Quantitative Strength Measurements Research Articles

Instruments and Parameters for Evaluating Upper Limb Motor Fatigability in Individuals with Neuromuscular Diseases: Systematic Review

Background. Neuromuscular diseases present a set of clinical and pathological disabilities that include muscle weakness and atrophy, perception of fatigue, fatigability, and contracture. Motor fatigability compromises the ability of the individual to generate muscle strength and perform their daily activities. Quantitative measures of strength and motor fatigability are important to determine the clinical progression of the disease and the response to the proposed treatments. Thus, the aim of this study was to identify the equipment and protocols frequently used to assess upper limb motor fatigability in patients with neuromuscular disease. Methods. Information such as equipment used to induce motor fatigability, body segment or joint studied, movement analyzed, type of contraction, and protocol utilized for the test was analyzed. Joanna Briggs Scale and Newcastle-Ottawa Scale assessed the methodological quality of the studies. In addition, a checklist was prepared by the research group to assess the protocols presented in the referred studies. Results. The isokinetic and handgrip dynamometers were the most utilized equipment to induce motor fatigability. 83% of the studies had a design with low methodological rigor and half of them with high risk of bias. In the analysis of the protocols utilized to induce motor fatigability, one study was classified as regular and the other ones as good. Conclusion. The methodological topics to assess motor fatigability were incompletely described considering the electrophysiological and biomechanical approach. Although the motor fatigability in the upper limb was evaluated using isokinetic and handgrip equipment, the absence of a gold standard protocol still compromises the understanding of clinical progression and responses to the treatments in the neuromuscular diseases. This trial is registered with CRD42021206934.

Impact of strength and balance on Functional Gait Assessment performance in older adults

BackgroundThe Functional Gait Assessment (FGA) evaluates postural stability in gait and predicts fall risk in older adults. Individual tasks within the FGA consider aspects of mobility assumed to require strength and/or balance to complete. Identifying how quantitative measures of strength and balance relate to FGA performance would allow for more targeted interventions based on one’s pattern of performance on different tasks. Research QuestionIs performance on the FGA (total score and individual task scores) related to measures of strength and balance in healthy older adults? MethodsIn a cross-sectional study, healthy older adults (N = 46) were evaluated with the FGA, measures of knee extensor strength, and balance (static stance and weight shifting) (N = 46). Correlational analyses were performed between FGA scores (total and individual) and measures of strength and balance. ResultsTotal FGA performance was positively correlated with knee extensor strength (maximum torque and rate of torque development). Individual FGA tasks of walking backwards (task 9) and stair climbing (task 10) had the highest correlations with strength measures. Total FGA performance was correlated with reduced postural sway in static balance tasks, but not with balance performance on the weight shifting tasks. The individual FGA task that challenged proprioceptive (task 7) inputs for balance was associated with static balance. SignificanceThe total FGA score is related to domains of strength and static balance. The results indicate that the FGA can be influenced by reduced strength and balance. The pattern of performance on individual FGA tasks may indicate whether reduced postural stability in gait is related to deficits in strength or balance domains in this older population.

Longitudinal study of MRI and functional outcome measures in facioscapulohumeral muscular dystrophy

BackgroundFacioscapulohumeral muscular dystrophy (FSHD) is a patchy and slowly progressive disease of skeletal muscle. For MRI to be a useful biomarker in an FSHD clinical trial, it should reliably detect changes over relatively short time-intervals (~ 1 year). We hypothesized that fatty change over the study course would be most likely in muscles already demonstrating disease progression, and that the degree of MRI burden would be correlated with function.MethodsWe studied 36 patients with FSHD and lower-extremity weakness at baseline. Thirty-two patients returned in our 12-month longitudinal observational study. We analyzed DIXON MRI images of 16 lower-extremity muscles in each patient and compared them to quantitative strength measurement and ambulatory functional outcome measures.ResultsThere was a small shift to higher fat fractions in the summed muscle data for each patient, however individual muscles demonstrated much larger magnitudes of change. The greatest increase in fat fraction was observed in muscles having an intermediate fat replacement at baseline, with minimally (baseline fat fraction < 0.10) or severely (> 0.70) affected muscles less likely to progress. Functional outcome measures did not demonstrate marked change over the interval; however, overall MRI disease burden was correlated with functional outcome measures. Direct comparison of the tibialis anterior (TA) fat fraction and quantitative strength measurement showed a sigmoidal relationship, with steepest drop being when the muscle gets more than ~ 20% fatty replaced.ConclusionsAssessing MRI changes in 16 lower-extremity muscles across 1 year demonstrated that those muscles having an intermediate baseline fat fraction were more likely to progress. Ambulatory functional outcome measures are generally related to overall muscle MRI burden but remain unchanged in the short term. Quantitative strength measurement of the TA showed a steep loss of strength when more fatty infiltration is present suggesting that MRI may be preferable for following incremental change or modulation with drug therapy.

FSHD / OPMD / MYOTONIC DYSTROPHY: P.233 Longitudinal changes in MRI and functional outcome measures in facioscapulohumeral dystrophy

Thirty-two patients with facioscapulohumeral dystrophy (FSHD) underwent a prospective, longitudinal, observational study assessing MRI, quantitative strength measurements, and ambulatory functional outcome measures over a 12-month interval. While there was no significant decline in functional outcome measures or quantitative tibialis anterior strength, there was a small overall shift to higher fat fractions. The greatest increase in fat fraction were observed in muscles having intermediate fat replacement; with minimally (baseline fat fraction < 0.10) or severely (> 0.70) affected muscles less likely to progress.

Abstract TP147: Quantitative Measures of Strength and Synergy Differentiate Individuals With Chronic Stroke With and Without Clinically Detectable Elbow Contracture

Many individuals with chronic stroke demonstrate contracture of the elbow flexors. The development of contracture may be attributable to underlying impairments such as weakness, flexion synergy, and hyperactive reflexes. This study explored differences in motor impairment and function between 17 individuals with clinically detectable elbow flexor contracture and 17 individuals with full passive range of motion. The groups did not differ in age (61.61 ± 7.99, 55.06 ± 12.48, p = 0.078), years post-stroke (12.92 ± 9.34, 10.60 ± 7.16, p = 0.423), or Fugl-Meyer Motor Assessment score (FMA, 26.35 ± 5.86, 26.47 ± 8.70, p = 0.963). The passive range limitation in the contracture group was 3 to 36° (11.65 ± 8.30°). Kinetics, kinematics, and EMG were used to quantify four motor impairments and reaching function. Shoulder abduction and elbow extension strength were measured isometrically and normalized to the unaffected side. Flexion synergy was quantified as a force-based measure assessing independent joint control. Flexor spasticity was quantified while reaching at 50% of maximum shoulder abduction as the change in biceps EMG from reach onset to peak angular velocity, normalized by maximal EMG activity. Reaching function was defined as maximum reaching distance against gravity and normalized by target distance (-10° of full extension). The groups differed in elbow extension strength (Contracture, 0.315 ± 0.129; No contracture, 0.559 ± 0.153; p &lt; 0.001) and flexion synergy (0.146 ± 0.186, 0.397 ± 0.229, p = 0.009). The groups did not differ in shoulder abduction strength (0.500 ± 0.174, 0.615 ± 0.199, p = 0.080), flexor spasticity (0.079 ± 0.090, 0.056 ± 0.115, p = 0.523), or reaching function (0.501 ± 0.391, 0.714 ± 0.296, p = 0.082). The findings of this study suggest a relationship between elbow contracture and the concurrent presence of elbow extension weakness and flexion synergy. The quantitative measure of reaching function will likely differentiate individuals with and without contracture if the assessment is modified so that the standardized reaching target is located at 0° of elbow extension (normal range). Future research should use quantitative metrics to further explore the temporal recovery of impairments in order to prevent the development of contracture.

P.197Use of the D3-creatine dilution test as a non-invasive and accurate measurement of total body muscle mass in Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) results in progressive loss of functional capacities, which is a reflection of loss of muscle mass with contractile tissue being replaced by fat tissue. Currently, measurements of lean body mass (LBM) in DMD include dual energy x-ray absorptiometry (DEXA) and magnetic resonance imaging (MRI). Studies have shown that a decrease in LBM correlates with decreased quantitative strength measurements. However, DXA and MRI require cooperation from the subject and scanning can be uncomfortable for subjects in a more advanced stage of the disease with severe contractures or spine deformities. In addition, MRI requires specialized centers. Neither DEXA nor MRI provides an accurate assessment of functional skeletal muscle mass. In this on-going study we set the goal to investigate the D3-creatine dilution method in 10 DMD boys to determine total body muscle mass and lean mass and to compare these values with age-matched male control participants. This method uses a small oral dose of deuterated creatine to label the body pool of creatine, about 98% of which is found in skeletal muscle. Creatine is turned over through an irreversible conversion to creatinine and excreted in urine. The enriched urinary D3-creatinine reveals the endogenous whole body creatine pool size enabling determination of skeletal muscle mass. The method is not affected by renal function or changes in hydration status. The method has been validated in adults of all ages as well as infants and children. The advantage of this methodology is that it requires only a single dose of D3-creatine followed by a single spot urine sample 48-72 hours later. This method may provide an accurate, non-invasive tool to determine functional muscle mass in patients with neuromuscular disease. In this study, the total body D3-Cr muscle will be compared to LBM by DEXA in boys with DMD and age-matched healthy controls. Results will be presented.

Effects of weakness of orofacial muscles on swallowing and communication in FSHD.

This study explores the use of quantitative data on strength and fatigability of orofacial muscles in patients with facioscapulohumeral muscular dystrophy (FSHD) and assesses the frequency of swallowing and communication difficulties and their relationship to orofacial muscle involvement. We included 43 patients with FSHD and 35 healthy controls and used the Iowa Oral Performance Instrument (IOPI) to obtain quantitative measurements of strength and endurance of lip compression, cheek (buccodental) compression, and tongue elevation. For the assessment of swallowing and communication difficulties, we used the dysphagia-specific quality of life (SWAL-QOL) and Communicative Participation Item Bank questionnaires. Cheek compression strength was reduced in patients with FSHD compared to healthy controls. Dysphagia and difficulty with verbal communication were reported by 25% and 35% of patients, respectively, and correlated to cheek compression strength and endurance and to anterior tongue elevation endurance. Prolonged cheek compression or anterior tongue elevation endurance (decreased fatigability) made swallowing or speech problems less likely to occur. Cheek compression strength is the most sensitive IOPI measure for orofacial weakness in FSHD. Orofacial weakness contributes to dysphagia and speech difficulties in FSHD, which are both common, though generally mild. Higher endurance of orofacial muscles was associated with a lower chance of dysphagia or speech problems. More research is required for further refinement of the pattern of facial muscle involvement in FSHD and to provide new insights for improvement of speech and language therapy.

Use of Isokinetic Dynamometry To Assess Muscle Function In Burned Patients Is A Reliable Tool To Assist Progressive Resistance Exercise Prescription.

Isokinetic dynamometry is used during exercise testing and rehabilitation to obtain a quantitative strength measurement on which progressive strength training programs can be based. This study assesses the test-retest reliability of isokinetic leg function in the knee flexors and extensors at 150°/s in children and young adults with severe burns to be used for rehabilitation exercise program prescription. In 39 severely burned patients (49 ± 14% total body surface area burn [TBSA], mean ± SD; 34 ± 21% TBSA 3rd degree; 14 ± 5 years, 153.3 ± 16.5 cm height; 53.8 ± 17.9 kg) knee flexion/extension isokinetic dynamometry at 150°/s was performed on each patient's dominant leg in two sessions. The patient was acquainted with the test and performed 1 set of 10 repetitions at 150°/s. A second session of 1 set of 10 repetitions at 150°/ was performed within 24 h of the first. Muscle function outcomes were knee flexion/extension peak torque, average peak torque, and average power. One-sample paired t tests were performed for all muscle function outcomes; intraclass correlation coefficients and r2 values with session two as a function of session one were calculated. Sessions did not differ significantly in knee extension or flexion for any muscle function outcome or the hamstrings to quadriceps ratio. All intraclass correlation coefficients were >0.89 and r2 > 0.79. Test-retest isokinetic dynamometry functional measurements in the knee flexors and extensors at 150°/s are reliable in the burn population and may aid resistance rehabilitation program prescriptions.

Quantitative measures of walking and strength provide insight into brain corticospinal tract pathology in multiple sclerosis.

At least 85% of individuals with multiple sclerosis report walking dysfunction as their primary complaint. Walking and strength measures are common clinical measures to mark increasing disability or improvement with rehabilitation. Previous studies have shown an association between strength or walking ability and spinal cord MRI measures, and strength measures with brainstem corticospinal tract magnetization transfer ratio. However, the relationship between walking performance and brain corticospinal tract magnetization transfer imaging measures and the contribution of clinical measurements of walking and strength to the underlying integrity of the corticospinal tract has not been explored in multiple sclerosis. The objectives of this study were explore the relationship of quantitative measures of walking and strength to whole-brain corticospinal tract-specific MRI measures and to determine the contribution of quantitative measures of function in addition to basic clinical measures (age, gender, symptom duration and Expanded Disability Status Scale) to structural imaging measures of the corticospinal tract. We hypothesized that quantitative walking and strength measures would be related to brain corticospinal tract-specific measures, and would provide insight into the heterogeneity of brain pathology.Twenty-nine individuals with relapsing-remitting multiple sclerosis (mean(SD) age 48.7 (11.5) years; symptom duration 11.9(8.7); 17 females; median[range] Expanded Disability Status Scale 4.0 [1.0–6.5]) and 29 age and gender-matched healthy controls (age 50.8(11.6) years; 20 females) participated in clinical tests of strength and walking (Timed Up and Go, Timed 25 Foot Walk, Two Minute Walk Test ) as well as 3 T imaging including diffusion tensor imaging and magnetization transfer imaging.Individuals with multiple sclerosis were weaker (p = 0.0024) and walked slower (p = 0.0013) compared to controls. Quantitative measures of walking and strength were significantly related to corticospinal tract fractional anisotropy (r > 0.26; p < 0.04) and magnetization transfer ratio (r > 0.29; p < 0.03) measures. Although the Expanded Disability Status Scale was highly correlated with walking measures, it was not significantly related to either corticospinal tract fractional anisotropy or magnetization transfer ratio (p > 0.05). Walk velocity was a significant contributor to magnetization transfer ratio (p = 0.006) and fractional anisotropy (p = 0.011) in regression modeling that included both quantitative measures of function and basic clinical information.Quantitative measures of strength and walking are associated with brain corticospinal tract pathology. The addition of these quantitative measures to basic clinical information explains more of the variance in corticospinal tract fractional anisotropy and magnetization transfer ratio than the basic clinical information alone. Outcome measurement for multiple sclerosis clinical trials has been notoriously challenging; the use of quantitative measures of strength and walking along with tract-specific imaging methods may improve our ability to monitor disease change over time, with intervention, and provide needed guidelines for developing more effective targeted rehabilitation strategies.

Strength Testing in Motor Neuron Diseases.

Loss of muscle strength is a cardinal feature of all motor neuron diseases. Functional loss over time, including respiratory dysfunction, inability to ambulate, loss of ability to perform activities of daily living, and others are due, in large part, to decline in strength. Thus, the accurate measurement of limb muscle strength is essential in therapeutic trials to best understand the impact of therapy on vital function. While qualitative strength measurements show declines over time, the lack of reproducibility and linearity of measurement make qualitative techniques inadequate. A variety of quantitative measures have been developed; all have both positive attributes and limitations. However, with careful training and reliability testing, quantitative measures have proven to be reliable and sensitive indicators of both disease progression and the impact of experimental therapy. Quantitative strength measurements have demonstrated potentially important therapeutic effects in both amyotrophic lateral sclerosis and spinobulbar muscular atrophy, and have been shown feasible in children with spinal muscular atrophy. The spectrum of both qualitative and quantitative strength measurements are reviewed and their utility examined in this review.

When a discriminating dose assay is not enough: measuring the intensity of insecticide resistance in malaria vectors.

BackgroundGuidelines from the World Health Organization for monitoring insecticide resistance in disease vectors recommend exposing insects to a predetermined discriminating dose of insecticide and recording the percentage mortality in the population. This standardized methodology has been widely adopted for malaria vectors and has provided valuable data on the spread and prevalence of resistance. However, understanding the potential impact of this resistance on malaria control requires a more quantitative measure of the strength or intensity of this resistance.MethodsBioassays were adapted to quantify the level of resistance to permethrin in laboratory colonies and field populations of Anopheles gambiae sensu lato. WHO susceptibility tube assays were used to produce data on mortality versus exposure time and CDC bottle bioassays were used to generate dose response data sets. A modified version of the CDC bottle bioassay, known as the Resistance Intensity Rapid Diagnostic Test (I-RDT), was also used to measure the knockdown and mortality after exposure to different multipliers of the diagnostic dose. Finally cone bioassays were used to assess mortality after exposure to insecticide treated nets.ResultsThe time response assays were simple to perform but not suitable for highly resistant populations. After initial problems with stability of insecticide and bottle washing were resolved, the CDC bottle bioassay provided a reproducible, quantitative measure of resistance but there were challenges performing this under field conditions. The I-RDT was simple to perform and interpret although the end point selected (immediate knockdown versus 24 h mortality) could dramatically affect the interpretation of the data. The utility of the cone bioassays was dependent on net type and thus appropriate controls are needed to interpret the operational significance of these data sets.ConclusionsIncorporating quantitative measures of resistance strength, and utilizing bioassays with field doses of insecticides, will help interpret the possible impact of resistance on vector control activities. Each method tested had different benefits and challenges and agreement on a common methodology would be beneficial so that data are generated in a standardized format. This type of quantitative data are an important prerequisite to linking resistance strength to epidemiological outcomes.

Impact of habitual exercise on the strength of individuals with myotonic dystrophy type 1.

It remains unclear whether habitual physical activity can attenuate the rate of progressive muscle strength loss in individuals with myotonic dystrophy type 1 (DM1). The aim of this study was to identify whether there were any strength differences between DM1 patients who were habitually active or sedentary. Knee extension, handgrip, and elbow flexion quantitative strength measurements were investigated in the DM1 patients using isokinetic dynamometry. Strength was compared between the patients who followed self-selected formal exercise plans for at least 1 yr, those who were sedentary (controls), and those who initiated or terminated a formal exercise routine. Physically active DM1 patients with midrange CTG repeat size (100-500 CTG repeat sizes) had significantly stronger handgrip and knee extension and elbow flexion torques as compared with their sedentary counterparts with the same CTG repeat range. The DM1 patients who began a formal exercise routine experienced a significant improvement in knee extension torque measurements (+24.3%) in comparison with those who were habitually active or sedentary. These data suggest that there is an association between physical activity and strength. This may be shown to be a useful tool for the management of this condition. Further investigations into the relationships between physical exercise, muscle weakness, and genetic factors are needed before evidence-based recommendations can be made.

A crossover pilot study evaluating the functional outcomes of two different types of robotic movement training in chronic stroke survivors using the arm exoskeleton BONES

BackgroundTo date, the limited degrees of freedom (DOF) of most robotic training devices hinders them from providing functional training following stroke. We developed a 6-DOF exoskeleton (“BONES”) that allows movement of the upper limb to assist in rehabilitation. The objectives of this pilot study were to evaluate the impact of training with BONES on function of the affected upper limb, and to assess whether multijoint functional robotic training would translate into greater gains in arm function than single joint robotic training also conducted with BONES.MethodsTwenty subjects with mild to moderate chronic stroke participated in this crossover study. Each subject experienced multijoint functional training and single joint training three sessions per week, for four weeks, with the order of presentation randomized. The primary outcome measure was the change in Box and Block Test (BBT). The secondary outcome measures were the changes in Fugl-Meyer Arm Motor Scale (FMA), Wolf Motor Function Test (WMFT), Motor Activity Log (MAL), and quantitative measures of strength and speed of reaching. These measures were assessed at baseline, after each training period, and at a 3-month follow-up evaluation session.ResultsTraining with the robotic exoskeleton resulted in significant improvements in the BBT, FMA, WMFT, MAL, shoulder and elbow strength, and reaching speed (p < 0.05); these improvements were sustained at the 3 month follow-up. When comparing the effect of type of training on the gains obtained, no significant difference was noted between multijoint functional and single joint robotic training programs. However, for the BBT, WMFT and MAL, inequality of carryover effects were noted; subsequent analysis on the change in score between the baseline and first period of training again revealed no difference in the gains obtained between the types of training.ConclusionsTraining with the 6 DOF arm exoskeleton improved motor function after chronic stroke, challenging the idea that robotic therapy is only useful for impairment reduction. The pilot results presented here also suggest that multijoint functional robotic training is not decisively superior to single joint robotic training. This challenges the idea that functionally-oriented games during training is a key element for improving behavioral outcomes.Trial registrationNCT01050231.

Interpreting arterial blood gases

Objective This study explores the use of quantitative data on strength and fatigability of orofacial muscles in patients with facioscapulohumeral muscular dystrophy (FSHD) and assesses the frequency of swallowing and communication difficulties and their relationship to orofacial muscle involvement. Methods We included 43 patients with FSHD and 35 healthy controls and used the Iowa Oral Performance Instrument (IOPI) to obtain quantitative measurements of strength and endurance of lip compression, cheek (buccodental) compression, and tongue elevation. For the assessment of swallowing and communication difficulties, we used the dysphagia-specific quality of life (SWAL-QOL) and Communicative Participation Item Bank questionnaires. Results Cheek compression strength was reduced in patients with FSHD compared to healthy controls. Dysphagia and difficulty with verbal communication were reported by 25% and 35% of patients, respectively, and correlated to cheek compression strength and endurance and to anterior tongue elevation endurance. Prolonged cheek compression or anterior tongue elevation endurance (decreased fatigability) made swallowing or speech problems less likely to occur. Conclusion Cheek compression strength is the most sensitive IOPI measure for orofacial weakness in FSHD. Orofacial weakness contributes to dysphagia and speech difficulties in FSHD, which are both common, though generally mild. Higher endurance of orofacial muscles was associated with a lower chance of dysphagia or speech problems. More research is required for further refinement of the pattern of facial muscle involvement in FSHD and to provide new insights for improvement of speech and language therapy.

Assessing Weakness in Patients with Ulnar Neuropathy

The aim of this study was to compare the use of a custom intrinsic hand dynamometer (HD) with that of a standard pinch dynamometer (PD) in assessing strength in patients with ulnar neuropathy at the elbow. Nine patients (age, 53 ± 3 yrs) with clinical and electrophysiological features of ulnar neuropathy at the elbow with conduction block (CB) were studied. All underwent bilateral ulnar motor nerve conduction studies recording from the first dorsal interosseous and a quantitative measurement of strength of the first dorsal interosseous using a custom-made HD and a standard PD. The maximal strength of the ulnar neuropathy at the elbow-affected side (16.2 ± 8.0 N) was found to be significantly lower than that of the unaffected side (27.9 ± 11.2 N), as measured by HD. Strength differences were not significant between the affected (62.7 ± 26.4 N) and unaffected sides (48.0 ± 20.5 N) using PD. HD force decrement (in comparison with the unaffected limb) correlated strongly with CB percentage (r = 0.74). No relationship was found between PD and CB (r = 0.05). HD was better able to measure the weakness of affected muscles than did PD, and its results correlated well with the extent of electrophysiological CB. Therefore, a custom HD would provide a better indication of disease severity, progression, or improvement in strength in studies of ulnar neuropathy at the elbow with CB.

Effect of Demyelinating Ulnar Nerve Injury on Strength and Fatigue

Conduction block (CB) from focal neuropathy is often associated with weakness and fatigue in affected muscles. Ulnar neuropathy at the elbow (UNE) provides an excellent model to examine the relationships between electrophysiologically defined CB and quantitative measurement of weakness and fatigue. Eight healthy control subjects (47 ± 14 years) and nine patients (53 ± 3 years) with clinical and electrophysiological features of UNE with CB were studied. All underwent bilateral, ulnar motor nerve conduction studies recording from the first dorsal interosseous muscle as well as quantitative measurement of strength and fatigue of the first dorsal interosseous with a custom dynamometer. Strength and fatigue were similar in the dominant and nondominant hands of control subjects and unaffected limb in patients. Varying degrees of conduction block (14-62%, mean 36%) and conduction slowing (31 m/s ± 7) were observed in those with UNE. CB was associated with significant reductions in strength (42%) and fatigue (23%) on a timed fatigue task. The reductions in strength (r = 0.74) and fatigue (r = 0.60) were strongly correlated with the degree of CB. CB in UNE defined by electrophysiological criteria was strongly correlated with weakness and fatigue in the first dorsal interosseous. Fatigue may be simply related to the reduction in strength, but activity or frequency dependent CB may also contribute.

Contributors to fatigue resistance of the hamstrings and quadriceps in cerebral palsy

Background The purpose of this study was to elucidate relationships between quadriceps and hamstrings voluntary muscle fatigue and upper motor lesion impairments in cerebral palsy in order to gain a better understanding of their contribution to the observed fatigue resistance. Methods Seventeen ambulatory subjects with cerebral palsy (mean age: 17.0, SD = 4.8 years) were recruited. Quantitative measures of strength, spasticity, cocontraction, and stiffness for both muscle groups were collected on an isokinetic dynamometer and entered in a factor analysis. The resulting factors were used as independent variables in a multiple regression analysis with quadriceps and hamstrings fatigue as dependent variables. Findings Five independent factors explained 90% of the variance. In order of loadings, higher hamstring cocontraction and spasticity and lower hamstring strength were associated with lower levels of hamstring fatigue. Higher quadriceps cocontraction and lower quadriceps strength were the most predictive of lower levels of quadriceps fatigue. Interpretation Greater motor impairments of the agonist muscle, particularly cocontraction, spasticity, and weakness, were associated with lower rates of muscle fatigue of the same muscle during performance of a voluntary fatigue protocol for the hamstrings and quadriceps. Muscles are highly adaptable; therefore, the results of this study suggest that the observed fatigue resistance may be due to the effect of the primary neural insult on motor unit recruitment and rate modulation or the result of secondary adaptations to spasticity, weakness, or excessive cocontraction.

Endoscopic Revision of Carpal Tunnel Release

Open revision has been the standard approach for treatment of recurrent carpal tunnel syndrome. The authors hypothesized that endoscopic revision would yield results comparable to those with open revision. Forty-one patients with unilateral recurrence were analyzed prospectively before and after endoscopic revision for a period of 1 year. All had clinical signs or symptoms, a positive response to a steroid injection, and electrodiagnostic findings consistent with carpal tunnel syndrome after primary open release and had failed to improve after an average of 16 months. Follow-up evaluations were performed with validated outcome instruments and quantitative measurements of strength and sensation. Thirty-seven of the 41 patients reported improvement after the endoscopic revision. Significant improvement was seen at 3 and 12 months after the procedure in the Carpal Tunnel Syndrome Symptom Severity Score, the Carpal Tunnel Syndrome Functional Status Score, the University of Washington satisfaction score, pinch strength and sensation, and a decrease in scar sensitivity. An improvement in grip strength was measured after 12 months. The satisfaction score was found to be significantly correlated to the Symptom Severity Score and the Functional Status Score. Endoscopic release of recurrent carpal tunnel syndrome may be performed safely using standard technique with good results. The advantage of the procedure is the ability to approach the tunnel while avoiding the scarring related to the previous open approach. This technique is not adequate for cases after several open revisions, suspected nerve injury, or extension of the previous open approach proximal to the wrist crease.

Strength and Reversibility of Stereotypes for a Rotary Control with Linear Scales

Using real mechanical controls, this experiment studied strength and reversibility of direction-of-motion stereotypes and response times for a rotary control with horizontal and vertical scales. Thirty-eight engineering undergraduates (34 men and 4 women) ages 23 to 47 years (M=29.8, SD=7.7) took part in the experiment voluntarily. The effects of instruction of change of pointer position and control plane on movement compatibility were analyzed with precise quantitative measures of strength and a reversibility index of stereotype. Comparisons of the strength and reversibility values of these two configurations with those of rotary control-circular display, rotary control-digital counter, four-way lever-circular display, and four-way lever-digital counter were made. The results of this study provided significant implications for the industrial design of control panels for improved human performance.

Creatine monohydrate in ALS: effects on strength, fatigue, respiratory status and ALSFRS.

Our objective was to determine the effect of creatine monohydrate on disease progression in patients with amyotrophic lateral sclerosis (ALS). One hundred and seven patients with the diagnosis of probable or definite ALS, of less than five years duration from symptom onset, were randomized to either treatment with daily creatine monohydrate (5 g/d) or placebo. In this multicenter, double-blinded study we followed changes in disease progression: using quantitative measures of strength via maximal isometric voluntary contraction, forced vital capacity, ALSFRS, quality of life, fatigue and survival. Patients were followed for nine months. The results showed that creatine monohydrate did not significantly improve motor, respiratory or functional capacity in this patient population. The drug was well tolerated and the study groups well balanced, especially considering the absence of forced vital capacity criteria for entrance into the study. There was a trend toward improved survival in patients taking daily creatine monohydrate and this was identical to the trend seen in another recently published report of creatine in ALS patients . In conclusion, creatine monohydrate (5 g/d) did not have an obvious benefit on the multiple markers of disease progression measured over nine months. We measured fatigue during isometric contraction and found no significant improvement despite anecdotal patient reports prior to and during the study. The trend toward improved survival was also found in another recently completed blinded trial using creatine monohydrate. Further investigation on the possible survival benefit of creatine in this patient population is ongoing.