Effects of fatigue on knee proprioception

Effects of active fatiguing movement versus passive repetitive movement on knee proprioception

BACKGROUND

Proprioception can be affected by many factors such as age, gender, injury, disease, exercise, and fatigue. To date, the mechanisms or pathways by which fatigue influences proprioception have not been elucidated. Generally, it is accepted that local muscular effects occurred during fatigue state may negatively affect proprioception. Research has indicated that metabolic acidosis resulting from active muscle activities, along with tissue stretching and joint laxity resulting from repetitive joint movements, are likely related to proprioceptive deterioration. So far, little direct evidence or research supports these statements. The purpose of this study was to examine the effects of fatigue exercises (repetitive active movement) and repetitive passive movements on knee proprioception.

METHODS

A quasi-experimental design with repeated measure on proprioception following two forms of knee joint movement (repetitive active/passive movement in 120 degrees /s with 60 repetitions over a 10 degrees -100 degrees range) was conducted. Fifteen healthy volunteers underwent two forms of movement intervention in two consecutive days in a counter-balanced manner. Knee joint repositioning errors were measured before and after the movement intervention.

FINDINGS

Study results showed a statistically significant increase in absolute repositioning error following repetitive active movement, but a decrease following repetitive passive movement intervention.

INTERPRETATION

This study concluded that a repetitive passive movement protocol was capable of improving knee joint position sense. Meanwhile, the negative effect from the muscle receptors following the repetitive active movement overwhelmed the positive effect from the repetitive passive movement intervention. It supports the clinical utilization of repetitive passive movement to promote proprioception. This utilization can be implemented for proprioceptive training in sports activities, plus injury prevention and rehabilitation.

The effect of fatigue from exercise on human limb position sense

We have previously shown, in a two-limb position-matching task in human subjects, that exercise of elbow flexors of one arm led the forearm to be perceived as more extended, while exercise of knee extensors of one leg led the lower leg to be perceived as more flexed. These findings led us to propose that exercise disturbs position sense because subjects perceive their exercised muscles as longer than they actually are. In order to obtain further support for this hypothesis, in the first experiment reported here, elbow extensors were exercised, with the prediction that the exercised arm would be perceived as more flexed after exercise. The experiment was carried out under three load conditions, with the exercised arm resting on a support, with it supporting its own weight and with it supporting a load of 10% of its voluntary contraction strength. For each condition, the forearm was perceived as more extended, not more flexed, after exercise. This result was confirmed in a second experiment on elbow flexors. Again, under all three conditions the exercised arm was perceived as more extended. To explore the distribution of the phenomenon, in a third experiment finger flexor muscles were exercised. This had no significant effect on position sense at the elbow. In a fourth experiment, position sense at the knee was measured after knee flexors of one leg were exercised and, as for knee extensors, it led subjects to perceive their exercised leg to be more flexed at the knee than it actually was. Putting all the observations together, it is concluded that while the influences responsible for the effects of exercise may have a peripheral origin, their effect on position sense occurs centrally, perhaps at the level of the sensorimotor cortex.

Is activation of the back muscles impaired by creep or muscle fatigue?

STUDY DESIGN

Intervention study on healthy human subjects.

OBJECTIVE

To determine whether reflex activation of the back muscles is influenced by muscle fatigue or soft tissue creep in the spine.

SUMMARY OF BACKGROUND DATA

Reflex contraction of the back muscles normally acts to limit spinal flexion, and hence protect the underlying spine from injury. However, repeated flexion allows bending moments on the spine to increase. Impaired reflexes as a result of fatigue or soft tissue creep may be contributing factors.

METHODS

A total of 15 healthy volunteers (8 females/7 males aged 23-55 years) underwent 2 interventions, on separate days: (a) sitting flexed for 1 hour to induce creep and (b) performing the Biering-Sorensen test to induce back muscle fatigue. Before and after each intervention, reflex activation of the erector spinae in response to sudden trunk flexion (initiated by a Kin-Com dynamometer) was monitored bilaterally at T10 and L3 using surface electromyography (EMG) electrodes. These recordings indicated the onset latency of reflex activation, the peak EMG, and time to peak, at each site. Measurements before and after each intervention and between muscle sites were compared using a 2-way repeated measures Analysis of Variance.

RESULTS

Spinal creep was confirmed by an increase in maximum flexion of 2.3 degrees +/- 2.5 degrees (P = 0.003), and fatigue by a significant fall in median frequency at one or more sites. Following creep, onset latency increased from 60 +/- 12 milliseconds to 96 +/- 26 milliseconds (P < 0.001) but there was no change in peak EMG or time to peak EMG. Differences between sites (P = 0.004) indicated greater latencies in lumbar compared to thoracic regions, especially after creep. Muscle fatigue had no significant effects on any of the measured parameters.

CONCLUSION

Prolonged spinal flexion can impair sensorimotor control mechanisms and reduce back muscle protection of the underlying spine. The effect is due to time-dependent "creep" in soft tissues rather than muscle fatigue.

Degradation of cervical joint position sense following muscular fatigue in humans

STUDY DESIGN

Before and after intervention trials.

OBJECTIVE

To investigate the effect of cervical muscular fatigue on joint position sense.

SUMMARY OF BACKGROUND DATA

Although fatigue-related degradation of proprioceptive acuity at lower and upper limbs is well documented, to date no study has investigated whether muscular fatigue induced at the neck could modify joint position sense.

METHODS

A total of 9 young healthy adults were asked to perform the cervicocephalic relocation test to the neutral head position, that is, to relocate the head on the trunk, as accurately as possible, after full active cervical rotation to the left and right sides. This experimental task was executed in 2 conditions of No fatigue and Fatigue of the scapula elevator muscles. Absolute and variable errors were used to assess the cervical joint repositioning accuracy and consistency, respectively.

RESULTS

Less accurate and less consistent repositioning performances were observed in Fatigue relative to No fatigue condition, as indicated by increased absolute and variable errors, respectively.

CONCLUSION

Results of the present experiment evidence that cervical joint position sense, assessed through the cervicocephalic relocation test to the neutral head position, is degraded by muscular fatigue.

Effects of repeated ankle plantar-flexions on H-reflex and body sway during standing

The study investigated relations between effects of repeated ankle plantar-flexion movements exercise on the soleus Hoffmann (H) reflex and on postural body sway when maintaining upright stance. Ten young volunteers performed five sets of ankle plantar-flexions of both lower limbs. Assessment of the feet centre-of-pressure (COP) displacement and H-reflex tests were carried out in quiet stance before, during and after the exercise. H-max and M-max responses were obtained in 8 subjects and reported as the peak-to-peak amplitudes of the right soleus muscle electromyographic waves. Mean dispersion of COP along the antero-posterior direction increased significantly during the exercise; whilst the overall H-reflex response indicated a reduction without a concomitant modification in the M-max response. H-reflex responses, however, varied between participants during the first sets of exercise, showing two main trends of modulation: either depression or early facilitation followed by reduction of the H-reflex amplitude. The extent of reflex modulation in standing position was correlated to the concentric work performed during the exercise (r=0.85; p<0.01), but not to the antero-posterior COP dispersion. These results suggest that during a repeated ankle plantar-flexions exercise, modulation of the H-reflex measured in upright stance differs across individuals and is not related to changes of postural sway.

Effects of lower extremity muscle fatigue on the outcomes of slip-induced falls

Slip-induced fall accidents continue to be a significant cause of fatal injuries and economic losses. Identifying the risk factors causing slip-induced falls is key to developing better preventive measures to reduce fall accidents. Although epidemiological studies suggest localised muscle fatigue may be one of the risk factors for slip-induced falls, there has been no documented biomechanical study examining the relationship between fatigue and fall accidents. As such, the overall objective of the current study was to investigate the effects of localised muscle fatigue of the quadriceps on the slip initiation and slip recovery phases of slip-induced falls. Sixteen healthy, young participants were recruited to walk across a vinyl floor surface in two different sessions (fatigue and no fatigue). Kinematic and kinetic data were collected using a 3-D motion analysis system and force plates during both sessions. Results suggest that localised muscle fatigue of the quadriceps affected various kinematic and kinetic gait variables that are linked with a higher risk of slip-induced falls. Additionally, the results indicated that localised muscle fatigue of the knee extensor muscle caused a delayed response in producing an effective joint moment and base of support using the trailing limb to recover from a fall. The findings from this study indicate that localised muscle fatigue is a potential risk factor causing slip-induced falls.

Effects of quadriceps fatigue on the biomechanics of gait and slip propensity

This study examines how lower extremity fatigue of the quadriceps alters gait variables related to slip propensity. Sixteen healthy young adults were recruited to walk across vinyl floor surfaces in states of fatigue and no fatigue. Kinematic and kinetic data were collected using a three-dimensional motion analysis system and force plates. The results indicated a significant increase in both the heel contact velocity and required coefficient of friction and a decrease in the transitional acceleration of the whole body center of mass and peak knee joint moment in the fatigue trials. Thus, suggesting that slip propensity could increase with fatigue. Additionally, there was increased knee flexion and reduced ankle dorsiflexion at the heel contact phase of the gait cycle during fatigue trials. These findings provide new insights into the biomechanical relationship between localized muscle fatigue and gait parameters associated with slip propensity. The present study concluded that localized muscle fatigue affects gait parameters and hence can be considered as a potential risk factor for slip-induced falls.

Decreased quadriceps activation measured hours prior to a noncontact anterior cruciate ligament tear

STUDY DESIGN

Case report.

BACKGROUND

Decreased quadriceps activation has been shown to be present following anterior cruciate ligament (ACL) injury, but its presence prior to ACL injury is unknown. The purpose of this case report was to describe the level of quadriceps activation measured hours before a noncontact ACL injury in an individual who previously demonstrated known biomechanical risk factors for ACL injury.

CASE DESCRIPTION

A 23-year-old female (height, 176.9 cm; mass, 72.4 kg), sustained a left noncontact ACL injury while landing from a jump stop during a recreational basketball game. This case was unique because data regarding landing biomechanics and quadriceps force and activation were gathered in 2 separate, unrelated studies prior to injury.

OUTCOMES

Peak external knee abduction moment (-65.3 Nm) during a drop jump landing 8 months prior to injury indicated elevated risk for ACL injury. Involved quadriceps central activation ratios (CAR) were obtained 1 week (CAR, 0.81) and 4 hours (CAR, 0.77) prior to injury. Strength and CAR (0.76) measurements changed very little within 36 hours of injury and both strength, and activation (CAR, 0.90) improved following surgical reconstruction and formal rehabilitation.

DISCUSSION

An individual with known biomechanical risk factors for ACL injury may compound risk for noncontact ACL injury if decreased quadriceps activation is also present.

LEVEL OF EVIDENCE

Prognosis, level 4.

The effects of a neoprene knee sleeve on subjects with a poor versus good joint position sense subjected to an isokinetic fatigue protocol

OBJECTIVES

It has been shown that muscle fatigue has a negative influence on proprioception. Several studies already have demonstrated improvement of proprioception by using knee sleeves.

HYPOTHESIS

Neoprene knee sleeves have different effects on the joint position sense in locally fatigued subjects with good or poor proprioceptive acuity.

DESIGN

A true experimental design with random assignment to intervention and control limbs.

SETTING

Military hospital, department of physical medicine and rehabilitation.

PARTICIPANTS

Sixty-four healthy subjects.

INTERVENTIONS

All subjects underwent four consecutive assessments of the same active joint-repositioning test under different conditions (braced, nonbraced, fatigued, and nonfatigued).

MAIN OUTCOME MEASUREMENTS

A three-way analysis of variance with repeated-measures design was conducted to investigate the effects of side (braced versus control side), assessment sequence (one to four), and proprioceptive acuity ("good" versus "poor"), and their interactive effect on the joint position sense.

RESULTS

Post hoc analysis revealed that only subjects with "poor" proprioceptive acuity benefit from the braced condition before the isokinetic fatigue protocol (P < 0.001). In contrast, all subjects benefit from the braced condition after the fatigue test.

CONCLUSIONS

Bracing is helpful in individuals with a poor baseline proprioceptive acuity in both fatigued and nonfatigued states. Subjects with a good joint position sense benefit from bracing only when in a fatigued state. The present findings suggest a rationale for using neoprene knee sleeves as a preventative measure or treatment in subjects and patients to enhance proprioceptive acuity in a fatigued state. Classification into "poor" and "good" proprioceptive acuity is only relevant in the nonfatigued condition.

Fatigue alters lower extremity kinematics during a single-leg stop-jump task

To examine the kinematic characteristics of the hip and knee during a single-leg stop-jump task before and after exercise-to-fatigue, and to determine if the fatigue response is gender-dependent. Lower extremity kinematic measurements were taken of male and female subjects while they performed a sports functional task before and after fatigue developed from exhaustive running. Thirty healthy, physically active subjects (15 males and 15 females) Knee and hip joint kinematics were calculated utilizing three-dimensional video analysis. Each subject performed five single-leg stop-jumps before and after an exercise-to-fatigue bout. All subjects underwent a fatigue protocol using the modified Astrand protocol. Fatigue was verified using the Rating of Perceived Exertion along with the subject's heart rate. All data were analyzed using two factor (test x gender) repeated measures ANOVA (P<0.05). Both males and females demonstrated significantly less maximal knee valgus (P=0.038) and decreased knee flexion at initial contact (P=0.009) post-fatigue. No significant differences were identified in hip joint angles between sessions or between sexes. The results show that fatigue developed from exhaustive running alters lower extremity kinematics during a single-leg stop-jump task. The more neutral position in the frontal plane might be an effort to protect the knee. The decrease in knee flexion at initial contact may be an attempt to increase knee stability following fatigue. Our results did not reveal any gender differences in this specific task.

A new measurement method for spine reposition sense

Background

A cost effective tool for the measurement of trunk reposition sense is needed clinically. This study evaluates the reliability and validity of a new clinical spine reposition sense device.

Methods

The first part of this three part investigation included 45 asymptomatic subjects examined in the first 20 repeated trials portion assessing spine reposition sense. The second portion, test-retest, examined 57 asymptomatic subjects. Initial testing consisted of subjects sitting on the device and performing 20 trials of a self-determined 2/3 trunk flexion position. The second portion of the study involved 7 trials of trunk flexion performed twice. The angular position for each trial was calculated and the mean reposition error from the initial 2/3 position was determined. For the third portion, the new device was compared to the Skill Technologies 6D (ST6D) Imperial Motion Capture and Analysis System.

Results

ICC (3,1) for trials 4–7 was 0.79 and 0.76 for time one and time two, respectively and the test-retest ICC (3,k) was 0.38. Due to the poor test-retest ICC, the Bland Altman method was used to compare test and retest absolute errors. Most measurement differences were small and fell within the 95% confidence interval. Comparable measures between the two methods were found using the Bland Altman method to compare the reposition sense device to the ST6D system.

Conclusion

The device may be a cost effective clinical technique for sagittal trunk reposition sense measurement.

[Isokinetic, functional and proprioceptive assessment of soccer players two years after surgical reconstruction of the anterior cruciate ligament of the knee]

Injuries to the anterior cruciate ligament (ACL) of the knee are common in sport and are treated routinely in the world of sports medicine. In order to resume competitive sport in safety, it is important to know the actual level of performance achieved by the operated leg some time after the ligament repair.

OBJECTIVES

The objective of this work was to evaluate the recovery of the operated leg in Tunisian sportsmen two years after surgery by using isokinetic testing (60 degrees s(-1)), the one-leg hop distance test (i.e. a functional activity that one often finds in sport) and proprioceptive assessment. A secondary objective was to detect any possible correlations between the various outcomes.

MATERIALS AND METHOD

The ACL group was composed of 26 top-level Tunisian footballers having undergone ACL ligament repair. Two years after surgery, the following assessments were performed: an isokinetic test with an angular velocity of 60 degrees s(-1), a proprioceptive assessment in both active and passive modes and the functional one-leg hop distance test.

RESULTS

Our investigations confirmed a muscle deficit of 16% in the hamstring muscles of the injured leg. In both active and passive modes, normal proprioception is observed at a flexion of 60 degrees and in total extension but not in a mid-way position. The performance level of the operated leg (in terms of distance) had an average symmetry value of 93.40+/-2.7%.

CONCLUSION

Playing football appears to influence the isokinetic strength profile in sportsmen after ACL repair. The repair procedure leads to bilateral proprioceptive disruption at 15 degrees of knee flexion, on average.

Efficacy of a target-matching foot-stepping exercise on proprioception and function in patients with knee osteoarthritis

STUDY DESIGN

A randomized clinical trial design.

OBJECTIVE

To investigate the efficacy of high, repetitive, target-matching foot-stepping exercise (TMFSE) performed in a sitting position on proprioception, functional score, and walking velocity for patients with knee osteoarthritis (OA).

BACKGROUND

Researchers have suggested that exercises to address knee OA should include proprioceptive training. However, most patients cannot tolerate conventional proprioceptive training performed in a standing position.

METHODS AND MEASURES

Forty-nine subjects (mean age +/- SD, 63.3 +/- 8.1) with knee OA were randomly assigned to the exercise or no intervention groups. The exercise group practiced TMFSE in sitting, 3 sessions weekly for 6 weeks. All subjects underwent assessments of knee reposition error, functional incapacity score, and walking velocity prior to and after intervention.

RESULTS

The TMFSE significantly improved reposition error from a mean +/- SD of 3.0 degrees +/- 1.6 degrees to 1.5 degrees +/- 0.6 degree, walking velocity on ground level from 44.1 +/- 2.9 to 38.6 +/- 2.5 sec for 60 meters, time to complete a stairs task from 34.2 +/- 2.1 to 26.5 +/- 2.3 seconds, time to complete a figure-of-eight from 51.3 +/- 6.7 to 29.1 +/- 3.6 seconds, and score on a functional incapacity scale from 12.0 +/- 3.1 to 4.9 +/- 1.7, in subjects with knee OA after 6-week intervention (P <.0125). In contrast, the control group showed no change in any of the measured tests.

CONCLUSION

TMFSE in sitting appears to be an option for exercise in patients with mild to moderate knee OA. This may be an especially attractive option for patients who may have pain with weight-bearing exercises. A longitudinal study with a larger sample size is needed to confirm the potential use of TMFSE for patients with knee OA.

The effect of quadriceps muscle fatigue on position matching at the knee

This is a report of the effects of exercise on position matching at the knee. Young adult subjects were required to step down a set of stairs (792 steps), representing eccentric-biased exercise of the quadriceps muscle, or step up them, concentric-biased exercise. Immediately after eccentric exercise subjects showed a mean force drop of 28% (+/- 6%, s.e.m.) of the control value in their exercised quadriceps muscle, which was accompanied by 4.8 deg (+/- 0.8 deg) of error between reference and matching legs in a position matching task at the knee. Similarly concentric exercise was followed by a force drop of 15% (+/- 3%) and matching errors of 3.7 deg (+/- 0.4 deg). These effects were significant. The direction of the errors suggested that subjects perceived their exercised muscles to be longer that they actually were. This finding was not consistent with the hypothesis that the increase in effort required to support the leg after fatigue from exercise was responsible for the errors. It is hypothesized that position sense in an unsupported leg arises, in part, from operation of an internal forward model. When the motor command is increased to compensate for the effects of fatigue, the comparison between predicted and actual feedback from quadriceps leads to the impression that the muscle is longer than it actually is. The exercise effects on proprioception may have implications for sports injuries and for evaluation of the factors leading to falls in the elderly.

Tongue-placed tactile biofeedback suppresses the deleterious effects of muscle fatigue on joint position sense at the ankle

Whereas the acuity of the position sense at the ankle can be disturbed by muscle fatigue, it recently also has been shown to be improved, under normal ankle neuromuscular state, through the use of an artificial tongue-placed tactile biofeedback. The underlying principle of this biofeedback consisted of supplying individuals with supplementary information about the position of their matching ankle position relative to their reference ankle position through electrotactile stimulation of the tongue. Within this context, the purpose of the present experiment was to investigate whether this biofeedback could mitigate the deleterious effect of muscle fatigue on joint position sense at the ankle. To address this objective, sixteen young healthy university students were asked to perform an active ankle-matching task in two conditions of No-fatigue and Fatigue of the ankle muscles and two conditions of No-biofeedback and Biofeedback. Measures of the overall accuracy and the variability of the positioning were determined using the absolute error and the variable error, respectively. Results showed that the availability of the biofeedback allowed the subjects to suppress the deleterious effects of muscle fatigue on joint position sense at the ankle. In the context of sensory re-weighting process, these findings suggested that the central nervous system was able to integrate and increase the relative contribution of the artificial tongue-placed tactile biofeedback to compensate for a proprioceptive degradation at the ankle.

Impact of fatigue on gender-based high-risk landing strategies

PURPOSE

Noncontact anterior cruciate ligament (ACL) injuries carry significant short- and long-term morbidity, particularly in females. To combat this epidemic, neuromuscular training has evolved aimed at modifying high-risk lower-limb biomechanics. However, injury rates and the gender disparity in these rates remain, suggesting that key components of the injury mechanism continue to be ignored. This study examined the potential contributions of neuromuscular fatigue to noncontact ACL injuries.

METHODS

Ten male and 10 female NCAA athletes had 3D lower-limb-joint kinematics and kinetics recorded during 10 drop jumps, both before and after fatigue. Mean subject-based initial-contact (N = 9) and peak stance-phase kinematic (N = 9) and normalized (mass x height) kinetic (N = 9) parameters were quantified before and after fatigue and submitted to a three-way ANOVA to determine for the main effects of leg, gender, and fatigue. A Bonferroni corrected alpha level of 0.002 was adopted for all statistical comparisons.

RESULTS

Females landed with more initial ankle plantar flexion and peak-stance ankle supination, knee abduction, and knee internal rotation compared with men. They also had larger knee adduction, abduction, and internal rotation, and smaller ankle dorsiflexion moments. Fatigue increased initial and peak knee abduction and internal rotation motions and peak knee internal rotation, adduction, and abduction moments, with the latter being more pronounced in females.

CONCLUSIONS

Fatigue-induced modifications in lower-limb control may increase the risk of noncontact ACL injury during landings. Gender dimorphic abduction loading in the presence of fatigue also may explain the increased injury risk in women. Understanding fatigue effects at both the central and peripheral levels will further afford elucidation of the ACL injury mechanism and, hence, more successful prevention strategies.

The use of a neoprene knee sleeve to compensate the deficit in knee joint position sense caused by muscle fatigue

The importance of good proprioceptive abilities is stressed in many rehabilitation protocols. In contrast, it has been shown that muscle fatigue has a negative influence on proprioception. The objective of this study was to evaluate the effects of a neoprene knee sleeve (NKS) on the joint position sense in a fatigued knee joint. Sixty-four healthy subjects underwent four successive assessments of the same active joint repositioning test (AJRT) in an open kinetic chain setting under different conditions. First, each subject performed the AJRT without brace. One knee was braced during the second assessment. Subjects wore the brace for 6 h and were submitted to a fatigue protocol, followed by the third assessment under the same conditions as the previous one. The fourth and last AJRT was performed immediately after the third one but both knees were non-braced. When the subjects wore an NKS, significant differences in repositioning error were demonstrated between both sides. On the braced side, no significant differences were observed between the baseline assessment and the third assessment. NKS compensate the deficit in joint position sense due to fatigue. The use of NKS could be justified as a preventive measure or treatment in subjects to enhance proprioception.

Submaximal fatigue of the hamstrings impairs specific reflex components and knee stability

Rupture of the anterior cruciate ligament (ACL) is one of the most serious sports-related injuries and requires long recovery time. The quadriceps and hamstring muscles are functionally important to control stability of the knee joint complex. Fatigue, however, is an important factor that may influence stabilizing control and thus cause ACL injuries. The objective of this study was therefore to assess how submaximal fatigue exercises of the hamstring muscles affect anterior tibial translation as a direct measure of knee joint stability. While 15 test participants were standing upright with the knees in 30 degrees of flexion, anterior tibial translation was induced by a force of 315 N. Two linear potentiometers placed on the tibial tuberosity and the patella recorded tibial motion relative to the femur. Reflex latencies and neuromuscular hamstring activity were determined using surface electromyography (EMG). Muscle fatigue produced a significant longer latency for the monosynaptic reflex latencies, whereas no differences in the latencies of the medium latency component were found. Fatigue significantly reduced EMG amplitudes of the short and medium latency components. These alterations were in line with significantly increased anterior tibial translation. Our results suggest that hamstring fatigue is effectively associated with mechanical loss of knee stability. This decrease in joint stability may at least in part explain higher risk of ACL injury, especially in fatigued muscles. Furthermore, we discuss why the present findings indicate that reduced motor activity rather than the extended latency of the first hamstring response is the reason for possible failure.

The effect of eccentric exercise on position sense and joint reaction angle of the lower limbs

Impaired position sense and impaired joint reaction angle of the lower limbs after muscle-damaging activities is a serious functional limitation that may lead to an increased risk of injury, particularly in older populations. The purpose of the present study was to examine whether position sense and joint reaction angle to release can be affected by eccentric exercise-induced muscle damage. Twelve women underwent an isokinetic exercise session of the lower limb. Isometric peak torque, delayed-onset muscle soreness, serum creatine kinase, position sense, and knee joint reaction angle to release were examined before, immediately after, and 24, 48, and 72 h post-exercise. Due to the effect of eccentric exercise, subjects persistently placed their lower limb at a more extended position, representing a shorter knee extensor muscle. Eccentric exercise increased the knee reaction angle of the lower limb after release from 0 degrees and 15 degrees but not from 30 degrees and 45 degrees . Position sense and joint reaction to release were similarly affected by eccentric exercise and independently of visual feedback. Position sense was impaired only immediately post-exercise (probably due to muscle fatigue), whereas impairment of the reaction angle to release persisted up to 3 days post-exercise (probably due to muscle damage). Attenuation of position sense and joint reaction angle of the lower limbs after damaging activities is a serious functional limitation that may lead to an increase risk of injury, particularly in older populations.

Effect of exercise-induced fatigue on position sense of the knee in the elderly

Previously, data on the effects of muscle fatigue on joint position sense (JPS) have been provided. However, to our knowledge, no studies have been conducted so far to assess the effects of local muscle fatigue on elderly proprioception. Thus, the purpose of the present study was to determine the effects of local muscle fatigue on knee JPS in old-age-subjects. Sixteen male volunteers (mean age +/- SD: 69.81 +/- 3.92 years) participated in this study. Each subject completed all of the data collection in one morning session; JPS measures were obtained prior to and immediately after the fatigue protocol. JPS was evaluated by the technique of open-kinetic chain and active knee positioning, and was reported using absolute, relative and variable angular errors. The fatigue protocol applied to the lower extremity consisted of 30 maximum concentric repetitions of the knee extensors and flexors muscles on an isokinetic dynamometer at an angular velocity of 120 s(-1) (2.09 rad s(-1)). The results showed that peak torque of knee extensor and flexor muscles was significantly decreased from rest to post exercise-induced fatigue. After local load to the knee muscles, a significant increase of absolute angular error was observed (2.56 degrees ). The relative error showed the directional bias in the extension movement. However, the reliability and accuracy of estimating knee angles as showed by the variable error is similar at both times. It can be concluded that exercise-induced local muscle fatigue alters knee JPS in old age adults.

Postural sway and joint kinematics during quiet standing are affected by lumbar extensor fatigue

The purpose of this study was to investigate changes in postural sway and strategy elicited by lumbar extensor muscle fatigue. Specifically, changes in center of mass (COM), center of pressure (COP), and joint kinematics during quiet standing were determined, as well as selected cross correlations between these variables that are indicative of movement strategy. Twelve healthy male participants stood quietly both before and after exercises that fatigued the lumbar extensors. Whole-body movement and ground reaction force data were recorded and used to calculate mean body posture and variability of COM, COP, and joint kinematics during quiet standing. Three main findings emerged. First, participants adopted a slight forward lean post-fatigue as evidenced by an anterior shift of the COM and COP. Second, post-fatigue increases in joint angle variability were observed at multiple joints including joints distal to the fatigued musculature. Despite these increases, anterior-posterior (AP) ankle angle correlated well with AP COM position, suggesting the body still behaved similar to an inverted pendulum. Third, global measures of sway based on COM and COP were not necessarily indicative of changes in individual joint kinematics. Thus, in trying to advance our understanding of how localized fatigue affects movement patterns and the postural control system, it appears that joint kinematics and/or multivariate measures of postural sway are necessary.

Recovery of Joint Position Sense in the Shoulder after Muscle Fatigue

Context:

Fatigue of the shoulder rotator muscles may negatively affect joint position sense (JPS) and ultimately lead to injury.

Objective:

Recovery of shoulder JPS after muscle fatigue.

Design:

A repeated-measures study.

Setting:

Musculoskeletal research laboratory.

Patients:

Thirteen subjects participated in joint position error tests and isokinetic concentric strength assessment in shoulder rotation, before and after rotator muscle fatigue.

Interventions:

Local muscle fatigue was induced using isokinetic concentric contractions of the shoulder rotator muscles.

Main Outcome Measurements:

Shoulder rotator strength and JPS error signals were measured before fatigue, immediately after fatigue, and every ten minutes thereafter for one hour.

Results:

Before shoulder rotation muscle fatigue, the accuracy of shoulder JPS was 2.79 ± 1.67 degrees. After muscle fatigue, the accuracy decreased to 6.39 ± 2.90 degrees. Shoulder JPS was influenced up to 40 minutes after muscle fatigue, but shoulder strength was only affected for 10 minutes after muscle fatigue.

Conclusions:

Proprioceptive recovery was slower than strength following fatigue of the shoulder rotators.

Lumbar extensor fatigue and circumferential ankle pressure impair ankle joint motion sense

Fatigue of the lumbar extensor muscles has been associated with a degradation of balance, but the mechanism is not well understood. The ankle plays a major role in upright standing, and loss of proprioceptive acuity at the ankle could contribute to a degradation of balance. Therefore, the first objective of this study was to investigate the effect of lumbar extensor fatigue on ankle proprioceptive acuity. The second objective was to investigate the effect of circumferential ankle pressure (CAP) on ankle proprioceptive acuity to evaluate CAP as a potential intervention to mitigate any loss of proprioceptive acuity at the ankle with lumbar extensor fatigue. To address these objectives, ankle joint motion sense was evaluated with and without CAP, both before and after the lumbar extensors were fatigued. Results showed an impairment in joint motion sense with both fatigue and CAP. These results indicate that lumbar extensor fatigue impairs ankle proprioceptive acuity, which may help explain observed increases in postural sway subsequent to lumbar extensor fatigue.

The Effects of Calf-Muscle Fatigue on Sagittal-Plane Joint-Position Sense in the Ankle

Context:

There is limited information on the effect of dynamic fatiguing of the plantar flexors on joint-position sense (JPS).

Objective:

To examine the effects of fatigue on JPS for ankle plantar flexion (PF) and dorsiflexion (DF).

Design:

A 2 × 2 factorial design.

Setting:

Research laboratory.

Participants:

20 healthy subjects (10 men, 10 women; age 21.75 ± 1.48 years).

Interventions:

The subjects were tested at 10° DF and 20° PF in the nonfatigued and fatigued conditions on a custom-built JPS device. To induce fatigue, subjects stood with both feet in the plantar-flexed position until they could no longer hold the posture.

Main Outcome Measures:

JPS absolute error was measured at 10° DF and 20° PF.

Results:

There was no significant main effect for condition, measurement, or interaction between condition and measurement.

Conclusion:

With no difference between conditions, the main controller of conscious JPS of the lower extremity might be the tibialis anterior.

The effect of short-duration sub-maximal cycling on balance in single-limb stance in patients with anterior cruciate ligament injury: a cross-sectional study

Background

It has previously been shown that an anterior cruciate ligament (ACL) injury may lead to impaired postural control, and that the ability to maintain postural control is decreased by fatigue in healthy subjects. To our knowledge, no studies have reported the effect of fatigue on postural control in subjects with ACL injury. This study was aimed at examining the effect of fatigue on balance in single-limb stance in subjects with ACL injury, and to compare the effects, and the ability to maintain balance, with that of a control group of uninjured subjects.

Methods

Thirty-six patients with unilateral, non-operated, non-acute ACL injury, and 24 uninjured subjects were examined with stabilometry before (pre-exercise) and immediately after (post-exercise) short-duration, sub-maximal cycling. In addition, the post-exercise measurements were compared, to evaluate the instantaneous ability to maintain balance and any possible recovery. The amplitude and average speed of center of pressure movements were registered in the frontal and sagittal planes. The paired t-test was used for the intra-group comparisons, and the independent t-test for the inter-group comparisons, with Bonferroni correction for multiple comparisons.

Results

No differences were found in the effects of exercise between the patients and the controls. Analysis of the post-exercise measurements revealed greater effects or a tendency towards greater effects on the injured leg than in the control group. The average speed was lower among the patients than in the control group.

Conclusions

The results of the present study showed no differences in the effects of exercise between the patients and the controls. However, the patients seemed to react differently regarding ability to maintain balance in single-limb stance directly after exercise than the control group. The lower average speed among the patients may be an expression of different neuromuscular adaptive strategies than in uninjured subjects.

Effects of Lower Extremity Fatigue on Indices of Balance

Context:

Use of selective joints in fatiguing protocols might not represent athletic activity and limits generalizability.

Objective:

To quantify changes in balance indices after a generalized fatiguing activity.

Design:

Repeated measures.

Setting:

Clinical laboratory.

Participants:

16 men (24 ± 3 y) with no orthopedic problems.

Intervention:

Balance was assessed using the KAT-2000 system before (PRE) and immediately (IMMED) and 10 min (10MIN) after serial Wingate tests and at similar time points under nonfatigue conditions.

Main Outcome Measures:

Balance index (BI), fore:back ratio, and right:left ratio.

Results:

MANOVA revealed a significant Condition × Time effect (P= .023). ANOVA revealed that only BI was significant for the condition, time, and Condition × Time effects (P= .020, .007, and .003, respectively). BI increased PRE to IMMED, decreased IMMED to 10MIN, and was different from the nonfatigue condition only for IMMED (P= .002, < .001, and < .001, respectively).

Conclusions:

Fatigue adversely affects BI; recovery might occur within 10 min.

Effect of Rehabilitation on Hip and Knee Proprioception in Older Adults After Hip Fracture

OBJECTIVE

Impaired proprioception may predispose patients with hip fracture to increased risk of future disability. The purpose of the study was to determine the effect of rehabilitation on proprioceptive changes in both the hip and knee joints of patients after hip fracture.

DESIGN

Data were collected on 30 patients with hip fracture (mean age, 79.6 +/- 6.7 yrs) who attended physical and occupational therapy sessions five times per week during a rehabilitation hospital stay of 24.8 +/- 8.1 days. Proprioception was assessed with an electrogoniometer within 48 hrs of admission to and discharge from the rehabilitation unit. The passive-to-active reproduction of joint angle technique determined absolute angular error in non-weight-bearing positions at 15, 30, and 60 degrees of hip flexion and knee extension in both injured and noninjured sides.

RESULTS

Absolute angular error decreased significantly (P < 0.05) from admission (5.3 +/- 2.6 degrees, 4.1+/- 3.1 degrees) to discharge (3.0 +/- 2.3 degrees, 2.8 +/- 3.1 degrees) in hip flexion and knee extension, respectively, on the injured side. Absolute angular error was significantly less (P < 0.05) at 15 degrees compared with 30 and 60 degrees of hip flexion at admission and discharge on the injured side.

CONCLUSIONS

Hip and knee joint proprioception significantly improved in the injured side after the rehabilitation program. This may be an important outcome regarding future disability in this population.

The effect of local and general fatigue on knee proprioception

PURPOSE

The purpose of this study was to compare the effects of local and general fatigue loads on knee proprioception.

TYPE OF STUDY

Experimental controlled study.

METHODS

Proprioception of the knee joint was evaluated by measuring absolute angular error (AAE) at matching defined index angles before and after 2 different types of fatigue protocols (local load and general load) in 27 healthy male volunteers. Local load was provided with maximum isokinetic knee flexion-extension on the isokinetic dynamometer, and general load was 5 minutes running on a treadmill.

RESULTS

After local load, a significant decrease in peak torque of knee flexors and extensors was found, but no significant change in AAE was seen. In contrast, after general load, a significant increase of AAE was noted without significant muscle weakness.

CONCLUSIONS

The different results in previous studies evaluating the effect of fatigue on knee proprioception may have been affected by the difference of fatigue protocols, whether local or general load. Although local load was intended to produce local fatigue of the knee, which may cause dysfunction of muscle mechanoreceptors, general load may have produced general fatigue and affected other mechanisms in the proprioceptional pathway. The results of the present study suggest that decreased reproduction ability after general load is not due to the loss of peripheral afferent signals, but to other factors, especially deficiency of central processing of proprioceptive signals.

CLINICAL RELEVANCE

To prevent knee injury caused by fatigue-induced proprioceptional decline, muscle endurance training alone is not enough, and neuromuscular training, including central motor programming, is essential.

Effects of short-term cycling on knee joint proprioception in healthy young persons

BACKGROUND

Criteria are needed for measuring the effects of exercise and fatigue on proprioception.

PURPOSE

To measure knee joint proprioception in healthy subjects before and after exercise and to establish a reference for further comparisons of patients with knee injuries.

STUDY DESIGN

Controlled laboratory study.

METHODS

We tested proprioception in the knees of 24 healthy subjects with a mean age of 24 years and median Tegner score of 5. Subjects were tested to estimate their thresholds for detecting slow passive motion, from starting positions of 20 degrees and 40 degrees before and after cycling on an ergometer bicycle until the pulse rate reached a steady state level and they reached a score of 14 to 17 on Borg's Ratio of Perceived Exertion scale.

RESULTS

After cycling, significantly higher threshold values were found for perception of movement toward flexion from both 20 degrees and 40 degrees. No significant differences were seen in measurements of movement toward extension.

CONCLUSIONS

Knee joint proprioception seems to be impaired by exercise or training.

CLINICAL RELEVANCE

This impairment may lead to defective dynamic stabilization of the joint, leading to an increased risk of injuries.

Effects of local fatigue of the lower limbs on postural control and postural stability in standing posture

Postural stability and postural control were studied before and after a fatigue protocol of soleus muscles. Postural stability was assessed by the centre of gravity motion, which was computed from the motion of the centre of pressure, evaluating the postural control. Ten healthy male subjects were asked to stand as still as possible with eyes open before and after the fatigue protocol, performed in a sitting position. Fatigue was assumed on the basis of a shortening of the exertion time of the soleus muscles at 60% of their maximal voluntary contraction. Results of the whole group showed that fatigue modified postural control but did not change postural stability. The same results were observed only for some subjects. However, these results indicate an increase of the neuromuscular activity in high frequencies.

Recent advances in the rehabilitation of isolated and combined anterior cruciate ligament injuries

The rehabilitation process begins immediately following ACL injury, with emphasis on reducing swelling and inflammation; improving motion; regaining quadriceps control; allowing immediate weight-bearing; and restoring full passive knee extension and, gradually, flexion. The goal of preoperative rehabilitation is to prepare the patient mentally and physically for surgery. Once the ACL surgery is performed, it is important to alter the rehab program based on the type of graft used and any concomitant procedures performed. This will aid in preventing several postoperative complications, such as loss of motion, patellofemoral pain, graft failure, and muscular weakness. The goal of this article has been to provide an overview of the application and the scientific basis for formulating a rehabilitation protocol following ACL surgery. For an athlete to return to competition, it is imperative that he or she regain muscular strength and neuromuscular control in their injured leg while maintaining static stability. In the past, rehabilitation programs attempted to prepare the athlete for return to sports by using resistance exercise alone. Current rehabilitation programs focus not only on strengthening exercises, but also on proprioceptive and neuromuscular control drills in order to provide a neurologic stimulus so that the athlete can regain the dynamic stability needed in athletic competition. We believe that it is important to use this approach not only possible causes that might predispose the individual to future injury.

Effects of localization and intensity of experimental muscle pain on ankle joint proprioception

Accurate proprioceptive input is a prerequisite for balance control and coordination of movement. The present study investigated whether experimental muscle pain induced in healthy human subjects disturbed movement sense (detection of movement) or position sense (recognition of a reference position). Muscle pain was produced by infusion of 6% hypertonic saline simultaneously in m. tibialis anterior (TA) and m. soleus (experiment 1), by infusion of 6% hypertonic saline in TA (experiment 2) and by infusion of 9% hypertonic saline in TA (experiment 3). Control measurements were done with infusions of 0.9% isotonic saline. All infusions of 6% and 9% saline produced pain intensities significantly higher than the corresponding control infusions. Only infusion of 6% saline in two muscles (visual analogue scale=4-5) produced an elevation in movement detection thresholds which was significantly higher, compared with before infusion. No other significant changes in movement and position sense were found during the painful or control infusions. Pain of relatively high intensity in two antagonist muscles is necessary to disturb the movement detection threshold. The ability to recognize a reference position is not disturbed by experimentally induced muscle pain. Whether the disturbed movement sense is caused by sensitivity changes in muscle spindle afferents or altered processing of proprioceptive input cannot be answered. The present findings indicate that human ankle proprioception is rather robust to muscle pain.

Does wearing a functional knee brace affect hamstring reflex time in subjects with anterior cruciate ligament deficiency during muscle fatigue?

OBJECTIVE

To evaluate the effects of wearing a functional knee brace and muscle fatigue on hamstring reflex time in subjects with anterior cruciate ligament (ACL) deficiency.

DESIGN

Repeated-measures clinical trial.

SETTING

Outpatient physical therapy department.

PARTICIPANTS

Sixteen subjects with ACL deficiency.

INTERVENTION

Subjects tested with and without a functional knee brace before and after an exercise protocol designed to fatigue the knee muscles.

MAIN OUTCOME MEASURE

Latency of hamstring reflex muscle activity after sudden perturbation of the knee.

RESULTS

Wearing a knee brace shortened the hamstring reflex latency regardless of fatigue (F(1,15)=20.62, P<.001). Muscle fatigue lengthened the hamstring reflex time regardless of the bracing condition (F(1,15)=7.57, P<.015).

CONCLUSION

Wearing a functional knee brace facilitated hamstring muscle reflex, but muscle fatigue lengthened the hamstring reflex latency. Subjects with ACL deficiency should not rely on the knee brace to facilitate hamstring reflex for joint protection during prolonged sporting activities when muscles are fatigued.

Scapular muscle recruitment pattern: electromyographic response of the trapezius muscle to sudden shoulder movement before and after a fatiguing exercise

STUDY DESIGN

Test-retest reliability study and single-group repeated measures design.

OBJECTIVES

To evaluate the muscle latency times of the 3 portions of the trapezius muscle to a sudden arm movement in normal shoulders and to determine if this recruitment pattern is altered as a result of fatigue.

BACKGROUND

It has been suggested that shoulder impingement may be related to altered muscle activity and muscle fatigue in the scapular stabilizers. Fatigue-induced changes in latency times of the trapezius might influence scapular stability.

METHODS AND MEASURES

Muscle latency times were investigated in 30 healthy shoulders with surface electromyography. Muscle activity was measured in all 3 sections of the trapezius and the middle deltoid muscle during a sudden downward falling movement of the arm. Subsequently the shoulder was fatigued on an isokinetic dynamometer, after which muscle latency time measurement was repeated.

RESULTS

ANOVA for repeated measures revealed significant differences in latency times (P < 0.05) among the 4 muscles of interest. Although there were no significant differences among the 3 sections of the trapezius muscle, they all were recruited after the initialization of the deltoid muscle. The recruitment order of the shoulder muscles did not change with muscle fatigue. However, after fatigue, muscle responses were significantly slower in all muscles except for the lower trapezius (P < 0.05).

CONCLUSIONS

There is a specific recruitment sequence in the shoulder muscles in response to a sudden arm movement characterized by initial activation of the middle deltoid muscle and followed by simultaneous contraction of all 3 sections of the trapezius. This muscle activation pattern is delayed but not altered with fatigue.

Effects of isokinetic ankle fatigue on the maintenance of balance and postural limits

OBJECTIVE

To quantify changes in balance parameters and ranges of postural control at the ankle after isokinetic fatigue.

DESIGN

Before-after trials, with a 5 x 6 repeated-measures design.

SETTING

General community.

PARTICIPANTS

Twenty-four men (age, 24.9 +/- 3.92y; height, 177.79 +/- 6.36cm; weight, 80.78 +/- 13.22kg) without ankle trauma within 2 years.

INTERVENTIONS

Fatigue of the plantarflexors and dorsiflexors was induced by isokinetic contractions. Balance was assessed by using a unilateral test (15-s quiet stance, 10-s lean test) on a force platform immediately before and at 0 (T0), 10 (T10), 20 (T20), and 30 (T30) minutes postfatigue.

MAIN OUTCOME MEASURE

Mediolateral (ML) and fore-aft (FA) sway as well as ML and FA displacement were analyzed by analysis of variance with repeated measures for time (alpha =.05).

RESULTS

In quiet stance, ML sway was greater at T0, whereas total sway increased at all time points postfatigue (P < .05). For the lean test, FA sway increased at T0 and T10, and total sway increased at all time points (P < .05). Both ML and FA displacement significantly differed at T0 (P < .05). All sway parameters returned to baseline within 20 minutes.

CONCLUSIONS

Isokinetic fatigue of ankle plantarflexors and dorsiflexors significantly influences sway parameters and ranges of postural control in healthy young men. These perturbations are transient, and recovery occurs within 20 minutes.

The Effect of Muscle Fatigue on Muscle Force-Couple Activation of the Shoulder

Context:

Muscle fatigue is an important concept in regard to the muscle function of the shoulder joint. Its effect on the muscle force couples of the glenohumeral joint has not been fully identified.

Objective:

To examine the effects of muscle fatigue on muscle force-couple activation in the normal shoulder.

Design:

Pretest, posttest.

Patients:

Ten male subjects, age 18–30 years, with no previous history of shoulder problems.

Main Outcome Measures:

EMG (area) values were assessed for the anterior and middle deltoid, subscapularis, and infraspinatus muscles during 4 dynamic stabilizing exercises before and after muscle fatigue. The exercises examined were a push-up, horizontal abduction, segmental stabilization, and rotational movement on a slide board.

Results:

No significant differences were observed for any of the muscles tested.

Conclusions:

The results of our study indicate that force-couple coactivation of the glenohumeral joint is not significantly altered after muscle fatigue.

Spinal and supraspinal factors in human muscle fatigue

Muscle fatigue is an exercise-induced reduction in maximal voluntary muscle force. It may arise not only because of peripheral changes at the level of the muscle, but also because the central nervous system fails to drive the motoneurons adequately. Evidence for "central" fatigue and the neural mechanisms underlying it are reviewed, together with its terminology and the methods used to reveal it. Much data suggest that voluntary activation of human motoneurons and muscle fibers is suboptimal and thus maximal voluntary force is commonly less than true maximal force. Hence, maximal voluntary strength can often be below true maximal muscle force. The technique of twitch interpolation has helped to reveal the changes in drive to motoneurons during fatigue. Voluntary activation usually diminishes during maximal voluntary isometric tasks, that is central fatigue develops, and motor unit firing rates decline. Transcranial magnetic stimulation over the motor cortex during fatiguing exercise has revealed focal changes in cortical excitability and inhibitability based on electromyographic (EMG) recordings, and a decline in supraspinal "drive" based on force recordings. Some of the changes in motor cortical behavior can be dissociated from the development of this "supraspinal" fatigue. Central changes also occur at a spinal level due to the altered input from muscle spindle, tendon organ, and group III and IV muscle afferents innervating the fatiguing muscle. Some intrinsic adaptive properties of the motoneurons help to minimize fatigue. A number of other central changes occur during fatigue and affect, for example, proprioception, tremor, and postural control. Human muscle fatigue does not simply reside in the muscle.

Effect of fatigue on knee proprioception: implications for dynamic stabilization

The high incidence of injuries that occur later during a session of sports or recreational activities suggests that fatigue may contribute to altered neuromuscular control of the lower limb and an individual's subsequent altered ability to dynamically stabilize the knee joint. One possible mechanism is a fatigue-mediated alteration in proprioception. This paper reviews experimental evidence of fatigue-induced changes in knee joint position sense and movement sense, or kinesthesia. We will discuss the possible physiological mechanisms behind these changes, including the role of joint and muscle receptors in proprioception and neuromuscular control of the knee, and the role of fatigue in changes in afferent output from muscle and joint receptors. We will then explore the implications that alteration in proprioception may have for dynamic stabilization of the knee joint.

Viscosupplementation effect on proprioception in the osteoarthritic knee

OBJECTIVE

To test the hypothesis that treatment of the osteoarthritic knee with intraarticular hyaluronan may improve proprioception.

METHODS

Forty-six patients with unilateral osteoarthritis of the knee were recruited for this study from primary care clinics in the Department of Family Medicine at the University of Western Ontario. Inclusion required (1) the presence of pain with activities of daily function and (2) radiographic confirmation of medial compartment osteoarthritis. Proprioception was measured with an electrogoniometer attached to the study knee. Subjects performed an angle reproduction test in the closed kinetic position. The difference between the target test angle and the reproduced angle was labeled the absolute angular error (AAE). Eleven angles were tested in random order before beginning therapy, after 3 weeks, and after 12 weeks.

RESULTS

Twenty-one men and 19 women completed the study (22 subjects received hyaluronan injections and 18 subjects received a placebo injection). No significant differences existed between the study groups in age, the timing of injections, or proprioceptive testing. A 2 x 3 repeated measures analysis of variance (ANOVA) comparing injection groups at all times revealed no significant differences in AAE. The AAE proprioception data was examined for differences due to fatigue caused by the number of test angles (p < .001) and differences explained by angulations in various divisions of the normal range of motion (p < .001). After accounting for these potential confounds, a two-way ANOVA still did not detect any significant differences in AAE between hyaluronan and placebo groups.

CONCLUSION

Other studies have found that proprioception may be impaired in osteoarthritic knees and that viscosupplementation therapy with hyaluronan may decrease pain and increase function in these knee joints. The results of the present study suggest that this therapy does not adversely affect proprioception and that a longer, longitudinal study is required to determine if viscosupplementation treatments could attentuate proprioceptive decline.

Reliability of position sense testing assessed with a fully automated system

Position sense testing has increased as a tool for augmenting evaluation of joint injury. In the present study, we investigated the inter-day reliability for four different types of position sense tests using a fully automated system. The tests included (1) passive presentation/active replication, (2) passive presentation/passive replication, (3) semi-passive presentation/semi-passive replication (where semi-passive denotes passive movement during antagonist muscle contraction), and (4) active presentation/active replication. The absolute difference between presented target and replicated position was used as a measure of position sense accuracy. Ten healthy subjects who were blindfolded and seated with the arm in a moveable rig performed the tests on two occasions, separated by 3-4 days. For each type of position sense test, horizontal abduction from a starting position of 0 degrees (relative to the sagittal plane) to target positions of 32 degrees and 64 degrees, and horizontal adduction from a starting position of 80 degrees to 48 degrees and 16 degrees were conducted. A two-way ANOVA revealed no differences in absolute error between days or between testing procedures. However, intra-class correlations (ICC), which are most often used to express test-retest reliability, were moderate at best, ranging from 0.40 to 0.61 for the four types of position sense tests. Hence, the present study indicates that the ability of repositioning tests to detect alterations in proprioceptive function is limited, suggesting that their use in clinical evaluation be approached with prudence.

The effect of lumbar fatigue on the ability to sense a change in lumbar position. A controlled study

STUDY DESIGN

A cross-sectional study in patients with recurrent/chronic low back trouble and healthy control subjects.

OBJECTIVE

To evaluate the effect of paraspinal muscle fatigue on the ability to sense a change in lumbar position.

SUMMARY OF BACKGROUND DATA

Protection against spinal injury requires proper anticipation of events, appropriate sensation of body position, and reasonable muscular responses. Lumbar fatigue is known to delay lumbar muscle responses to sudden loads. It is not known whether the delay is because of failure in the sensation of position, output of the response, or both.

METHODS

Altogether, 106 subjects (57 patients with low back trouble [27 men and 30 women] and 49 healthy control subjects [28 men and 21 women]) participated in the study. Their ability to sense a change in lumbar position while seated on a special trunk rotation unit was assessed. A motor rotated the seat with an angular velocity of 1 degree per second. The task in the test involved reacting to the perception of lumbar movement (rotation) by releasing a button with a finger movement. The test was performed twice, before and immediately after a fatiguing procedure. During the endurance task, the participants performed upper trunk repetitive extensions against a resistance, with a movement amplitude adjusted between 25 degrees flexion and 5 degrees extension, until exhaustion.

RESULTS

Patients with chronic low back trouble had significantly poorer ability than control subjects on the average to sense a change in lumbar position (P = 0.007), which was noticed before and after the fatiguing procedure. Lumbar fatigue induced significant impairment in the sensation of position change (P < 0.000001).

CONCLUSIONS

Lumbar fatigue impairs the ability to sense a change in lumbar position. This feature was found in patients and control subjects, but patients with low back trouble had poorer ability to sense a change in lumbar position than control subjects even when they were not fatigued. There seems to be a period after a fatiguing task during which the available information on lumbar position and its changes is inaccurate.

The role of muscle weakness in the pathogenesis of osteoarthritis

To date, very few studies have investigated the role of muscle dysfunction in the pathogenesis of osteoarthritis (OA). Using largely indirect evidence, this article hypothesizes that motor and sensory dysfunction of muscle may be important factors in the pathogenesis of articular damage and are not simply a consequence of joint damage. A new paradigm is constructed to better describe the complex interrelationship between muscle sensorimotor dysfunction, joint damage, and disability in OA. If the hypothesis is correct, because muscle is a relatively plastic tissue, maintaining well-conditioned muscles may delay or prevent the onset of OA, and rehabilitation exercise therapy that reverses muscle sensorimotor dysfunction may ameliorate the effects of OA.