Photobiomodulation Decreases Fatigue of the Wrist Extensors: Electromyographic and Dynamometric Analysis

This study analyzed the effects of photobiomodulation, on wrist extensor muscles when applied before a fatigue protocol. Twenty-eight men participated in a crossover, blinded, and controlled trial. Subjects performed grip dynamometry associated with superficial electromyography of the extensor carpi radialis, extensor carpi ulnaris, and flexor digitorum superficialis, which was used to evaluate muscle recruitment pattern by median frequency. The initial assessment was performed with a onerepetition maximum test. Twenty-four hours later the allocation was performed in two moments, and randomization was initially performed with 28 volunteers, divided between the two groups: control group, and the Low-Level Laser Therapy (30 mW, 0.06 cm2, 20 J/cm2, 1.2 J per point, and total energy of 10.8 J). Median frequency demonstrated Extensor Carpi Ulnaris fatigue in the control group as well as when compared after the fatigue protocol in the laser group. Exhaustion time was greater in the laser group and the fatigue protocol was effective at decreasing grip strength, with significant difference in the control group (p < 0.05). After the fatigue protocol, Low-Level Laser Therapy was effective in maintaining grip strength to increase exhaustion time and does not promote alterations in Median Frequency behavior at wrist extensor muscles.

Sensory enhancement amplifies interlimb cutaneous reflexes in wrist extensor muscles

Interlimb neural connections support motor tasks such as locomotion and cross-education strength training. Somatosensory pathways that can be assessed with cutaneous reflex paradigms assist in subserving these connections. Many studies show that stimulation of cutaneous nerves elicits reflexes in muscles widespread across the body and induces neural plasticity after training. Sensory enhancement, such as long-duration trains of transcutaneous stimulation, facilitates performance during rehabilitation training or fatiguing motor tasks. Performance improvements due to sensory stimulation may be caused by altered spinal and corticospinal excitability. However, how enhanced sensory input regulates the excitability of interlimb cutaneous reflex pathways has not been studied. Our purpose was to investigate the effects of sensory enhancement on interlimb cutaneous reflexes in wrist extensor muscles. Stimulation to provide sensory enhancement (2-s trains at 150 Hz to median or superficial radial nerves) or evoke cutaneous reflexes (15-ms trains at 300 Hz to superficial radial nerve) was applied in different arms while participants ( n = 13) performed graded isometric wrist extension. Wrist extensor electromyography and cutaneous reflexes were measured bilaterally. We found amplified inhibitory reflexes in the arm receiving superficial radial and median nerve sensory enhancement with net reflex amplitudes decreased by 709.5% and 695.3% repetitively. This suggests sensory input alters neuronal excitabilities in the interlimb cutaneous pathways. These findings have potential application in facilitating motor function recovery through alterations in spinal cord excitability enhancing sensory input during targeted rehabilitation and sports training. NEW & NOTEWORTHY We show that sensory enhancement increases excitability in interlimb cutaneous pathways and that these effects are not influenced by descending motor drive on the contralateral side. These findings confirm the role of sensory input and cutaneous pathways in regulating interlimb movements. In targeted motor function training or rehabilitation, sensory enhancement may be applied to facilitate outcomes.

Comparison of the electrical activity in upper trapezius and wrist extensor muscles during two typewriting conditions

Introduction The proper use of the position of the arm and wrist while typing may reduce muscle overload and prevent musculoskeletal disorders.Objective To evaluate the electromyographic activity of upper trapezius and wrist extensor muscles during two typewriting conditions.Materials and methods : Six healthy females (Xage = 42 years,SD= 10), (Xheight = 1.65m, SD = 0.05) and (Xweight = 71kg, SD = 16) participated in this study. The task was performed with a newly developed arm support and without the support. A perceived exertion scale was used with all subjects. An ANOVA with repeated measures was used to verify differences in perceived exertion and root mean square (RMS).Results There were no statistically significant differences for the RMS between the typewriting tasks. The condition without arm support presented a significantly greater mean velocity and amount of words typed (P= 0.02; P= 0.03) and there was a significant difference in perceived exertion during the condition without arm support (P= 0.03). Electromyographic activity did not present differences.Conclusion The muscle electrical activity was not altered regardless the arm support and occurred the improvement of the perceived exertion after 10 minutes of typing without support. Long-term studies are needed.

Lack of Effect of Acupuncture on Electromyo-Graphic (Emg) Activity – a Randomised Controlled Trial in Healthy Volunteers

Background Acupuncture is used clinically to treat muscle spasticity and flaccidity. Claims have been made that acupuncture can affect muscle EMG activity, though there is some doubt about the reliability of these studies. This study's aim was to examine the immediate effects of acupuncture on the EMG activity of the common wrist extensor muscles. Methods Thirty five right-handed healthy volunteers, 17 male and 18 female, aged 18-70 years were recruited from a convenience sample. Five subjects provided reliability data, and the remaining 30 took part in the main study. The study was a crossover, within-subject design, with the interventions counterbalanced. The three conditions were genuine acupuncture to LI4 ( Hegu) and LI10 ( Shousanli) for 20 minutes, with de qi; inappropriate acupuncture to PC3 ( Quze) and PC6 ( Neiguan) for 20 minutes; and 20 minutes of a no intervention control. All participants received each condition in random order. The outcome measure was surface EMG activity recorded over the common wrist extensor muscles during a 10 second, sub-maximal, isometric contraction. The average of three readings was used. The reliability of the outcome measurement was assessed in five volunteers selected at random who received repeated EMG recordings without acupuncture. Results The reliability tests showed the EMG procedure was highly reliable, with an intraclass correlation coefficient (ICC 2,1) of 0.9996 and a standard error of measurement of 0.014mV. In the main study, paired t tests for the effect of the order of the first two interventions showed no detectable carry-over effect. Freidman analysis of variance found no difference between the three conditions (P=0.573). Conclusion No meaningful change was detected in EMG activity following acupuncture interventions, but this study provides a sound protocol and normative values on which to plan future research.