Unpleasant muscle soreness often arises after performing exercises that are new, that have not been performed in a long time, or that include a large volume of eccentric contraction (muscle contracting/shortening against its lengthening, as when you lower yourself down from the top of a pull-up). In many cases, the pain from these exercises does not appear immediately, but surfaces a day or two later, giving rise to the term Delayed Onset Muscle Soreness (DOMS). Once DOMS has set in, pain occurs whenever the affected muscle is moved, stretched or pressed. A variety of prior studies have looked at DOMS and damage to the muscle fibers was a fairly consistent observation. However, the specific areas within the muscle that were found to be damaged and the presence of inflammation has not been consistent among studies. Therefore, many researchers believe we are missing part of the picture. In a recent study by Lau et al. (2015), findings suggest that DOMS may result more from fascia damage than muscle damage.
The Takehome: Delayed onset muscle soreness is generally attributed to muscle damage, but fascia, connective tissue that separates, encloses and supports muscle, might also be important. This study could not immediately look at muscle and fascia’s contribution to delayed onset muscle soreness (DOMS), though. The authors first had to find an external (non-invasive) readout for DOMS that could be linked to a more precise readout which targets a specific tissue type. They found that pressure pain threshold (pain from pressing on the affected muscle) correlated with electrical pain threshold (EPT) read via a needle inserted into specific tissues. Therefore EPT was used to see which tissue (muscle or fascia) was more sensitive to pain after eccentric exercise that resulted in DOMS. The authors observed that changes in pain from pressing the muscle correlated with changes in electrical pain thresholds in the fascia, but not in the muscle itself. In addition, as time progressed after exercise, fascia tended to be more sensitive to this electrical stimulation (maintaining a lower pain threshold) than the muscle. The study is a pairing of associations and correlations, but the authors present a lot of data to support the relevance of their model and don’t over-interpret their results. Their findings suggest that fascia is a greater contributor to pain from DOMS that muscle, but fascia and muscle are intricately linked, so more research is needed to see if the two are truly independent.
- 10 Men (ages 22-28) with no resistance training of upper arm for the past 6 months.
- 2 exercise bouts (separated by 4 weeks) were performed.
- Exercise was 10 sets of 6 isokinetic (constant speed) eccentric elbow flexor contractions on a dynanometer.
- Elbows were forcibly extended from 60 degrees by the machine while subjects tried to maximally resist the extension.
- Indirect markers of muscle damage were voluntary isometric contraction torque (MVC), range of motion of the elbow joint (ROM), muscle soreness assessed by visual analogue scale (VAS), pressure pain threshold (PPT), and electrical pain threshold (EPT). Markers were assessed before, after, and 1-5 days after exercise.
- Tissues examined were: biceps brachii fascia (BBF), biceps brachii muscle (BBM), and brachialis fascia (BF).
- Muscle damage markers were, as expected for repeated bouts of eccentric exercise, less prominent after the 2nd bout of eccentric exercise than after the 1st (e.g., VAS increased after both bouts and PPT and decreased after both bouts, but the magnitudes were smaller for the second bouts as compared to the first).
- A comparison of BBF, BBM, and BF indicated that after the initial bout of exercise, electrical pain threshold decreased (pain tolerance worsened) more in the fascia (BBF, BF) than in the muscle (BBM).
- There was a significant correlation between electrical pain threshold (EPT) and physical pain threshold (PPT) of both the BBF and BF 1 and 2 days after the first exercise bout. This correlation was not present for the muscle itself.
- Women were not included in the study, so sex-differences cannot be accounted for.
- Life-history of arm training (particularly eccentric work) was not accounted for in the study and might yield different results if training history were different (extensive training vs no training).
- Of all the markers for damage/pain, only EPT can be measured separately on fascia or muscle. All other markers are a readout of fascia and muscle combined.
- Cause and effect cannot be conclusively established in this type of study as there was no way to separately damage the muscle and fascia.