Citations
To determine the effect of very high stimulation frequency (150 and 200 Hz) with wide pulse duration versus 50 Hz with wide pulse duration on stimulated force and fatigue of quadriceps femoris in healthy participants.
Thirty-four healthy participants underwent fatigue test using three stimulation frequency conditions (50, 150, and 200 Hz) with pulse duration of 0.9 ms. Normalized force values at the end of each fatigue protocol and curve fitting patterns were compared among stimulated frequencies.
Very high stimulation frequency (150 and 200 Hz) conditions showed a trend of having more decline in normalized stimulated force during fatigue test compared to a low stimulation frequency at 50 Hz. However, the difference was not statistically significant. Responder group showed the same slope of a linear fitting pattern, implying the same pattern of muscle fatigue among three stimulation frequency conditions (−3.32 in 50 Hz, −2.88 in 150 Hz, and −3.14 in 200 Hz, respectively).
There were high inter-subject variations in the response to different frequency stimulation conditions. However, very high stimulation frequency generated the same fatigue pattern as the low stimulation frequency in the responder group. Further research is needed to explore the mechanism involved.
Citations
To investigate the reliability and validity of a new method for isometric back extensor strength measurement using a portable dynamometer.
A chair equipped with a small portable dynamometer was designed (Power Track II Commander Muscle Tester). A total of 15 men (mean age, 34.8±7.5 years) and 15 women (mean age, 33.1±5.5 years) with no current back problems or previous history of back surgery were recruited. Subjects were asked to push the back of the chair while seated, and their isometric back extensor strength was measured by the portable dynamometer. Test-retest reliability was assessed with intraclass correlation coefficient (ICC). For the validity assessment, isometric back extensor strength of all subjects was measured by a widely used physical performance evaluation instrument, BTE PrimusRS system. The limit of agreement (LoA) from the Bland-Altman plot was evaluated between two methods.
The test-retest reliability was excellent (ICC=0.82; 95% confidence interval, 0.65–0.91). The Bland-Altman plots demonstrated acceptable agreement between the two methods: the lower 95% LoA was −63.1 N and the upper 95% LoA was 61.1 N.
This study shows that isometric back extensor strength measurement using a portable dynamometer has good reliability and validity.
Citations
To compare transverse abdominis (TrA) contractility in stroke patients with hemiparesis and healthy adults using musculoskeletal ultrasonography.
Forty-seven stroke patients with hemiparesis and 25 age-matched healthy control subjects participated in this study. Stroke patients were divided into three groups on the basis of their degree of ambulation. Group A consisted of 9 patients with wheelchair ambulation, group B of 23 patients with assisted ambulation, and group C of 15 patients with independent ambulation. Inter-rater reliability regarding ultrasonographic measurement of abdominal muscle thickness in the control group was assessed by two examiners. The TrA contraction ratio (TrA contracted thickness/TrA resting thickness) was measured during abdominal drawing-in maneuver and was compared between the patients and the control group and between the ambulation groups.
The inter-rater reliability ranged from 0.900 to 0.947. The TrA contraction ratio was higher in the non-paretic side than in the paretic side (1.40±0.62 vs. 1.14±0.35, p<0.01). The TrA contraction ratio of the patient group was lower in the non-paretic side as well as in the paretic side than that of the control group (right 1.85±0.29, left 1.92±0.42; p<0.001). No difference was found between the ambulation regarding the TrA contraction ratio.
The TrA contractility in hemiparetic stroke patients is significantly decreased in the non-paretic side as well as in the paretic side compared with that of healthy adults. Ultrasonographic measurement can be clinically used in the evaluation of deep abdominal muscles in stroke patients.
Citations
Evaluation of Postural Stability and Transverse Abdominal Muscle Activity in Overweight Post-Stroke Patients: A Prospective, Observational Study
To determine the reliability and validity of hand-held dynamometer (HHD) depending on its fixation in measuring isometric knee extensor strength by comparing the results with an isokinetic dynamometer.
Twenty-seven healthy female volunteers participated in this study. The subjects were tested in seated and supine position using three measurement methods: isometric knee extension by isokinetic dynamometer, non-fixed HHD, and fixed HHD. During the measurement, the knee joints of subjects were fixed at a 35° angle from the extended position. The fixed HHD measurement was conducted with the HHD fixed to distal tibia with a Velcro strap; non-fixed HHD was performed with a hand-held method without Velcro fixation. All the measurements were repeated three times and among them, the maximum values of peak torque were used for the analysis.
The data from the fixed HHD method showed higher validity than the non-fixed method compared with the results of the isokinetic dynamometer. Pearson correlation coefficients (r) between fixed HHD and isokinetic dynamometer method were statistically significant (supine-right: r=0.806, p<0.05; seating-right: r=0.473, p<0.05; supine-left: r=0.524, p<0.05), whereas Pearson correlation coefficients between non-fixed dynamometer and isokinetic dynamometer methods were not statistically significant, except for the result of the supine position of the left leg (r=0.384, p<0.05). Both fixed and non-fixed HHD methods showed excellent inter-rater reliability. However, the fixed HHD method showed a higher reliability than the non-fixed HHD method by considering the intraclass correlation coefficient (fixed HHD, 0.952-0.984; non-fixed HHD, 0.940-0.963).
Fixation of HHD during measurement in the supine position increases the reliability and validity in measuring the quadriceps strength.
Citations
Objective: To determine the effects of the voluntary contraction of muscles and magnetic stimulation intensity on the motor evoked potential (MEP) and the silent period (SP).
Method: We studied MEPs and SPs in opponens pollicis muscle in 30 healthy adults (male: 16, female: 14) while varying the amount of the voluntary contraction and the stimulation intensity. We analyzed MEPs and SPs in relation to sex, recording site, opposition power and height.
Results: 1) During the contraction, the latencies of MEP were significantly shorter than during the relaxation. 2) The amplitudes of MEP reached plateau at 30% of maximal voluntary
contraction and increased with increment of stimulation intensity without limitation. The amplitudes of MEP of right hand were bigger than left hand. There were no significant differences according to sex and recording site. 3) The durations of SP were directly proportional to the degrees of voluntary contraction and the stimulation intensity.
Conclusion: Transcranial magnetic stimulation should be performed under the same voluntary contraction and magnetic stimulation intensity. (J Korean Acad Rehab Med 2002; 26: 140-146)
Objective: To investigate the association of the muscle contraction with gating of the sensory input at central and peripheral levels according to the intensity of muscle contraction and location of the muscles, somatosensory evoked potentials (SSEPs) studies were evaluated at different levels of isometric contraction in the different muscles.
Method: Median nerve SSEPs were recorded at Erb's point and scalp in the ten healthy adult subjects with isometric contraction of ipsilateral abductor pollicis brevis (APB), ipsilateral abductor digiti minimi (ADM) and contralateral APB. Median nerve SSEPs were recorded in each of these conditions during precontraction, weak contraction, strong contraction and 4 minutes after contraction.
Results: 1) N9 amplitudes of median SSEPs recorded at Erb's point were augumented during weak contraction and these amplitude augumentations were statistically significant in the ipsilateral APB contraction (p＜0.05). 2) N20 amplitudes recorded at scalp were inhibited during strong isometric contraction and these amplitude inhibitions were statistically significant in the ipsilateral APB contraction (p＜0.05). 3) The latencies of N9 and N20 potentials were not significantly changed during isometric contraction.
Conclusion: Therefore peripheral nervous system as well as central nervous system is responsible for gating, so the subject should be asked for the best relaxation possible for higher reliability of SSEPs.
Objective: To investigate waveform changes of compound muscle action potentials (CMAPs) related to voluntary muscle contraction and alteration of muscle length and to evaluate the effect of peripheral neuropathy on temporal and spatial summations of CMAPs.
Method: The influence of voluntary muscle contraction and alteration of muscle length on CMAP was studied in 37 median nerves of 21 patients with median neuropathy.
Results: In patients with no apparent axonopathy, temporal summation was partially disturbed without significant change of spatial summation. Shortening of muscle length or voluntary contraction produced a physiologic improvement of spatial and temporal summations. There was a decrease in temporal and spatial summations, more prominent in temporal summation, with lengthening of the muscle. In axonopathy, spatial summation was markedly deteriorated with partial reduction of temporal summation. Spatial summation was not affected by the change of muscle length or voluntary contraction. Temporal summation was improved by muscle shortening or voluntary contraction and was decreased by muscle lengthening.
Conclusion: Peripheral neuropathy has an effects on physiological spatial and temporal summations of CMAPs. Temporal summation is preferentially decreased in cases without axonopathy. When axonopathy is apparent, spatial summation is profoundly disturbed with partial reduction of temporal summation.
Objective: Inappropriate neural control of the quadriceps femoris muscle group has been implicated in patellofemoral pain syndrome (PFPS) and the methods of biomechanical assessment of PFPS has been developed recently. The aims of the present investigation were to evaluate the effects of therapeutic exercise in the alleviation of PFPS and to develope objective clinical test for PFPS.
Method: We investigated the onset time of the isometric contraction of vastus medialis oblique muscle (VMO) and the vastus lateralis muscle (VL) under four different conditions: knee flexion and extension in weight bearing (standing) and non-weight bearing (sitting on chair) situations. For each condition, onset times of EMG activities and onset times for VMO and VL were determined from five trials of isometric contraction. In addition, we compared knee flexor and extensor torques in control group and subjects with PFPS. To evaluate the effects of the exercise we compared the onset time difference (onset time of VL-onset time of VM) and quadriceps muscle torque at pre- and post- exercise in PFPS groups.
Results: In PFPS group, onset time of VMO during knee extension was significantly longer than the onset time of VL and the knee extensor torque was considerably weaker in comparison with normal group. Although onset time difference was not changed after exercise program, there were significant increase in knee extensor torque in subjects with PFPS.
Conclusion: The role of exercise in the rehabilitation of quadriceps functions is to reduce the pain, to strengthen the knee extensor, and further accurate diagnostic tools and methods for the result of therapeutic exercise in PFPS are needed.
Objectives: To determine the effect of facilitation on H reflex side-to-side amplitude ratio and to determine the effect of averaging under the assumption that an averaging could further stabilize the amplitude ratio in a facilitated condition.
Method: FCR H reflex amplitude ratios of direct and averaged potentials were measured in fifty asymptomatic subjects under three conditions, during rest, during a constant 5 pound isometric contraction under the hand-dynamometer monitoring, and during a moderate constant isometric contraction under the electromyographer's verbal guidance.
Results: The lower limits of the amplitude ratios that encompass 97.5% of subjects by the percentile method under three conditions were as follows; (1) during the rest (n=37); 0.47 (direct) and 0.50 (average), (2) during the constant 5 pound isometric contraction under the hand- dynamometer monitoring; 0.47 (direct) and 0.48 (average), and (3) during the moderate constant isometric contraction under the electromyographer's verbal guidance; 0.48 (direct) and 0.46 (average), respectively.
Conclusion: There seems to be no definite effect of facilitation and averaging on H reflex amplitude ratio. H reflex amplitude ratio measured in facilitated condition without averaging is still useful for the diagnosis of unilateral radiculopathy.
Objectives: To analyze the motor evoked potential (MEP) responses to a degree of voluntary contraction and stimulus intensity and to suggest the standardized optimal stimulation for MEP responses.
Methods: MEPs induced by a cortical stimulation were elicited at the thenar muscles in 15 normal subjects during the rest and gradual voluntary contraction, using the 10% of maximal voluntary contraction (MVC), 30%, 50%, and MVC. During rest and during each contraction, excitability threshold at rest (RET) and at contraction (CET) were determined. Consecutive stimuli were applied, according to the intensity of ratio increment (110% to 150% of excitation threshold).
Results: The RET showed a remarkable decrease (57.1⁑8.2% → 47.4⁑8.7%) after the voluntary contraction (P＜0.05). Shortening of latency reached the saturation level with 10% of MVC, irrespective of stimulus intensity. Amplitude reached a saturation level at 30% of MVC with 62.7% intensity of maximal output, which is equal to 140% intensity of its CET, and to 110% of RET. MEP amplitude at rest and at 10% of MVC were influenced by the excitation threshold (P＜0.05), but those at above 30% of MVC were not related.
Conclusion: The procedure for optimal facilitation for the MEPs is as follows; for minimal latency of MEPs, minimal contraction (10% of MVC) with RET intensity is enough. For maximal amplitude of MEPs, moderate contraction (30% MVC) with 110% intensity of RET is adequate.
The influence of voluntary muscle contraction and alteration of muscle length on compound muscle action potential (CMAP) was studied in 20 healthy volunteers. The CMAPs were evoked by a supramaximal stimulation and recorded by a surface electrode array. Onset latencies were not significantly changed regardless of the muscle length and contraction. On shortening of the muscle there was a decrease in an area and duration of CMAP with no significant changes in an amplitude. During muscle contractions, there was an increase in amplitude and a decrease in area and duration. On a lengthening of the muscle with relaxation, the amplitude of CMAP decreased with an increased area and duration. During a voluntary contraction, there was a decrease in amplitude, area, and duration. The results are considered due to a peripheral factor such as an alteration of temporal or spatial summation rather than a central mechanism. We conclude that in nerve conduction studies, it is important to monitor the finger position and muscle relaxation to differentiate the waveform changes from the muscle length or contraction and those from the nerve lesions.
Isotonic exercise occurs when the tension or torque generated by a muscle is constant throughout the movement. In practice it is very difficult to maintain the tension constant. Evaluation of isotonic exercise should include the works of concentric and eccentric contraction and the changes in tension and torque during joint motion. However, optimal evaluation tools for isotonic exercise has yet to be developed.
We authors, used virtual reality motion analysis system(VRMAS) which was codeveloped by us and EMG system(Cardwell Excel). Healthy male adult subjects(n=10) were recruited from hospital personnel. After dominant upper arm and trunk of each subject was fixed with velcro, he was instructed to repeat flexion and extension of his dominant elbow grasping dumbell (9 kg) in hand with maximal velocity as possible as can until the point of exhaustion. We measured the elbow angle, the angular velocity, torque, power, total work and the work of concentric and eccentric contraction during exercise.
The results were as follows: there were four distinct elbow flexor muscle contractions during flexion and extension of the elbow with the first and the second contractions during concentric contraction and the third and the fourth contractions during eccentric contraction. Between the peaks of contraction, motion was maintained due to the momentum that was generated. Of the ten subjects, seven had higher concentric work than eccentric work with the eccentric work being higher in the remaining three. But there was no statistic significance between the works of concentric contraction and eccentric contraction(p>0.05). The biggest work was observed in the fourth contraction, while the third contraction showed the least work(p<0.05).
In conclusion, there were four distinct muscle contractions during elbow isotonic exercise and the works of each muscle contraction were different. This result is contrary to the definition of isotonic exercise. This study also shows that the VRMAS could be a very useful evaluation tool for several types of isotonic exercise.
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