A master thesis from Aalborg University
Study proposal: The effects of local and remote ischemic preconditioning on motor unit properties in the tibialis anterior muscle of healthy adults
Author(s)
Term
4. semester
Education
Publication year
2020
Submitted on
2020-06-01
Pages
58 pages
Abstract
Der er udarbejdet et studieforslag, hvis formål er at undersøge, hvorvidt motoriske enheder (ansvarlig for muskelaktivering) kan optimeres hos raske voksne efter en intervention med iskæmisk prækonditionering (IPC). IPC er en intervention karakteriseret ved korte perioder med iskæmi og efterfølgende fri blodgennemstrømning. Tidligere undersøgelser har vist, at anvendelse af IPC kan have en forbedrende effekt på nervesystemet og dermed bevirke en forbedret muskelaktivering, men de bagvedliggende mekanismer er endnu ikke fuldt afdækket. Eftersom IPC som behandling er ikke-invasiv, billigt og let anvendelig, er der derfor et stort potentiale i anvendelsen af IPC, hvis der kan opnås en dybere forståelse af de underliggende mekanismer. I tillæg til at undersøge hvorvidt motoriske enheder kan optimeres hos raske voksne efter en intervention med IPC, vil studieforslaget desuden kunne belyse, om der er forskel mellem IPC placeret lokalt på den ekstremitet, der udfører muskelkontraktionen (LIPC), og på IPC placeret på en anden ekstremitet end den der udfører muskelkontraktionen (RIPC), hvilket vil kunne forbedre anvendelsen af IPC. Dette foreslås undersøgt med high density surface electromyography (hd-EMG), som er en ny teknologi indenfor muskelfysiologi, der muliggør undersøgelsen af IPC’s effekt på de motoriske enheder før og efter en intervention, hvilket vil kunne danne grobund for fremtidige undersøgelser. Studieforslaget indebærer rekrutteringen af 16 raske voksne, der vil gennemgå tre interventioner; LIPC, RIPC og kontrol i en tilfældig rækkefølge. Hver forsøgsgang indebærer måling af maksimale frivillige kontraktioner (MVC), hvorefter en submaksimal isometrisk rampekontraktion op til 40% af MVC udføres med skinnebensmusklen og måles med hd-EMG både før og efter hver intervention. På baggrund af tidligere undersøgelser og den eksisterende viden på området, forventes det, at såvel LIPC som RIPC vil forbedre aktiveringen af de motoriske enheder signifikant sammenlignet med kontrol-interventionen. For kontrol-interventionen forventes det, at resultaterne før og efter interventionen vil være de samme. Derudover forventes LIPC at have en større positiv effekt på aktiveringen af de motoriske enheder sammenlignet med RIPC.
Ischemic preconditioning (IPC) refers to a technique that includes brief rounds of ischemia and reperfusion and which has recently emerged as an intervention to improve muscle activity. IPC can be applied either locally to the tissue of interest (LIPC) or on the tissue of a remote limb (RIPC). The underlying mechanisms of IPC are still not fully understood, but it is suggested that IPC inhibits the ischemia sensitive group III/IV muscle afferents, which leads to an increase of the excitability of the spinal motor neurons. The effects from IPC on motor unit properties has only been investigated in chronic stroke survivors, and the study showed that LIPC increased muscle strength through improved muscle activation. The objective for the present study proposal is to investigate if IPC has an effect on the discharge rate and recruitment threshold for motor units in healthy adults when performing a submaximal isometric muscle contraction. An additional objective is to investigate whether the effect of LIPC and RIPC respectively differ. It is hypothesized that LIPC increases the discharge rate and decreases the recruitment threshold for the motor units to a larger extent than RIPC, and that both of these interventions will lead to a higher discharge rate and lower recruitment threshold of the motor units compared to a sham intervention. The proposed study will be carried out as a randomized counterbalanced crossover study with a required sample size of 16 healthy adults. During the proposed study, subjects will undergo three interventions: LIPC, RIPC and sham. Each intervention will consist of four cycles of 5x5 min occlusion/reperfusion, with a pressure of 225 mmHg for both LIPC and RIPC, and 25 mmHg for sham. Before and after each intervention, the subjects will perform three maximal voluntary contractions (MVC) and two submaximal isometric ramp contractions at 40% MVC with the dorsiflexors. During the experimental protocol, measurements of central motor drive (motor unit discharge rate and recruitment threshold) from the right tibialis anterior muscle will be conducted using high-density surface electromyography. Carrying out the study in practice can contribute with a unique perspective on the central motor drive after an IPC intervention and knowledge of the possible effects on motor unit properties.
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