Reproducibility of knee extensor and flexor contraction velocity in healthy men and women assessed using tensiomyography: A study protocol

Tensiomyography measures the radial displacement of a muscle during an electrically evoked twitch contraction. The rate of muscle displacement is increasingly reported to assess contractile properties. Several formulas currently exist to calculate the rate of displacement during the contraction phase of the maximal twitch response. However, information on the reproducibility of these formulas is scarce. Further, different rest intervals ranging from 10 s to 30 s are applied between consecutive stimuli during progressive electrical stimulation until the maximum twitch response. The effect of different rest intervals on the rate of displacement has not been investigated so far. The first aim of this study is to investigate the within and between-day reliability of the most frequently used formulas to calculate the rate of displacement. The second aim is to investigate the effect of changing the inter-stimulus interval on the rate of displacement. We will determine the rectus femoris and biceps femoris rate of displacement of twenty-four healthy subjects’ dominant leg on two consecutive days. The maximum displacement curve will be determined two times within three minutes on the first day and a third time 24 h later. On day two, we will also apply three blocks of ten consecutive stimuli at a constant intensity of 50 mA. Inter-stimuli intervals will be 10 s, 20 s or 30 s in each block, respectively, and three minutes between blocks. The order of inter-stimulus intervals will be randomized. This study will allow a direct comparison between the five most frequently used formulas to calculate the rate of displacement in terms of their reproducibility. Our data will also inform on the effect of different inter-stimulus intervals on the rate of displacement. These results will provide helpful information on methodical considerations to determine the rate of displacement and may thus contribute to a standardized approach.

An ontogenic study of receptor mechanisms by which acute administration of low-doses of methamphetamine suppresses DOI-induced 5-HT2A-receptor mediated head-twitch response in mice

Background Methamphetamine (MA) is a non-selective monoamine releaser and thus releases serotonin (5-HT), norepinephrine (NE) and dopamine (DA) from corresponding nerve terminals into synapses. DOI ((±)-2, 5-dimethoxy-4-iodoamphetamine) is a direct-acting serotonergic 5-HT2A/C receptor agonist and induces the head-twitch response (HTR) via stimulation of 5-HT2A receptor in mice. While more selective serotonin releasers such as d-fenfluramine evoke the HTR, monoamine reuptake blockers (e.g., cocaine) suppress the DOI-evoked HTR via indirect stimulation of serotonergic 5-HT1A- and adrenergic ɑ2-receptors. Since the induction of HTR by DOI is age-dependent, we investigated whether: (1) during development MA can evoke the HTR by itself, and (2) acute pretreatment with either the selective 5-HT2A receptor antagonist EMD 281014 or low-doses of MA can: (i) modulate the DOI-induced HTR in mice across postnatal days 20, 30 and 60, and (ii) alter the DOI-induced c-fos expression in mice prefrontal cortex (PFC). To further explore the possible modulatory effect of MA on DOI-induced HTR, we investigated whether blockade of inhibitory serotonergic 5-HT1A- or adrenergic ɑ2-receptors by corresponding selective antagonists (WAY 100635 or RS 79948, respectively), can prevent the effect of MA on DOI-induced HTR during aging. Results Although neither EMD 281014 nor MA by themselves could evoke the HTR, acute pretreatment with either EMD 281014 (0.01, 0.05 and 0.1 mg/kg, i.p.) or MA (1, 2.5, 5 mg/kg, i.p.), dose-dependently suppressed the DOI-induced HTR across ages. While WAY 100635 significantly reversed the inhibitory effect of MA in 20- and 30-day old mice, RS 79948 failed to significantly counter MA’s inhibitory effect. Moreover, DOI significantly increased c-fos expressions in several PFC regions. EMD 281014 prevented the DOI-induced increases in c-fos expression. Despite the inhibitory effect of MA on DOI-induced HTR, MA alone or in combination with DOI, significantly increased c-fos expression in several regions of the PFC. Conclusion The suppressive effect of MA on the DOI-evoked HTR appears to be mainly due to functional interactions between the HTR-inducing 5-HT2A receptor and the inhibitory 5-HT1A receptor. The MA-induced increase in c-fos expression in different PFC regions may be due to MA-evoked increases in synaptic concentrations of 5-HT, NE and/or DA.

Qualitative ultrasonography scale of the intensity of local twitch response during dry needling and its association with modified joint range of motion: a cross-sectional study

Background The relevance of local twitch response (LTR) during dry needling technique (DNT) is controversial, and it is questioned whether LTR is necessary for successful outcomes. Furthermore, because the LTR during the deep DNT may be evoked with different intensities, it is unknown whether the magnitude of LTR intensity is associated with optimal clinical results, especially concerning to the effects of joint maximal range of motion (ROM). This study aimed to (i) determine whether visual inspections can quantify the LTR intensity during the DNT through a qualitative ultrasonography scale of LTR intensity (US-LTR scale), and (ii) assess the differences of US-LTR scale associated with changes in the maximal joint ROM. Methods Using a cross-sectional design, seven asymptomatic individuals were treated with DNT in the latent myofascial trigger point in both medial gastrocnemius muscles. During DNT, three consecutive LTRs were collected. The US-LTR scale was used to classify the LTRs into strong, medium, and weak intensities. The categories of US-LTR were differentiated by the velocity of LTRs using the optical flow algorithm. ROM changes in ankle dorsiflexion and knee extension were assessed before and immediately after DNT. Results The US-LTR scale showed the third LTR was significantly smaller than the first one (p < 0.05). A significant difference in velocity was observed between US-LTR categories (p < 0.001). A significant difference in the ROM was observed between the strong and weak-medium intensity (p < 0.05). Conclusions The present findings suggest that the LTR intensity can be assessed using a qualitative US-LTR scale, and the effects of DNT on joint maximal ROM is maximized with higher LTR intensity. This study reports a novel qualitative method for LTR analysis with potential applications in research and clinical settings. However, further research is needed to achieve a broader application.

ASSESSMENT OF ROCURONIUM EFFECTIVENESS FOR PAITENTS

The study is based on succinylcholine which is a routine muscle relaxant for pediatric patients. Rocuronium is newer non depolarizing muscle relaxant. The objective of this study was to assess time, course and duration of both relaxants as well as intubation conditions. This study was blind and randomized in nature and conducted to test the intubating conditions with two separate kind of muscle relaxants in 50 ASA grade I and II pediatric patients who fall in age category of 2 to 6 years who undergone surgery of less than half an hour. Patients were anaesthetized with injection rocuronium 0.9 mg/kg i.v. or with injection succinylcholine 1.5 mg/kg after injection fentanyl 1ug/kg and injection thiopentone 5 mg/kg. The assessment of Neuromuscular blockade was conducted with twitch response of adductor pollicis longus after supra-maximal stimulation of ulnar nerve. We assessed Tracheal intubating conditions using the blinded anesthetist after 1 month and every 15 seconds till patient got intubated. The time of onset and percentage of neuromuscular blockage was also assessed.

Does postactivation potentiation (PAP) increase voluntary performance?

The transient increase in torque of an electrically evoked twitch following a voluntary contraction is called postactivation potentiation (PAP). Phosphorylation of myosin regulatory light chains is the most accepted mechanism explaining the enhanced electrically evoked twitch torque. While many authors attribute voluntary postactivation performance enhancement (PAPE) to the positive effects of PAP, few actually confirmed that contraction was indeed potentiated using electrical stimulation (twitch response) at the time that PAPE was measured. Thus, this review aims to investigate if increases in voluntary performance after a conditioning contraction (CC) are related to the PAP phenomenon. For this, studies that confirmed the presence of PAP through an evoked response after a voluntary CC and concurrently evaluated PAPE were reviewed. Some studies reported increases in PAPE when PAP reaches extremely high values. However, PAPE has also been reported when PAP was not present, and unchanged/diminished performance has been identified when PAP was present. This range of observations demonstrates that mechanisms of PAPE are different from mechanisms of PAP. These mechanisms of PAPE still need to be understood and those studying PAPE should not assume that regulatory light chain phosphorylation is the mechanism for such enhanced voluntary performance. Novelty The occurrence of PAP does not necessarily mean that the voluntary performance will be improved. Improvement in voluntary performance is sometimes observed when the PAP level reaches extremely high values. Other mechanisms may be more relevant than that for PAP in the manifestation of acute increases in performance following a conditioning contraction.