Wide-pulse-high-frequency neuromuscular electrical stimulation in cerebral palsy.

OBJECTIVE: The present study assesses whether wide-pulse-high-frequency (WPHF) neuromuscular electrical stimulation (NMES) could result in extra-force production in cerebral palsy (CP) patients as previously observed in healthy individuals. METHODS: Ten CP and 10 age- and sex-matched control participants underwent plantar flexors NMES. Two to three 10-s WPHF (frequency: 100 Hz, pulse duration: 1 ms) and conventional (CONV, frequency 25 Hz, pulse duration: 50 µs) trains as well as two to three burst-like stimulation trains (2s at 25 Hz, 2s at 100 Hz, 2s at 25 Hz; pulse duration: 1 ms) were evoked. Resting soleus and gastrocnemii maximal H-reflex amplitude (Hmax) was normalized by maximal M-wave amplitude (Mmax) to quantify α-motoneuron modulation. RESULTS: Similar Hmax/Mmax ratio was found in CP and control participants. Extra-force generation was observed both in CP (+18 ± 74%) and control individuals (+94 ± 124%) during WPHF (p<0.05). Similar extra-forces were found during burst-like stimulations in both groups (+108 ± 110% in CP and +65 ± 85% in controls, p>0.05). CONCLUSION: Although the mechanisms underlying extra-force production may differ between WPHF and burst-like NMES, similar increases were observed in patients with CP and healthy controls. SIGNIFICANCE: Development of extra-forces in response to WPHF NMES evoked at low stimulation intensity might open new possibilities in neuromuscular rehabilitation.

In vivo and in vitro investigations of heterozygous nebulin knock-out mice disclose a mild skeletal muscle phenotype.

Nemaline myopathy is the most common congenital skeletal muscle disease, and mutations in the nebulin gene account for 50% of all cases. Recent studies suggest that the disease severity might be related to the nebulin expression levels. Considering that mutations in the nebulin gene are typically recessive, one would expect that a single functional nebulin allele would maintain nebulin protein expression which would result in preserved skeletal muscle function. We investigated skeletal muscle function of heterozygous nebulin knock-out (i.e., nebulin(+/-)) mice using a multidisciplinary approach including protein and gene expression analysis and combined in vivo and in vitro force measurements. Skeletal muscle anatomy and energy metabolism were studied strictly non-invasively using magnetic resonance imaging and 31P-magnetic resonance spectroscopy. Maximal force production was reduced by around 16% in isolated muscle of nebulin(+/-) mice while in vivo force generating capacity was preserved. Muscle weakness was associated with a shift toward a slower proteomic phenotype, but was not related to nebulin protein deficiency or to an impaired energy metabolism. Further studies would be warranted in order to determine the mechanisms leading to a mild skeletal muscle phenotype resulting from the expression of a single nebulin allele.

Differences in twitch potentiation between voluntary and stimulated quadriceps contractions of equal intensity.

This study compared the extent of twitch and M-wave potentiation (POT) between voluntary and stimulated quadriceps contractions performed at the same intensity. Sixteen healthy men completed 10-s isometric knee extensions at 40% of the maximal voluntary contraction torque under electrical stimulation and voluntary conditions. Single stimuli were delivered to the femoral nerve to evoke twitches before (PRE) and from 3 to 600 s after the end of each conditioning contraction. Changes in twitch contractile properties and M-wave characteristics were compared between the conditions. The extent of twitch peak torque POT was smaller for the stimulated (122+/-20% of PRE) than for the voluntary condition (133+/-20% of PRE). The magnitude of POT for the maximal rate of twitch torque development was also smaller for the stimulated trial. Rectus femoris M-wave amplitude was potentiated by the voluntary but not by the stimulated contraction. It was concluded that stimulated contractions resulted in smaller twitch and M-wave POT than voluntary contractions, despite equivalent torque output and duration. The spatially and temporally fixed recruitment of motor units with electrical stimulation and therefore the lower number of activated motor units compared with voluntary actions of equal intensity could explain the present findings.

Random motor unit activation by electrostimulation.

Whether the involvement of motor units is different between surface neuromuscular electrostimulation and voluntary activation remains an unresolved issue. The aim of this pilot study was to verify if motor unit activation during electrostimulation is nonselective/random (i.e., without obvious sequencing related to fibre type), as recently suggested by Gregory and Bickel [6]. Sixteen healthy men randomly performed submaximal isometric contractions (10-s duration) of the quadriceps femoris muscle at 20, 40 and 60 % of maximal voluntary torque under both stimulated and voluntary conditions. During the contractions, paired stimuli were delivered to the femoral nerve (twitch interpolation technique) and the characteristics of the superimposed doublet were compared between the two conditions. For each torque level, time-to-peak torque was significantly longer (p range = 0.05 - 0.0002) during electrostimulation compared to voluntary contractions. Moreover, time-to-peak torque during voluntary trials decreased significantly when increasing the torque level from 20 to 60 % of maximal voluntary torque (p range = 0.03 - 0.0001), whereas it was unchanged during electrostimulation. In conclusion, over-the-muscle electrostimulation would neither result in motor unit recruitment according to Henneman's size principle nor would it result in a reversal in voluntary recruitment order. During electrostimulation, muscle fibres are activated without obvious sequencing related to fibre type.

Plantar flexion torque as a function of time of day.

The possible peripheral and/or central origin in the mechanisms responsible for day-time fluctuation in maximal torque of the triceps surae muscle were investigated with a special emphasis on antagonist muscle coactivation. Eleven healthy male subjects (physical education students) took part in this investigation. The electromechanical properties of the plantar flexor muscles were recorded at two different times of day: between 06:00 h and 08:00 h in the morning and between 17:00 h and 19:00 h in the evening. To investigate peripheral mechanisms, the posterior tibial nerve was stimulated at rest, using percutaneous electrical stimuli, to evoke single twitch, double twitch, and maximal tetanic contraction (100 Hz). Maximal voluntary contraction of the plantar flexors was also assessed by means of the relative electromyographic activity of respective agonist and antagonist muscles (soleus, gastrocnemius medialis, gastrocnemius lateralis, and tibialis anterior). A double twitch was delivered during maximal voluntary plantar flexion to record muscle activation (i.e., interpolated twitch technique). The coactivation level of the tibialis anterior muscle during plantar flexion was calculated. The results indicated a significant decrease in maximal voluntary muscle torque of triceps surae in the evening as compared with the morning (-7.0 %; p < 0.05). Concerning the central command, when extrapolated by the twitch interpolation technique, the decrease in mean activation level of -6.8 % was consistent with the fluctuation in torque (-7.0 %). Soleus muscle electromyographic activity (normalized to the M-wave) showed a significant decline (21.6 %; p < 0.001). Moreover, individual changes in MVC percentage were significantly related to those of normalized electromyographic activity of the soleus muscle (r = 0.688; p < 0.01). Thus, it indicated that the subject's capacity to activate the soleus muscle was affected by the time of day. The coactivation level in the tibialis anterior muscle during plantar flexion did not change significantly in the evening. Concerning peripheral mechanisms, we observed a decrease in maximal M-wave amplitude for soleus and gastrocnemii, associated with unchanged single twitch and tetanus torque. To conclude, impairment in soleus muscle central command seemed to be the mechanism in the origin of torque failure. Such information would be of importance in the investigation of day-time fluctuations in complex motor task performances implicating the triceps surae muscle.

Neural activation of the triceps surae is impaired following 2 weeks of immobilization.

The purpose of this study was to investigate the effect of 2 weeks of ankle joint immobilization on triceps surae neural activation, with particular emphasis on the potential differences between the monoarticular soleus and the biarticular gastrocnemius muscles. Seventeen male volunteers were divided into the immobilized group (IG, n = 8) and the control group (CG, n = 9). Elastic adhesive bandages and an ankle stabilization orthosis were used to immobilize the ankle joint only. The plantar flexor torque obtained during maximal voluntary contractions (MVC) and after single, paired and tetanic stimuli applied at rest was measured. The associated EMG activity from the soleus and gastrocnemius muscles was also recorded, and their activation levels were estimated by means of the twitch interpolation technique. After immobilization, triceps surae maximal voluntary torque significantly decreased by 17% (P < 0.001). Strength losses were accompanied by a decrement in activation level (-6%, average of the three techniques used) and in maximal 100 Hz tetanic force (-11%). A significant decrease in the soleus (-22%, P < 0.05) but not in the gastrocnemius EMG activity, normalized to respective M-waves, was also found. It was concluded that the reduced voluntary torque output after immobilization could be attributed to both muscular and neural alterations. These latter selectively involved the monoarticular soleus muscle, while neural drive to the biarticular gastrocnemii, which had not been immobilized in their function as knee flexors, was preserved.

[Health promotion and education: a diagnosis of sanitation conditions using participatory research and community education (São João dos Queiróz - Quixadá/Ceará, Brazil)]. / Promoção à saúde e educação: diagnóstico de saneamento através da pesquisa participante articulada á educação popular (Distrito São João dos Queiróz, Quixadá, Ceará, Brazil).

This study was conducted in a rural community, São João dos Queiróz, a township in the county of Quixadá, Ceará, Brazil, using a combination of participatory research and community education in compliance with the health promotion reference and principles of the 1986 Ottawa Charter. The project was joined by representatives of several local government institutions and organizations from the grassroots community movement. The theme generating the research, as defined by an assembly meeting of the community association, was a diagnosis of sanitation conditions in the community. The starting point was the assessment of local conditions. Results showed adverse local conditions in sanitation, literacy, income, and employment. Suggestions for solving the problems were organized so as to be included in the planning agenda for local health policies. Evaluation was procedural and enriched with daily research activities. The problem-solving pedagogical approach developed during the educational process contributed to a critical reconstruction, appropriation, and sharing of the resulting knowledge.