Knee power is an important parameter in understanding medial knee joint load in knee osteoarthritis.

OBJECTIVE: To determine the extent to which knee extensor strength and power explain variance in knee adduction moment (KAM) peak and impulse in clinical knee osteoarthritis (OA). METHODS: Fifty-three adults (mean ± SD age 61.6 ± 6.3 years, 11 men) with clinical knee OA participated. The KAM waveform was calculated from motion and force data and ensemble averaged from 5 walking trials. The KAM peak was normalized to body mass (Nm/kg). The mean KAM impulse reflected the mean total medial knee load during stride (Nm × seconds). For strength, the maximum knee extensor moment attained from maximal voluntary isometric contractions (MVIC) was normalized to body mass (Nm/kg). For power, the maximum knee extensor power during isotonic contractions, with the resistance set at 25% of MVIC, was normalized to body mass (W/kg). Covariates included age, sex, knee pain on the Knee Injury and Osteoarthritis Outcome Score, gait speed, and body mass index (BMI). Relationships of the KAM peak and impulse with strength and power were examined using sequential stepwise forward linear regressions. RESULTS: Covariates did not explain variance in the KAM peak. While extensor strength did not, peak knee extensor power explained 8% of the variance in the KAM peak (P = 0.02). Sex and BMI explained 24% of the variance in the KAM impulse (P < 0.05). Sex, BMI, and knee extensor power explained 31% of the variance in the KAM impulse (P = 0.02), with power contributing 7% (P < 0.05). CONCLUSION: Knee extensor power was more important than isometric knee strength in understanding medial knee loads during gait.

Relationship of intermuscular fat volume in the thigh with knee extensor strength and physical performance in women at risk of or with knee osteoarthritis.

OBJECTIVE: To determine the extent to which thigh intermuscular fat (IMF) and quadriceps muscle (QM) volumes explained variance in knee extensor strength and physical performance in women with radiographic knee osteoarthritis (ROA) and without. METHODS: Baseline data from 125 women (age ≥50 years) in the Osteoarthritis Initiative study, with or at risk of knee ROA were included. Knee extensor strength was measured using a fixed force transducer, normalized to body mass (N/kg). Physical performance was the time required for 5 repeated chair stands (seconds). The IMF and QM volumes, normalized to height (cm(3) /meter), were yielded from analyses of T1-weighted axial magnetic resonance images of the midthigh. Mean IMF and QM volumes, extensor strength, and physical performance were compared between women with and without ROA, controlling for age. Hierarchical multiple regressions determined whether IMF and QM volumes were related to strength and performance after controlling for age, ROA status (yes/no), alignment, and pain. RESULTS: Compared to subjects with ROA, the subjects without ROA were stronger and performed chair stands faster (P < 0.05). After adjusting for age, those subjects without ROA had less mean ± SD IMF (61.1 ± 20.3 cm(3) /meter) compared to mean ± SD ROA (72.0 ± 25.0 cm(3) /meter; P < 0.05). In the entire sample, 21.1% of variance in knee extensor strength was explained by alignment, pain, and IMF. A model explaining 13.4% of variance in physical performance included OA status and IMF. QM volume was unrelated to strength and physical performance. CONCLUSION: IMF volume explained a small amount of variance in knee extensor strength and physical performance among women with or at risk of knee ROA.

Sensory nerve action potentials and sensory perception in women with arthritis of the hand.

BACKGROUND: Arthritis of the hand can limit a person's ability to perform daily activities. Whether or not sensory deficits contribute to the disability in this population remains unknown. The primary purpose of this study was to determine if women with osteoarthritis (OA) or rheumatoid arthritis (RA) of the hand have sensory impairments. METHODS: Sensory function in the dominant hand of women with hand OA or RA and healthy women was evaluated by measuring sensory nerve action potentials (SNAPs) from the median, ulnar and radial nerves, sensory mapping (SM), and vibratory and current perception thresholds (VPT and CPT, respectively) of the second and fifth digits. RESULTS: All SNAP amplitudes were significantly lower for the hand OA and hand RA groups compared with the healthy group (p < 0.05). No group differences were found for SNAP conduction velocities, SM, VPT, and CPT. DISCUSSION: We propose, based on these findings, that women with hand OA or RA may have axonal loss of sensory fibers in the median, ulnar and radial nerves. Less apparent were losses in conduction speed or sensory perception.

Muscle activation during hand dexterity tasks in women with hand osteoarthritis and control subjects.

STUDY DESIGN: Descriptive cross-sectional study. INTRODUCTION: Hand osteoarthritis (OA) is a condition that results in hand pain and disability. It is important to understand how muscle function impairments contribute to impaired dexterity. PURPOSE OF THE STUDY: To compare muscle activation in women with and without hand OA and determine if the activation relates to measures of impairment and disability. METHODS: Electromyography (EMG) was recorded from four muscles of the hand/forearm while subjects threaded (assembly) and unthreaded (disassembly) a small bolt. The groups were compared on the integrated EMG (IEMG) of four muscles using two-way repeated-measures analyses of covariance for the assembly and disassembly tasks. RESULTS: No differences were found in muscle activation between groups when IEMG values were normalized by time (p>0.05). CONCLUSIONS: Patients with OA have some indicators of altered muscle function. It is unclear whether these are adaptive or predisposing changes. When controlling for the time to perform a task, there were no significant IEMG differences between women with hand OA and control subjects. LEVEL OF EVIDENCE: 2b.

Comparison of pQCT-based measures of radial bone geometry and apparent trabecular bone structure using manufacturer and in-house-developed algorithms.

Peripheral quantitative computed tomography (pQCT) provides noninvasive densitometric and morphometric measures of total, trabecular, and cortical bone compartments. Skeletal changes over time can be determined by repeated measurements. Image thickness of 2.5mm is thought to be advantageous with respect to test-retest reliability through interrogation of a significant tissue volume. However, the error associated with slight shifts in image location is unknown. The primary purpose of this study was to determine the effects of positional variability around the 4% site on radial bone measures. The secondary objective was to compare different software algorithms for estimating the same bone characteristics. Eight left cadaveric forearms (aged 65-88 yr) were imaged at 0.5-mm intervals around the 4% site of the radial bone using pQCT (10 slices; in-plane resolution: 0.2 × 0.2mm; thickness: 2.5mm; Stratec XCT2000L. We used the manufacturer's software (Stratec v6.0B) to determine the total bone mineral density (BD_tot), total bone mineral content (BMC_tot), total bone area (Area_tot), trabecular bone mineral density (BD_trab), trabecular bone mineral content (BMC_trab), and trabecular bone area (Area_trab) from each image. For comparison, in-house-developed software was also used to analyze Area_tot and Area_trab at the 4% site. The in-house software also produced measures of apparent trabecular structure, including number (App.Tb.N), thickness (App.Tb.Th), and spacing (App.Tb.Sp), quantified using 2 different stereological approaches: the parallel-plate method using trabecular perimeter lengths and mean intercept length analysis. The effect of slice position was assessed using a 1-way repeated-measures analysis of variance (ANOVA). Reliability of nonsignificant slice distances around the 4% site was determined using intraclass correlation coefficients (ICCs). One-way repeated-measures ANOVA was used to compare measures of similar bone characteristics at the 4% site. Bland-Altman plots were created to assess the level of agreement between pairs of algorithms quantifying comparable apparent trabecular structure. Area_tot and Area_trab differed significantly at greater than or equal to 1.0mm proximal and greater than or equal to 0.5mm distal to the 4% site. BMC_tot and BMC_trab differ significantly greater than or equal to 1.5mm proximally (for both) and greater than or equal to 2.0 and 1.0mm distally, respectively. BD_tot differed significantly at greater than or equal to 1mm proximal and distal to the 4% site. BD_trab did not differ among the 10 slices. For images acquired at the 4% site, and 0.5mm more proximally, reliability was excellent (ICC=0.98 to 0.99). Although the in-house software yielded a higher value for Area_tot and Area_trab at the 4% site (p<0.05), no systematic bias was observed. The parallel-plate method yielded higher values for App.Tb.N and lower values for App.Tb.Th (p<0.05), with no systematic bias. App.Tb.Sp values were smaller using the parallel-plate method, and the difference in methods increased as App.Tb.Sp values increased. Statistically, tolerance for repositioning around the 4% site of the radial bone is least for measures of bone area and greatest for BD_trab. On repeated measures, a proximal shift of 0.5mm will not influence the results.

Bayesian aggregation versus majority vote in the characterization of non-specific arm pain based on quantitative needle electromyography.

BACKGROUND: Methods for the calculation and application of quantitative electromyographic (EMG) statistics for the characterization of EMG data detected from forearm muscles of individuals with and without pain associated with repetitive strain injury are presented. METHODS: A classification procedure using a multi-stage application of Bayesian inference is presented that characterizes a set of motor unit potentials acquired using needle electromyography. The utility of this technique in characterizing EMG data obtained from both normal individuals and those presenting with symptoms of "non-specific arm pain" is explored and validated. The efficacy of the Bayesian technique is compared with simple voting methods. RESULTS: The aggregate Bayesian classifier presented is found to perform with accuracy equivalent to that of majority voting on the test data, with an overall accuracy greater than 0.85. Theoretical foundations of the technique are discussed, and are related to the observations found. CONCLUSIONS: Aggregation of motor unit potential conditional probability distributions estimated using quantitative electromyographic analysis, may be successfully used to perform electrodiagnostic characterization of "non-specific arm pain." It is expected that these techniques will also be able to be applied to other types of electrodiagnostic data.

Differences in EMG spike shape between individuals with and without non-specific arm pain.

The purpose of this study was to determine whether spike shape analysis of surface electromyographic (SEMG) activity is a useful tool to study muscle disorders. This study investigated SEMG spike shape parameters at low levels of contraction and changes in SEMG spike shape across different levels of isometric wrist extension contractions in individuals with non-specific arm pain (NSAP), asymptomatic subjects deemed at-risk for repetitive strain injury, and asymptomatic control subjects. Twenty-two asymptomatic control subjects, 8 at-risk subjects, and 16 subjects with NSAP participated. Bipolar SEMG data were recorded from the ECRB muscle during isometric wrist extension contractions at 10, 20, 30, 40, 50, 60, and 70% of maximum voluntary contraction (MVC) force performed in a randomized order. Five criterion measures: mean spike amplitude (MSA), mean spike duration (MSD), mean spike slope (MSS), mean spike frequency (MSF), and mean number of peaks per spike (MNPPS) were computed from each SEMG signal. A one-way analysis of covariance (ANCOVA) of the spike shape parameters computed from the 10% MVC data, with group as a main effect and age as a covariate, revealed a significant group by age interaction for MSA, and significant group main effects for MSS and MNPPS, where the NSAP group had lower MSS and lower MNPPS than the control subjects. An ANCOVA including group as a main effect and contraction level and age as covariates revealed that all three groups showed predictable changes in the spike shape analysis criterion measures over increasing contraction force levels, where motor unit recruitment and rate coding appear to be the primary mechanisms for increasing force output of the muscle. Significant interactions between group and contraction level were observed for MSD, MSA, MSS, and MNPPS. The NSAP group presented with differences in how the spike shape measures change with increasing contraction level that may be indicative of myogenic changes, a result that is consistent with previous quantitative EMG findings. This work provides evidence that NSAP involves myogenic changes in the ECRB muscle and that spike shape analysis may be a valuable non-invasive tool in the evaluation of neuromuscular disorders.

Motor unit potential morphology differences in individuals with non-specific arm pain and lateral epicondylitis.

BACKGROUND: The pathophysiology of non-specific arm pain (NSAP) is unclear and the diagnosis is made by excluding other specific upper limb pathologies, such as lateral epicondylitis or cervical radiculopathy. The purpose of this study was to determine: (i) if the quantitative parameters related to motor unit potential morphology and/or motor unit firing patterns derived from electromyographic (EMG) signals detected from an affected muscle of patients with NSAP are different from those detected in the same muscle of individuals with lateral epicondylitis (LE) and/or control subjects and (ii) if the quantitative EMG parameters suggest that the underlying pathophysiology in NSAP is either myopathic or neuropathic in nature. METHODS: Sixteen subjects with NSAP, 11 subjects with LE, eight subjects deemed to be at-risk for developing a repetitive strain injury, and 37 control subjects participated. A quantitative electromyography evaluation was completed using decomposition-based quantitative electromyography (DQEMG). Needle- and surface-detected EMG signals were collected during low-level isometric contractions of the extensor carpi radialis brevis (ECRB) muscle. DQEMG was used to extract needle-detected motor unit potential trains (MUPTs), and needle-detected motor unit potential (MUP) and surface detected motor unit potential (SMUP) morphology and motor unit (MU) firing rates were compared among the four groups using one-way analysis of variance (ANOVA). Post hoc analyses were performed using Tukey's pairwise comparisons. RESULTS: Significant group differences were found for all MUP variables and for MU firing rate (p < 0.006). The post-hoc analyses revealed that patients with NSAP had smaller MUP amplitude and SMUP amplitude and area compared to the control and LE groups (p < 0.006). MUP duration and AAR values were significantly larger in the NSAP, LE and at-risk groups compared to the control group (p < 0.006); while MUP amplitude, duration and AAR values were smaller in the NSAP compared to the LE group. SMUP duration was significantly shorter in the NSAP group compared to the control group (p < 0.006). NSAP, LE and at-risk subjects had lower mean MU firing rates than the control subjects (p < 0.006). CONCLUSION: The size-related parameters suggest that the NSAP group had significantly smaller MUPs and SMUPs than the control and LE subjects. Smaller MUPs and SMUPs may be indicative of muscle fiber atrophy and/or loss. A prospective study is needed to confirm any causal relationship between smaller MUPs and SMUPs and NSAP as found in this work.

Reliability of quantitative EMG analysis of the extensor carpi radialis muscle.

This study investigated the within-subject, intra- and inter-operator reliability of quantitative electromyographic (EMG) analysis using decomposition-based quantitative electromyography (DQEMG). Needle and surface-detected EMG signals were collected during low-level isometric contractions of the extensor carpi radialis (ECR) muscle. DQEMG was used to extract needle-detected motor unit potential (MUP) trains and surface-detected MUPs (SMUPs) associated with each train. Two independent experienced operators re-decomposed and processed the MUP data on two separate occasions. One-way analyses of variance (ANOVA) were performed to identify within-subject differences (test-retest, n=6), and operator and trial differences (intra- and inter-operator, n=20) for the MUP morphological variables. The within-subject reliability, as well as the intra- and inter-operator reliability were estimated using intraclass correlation coefficients (ICCs). The 95% limits of agreement were calculated to measure within-subject and between operator agreements. MUP durations were found to be significantly different between days (p<0.05). For intra- and inter-operator reliability, a significant difference was found within and between the operators for MUP duration, and between the operators for MUP number of turns (p<0.05). SMUP morphological parameters yielded higher ICC values for both intra (0.96-0.99) and inter (0.96-0.99) operator scores when compared to MUP morphological parameters (intra-operator: 0.81-0.99; and inter-operator: 0.67-0.98). Mean motor unit (MU) firing rate was found to be a highly reliable measure for both intra- and inter-operators (0.99-0.97, respectively). The between-operator agreement was above 95% for all morphological parameters. These results concerning within-subject, intra- and inter-operator reliability and levels of agreement for quantitative motor unit analysis suggest that DQEMG provides sufficiently consistent results to allow it to be effectively used for QEMG analysis. Needle-detected MUP morphology although clinically useful in the diagnosis and monitoring of neuropathies, was not as reliable as surface MUP QEMG measures.

Physiological characteristics of motor units in the brachioradialis muscle across fatiguing low-level isometric contractions.

The purpose of this study was to determine (i) if decomposition-based quantitative electromyography (DQEMG) could detect changes in motor unit potential (MUP) morphology and motor unit (MU) firing pattern statistics associated with muscle fatigue, (ii) if any detected changes are correlated with surface electromyographic (SEMG) signs of fatigue, and (iii) if significant fatigue-dependent changes are repeatable within individuals. Mean MU firing rates and the morphology of MUPs detected using needle and surface electrodes during constant-torque isometric contractions held until exhaustion were investigated in the brachioradialis (BR) muscle in 10 healthy volunteers (mean age=28.6 yr, SD+/-3.9). Time dependant changes were investigated using an analysis of variance with normalized time as a main effect. Partial correlation coefficients were computed using a repeated measures analysis of covariance to determine if changes in MU firing rates, needle-detected MUPs and surface-detected MUPs (SMUPs) were related to changes in SEMG signal amplitude and frequency parameters. Intraclass correlation coefficients (ICCs) were used to determine the within-subject repeatability of changes in MU firing rates, and MUP and SMUP parameters. Significant decreases in mean MU firing rates were found along with significant increases in various duration and area related parameters in both MUPs and SMUPs across the fatiguing contraction. The SEMG signal demonstrated the expected changes with fatigue: an increase in amplitude and a decrease in frequency content. SEMG amplitude was significantly positively correlated with SMUP peak-to-peak voltage (r=0.85, p<0.05), and SMUP area (r=0.86, p<0.05). Mean power frequency was significantly negatively correlated with SMUP negative peak duration (r=-0.74, p<0.05). The significant time-dependent changes were reliably observed (ICCs were 0.94 for MUP peak to peak amplitude, 0.97 for MUP area and 0.95 for MUP area to amplitude ratio, 0.95 for SMUP peak-to-peak voltage, 0.83 for SMUP area, 0.99 for SMUP negative peak amplitude and 0.88 for SMUP negative peak area). The decreases in mean MU firing rates measured along with the increases in amplitude, duration and area parameters of MUPs and SMUPs and their partial correlation with SEMG amplitude during submaximal fatiguing contractions of the BR, suggest that recruitment is a main cause of increased SEMG amplitude parameters with fatigue. We conclude that DQEMG can be effectively and reliably used to detect changes in physiological characteristics of MUs that accompany fatigue.

Adaptations during familiarization to resistive exercise.

This study focused on adaptations during familiarization to resistive exercise. It was also determined if familiarization requires one or more sessions. Twenty-six sedentary, college-aged females were matched and randomly assigned to one of two groups. Measurements were obtained during the initial familiarization period (Group 1: 15 trials on 1 day, Group 2: 5 trials on each of three consecutive days), and during retention tests scheduled two weeks and 3 months after the first test session. Elbow flexion torque and surface electromyography (SEMG) of the biceps and triceps were monitored concurrently. There were no significant differences between groups for any of the criterion measures. There was a significant (p<0.05) increase (12.4 Nm, or 38.8%) in maximal isometric elbow flexion torque. Biceps (agonist) root-mean-square (RMS) SEMG exhibited a significant (p<0.05) increase of 95 microV (29%). Triceps (antagonist) RMS SEMG underwent alternating decreases then increases, and each change was significant (p<0.05). The ratio of biceps to triceps RMS SEMG was used to assess cocontraction, and it followed the same pattern of change as triceps RMS SEMG. We concluded that both groups responded in the same way to testing, regardless of the pattern of the first 15 contractions. The increase in maximal isometric elbow flexion torque was due to neural drive to the bicep (agonist). There was a low level of triceps (antagonist) cocontraction to provide joint stability, and it was adjusted throughout the duration of testing.

Reliability of the biceps brachii M-wave.

BACKGROUND: The peak-to-peak (P-P) amplitude of the maximum M-wave and the area of the negative phase of the curve are important measures that serve as methodological controls in H-reflex studies, motor unit number estimation (MUNE) procedures, and normalization factors for voluntary electromyographic (EMG) activity. These methodologies assume, with little evidence, that M-wave variability is minimal. This study therefore examined the intraclass reliability of these measures for the biceps brachii. METHODS: Twenty-two healthy adults (4 males and 18 females) participated in 5 separate days of electrical stimulation of the musculocutaneous nerve supplying the biceps brachii muscle. A total of 10 stimulations were recorded on each of the 5 test sessions: a total of fifty trials were used for analysis. A two-factor repeated measures analysis of variance (ANOVA) evaluated the stability of the group means across test sessions. The consistency of scores within individuals was determined by calculating the intraclass correlation coefficient (ICC). The variance ratio (VR) was then used to assess the reproducibility of the shape of the maximum M-wave within individual subjects. RESULTS: The P-P amplitude means ranged from 12.62 +/- 4.33 mV to 13.45 +/- 4.07 mV across test sessions. The group means were highly stable. ICC analysis also revealed that the scores were very consistent (ICC = 0.98). The group means for the area of the negative phase of the maximum M-wave were also stable (117 to 126 mV.ms). The ICC analysis also indicated a high degree of consistency (ICC = 0.96). The VR for the sample was 0.244 +/- 0.169, which suggests that the biceps brachii maximum M-wave shape was in general very reproducible for each subject. CONCLUSION: The results support the use of P-P amplitude of the maximum M-wave as a methodological control in H-reflex studies, and as a normalization factor for voluntary EMG. The area of the negative phase of the maximum M-wave is both stable and consistent, and the shape of the entire waveform is highly reproducible and may be used for MUNE procedures.