<0.05). Post hoc analysis of BESS score across pretest and different posttests revealed significant differences between pretest and posttest 1,2,3,4,5 (p<0.05), posttest 1 and posttest 2,3,4,5 (p<0.05), posttest 2 and posttest 3, 4 5(p<0.05), posttest 3 and posttest 4, 5(p<0.05), posttest 4 and posttest 5 (p<0.05)

Analysis of RPE score within the condition revealed significant differences (F=6454.197, p<0.05).

Post hoc analysis of RPE score across pretest and different posttests revealed significant differences between pretest and posttest 1,2,3,5 (p<0.05), posttest 1 and posttest 2,3,4,5

(p<0.05), posttest 2 and posttest 3, 4 5(p<0.05), posttest 3 and posttest 4, 5(p<0.05), posttest 4 and posttest5 (p<0.05).

There was insignificant difference between pretest and posttest 4 (p>0.05)

Condition An

Analysis of BESS score across time within the condition revealed significant differences (F=2157.50, p<0.05). Post hoc analysis of BESS score across pretest and different posttests revealed significant differences between pretest and posttest 1,2,3,4,5 (p<0.05), posttest 1 and posttest 2,3,4,5 (p<0.05), posttest 2 and posttest 3, 4 5(p<0.05), posttest 3 and posttest 4, 5(p<0.05), posttest 4 and posttest 5 (p<0.05)

Analysis of RPE score within the condition revealed significant differences (F=3988.65, p<0.05).

Post hoc analysis of RPE score across pretest and different posttests revealed significant differences between pretest and posttest 1, 2,3,4,5 (p<0.05), posttest 1 and posttest 2,3,4,5 (p<0.05), posttest 2 and posttest 3, 4 5(p<0.05), posttest 3 and posttest 4, 5(p<0.05), posttest 4 and posttest 5 (p<0.05).

Condition M

Analysis of BESS score within the condition revealed significant differences (F=1922.15, p<0.05).

Post hoc analysis of BESS score across pretest and different posttests revealed significant differences between pretest and posttest 1,2,3,4,5 (p<0.05), posttest 1 and posttest 2,3,4,5 (p<0.05), posttest 2 and posttest 3, 4 5(p<0.05), posttest 3 and posttest 4,5(p<0.05), posttest 4 and posttest5 (p<0.05)

Analysis of RPE score within the condition revealed significant differences (F=8728.70, p<0.05).

Post hoc analysis of RPE score across pretest and different posttests revealed significant differences between pretest and posttest 1, 2,3,45 (p<0.05), posttest 1 and posttest 2,3,4,5 (p<0.05), posttest 2 and posttest 3, 4 5(p<0.05), posttest 3 and posttest 4, 5(p<0.05), posttest 4 and posttest 5 (p<0.05).

Between Conditions

One way ANOVA was used to compare the balance error scoring system score and rating of perceived exertion score for between conditions, aerobic, anaerobic and mixed. Post hoc analysis was also done for between condition comparisons, aerobic with anaerobic protocol, aerobic with mixed protocol and anaerobic with mixed protocol.

It revealed that the three conditions had effect on balance and rating of perceived exertion that was according to the condition performed and that the recovery time was different for three conditions.

Discussion

Overall findings demonstrate a decrease in balance and postural stability possibly as a result of fatigue from three different fatigue protocols as measured by total Balance Error Scoring System (BESS) scores and an increase in exertion level as measured by Rating of Perceived Exertion. A decrease in postural stability after fatigue has been found in previous studies using both central1,2,7,18,31 and local means of fatigue2,30 and different measures of postural stability.

Different sports have different metabolic demands and thus, athletes experience different levels of exertion. We used different fatigue protocols, aerobic, anaerobic and mixed protocol of aerobic and anaerobic exercises. The aerobic, anaerobic fatigue protocols were designed in such a way that athlete would stop exercising when he felt exhausted and fatigue was thus induced and the mixed protocol was the same as used by Wilkins et al2 in his study.

The protocols chosen were those that would replicate the fatigue athletes experience during the course of game orpractice and fatigue leads to decreased motor control so it is reasonable to hypothesize that fatiguing exercise will have an effect on postural control.

Although fatigue effect on balance has been studied using force platform systems or sensory organization tests and other computerized equipments, only few studies have used BESS performance to study the influence of fatigue protocol on balance1,2.

Wilkins et al2 studied effect of fatigue protocol consisting of sprinting, jogging, step ups, and found that fatigue group scored more errors than control groups on posttest than on pretest. They measured balance by balance error scoring system (BESS). They said that factors that could potentially cause a decrease in balance performance after fatigue could focus on both central and local means of fatigue.

Because balance depends upon central nervous systems and three sensory systems, alteration in CNS ability due to fatigue will affect one’s ability to maintain balance. Nardone et al17 assessed body sway variables by dynamometric platform in both eyes open and eyes closed condition following 25 minutes of treadmill run. There was significant increase in body sway path in both eyes open and eyes closed condition. They said that exercise of this duration caused failure of energy metabolism. Also Romberg Quotient was increased in eyes closed condition. They said that change in sensory inflow or possibly altered central processing of proprioceptive input occurred due to decreased spindle discharge.

Lepers et al18 investigated perturbations of equilibrium after prolonged exercise run by dynamic posturography and sensory organization test. The results showed that ability to maintain postural stability during conflicting sensory conditions decreased after exercise. Decrease in effector system efficiency due to muscle fatigue because of metabolic accumulation and changes in proprioceptive information led to impaired postural regulation.

Johnston et al30 studied effect of lower extremity isokinetic muscle fatigue on motor control performance. They assessed balance on instrumented balance system.

Findings revealed that fatigue significantly decreases the ability to balance on balancing device since there was no visual feedback to augment proprioception. Also fatiguing a muscle inhibits the joint’s neuromuscular feedback system. Motor control depends upon afferent sensory and proprioceptive mechanisms such as Golgi, spindle and joint receptors. Fatigue caused muscle spindle desensitization. This led to decreased efferent muscle response and poor ability to maintain balance.

Not all researchers of fatigue and postural stability have demonstrated a decrease in balance after exercise. Contrary to our results Derave et al7 found no change in center of pressure velocity measured by posturography after 2 hour cycling protocol indicating that exercise bout did not elicit decrease in postural stability. They however showed a significant exercise-hydration status interaction. Posttests results demonstrated higher COP velocities when subjects were not given fluid replacements during exertion protocol. It should be noted that posttest took 20-30 minutes after end of 2-hour cycle bout, thereby allowing recovery time before posttest.

Thus the factors that could potentially cause a decrease in balance after fatigue focus on both peripheral and central means of fatigue.

Localized muscle fatigue is influenced by decrease in metabolic substrates available for muscle contraction such as adenosine triphosphate, creatine phosphate and glycogen, as well as increase in metabolites including lactic acid in muscle, resulting in inability to maintain desired muscular force output. Contraction mechanism and neuromuscular junction impairments constitute peripheral fatigue14,39,76.

Limitation in energy supply has been always the classical hypothesis for muscle fatigue. This is supplemented by findings that coincide with specific intramuscular metabolic changes such as depletion of glycogen with prolonged exercise and depletion of PCr with high intensity exercise.40 Also reduced sarcoplasmic reticulum calcium release and impaired excitation contraction coupling have been implicated60.

CNS fatigue is a form of fatigue associated with specific alterations in CNS function that cannot be accounted for by peripheral dysfunction within the muscle itself. CNS has a profound effect in mediating fatigue since changes in motivational level have profound effect on performance and the first indication that fatigue may be imminent is increased perception of effort.

Inhibition of motor units, decreased firing rate, discharge rate of afferents such as Ia from muscle spindle 77, Ib from Golgi tendon organ and small diameter afferents are affected because of fatigue. This constitutes the Central component of fatigue35.

Sahlin et al65 demonstrated that during intense periods activity when anaerobic energy system is being taxed there is increase in muscle lactate concentration and muscle acidosis that caused fatigue and this high lactate and low pH impaired muscle performance.

Bangsbo et al42 showed that the development of fatigue during high intensity leg exercise is related to accumulation of potassium in muscle interstitium as shown by muscle biopsy taken from active leg muscle. It is elevated to around 12mmol/l in intense short-term exercise less than 3 minutes that is high enough to depolarize the muscle membrane potential and reduce the force development41. Also muscle pH was lowered.

Fatiguing effects of declining pH during exercise includes allosteric inhibition of rate limiting enzyme phosphofructokinase, glycogen phosphorylase, decrease release of calcium from sarcoplasmic reticulum hindering the excitation contraction coupling process, and reduction in number and force of muscle cross bridge activation11,43,64,75.

In efforts lasting less than 30 seconds it is decline in ATP production and increase in ADP concentration, caused by depletion of phosphocreatine and fall in rate of glycolyis that causes fatigue44,45,68. In exercise lasting 1-3 minutes hydrogen accumulation predominates71,72.

All this constitutes the peripheral mechanisms of fatigue. Thus it can be said that during anaerobic exercise the peripheral fatigue mechanisms were activated as a result of accumulation and depletion of various metabolites and impairment of contractile mechanism that leads to fatigue73,66.

Earlier it was thought that during prolonged aerobic exercise fatigue was associated with mechanisms that result in dysfunction of the contractile process. More recently CNS mechanisms have been implicated in the fatigue process13. Reduction in CNS drive to the muscle may be mediated by afferent feedback from muscle or reduction on corticospinal impulses reaching the motoneurones. Changes in afferent feedback from muscle may be result of changes in muscle metabolites during exercise. A reduction in corticospinal impulses reaching motoneurones could be result of alterations in neurotransmitter function in brain13.

In fatigue, changes in enkephalinergic, dopaminergic and serotonergic systems occur. These control vigilance, pain, motivation and tolerance while other neuroendocrine changes alter availability of substrates for muscle activation. Manipulation of these factors alter centrally mediated component of fatigue.

Nybo et al46 examined the neurohumoral alterations during prolonged exercise. They showed that serotonin levels in brain increase after aerobic exercise when plasma concentration of free tryptophan (TRP) also increased. This caused fatigue because of its role in arousal, sleepiness and mood.

There is change in stretch sensitivity of muscle spindle and tendon organ afferents during muscle fatigue. Muscle spindle discharge decreases during fatigue as demonstrated by Macfield et al79. Kniffki et al63, Kaufman et al67,81 in their experiments showed that the discharge of small diameter (group III and IV) muscle afferents increase in accordance to temperature, chemical, mechanical environment caused by fatigue. Following fatigue most group II non spindle afferents and group III mechanosensitive afferents have increased discharge rates increased sensitivity to stretch and reduced response to contractions and force47.

Pedersen et al48 showed that sensory information transmitted by ensembles of primary muscle spindle (MSA) after muscle fatigue of medial gastrocnemius muscle induced by isometric contractions was reduced because of changes in gamma motoneurones activity that is affected by group III and IV afferents80. Primary MSA’s have significant role in balance and proprioception and decreased capacity to discriminate after fatigue has important implications on position and balance.

Fatigue in exercise lasting greater than 15 minutes is also associated with glycogen depletion. Mc Conell et al50 examined the influence of carbohydrate availability on muscle metabolism during prolonged exercise. Muscle biopsies obtained immediately after exercise showed that ingestion of carbohydrate increases performance. Thus they concluded that fatigue during prolonged exercise is associated with muscle glycogen depletion or hypoglycemia. It is suggested that decrease in carbohydrate availability results in inability to resynthesize ATP at rate that matches ATP degradation which causes fatigue. Also carbohydrate ingestion improves endurance performance in subjects via alterations in central nervous system function.

Thus mainly CNS as well as some component of peripheral mechanisms influence fatigue during aerobic exercise. During exercise which involve both the aerobic as well as anaerobic systems such as the mixed fatigue protocol used in our study it can be said that both the central and peripheral mechanisms of fatigue were involved.

Thus its can be said that fatigue can result from combination of peripheral and central factors and fatigue caused by these resulted in impaired balance ability.

During exercise somatosensory inputs are stimulated. Under normal circumstance individual is more reliant on somatosensation than on visual inputs in correcting body sway. Alteration in somatosensory information leads to balance loss. There is decreased proprioception, increased joint laxity and a delay in muscle response after fatiguing exercise. The activity of joint receptors, muscle spindles and Golgi tendon organs may be reduced by fatigue, resulting in proprioceptive deficiency in muscle receptors and loss of muscular reflexes responsible for joint stability. Since this afferent information is important for the maintenance of postural control this may lead to decreased muscle response and poorer ability to maintain balance.51

Moreover muscle fatigue causes accumulation and depletion of metabolites and muscle damage. A decrease in effector system efficiency because of muscle fatigue and changes in proprioceptive information and their integration could probably impair postural control18.

Thus, if inaccurate information is provided by any of the 3 sensory systems because of local fatigue and if the central nervous system is suppressed through central fatigue, balance is disturbed1,78.

Another finding was that although balance was affected, post tests Balance Error Scoring system scores gradually decreased with time. This was because as the effect of fatigue weaned off balance deficit started to recover. In aerobic fatigue protocol it was seen that balance stared to recover in 15 minutes and had recovered by 20 minutes, 10 minutes in anaerobic protocol and 20 minutes in mixed fatigue protocol.

These findings agree with previous studies that placed balance recovery at approximately 20 minutes1,17,31. Also recovery from fatigue is very important before further exercises can be continued otherwise fatigue effects will lead to decreased performance and increased incidence of injuries. Recovery of muscle function is dependent on intensity, and duration of exercise as well as time allowed for recovery.

Hebestreit et al52 showed that after 30 seconds Wingate Anaerobic test recovery occurred in 2 minutes in boys and 10 minutes in adults. This was because fatigue was caused by peripheral factors, which recovered earlier, and also because of differences in recovery pattern between boys and adults.

Study by Ozturk et al54 showed that after Wingate Anaerobic test recovery period must be atleast 10 minutes and lactate accumulates more depending on intensity of exercise. Lower lactate after a given exercise bout may facilitate faster recovery55,56. Reduction in lactate during recovery is because it is distributed to sites of metabolism such as liver, heart, and inactive muscle or taken up by mild to moderate active skeletal muscle20.

Boska et al58 demonstrated recovery of phosphocreatine and inorganic phosphate in first 2 minutes and gradual recovery in next few minutes. Signorile et al57 showed that following exhaustive exercise ATP stores are approximated to be 90 95% repleted in 3 minutes because the phosphocreatine stores have been repleted.

Baker et al59 demonstrated that most of the anterior tibialis muscle force is recovered within 15 minutes after long duration fatigue protocol and after short duration fatigue protocol recovery occurred in 5 minutes. They said that during short duration activities metabolic processes come into play and this causes early recovery whereas during long duration it is the non-metabolic factors that delay the recovery. Susco et al1 showed that balance recovered within 20 minutes after mixed fatigue protocol because both the central and peripheral fatigue mechanisms were involved in fatigue process and central fatigue mechanisms require much more time for recovery as compared to peripheral. From these studies it seems reasonable that balance recovery should occur within 20 minutes.

Studies of the process of recovery from fatigue have had varied results, particularly because researchers have used different methods and fatigue protocols as well as different variables to measure fatigue effects. The fatigue protocol targeting only the peripheral mechanisms has more rapid recovery to baseline values as compared to central. The differences in fatigue protocol and the type of fatigue should be considered when attempting to compare fatigue effects and the recovery process36.

The results of our study demonstrated that RPE readings also increased as compared to pretest after all the three fatiguing protocol. Changes in RPE Scores demonstrate that the subjects were fatigued to a level representative of working at > 80% HRmax or VO2 max, and this fatigue elicited postural instability during the test.

Borg RPE scale is used in an attempt to quantify the amount of fatigue. It gives values of perceived feelings in relation to exertion level. Because perceived exertion and VO2 max are highly correlated, the RPE scale may be used as a substitute to determine exercise intensity2.

Perceived exertion is the single best indicator of degree of physical strain. The overall perceived exertion rating integrates various information, including the many signals elicited from the peripheral working muscles and joints, from the cardiovascular and respiratory functions and from central nervous system. All these signals, perceptions and experiences are integrated into perceived exertion26.

Using the 15-point Borg RPE scale, Seliga et al2 showed perceived exertion scores increased significantly with an increase in workload. The RPE values ranged from 9 to 10 during a light workload to 11 to 12 during a moderate workload to 14 to 16 during a heavy workload. They also noted that sway values were higher after exercise at higher workloads.

Other investigators have correlated RPE with percentage of maximum heart rate reserve, or percentage of VO2 max during various exercise tasks2,28. In a group of physically active males, RPE was measured during a treadmill exercise, cycle exercise, and simulated ski exercise at 70%, 80%, and 90% VO2 max. The RPE values ranged from 13 to 14.2 at 70% VO2 max across the exercise modes to 15.4 to 16 at 80% and 18 to 18.2 at 90%2.

Thus, during our protocol subjects were working at a level greater than 70% VO2max, and the decrease in BESS performance noted during the posttests was a result of their fatigue.

The RPE values noted in the studies previously done are all similar to RPE values in our study so we can say that subjects were fatigued and this fatigue caused balance impairment.

Another finding was that RPE readings in all protocols returned to baseline level within 20 minutes indicating that the subjects had recovered from fatigue. RPE values started returning to baseline in 15 minutes in aerobic protocol, 10 minutes in anaerobic protocol and 20 minutes in mixed fatigue protocol.

When comparing the three different fatigue protocols for BESS scores and rating of perceived exertion scores it showed that there was insignificant difference for the pretest readings which meant that the subjects pretest reading was similar in all the three conditions. But posttest revealed significant differences, which meant that fatigue protocols had effect on balance and each protocol caused balance deficit in accordance with the protocol used. It also revealed that the recovery was also different for all the conditions.

We attempted to quantify levels of fatigue by using the RPE scale, a clinical measurement tool that can easily be administered on the sidelines of athletic events. Yet various factors can influence RPE scores, including level of fitness, psychological state, and environmental conditions2. Thus it could be said that aerobic, anaerobic and mixed fatigue protocols all had effect on balance and balance recovered from these protocols within 20 minutes.

Relevance to clinical practice

Even minute changes in posture have shown to determine the outcome of performance and accuracy tasks such as rifle shooting33. Decreased postural control because of fatigue affects performance. It is suggested that individuals are at higher risk of injury after fatigue30.

It is seen that a tennis match may be lost simply because of fatigue and loss of concentration at the end of set.25 Studies have shown relation between performance under fatigue and increased incidence of injury16.

With the trend of injuries possibly occurring during the later half of games and practices, perhaps more can be done to prepare these athletes for central and local fatigue. If we can better train the athlete to operate in a fatigued environment, or limit the amount of fatigue an athlete is experiencing as a result of improved conditioning, then perhaps injuries may not be as correlated with the amount of fatigue that they are experiencing.

Although it is not realistic to expect a coach to stop practice or decrease practice times because someone is experiencing fatigue that may lead to injury, this topic needs attention. To be realistic, most coaches could rearrange how practices are conducted. For example, a coach who is having three-hour basketball practices could schedule the more difficult and higher risk activities in the first half of practice and leave the lower risk activities for the last hour when the athletes will be feeling the effects of fatigue.

Often balance assessment is done immediately after concussion injury apart from other neuropsychological tests to assess postural stability1,2. In most cases athlete has just come off the field and is fatigued. If balance testing is done at this time when the effects of concussion are clouded by effects of fatigue an athlete might score significantly greater number of errors due to combined effects of injury and fatigue and an accurate record of postural stability will not be recorded. Based on our findings it can be said that clinicians should wait for atleast 15 minutes after aerobic exercises ceases, 10 minutes after anaerobic exercise ceases and 20 minutes after mixed exercise ceases to allow athlete to return to resting baseline state and yield consistent measures.

Future research

More research in general needs to be conducted looking at activity related or functional fatigue and how it affects balance.

In the future use something besides the rating of perceived exertion to guarantee fatigue in the participants. A dynamometer could be used to measure local fatigue about the ankle, knee, and hip. A VO2 max test coupled with this could ensure proper cardiovascular endurance as well. In addition, blood samples can be taken and muscle biopsies can be done or invasive techniques can be used to detect blood lactate and other fatigue metabolites such as ATP level, phosphocreatine level.

Using an actual practice or competition instead of a fatiguing protocol may help demonstrate exactly what fatigue an athlete may experience during competition in their sport. However, this type of protocol would be difficult to standardize.

Since some studies say that recovery from fatigue after prolonged exercise takes longer time40,60,61 future researches can assess the recovery patterns after 1 hour, 2 hours and even 24 hours time interval so that exact time of recovery can be ascertained.

Since in this study only male patients were taken the results can only be generalized to male population. So future research can focus on taking female subjects as well and also comparing the balance deficits in both the sexes.

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Fig. 1.5

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Conclusions

From the results it can thus be concluded that different fatigue protocols, aerobic, anaerobic and mixed have effect on balance and balance is impaired as evident in increased posttest readings. Balance recovers within 20 minutes after all the fatigue protocols.

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