The gold standard marker of skeletal muscle injury is strength loss. Blood levels of muscle proteins (e.g., CK) are considered poor markers. See the attached review article on the topic. These recommendations apply for all types of muscle injury, not just eccentric contraction-induced injury.

Thank you Gordon L Warren , very interesting reference of Professor Armstrong and Warren. It will be definitely useful.

Skeletal Troponin I or myoglobin. As Gordon L Warren suggests biochemical markers are not great as they are so variable between individuals. However, if you have a repeated measures design, I have found they generally reflect the strength loss and muscle soreness.

It's good to know, Lynsey S James . However, should I perform biopsy to measure these variables? I was looking for less invasive and complex tests.

Thank you very much.

Both of these can be performed on serum/plasma. We use a clinical chemistry analyser Pentra C400 for myoglobin and an ELISA for skeletal troponin I.

Great. Tks.

I suggest to use MVIC as a non invasive marker, which has been shown to be a valid measure to estimate the amount of muscle damage.

Thank you Erich Hohenauer , I do work with an electronic dynamometer to measure MVIC of some muscle groups, however, I also want to use a biomarker for a specific objective.

Further to Lynsey's response and suggestion is to consider that it is also then possible to look at muscle fibre specific protein variations to the Troponin complex (slow and fast fibre Troponin variations) just as there are cardiac and skeletal muscle variations to CK.

Luis, I might suggest 3-methylhistidine, although the assay may be more expensive than CK. I think you can assay plasma or urine.

Thank you Dale Wilson Chapman , after Lynsey S James suggestions, I started looking at the Skeletal Troponin I. I'll look at these variations (slow and fast) and the chances and costs we'll have to assess in our lab.

Once again, thanks.

Interesting, Chad D Markert . I took a look at the literature, and saw some good references with 3-methylhistidine and exercise, most with urine analysis. Thank you very much.

I would suggest you to use ultrasound imaging, if you can add it. Using transverse images of the muscle you can asses the echo intensity (the grey scale of the image) and muscle thickness.

Article Comparison in eccentric exercise-induced muscle damage among...

Article Time Course of Strength and Echo Intensity Recovery After Re...

Obrigado Clarissa Müller Brusco .

We have used it for muscle thickness and pennation angle only, never for muscle damage.

I'll read the references.

Tks.

Myoglobin

Thank you Georgios Mavropalias

First, there is arguably no single best marker for muscle damage. Not even strength loss. Needless to say, strength loss can occur for a variety of reasons. You can have exercise-induced strength loss both due to reversible muscle cell damage (and of course also due to fatigue) and irreversible muscle cell damage, and any combination of these.

For example, in one of our projects on high-frequency blood-flow restricted resistance exercise, one of the participants became so weak in his quadriceps that he had to drop out from the study and walk on crutches for a few days. His peak CK on the 4th day of the study was > 4000 I/U (normal CK is ~100-200 I/U) and the CK was probably still on the rise. The next week he was essentially back to his normal self.

What happened to him that might explain the drastic loss of function? We will never know for sure and I can only speculate about some combination of reversible muscle damage and remodeling, irreversible muscle cell damage (probably only a smaller extent though) and temporary neuromuscular transmission failure.

Second, as already implied above: muscle damage is a very broad and rather vague term. What do you mean by "muscle damage"? Reversible or irreversible muscle cell damage, or both? If reversible, which candidate mechanisms? If irreversible, what kind(s) of cell death? Until you clearly define what you are looking for, finding "a good marker for muscle damage" is going to be even more difficult than it already is.

Against this background and complexity, it becomes apparent that you need to include several markers to cover the many different aspects of muscle damage and fatigue that you are likely to encounter when you are undertaking a project on exercise-induced muscle damage.

I agree with Mathias, that there is no single best marker. But I'd recommend a marker of force loss (MVC perhaps) as it gives you a holistic insight into the changes. Plus, if you're looking at this from an applied perspective (e.g. sport/exercise performance), then force changes underpin this. If you're looking for some sort of blood marker, then you'll need to think about what you're trying to get an insight into (e.g. sarcolemma disruption, inflammation, time-course of change etc) and then tailor the marker to this. Unfortunately, for the blood markers I don't believe there is a single best one.

Of course, it can be evaluated

Blood calcium can be considered as another marker of muscle damage