Biomedical subjects

Timothy J Doherty

Publications and source records attributed to Timothy J Doherty.

11 recordsLinked to original sources

PubMed2006

Within-subject reliability of motor unit number estimates and quantitative motor unit analysis in a distal and proximal upper limb muscle.

OBJECTIVE: To establish within-subject reliability of motor unit number estimates (MUNEs) and quantitative MU analysis using decomposition-based quantitative electromyography (DQEMG). METHODS: Following the acquisition of a maximum M-wave, needle and surface-detected EMG signals were collected during contractions of the first dorsal interrosseous (FDI) and biceps brachii (BB). DQEMG was used to extract motor unit potential (MUP) trains and surface-detected MUPs associated with each train, the mean size of which was divided into the maximum M-wave to obtain a MUNE. Retests were performed following the initial test to evaluate reliability. RESULTS: Subjects test-retest MUNEs were highly correlated (r=0.72 FDI; 0.97 BB) with no significant differences between test and retest MUNE values (P>0.10). Ninety-five percent confidence intervals were calculated to establish the range of expected retest MUNE variability and were +/-41 MUs for the FDI and BB. Quantitative information pertaining to MU size, complexity and firing rate were similar for both tests. CONCLUSION: MUNEs and quantitative MU data can be obtained reliably from the BB and FDI using DQEMG in individual subjects. SIGNIFICANCE: Establishing within-subject reliability of MUNEs and quantitative MU analysis allow clinicians to longitudinally follow changes in the MU pool of individuals with disorders of the central or peripheral nervous system in addition to assessing their response to treatments.

Adult↗

PubMed2006

Frequency-dependent conduction block in carpal tunnel syndrome.

Frequency-dependent conduction block (FDB) across segments of demyelination in response to high-frequency nerve stimulation has been well demonstrated in animals and has been explored in humans. However, attempts to demonstrate this phenomenon in sensory fibers involved in entrapment neuropathies have been unsuccessful. Therefore, we investigated the effects of high-frequency nerve stimulation in the median motor nerve in patients with carpal tunnel syndrome (CTS) with moderate to severely increased distal motor terminal latencies (MTL). As a group, the mean decrease in negative peak amplitude (npAmp) during 20 stimuli at 30-HZ frequency was significantly greater in CTS subjects (-11.3%) than in controls (+7.9%). The degree of FDB was greater when MTL was more prolonged (i.e., -4.9% at 5.0 ms and -25.3% at 9.4 ms) and FDB was more pronounced at higher stimulation frequencies (20 and 30 HZ). Our results suggest that the safety margin for impulse transmission is impaired in the motor axons of patients with a focal demyelinating lesion. These findings may correlate with the observation of weakness in the absence of conduction block in patients with entrapment neuropathies.

Action Potentials↗

PubMed2005

The effect of contraction intensity on motor unit number estimates of the tibialis anterior.

OBJECTIVE: To examine the effect of contractile level on motor unit number estimates (MUNEs) and establish the contraction intensity that will yield the most representative MUNE for the tibialis anterior (TA) muscle. METHODS: Surface and intramuscular electromyographic (EMG) signals were collected during a range of submaximal (threshold, 10, 20, 30 and 40% MVC) isometric dorsiflexion contractions using decomposition-enhanced spike-triggered averaging (DE-STA). Six MUNEs were calculated, one for each of the five intensities, and an ensemble sixth MUNE that had equal MU contributions from all intensities. RESULTS: Mean surface-motor unit potential sizes increased significantly (26-69 microV) and MUNEs decreased accordingly (226-91) as contraction intensity increased from threshold to 40% MVC, respectively (P<0.05). The ensemble MUNE was 153, and extrapolated to approximately 25% MVC. CONCLUSIONS: There was a significant and progressive decline in the MUNE as contraction intensity increased, confirming the importance of monitoring torque during data collection. The ensemble MUNE suggests that collecting EMG signals at a contraction intensity of approximately 25% MVC provides the most representative sample of the actual number and sizes of MUs in the TA. SIGNIFICANCE: Establishing appropriate contraction intensities improves the utility of DE-STA as a useful method for tracking changes to the MU pool in disease states and healthy aging.

Action Potentials↗

PubMed2005

Decomposition-based quantitative electromyography: effect of force on motor unit potentials and motor unit number estimates.

Decomposition-based quantitative electromyography (DQEMG) allows for the collection of motor unit potentials (MUPs) over a broad range of force levels. Given the size principle of motor unit recruitment, it may be necessary to control for force when using DQEMG for the purpose of deriving a motor unit number estimate (MUNE). Therefore, this study was performed to examine the effect of force on the physiological characteristics of concentric needle- and surface-detected MUPs and the subsequent impact on MUNEs obtained from the first dorsal interosseous (FDI) muscle sampled using DQEMG. Maximum M waves were elicited in 10 subjects with supramaximal stimulation of the ulnar nerve at the wrist. Intramuscular and surface-detected EMG signals were collected simultaneously during 30-s voluntary isometric contractions performed at specific percentages of maximal voluntary contraction (MVC). Decomposition algorithms were used to identify needle-detected MUPs and their individual MU firing times. These MU firing times were used as triggers to extract their corresponding surface-detected MUPs (S-MUPs) using spike-triggered averaging. A mean S-MUP was then calculated, the size of which was divided into the maximum M-wave size to derive a MUNE. Increased levels of contraction had a significant effect on needle- and surface-detected MUP size, firing rate, and MUNE. These results suggest that force level is an important factor to consider when performing quantitative EMG, including MUNEs with this method.

Adult↗

PubMed2005

Motor unit number estimates in the tibialis anterior muscle of young, old, and very old men.

The rate of motor unit (MU) loss and its influence on the progression of sarcopenia is not well understood. Therefore, the main purpose of this study was to estimate and compare numbers of MUs in the tibialis anterior (TA) of young men ( approximately 25 years) and two groups of older men ( approximately 65 years and >/=80 years). Decomposition-enhanced spike-triggered averaging was used to collect surface and intramuscular electromyographic signals during isometric dorsiflexions at 25% of maximum voluntary contraction. The mean surface-MU potential size was divided into the maximum M wave to calculate the motor unit number estimate (MUNE). The MUNE was significantly reduced in the old (91) compared to young (150) men, and further reduced in the very old men (59). Despite the smaller MUNE at age 65, strength was not reduced until beyond 80 years. This suggests that age-related MU loss in the TA does not limit function until a critical threshold is reached.

Adult↗

PubMed2004

Creatine monohydrate supplementation does not increase muscle strength, lean body mass, or muscle phosphocreatine in patients with myotonic dystrophy type 1.

Creatine monohydrate (CrM) supplementation may increase strength in some types of muscular dystrophy. A recent study in myotonic muscular dystrophy type 1 (DM1) did not find a significant treatment effect, but measurements of muscle phosphocreatine (PCr) were not performed. We completed a randomized, double-blind, cross-over trial using 34 genetically confirmed adult DM1 patients without significant cognitive impairment. Participants received CrM (5 g, approximately 0.074 g/kg daily) and a placebo for each 4-month phase with a 6-week wash-out. Spirometry, manual muscle testing, quantitative isometric strength testing of handgrip, foot dorsiflexion, and knee extension, handgrip and foot dorsiflexion endurance, functional tasks, activity of daily living scales, body composition (total, bone, and fat-free mass), serum creatine kinase activity, serum creatinine concentration and clearance, and liver function tests were completed before and after each intervention, and muscle PCr/beta-adenosine triphosphate (ATP) ratios of the forearm flexor muscles were completed at the end of each phase. CrM supplementation did not increase any of the outcome measurements except for plasma creatinine concentration (but not creatinine clearance). Thus, CrM supplementation at 5 g daily does not have any effects on muscle strength, body composition, or activities of daily living in patients with DM1, perhaps because of a failure of the supplementation to increase muscle PCr/beta-ATP content.

Activities of Daily Living↗

PubMed2004

Motor unit number estimation by decomposition-enhanced spike-triggered averaging: control data, test-retest reliability, and contractile level effects.

Decomposition-enhanced spike-triggered averaging (DE-STA) has been developed as a method for obtaining a motor unit number estimate (MUNE). We describe the method and report control data for the first dorsal interosseous/adductor pollicis and thenar muscles and reliability in the thenar muscles. Seventeen subjects (ages 20-50 years) took part in the study. The maximum M potential was elicited with supramaximal stimulation of the ulnar or median nerve at the wrist. Surface and intramuscularly detected electromyographic signals were then collected simultaneously during mild to moderate contractions. Decomposition algorithms were used to detect and sort the individual motor unit potential (MUP) occurrences of several concurrently active motor units in the needle-detected signals. The MUP occurrences were used as triggering sources to estimate their corresponding surface-detected MUPs (S-MUPs) using STA. The mean S-MUP size was calculated and divided into the maximum M-potential size to derive a MUNE. The MUNE values were consistent with those previously reported with other methods, and thenar MUNEs for the two trials were similar (249 +/- 78 and 246 +/- 90), with high test-retest reliability (r = 0.94, P < 0.05). DE-STA thus appears to be a valid and reliable method to obtain MUNEs.

Action Potentials↗

PubMed2004

Reliability of hand-held dynamometry in assessment of knee extensor strength after hip fracture.

OBJECTIVES: To examine the reliability of hand-held dynamometry in assessing knee extensor strength in inpatients undergoing rehabilitation after hip fracture and to examine the discriminant validity of this measure. DESIGN: A total of 16 subjects (14 women; mean +/- SD, 79 +/- 7 yrs) undergoing inpatient rehabilitation after hip fracture volunteered to participate. Isometric knee extensor strength of the fractured and unfractured sides was determined with a hand-held dynamometer. Subjects were retested 1-2 days after the initial testing session. RESULTS: Test-retest intraclass correlation coefficients were high for both the fractured (0.91) and unfractured legs (0.90). A low coefficient of variation was observed for both the fractured (15.3%) and unfractured (14.7%) sides. The maximal knee extensor strength was significantly different when comparing the fractured (7.9 +/- 3 kg) and unfractured (15.6 +/- 4 kg) legs. When comparing test 1 and test 2 mean values for the fractured leg, the scores significantly differed (t = 3.14, P < 0.01), with 13 of 16 subjects scoring higher on test 2. CONCLUSIONS: Hand-held dynamometry is a reliable and valid tool for assessment of knee extensor strength after hip fracture. Reduced knee extensor strength in the fractured leg may be an important component limiting rehabilitation progress in these patients.

Aged↗

PubMed2003

Decomposition-based quantitative electromyography: methods and initial normative data in five muscles.

Quantitative electromyographic (EMG) techniques provide clinically useful information to aid in the diagnosis and follow the course or response to treatment of diseases affecting the motor system. The purpose of this study was to describe a decomposition-based quantitative electromyography method (DQEMG) designed to obtain clinically applicable information relating to motor unit potential (MUP) size and configuration, and motor unit (MU) firing characteristics. Additionally, preliminary normative data were obtained from the deltoid, biceps brachii, first dorsal interosseous, vastus medialis, and tibialis anterior muscles of 13 control subjects. DQEMG was capable of efficiently and accurately extracting MUP data from complex interference patterns during mild to moderate contractions. MUP amplitude, surface-detected MUP (S-MUP) amplitude, MUP duration, number of phases, and MU firing frequencies varied significantly across muscles. The mean parameter values for the individual muscles studied were similar to previous reports based on other quantitative methods. The main advantages of this method are the speed of data acquisition and processing, the ability to obtain MUPs from MUs with low and higher recruitment thresholds, and the ability to obtain both S-MUP or macro-MUP data as well as MU firing rate information.

Adult↗

PubMed2003

Invited review: Aging and sarcopenia.

Aging is associated with progressive loss of neuromuscular function that often leads to progressive disability and loss of independence. The term sarcopenia is now commonly used to describe the loss of skeletal muscle mass and strength that occurs in concert with biological aging. By the seventh and eighth decade of life, maximal voluntary contractile strength is decreased, on average, by 20-40% for both men and women in proximal and distal muscles. Although age-associated decreases in strength per unit muscle mass, or muscle quality, may play a role, the majority of strength loss can be accounted for by decreased muscle mass. Multiple factors lead to the development of sarcopenia and the associated impact on function. Loss of skeletal muscle fibers secondary to decreased numbers of motoneurons appears to be a major contributing influence, but other factors, including decreased physical activity, altered hormonal status, decreased total caloric and protein intake, inflammatory mediators, and factors leading to altered protein synthesis, must also be considered. The prevalence of sarcopenia, which may be as high as 30% for those >/=60 yr, will increase as the percentage of the very old continues to grow in our populations. The link between sarcopenia and disability among elderly men and women highlights the need for continued research into the development of the most effective interventions to prevent or at least partially reverse sarcopenia, including the role of resistance exercise and other novel pharmacological and nutritional interventions.

Age Distribution↗

PubMed2002

A moderate dose of pseudoephedrine does not alter muscle contraction strength or anaerobic power.

OBJECTIVE: To investigate the effect of an acute oral administration of pseudoephedrine (PSE) on muscle function, fatigue, and anaerobic power output. DESIGN AND MATERIALS: Healthy males (N = 10) and females (N = 10) were allocated to receive both a placebo and PSE (120 mg) using a randomized, double-blind, crossover experimental design. Each subject had their maximal voluntary contraction strength and fatigability measured for both handgrip and ankle dorsi-flexion. Following the strength measurements, a 30-second maximal cycle test was performed to determine lower extremity anaerobic power and fatigue. Plasma lactate was measured before and after exercise. RESULTS: There were no significant differences in any of the outcome variables between the placebo and PSE trials. CONCLUSIONS: These results demonstrated that a 120 mg dose of PSE did not enhance force production, time to fatigue, fatigue index, or power output in young men or women. Therefore, there does not appear to be an ergogenic benefit from the ingestion of 120 mg PSE in high-intensity exercise performance.

Adult↗