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I apologise pre-emptively for how awful it looks

No worries.
Animating characters can be complicated and requires practice, but also some prior studies.
If you have not done the basic animation tests such as the Bouncing Ball, and Flour Sack, I highly encourage you to do so.

Be careful of drawing animations in a literal descriptive way.
Each part feels as if it moves independently rather than coming together to create a cohesive piece of functional art.

You're being very timid with the pixels, keeping things looking the same through out the animation.
While that can help to save time, and I use the same concept quite often, there are ways to better balance unique and static parts of a frame.

For me it helps to do the same animation 5 to 8 times.
Here's my first vartiation:


Many parts of it could be improved, but I would most likely stop at this point, save it to branched filename, and then start over.
The next time I would do it differently.
It would still be a sword swing, but I would start from the first frame, or completely from scratch.
Then compare them all, figure out what works, what doesn't.
Maybe combine a few ideas or just choose the best one and then finish it off.

Also realize that its all a choice.
Everything I've said can be done the complete opposite way and yield a valid result.
In the correct context with intention, your animation could work fine.
As Alcopopstar mentioned, the motion is sort of undead like.

Thanks so much for the advice, critique and edit. It's actually made me consider switching the angle of the character when he attacks. I'll confess i have little to no previous knowledge of animation or even art in general prior to picking up pixel-art, so this is sort of my first foray into art (although i have been pixelling for over a year+ now).

Often when im animating i focus solely on trying to get the (specific) limb moving in the correct way, often neglecting the bigger picture (the body and how it'd react), like Alcopopstar pointed out. I wasn't aware that i was being too literal with the advice given, i tend to take things literally, be they advice or words in general. Not an excuse, just wanted to explain my thought process.

Edit: I really like the edit, but i don't want to copy it, so im going to try to take elements of it and learn from it. Is that okay?

Sorry for the lack of updates for the last month or so.

Been mainly concentrating on smaller pieces like the below:



Or practicing animating:

Will definitely try what you said!

Just want to clarify something; im not wanting to be a slave to anatomical correctness as much as i want to be able to to make characters that look "right" if that makes sense?

Left one side free of muscles so i could show the changes i made (thanks Night for pointing some of them out!) and still working on in regards to the bones:



I've probably got the muscles all wrong, alot of them seem to blend in together, but i did try to to get their general shape down.

Thanks! Had to look up what Ecorche meant  as i wasn't sure what you meant.

I've done most of the muscles (barring chest), yet im not happy with them. I'm unsure of how i'd be able to put the skin over them and make a character look at least slightly realistic.

I'm currently reworking the arms, feet and hands as well as the muscles on them, I'll post pictures when i've gotten them done (skeleton and muscle wise) i also won't include the pink  silhouette, apologies about that!

Edit:

Sorry for the slow progress, spent a few hours looking at arms today.

Here's some highly simplified muscle placement on the arms also tried to make the arm look uh, more arm like:



Key:

Blue = Deltoid
Yellow = Triceps
Pink = Biceps
Green = Brachio
Red = Flexor

An update:



Came to the realization that it's more about depicting what muscles show through the skin and are prominent then necessarily every oneof the muscles.

Basically redone the arms, chest and legs, trying to depict the lines of the muscles that actually show through, but right now it's basically a simplified version.

Also overlaid the skeleton on top it of it, just to ensure it still looks vaguely anatomically correct in terms of bones etc.

I think, like Cyangmou said, the shoulders may be a bit too broad.