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The article reports on research which was conducted to investigate the effect strength and endurance training on muscle fiber membrane properties and discharge rates of low-threshold motor units of the vasti muscles during fatiguing contractions. Researchers evaluated 25 sedentary healthy men who were randomly assigned to one of three groups: strength training, endurance training, or a control group. They found that short-term strength and endurance training induces alterations of the electrophysiological membrane properties of the muscle fiber and that endurance training lowers the rate of decline of motor unit conduction velocity during sustained contractions more than strength training.

Introduction: When performing an exercise or a functional test, pain that is evoked by movement or muscle contraction could be a stronger stimulus for changing how individuals move compared to tonic pain. We investigated whether the decrease in muscle force production is larger when experimentally‐induced knee pain is directly associated to the torque produced (movement‐evoked) compared to a constant painful stimulation (tonic). Methods: Twenty‐one participants performed three isometric knee extension maximal voluntary contractions without pain (baseline), during pain, and after pain. Knee pain was induced using sinusoidal electrical stimuli at 10 Hz over the infrapatellar fat pad, applied continuously or modulated proportionally to the knee extension torque. Peak torque and contraction duration were averaged across repetitions and normalized to baseline. Results: During tonic pain, participants reported lower pain intensity during the contraction than at rest (p < 0.001), whereas pain intensity increased with contraction during movement‐evoked pain (p < 0.001). Knee extension torque decreased during both pain conditions (p < 0.001), but a larger reduction was observed during movement‐evoked compared to tonic pain (p < 0.001). Participants produced torque for longer during tonic compared to movement‐evoked pain (p = 0.005). Conclusion: Our results indicate that movement‐evoked pain was a more potent stimulus to reduce knee extension torque than tonic pain. The longer contraction time observed during tonic pain may be a result of a lower perceived pain intensity during muscle contraction. Overall, our results suggest different motor adaptation to tonic and movement‐evoked pain and support the notion that motor adaptation to pain is a purposeful strategy to limit pain. This mechanistic evidence suggests that individuals experiencing prevalently tonic or movement‐evoked pain may exhibit different motor adaptations, which may be important for exercise prescription. [ABSTRACT FROM AUTHOR]

Supplemental digital content is available in the text. Purpose: Motor unit conduction velocity (MUCV) represents the propagation velocity of action potentials along the muscle fibers innervated by individual motor neurons and indirectly reflects the electrophysiological properties of the sarcolemma. In this study, we investigated the effect of a 4-wk strength training intervention on the peripheral properties (MUCV and motor unit action potential amplitude, RMSMU) of populations of longitudinally tracked motor units (MU). Methods: The adjustments exhibited by 12 individuals who participated in the training (INT) were compared with 12 controls (CON). Strength training involved ballistic (4 × 10) and sustained (3 × 10) isometric ankle dorsiflexions. Measurement sessions involved the recordings of maximal voluntary isometric force and submaximal isometric ramp contractions, whereas high-density surface EMG was recorded from the tibialis anterior. High-density surface EMG signals were decomposed into individual MU discharge timings, and MU was tracked across the intervention. Results: Maximal voluntary isometric force (+14.1%, P = 0.003) and average MUCV (+3.0%, P = 0.028) increased in the INT group, whereas normalized MU recruitment threshold (RT) decreased (−14.9%, P = 0.001). The slope (rate of change) of the regression between MUCV and MU RT increased only in the INT group (+32.6%, P = 0.028), indicating a progressive greater increase in MUCV for higher-threshold MU. The intercept (initial value) of MUCV did not change after the intervention (P = 0.568). The association between RMSMU and MU RT was not altered by the training. Conclusion: The increase in the rate of change in MUCV as a function of MU RT, but not the initial value of MUCV, suggests that short-term strength training elicits specific adaptations in the electrophysiological properties of the muscle fiber membrane in high-threshold MU. [ABSTRACT FROM AUTHOR]

Objective To compare the effects of dry needling or manual pressure release on an active trigger point in the upper trapezius on craniocervical flexion test performance, pressure pain thresholds, and cervical range of motion in chronic neck pain. Design A parallel randomized clinical trial. Setting Physical therapy service. Subjects Individuals with chronic neck pain. Methods Subjects were randomized to receive dry needling (n = 25) or manual trigger point pressure release (n = 25) on upper trapezius active trigger points. Surface electromyography from the upper trapezius, splenius capitis, sternocleidomastoid, and scalene muscles during performance of the craniocervical flexion test was assessed before and immediately after the intervention as the primary outcome. Neck pain intensity, range of motion, and pressure pain thresholds were the secondary outcomes. Results A decrease in sternocleidomastoid activity at all stages of the craniocervical flexion test (time effect, P  < 0.001) was found in both groups after the interventions, with no significant between-group difference. Pressure pain thresholds measured over the cervical spine and second metacarpal increased after dry needling when compared with manual trigger point pressure release (P  < 0.05). Pain intensity decreased immediately after both treatments with moderate to large effect sizes, whereas cervical range of motion increased for both groups but with small effect sizes. Conclusion A single session of dry needling or manual pressure release over upper trapezius active trigger points promotes limited effects on muscle performance during the craniocervical flexion test, pressure pain thresholds, and cervical range of motion in patients with chronic neck pain. [ABSTRACT FROM AUTHOR]