Effect of rearfoot orthotics on postural sway after lateral ankle sprain.

OBJECTIVE: To investigate the effects of different rearfoot orthotics on postural sway during unilateral stance after lateral ankle sprain. DESIGN: Repeated-measures 3-factor analysis of variance on postural sway length and velocity in the frontal and sagittal planes with factors being stance leg (injured, uninjured), session (within 3 d, 2 wk, 4 wk postinjury), and condition (6 orthotic conditions). SETTING: University biomechanics laboratory. PATIENTS: Fifteen collegiate athletes with acute, unilateral first- or second-degree lateral ankle sprain. INTERVENTIONS: Balance testing was performed under 6 conditions: (1) shoe only, (2) molded Aquaplast orthotic, (3) lateral heel wedge, (4) 7 degrees medially posted orthotic, (5) 4 degrees laterally posted orthotic, and (6) neutral orthotic. MAIN OUTCOME MEASURES: Postural sway length and postural sway velocity in the frontal and sagittal planes. RESULTS: Significant main effects were found for side and session, but not orthotic condition, for all 4 dependent variables. Postural sway length and velocity were greater on the injured limbs as compared with the uninjured limbs during the first 2 sessions but not during the third session. None of the orthotics significantly reduced postural sway compared with the shoe-only condition after lateral ankle sprain. CONCLUSIONS: Rearfoot orthotics, irrespective of design or posting, were ineffective at improving postural sway after lateral ankle sprain.     

Effect of lower-extremity muscle fatigue on postural control

OBJECTIVE: To examine the effects of fatigue of the lower extremity on postural control during single-leg stance. DESIGN: Pretest-posttest. SETTING: University research laboratory. PARTICIPANTS: Fourteen healthy volunteers (age, 21+/-2y) with no history of lower-extremity injury or neurologic deficits. INTERVENTIONS: Testing consisted of isokinetically fatiguing the sagittal plane movers of the ankle, knee, or hip with measures of static postural control. Postural control was assessed with three 30-second trials during unilateral stance with eyes open. MAIN OUTCOME MEASURES: Center of pressure excursion velocity (COPV) in the frontal and sagittal planes. RESULTS: Fatigue at the knee and hip led to postural control impairment in the frontal plane, whereas fatigue at the ankle did not. In the sagittal plane, fatigue at all 3 joints contributed to postural control impairment. CONCLUSIONS: Our results suggest that there is an effect of localized fatigue of the sagittal plane movers of the lower extremity on COPV. It appears that fatigue about the hip and knee had a greater adverse affect on COPV.     

Effects of arthritis exercise programs on functional fitness and perceived activities of daily living measures in older adults with arthritis

OBJECTIVE: To ascertain the effectiveness of the National Arthritis Foundation (NAF) aquatic and on-land exercise programs on functional fitness and perceived ability to perform activities of daily living (ADL) measures in older adults with arthritis. DESIGN: The effects of aquatic and on-land exercise intervention programs were analyzed by repeated-measures analysis of variance by using a planned comparison approach with an independent 3 x 2 (group by test) design. omega(2) analyses were used to ascertain the relative treatment magnitude of each dependent variable. SETTING: Testing in an indoor track facility; exercise programs conducted in community settings. PARTICIPANTS: A volunteer sample of 30 men and women with arthritis (osteoarthritis, n=22; rheumatoid arthritis, n=8), randomly assigned into either an aquatic exercise (n=10), on-land exercise (n=10), or control group (n=10). INTERVENTION: Eight-week on-land and aquatic exercise program. MAIN OUTCOME MEASURES: Functional fitness, ADLs, and hand-held dynamometry measures assessed on a 1-day pretest and posttest session, before and after an 8-week exercise program. RESULTS: Aquatic and on-land exercise subjects showed significant improvements on 9 of 12 functional fitness, 3 of 4 ADLs, and 7 of 8 hand-held isometric strength tests after their respective exercise programs. No significant changes were found in any of these measures for the control group. CONCLUSION: Both NAF exercise programs appear to be effective in improving functional physical fitness and perceived ability to perform ADL measures in older adults with arthritis.     

Postural sway biofeedback: its effect on reestablishing stance stability in hemiplegic patients

A static force plate system was used to examine postural sway characteristics in 16 hemiplegic patients and in 34 normal elderly subjects. The effectiveness of postural sway (center of pressure) biofeedback was compared to conventional physical therapy practices in reestablishing stance stability in hemiplegic patients. Postural sway abnormalities in hemiplegic patients included significant mean lateral displacement of sway towards the nonaffected leg and increased total sway area. Postural sway biofeedback was more effective than conventional physical therapy practices in reducing mean lateral displacement of sway. This was associated with increased loading of the affected leg. Posttreatment changes in total sway area were not significantly different between experimental and control groups.     

Gait and postural stability in obese and nonobese prepubertal boys

OBJECTIVE: To examine differences in gait and postural stability of obese and nonobese prepubertal boys. DESIGN: Percentage of gait cycle in double support was examined to determine significant differences. Postural stability was compared using temporal and frequency measures of the center of pressure in static stance. SETTING: Gait was examined using videography on a 30-meter walkway. Postural stability was examined using a measurement platform. PARTICIPANTS: Ten obese (>95th percentile in body mass index) and 10 nonobese (15th to 90th percentile in body mass index) prepubertal boys aged 8 to 10yrs. INTERVENTION: Participants were examined at three walking cadences as determined by preferred gait cadence. Full vision, darkness, and visually confused conditions were used to accentuate static postural stability differences. MAIN OUTCOME MEASURES: In the presence of dynamic stability differences (gait), static stability measures further investigated stability differences. RESULTS: Obese boys spent significantly (p < .02) greater percentage of gait cycle in dual stance. Obese boys showed significantly (p < .01) greater sway areas, energy, and variability primarily in the medial/lateral direction. CONCLUSIONS: Dual stance differences suggest diminished dynamic stability in obese boys. Greater sway areas in medial/lateral direction in obese boys and the absence of significant frequency measures suggest that the instability observed in obese boys is caused by excess weight rather than underlying postural instability.     

The effect of walking aids on balance and weight-bearing patterns of patients with hemiparesis in various stance positions

BACKGROUND AND PURPOSE: Standard and quad canes are often prescribed to patients with hemiparesis, yet their effect on postural control remains unclear. Thus, the objective of this study was to examine the effects of standard and quad canes on postural sway and on weight-bearing patterns in patients with hemiparesis. SUBJECTS: Thirty subjects with a diagnosis of unilateral hemiparesis following a stroke (patient group; mean age=71.2 years, SD=7.0) and 20 age-matched, community-dwelling volunteers without hemiparesis (comparison group; mean age=72.1 years, SD=5.2) participated in the study. METHODS: Postural sway and percentage of body weight (%BW) borne by each extremity were measured in 3 positions: with the heels aligned with each other (aligned position) and in staggered foot positions with either the affected or unaffected extremity placed forward (affected FW and unaffected FW positions). All subjects were tested in each position with no cane, a standard cane, and a quad cane. The order of tests was randomized, and analysis of data included use of an analysis of variance and adjusted Tukey-Kramer tests. RESULTS: In both the aligned and unaffected FW positions, postural sway was reduced only with the quad cane. Both types of canes reduced postural sway in the affected FW position; however, the quad cane had a greater effect. An asymmetrical weight distribution between the lower extremities did not change in the patient group across positions, even with walking aids. DISCUSSION AND CONCLUSION: A quad cane appears to be more effective than a standard cane in decreasing postural sway in patients with moderate impairment secondary to hemiparesis during stance. The greatest effect on postural sway occurred when the assistive device was contralateral to the foot placed forward. The use of a cane does not appear to adversely affect the asymmetrical weight-bearing pattern during stance that is characteristic of patients with hemiparesis, even when balance is challenged by decreasing the base of support.     

The effect of immersion cryotherapy on medial‐lateral postural sway variability in individuals with a lateral ankle sprain

Background and Purpose . Postural stability has been shown to be impaired after a lateral ankle sprain (LAS) and after immersion cryotherapy in healthy ankles. This study was performed to determine the effects of cryotherapy on postural stability after LAS. Method . A single‐session, repeated measures design was used. Fifteen 18‐ to 29‐year‐old males (mean age 21.33 ± 3.54, height 71.23 ± 2.50 cm, mass 170.33 ± 19.77 kg) with relatively recent grade I LAS volunteered. Medial‐lateral postural sway variability was assessed during single‐leg barefoot stance using a Bertec force platform. Sway was tested before cryotherapy (‘Pre’), immediately after 20 minutes of lower‐leg immersion cryotherapy (‘Post₀’), and 10 and 20 minutes after cryotherapy (‘Post₁₀’ and ‘Post₂₀’). Both legs were tested (individually) before cryotherapy; the involved leg was tested alone after cryotherapy. The uninvolved leg served as a control. Results . Postural sway variability of the involved le was significantly greater than the uninvolved le before cryotherapy (p = 0.001). Postural sway variability of the involved le was also significantly greater than the uninvolved LE during Post₀ (p = 0.000), Post₁₀ (p = 0.000) and Post₂₀ testing (p = 0.003) with the largest increase in sway variability occurring at Post₀. Conclusions . Medial‐lateral postural sway variability was greater after LAS. This effect was augmented by immersion cryotherapy. Copyright © 2008 John Wiley & Sons, Ltd.     

Age differences in postural sway during volitional head movement

OBJECTIVE: To examine the role of a volitional self-paced head-turn movement on the postural sway characteristics of healthy young and elderly subjects. DESIGN: Cross-sectional design. SETTING: Motor control research laboratory. SUBJECTS: Ten young adults and 10 elderly subjects. MAIN OUTCOME MEASURES: Postural sway characteristics of each subject were examined using a Kistler force platform. Each subject was tested under four experimental conditions: (1) static postural sway with vision; (2) static postural sway without vision; (3) postural sway with vision and self-paced head-turn movement; and (4) postural sway with no vision and a self-paced head-turn movement. Subjects performed six 15-second trials in each experimental condition. Dependent variables analyzed on each trial were mean sway amplitude (in millimeters), sagittal sway standard deviation, lateral sway standard deviation, and frequency of sway (in hertz). RESULTS: During the static conditions (e.g., no voluntary movement), the young subjects produced significantly less postural sway than the elderly in both the vision condition (sway amplitude in the young, 3.80 mm; in the elderly, 4.89 mm) and the no-vision condition (young, 5.44 mm; elderly, 5.95 mm). This increased sway was the result of greater lateral sway in the elderly for the vision condition (3.73 vs. 2.68 mm), and greater sagittal sway for the elderly in the no-vision condition (5.55 vs. 4.70 mm). There were no significant differences between the groups in the frequency of sway. When asked to initiate and complete the head-turn, elderly subjects significantly increased their mean sway amplitude and decreased their frequency of sway, whereas the young subjects did not significantly alter their postural sway profiles. CONCLUSIONS: These results demonstrate different postural sway control strategies for young and elderly subjects when asked to perform volitional movements.     

Effect of orthoses on postural stability in asymptomatic subjects with rearfoot malalignment during a 6-week acclimation period

OBJECTIVE: To determine the effect of custom-fitted orthoses on postural sway over a 6-week acclimation period. DESIGN: Repeated-measures analysis of variance on postural sway measures with factors being group (control, malaligned), time (initial, 2 wk, 4 wk, 6 wk postintervention), and condition (with orthoses, without orthoses). For single-limb stance, side (right, left) was analyzed to determine bilateral differences. SETTING: Biodynamics laboratory. PARTICIPANTS: Twenty-one subjects, 11 asymptomatic with rearfoot malalignment and 10 asymptomatic with normal rearfoot alignment. INTERVENTIONS: Orthoses were prescribed and worn for 6 weeks. Balance testing was performed on 4 different dates with each subject tested in both orthotic conditions. Postural control was measured with three 10-second eyes-closed trials for single-limb stance, one 20-second eyes-closed bilateral stance with the platform moving, and one 20-second eyes-open bilateral stance with the platform and surroundings moving. MAIN OUTCOME MEASURES: Sway velocity (in deg/s) for single-limb stance and equilibrium score for bilateral stance. RESULTS: Postural sway measures were significantly decreased during single-limb testing with orthoses versus without orthoses, regardless of group. The orthotic intervention significantly improved bilateral stance equilibrium score in the malaligned group at weeks 2, 4, and 6 when compared with measures at the initial week. Equilibrium score of the malaligned group with orthoses at initial week was significantly lower (worse) than the control group with orthoses at initial week; however, these results were not repeated during measurements taken at weeks 2, 4, or 6. CONCLUSIONS: The application of orthoses decreased sway velocity for single-limb stance, improving postural stability regardless of group when visual feedback was removed. During bilateral stance, postural stability was initially worse for the malaligned group with and without orthoses when compared with the control group; however, improvements were seen by week 2 and continued throughout the remainder of testing. Clinically, the application of orthoses appears to improve postural control in people with rearfoot malalignment, particularly when vision is removed.     

Stance ataxia and delayed leg muscle responses to postural perturbations in cervical spondylotic myelopathy

OBJECTIVE: We studied balance control in patients with cervical spondylosis, on the hypothesis that ataxia and changes in postural responses occur concurrently as a consequence of structural problems in the cervical cord. Subjects and patients: Seventeen patients and 17 healthy subjects were recruited. Based on magnetic resonance imaging, the patients were divided into 2 groups, with (n=9) and without (n=8) signs of myelopathy. METHODS: Body sway was recorded under quiet stance on a force platform. Postural perturbations evoked early and late responses in soleus and tibialis anterior. RESULTS: Most patients showed increased body sway during stance, which was larger in cervical spondylosis with myelopathy than cervical spondylosis. Early postural responses in the soleus were not affected. Late responses in soleus and tibialis anterior were delayed in cervical spondylosis with myelopathy. Across all patients, latency of tibialis anterior late response was correlated with lower limb sensory impairment and amplitude of body sway. CONCLUSION: Abnormal transmission through the cervical cord of proprioceptive input to supraspinal centres and of descending commands to caudal cord levels are accountable for ataxia in cervical spondylosis with myelopathy. Stabilometry may be an economic and easy way in a clinical and rehabilitative setting to distinguish severe from mild forms of cervical spondylosis prior to physical treatment and to help the differential diagnosis from other diseases featuring similar signs.     

Analysis of the correlation between the differences in muscle strengths between the bilateral lower extremities and postural stability in healthy adults

[Purpose] The purpose of this study was to examine the correlation between the differences in muscle strengths between the bilateral lower extremities and the level of postural sway that indicates postural stability. [Subjects and Methods] A total of 49 students (18 males and 31 females) at Y University in Gyeongsangnam-do, South Korea, participated in this study. Partial correlation analysis was performed to determine the effects of sway length and velocity on the differences in muscle strengths between the lower extremities. [Results] Both sway length and sway velocity showed a negative correlation with the difference in bilateral ankle dorsiflexion strength. Both sway length and sway velocity showed a positive correlation with the difference in bilateral hip flexion strength. [Conclusion] Difference in left-right muscle strengths of hip flexion and ankle dorsiflexion can affect postural stability when the levels of lower extremity muscle strengths are excluded.Key words: Postural sway, Muscle strength, Postural balance     

Anterior ankle-foot orthosis effects on postural stability in hemiplegic patients

OBJECTIVES: To evaluate the effects of an anterior ankle-foot orthosis (AFO) on static and dynamic postural stability in hemiplegic patients. DESIGN: A cross-sectional assessment of hemiplegic subjects with and without an AFO. SETTING: Outpatient department of a rehabilitation hospital. PATIENTS: A convenience sample of 24 subjects who had been prescribed an anterior AFO. OUTCOME MEASURES: Postural sway index and postural symmetry (body weight distribution through the affected leg) when standing were measured as static postural stability. Maximal balance range in anterior-posterior and lateral directions and the affected leg's weight bearing after weight shift to affected side were measured as dynamic postural stability. RESULTS: When wearing the anterior AFO, there was no significant difference and small effect size (r<0.3) in postural sway index (p = .35), postural symmetry (p = .21), and maximal balance range in anterior-posterior direction (p = .46). There was a significant improvement and large effect size (r>0.5) in lateral weight shifting (p<.01) and weight bearing through the affected leg after weight shifted to the affected side (p<.01). CONCLUSIONS: The significant effects of the anterior AFO in long-term hemiplegic patients were on lateral weight shifting and weight bearing through affected leg after weight shifted to the affected side. Postural sway, postural symmetry, and anterior-posterior weight shifting were not significantly affected.     

Postural Response Latencies Are Related to Balance Control During Standing and Walking in Patients With Multiple Sclerosis

Objective

To understand and examine the relation between postural response latencies obtained during postural perturbations and representative measures of balance during standing (sway variables) and walking (trunk motion).

Design

Cross-sectional.

Setting

University medical center.

Participants

Persons with multiple sclerosis (MS) (n=40) were compared with similar aged control subjects (n=20). There were 20 subjects with MS in the normal walking velocity group and 20 subjects with MS who had slow walking velocity based on a timed 25-foot walk (T25FW) of <5 seconds.

Interventions

None.

Main Outcome Measures

Postural response latency, sway variables, trunk motion variables.

Results

We found that subjects with MS with both slow or normal walking velocities had significantly longer postural response latencies than the healthy control group. Postural response latency was not correlated with the T25FW. Postural response latency was significantly correlated with center of pressure sway variables during quiet standing (root mean square: ρ=.334, P=.04; range: ρ=.385, P=.017; mean velocity: ρ=.337, P=.038; total sway area: ρ=.393, P=.015). Postural response latency was also significantly correlated with motion of the trunk during walking (sagittal plane range of motion: ρ=.316, P=.05; SD of transverse plane range of motion: ρ=−.43, P=.006).

Conclusions

These findings clearly indicate that slow postural responses to external perturbations in patients with MS contribute to disturbances in balance control during both standing and walking.     

A clinical trial of strengthening and aerobic exercise to improve gait and balance in elderly male nursing home residents.

The purpose of this study was to determine whether a moderate to high intensity strengthening and aerobic exercise program can improve the strength, exercise capacity, gait and balance of deconditioned male nursing home residents. Ambulatory subjects who scored 30 or less on the modified Tinetti gait and balance assessment scale, who demonstrated less than 80% of age-matched lower extremity strength on isokinetic muscle testing and who gave informed consent were enrolled. Subjects were randomized to either an exercise (n = 8) or a control (n = 6) group. All participants underwent an exercise test to determine maximal oxygen uptake (VO2max) and received quantitative gait and balance measurements. The subjects assigned to the exercise group than completed a 12-wk program of weight training for the lower extremities and stationary cycling. Both the exercise and control groups were then retested. Ten outcome variables were assessed: Tinetti mobility scores, VO2max, isokinetic-tested lower extremity strength and endurance, stride length, gait velocity, stance time, gait duration, cadence and balance. The exercise group, after completion of the program, demonstrated significant improvements in Tinetti mobility scores (P < 0.05), combined right and left quadricep muscle strength (P < 0.01), right and left lower extremity muscular endurance (P < 0.01), left stride length and gait velocity (P < 0.05), although other outcome variables changed insignificantly. The control group revealed no changes of significance with the exception of improvement of the combined right and left hamstring muscle strength (P < 0.05). Nevertheless, for those outcome variables that had improved significantly in the exercise group, the changes amounted to only a 5 to 10% increase over the baseline measurements. These findings showed that an appropriately designed high intensity exercise program can result in significant although limited improvements for clinical mobility scores, strength, muscular endurance and certain gait parameters.     

Changes in Postural Sway According to Footwear Types of Hemiparetic Stroke Patients

[Purpose] The purpose of the current study was to investigate the influence of footwear type on postural sway of hemiparetic stroke patients. [Subjects] Thirty-two stroke patients who were undergoing a rehabilitation program were recruited on a voluntary basis from local rehabilitation unit. [Methods] This study had a single-group repeated-measures design. The Good Balance system was used to measure the postural sway velocity (anteroposterior and mediolateral) and velocity moment of the subjects under the eyes open and eyes closed conditions in the standing posture. Postural sway of the subjects in four types of footwear was measured, including barefoot, high heel-collar shoes, flat shoes, or slippers. [Results] The postural sway when wearing the flat shoes or slippers was significantly higher than that when barefoot or wearing high heel-collar shoes. In addition, postural sway velocity and velocity moment of all the footwear types were significantly higher under the eyes closed condition than under the eyes open condition. [Conclusion] Our results reveal that when the subjects wore flat shoes or slippers they had more difficulty than when they wore the high heel-collar shoes in postural control when maintaining standing balance. We believe that this result provides basic information for improvements in postural control and may be useful in balance training to prevent falls after stroke.Key words: Footwear, Postural sway, Stroke     

The correlation between physical and emotional stabilities: a cross-sectional observational preliminary study

BackgroundPostural stability and gait are affected by an individual’s emotional state. Physical therapy practice does not usually include an explicit assessment of the individual’s emotional status. In contrast, complementary movement therapies often include the assessment of “grounding quality”, which refers to the individual’s physical and emotional stabilities. This study examined the correlation between conventional physical stability measures and grounding quality.MethodA computerized balance board and an inertial sensor system measured the postural stability and gait parameters of 36 healthy volunteers (aged 19–35 years). Grounding was assessed using an observation-based assessment tool (Grounding Assessment Tool [GAT]). Spearman’s correlation and Cohen’s standard were used to assess correlation.ResultsNo correlation was observed between gait parameters and GAT scores. However, significant negative moderate correlations were noted between postural sway measures and scores of several GAT items in the more demanding stance conditions.ConclusionAlthough grounding quality and sway measures are somewhat correlated, they focus on different aspects of movement stability. A comprehensive assessment and holistic intervention strategies require incorporating multiple approaches to stability assessment. Further research is necessary to determine the contribution of combining these approaches among individuals with balance impairments.

KEY MESSAGES

• Gait stability measures were not correlated to “grounding quality” (a measure of emotional regulation and emotional awareness).
• Postural sway measures were found to be correlated to “grounding quality” items in the more demanding stance conditions.
• A comprehensive evaluation of an individual’s stability may facilitate reliable and valid objective measurement instruments for both physical and emotional aspects of the movement.

     

Impact of Extremity Manipulation on Postural Sway Characteristics: A Preliminary,Randomized Crossover Study

ObjectiveEvaluate multisegmental postural sway after upper- vs lower-extremity manipulation.MethodsParticipants were healthy volunteers (aged 21-40 years). Upper- or lower-extremity manipulations were delivered in a randomized crossover design. Postural assessments were made pre-post manipulation, in floor and rocker board conditions. Analysis included traditional balance measures of pathlength and range and sample entropy (SampEn) to examine the temporal structure of sway of the head, trunk, and surface.ResultsNo statistical changes in pathlength or sway range on the ground surface condition were observed. No increases in the amount of sway occurred in any condition. Chiropractic manipulation of either upper or lower extremities led to reductions in traditional measures of postural control on the rocker board. In the anteroposterior direction (sagittal plane), lower-extremity manipulation led to increased trunk SampEn while on the ground, and conversely a decreased SampEn while on the rocker board. In the mediolateral rocker board condition (frontal plane), manipulation elicited a change in SampEn that differed according to site of manipulation; upper-extremity manipulation increased SampEn, whereas lower-extremity manipulation reduced SampEn.ConclusionBoth upper- and lower-extremity manipulation influenced several measures of postural sway on both the ground and the rocker board. Lower-extremity manipulation improved the organization of sway at the trunk (anteroposterior direction) and the board (mediolateral direction). Given the reduction and reorganization of sway metrics seen in this study, we propose extending this line of research to the elderly who are at greatest risk of increased sway and falls.     

Does adherence make a difference? Results from a community-based aquatic exercise program

BACKGROUND: Evidence exists demonstrating the benefits of exercise for people with osteoarthritis, but little is known about whether exercise programs are effective, that is, whether the benefits of exercise can be seen in "real life" programs for "normal" people under nonlaboratory conditions. OBJECTIVE: To identify characteristics of and outcomes for participants who adhere to a community-based aquatic exercise program. METHOD: Two hundred and forty-nine adults with osteoarthritis were recruited from Washington State for randomization to a 20-week Arthritis Foundation aquatic exercise program (n = 125) or a wait-list control group (n = 124). Adherers were defined as those attending at least two classes per week for 16 of 20 weeks. Measures included: Quality of Well Being Scale, Health Assessment Questionnaire, Center for Epidemiological Studies-Depression Scale, and a single arthritis quality of life rating-item. RESULTS: Baseline to postintervention change scores revealed that treatment-group adherers (N = 35) reported improved quality of well-being, physical function, and change in arthritis quality of life compared to controls (N = 124). When comparing treatment-group adherers (N = 35) to treatment-group nonadherers (N = 67), quality of well-being and depressed mood improved for adherers, but not for nonadherers. CONCLUSION: When analyzed for level of participation, exercise benefits adults with osteoarthritis. Consistent participation in exercise programs results in better outcomes. Improved methods are needed to enhance adherence, with increased attention to the role of intrinsic factors such as self-efficacy and belief systems.