Hand-held dynamometry

Muscle strength was also measured quantitatively using a MicroFET 2™ HHD (HOGGAN Health Industries, West Jordan, UT) to assess the peak force generated by scapular elevation and elbow flexion. Prior to testing, the HHD was calibrated, and subjects positioned supine with their arms at their sides on an examination table which was elevated to the evaluator’s hip level. A curved transducer pad was utilized for both muscle groups, and the HHD was set to ‘low’ threshold.

Scapular elevation was assessed first for each study visit, with the subject instructed to elevate their shoulder partially, and the HHD held by the evaluator just proximal to the acromioclavicular joint. To assess elbow flexion, the subject’s arm was

positioned in 90 degrees of elbow flexion, with the upper arm in contact with the examination table and the forearm in neutral position. The transducer pad of the HHD was held by the examiner on the radial surface of the forearm, just proximal to the radial styloid process.

For both muscle groups, the subject was instructed to hold a maximal voluntary contraction against the HHD, while the evaluator applied matching force in the opposite

direction, simultaneously providing subject encouragement. After matching the subject’s level of force for at least 2 s, the evaluator increased the force of resistance to attempt to break the contraction. The resulting peak force value on the HHD in pounds was recorded and note was made as to whether the contraction was broken. If it was

suspected that pain was an important contributing factor in breaking the contraction, this was also noted. Following a brief rest period, the protocol was repeated. A third trial was performed if the percentage difference between the first two tests was greater than 15% (Equation 1). Lastly, the maximum peak force value from the greatest two trials demonstrating a percentage difference of less than 15% was recorded as the subject’s

result.29

5.1.2.3 Equation 1

% difference = ([maximum value – minimum value]/maximum value)*100

5.1.2.4 Motor unit number estimation

Electromyographic (EMG) signals were acquired using decomposition-based quantitative electromyography (DQEMG) (version 3.2) and Acquire EMG software on a Neuroscan Comperio (Neuroscan Medical Systems, El Paso, TX). Data collection was performed by one evaluator (C.I.), with the exception of one subject at one time point, for whom another evaluator (T.D.) completed the protocol. Self-adhering Silver Mactrode® electrodes (GE Medical Systems, Milwaukee, WI) were used to detect surface signals, and 25 mm x 30 gauge TECA™ elite Disposable Concentric Needle Electrodes

(CareFusion, Middleton, WI) were used to detect intramuscular signals, with bandpass settings of 5 Hz to 5 kHz and 10 Hz to 10 kHz, respectively.7, 30

Surface electrodes were cut in strips (1 cm x 3.5 cm) for use as the active and reference electrodes, with a full-sized electrode serving as a ground. The skin was cleansed with isopropyl alcohol and surface electrodes positioned appropriately. The active electrode was positioned transversely over the belly of the muscle, approximately midway between the acromion process and C7 spinous process, with the reference

electrode placed over the acromion process, and the ground electrode over the deltoid.19 A handheld bipolar stimulator was used in order to elicit a maximum compound muscle action potential (CMAP), with the spinal accessory nerve stimulated posterior to the sternocleidomastoid.19 If necessary, the active electrode was moved in small

increments to a position where the CMAP negative peak amplitude was maximized and the rise time minimized. Following optimal positioning of the active electrode, the surface electrode positions were reinforced with surgical tape to ensure that no movement occurred during the study. Gradually, the stimulation intensity was increased until the CMAP negative peak amplitude reached a plateau. Automatically positioned markers indicating onset, negative peak, positive peak, and end of the maximum CMAP were reviewed and manually adjusted if necessary. Subsequently, size-related parameters of the maximum CMAP including negative peak amplitude were calculated automatically.

Following the determination of the maximal voluntary contraction-root mean square (MVC-RMS) (described in Chapter 3), the concentric needle electrode was inserted into the UT, approximately 2-10 mm proximal or distal to the active surface electrode. Subjects were asked to perform minimal isometric contractions while an optimal needle position was located that minimized the rise times of the MUPs of the first two to three recruited MUs. With the needle manually maintained in this position by the

evaluator, the subject was instructed to increase the contraction force to approximately 10-20% of the MVC-RMS. Each sub-maximal isometric contraction was maintained for 30 s, during which the subject received visual and auditory feedback from the EMG signal and % MVC-RMS information displayed on the screen to assist in the maintenance of a stable contraction. Contractions were performed until a minimum of 20 MUP trains were collected, with each contraction separated by a rest period of approximately 30-60 s, or as required by the subject. The needle position was adjusted between contractions to collect data from different portions of the muscle, and, if necessary, inserted at a new site to complete the collection of MUP trains.7, 30

Following EMG signal decomposition and the review of the acceptability of acquired MUPs, surface-detected motor unit potentials (S-MUPs), and MUP trains, as has been previously described (Chapters 1, 3), the onset, positive peak, negative peak, and end markers of the MUP templates and the negative onset, negative peak, and positive peak markers of the S-MUP templates were checked visually and repositioned if necessary.

Descriptive statistics for various parameters were calculated automatically based on all accepted MUPs, S-MUPs, and MUP trains. Additionally, the mean S-MUP was calculated by way of data point-by-data point averaging all accepted S-MUPs, aligned based on their onsets. Lastly, the MUNE was calculated automatically through division of the negative peak amplitude of this mean S-MUP into the negative peak amplitude of the maximum CMAP previously obtained (Equation 2).7 MUNE, maximum CMAP, mean S-MUP, and MUP peak-to-peak voltage values were recorded for each subject.