<p><b>Background </b>The main objective of this thesis was to establish new insight into the motor control of low-threshold motor units in the trapezius muscle. Special attention was given to motor unit recruitment threshold related to firing behavior. The extensive literature on motor control mainly concerns firing behavior of extremity muscles. Motor control of the upper trapezius shows features that indicate deviations from the control scheme generally assumed to apply to muscles of the extremities. Knowledge of motor control of the trapezius is important in a pain development perspective, since shoulder/neck complaints are frequently localized to this muscle.</p><p><b>Methods </b>Constant amplitude contractions of 2 to 30 min duration, with amplitudes between ~2–7% of maximal voluntary contraction (2-7% EMGmax), were used to study time-dependent changes in motor unit firing. Transient force increases reaching 15-20% EMGmax were superimposed on some of these contractions in an attempt to induce motor unit substitution. Sinusoidal contraction profiles were used to study firings in response to dynamic contractions. Motor unit firing was studied in 10 min contractions with vocational (typing) tasks and mental stress. The spike-triggered averaged (STA) technique was used to examine motor unit potentials and their dependence on contraction amplitude and firing history. The individual motor unit firings were recorded by intramuscular fine wire electrodes, while simultaneously recording the surface electromyographic (SEMG) signal. The Precision Decomposition technique was used to identify individual motor units with near 100% accuracy. </p><p><b>Results </b>The results show that some low-threshold motor units stopped firing at the end of the EMG-pulses while motor units with initially higher threshold were recruited or stayed active. The lowest threshold motor units showed only brief silent periods. The mean firing rate increased from 10.5 to 12.5 pulses per second (pps) in response to contraction amplitudes of <2% and >4% EMGmax, but the mean firing rate the same for all motor units regardless of task and recruitment threshold given the SEMG amplitude. There was a strong rate modulation in dynamic contractions. STA-derived motor unit potentials indicated that motor units recruited below EMGmax had similar area at the same contraction amplitude. However, the area increased four-fold when SEMG amplitude increased from 1.5 to 10% EMGmax. Motor unit synchronization showed an average of 2.8% additional firings within of the triggering motor unit, estimated by peristimulus time histograms (PSTHs). A surprising finding was respiratory modulation of the firing rate at low contraction amplitudes. This modulation was attenuated by induced mental stress.</p><p><b>Conclusions </b>Transient force increases promote derecruitment of motor units and may be attributed to inactivation of non-inactivating inward currents (plateau potentials). Silencing of motor units can be considered a protective mechanism to reduce the metabolic load on low-threshold motor units. The similar firing rates in sustained contractions independent of task and recruitment threshold suggest that the duration and pattern of silent periods are the most important variables to investigate in relation to motor unit over-exertion and subsequent pain development. The strong rate modulation in response to dynamic contractions indicates a control strategy resembling that of extremity muscles. STA-derived motor unit potentials indicate that units recruited below 10% EMGmax are of similar size, thus suggesting a deviation from the Henneman size principle. This may be an adaptation to postural functionality. The increase in STAderived potentials is largely due to motor unit synchronization. This points out limitations for this method when quantifying motor unit size, numbers and conduction velocity. Finally, respiratory modulation of firing rate and the attenuation by mental stress suggest at least two different sources of autonomic input that may facilitate motor unit activity.</p>

<b>Background </b>The main objective of this thesis was to establish new insight into the motor control of low-threshold motor units in the trapezius muscle. Special attention was given to motor unit recruitment threshold related to firing behavior. The extensive literature on motor control mainly concerns firing behavior of extremity muscles. Motor control of the upper trapezius shows features that indicate deviations from the control scheme generally assumed to apply to muscles of the extremities. Knowledge of motor control of the trapezius is important in a pain development perspective, since shoulder/neck complaints are frequently localized to this muscle. <b>Methods </b>Constant amplitude contractions of 2 to 30 min duration, with amplitudes between ~2–7% of maximal voluntary contraction (2-7% EMGmax), were used to study time-dependent changes in motor unit firing. Transient force increases reaching 15-20% EMGmax were superimposed on some of these contractions in an attempt to induce motor unit substitution. Sinusoidal contraction profiles were used to study firings in response to dynamic contractions. Motor unit firing was studied in 10 min contractions with vocational (typing) tasks and mental stress. The spike-triggered averaged (STA) technique was used to examine motor unit potentials and their dependence on contraction amplitude and firing history. The individual motor unit firings were recorded by intramuscular fine wire electrodes, while simultaneously recording the surface electromyographic (SEMG) signal. The Precision Decomposition technique was used to identify individual motor units with near 100% accuracy. <b>Results </b>The results show that some low-threshold motor units stopped firing at the end of the EMG-pulses while motor units with initially higher threshold were recruited or stayed active. The lowest threshold motor units showed only brief silent periods. The mean firing rate increased from 10.5 to 12.5 pulses per second (pps) in response to contraction amplitudes of &lt;2% and &gt;4% EMGmax, but the mean firing rate the same for all motor units regardless of task and recruitment threshold given the SEMG amplitude. There was a strong rate modulation in dynamic contractions. STA-derived motor unit potentials indicated that motor units recruited below EMGmax had similar area at the same contraction amplitude. However, the area increased four-fold when SEMG amplitude increased from 1.5 to 10% EMGmax. Motor unit synchronization showed an average of 2.8% additional firings within of the triggering motor unit, estimated by peristimulus time histograms (PSTHs). A surprising finding was respiratory modulation of the firing rate at low contraction amplitudes. This modulation was attenuated by induced mental stress. <b>Conclusions </b>Transient force increases promote derecruitment of motor units and may be attributed to inactivation of non-inactivating inward currents (plateau potentials). Silencing of motor units can be considered a protective mechanism to reduce the metabolic load on low-threshold motor units. The similar firing rates in sustained contractions independent of task and recruitment threshold suggest that the duration and pattern of silent periods are the most important variables to investigate in relation to motor unit over-exertion and subsequent pain development. The strong rate modulation in response to dynamic contractions indicates a control strategy resembling that of extremity muscles. STA-derived motor unit potentials indicate that units recruited below 10% EMGmax are of similar size, thus suggesting a deviation from the Henneman size principle. This may be an adaptation to postural functionality. The increase in STAderived potentials is largely due to motor unit synchronization. This points out limitations for this method when quantifying motor unit size, numbers and conduction velocity. Finally, respiratory modulation of firing rate and the attenuation by mental stress suggest at least two different sources of autonomic input that may facilitate motor unit activity.

Diss. (sammanfattning) Stockholm : Karol. inst., 2001. / Härtill 6 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2001. / Härtill 5 uppsatser.

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2001. / Härtill 5 uppsatser.

According to the study [1] several firefighters are killed in action each year. This happens naturally in various ways. One of the major factors is that firefighters often do not know how the environment looks like, for example that a building in an industrial area contains hazardous gas cylinders. Without a solution, fire-fighters will continue to die in duty. It is therefore important to solve this problem so that we can minimize the risks and save lives.The goal of this project was a control system for pneumatic artificial muscles. To demonstrate that the desired functions of pneumatic artificial muscles worked properly, we created a simple arm with three degrees of freedom, with two muscles at each degree of freedom. The work consists mainly of pneumatic muscle, valves, programming and wireless communications. The focus was on controlling the robot arm using pneumatic artificial muscles.In order to achieve the arm to move to the desired position, we used wireless communication, the transmitter and receiver, and the pneumatic artificial muscles. This includes also programming, which was created on the programming language Spin.

<p>Aim</p><p>The main aim of the study was to investigate the difference in bilateral deficit between rowers and sprinters during maximal eccentric/concentric muscle actions.</p><p>• Are there any significant differences in bilateral deficit between rowers and sprinters?</p><p>• Do the amount of years in practice effect the bilateral deficit?</p><p>Method</p><p>Fourteen male subject participants divided in 2 equal sized groups (7 individuals in each group; rowers and sprinters) performed maximal unilateral/bilateral eccentric and concentric muscle actions in a leg press machine at a velocity of 0.2m/s. The range of motion in the knee joint was 70° – 140°. Dependent t-tests have been performed within each group pre and post test. P was set to 0,05 to prevent type I faults (false positive) a Bonferroni test was made for two comparisons and set to 0,0253.</p><p>Results</p><p>Average bilateral deficit for rowers were: 11% concentric and 33% eccentric. Number of years in practice and bilateral deficit: practiced >8years concentric 7% and eccentric 24%. Practiced <8 years concentric 21% and eccentric 55%.</p><p>Average bilateral deficit for sprinters were: 5% concentric and 24% eccentric. Number of years in practice and bilateral deficit: practiced >8years concentric 4% and eccentric 26%. Practiced <8years concentric 16% and eccentric 11%.</p><p>Conclusions</p><p>The main explanation for the larger differences in bilateral deficit for rowers in eccentric muscle action compared to sprinters may be related for the fact that the rowers have an almost non - eccentric phase during rowing. When comparing the amount of years in practice and bilateral deficit we saw that it decreased with the number of practiced years for booth rowers and sprinters. The reason to this pattern is probably on a neural base.</p> / <p>Syfte och frågeställningar</p><p>Syftet med studien är att studera bilateral deficit hos roddare och sprinters vid maximal excentrisk/koncentrisk muskelaktion.</p><p>• Finns det någon signifikant skillnad mellan roddare och sprinters i bilateral deficit?</p><p>• Påverkar antalet tränade år den bilaterala deficiten?</p><p>Metod</p><p>14 manliga testpersoner fördelade på två lika stora grupper (7 per grupp; rodd och sprint) genomförde maximal unilateral/bilateral muskelaktion excentriskt och koncentriskt i en benpressmaskin (ECCON). Rörelseomfånget i knäled vid muskelaktion sattes från 70° – 140°. Hastigheten för fotplattan vid muskelaktionen sattes till 0,2m/s. Dataanalysen har gjorts inom respektive undergrupp där vi genomförde ett beroende T-test där höger + vänster kraftmoment och bilateral kraft. P-värdet sattes till 0,05 och den parade jämförelsen justerades med en Bonferroni - korrektionsfaktor 0,0253.</p><p>Resultat</p><p>Medelvärdet för roddgruppens bilaterala deficit: 11% koncentriskt och 33% excentriskt. Antal tränade år och bilateral deficit vid benpress: tränat >8år koncentriskt 7% och excentriskt 24%. Tränat <8år koncentriskt 21% och excentriskt 55%.</p><p>Medelvärdet för sprintgruppens bilaterala deficit: 5% koncentriskt och 24% excentriskt. Antal tränade år och bilateral deficit: tränat >8år koncentriskt 4% och excentriskt 26%. Tränat <8år koncentriskt 16% och excentriskt 11%.</p><p>Diskussion</p><p>Skillnaden i bilateral deficit mellan excentrisk och koncentrisk muskelaktion hos roddare och sprinters kan bero på att roddare har en minimal excentrisk fas när de ror. Vid jämförelse av antal tränade år och den bilaterala deficitens storlek så fanns det en tendens till att deficiten minskade i takt med att antalet tränade år för båda grupperna. Orsaken till detta mönster är troligtvis på neuronal nivå.</p>

Aim The main aim of the study was to investigate the difference in bilateral deficit between rowers and sprinters during maximal eccentric/concentric muscle actions. • Are there any significant differences in bilateral deficit between rowers and sprinters? • Do the amount of years in practice effect the bilateral deficit? Method Fourteen male subject participants divided in 2 equal sized groups (7 individuals in each group; rowers and sprinters) performed maximal unilateral/bilateral eccentric and concentric muscle actions in a leg press machine at a velocity of 0.2m/s. The range of motion in the knee joint was 70° – 140°. Dependent t-tests have been performed within each group pre and post test. P was set to 0,05 to prevent type I faults (false positive) a Bonferroni test was made for two comparisons and set to 0,0253. Results Average bilateral deficit for rowers were: 11% concentric and 33% eccentric. Number of years in practice and bilateral deficit: practiced &gt;8years concentric 7% and eccentric 24%. Practiced &lt;8 years concentric 21% and eccentric 55%. Average bilateral deficit for sprinters were: 5% concentric and 24% eccentric. Number of years in practice and bilateral deficit: practiced &gt;8years concentric 4% and eccentric 26%. Practiced &lt;8years concentric 16% and eccentric 11%. Conclusions The main explanation for the larger differences in bilateral deficit for rowers in eccentric muscle action compared to sprinters may be related for the fact that the rowers have an almost non - eccentric phase during rowing. When comparing the amount of years in practice and bilateral deficit we saw that it decreased with the number of practiced years for booth rowers and sprinters. The reason to this pattern is probably on a neural base. / Syfte och frågeställningar Syftet med studien är att studera bilateral deficit hos roddare och sprinters vid maximal excentrisk/koncentrisk muskelaktion. • Finns det någon signifikant skillnad mellan roddare och sprinters i bilateral deficit? • Påverkar antalet tränade år den bilaterala deficiten? Metod 14 manliga testpersoner fördelade på två lika stora grupper (7 per grupp; rodd och sprint) genomförde maximal unilateral/bilateral muskelaktion excentriskt och koncentriskt i en benpressmaskin (ECCON). Rörelseomfånget i knäled vid muskelaktion sattes från 70° – 140°. Hastigheten för fotplattan vid muskelaktionen sattes till 0,2m/s. Dataanalysen har gjorts inom respektive undergrupp där vi genomförde ett beroende T-test där höger + vänster kraftmoment och bilateral kraft. P-värdet sattes till 0,05 och den parade jämförelsen justerades med en Bonferroni - korrektionsfaktor 0,0253. Resultat Medelvärdet för roddgruppens bilaterala deficit: 11% koncentriskt och 33% excentriskt. Antal tränade år och bilateral deficit vid benpress: tränat &gt;8år koncentriskt 7% och excentriskt 24%. Tränat &lt;8år koncentriskt 21% och excentriskt 55%. Medelvärdet för sprintgruppens bilaterala deficit: 5% koncentriskt och 24% excentriskt. Antal tränade år och bilateral deficit: tränat &gt;8år koncentriskt 4% och excentriskt 26%. Tränat &lt;8år koncentriskt 16% och excentriskt 11%. Diskussion Skillnaden i bilateral deficit mellan excentrisk och koncentrisk muskelaktion hos roddare och sprinters kan bero på att roddare har en minimal excentrisk fas när de ror. Vid jämförelse av antal tränade år och den bilaterala deficitens storlek så fanns det en tendens till att deficiten minskade i takt med att antalet tränade år för båda grupperna. Orsaken till detta mönster är troligtvis på neuronal nivå.

Diss. (sammanfattning) Stockholm : Karol. inst., 2001. / Härtill 4 uppsatser.

Syfte och frågeställningar Syftet med den här studien var att undersöka huruvida högfrekvent (HF) styrketräning motsvarande fem pass/vecka kan generera större muskelhypertrofi och styrka än lågfrekvent (LF) styrketräning motsvarande två pass/vecka. Frågeställning; Kan träningsprogram med högre träningsfrekvens ge större respons på muskelhypertrofi och styrka än normal träningsfrekvens trots samma träningsvolym? Metod Sex försökspersoner (ålder 26 ± 3,3 år, längd 180,4 ± 6 cm, vikt 81,6 ± 6,7 kg) testades för muskeltjocklek (ultraljudsmätning på vastus lateralis och rectus femoris) och muskelstyrka (1RM i unilateral benpress och benspark) på respektive ben. Fp tränade ena benet högfrekvent (fem pass/vecka) och andra benet lågfrekvent (två pass/vecka) under sju veckor. Träningsvolymen kontrollerades så att den var lika mellan benen. Därefter utfördes återtester enligt samma protokoll som före interventionen. Resultat Muskeltjocklek i båda musklerna var oförändrad i LF-benet 2,0 % och ökade i HF-benet 4,7 % (p = 0,04). Vastus lateralis var oförändrad i LF-benet -0,9 % och HF-benet 6,5 %. Rectus femoris ökade i LF-benet 5,1 % (p = 0,04) och var oförändrat i HF-benet 2,5 %. Ingen statistisk differens sågs för muskeltjocklek mellan benen efter interventionen för vastus lateralis och rectus femoris. Muskelstyrka i benpress ökade i LF-benet med 17 % (p = 0,02) och HF-benet med 15,8 % (p = 0,02). Benspark ökade i LF-benet med 15,8 % (p = 0,02) och HF-benet med 17,4 % (p = 0,02). Ingen statistisk differens sågs för muskelstyrka mellan benen efter interventionen för benpress och benspark. Slutsats Slutsatsen av den här studien var att ingen statistisk skillnad uppmättes mellan muskelhypertrofi och styrka för träning enligt det högfrekventa kontra det lågfrekventa träningsprogrammet hos unga aktiva motionärer vana vid styrketräning. Således kan samma träningseffekt i form av muskelhypertrofi och styrka uppnås vid korta pass med låg volym och högre träningsfrekvens som längre pass med högre volym och lägre träningsfrekvens. / Aim The purpose of this study was to investigate if high frequency strength training (HF) of five sessions/week can produce larger increases in muscle hypertrophy and strength compared to low frequency strength training (LF) of two sessions/week. Method Six participants (age 26 ± 3,3 years, length 180,4 ± 6 cm, weight 81,6 ± 6,7 kg) were tested for muscle thickness in quadriceps (ultrasound measurements on vastus lateralis and rectus femoris) and strength (1RM in unilateral leg press and leg extension). One leg exercised with a high frequency (five sessions/week) and the other leg with a low frequency (two sessions/week) during seven weeks. The training volume was equated between both legs. Retests were conducted after the intervention. Results Muscle thickness in both muscles together was unchanged in LF 2,0 % and increased in HF 4,7 % (p = 0,04). Vastus lateralis was unchanged in LF -0,9 % and HF 6,5 %. Rectus femoris increased in LF 5,1 % (p = 0,04) and was unchanged in HF 2,5 %. No statistical difference was seen for muscle thickness between legs for vastus lateralis and rectus femoris. Strength increased in leg press for LF with 17 % (p = 0,02) and for HF with 15,8 % (p = 0,02). Leg extension increased for LF with 15,8 % (p = 0,02) and for HF with 17,4 % (p = 0,02). No statistical difference was present for strength between legs for leg press and leg extension. Conclusions The conclusions of this study were that no statistical difference was seen for muscle hypertrophy and strength between high and low frequency training programmes when the volume was equated. This means that comparable training effects can be reached between short duration and low volume strength training workouts at high frequency as to longer duration and higher volume strength training workouts at low frequency.