Isometric Steadiness Research Articles

DIFFERENCES IN KNEE SENSORIMOTOR CONTROL BY PHYSICAL ACTIVITY LEVEL AND SEX.

ABSTRACTObjective:The aim of this study was to compare the differences in knee sensorimotor control between healthy men and women by measuring the joint position sense (JPS), sensation of muscle tension (steadiness), and onset of muscle activation (OMA).Methods:Twenty-four healthy women and 27 healthy men were tested. Knee sensorimotor control was assessed using the JPS test with electrogoniometers in 3 different ranges of motion, sensation of muscle tension using the isometric steadiness technique, and OMA against a mechanical perturbation. Each assessment was compared by sex, physical activity level, and right or left lower limb.Results:The men obtained better values in the JPS test between 90º and 60º and between 30º and 0º than the women. The subjects with higher levels of physical activity also showed better values, between 90º and 60º and between 30º and 0º. The best results for steadiness were found in the women and the subjects with higher levels of physical activity. In the OMA test, no significant differences were found in the studied variables.Conclusion:The results suggest that higher levels of physical activity may determine better sensorimotor control. Men have better articular sensation, and women have better muscle strength control. Level of evidence III, Cross sectional study.

Knee sensorimotor control following anterior cruciate ligament reconstruction: A comparison between reconstruction techniques

The sensorimotor system helps to maintain functional joint stability during movement. After anterior cruciate ligament (ACL) injury and reconstruction, several sensorimotor deficits may arise, including altered proprioception and changes in neuromuscular control. It is still unknown whether the type of autograft used in the reconstruction may influence knee sensorimotor impairments. The aim of this study was to comparatively assess the effects of the hamstring tendon (HT) and bone-patellar tendon-bone (BPTB) ACL reconstruction techniques on knee sensorimotor control 6–12 months post-operation. A total of 83 male subjects participated in this study: 27 healthy participants, 30 BPTB-operated patients and 26 HT-operated patients. Active joint position sense in 3 ranges of motion (90–60°, 60–30°, and 30–0° of knee flexion), isometric steadiness, and onset of muscle activation were used to compare sensorimotor system function between groups. Both operated groups had a small (< 5°) but significant joint position sense error in the 30–0° range when compared to the healthy group. No significant differences were found between the operated and the control groups for isometric steadiness or onset of muscle activation. The results of this study suggest that operated patients present knee proprioceptive deficits independently of surgical technique. Nevertheless, the clinical implications of this impairment are still unknown. It seems that selected surgical approach for ACL reconstruction do not affect functioning of the sensorimotor system to a large degree.

Impact of joint status on contraction steadiness of m. quadriceps femoris in people with severe haemophilia.

Impaired contraction steadiness of lower limb muscles affects functional performance and may increase injury risk. We hypothesize that haemophilic arthropathy of the knee and the strength status of quadriceps are relevant factors which compromise a steady contraction. This study addresses the questions if impaired steadiness of the quadriceps is verifiable in people with haemophilia (PWH) and whether a connection between the status of the knee joint and quadriceps strength exists. A total of 157 PWH and 85 controls (C) performed a strength test with a knee extensor device to evaluate their bilateral and unilateral maximal quadriceps strength and steadiness. Isometric steadiness was measured by the coefficient of variation of maximum peak torque (CV-MVIC in %). For classification of the knee joint status the World Federation of Haemophilia (WFH) score was used. Lower steadiness (higher CV values) was found in PWH compared with C during bilateral [PWH vs. C; 0.63 (0.36/1.13) vs. 0.35 (0.15/0.72), median (Q25/Q75) P<0.001] and unilateral trials [left leg: 0.70 (0.32/1.64) vs. 0.50 (0.23/1.04), P<0.05; right leg: 0.68 (0.29/1.51) vs. 0.39 (0.18/0.68), P<0.001]. PWH with a WFH score difference (≥1) between their extremities showed a less steady contraction in the more affected extremity (P<0.05). More unsteady contractions have also been found in extremities with lower quadriceps strength compared with the contralateral stronger extremities (P<0.001), whereby the weaker extremities were associated with a worse joint status (P<0.001). The results of this study verify an impaired ability to realize a steady contraction of quadriceps in PWH and the influence of joint damage and strength on its manifestation.

Steadiness of quadriceps contractions in young and older adults with and without a history of falling

Decreased steadiness of muscle force may be associated with ageing and could be a cause of falls in older people. We studied this in isometric and anisometric quadriceps contractions in healthy young and older people. The older group contained people with and without a history of medically unexplained falls. Forty-four young (aged 18-40 years) and 78 older (aged > 70 years) subjects participated. In the latter group 34 people had a history of falling (fallers) and 44 did not (non-fallers). Isometric steadiness was measured by the coefficient of variation (CoV) of force at 10, 25 and 50% maximal voluntary force (MVC). Anisometric steadiness was measured by the SD of acceleration during concentric and eccentric contractions against two external loads (1 and 5 kg). There was an overall trend for the younger subjects to be most steady and the fallers the least but the differences were not consistently significant. Isometric steadiness was unaffected by force in all groups. The fallers were less steady (P < 0.001) than both the young and non-fallers, who had similar values. During anisometric contractions, steadiness was similar with both external loads and types of contraction in all groups. During dynamic contractions the older subjects were less steady (P < 0.002). Only eccentric contractions distinguished between the two older groups, with the fallers being less steady by 31% (P = 0.013). These data indicate ageing per se is associated with decreased anisometric, but not isometric, steadiness. Greater unsteadiness during eccentric contractions in the fallers could be an important mechanism of medically unexplained falls.

Steadiness Training with Light Loads in the Knee Extensors of Elderly Adults

This study was conducted to determine the effect of steadiness training with light loads in the knee extensors of elderly adults. Twenty-one elderly adults (72 +/- 4.6 yr) performed 16 wk of closely supervised knee extensor training that consisted of lifting and lowering 30% of the one-repetition maximum (1-RM) load as steadily as possible (10 reps per set, three sets per session, three sessions per week). Nine subjects served in a control group. Unilateral and bilateral maximal voluntary contraction (MVC) force; 1-RM load; force fluctuations during submaximal isometric, concentric, and eccentric contractions; timed functional performance (gait, chair rise, stair ascent and descent); muscle volume via magnetic resonance imaging (MRI); and the electromyogram (EMG) were measured. The training group exhibited modest average gains in MVC force and 1-RM load; muscle volume and EMG were unaltered. Although isometric steadiness was unchanged on average, training elicited the greatest improvements in the least steady subjects. Force fluctuations during concentric and eccentric contractions were significantly reduced. Of 21 subjects, 14 responded to training with gains in 1-RM load greater than the typical change (6%) in the control group. Before training, these responders exhibited greater force during bilateral compared with unilateral contractions. The small changes in physical functional performance were similar for the training and control groups. The training group could lift the pretraining 1-RM load 4.6 times after training (5.6 times for responders). Steadiness training with the knee extensors thus produced neural adaptations that increased strength in elderly adults who exhibited bilateral facilitation, improved isometric steadiness in unsteady subjects, improved steadiness during concentric and eccentric contractions, and enhanced the ability to lift heavy loads repeatedly.

Power output, isometric strength and steadiness in the leg muscles of pre- and postmenopausal women; the effects of hormone replacement therapy

There are conflicting reports of the effects of hormone replacement therapy (HRT) on strength preservation in postmenopausal women, while any effect on power output has received little attention. Decreased steadiness of force generation has been reported in older muscles and may be related to the hormonal changes associated with the menopause, but the effect of HRT has not been investigated. We have studied the effect of HRT on strength, power output and isometric force steadiness in healthy women. Sixteen young (aged 27.4 +/- 1.4 years, mean +/- SEM) and 29 postmenopausal women were studied. Fifteen of the latter were taking HRT (68.1 +/- 1.4 years, HRT+) and 14 (70.5 +/- 1.5 years, HRT-) had never done so. During isometric quadriceps contractions the force steadiness (coefficient of variation of force) was measured at 10, 25, 50 and 100% maximum voluntary contraction (MVC). The average power generated by an explosive leg extension was recorded. The HRT- group generated less power (110.2 +/- 7.2 W) than both the HRT+ (136.5 +/- 10.9 W, P = 0.027) and young (136.2 +/- 5.8 W, P = 0.027) subjects. Power output was similar in the HRT+ and younger subjects. The HRT- subjects were weaker than the younger ones (241.3 +/- 14.0 N vs. 297.6 +/- 13 N, P = 0.006). The strength of the HRT+ group (255.5 +/- 14 N) was not significantly different to the other two groups. There was no difference in steadiness between the three groups at any of the force levels. HRT appears to maintain power output to a greater extent than isometric strength in postmenopausal women. There was no evidence for an effect of either age or HRT on isometric steadiness in the quadriceps.

Force Steadiness in the Lower Extremities as an Independent Predictor of Functional Performance in Older Women

The relationship between isometric force control and functional performance is unknown. Submaximal steadiness and accuracy were measured during a constant force-matching task at 50% of maximal isometric voluntary contraction (MVC) of the knee extensors in 19 older women (70-89 years). Other variables included MVC, rate of torque development, and EMG activity. Functional performance was assessed during maximal performance of walking endurance, chair rising, and stair climbing. Isometric steadiness (but not accuracy) was found to independently predict chair-rise time and stair-climbing power and explained more variance in these tasks than any other variable. Walking endurance was related to muscle strength but not steadiness. These results suggest that steadiness is an independent predictor of brief, stressful functional-performance tasks in older women with mild functional impairment. Thus, improving steadiness might help reduce functional limitations or disability in older adults.

Resistance and functional training reduces knee extensor position fluctuations in functionally limited older adults

The purpose of this study was to determine the effect of task-specificity on knee extensor steadiness adaptations in functionally limited older adults. Twenty-four functionally limited older adults (74.6+/-7.6 years: 22 women, 2 men) completed a 10-week control period followed by 10 weeks (2 days/week) of resistance (RT), functional (FT) (practicing everyday tasks, i.e., chair rises) or functional + resistance (FRT) training, which featured both shortening and lengthening movements. During testing, subjects performed a steady isometric [10, 25, 50% of maximal voluntary contraction (MVC)] and shortening/lengthening (5, 30, 65% of MVC) knee extensor contractions. There were no steadiness (isometric, shortening or lengthening contractions) changes in the control period and no adaptations in isometric steadiness due to training. RT induced a 37% reduction in shortening fluctuations at 5% of MVC and 35% reduction in lengthening fluctuations at both 30% and 65% of MVC. FRT induced a 60% reduction in shortening fluctuations at 30% of MVC. No adaptations in dynamic steadiness were observed in the FT group. Further analysis indicated that those who were the least steady at baseline showed the greatest training effects during isometric (RT: R (2)=0.25, FRT: R (2)=0.49, FT: R (2)=0.38), shortening (RT: R (2)=0.36, FRT: R (2)=0.36, FT: R (2)=0.35) and lengthening (RT: r (2)=0.29, FRT: r (2)=0.44) contractions. In conclusion, steadiness improvements in groups performing resistance exercise, without a concomitant improvement in the FT group, supports a role for task-specificity in explaining steadiness adaptations, particularly for unsteady older adults.

Test-Retest Reliability Of Knee Extension And Flexion Torque Steadiness

The ability to perform steady contractions is quantified by measuring the fluctuations in torque. Although many studies have assessed submaximal steadiness, the reliability of these measures has not been reported. PURPOSE To determine the test-retest reliability of knee extension (KE) and flexion (KF) isometric torque steadiness for a range of submaximal loads. METHODS Eleven healthy young adults participated in two separate evaluation sessions, separated by two to eight days. In preparation for these evaluations, a familiarization session for all testing procedures was performed on a separate day. During each testing session, KE and KF isometric strength was assessed by maximal voluntary contractions (MVC). Submaximal constant-load isometric steadiness, defined as the standard deviation of fluctuations, was then assessed by subjects performing two trials each to match computer generated targets at 5, 25, and 50% MVC, 5% body mass, and 25 Nm. All assessments were performed utilizing a Biodex System 3 Pro Dynamometer interfaced with a National Instruments data acquisition system. Using this system, data was collected at 1000 Hz and torque resolution was enhanced up to 16 fold over normal Biodex system capabilities (0.1152 V/Nm for lower torque targets). Standard errors of measurement (SEM) and intraclass correlation coefficients (ICC) were determined for each direction of contraction and load level. RESULTS High precision reliability was demonstrated by small SEMs (range = 0.03 – 0.31 Nm) across all steadiness assessments. Reliability was also demonstrated by high ICCs (range = 0.84 – 0.97) for KE 25% MVC, KF 25% and 50% MVC, KF 5% body mass, and KF 25 Nm. Assessments with moderate level ICCs (range = 0.61 – 0.79) included KE 5% and 50% MVC, KE 5% body mass, KE 25 Nm, and KF 5% MVC. CONCLUSION Results indicate reliable and precise between day measures of knee extension and flexion isometric steadiness can be obtained for a wide range of submaximal constant-loads. Supported by UAB Center for Aging Grant.

Knee Extensor Isometric Unsteadiness Does Not Predict Functional Limitation in Older Adults

To determine how knee extensor steadiness is related to age and difficulty performing everyday tasks. In this cross-sectional study performed at a research laboratory, 50 older adults (age range, (56-95 yrs) performed steadiness testing at 50% of maximum strength and were timed and rated on four tasks of daily living: chair rise, stair ascent and descent, and walk. The independent variables of age, steadiness, and strength-to-weight ratio were entered into regression models with the ratings and time to complete the four everyday tasks as dependent variables. The strength-to-weight ratio was the only significant predictor in the multiple regression models, explaining 29%, 33%, 14%, and 14% of the variance in gait speed and time to complete a chair rise, stair ascent, and stair descent, respectively. Similar results were seen with task ratings. Age was not correlated with steadiness (r = 0.25, P = 0.07). This study suggests that knee extensor isometric steadiness performance does not carry over to tasks of everyday living, and older subjects, regardless of age, have similar steadiness values. Because the strength-to-weight ratio predicted the most variance in functional performance, it is recommended that muscle strength be improved to increase function in older adults.

Isotonic Force Steadiness of the Leg Extensors is Dependent on Intensity and Contraction Type in Pre-Clinically Disabled Older Adults

0835 Various studies have indicated that apparently healthy older adults have reduced steadiness during eccentric contractions and at low intensities in the finger and elbow flexor muscles, with no difference in the knee extensors. Because of their difficulty performing tasks of everyday living, pre-clinically disabled older adults may show altered steadiness patterns compared to previous research in older adults. Purpose: The purpose of this study was to determine the effect of contraction type and intensity on isotonic and isometric steadiness in pre-clinically disabled older adults. Methods: Thirty older subjects (aged 74.7 ± 7.64 years) with difficulty performing either a chair rise or stair ascent/descent tasks were enrolled into the study. Following assessment of maximal voluntary contraction (MVC), subjects performed two concentric, eccentric and isometric contractions at three different intensities. During isotonic tasks subjects lifted and lowered a load at 0.23 rad/sec with 5%, 30% and 65% of MVC. During isometric tasks, subjects were asked to hold 10, 25 & 30% of MVC. Fluctuations around the average force level during isotonic tasks and coefficient of variation for force during isometric tasks were used for statistical analysis. Data was analyzed using a two-way (Factors: contraction type*intensity for isotonic contractions) and one-way (Factor: intensity for isometric contractions) repeated measures analysis of variance. Results: For isotonic contractions, there was no intensity*contraction type interaction (p = 0.88). However, subjects were significantly less steady during high intensity compared to low intensity contractions (5% = 0.08 ± 0.04, 30% = 0.15 ± 0.09, 65% = 0.22 ± 0.14; p 0.00). Additionally, the main effect for intensity showed that older adults were less steady during concentric (0.17 ± 0.12) compared to eccentric (0.13 ± 0.10) contractions. Subjects showed similar force fluctuations between each intensity during isometric contractions (10% = 1.5 ± 1.3, 25% = 1.3 ± 1.1, 50% = 1.2 ± 0.58; p = 0.23). Conclusion: These results suggest that pre-clinically disabled older adults show reduced steadiness at higher intensities and during concentric contractions.

STRENGTH TRAINING DOES NOT IMPROVE THE STEADINESS OF MUSCLE CONTRACTIONS IN THE KNEE EXTENSORS OF OLDER ADULTS

The steadiness of muscle contractions is reduced in both the upper and lower extremities of old compared with young adults. Strength training of a hand muscle, however, decreases the fluctuations in force during submaximal contractions in older adults. The purpose of this study was to determine the effect of strength or steadiness training on the steadiness of muscle contractions in the knee extensors of older adults. Healthy adults (65 - 80 yrs) underwent 16 weeks of heavy-load strength training (H, 73 ± 1.5 yrs, N = 11), heavy-load steadiness training (HLS, 70 ± 1.5 yrs, N = 6), light-load steadiness training (LLS, 70 ± 1 yrs, N = 16), or no training (CON, 76 ± 1 yrs, N = 6). Heavy-load training was performed at 80% IRM, and light-load at 30% IRM. Steadiness training involved matching angular displacement about the knee to a constant-velocity template on an oscilloscope screen. Maximum force during an MVC and force fluctuations during constant-force tasks at 2, 5, 10, and 50% MVC were measured at 0, 2, 8, and 16 weeks. For the constant-force task, subjects were asked to match a target force with visual feedback for 10 seconds. Steadiness was expressed as the coefficient of variation (CV) for the force. CV was calculated by dividing the standard deviation of the force by the average force. MVC force increased by 26 ± 3% in H, 22 ± 5% in HLS, 8 ± 2% in LLS, and −0.95 ± 3% in CON. The CV for force during the submaximal contractions, which ranged from 1.8 - 3.5%, did not change with training in any of the experimental groups. Therefore, impaired isometric steadiness in the knee extensors of healthy older adults compared with young adults was not improved with strength training or steadiness training. Supported by NIH AG13929 to RME and F32 AG05878 to BLT